The present invention relates to acoustic and electronic identification apparatus. Specifically, the present invention relates to improvements in an identification apparatus, such as a transponder. Related Application

The present invention, in part, relates to an improvement in identification apparatus, particularly the transponder apparatus the subject of US Patent No. 5153583, owned by the present applicant. The subject matter of US 5153583 is incorporated herein by reference. Prior Art:

Prior art transponders known to the inventors derive their power from an internal battery (active transponders) or externally from the interrogator (passive transponders). Passive transponders are generally powered inductively as shown in US 3,964,024 Hutton et al, AU-B-45334/84 Hook et al and GB 2163324 A Buttemer, capacitively as shown in US 4,364,043 Cole et al and by electromagnetic radiation as per US 4,040,053.

Transponders which utilise inductive or capacitive powering suffer from several disadvantages. The magnetic or electric fields must be limited in intensity for occupational health reasons. These limitations are often set by law. This may reduce operational range or necessitate special shielding. Field strength must be below the statutory radiation limits and may be interfered with by signals from other or proximate electrical equipment. Also, highly directive interrogation beams necessary for interrogating transponders at relatively long ranges pose a health hazard due to their concentrated energy density.

Some forms of acoustic transponders are known, such as those disclosed in US 3293595 and US 3755803. These acoustic transponders, however, are limited in their communication abilities. This reduces the ability of these acoustic transponders to be used effectively as a means of identification. Other types of identification apparatus are "active". However these active identification apparatuses are also relatively limited in their ability to communicate with an external interrogator, due to limitations on their ability to

receive and transmit signals simultaneously. This relatively limited communication ability can be linked to another problem associated with known identification apparatus which is attached to an article and which is moving past an interrogating point. There is only a relatively limited time in which communication can occur between the apparatus and interrogator. This limited time does have an effect on the speed and number of identification apparatuses which can be processed in any given time. Objects of Invention

The present invention seeks to alleviate at least one problem associated with prior art identification apparatus.

The present invention also seeks to improve the range at which an identification apparatus is operable. Summary of Invention

The present invention, in one form, is predicated on the discovery that simultaneous signal transmission and signal reception can occur by overlapping a portion of each of receiver and transmitter means. The invention is applicable, in one form, to an inductive and/or capacitive and/or acoustic means, such as a coil or capacitor plate or PVDF. This advantageously enables an identification apparatus to communicate relatively rapidly with an interrogator by providing the ability for simultaneous and independent transmission and reception of signals.

The present invention provides an identification apparatus having an inductive means in which there is a first portion and a second portion, where receiver means is adapted to receive a first signal coupled to the first portion and transmitter means is adapted to transmit a second signal coupled to the second portion and where the first and second portions are partially overlapped.

The present invention also provides an apparatus as disclosed above, which additionally comprises a voltage supply means which is adapted to power the apparatus, the voltage supply means being further adapted to receive acoustic, optical or battery powering energy.

The signals received and/or transmitted by the present invention may be acoustic, optical, mechanical, electronic or electromagnetic.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, wherein:

Figure 1 shows a schematic model for piezoelectric material. Figure 2 illustrates acoustic signals applied to a transponder. Figure 3 illustrates several rectifying structures.

Figure 4 illustrates a timing reference point in a transponder circuit. Figure 5 illustrates a PLL, carrier generator. Figures 6a to 6d illustrate a number of inductive transponders. Figures 7a to 7e illustrate examples of capacitive reply transponders. Figure 8 illustrates radiative antennas coupled to a transponder.

Figure 8a illustrates a Chladni Figure. Figure 9 illustrates an example of acoustic reply. Figure 9a illustrates bimorphs.

Figure 10 illustrates transponder reply based on re-radiation. Figure 11 illustrates inductive interrogation, acoustic reply.,

Figures 12a to 12f illustrate a number of receiver/transmitted schematic embodiments. Figure 13 illustrates a basic passive device topology. Figure 14 illustrates a basic active device topology. Figure 15 illustrates a shunt regulator in conjunction with the present invention. Figure 16 illustrates in schematic form an active topology without a rectifying diode. Figure 17 illustrates in schematic form the topology of Figure 16, but with counter wound coils.

Acoustic Embodiment

In this embodiment, the terms "acoustic" or "ultrasound" are to be construed to have a value of any frequency above OHz, preferably 0 to 20 Hz or above 20 KHz. Also, although we refer to a transponder in this embodiment, the invention equally applies to any device.

SUBSTITUTE SHEET

Materials are available which possess piezoelectric properties, that is a mechanical flexure of the material is translated into a displacement of charge across the material. This charge displacement produces a voltage across the material. Electrodes deposited on either side of the piezo material can be used to extract the displacement charge or sense the voltage generated by the charge injected onto the electrode capacitance.

Recently plastic film materials with piezoelectric properties have been produced. These materials have exceptional mechanical properties being flexible and tough. One such material is PVDF. Whilst the balance of this embodiment description is aimed at these new flexible film piezoelectric materials it is not intended to be limited in generality. Any piezoelectric transducer or ultrasonic transducer (piezoelectric or otherwise) can suffice for many of the applications revealed in the following description.

Figure 1 shows a model for the dielectric and electrode combination. It is worth noting that piezoelectric action is symmetric, a voltage applied to the material produces a mechanical flexure. Piezoelectric materials are fashioned into sensors for mechanical movements, vibrations, impact and acoustic signals. They are used to fashion acoustic ultrasonic transducers for generating and receiving ultrasonic acoustic signals. We propose in this embodiment the use of sonic energy for communicating with and/or for the remote powering of an electronic transponder. Sonic energy has a number of advantages over more conventional methods of powering transponders. They are safe, not limited by static, easily generated, do not require special components or assemblies and are easily focused into a directed beam.

Figure 2 shows the basic principle involved. An ultrasonic acoustic transducer (1) transmits energy to the ultrasonic receiver (2) (attached to the transponder) which converts the acoustic energy to an electrical signal for delivery to the transponders circuitry(3). The ultrasonic signal may otherwise, or in addition, serve simply as a trigger to the transponder initiating the transmission of prestored data, identifying codes or externally connected inputs. The acoustic signals may be used to

communicate to and/or from the transponder. The signals may be modulated. Such a transponder will require a local energy source, typically from a battery or RF field.

The ultrasonic signal may also serve to supply the electrical power for the transponder. Rectifying structures can convert the AC voltage generated across the ultrasonic receiver into a DC voltage suitable for transponder circuits.

Figure 3 shows several rectifying structures. Where the ultrasonic received has a high impedance or is a piezoelectric material then a tuned circuit connected across the receiver will convert the AC current to an AC voltage with near ideal efficiency. The capacity associated with the receiver is absorbed into the total tuning capacity required for the tuned circuit.

A tuned circuit serves to filter the charge delivered by the receiver. Where a piezoelectric film is used, mechanical flexure can produce low frequency high value charge movements which normally cause high voltages across the material. A tuned circuit or shunt regulator filters out these voltages preventing damage to the transponder circuity connected to the receiving antenna.

Figure 4 shows a transponder circuit which is readily integrated and may use a piezoelectric receiving antenna connected to a tuned circuit as shown. A thorough description of this transponder circuit adapted for inductive powering can be found in US Patent No. 5153583.

In Australian Patent No. 626539 a tuned circuit antenna made by folding a metallised plastic film is described which may be used to form an energy receiving antenna for a transponder. If a piezoelectric plastic film is used to construct the tuned circuit then ultrasonic energy impinging upon the tuned circuit may be converted into electrical energy in the tuned circuit. The circuit will have two resonant frequencies. One at the electrical resonant frequency of the tuned circuit, the other at the mechanical resonant frequency of the folded antenna. These frequencies may or may not be identical.

Such a structure could be made to work with a bimodal action. Recovering energy at the resonant frequency of the tuned circuit while being driven by the transponder at a second frequency (the mechanical resonant frequency).

The receiving antenna can be made to mechanically resonate at the same frequency as the timed circuit. When this occurs the antenna will extract energy from an impinging acoustic signal with high efficiency. The antenna can be made to mechanically resonate at higher or lower order modes to transmit or receive further signals.

The period of the voltage induced in the receiving antenna can be used as a timing reference for the transponder's circuits. US Patent No. 5153583 illustrates how the period is used for an internal clock signal (following division if necessary). Figure 4 shows the transponder circuit with the timing reference point (TR) specially marked.

In addition to providing a clock signal, data and commands can be transmitted to the transponder by modulating the interrogating signal. Any form of modulation may be used. Continuous phase frequency modulation (CFSK) may be advantageously used for transmitting data/commands to the transponder. A phase locked loop decoder in the transponder can demodulate the CFSK modulations.

Demodulated data/commands can be used to program data into memory in the transponder, initiate or control some function the transponder is performing, read data from memory, control the output of energy to a device(s) external to the transponder (see Australian Patent No. 624377) transmit data to external devices or read in data from external devices or sensors.

In addition to receiving data commands, the transponder will usually need to transmit a reply to the interrogator. The reply signal can be transmitted acoustically, inductively, capacitively, optically or electromagnetically. The generation of the reply carrier frequency can be done for example by a PLL multiplier-divider locked to the period of the interrogation signal TR. Figure 5 shows such a PLL system that generates a frequency midway between harmonics of the interrogation signal /c. US Patent No. 5153583 gives a more detailed description of this method and its advantages. Subharmonics of /c can also be generated using this method. Alternatively, simple division can be used to generate subharmonics.

For an inductive reply link a reply carrier current modulated with data is passed through a coil to generate a local magnetic field. The coil can be separate from the tuned circuit coil shown in Figure 6a or co-wound with Lj or a tap off Lj. The current should be supplied by a constant current source. A saturated MOS transistor can serve as an ideal current source if properly biased. US Patent No. 5153583 details the use of current sources to pass currents through a transmitting coil. Figures 6a and 6b show several embodiments of inductive transmitters.

For a capacitive reply channel, a reply carrier voltage modulated with data may be applied to capacitive plates on the transponder to generate a local electric field. A pair of counter driven plates can be used to generate an electric dipole. Alternatively, the body of the transponder can be used as the second capacitive plate or counter point for a single driven plate. PVDF material may be used constructively as a capacitive plate, having metallisation on one or both sides thereof. Figure 7 shows examples of capacitive reply transponders. Powering energy and/or data may be received capacitively or acoustically by all or a portion of the capacitive plates. Data may be transmitted by coil provided on, or a portion of, the capacitive plate as illustrated in Figures 7c, 7d or 7e.

The data modulated carrier reply can be applied to a radiative antenna attached to the transponder as shown in Figure 8.

The transponder can reply using an acoustic reply carrier modulated with data. A separate acoustic transducer can be driven by the transponder. Alternatively the receiving transducer can be driven. Thus, the transponder is adapted to transmit and receive signals simultaneously. This is advantageous if it has a bimodal resonant mode (that is, as previously described, it has separate electrical and mechanical resonant frequencies) or if the mechanical resonant mode can be driven at a different frequency to the tuned circuit resonant frequency. Figure 9 shows examples of these embodiments.

If the receiving antenna is resonant at the acoustic interrogation frequency then the mechanical vibration of the receiving antenna will radiate an acoustic signal. The magnitude of the acoustic signal re-radiated will be proportional to the amplitude of the vibration and the radiation pattern of the antenna. By

varying the electrical load on the receiving antenna the amplitude and/or phase of the re-radiated acoustic signal may be controlled. In this manner, modulation can be superimposed on the acoustic signal re-radiated by the acoustic receiving antenna. Australian Patent No. 624377 details a similar system based upon magnetic rather than acoustic coupling. The re-radiated signal can be detected by the interrogating transducer in the interrogator. Figure 10 shows various embodiments of a reply channel based upon re-radiation by the transponder's receiving transducer.

Alternatively, a separate acoustic receiving transducer can be used by the interrogator to receive the re-radiated signal from the transponder.

It should be appreciated that a transponder as described may be interrogated inductively while the reply signal is an acoustic signal. Thus a tuned circuit could serve as an inductive antenna while a piezoelectric transducer (possibly part of the timed circuit) transmits the reply signal. By using a PLL multiplier (XN) followed by a divider (÷M) fractional harmonics or subharmonics can be generated coherently from the interrogation frequency. These can be used to generate the reply carrier. Figure 11 shows an embodiment of this.

An interrogator generating a directed beam of acoustic energy can interrogate transponders at a distance. Such a feature is advantageous when transponders are attached to animals, cargo containers or waste bins.

Given the finite propagation velocity of ultrasonic acoustic signals, the range from an interrogator to a transponder can be ascertained when a directed beam of acoustic energy is used. Where distance is not an issue and transponder orientation is not fixed then a three-dimensional interrogation unit can be used. Interrogation can occur inductively, acoustically or both simultaneously if the transponder is made so that it responds to both types of interrogation signals. Australian Patent No. 635198 details a three-dimensional inductive powering system that can be easily adapted to perform acoustically.

Where transponders can be interrogated in close proximity such as credit card applications, then some or all of the techniques described above can be advantageously used.

It has been indicated that acoustic transducers ("antennas") for the invention may be fabricated from PVDF piezo film, or similar materials. A flat plate (be it square, circular or of other form) may be caused to vibrate in a variety of mechanical modes. Examples of such vibrations may be seen in many physics books, under the name of Chladni Figures. These "Figures" or forms are obtained by covering a suitable plate with fine powder, and causing it to vibrate. The powder forms itself into various shapes, indicative of the vibrational mode.

If electrodes are deposited (as aforesaid) on suitable piezo plates or

PVDF, in patterns corresponding to these Chladni Figures, the plate may be caused to vibrate in the corresponding mode. An example is shown in Figure

8(a). The effect is reciprocal; such a structure is equally adapted to convert acoustic energy to electrical, as to the converse.

By suitable partitioning such electrodes, and interconnecting the partitioned areas via frequency-selective tuned circuits, these same electrodes may save as the capacitive transmitting plates of Figure 7. Alternatively, the entire electrode array may be surrounded by a co-deposited winding, acting as the inductive element of Figure 6. The winding may be solenoidal, spiral or serpentine.

Planar piezo structures may advantageously be fabricated as so-called "bimorphs"; that is as two parallel piezo plates, layered with 3 conducting electrodes, as in Fig 9(a) wherein the direction of polarization of the piezo film is indicated by arrows. Such elements exhibit piezo motion in a flexural, rather than an extensional mode, and may be especially well suited for the construction of antennas of the type herein described.

In another form, conductive film may be placed on PVDF in order to form solenoid or spiral coils for implementation of coil structures illustrated in Figures 12a to 12f. In this structure, acoustic energy can be used to provide power

(supply voltage) and/or an impinging receiving information or code signal and/or transmitting information or code signal.

The basic passive device topology is shown in Figure 13. IRF injects a transmission current into the coil and VQC comes from the received voltage (signal). R _x is the received signal. It is contemplated to couple a suitable power supply to VDC. such that the device can receive power by way of acoustic, optical, mechanical or RF energy. In the case of an acoustic impinging energy source, PVDF or other suitable means may be used to "convert" or transform acoustic energy to electrical energy.

Active Embodiment

In this embodiment, the present invention is illustrated as applied to an identification device which does not require a powering signal to be supplied externally via magnetic radiation, acoustic or optical.

The embodiment as illustrated in Figure 14 in schematic form replaces C _s of Figure 13 with a battery or other suitable power source. This would not change the identification abilities of the device, since the battery would supply D.C. current just like the storage capacitor. The diode is no longer needed.

In this embodiment, an identification device may be provided which includes any of the coil structures of Figures 12a to 12f. The diode, however, may not be required as noted above. RF signals may impinge and/or radiate simultaneously from such structures, as detailed in US Patent No. 5153583 where the coil structures include an overlapping first and second portion of coil. Alternatively, or in admixture, one or more acoustic antennas and/or one or more inductive coils can be provided. The acoustic antennas may operate singularly or simultaneously receiving and transmitting acoustic signals, as noted earlier. In this embodiment a shunt regulator, preferably but not exclusively of the type disclosed in Australian Patent No. 5045770, may be provided as illustrated in Figure 15 to limit damage resultant from very high received voltages that might result from a too strong field or energy source.

Furthermore, it is to be noted that the tuning capacitor is not essential, and that counter wound coils are preferred for better performance. Figures 16 and 17 illustrate these features in schematic form.

Optical Embodiment

The previous embodiments may be modified to include optical powering and/or communication abilities. Optics, particularly lasers, provide relatively long range transmission/reception abilities in a communication device. Optics provide advantages in relatively noisy environments, which environments may adversely affect acoustic or ultrasonic signals. A mixture of optical, magnetic, active or acoustic powering and/or communication is also contemplated by implementing the principles and concepts disclosed hereinbefore.