HAVING RADIO FREQUENCY BASED SENSORS BACKGROUND

[0001] The invention relates to sensing devices, and more particularly to multivariable sensing devices.

[0002] Radio frequency identification (RFID) tags are widely employed for automatic identification of objects (e.g. animals, garments, etc.) and monitoring and detection of containers (such as, unauthorized access to contents of containers). Generally, RFID readers are used to obtain digital data from the RFID tags for such automatic identification. Digital data may include, for example, digital identification of the tag, or any other information written and/or stored in a memory chip of the RFID tags. The RFID tags transmit electromagnetic signals at different relative levels of transmitted power at different times. Signals received by the RFID reader in combination with the transmitted relative power levels of the received signals from the RFID tags are employed to locate the RFID tags, and read the digital identification information from the RFID tags (e.g., from a memory chip or a back-reflector structure of a RFID tag).

[0003] Further, radio frequency based sensors are used for sensing physical, chemical and biological constituents in a sample. Moreover, the radio frequency based sensors are cost- effective, and easy to incorporate in a component or a system for measuring physical, chemical or biological constituents of the component or the system. Typically, analog or sensor data from the radio frequency based sensors is read using an impedance reader. Further, the sensor data is read with the help of a pick-up coil that is integral part of the radio frequency based sensor.

BRIEF DESCRIPTION [0004] In accordance with aspects of the present specification, a multivariable sensing device for sensing one or more parameters of a process fluid disposed in a container is provided. The multivariable sensing device includes a radio frequency based sensor configured to sense a physical parameter, a chemical parameter, a biological parameter, or combinations thereof, representative of the process fluid. The radio frequency based sensor includes a sensor substrate, a radio frequency coil disposed on at least a portion of the sensor substrate, and a support structure configured to be physically coupled to the container. Further, the support structure is configured to position the radio frequency based sensor in operative proximity to an inside of the container. [0005] In accordance with another aspect of the present specification, a multivariable sensing system having a multivariable sensing device, a sensor reader, and a pick-up coil is provided. The multivariable sensing device is configured for sensing one or more parameters of a process fluid disposed in a container. The multivariable sensing device includes a radio frequency based sensor configured to sense a physical parameter, a chemical parameter, a biological parameter, or combinations thereof, representative of the process fluid. Further, the radio frequency based sensor includes a sensor substrate, a radio frequency coil disposed on at least a portion of the sensor substrate, and a support structure configured to be physically coupled to the container. Moreover, the support structure is configured to position the radio frequency based sensor in operative proximity to an inside of the container. The sensor reader is configured to transmit interrogating radio frequency signals to the radio frequency based sensor and receive response signals from the radio frequency based sensor. Further, the pick-up coil is operatively coupled to the radio frequency based sensor and the sensor reader. Also, the pick-up coil is configured to receive the response signals from the radio frequency based sensor and transmit the response signals to the sensor reader.

[0006] In accordance with yet another aspect of the present specification, a method of multivariable sensing for a process fluid disposed in a container is provided. The method includes operatively coupling a radio frequency based sensor to a support structure to form a multivariable sensing device. Further, the radio frequency based sensor includes a sensor substrate and a radio frequency coil disposed on at least a portion of the sensor substrate. The method also includes operatively coupling the multivariable sensing device to the container, providing a sensor reader operatively coupled to the radio frequency based sensor, and providing a pick-up coil disposed outside the support structure, and operatively coupling a pickup coil to the radio frequency based sensor. Moreover, the method includes sensing one or more parameters from the container, transmitting data pertaining to the one or more measurements to the sensor reader using the pick-up coil, and determining one or more parameters associated with the process fluid disposed in the container.

DRAWINGS [0007] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0008] FIG. 1 is a cross-sectional view of a multivariable sensing device having a radio frequency based sensor disposed in a support structure, in accordance with aspects of the present specification;

[0009] FIG. 2 is a cross-sectional view of a multivariable sensing device having a radio frequency based sensor disposed in a support structure, where the support structure includes a mechanical stopper, in accordance with aspects of the present specification;

[0010] FIG. 3 is a top view of a multivariable sensing device disposed on a container, in accordance with aspects of the present specification;

[0011] FIG. 4 is a schematic representation of a multivariable sensing system employing a multivariable sensing device having a plurality of radio frequency based sensors and a memory chip, in accordance with aspects of the present specification;

[0012] FIG. 5 is a schematic representation of an exemplary multivariable sensing device operatively coupled to a container having a process fluid, where the multivariable sensing device includes a radio frequency based sensor having a sensing coil, a sensor substrate and a protection layer, in accordance with aspects of the present specification;

[0013] FIG. 6 is a schematic representation of an exemplary multivariable sensing device operatively coupled to a container having a process fluid, where the multivariable sensing device includes a radio frequency based sensor having a sensing coil and a sensor substrate, and where the sensor substrate is configured to be in physical contact with the process fluid disposed in the container, in accordance with aspects of the present specification;

[0014] FIG. 7 is an exemplary flow chart of a method of use of a multivariable sensing device, in accordance with aspects of the present specification; [0015] FIG. 8 is a graphical representation of examples of real and imaginary portions of a measured analog response of the radio frequency based sensor, in accordance with aspects of the present specification;

[0016] FIGS. 9-10 are graphical representations of measurements of electrical conductivity of aqueous solutions over a broad dynamic range using individual radio frequency based resonance sensors having protection layers of different thickness values, in accordance with aspects of the present specification;

[0017] FIG. 11 is a graphical representation of a sensitivity of a radio frequency based sensor as a function of different thickness values of protection layers, in accordance with aspects of the present specification; and

[0018] FIGS. 12-13 are graphical representations of measurements of electrical conductivity of aqueous solutions over a broad dynamic range using individual radio frequency based sensors having different thickness values of sensor substrates of the individual radio frequency based sensors, in accordance with aspects of the present specification. DETAILED DESCRIPTION

[0019] Embodiments of the present specification relate to disposable multivariable sensing devices employing one or more radio frequency based sensors. In certain embodiments, the one or more radio frequency based sensors of the multivariable sensing devices may be used to sense one or more parameters inside a container, such as a container used in a bioprocess. Further, the radio frequency based sensors may be configured to measure a plurality of parameters inside the container, thereby attributing the multivariable nature to the multivariable sensing devices by enabling the radio frequency based sensors to sense more than one parameter. Non-limiting examples of such parameters may include electrical conductivity, pH level, temperature, blood relevant measurement, ionic measurement, non-ionic measurement, non-conductivity measurement, electromagnetic radiation level measurement, pressure, vapor concentration, biological material concentration, multiphase composition, or any combinations thereof.

Moreover, in one embodiment, the disposable multivariable sensing devices may be employed for monitoring and control of in-line manufacturing.

[0020] In some embodiments, the disposable multivariable sensing device may be at least partly disposable in nature. In some other embodiments, the disposable multivariable sensing device may include one or more components that may be single use components. In particular, the one or more single use components may not be usable after being used once. Further, some or all of the components of the multivariable sensing device may be disposable in nature. As used herein, the terms "single use component" refers to a component that, after operation, may be reconditioned for reuse. As used herein, the term "disposable component" refers to a component that may be disposed of after use. It may be noted that the terms "multivariable sensing device" and "disposable multivariable sensing device" may be used interchangeably throughout the application.

[0021] In certain embodiments, a multivariable sensing device of the present specification includes a radio frequency based sensor that is configured to sense a physical parameter, a chemical parameter, a biological parameter, or combinations thereof of a process fluid disposed in a container. The radio frequency based sensor includes a sensor substrate and a radio frequency coil disposed on at least a portion of the sensor substrate. Further, the radio frequency based sensor may be disposed in a support structure that is configured to be physically coupled to the container. Moreover, the support structure is configured to position the sensor in operative proximity to the inside of the container to enable the radio frequency based sensor to sense one or more parameters of the contents disposed in the container. The multivariable sensing device may further include a memory chip operatively coupled to at least one of the radio frequency based sensor and the container.

[0022] In certain embodiments, radio frequency based sensor of the multivariable sensing device may be configured to sense one or more parameters of the process fluid disposed in the container, e.g., one or more parameters of a fluid disposed in the container. To sense the one or more parameters, the radio frequency based sensor may be configured to receive interrogation signals from a sensor reader. Further, the radio frequency based sensor is configured to transmit response signals to the sensor reader. The signals may be received and/or transmitted by the radio frequency based sensor using a wired communication or a wireless communication with the sensor reader. Further, the interrogation signals may be configured to activate the radio frequency based sensor to send the one or more parameters of the container or the constituents disposed in the container.

[0023] Non-limiting examples of sensor parameters that are measured using an analog portion of the response signals may include impedance spectrum, a real part of the impedance spectrum, an imaginary part of the impedance spectrum, both real and imaginary parts of the impedance spectrum, a frequency of the maximum of the real part of the impedance (Fp), a magnitude of the real part of the impedance (Zp), a resonant frequency (Fi) and its magnitude (Zi) of the imaginary part of the impedance, anti-resonant frequency (F ₂ ) and its magnitude (Z ₂ ) of the imaginary part of the impedance, or combinations thereof. Further, other parameters of the analog signal that may also be measured may include a quality factor, a zero crossing resonance frequency, and the like. In one embodiment, individual parameters (for example, Fp, Zp) may be utilized for quantitative measurements. Further, combinations of the individual measured parameters may be processed using well known multivariate techniques, for example principal components analysis, partial least squares, support vector machine, and many others.

[0024] In one example, a radio frequency based sensor of the disposable multivariable sensing device may be disposable. In this example, after operation, the radio frequency based sensor may be removed from the remaining reusable portion of the multivariable sensing device. Further, the radio frequency based sensor may be replaced by another radio frequency based sensor. In another example where the whole structure of the multivariable sensing device is disposable, the entire multivariable sensing device may be replaced by another multivariable sensing device to prepare the container for next operation. [0025] Further, in some embodiments, the container may be configured to house a solution, also referred to as a "process fluid" or a "bio-processing fluid." The solution may be disposed in the container for storing, processing, transferring, or combinations thereof. Further, the solution in the container may be liquid, gas, solid, or a combination of liquid and solid. For example, the solution may be blood, water, electrically conductive fluid, electrically non- conductive fluid, oil, fuel, a biological buffer, or combinations thereof. Alternatively, the solution may contain a toxic industrial material, a chemical warfare agent, a gas, a vapor, an explosive, a disease marker in exhaled breath, a bio-pathogen in water, a virus, bacteria, and other pathogens. In certain embodiments, the container may be disposable or reusable. In some of these embodiments, the container may be a disposable bioprocess component and the multivariable sensing device may be configured to sense one or more parameters of the solution disposed in the disposable process component before, during or after operation in the disposable bioprocess component, e.g., during biopharmaceutical manufacturing.

[0026] In embodiments where the container is a disposable container, the multivariable sensing device may be permanently fixed to the container. Whereas, in embodiments where the container is a reusable container, the multivariable sensing device may be removably coupled to the container, such that the multivariable sensing device may be coupled and decoupled a number of times from the container as desirable. In certain embodiments, the disposable process component may be a filter, a connector, a valve, or the like. Further, the container may be a vessel used in a bioprocess, a chemical process, a chemical reaction, a biological interaction, or the like. Moreover, the container may be a storage container, a process container, or a flow container. Also, the container may have a steady state fluid. Alternatively, the container may be configured to receive a flowing fluid from one port and provide an outlet to the flowing fluid from another port with or without interrupting the flow of the fluid. It may be noted that in some embodiments, the radio frequency based sensor may be disposed in the support structure such that the radio frequency based sensor forms a hermetic sealing with portions of the support structure that are adjacently disposed to the radio frequency based sensor. The hermetic sealing may be configured to prevent any process fluid from the container from leaking into the multivariable sensing device. Further, it may be noted that the

multivariable sensing device may be sterilized prior to being coupled to the container.

[0027] In one embodiment, the radio frequency based sensor may be disposed in the support structure such that the sensor substrate of the radio frequency based sensor is disposed towards a side of the support structure that is in physical contact with the container. In this embodiment, the sensor substrate of the radio frequency based sensor may be exposed to the process fluid disposed in the container. In a particular embodiment, the radio frequency based sensor may be disposed in the support structure such that the contents in the container may be in direct physical contact with the sensor substrate. Further, thickness values of the sensor substrate may be varied depending on desirable value of sensitivity in sensed parameters, while managing physical integrity of the multivariable sensing device. In one example, a thickness of the sensor substrate may be in a range from about 100 nanometers to about 10 centimeters. In some of these embodiments, the sensor substrate may be made of a dielectric material.

[0028] Alternatively, in another embodiment, the radio frequency based sensor may be disposed in the support structure such that the radio frequency coil is disposed towards a side of the support structure that is in physical contact with the container. In this embodiment, the radio frequency coil may be exposed to the process fluid disposed in the container. Further, in this embodiment, a protection layer may be disposed on the radio frequency coil to prevent direct interaction between the radio frequency coil and the process fluid.

[0029] It may be noted that the orientation of the radio frequency based sensor in the support structure may be decided based on the type of parameters that need to be measured. In a non- limiting example, an electrical conductivity or temperature of a liquid sample disposed in the container may be measured by disposing the support structure in the container such that the radio frequency coil is directed towards the side of the support structure that is physically coupled to the sensor. In another example, a pressure of the process fluid may be measured by bringing the sensor substrate in direct physical contact with the process fluid.

[0030] Further, typically, in addition to the sensor coil or the radio frequency coil, a pick-up coil is coupled to the radio frequency based sensor to communicate with a sensor reader. In embodiments of the present specification, the pick-up coil does not form part of the radio frequency based sensor. In particular, in certain embodiments, the pick-up coil may be an entity that is independent of the multivariable sensing device. Further, in certain other embodiments, the pick-up coil may be an entity that is independent of the sensor reader. Alternatively, the pick-up coil may be a part of the sensor reader. Advantageously, absence of the pick-up coil from the structure of the radio frequency based sensor results in simplification of the design of the multivariable sensing device. Further, absence of the pick-up coil from the structure of the multivariable sensing device reduces the cost of the multivariable sensing device. Moreover, when the pick-up coil is used as a separate entity from the radio frequency based sensor or as a part of the sensor reader, a single pick-up coil may be used to acquire signals from one or even more than one radio frequency based sensors of one or more multivariable sensing devices. Accordingly, a single pick-up coil may be associated with one or more radio frequency based sensors and/or multivariable sensing devices, thereby reducing the overall cost of the system. Moreover, in absence of physical presence of the pick-up coil from the radio frequency based sensor, capacitance and inductance otherwise associated with the pick-up coil do not affect the radio frequency based sensor. It may be noted that the inclusion of the pick-up coil requires an additional set of calibration parameters such as pick-up coil resistance, pick-up coil capacitance, pick-up coil inductance, and others such as temperature effects on pick-up coil metallic and dielectric components. Further, exposing of the sensor and the pick-up coil to the environments of interest such as temperature, pressure, and others needed in bioprocess applications, adds a complexity in such calibrations. Advantageously, absence of the pick-up coil from the radio frequency based sensor simplifies the sensor design, and also eliminates the need for calibration of the radio frequency based sensor to account for the pick-up coil. Further, in embodiments where the pick-up coil is an individual independent entity, the pick-up coil may be wirelessly coupled to the radio frequency based sensor. Additionally, the pick-up coil may be coupled to the sensor reader in a wireless or wired manner. In embodiments where the pick-up coil is a part of the sensor reader, the pick-up coil may be disposed in the housing of the sensor reader.

[0031] In certain embodiments, a multivariable sensing assembly includes a multivariable sensing device and a pick-up coil. Further, the multivariable sensing assembly may be formed by disposing the multivariable sensing device and the pick-up coil in a determined relative physical configuration. It may be noted that the determined relative physical configuration may include a constant physical distance between the multivariable sensing device and the pick-up coil. In some embodiments, the pick-up coil may be disposed at a determined distance from the multivariable sensing device to be in operative association with the multivariable sensing device. Further, in some of these embodiments, the pick-up coil may be physically coupled to the sensor reader using an electrical cable. Whereas, in some other embodiments, the pick-up coil may be wirelessly coupled to the sensor reader. In these embodiments, the wireless coupling between the pick-up coil and the sensor reader may be provided by inductive coupling, capacitive coupling, or the like.

[0032] Further, in some embodiments, the sensor reader may be wired to the multivariable sensing device, in these instances, the wired communication between the sensor reader and the radio frequency based sensor may be performed by connecting the radio frequency based sensor to the sensor reader by an electrical cable. Alternatively, the wired communication between the sensor reader and the radio frequency based sensor may be performed by a direct electrical connection to the radio frequency based sensor without the need for an electrical cable. It may be noted that such direct connection may be achieved when the size of the sensor reader is approximately the size of the sensor. In some other embodiments, the sensor reader may be in wireless communication with the sensor reader. In these embodiments, the pick-up coil may be coupled to the sensor reader and the radio frequency based sensor in a wired or wireless fashion.

[0033] In certain embodiments, the sensor reader may include a network analyzer or an impedance analyzer to read analog portion of the response signals and a reader/writer to read digital portion of the response signals from the radio frequency based sensor. It may be noted that the analog and digital portions of the response signals from the radio frequency based sensor may be read in several ways. In one embodiment, the analog and digital portions of the response signals may be read in a sequential manner during installation and operation of a corresponding container, such as, but to limited to a disposable bioprocess component, with a radio frequency based sensor of a disposable multivariable sensing device, also referred to as "an integrated radio frequency based sensor". Further, in another embodiment, the digital portion of the response signals of the radio frequency based sensor may be read before and/or during installation of the disposable bioprocess component with an integrated radio frequency based sensor and the analog portion of the response signals of the radio frequency based sensor may be read during the operation of the disposable bioprocess component. Further, in one embodiment, an operational frequency range of the analog portion of the response signals of the integrated radio frequency based sensor during the operation of the disposable bioprocess component may be within a frequency range that is desirable for reading the memory chip using the radio frequency based sensor. However, if in this embodiment, the operational frequency range of the analog portion of the response signals during the operation of the disposable bioprocess component falls outside the frequency range of reading the memory chip using the radio frequency based sensor, the memory chip may be unreadable during operations in the disposable bioprocess component.

[0034] In yet another embodiment, the digital portion of the response signals may be read before and during the installation of the disposable bioprocess component and after the operation of the disposable bioprocess component with a radio frequency based sensor of a disposable multivariable sensing device operatively coupled to the disposable bioprocess component. Further, the analog portion of the response signals may be read during the operation of the disposable bioprocess component using the integrated radio frequency based sensor. In another embodiment, the digital portion of the response signals may be read before and during the installation of the disposable bioprocess component with the multivariable sensing device and after the operation of the disposable bioprocess component with the integrated radio frequency based sensor of the multivariable sensing device. Further, in this embodiment, the analog portion of the response signals may be read during the operation of the disposable bioprocess component with the integrated radio frequency based sensor. [0035] In certain embodiments, a radio frequency based sensor of a multivariable sensing device may have at least two resonances. Further, one resonance of the at least two resonances may be used to read the digital portion of the sensor response signals with the ability to read/write information from/into the memory chip. While, another resonance of the at least two resonances of the sensor may be used to read the analog portion of the sensor response signals with the ability to quantitatively measure environmental parameters of the process fluid.

[0036] In one embodiment, the radio frequency based sensor may be calibrated before disposing the radio frequency based sensor in the support structure. In particular, the radio frequency based sensor may be calibrated before operation in the container commences.

Further, the radio frequency based sensor may be re-calibrated after the operation in the container is completed. In particular, the radio frequency based sensor may be removed from the support structure after the operation, re-calibrated and then re-installed in the support structure. Accordingly, depending on the application, the radio frequency based sensor and the support structure may be permanently attached or removably attached to the support structure such that the radio frequency based sensor may be de-attached and attached several number of times from the support structure. For example, in applications requiring re-calibration of the radio frequency based sensor post operation, the radio frequency based sensor may be removably attached to the support structure. Whereas, in single use applications, the radio frequency based sensor may be permanently fixed to the support structure. Further, in single use applications, the multivariable sensing device may be permanently fixed to the container. In embodiments where the sensor is removably attached to the container, it is possible to remove the radio frequency based sensor from the support structure, or remove and subsequently re-fix the radio frequency based sensor in the support structure, after use, calibration and/or validation. For example, post operation, the radio frequency based sensor may be removed from the support structure for calibration and then disposed back in the support structure for further operation in the container.

[0037] FIG. 1 illustrates an exemplary embodiment of the multivariable sensing device 100 of the present specification. Further, the multivariable sensing device 100 includes a support structure 102, a radio frequency based sensor 104 and a memory chip 106. The support structure 102 has a first end 107 and a second end 109. Further, the radio frequency based sensor 104 includes a sensor substrate 110 and a radio frequency coil 112. In the illustrated embodiment, the first end 107 of the support structure 102 is configured to receive the radio frequency based sensor 104. [0038) Further, the first end 107 or the second end 109 of the support structure 102 may be configured to be coupled to a container (not shown in FIG. 1), such as a bioprocess component, for measuring one or more parameters of a process fluid present in the container. Consequently, in the presently contemplated configuration, if the first end 107 of the support structure 102 is coupled to the container, at least a portion of the sensor substrate 110 of the radio frequency based sensor 104 may be disposed in close proximity to the container and thus the process fluid. Whereas, if the second end 109 of the support structure 102 is coupled to the container, the radio frequency coil 112 of the radio frequency based sensor 104 may be disposed in close proximity to the process fluid present in the container. In this embodiment, a protection layer (not shown in FIG. 1) may be disposed on at least a portion of the radio frequency based sensor 104, such that the protection layer is disposed between the process fluid and the radio frequency coil 112 to protect the radio frequency coil 112 from being adversely affected by physical contact with the process fluid. By way of example, in instances where the process fluid is an electrically conductive liquid, the presence of the protection layer on the radio frequency coil may prevent portions of the radio frequency coil 112 from being electrically shorted due to presence of the process fluid. For example, the protection layer may be employed for applications such as, but not limited to, pH sensing, glucose sensing, carbon dioxide sensing, oxygen sensing, pressure sensing, temperature sensing, and gamma radiation sensing. However, in embodiments where the radio frequency based sensor 104 is disposed such that the sensor substrate 110 and not the radio frequency coil 112 is in direct physical contact with the contents in the container, it may not be required to employ the protection layer on the radio frequency based sensor 104. In some embodiments, the protection layer may include materials, such as, but not limited to, Si0 ₂ , S1 ₃ N ₄ , SiC, A1 ₂ 0 ₃ , parylene, parylene D, parylene N, parylene C, or combinations thereof

[0039] In certain embodiments, the radio frequency based sensor 104 is configured to sense one or more conditions including a physical condition, a biological condition or a chemical condition. The multivariable sensing device 100 is configured to provide a quantitative response for one or more desirable parameters inside a container. For example, the

multivariable sensing device 100 may be employed to monitor magnitudes of environmental parameters of interest such as, but not limited to, conductivity measurement, pH level, temperature, blood relevant measurement, ionic measurement, non-ionic measurement, non- conductivity measurement, electromagnetic radiation level measurement, pressure, vapor concentration, biological material concentration, and other types of measurements that may be taken from a typical fluid (solution or gas). In one example, the multivariable sensing device 100 may be used in conjunction with disposable bioprocess components to monitor the parameters inside the components during or after the operation.

[0040] In certain embodiments, the support structure 102 may include a circular cross-section or any other geometrical or non-geometrical shaped cross-section. Further, the support structure 102 may or may not be a closed structure. By way of example, the support structure 102 may be in the form of a sleeve, casing, sheath, or any other form that is configured to receive the radio frequency based sensor 104 and retain the radio frequency based sensor 104 in its position at least during operation of the container. Further, the support structure 102 may be configured to receive the radio frequency based sensor 104 from the first end 107 or from the second end 109.

[0041] Further, in certain embodiments, the support structure 102 may be removably or temporarily coupled to the container. One example of removable coupling the support structure 102 may entail simply sliding a portion of the support structure 102 in a corresponding provision in the container. In these embodiments, the support structure 102 may be removed from the container, when desirable. In one example, the support structure 102 may be decoupled from the container, for example, after completion of the process in the container. Further, the support structure 102 may be re-inserted for another process to the same or a different container.

Optionally, in case of a re-use of the multivariable sensing device 100, the multivariable sensing device 100 may be sterilized prior to re-inserting the support structure 102 to the same or different container. Further, to prevent contamination and/or undesirable carryover of the sample from one process to another, the radio frequency based sensor 104 may be replaced by another radio frequency based sensor at the end of the process, or whenever the support structure 102 is de-coupled from the container. In some other embodiments, the support structure 102 may be permanently fixed to the container using techniques, such as, but not limited to, ultrasonic welding, dielectric welding (also known as high frequency (HF) welding or radio frequency (RF) welding), laser welding, hot plate welding, hot knife welding,

induction/impulse, insert molding, in-mold decoration and the other standard types of material welding and joining methods.

[0042] In some embodiments, the radio frequency based sensor 104 may be coupled to a portion of the support structure 102 using chemical ways, mechanical ways, or both. By way of example, the radio frequency based sensor 104 may be retained or coupled to the support structure 104 using mechanical retainers 116 such as, but not limited to, clamps, rings, latch, fastener, pins, or combinations thereof. Alternatively, the radio frequency based sensor 104 may be retained or coupled using adhesives, such as, but not limited to, epoxy based adhesives.

[0043] In some embodiments, the radio frequency based sensor 104 may be disposable in nature. In one embodiment, the radio frequency based sensor 104 may be a radio frequency identification (RFID) tag. Further, the RFID tag may be disposable in nature. In certain embodiments, the radio frequency based sensor 104 is configured to operate based on codes of radio frequency signal generation. Further, the radio frequency based sensor 104 may be configured to resonate at a radio frequency in a range from about 0.01 MHz to about 3000 MHz. Further, the radio frequency based sensor 104 may be configured to communicate with a sensor reader (not shown in FIG. 1) in a radio frequency range from about 0.01 MHz to about 3000 MHz.

[0044] In certain embodiments, commercially available RFID tags may be used to form the radio frequency based sensor 104. These commercially available RFID tags may operate at different frequencies ranging from about 125 kHz to about 2.4 GHz. Suitable RFID tags available from different suppliers and distributors, such as Texas Instruments, TagSys, Digi Key, Fujitsu, Amtel, Hitachi and others, may be used to make the radio frequency based sensor 104. Further, suitable RFID tags may be configured to operate in passive, semi-passive and active modes. It may be noted that the passive RFID tags are not required to be coupled to a power source (for example, a battery) for operation, while the semi-passive and active RFID tags rely on the use of onboard power sources for their operation. Moreover, typically, the RFID tags have a digital ID and a frequency response of corresponding antenna circuit of the RFID tags may be measured as the impedance with real and imaginary parts of the impedance. Further, a sensing or a protection layer may be applied onto the RFID tag and the impedance may be measured as a function of environment in proximity to the resulting sensor. Such sensor is fabricated as described in U.S. Patent Application, Serial No. 11/259,710 entitled "Chemical and biological sensors, systems and methods based on radio frequency identification" and U.S. Patent Application, Serial No. 11/259,711. Also, the RFID tag may be a transponder. Further, the RFID tag may be another type of transponder that transmits a predetermined message in response to a predefined received signal. Such RFID tag may include, but is not limited to, one or more RFID tags disclosed in U.S. Patent Applications, Serial No. 11/259,710, entitled "Modified RF Tags and their Applications for Multiplexed Detection" filed on October 26, 2005 and U.S. Patent Application Serial No. 11/259,711, entitled "Multivariate Methods of Chemical and Biological Detection Using Radio -Frequency Identification Tags" filed on October 26, 2005, which are hereby incorporated by reference. In one embodiment, the RFID tag may have an analog input into a memory chip associated with the RFID tag. In one embodiment, a separate chemical, biological or physical sensor may be connected to the analog input of the memory chip of RFID tag. In another embodiment, at least one chemical, biological or physical sensor is an integral part of the memory chip of the RFID tag where the sensor part of the RFID tag is fabricated during the fabrication process of the memory chip itself. Memory chips of the RFID tags are fabricated using known integrated circuit fabrication processes and organic electronic fabrication processes. [0045] In embodiments where the radio frequency based sensor 104 is disposable, the radio frequency based sensor 104 and/or the support structure 102 may form detachable portions of a given container. Further, the radio frequency based sensor 104 and/or the support structure 102 may be disposed of or re-used, depending on the application and environment in which they are used. Further, the support structure 102 may be made of materials, such as, but not limited to, plastic, polymer, metal, metal composite, ceramics, or combinations thereof. Primarily, the support structure 102 may be made of a material having a suitable mechanical strength, where the material of the support structure 102 does not adversely interact or affect interrogation or sensor signals.

[0046] In one embodiment, the radio frequency based sensor 104 may be gamma-radiation sterilizable to the extent required for pharmaceutical processing (25 kGy to 50 kGy). In particular, the radio frequency based sensor is capable of sensing the parameters even after being exposed to gamma radiation. In one example embodiment, the RFID tags themselves are capable of withstanding gamma radiation without substantive damage to the function of the

RFID tags as radio frequency based sensors. It may be noted that conventional RFID tags may not be resistant to gamma radiation. That is, upon exposure to gamma radiation, the stored information in these conventional RFID tags may be completely or partially lost, or undesirably modified to an extent that the stored information may no longer be a true representation of the parameters being monitored. Therefore, such conventional RFID tags are difficult to use in settings that require gamma sterilization. In certain embodiments, the radio frequency based sensors may be made gamma radiation sterilizable as disclosed in U.S. Patent Publication No. 2009/0256679, entitled "RFID based methods and systems for use in manufacturing and monitoring applications" and U.S. Patent Publication No. 2011/0012736, entitled "Methods and systems for sensing upon radiation exposure," and incorporated herein in their entirety. [0047] In some other embodiments, the protection layer may not be employed by the radio frequency based sensor. Further, to enhance sensitivity of the radio frequency based sensors that do not employ protection layers, other structural elements and parameters may be adjusted to enhance sensitivity of the radio frequency based sensors. In an example embodiment, a thickness of a sensor substrate of the radio frequency based sensor may be adjusted to enhance the sensitivity of the radio frequency based sensor. For example, the sensitivity of conductivity measurements with a resonant sensor in the range from about 10 to 200 milli-siemens per centimeter increases with the increase in the thickness of the protection layer for thickness values of the protection layers in a range from about 5 microns to 600 microns and the sensing coil of about 15 millimeters in diameter and having electrode width of about 70 - 150 millimeters and spacing between electrode turns of about 70-150 millimeters and connected to a memory chip that has about 24 picoFarad capacitance value. Also, the sensitivity of pressure measurements with a resonant sensor with a similar sensing coil increases with the decrease of the gap between the metallic or metallized film and the sensor coil.

[0048] In certain embodiments, the radio frequency based sensor 104 may be calibrated after disposing the radio frequency based sensor 104 in the support structure 102. In one example, the radio frequency based sensor 104 may be pre-fitted in the support structure and calibrated after being disposed in the support structure 102. In certain other embodiments, the radio frequency based sensor 104 may be pre-calibrated before disposing the radio frequency based sensor 104 in the support structure 102. Further, in some of these embodiments, the radio frequency based sensor 104 is adapted to be removed from the support structure 102 for additional recalibration or validation. The radio frequency based sensor 104 may be recalibrated during or after the operation in the container. In one embodiment, post recalibration, the radio frequency based sensor 104 may be installed back in the support structure 102 for the monitoring of the process. However, in another embodiment, where the multivariable sensing device 100 is employed in a single use component, it may not be desired to re-install the radio frequency based sensor 104.

[0049] Further, the memory chip 106 may be in operative association with the radio frequency based sensor 104. In some embodiments, the memory chip 106 may be disposed in the support structure 102, on the support structure 102, or on the container. Moreover, the memory chip 106 may be used for storing information. By way of example, the memory chip 106 may be used to store digital information that can be read by the sensor reader. Further, the information stored in the memory chip 106 may be representative of one or more of the radio frequency based sensor 104 and the container. For example, the information stored in the memory chip 106 may be used to identify the container. In one embodiment, the memory chip 106 may be activated by the interrogation signals transmitted from the read/write unit. In some embodiments, the memory chip 106 may be readable throughout the operation of the container. Whereas, in some other embodiments, the memory chip 106 may be readable only during a portion of the operation of the container. In one example, the memory chip 106 may be readable in the beginning of the operation of the containers and may not be readable later on. In some of these embodiments where the memory chip 106 is disposed in the support structure 102, the memory chip may be operatively coupled to the radio frequency based sensor 104. By way of example, the memory chip 106 may be operatively coupled to the radio frequency based sensor 104 to provide calibrating factors to the radio frequency based sensor 104 to facilitate calibration of the radio frequency based sensor 106. In one example, the memory chip 106 may form part of the radio frequency based sensor 104. In embodiments where the memory chip 106 is disposed on the support structure 102 or on the container, the memory chip 106 may or may not be operatively coupled to the radio frequency based sensor 104. By way of example, the memory chip 106 may be coupled to the container and may be used to identify the container. In the illustrated embodiment, the memory chip 106 is disposed on the support structure 102.

Further, the memory chip 106 may or may not be operatively coupled to the radio frequency based sensor 104.

[0050] FIG. 2 illustrates another exemplary multivariable sensing device 200 of the present specification. In the illustrated embodiment, the multivariable sensing device 200 includes a support structure 202, a radio frequency based sensor 204 and a memory chip 206. In the illustrated embodiment, the memory chip 206 is integral part of the radio frequency based sensor 204. [0051] Further, the support structure 202 includes a body 208 and a projection 210. The body 208 includes a first end 207 and a second end 209. Moreover, the body 208 is configured to receive and retain the radio frequency based sensor 204 at the first end 207. In particular, at least a portion of the radio frequency based sensor 204 is coupled to the first end 207 of the body 208 of the support structure 202. Moreover, the projection 210 is configured to act as a mechanical stopper to restrict entry of a portion of the body 208 of the support structure 202 in the container to a desirable length. Additionally, the projection 210 may also be configured to facilitate physical coupling between the container and the multivariable sensing device 200. By way of example, the projection 210 may be screw fitted or chemically bonded to a portion of the container to provide physical coupling between the support structure 202 and the container. Also, although illustrated as a circular disc with a hollow center, other embodiments of the projection are also envisioned. By way of example, the projection 210 may be in the form of a plurality of discontinuous bars, and the like.

[0052] In some embodiments, the body 208 of the support structure 202 may be divided into portions 212 and 214. Further, .a cross-sectional area of a portion 212 of the body 208 closer to the first end 207 of the body 208, where the first end 207 is configured to be disposed in the container may be maintained smaller than a cross-section of a portion 214 of the body 208 closer to the second end 209 of the body 208 to limit the amount of length of the body 208 of the support structure 202 that may be disposed in the container. Accordingly, in some

embodiments, the body 208 of the support structure 202 may have a uniform cross-section, however, in some other embodiments; the cross-section of the body 208 may vary from one place to another in the body 208. The variation in the cross-section of the cross-section of the body 208 may be in terms of one or both of shape and size.

[0053] In certain embodiments, the projection 210 may be configured to define an amount of a length of the body 208 of the support structure 202 that may be disposed in a container (not shown in FIG. 2). In some embodiments the position of the projection 210 on the body 208 may be adjustable. By way of example, a plurality of notches may be provided on the body 208 as provisions to dispose the projection 210 at a desirable distance 216 from the first end 207 of the body 208. The distance 216 between the projection 210 and the first end 207 of the body 208 of the support structure 202 may vary depending on the size and type of container where the radio frequency based sensor 204 is employed.

[0054] FIG. 3 is a schematic representation 300 of an exemplary multivariable sensing device 302 employed in a container 304. In one or more non-limiting examples, the container 304 may be a disposable container, a disposable bioprocess component, a bioreactor, a stainless steel container, a plastic container, a polymeric material container, or a pre-sterilized polymeric material container. Further, the container 304 may be of different size and shape, for example, micro fluidic channel, a Petri dish, a glove box, a hood, or a plastic bag. The container 304 may or may not have a predetermined shape.

[0055] In some other embodiments, the container 304 may include a disposable bioprocess component, a stainless steel container, a plastic container, a polymeric material container, a chromatography device, a filtration device, a chromatography device with any associated transfer conduits, a filtration device with any associated transfer conduits, centrifuge device, centrifuge device with any associated transfer conduits, a pre-sterilized polymeric material container or any type of container known to those of ordinary skill in the art. Further, non- limiting examples of the disposable bioprocess component include a disposable storage bag, a disposable container, a product transfer line, a filter, a connector, a valve, a pump, a bioreactor, a separation column, a mixer, or a centrifugation system. Further, the disposable bioprocess component may include one or more ports for operatively coupling the multivariable sensing device.

[0056] In one embodiment, the container 304 may be made from, materials, such as, but not limited to, a multi-layer film: ethylene vinyl acetate (EVA) low or very low-density

polyethylene (LDPE or VLDPE) ethyl- vinyl-alcohol (EVOH) polypropylene (PP), polyethylene, low-density polyethylene, ultra-low density polyethylene, polyester, polyamid, polycarbonate, elastomeric materials all of which are well known in the art. RFID tags typically comprise front antennas and microchip with a plastic backing (e.g., polyester, polyimide etc.), or combinations thereof. Further, the container 304 may also be a vessel that contains a fluid such as liquid or gas, where the vessel can have an input and an output. Further, the container 304 may have a liquid flow or no liquid flow. Furthermore, the container 304 may be a bag or a tube, or pipe, or hose.

[0057] In some embodiments, the container 304 may be partly filled with a process fluid, where the solution may be a liquid, fluid or gas, a solid, a paste or a combination of liquid and solid. For example, the solution may be water, a biological buffer, blood, or gas. Further, the container 304 may have a port 305 for inserting the multivariable sensing device 302. In addition, although not illustrated, a plurality of ports for coupling a plurality of multivariable sensing devices is envisioned. [0058] In the illustrated embodiment, the multivariable sensing device 302 includes a radio frequency based sensor 306 disposed in a support structure 308. Further, the multivariable sensing device 302 also includes a memory chip 310. In the illustrated embodiment, the memory chip 310 is disposed outside the support structure 308 and on the container 304.

Accordingly, the memory chip 310 of the illustrated embodiment of FIG. 3 may be used to provide identification details for the container 304. However, in embodiments where the memory chip 310 is disposed in the support structure 308, the memory chip 310 may be configured to also provide calibration parameters for the radio frequency based sensor 306. Further, the multivariable sensing device 302 includes a mechanical stopper in the form of a projection 312 to define a portion of the support structure 308 that is disposed in the container 304.

[0059] FIG. 4 is a schematic representation of a multivariable sensing system 400 employing a multivariable sensing device 402 operatively coupled to a container 404. Further, the multivariable sensing system 400 also employs a sensor reader 406 in operative association with the multivariable sensing device 402. In the illustrated embodiment, the sensor reader 406 includes reader circuitry 408, a pick-up coil 410 operatively coupled to the reader circuitry 408 and a housing 412. In the illustrated embodiment, at least a portion of the reader circuitry 408 and the pick-up coil 410 is disposed in the housing 412 to provide a mechanical integrity and structure to the sensor reader 406. Further, the pick-up coil 410 may be disposed in the same housing 412 as the reader circuitry 408 and electrically coupled to the reader circuitry 408. Accordingly, in these embodiments, the pick-up coil 410 is part of the sensor reader.

[0060] Further, the multivariable sensing device 402 includes radio frequency based sensors 414 operatively coupled to the container 404 to sense one or more parameters of the sample disposed in the container 404. Moreover, the radio frequency based sensors 414 are disposed in a support structure 405. The pick-up coil 410 is part of the sensor reader 406 and configured to relay interrogation signals from the reader circuitry 408 to the radio frequency based sensors 414. Further, the pick-up coil 410 is configured to receive response signals from the radio frequency based sensors 414 and transmit the response signals to the reader circuitry 408.

Accordingly, the sensor reader 406 is fashioned to have the pick-up coil 410 as one of the components of the sensor reader 406. The pick-up coil 410 does not form part of the radio frequency based sensors 414. Accordingly, capacitance and inductance associated with the pick-up coil 410 is not present in the radio frequency based sensor 414, thereby, enhancing the sensor response. [0061] Although not illustrated, in some embodiments, two or more sensor readers, such as the sensor reader 406, may be used to sense one or more parameters of the container 404. In some of these embodiments, each sensor reader 406 may have a corresponding pick-up coil 410. In one embodiment, the pick-up coil 410 may be non-disposable in nature. For example, the pick-up coil 410 may be made of metal, or a metallic material that is preferably re-usable for efficiency (of assembling the multivariable sensing device assembly) and/or economic purposes. The pick-up coil 410 may be either fabricated or bought off the shelf. In embodiments where the pick-up coil 410 is fabricated, the pick-up coil 410 may be fabricated employing standard fabrication techniques such as lithography, masking, forming a metal wire in a loop form, or integrated circuit manufacturing processing. For example, the pick-up coil 410 may be fabricated using photolithographic etching of copper-clad laminates, or coiling of copper wire on a form.

[0062] Further, the pick-up coil 410 may be electrically coupled to the reader circuitry 408 and/or the housing 412. The pick-up coil 410 may be electrically coupled to receive continuous or intermittent electrical power supply from one or more components of the sensor reader 406, such as, but not limited to, the reader circuitry, an electrical connector, or both. For example, an electrical connector may include standard electronic connectors, such as gold-plated pins.

Further, the pick-up coil 410 may be coupled to the reader circuitry and/or the housing in several different ways. For example, the pick-up coil may be attached to the reader circuitry 408 and/or the housing 412 using an adhesive, or by molding the pick-up coil with the housing, or by fastening the pick-up coil to the reader circuitry 408 and/or the housing 412 using screws.

Alternatively, holders may be provided in the reader circuitry 408 and/or the housing 412 such that the pick-up coil 410 can rest on the holders in the housing 412.

[0063] In operation, signals transmitted by antennae of one or more radio frequency based sensors 414 may be picked up by the pick-up coil 410 of the sensor reader 406. The radio frequency based sensor 414 and the pick-up coil 410 are placed in operative proximity. In one example, the radio frequency based sensor 414 and the pick-up coil 410 may be coupled via inductive coupling or physical electrical connections. In embodiments where the pick-up coil 410 is an independent element or where the pick-up coil 410 is part of the sensor reader 406, the pick-up coil 410 may be operatively coupled to the radio frequency based sensor 414 using wired or wireless connections.

[0064] It may be noted that in the illustrated embodiment of FIG. 4, the radio frequency based sensors 414 may include individual memory chips (not shown), or one or more memory chips that are shared by two or more radio frequency based sensors 414. In a particular example, a single memory chip may be shared by the plurality of radio frequency based sensors 414. In this particular example, the single memory chip may be disposed in the support structure 405 in instances where the memory chip is configured to be used for providing calibration parameters during calibration of one or more radio frequency based sensors 414. Further, the single memory chip may be disposed outside the support structure 405, such as the container 404, in instances where the memory chip is used to provide identification parameters, such as an identification code, for the container.

[0065] Further, although not illustrated, it may be noted that in some embodiments, the pick- up coil, such as the pick-up coil 410 may be disposed outside the housing 412 of the sensor reader. Further, the pick-up coil 410 may be disposed outside the housing 412 at a location, such that the pick-up coil 410 is operatively coupled to both the radio frequency based sensors 414 of the multivariable sensing device 402 as well as the sensor reader 406.

[0066] FIG. 5 and 6 illustrate alternate embodiments of multivariable sensing devices of the present specification. FIG. 5 depicts a design of a multivariable sensing device 500, where a radio frequency based sensor 502 of the multivariable sensing device 500 is disposed in a support structure 504 such that a sensing region of the radio frequency based sensor 502 is exposed to a process fluid 508 disposed in a container 512. The sensing region includes coil turns 506. Further, the sensing region may be protected from direct physical contact with the process fluid 508 using a protection layer 514 that may be disposed on at least a portion of the sensing region. In certain embodiments, the protection layer 514 may be a barrier layer, a semipermeable layer, or a perm-selective layer. This protection layer 514 may be used to prevent components of the radio frequency based sensor 502, such as a sensing coil forming the sensing region from coming in direct physical contact of the solution in the container. Also, the protection layer 514 prevents the solution in the container from being contaminated by any leachable or extractable material that may be present in the radio frequency based sensor 502.

[0067] Alternatively, FIG. 6 depicts a design of a multivariable sensing device 600, where a radio frequency based sensor 602 of the multivariable sensing device 600 is disposed in a support structure 604 such that the radio frequency based sensor 602 interacts with a process fluid 608 disposed in a biological container 610 through the sensor substrate 612. The radio frequency based sensor 602 includes a sensing region having coil turns 606. In particular, in the illustrated embodiment of FIG. 6, the radio frequency based sensor 602 is disposed in the support structure 604 such that a sensor substrate 612 of the radio frequency based sensor 602 may be exposed to the process fluid 608 when the support structure 604 is operatively coupled to the biological container 610. Consequently, the sensing region of the radio frequency based sensor 602 may not be in direct physical contact with the process fluid 608 at any time before, during or after operation of the biological container. Further, the sensor substrate 612 of the radio frequency based sensor 602 may be suitable for exposures to the process fluid 608. In some embodiments, the sensor substrate 612 may be made of a polymer material that is not susceptible to chemical reactions with the process fluid 608.

[0068] Further, in certain embodiments, a sensing layer 614 may be disposed on at least a portion of the sensor substrate 612 such that in operation, the sensing layer 614 is disposed between the portion of the sensor substrate 612 and the process fluid 608. It may be noted that the sensing layer 614 may be an optional layer. Non-limiting examples of material for the sensing layer may include sulfonated polymer such as Nation, an adhesive polymer such as silicone adhesive, an inorganic film such as sol-gel film, a composite film such as carbon black- polyisobutylene film, a nanocomposite film such as carbon nanotube-Nafion film, gold nanoparticle-polymer film, metal nanoparticle-polymer film, zeolites, metal-organic

frameworks, cage compounds, clathrates, inclusion compounds, electrospun polymer nanofibers, electrospun inorganic nanofibers, electrospun composite nanofibers, and any other sensor material, or combinations thereof.

[0069] With returning reference to FIG. 5, in certain embodiments, the configuration of FIG. 5, where the protection layer 514 is employed by the radio frequency based sensors 502 may be desirable in instances where conductivity measurements, temperature measurements, dielectric property measurements, or the like, are to be carried out when there is a need for a protection layer thickness, ranging from 0.5 nanometer to 1000 microns. Alternatively, for solution conductivity, pressure, and other measurements, the configuration of FIG. 6 may be used, where the sensor substrate 612 may be exposed to the process fluid. In this embodiment, the sensor substrate 612 of the radio frequency based sensor 602 may be configured to act as a protection layer for the radio frequency based sensor 602. Non-limiting examples of the material for the sensor substrate may include glass, silicon, silicon nitride, silicon carbide, gallium nitride, alumina, zirconia, or combinations thereof. [0070] FIG. 7 illustrates an exemplary method 700 for using a multivariable sensing device for measuring one or more parameters of contents disposed in the container. At step 702, a support structure having a first end and a second end may be provided, where the first end of the support structure is configured to be coupled to a container. At step 704, one or more radio frequency based sensors are disposed in the support structure to form a multivariable sensing device. Further, the step of disposing the radio frequency based sensors may include the step of bonding or positioning the radio frequency based sensors in the support structure such that the radio frequency based sensors are maintained in their respective positions. In one example, one or more radio frequency based sensors may be disposed in a slot in the support structure configured to receive and hold the radio frequency based sensors. In another example, one or more radio frequency based sensors may be chemically bonded to a wall of the support structure.

[0071] The one or more radio frequency based sensors may or may not be pre-calibrated. In embodiments where the radio frequency based sensors are not pre-calibrated, at step 706, the radio frequency based sensors disposed in the support structure may be calibrated. In one embodiment, calibration parameters for calibrating the radio frequency based sensors may be provided by one or more memory chips disposed in the support structure.

[0072] At step 708, the multivariable sensing device having the support structure and the radio frequency based sensors may be operatively coupled to a container. In particular, the support structure of the multivariable sensing device may be coupled to a respective port in the container. Further, the support structure may be removably or permanently coupled to the container. It may be noted that the radio frequency based sensors disposed in the support structure may be calibrated before or after coupling the support structure to the container. In one embodiment, the support structure may be coupled to the container by disposing at least a portion of the support structure closer to the first end of the container. Further, in one embodiment, one or more projections may be used to retain the support structure in place with respect to the container.

[0073] Optionally, at step 710, if a memory chip is not part of the radio frequency based sensors, a memory chip may be operatively coupled to one or more radio frequency based sensors, the support structure, the container, or combinations thereof. Further, at step 712, the multivariable sensing device and/or the container may be sterilized. For example, the container along with the sensing device may be exposed to gamma radiation for sterilizing.

[0074] At step 714, the operation is performed in the container. For example, in case of a bioprocess component, the bioprocessing is carried out. At step 715, before, during and/or after operation in the container, the multivariable sensing device may be used to sense one or more parameters of the container and/or the process fluid disposed in the container. The parameters that may be measured may include physical (temperature, pressure, electrical conductivity), chemical and/or biological parameters.

[0075] Moreover, steps 716-720 illustrate optional steps that may be performed if re- calibration or validation of the radio frequency based sensors is required after performing the operation in the container. At step 716, the multivariable sensing device having the support structure and the radio frequency based sensors is removed from the container. Next, at block 718, the sensor is re-calibrated. Subsequently and optionally, the multivariable sensing device is re-fitted in the container (step 720) for further use.

[0076] In certain embodiments, a radio frequency based sensor of a multivariable sensing device of the present specification may be configured to monitor one or more impedance spectrum, real part of the impedance spectrum, imaginary part of the impedance spectrum, both real and imaginary parts of the impedance spectrum, frequency of the maximum of the real part of the complex impedance (Fp), magnitude of the real part of the complex impedance (Zp), resonant frequency (Fi) and its magnitude (Zi) of the imaginary part of the complex impedance, and anti-resonant frequency (F ₂ ) and its magnitude (Z ₂ ) of the imaginary part of the complex impedance. Additionally, other parameters of the analog signal may also be measured, for example, quality factor, zero crossing resonance frequency, and the like. Details of such parameters are provided in U.S. Patent No. 7,911,345, entitled, "Methods and systems for calibration of RFID sensors" and U.S. Patent No. 8,542,023, entitled, "Highly selective chemical and biological sensors," incorporated here by reference. Individual measured parameters can be further processed in their combinations using well known multivariate techniques, for example principal components analysis, partial least squares, support vector machine, and many others. Further, individual parameters (for example, Fp, Zp) can be also utilized for quantitative measurements. Moreover, these parameters may be measured using an analog portion of response signals of the radio frequency based sensor. The combination of components of sensor circuit result in the generation of an impedance response formed by resonant circuit parameters such as F _p , Z _p , F _{l s} F ₂ , Fz, Z _{l s} Z ₂ and some others produced simultaneously from the resonant sensor.

[0077] FIG. 8 illustrates examples of real and imaginary portions of the impedance of a single sensor at three different states. Non-limiting examples of the three different states may include three different values of a protection layer, a sensor substrate, or both. As illustrated by curves 802, 804 and 806 real parts of impedance values include parameters F _p 808 and Z _p 810. The parameter F _p 808 represents the frequency of the maximum of the real part of the impedance, and the parameter Z _p 810 represents the magnitude of the real part of the impedance. Similarly, as illustrated by curves 812, 814 and 816, imaginary parts of impedance include Fi 818 and F ₂ 820. The parameter Fi 818 represents resonant frequency of the imaginary part of the impedance, and the parameter F ₂ 820 represents anti-resonant frequency of the imaginary part of the impedance. The parameters Fi 818 and F ₂ 820 are related to different components of the equivalent circuit. Additional non-limiting examples of the sensor parameters include parameters that can be extracted from the response of the equivalent circuit of the RFID sensor, for example, the quality factor of resonance, phase angle, and magnitude of impedance of the resonance circuit response of the RFID sensor, and others known in the art. The difference between Fi 818 and F ₂ 820 is related to peak width. In this example, since Fi 818 and F ₂ 820 are related to different components of an equivalent circuit, Fi 818 and F ₂ 820 are not correlated. Further, it may be noted that peak symmetry may be affected by changes in impedance. Other parameters that may be measured using the impedance spectrum, may include, a quality factor of resonance, phase angle, and magnitude of impedance, signal magnitude (Zi) 822 at the resonant frequency of the imaginary part of the complex impedance (Fi) 818, signal magnitude (Z ₂ ) 824 at the anti-resonant frequency of the imaginary part of the complex impedance (F ₂ ) 820, and zero-reactance frequency (Fz, frequency at which the imaginary portion of impedance is zero). Multivariable response parameters are described in U.S. Patent Application, Serial No. 12/118,950 entitled, "Methods and systems for calibration of RFID sensors", which is incorporated herein by reference.

Example 1

[0078] Conductivity of aqueous solutions was measured over a broad dynamic range using individual using radio frequency based sensors. Further, the radio frequency based sensors were made in the form of a metallic coil disposed on a dielectric substrate. For measurements over a broad range of conductivities, the radio frequency based sensors were coated with corresponding layers of parylene polymer. In particular, three different thicknesses of the protection layers were evaluated using three radio frequency based sensors. The three different thickness values of the parylene polymer were 10 microns, 15 microns, and 25 microns. Further, the protection layers of the radio frequency based sensors were in direct physical contact with a process fluid disposed in a container to which the radio frequency based sensors were operatively coupled. Moreover, sensor readouts for the three different radio frequency based sensors were performed with a pick-up coil positioned at a constant distance from the radio frequency based sensors. The responses of the three radio frequency based sensors were acquired as Fp and Zp responses. Responses Fp and Zp of the three radio frequency based sensors were normalized as represented by Equations (1) and (2) respectively.

Fp (normalized) = (Fp - Fp°) / Fp° Equation (1)

Zp (normalized) = (Zp - Zp°) / Zp° Equation (2) where, Fp and Zp are sensor responses measured in water of any conductivity, and

Fp° and Zp° are sensor responses measured in water of minimal conductivity.

[0079] FIGS. 9-10 depict results of measurements of conductivity of aqueous solutions over a broad dynamic range using the three radio frequency based sensors having the corresponding protection layers (as depicted in FIG 5) with different thickness values. FIG. 9 depicts normalized Fp responses over solution conductivity for the three radio frequency based sensors. In particular, graph 902 represents normalized Fp response for the radio frequency based sensor having a protection layer with a thickness of about 10 microns. Similarly, graphs 904 and 906 represent normalized Fp responses for the radio frequency based sensors having protection layers having thicknesses of about 15 microns and 25 microns. Further, x-axis 908 represents electrical conductivity of water and y-axis 910 represents normalized Fp values. FIG. 10 depicts normalized Zp responses over solution conductivity for the 3 radio frequency based sensors. Further, graphs 1002, 1004 and 1006 represent normalized Zp responses for the radio frequency based sensors having the protection layers with thickness values of about 10 microns, 15 microns and 25 microns. Further, x-axis 1008 represents electrical conductivity of water and y- axis 1010 represents normalized Zp values.

[0080] Electrical conductivity measurements of solutions are known by different methods. For example, sensors with two bare electrodes have been utilized in the past for measurements of solutions of low conductivity. However, using only two bare electrodes did not provide the desirably broad dynamic range of conductivity measurements. Thus, measurements of broad range of conductivities were typically achieved with sensors that were built using four bare electrodes. In particular, sensors with four bare electrodes were built where a voltage drop across two inner electrodes was monitored while an alternating current was applied over the two outer electrodes. However, the bare electrodes are well known to be affected by the high conductivity solutions if the bare electrodes are exposed for relatively long periods of time (for example, few hours or days), thereby causing sensor drift due to the deposits or corrosion of the bare electrodes. To address this problem of instability of the bare electrodes, inductive toroidal sensors were introduced. These sensors were made of two toroidal coils protected from a solution with a dielectric material. In these sensors, one coil was used to produce an electric field into a solution. Further, the generated ionic current was monitored by the second coil. The key advantage of the sensors with the toroidal coils was the enhanced sensor stability because there were no bare electrodes in contact with solution. However, the limitation of the inductive toroidal sensors is their ability to measure only high solution conductivity. The radio frequency based sensors having a protection layer are configured to overcome at least some or all of the limitations of other known conductivity sensors and measure solution conductivity over the broad range without the need for a direct physical contact between the bare electrodes with the process fluid.

Example 2 [0081] Conductivity of aqueous solutions was further measured over a broad dynamic range using individual using radio frequency based resonant sensors each having a protection layer (as depicted in FIG 5) that has a thickness value different from protection layers of the other radio frequency based sensors. Further, the radio frequency based sensors as described in Example 1 were used for comparison. The sensitivity of the radio frequency based sensors was measured as Zp responses. Also, the sensitivity was compared in the range of high conductivity (about 50 - 200 mS/cm).

[0082] Comparative study was performed for the radio frequency based sensors that had the protection layers of different thickness values (x-axis 1102) ranging from about 10 microns to 85 microns with respect to sensitivity (y-axis 1104) of the individual radio frequency based sensors. Further, FIG. 11 depicts different sensitivity values (1106) of the individual radio frequency based sensors represented as sensor signal in normalized values of Zp as defined in Example 1 and taken as part-per-million (ppm) values per unit of solution conductivity

(mS/cm). It may be noted that absolute values of the sensitivity values are considered while deriving a relationship between the thickness values of the protection layer and the conductivity. By way of example, a sensitivity values represented as -200 and +200 on the y-axis 1104 were considered as 200 for studying the effect of thickness of the protection layer on the sensitivity of the conductor. The comparative study showed that the most sensitive radio frequency based sensor with its largest absolute values of sensitivity over the tested solution conductivity range was the sensor with the highest value of thickness for the protection layer. Example 3

[0083] Conductivity of aqueous solutions was further measured over a broad dynamic range using individual radio frequency based sensors, each radio frequency based sensor having a sensor substrate. Further, the radio frequency based sensors were operatively coupled to a process fluid or aqueous solutions such that the respective sensor substrates were in direct physical contact with the process fluid (as depicted in FIG 6). Moreover, the different radio frequency based sensors had sensor substrates with different thickness values. The radio frequency based sensors included a metallic coil deposited on alumina (AI ₂ O ₃ ) substrates of 150 microns and 300 microns thickness. Responses Fp and Zp of the radio frequency based sensors were normalized as described in Example 1.

[0084] FIGS. 12-13 depict results of measurements of solution conductivity (x-axis 1202) of aqueous solutions over a broad dynamic range using individual radio frequency based sensors protected with a dielectric layer of different thickness that also served as a sensor substrate. In particular, FIG. 12 depicts normalized Fp responses (y-axis 1304) over solution conductivity, and FIG. 13 depicts normalized Zp (y-axis 1302) responses with respect to the solution conductivity. In FIG. 12, graphs 1206 and 1208 represent Fp responses for radio frequency based sensors having substrates that have thickness values of about 150 microns and 300 microns, respectively. Further, in FIG. 13, graphs 1304 and 1306 represent Zp responses for radio frequency based sensors having substrates that have thickness values of about 150 microns and 300 microns, respectively.

[0085] Advantageously, the multivariable sensing device and the multivariable sensing device assembly may be employed in new and existing systems with ease. Moreover, the current configuration enables the radio frequency based sensor to be easily operatively coupled to a container. Additionally, two or more such radio frequency based sensors may be read using a single pick-up coil. Further, absence of the pick-up coil from the structure of the radio frequency based sensor results in simplification of the design of the multivariable sensing device. Moreover, absence of the pick-up coil from the structure of the multivariable sensing device reduces the cost of the multivariable sensing device.

[0086] While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the invention.