CLAIM OF PRIORITY

This application claims the benefit of priority of U.S. Provisional Patent Application Serial Number 62/278,107, titled "AIR FLOW SENSOR FOR FAN COOLED INSTRUMENTS/SYSTEMS" to William A. Lane et al. and filed on January 13, 2016, which is herein incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a flow sensor for measuring gaseous or liquid or other fluid flow.

BACKGROUND

To increase or maximize the processing capability, Integrated Circuits (ICs) can be operated to or near their maximum safe die temperature limit. By introducing external cooling, such as from a fan and forced airflow, the die temperature can be reduced or the processing throughput can be increased, such as while still maintaining the 1C below the maximum temperature limit. The more heat that can be extracted from the system, the more processing throughput can be achievable. As electronic systems can be operated close to their maximum temperature limit it is helpful that the cooling system is reliable and robust.

Fans generating forced airflow are the most common form of electronic system cooling. Particulate/dust filters in the flow path can get clogged over time so regular maintenance/replacement can be required. This is highly

unpredictable so electronic systems can benefit from monitoring the cooling process.

ICs can have embedded temperature sensors that can be used to monitor safe operating limits. However this has limitations. For example, not all components have embedded temperature sensors. Also, some components will have faster thermal response times man others and therefore can become the 'weak link' from a thermal management point of view. Further, it can be impossible to tell if a temperature rise has resulted from increased power consumption or a cooling reduction.

SUMMARY OF THE DISCLOSURE

This disclosure describes techniques for real-time monitoring of a cooling process using a flow sensor system described herein that can detect a failure or a reduction in efficacy, which can prompt corrective action to be taken. In certain systems, it can often be more desirable to 'throttle back' or reduce the processing capacity (reducing power consumption) so as to maintain some minimum level of system functionality.

In some aspects, this disclosure is directed to an air or other gaseous or liquid or other fluid flow or temperature measurement device, the device comprising a substrate, a combined temperature sensor/heater first node, at least a portion of which is integrated with and projects above an upper surface of the substrate, and a combined temperature sensor/heater second node, at least a portion of which is formed with and projects above an upper surface of the same substrate, and wherein the first and second nodes are arranged and integrated with the substrate to permit the fluid flow passing by the first node to also pass by the second node.

In some aspects, this disclosure is directed to a method of measuring an air or other gaseous or liquid or other fluid flow or temperature, the method comprising providing a substrate, a combined temperature sensor/heater first node, at least a portion of which is integrated with and projects above an upper surface of the substrate, and a combined temperature sensor/heater second node, at least a portion of which is formed with and projects above an upper surface of the same substrate, and wherein the first and second nodes are arranged and integrated with the substrate to permit the fluid flow passing by the first node to also pass by the second node. The method includes heating the first node, determining a resistance between a first contact and a second contact of the second node, and determining the flow or temperature using the determined resistance.

This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and IB depict an example of an instrument airflow cooling sensor that can implement various techniques of this disclosure.

FIG. 2 is a perspective view of an example of an airflow sensor on a flex cable.

FIG. 3 is a perspective view of an example of an airflow sensor on a flex cable forming a flow tube.

FIG. 4 is a perspective view of an example of an airflow sensor in a leaded package.

FIG. 5 is a perspective view of another example of an airflow sensor in a leaded package.

FIG. 6 is a conceptual diagram depicting an example of an airflow sensor utilizing a micro thermal transfer principle.

FIG. 7 is a conceptual diagram depicting the example of an airflow sensor of FIG. 6 in detail.

FIG 8 is a conceptual diagram depicting an example of an airflow sensor.

FIG. 9 is a conceptual diagram depicting an example of an airflow sensor.

FIG. 10 is a conceptual diagram depicting an example of an airflow sensor.

FIG. 11 is a cross-sectional view of an example of a combined heater/sensor node including a heater with a lateral thermistor.

FIG. 12 is a plan view of an example of the micro-heater electrode depicted in FIG. 11.

FIG. 13 is a plan view of another example of the micro-heater electrode depicted in FIG. il.

FIG. 14 is a cross-sectional view of an example of a combined heater/sensor node including a heater with a vertical thermistor. FIG. 15 is a plan view of an example of the heater with a vertical thermistor depicted in FIG. 14.

FIG. 16 is perspective view of an example of a pair of sensor/heater nodes formed on a substrate to permit a plug-in edge connection.

FIG. 17 is a perspective view of an example flow sensor bridge implemented using the combined heater/temperature sensor techniques of mis disclosure.

FIG. 18 is a schematic diagram of an example of a circuit using a flow sensor bridge.

FIG 19 is a plan view of an example of a flow sensor in combination with a humidity sensor.

FIG. 20 is a flow diagram showing an example of a method that can implement various techniques of this disclosure.

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

DETAILED DESCRIPTION

Airflow is a measure of the quantity of air flowing through a constrained region in a given time and can be measured in liters per second (L/s), cubic meters per second (m3/s), or kilograms per second (kg/s). Manufacturers of cooling fans generally quote the airflow capacity versus flow resistance or the pressure drop across the system housing.

In some systems, it can be more desirable to 'throttle back' or reduce the processing capacity, e.g., reducing power consumption, so as to maintain some minimum level of system functionality'. This disclosure describes techniques for real-time monitoring of a cooling process using an airflow cooling sensor system that can detect a failure or a reduction in efficacy, which can prompt corrective action to be taken and can allow the system to maintain a level of functionality.

FIGS. 1 A and IB depict an example of an instrument airflow cooling sensor that can implement various techniques of this disclosure. The instrument airflow cooling sensor 100 of FIGS. 1A and IB can include a programmable airflow sensor 102 be formed on substrate, and a flow coupler 104. Although referred to as an integrated circuit (IC) substrate within mis disclosure, the substrate can include, for example, a printed circuit board (PCB) or plastic.

FIG. 1 A is a cross-sectional view of a sensor 102 and a coupler 104 and

FIG. IB is an end view of the sensor 102 and the coupler 104. For purposes of conciseness, FIGS. 1 A and IB will be described together.

The programmable airflow sensor IC 102 can include an open cavity airflow sensor IC based on a micro thermal transfer principle and can be software or otherwise programmable, such as to accommodate different flow conditions across a wide range of applications. The sensor IC 102 can operate in conjunction with a duct, cone, funnel, coupler, or other flow guide that couples the airflow 106 to the sensor 104. The dimensions of the coupler 104 can define a region through which the flow volume can be calibrated. The coupler 104 can be implemented in various forms.

In some example implementations, the coupler 104 can include an attachable and/or detachable mounting, such as which fits over and couples the airflow to the sensor IC 102. The coupler can be attachable and/or detachable via a snap fit mechanism, a clamp on mechanism, and the like. The coupler can be attachable and/or detachable at manufacture, by a user, or both. Additionally or alternatively, the airflow sensor can be mounted or attached to the interior of a plastic or other flow coupler, such as with metal or other conductive traces for connecting to the terminals of sensor/heater nodes within the airflow sensor that is located within the coupler. Couplers of different shapes and/or sizes can be provide, (e.g., in a kit or individually 3D printed) such as to "impedance match" one or more of the flow characteristics of a given system to the sensor IC 102. In this way, one airflow sensor platform, using a selected one of different couplers 104, can meet the requirements of multiple different applications. Matching one or more of the characteristics of the coupler 104 to match the sensor IC 102 can allow for an accurate absolute airflow measure, e.g. L/s.

It should be noted mat although the sensor is described as an "airflow sensor", the sensor techniques of this disclosure are not limited to airflow.

Rather, the sensor 102 can be used for air or other gaseous or liquid or other fluid flow or as a temperature measurement device. As described in detail below, the sensor 102 can include two similar or identical combined temperature sensor/heater nodes 122, 124 such as can be positioned in line with the axis of the airflow 106. Each node 122, 124 can independently operate as either a heater or a temperature sensor.

FIG. 2 is a perspective view of an example of an airflow sensor on a flex cable. As seen in FIG. 2, the airflow sensor IC 102 or die can be mounted on a flexible PCB 108 (or "flex" or "flex circuit") to allow for good (e.g., unobstructed) or optimum positioning in the airflow 106. In an example, the housing 110 of the sensor 102 defines the constraining region for the flow measurement, which can help provide an accurate absolute flow measurement. The flex circuit 108 can be coupled to an integrated circuit substrate of the sensor 102 (shown at 130 in FIG. 7, for example), to position the integrated circuit substrate with respect to the airflow passing by the two nodes of the sensor (shown as nodes 122, 124 in FIG. 7). The sensor 102 can either be calibrated in the end system to permit a high accuracy absolute flow output (L/s) or can be used in a relative sensing mode.

FIG. 3 is a perspective view of an example of an airflow sensor 102 on a flex cable forming a flow tube. As seen in FIG 2, the airflow sensor IC 102 or die can be mounted on a flexible PCB 108 (or "flex"). The flex can be wrapped to form a tube 112 such that the dimensions of the tube 112 define the constraints for an absolute flow measurement or such that the nodes 122, 124 can be aligned with the axis of airflow 106. Furthermore, the sensor 102 and the flex assembly 108 can be calibrated to provide a high accuracy absolute flow measurement. The flex assembly and sensor structure can itself be placed within a flow coupler, such as a funnel-like flow concentrator or flow spreader.

FIG. 4 is a perspective view of an example of an airflow sensor 102 in a leaded package 114. As seen in FIG. 4, the leads 116 can be straight and can be used to adjust the height of the sensor 102 such as to optimize positioning in the airflow 106.

FIG. 5 is a perspective view of another example of an airflow sensor 102 in or on a leaded package 102. As seen in FIG. 5, the leads 118 can include at least one bend 120 and can be used to adjust the flow alignment of the sensor 102 to optimize positioning in the airflow 106. The sensors in FIGS. 3-5 can either be calibrated in the end system to give an absolute flow output (L/s) or can be used in a relative sensing mode.

FIG. 6 is a conceptual diagram depicting an example of an airflow sensor 102 utilizing a micro thermal transfer principle. The sensor 102 can include or consist of two similar dual-purpose combined temperature sensor/heater nodes 122, 124, e.g., thermistor, such as can be positioned in line with the directional axis of the airflow 106 to be measured. Each of these two nodes can

independently operate as either a heater or a temperature sensor, and each such node can operate concurrently as both a heater and a temperature sensor.

In FIG. 6, air flowing from left to right is heated as it passes over upstream node 122 (which can be configured as a heater) and some of this energy is then transferred via the airflow to downstream node 124 (which can be configured as a temperature sensor). This heat transfer via the airflow 106 causes an increase in temperature, at the temperature sensor node 124, which is proportional to the airflow rate, and which therefore can be converted into an indication of airflow. In an example, each of nodes 122 and 124 can be concurrently operating both as a heater and a temperature sensor, and a feedback loop can be used to maintain each temperature sensor at a target temperature value, and the power consumption of each can be monitored, with the difference in power consumption between the two nodes being proportional to airflow.

Because the nodes are dual purpose, they can be reconfigured such as for sensing airflow in the opposite direction, such as by switching their respective roles, e.g., from heater to temperature sensor and from temperature sensor to heater, respectively. Bidirectional airflow sensing ability can be important in numerous applications such as, for example, respiration sensing of the bidirectional airflow associated with breathing by a human or animal subject.

FIG. 7 is a conceptual diagram depicting the example of an airflow sensor 102 of FIG. 6 in detail. As seen in FIG. 7, each node 122, 124 can include a thermistor portion 126 and a heater portion 128 to provide combined heater/temperature sensor functions. In some examples, the nodes 122, 124 can provide fully symmetrical independent heater/thermistor operation.

At least a portion of each of the nodes 122, 124 can be integrated with and project above an upper surface of an integrated circuit substrate 130. The nodes 122, 124 can be arranged and integrated with the same integrated circuit substrate 130 to permit the airflow passing by the first node 122 to also pass by the second node 124, e.g., by positioning in line with the axis of the airflow 106.

For improved or optimum performance, it can be desirable for the heater/sensor nodes to be thermally isolated from an integrated circuit substrate 130 while thermally coupled to the airflow 106. This can be achieved by depositing or otherwise forming or locating the nodes 122, 124 on a thermal insulator barrier 132, e.g., polyimide, such as to provide such thermal isolation from the substrate 130. The thermal insulator barrier can have a lower thermal conductivity than the substrate 130. One or more of a number of approaches can be used to increase or maximize the thermal coupling between the heater/sensor nodes 122, 124 and the airflow to be sensed using the microthermal transfer principle.

For instance, a thermal insulating material 132 can be deposited as a thick film mound that can provide a platform raising the heater/sensor nodes 122, 124 into the airflow 106. In addition, as seen in FIGS. 8 and 9, a height profile and/or an edge profile of the platform can be engineered to optimise the airflow over the heater/sensor nodes 122, 124. The degree of slope can be selected based on one or more user input parameters or factors such as the expected magnitude or one or more other characteristics of the airflow to be sensed.

In an example, the thermistor material, which can also double as a heat spreader, can be deposited or otherwise formed as a thick film, such as to help each sensor/heater node to protrude further into the airflow, thereby enhancing thermal coupling between the sensor/heater node and the airflow. Additional thermistor or other surface material (e.g., silicon nitride or other material having good thermal conductivity) can optionally be used, such as shown in FIG. 10, such as can help heat spreading or passivating the sensor heater node.

In an example, the heater/sensor node surface characteristics can be modified (e.g., textured or roughened) such as to increase or maximize thermal coupling between the sensor/heater node and the airflow, see, e.g., FIG. 10.

A trench can be provided between the heater/sensor nodes, such as to provide air gap thermal isolation between the heater/sensor nodes by effectively giving each individual heater/sensor node its own mound of polyimide (e.g., if the trench extends all the way from the surface of the mound to the substrate, or the trench can extend partially to the substrate). Similarly, a common base mound can be provided for both of the heater/ sensor nodes, upon which individual mounds can be provided for individual heater/sensor nodes, such as to provide air gap thermal isolation between the individual heater/sensor nodes and their respective individual mounds. This can be useful such as when there is a mound deposition process height limitation, such that successive mound deposition process steps can be used. The heater/sensor node material can be formed so as to include a portion on one or more sides of the mound as well as on top of the mound. Air gap thermal isolation from the substrate can also include forming a trench in the substrate under the mound or in an underside portion of the mound.

FIG. 8 is a conceptual diagram depicting an example of an airflow sensor. As seen in FIG. 8, a height of the thermal insulating material 132 can be deposited to various heights 134A-134C, for example, to improve or optimize thermal coupling.

FIG. 9 is a conceptual diagram depicting an example of an airflow sensor. As seen in FIG. 9, the thick film platform 132 of the sensor 102 can include at least one leading or trailing edge 136, which can be adjusted to various profiles 138A-138C, for example, to provide a flow ramp that can improve airflow and/or thermal coupling. The one or more flow ramps can be positioned upstream or downstream of at least one of the nodes 1221, 124, to provide a transition between an upper surface 140 of the integrated circuit substrate 130 and an upper surface 142, 144 of at least one of the nodes 122, 124, respectively.

FIG. 10 is a conceptual diagram depicting an example of an airflow sensor. As seen in FIG. 10, in some example configurations, the thermistor material, e.g., material 126 of FIG. 7, which can also double as a heat spreader, can deposited as a thick film 146 causing one or both nodes 122, 124 (node 122 shown in FIG. 10) to protrude further into the airflow 106 thereby enhancing thermal coupling.

In addition, in some examples, the surface 148 of one or both nodes 122, 124 (node 122 shown in FIG. 10) can include a surface treatment to enhance thermal coupling. For example, as seen in FIG. 10, the surface 148 can be treated to include a plurality of peaks 150 and troughs 152 to increase the amount of surface area in contact with the airflow 106 or the additional surface material, e.g., thick film 146. In this manner, the heater/sensor node surface characteristics can be modified to increase or maximize thermal coupling.

As described in detail below, the combined heater/sensor nodes of this disclosure can implemented, for example, as a heater with a lateral thermistor or as a heater with a vertical thermistor.

FIG. 11 is a cross-sectional view of an example of a combined heater/sensor node including a heater with a lateral thermistor. Each of nodes 122, 124 can be a combined temperature sensor/heater node, at least a portion of which is integrated with and projects above an upper surface of the integrated circuit substrate 130. The nodes 122, 124 can be arranged and integrated with the same integrated circuit substrate 130 to permit the airflow passing by the first node, e.g., node 122, to also pass by the second node, e.g., node 124.

As seen in FIG. 11, the node 122 can include a substrate 130 and a low thermal conductivity platform 132, e.g., polyimide, positioned adjacent the substrate 130. The node 122 can further include an electrical resistor heating element 154, e.g., a micro-heater, that can be thermally separated or isolated from the substrate 130, such as by at least a portion of a thermal insulator barrier, e.g., the thick film platform 132. The node 122 can include a thermistor material 156, e.g., a thermistor thick film 156, in electrical contact with the heating element 154. At least a portion of the thermistor material 156 can be deposited above or on top of the heating element 154 toward a flow region, e.g., as shown in FIGS. 12 and 13, to provide an electrical resistance that varies with temperature, e.g., a temperature sensor, and which can double as a heat spreader in heater mode. In some examples, the node 122 can include a well or tub 158 formed in the platform such as to aid adhesion of the thermistor 156.

As described below with respect to FIG. XX, a system XX can include a temperature measurement circuit XX mat can include a first input electrically coupled to at least one thermistor connector, e.g., connector 172, and including a second input electrically coupled to at least one of the first terminal HI or the second terminal H2 of the heating element 154.

FIG. 12 is a plan view of an example of the micro-heater electrode 160 of the heating element 154 depicted in FIG. 11. The micro-heater electrode 160 of node 122 can include first and second terminals HI, H2 that are electrically connected to circuitry on or in the substrate 130 of FIG. 11. As seen in FIG. 12, the micro-heater electrode 160 can be arranged in a serpentine pattern, switchback pattern, or some other high resistance morphology, for example. The nodes 122, 124 of FIG. 11, for example, can also include two thermistor connectors 162, 164.

The thermistor connectors 162, 164 include terminals Rl, R2, respectively. Each of connectors Rl, R2 can include a first region contacting the thermistor material, e.g., thick film 1S6 of FIG. 11, and a second region that is electrically connected to circuitry on or in the substrate, e.g., substrate 130 of FIG. 11. In some example configurations, such as shown in FIG. 11, the thermistor connectors 162, 164 can be interdigitated. In a sensing mode, the resistance of the thermistor material 1S6 can be measured between nodes Rl and one of HI, H2 and R2 and one of HI, H2.

The material used for the traces between HI and H2 can be different than the material used for the thermistor contacts Rl, R2. For example, the material used for the traces between HI and H2 can be selected to provide high resistivity, so that an electrical current passing between HI and H2 is efficiently converted into heat. The material used for the traces associated with thermistor contacts Rl and R2 can be selected to provide a good electrical connection to the thermistor material being used for temperature sensing. For example, the material associated with the thermistor contacts Rl and R2 can be selected to avoid metal-semiconductor junction diode (e.g., Schottky diode) effect at its interface with the thermistor material. The node 124 can be constructed and arranged similar to the node 122 and, for purposes of conciseness, will not be described in detail.

FIG. 13 is a plan view of another example of the micro-heater element depicted in FIG. 11. As seen in FIG. 13, the micro-heater electrode 166 can include first and second terminals HI, H2 that are electrically connected to circuitry on or in the substrate 130 of FIG. 11. The micro-heater electrode 166 can be arranged in a serpentine pattern, switchback pattern, or other pattern. The thermistor connectors 168, 170 include terminals Rl, R2. In contrast to the configuration shown in FIG. 12, the thermistor connectors 168, 170 are not interdigitated, but instead extend around at least a portion of the periphery of the thick film 156. The node 124 can be constructed and arranged similar to the node 122 and, for purposes of conciseness, will not be described in detail.

This is primarily a lateral resistance that is dominated by the thermistor material closest to the electrodes and consequently furthest away from the top surface of the heater/sensor node adjacent the airflow being sensed using the microthermal transfer principle. This is less sensitive and therefore is not an optimum configuration. The present inventors have recognized that, ideally, it is desirable mat the surface material where the heat transfer has its maximum impact to be the dominant region defining the thermistor resistance for higher sensitivity temperature sensing. This limitation of the lateral thermistor structure is addressed in the Vertical Thermistor implementation. Such a configuration is shown in the vertical thermistor implementation of FIG. 14.

In operation, a source can generate a voltage or current between terminals HI and H2 to heat the electrode 160 (or 166) of the heating element 154. In a sensing mode, to detect the temperature, the resistance of the thermistor material 156 can be measured between node Rl and one of HI, H2 and between node R2 and one of HI, H2. For example, a system controller can control a known current, e.g., using a current source, to be applied between node Rl and one of HI, H2 and between node R2 and one of HI, H2 and measurement circuitry can measure a resistance between the thermistor contact and the heater element contact. Under zero flow, e.g., zero air flow, the resistance can be the same for each node 122, 124. Under flow conditions, heat can be transferred from the upstream node to the downstream node. On the upstream node, the current can increase to maintain the resistance across its thermistor material and, on the downstream node, the current can decrease to maintain the resistance across its thermistor material. For power efficiency, the controller can control this operation in a pulsed mode, for example.

In some example implementations, a time of flight can be used to determine flow. For example, a system controller can control a known current, e.g., using a current source, to be applied to an upstream node, e.g., by passing a short burst of current through the heater portion of the node, to generate a pulse of heat into the environment. Measurement circuitry can monitor and measure the resistance of a downstream node over time. In some example

implementations, the peak or maximum change in the resistance of the downstream node can be considered to be when the peak of the heat is transferred from the first node to the second node. This technique can negate the need to know the environmental conditions because it is the time of the heat maximum from emission to absorption that is being monitored. The operation can be reversed to determine flow in the opposite direction.

FIG. 14 is a cross-sectional view of an example of a combined heater/sensor node including a heater with a vertical thermistor. Each of nodes 122, 124 can be a combined temperature sensor/heater node, at least a portion of which is integrated with and projects above an upper surface of the integrated circuit substrate 130. The nodes 122, 124 can be arranged and integrated with the same integrated circuit substrate 130 to permit the airflow passing by the first node, e.g., node 122, to also pass by the second node, e.g., node 124.

As seen in FIG. 14, the node 122 can include an integrated circuit substrate 130 and a low thermal conductivity platform 132, e.g., polyimide, positioned adjacent the substrate 130. The node 122 can further include an electrical resistor heating element 154, e.g., a micro-heater, that can be thermally separated or isolated from the substrate 130 by at least a portion of a thermal insulator barrier, e.g., the thick film platform 132. The node 122 can include a thermistor material 156, e.g., a thermistor thick film 156, at least a portion of which can be deposited on above or on top of the micro-heater 154 toward a flow region, e.g., as shown in FIG. 15, to provide an electrical resistance that varies with temperature, e.g., a temperature sensor, and to double as a heat spreader in heater mode. In some examples, the node 122 can include a well or tub 158 formed in the platform mat can aid adhesion of the thermistor 156.

In addition, the node 122 can include a thermistor connector or electrically conductive electrode 172, e.g., metal, deposited on top of the thermistor material 156. In sense mode, the thermistor material 156 can be measured between the top electrode 172 and a selected one or both of heating element contacts HI, H2 of FIG. 15. The thermistor connector 172 can be separated from the heating element 154 by a second thermal insulator barrier 174 having a lower thermal conductivity than the substrate 130. The node 124 can be constructed and arranged similar to the node 122 and, for purposes of conciseness, will not be described in detail. This structure can form a vertical structure where the top surface of the thermistor (which can be most influenced by heat transfer) can be a dominant component in the total resistance. In addition, the top metal electrode 172 can seal the thermistor material 156 from direct contact with the environment, which can help reduce or eliminate resistance variations or sensor degradation due to humidity or surface contamination.

FIG. 15 is a plan view of an example of the heater with a vertical thermistor depicted in FIG. 14. The micro-heater electrode 160 of FIG. 15 is similar to the electrode 160 of FIG. 13 and can include first and second terminals HI, H2 that are electrically connected to circuitry on or in the substrate 130 of FIG. 11. As seen in FIG. 15, the micro-heater electrode 160 can be arranged in a serpentine or switchback pattern, for example.

FIG. 16 is perspective view of an example of a pair of sensor/heater nodes 122, 124 formed on a substrate to permit a plug-in edge connection. For example, the nodes 122, 124 can be formed on a plastic or other substrate 176, e.g., PCB, with conductive traces 178A-178H run to an edge 180 of the substrate 176 to permit plug-in edge connection, or bonding thereto. The substrate 176 can be located within a flow coupler, e.g., coupler 104 of FIG. 1, or can be shaped to form a flow coupler, e.g., tube, funnel, duct, or the like.

The combined heater/temperature sensor techniques of this disclosure can be used to implement a flow sensor Wheatstone bridge, such as shown in FIG. 17.

FIG. 17 is a perspective view of an example flow sensor bridge implemented using the combined heater/temperature sensor techniques of this disclosure. The flow sensor bridge 200 of FIG. 17 can include an insulating layer 202, e.g., polyimide, such as can provide thermal isolation between the heater/sensor node bridge resistors and the substrate 204.

The flow sensor bridge 200 of FIG. 17 can include four combined temperature sensor/heater nodes 205A-205D, at least a portion of each located on and projecting above an upper surface of an integrated circuit substrate 204.

The nodes 205A-205D can concurrently act as a heater and as a resistor temperature sensor. The four sensor/heater nodes 205A-205D can be arranged to form the resistors of a Wheatstone bridge. Baffles can be provided, such as to inhibit airflow around the structure from cooling the backside heater/sensor node bridge resistors or to promote a difference in cooling with the front side heater/sensor node bridge resistors receiving more cooling than the backside heater/sensor node bridge resistors.

The bridge 200 can include a raised, shaped polyimide layer 206 on which to place two of the bridge resistors Rl, R4 in the air flow path 208 for a given direction of airflow. In some example configurations, the raised/shaped polyimide layer 206 (or other thermally insulative layer) can be sized and shaped to place two of the heater/sensor node bridge resistors in the air flow path for a given direction, such as by locating them on an upstream slope of a mound or platform of the polyimide layer, and optionally separated from each other or otherwise constrained by lateral fins.

For example, at least a portion of node 205 A can be formed on a ramp 207 A and at least a portion of node 205C can be formed on a ramp 207C. Nodes 205B-205D can be formed on similar ramps (not labeled). The ramps 207 A,

207C for nodes 205 A, 205C can be facing in an upstream direction of the airflow 208, and at least a portion of the nodes 205B, 205D can be formed on ramps (not depicted) facing in a downstream direction of the flow 208 or with a barrier 209 between the second node and third node and a direction of the flow 208.

Bridge resistors R2, R3 are on the opposite side (not shown). The sensor

200 can include electrically conductive interconnects 210, e.g., gold

interconnects, to electrically connect the resistors, e.g., R1-R4, and the other circuitry, e.g., such as shown in FIG. 18.

FIG. 18 is a schematic diagram of an example of a circuit using a flow sensor bridge. The circuit can include an amplifier 212, e.g., voltage sensing amplifier, having a first input 214, e.g., non-inverting input, and a second input 216, e.g., inverting input, and four resistors R1-R4, e.g., of the sensor 200 of FIG. 16. The resistors Rl, R2 can be arranged as a first voltage divider and the first input 214, e.g., non-inverting input, of the amplifier 212 can be connected to an interconnection or node 218 between Rl , R2, where Rl can see the front of the airflow as in FIG. 17. The resistors R3, R4 can be arranged as a second voltage divider and the second input 216, e.g., inverting input, of the amplifier can be connected to an interconnection or node 220 between R3, R4, where R4 can see the front of the airflow as in FIG. 17. The circuit 222 can include a digital-to-analog converter 224 having an output 226, e.g., voltage VHEAT, driving the resistors R1-R4 of the bridge 200.

Hie flow bridge sensor can be configured such that two resistors in the flow bridge sensor, e.g., resistors Rl and R4 of the bridge 200 of FIG. 17, can be in the airflow path at a given time. The cooling effect of the airflow 208 can alter the resistance of the temperature dependent exposed resistors (e.g., those facing the airflow) and the voltage in the bridge 200 can become unbalanced. This voltage differential can be fed into the amplifier 212 as a measure of the airflow. The sign of the voltage differential can provide information as to the direction of the airflow.

A supply or other reference voltage circuit 224 can be configured to provide a voltage VHEAT to a parallel combination of (1) a series combination of the node 20SA and the node 205B and (2) a series combination of the node 205C and the node 205D. An example of a reference voltage circuit 224 can include a digital-to-analog converter, as shown. The DAC 224 driving the resistors on the bridge 200 can drive different voltages VHEAT to the parallel combination. Using the measurements obtained at the different voltages, the absolute ambient temperature can be derived. This derived temperature can be used to compensate for any temperature impacts on the measurement of airflow.

In some implementations, a software design suite, e.g., an Airflow

Sensor Development Environment (ASDE), can be used that can enable the end- user to select a coupler from a selection of predesigned structures that vary in shape and size (or both), such as can accommodate a wide range of airflow rates by selecting the appropriate Coupler, such as can be based upon one or more user-provided input parameters (e.g., expected flow rate range, turbulence, height from substrate, size restriction, flow concentration/funnelling, etc.) The ASDE can also generate a sensor configuration table for the airflow sensor IC (e.g., alone or in combination with the selected Coupler) such as to establish or optimize one or more or all aspects of the total system performance, e.g., flow rate, operating temperature and relative humidity (RH) range, sampling rate, power consumption, etc. The ASDE can also generate driver source code that can be loaded as a library component for ease of software integration. The ASDE can also allow an end user to design custom couplers for unique applications/housings, for example. These software design techniques can allow one IC to support many different flow sensing requirements by choosing an appropriate coupler.

This has potential commercial benefit as one IC can support many different flow sensing requirements, such as by choosing an appropriate coupler. Couplers can be available for purchase from a device manufacturer, such as ADI, or CAD drawings and 3D printable downloads of standard parts can be available on a website, such as analog.com

The principle of thermal transfer can be used in airflow sensing but certain features of the various designs of this disclosure can help offer certain potential advantages. For example, the use of a solid film of low thermal conductivity material, e.g., polyimide, to provide isolation from a substrate, as described above. In addition, a solid substrate can provide a more mechanically robust alternative to microelectromechanical system (MEMS) isolated table approaches and can be less sensitive to particulate contamination in the airflow.

As another example, combining the heater and thermistor (temperature sensor) node, as described above. This can provide a fully symmetrical design. The heat and sense operations can be swapped electronically, which can be advantageous for certain applications, such as for allowing bidirectional airflow to be measured. Other approaches can use separate dedicated heater and sensor elements. In such an arrangement, the heater node is located in the middle with one temperature sensor located upstream and the other downstream in the airflow. With the combined heater/sensor node only two sites are needed (e.g., for bidirectional flow sensing) thus saving area, such as die area

In cost and size sensitive applications, a single heater/sensor node can be used, such as to provide a relative measure of airflow.

As another example, as described above, the thermistor material can be deposited as a thick film causing it to protrude into the airstream As a result, the surface area can be increased and the thermal contact with the airflow can be enhanced.

For any two identical heater/sensor nodes, the thermal time constants can be very well matched and should be identical under zero flow conditions.

However in non-zero flow conditions, there will be heat transfer between nodes, which alters the temperature profile versus time. By using a sampled data approach of observing the temperature time profiles of identical structures the flow rate can be extracted. This sampled data approach can provide a power efficient architecture that can allow flow rate to be measured very quickly on demand.

As another example, the top electrode of the vertical thermistor example configuration described above can be advantageous in that the top electrode completely seals the thermistor material from the airflow. In particular, the top electrode can present a barrier to humidity ingression and airborne contaminants.

The sensor described above can be configured in several operating modes. For example, the sensor can be operated as continuous time analog out sensor. The two sensors nodes can be controlled independently such as by a closed loop feedback circuit such as can work to maintain each node at a predetermined temperature. In the presence of airflow, one node will be cooled and the second will experience heat gain. The closed loop heater/sensor drivers can adapt to these conditions such as to maintain a constant operating temperature at each node. Comparing the control variables of each feedback loop can give a measure of the airflow. In such an implementation the heaters can be constantly on and consuming power.

The sensor of this disclosure can also be operated as pulse powered heaters. A more power efficient architecture can pulse power the heaters and monitor the time temperature profiles to calculate the airflow rate.

The sensor of this disclosure can also be operated in a hybrid mode. For example, pulse powering one node (e.g., a heater/sensor node configured as a heater) and constant ongoing monitoring the temperature on the second node (e.g., a heater/sensor node configured as a temperature sensor).

When operated as a heater, the heater can be operated in a number of modes. In a constant temperature mode, the heater can be forced to a known temperature and maintained at that temperature by a closed loop control circuit. In a constant power mode, the heater can be driven with a constant power. For example, the constant power can be from a fixed voltage source where the current is controlled to maintain a constant power (V*I). Alternatively, in constant power mode, the heater can be driven from a constant current source and the voltage can be controlled to maintain constant power (V*I). The heater can also be operated in constant voltage or constant current mode. The sensor of this disclosure can also provide for sensor fusion techniques. That is, the airflow sensor of this disclosure can incorporate or be accompanies by one or more additional sensor elements (e.g., temperature sensors or non-temperature sensors) such as to mitigate for environmental variations such as temperature or other than temperature. For example, a humidity sensor can be incorporated. Heat transfer due to airflow can be dependent on the moisture content or humidity of the air. To correct the airflow measure for different ambient conditions a relative humidity sensor can be inserted beside the flow sensors, as seen in FIG. 19.

System compensation of effects due to ambient temperature change can be implemented by incorporating or including a sensor to measure absolute ambient temperature and corrections to airflow measure can be made accordingly using information about the ambient temperature from the ambient temperature sensor.

FIG. 19 is a plan view of an example of a flow sensor in combination with a humidity sensor. The flow sensor A 230 and flow sensor B 232 can be similar to the flow sensors depicted and described above with respect to FIG. IS. The flow sensors A, B can include electrodes arranged in a serpentine pattern.

In addition, the combination can include one or more humidity sensors, such as humidity sensor 1 234 and humidity sensor 2 236. The one or more humidity sensors can be located on the same integrated circuit substrate as the flow sensors 230, 232, e.g., nodes 122, 124. In the example shown in FIG 18, the humidity sensors 234, 236 can include interdigitated electrodes. For example, humidity sensor 1 can include interdigitated electrodes 238, 240.

In some example configurations, a humidity sensor can include interdigitated metal fingers with a material disposed between the fingers, e.g., polyimide in between the fingers. Moisture can be absorbed by the material, e.g., polyimide, which can change the dielectric constant of the material. This can alter the capacitance between the interdigitated fingers. A capacitance-to- digital converter can measure the capacitance and the system controller can determine the humidity based on the change in measured capacitance. In some example implementations, one or more reference structures with interdigitated metal fingers and material, e.g., polyimide, between the fingers but with a coating with a moisture proof film can be used to ensure that the influence of the moisture can be measured.

FIG. 20 is a flow diagram showing an example of a method 300 mat can implement various techniques of this disclosure. At block 302, the method can include providing a substrate, e.g., substrate 130 of FIG. 6, a combined temperature sensor/heater first node, at least a portion of which is integrated with and projects above an upper surface of the substrate, e.g., node 122 of FIG. 6, and a combined temperature sensor/heater second node, e.g., substrate 124 of FIG. 6, at least a portion of which is formed with and projects above an upper surface of the same substrate, and wherein the first and second nodes are arranged and integrated with the substrate to permit the fluid flow passing by the first node to also pass by the second node.

At block 304, the method can include heating the first node, e.g., node 122 of FIG. 6. When the node is operated as a heater, the heater can be operate in a number of modes. In a constant temperature mode, the heater can be forced to a known temperature and maintained at that temperature by a closed loop control circuit. In a constant power mode, the heater can be driven with a constant power. For example, the constant power can be from a fixed voltage source where the current is controlled to maintain a constant power (V*I). Alternatively, in constant power mode, the heater can be driven from a constant current source and the voltage can be controlled to maintain constant power (V*I). The heater can also be operated in constant voltage or constant current mode.

At block 306, the method can include determining a resistance between a first contact and a second contact of the second node. Measurement circuitry can monitor and measure the resistance of a downstream node over time. In some example implementations, the peak or maximum change in the resistance of the downstream node can be considered to be when the peak of the heat is transferred from the first node to the second node.

At block 308, the method can include determining the flow or temperature using the determined resistance. In some examples, the flow can be determined using a time of flight measurement. Heating the first node can include generating a heat pulse, and then a system controller can determine a resistance between a first contact and a second contact of the second node. The controller can determine a time of flight of the heat pulse between the first node and the second node by determining, for example, a maximum change in the resistance between the first contact and the second contact of the second node. Then, the flow or temperature can be determined using the time of flight.

Optionally, the method 300 can include determining a humidity of the air or other gas including determining a change in a capacitance of a material between portions of a humidity sensor.

Although this document has used the term "airflow," it should be understood that the systems, devices, and methods described herein can be used or applied to detect other gaseous fluid flow or even liquid fluid flow.

Various Notes and Aspects

Aspect 1 includes subject matter (such as a device, system, circuit, apparatus, or machine) for measuring an air or other gaseous or liquid or other fluid flow or temperature measurement device, the device comprising: a substrate; a combined temperature sensor/heater first node, at least a portion of which is integrated with and projects above an upper surface of the substrate; and a combined temperature sensor/heater second node, at least a portion of which is formed with and projects above an upper surface of the same substrate, and wherein the first and second nodes are arranged and integrated with the substrate to permit the fluid flow passing by the first node to also pass by the second node.

In Aspect 2, the subject matter of Aspect 1 can optionally include, wherein at least one of the first and second nodes includes: a first thermal insulator barrier, located on the substrate, the first thermal insulator barrier having lower thermal conductivity than the substrate; an electrical resistor heating element, separated from the substrate by at least a portion of the first thermal insulator barrier, the heating element including first and second terminals that are electrically connected to circuitry on or in the substrate; a thermistor material, at least a portion of which is located above the heating element toward a flow region, the thermistor material providing an electrical resistance that varies with temperature; and at least one thermistor connector, including a first region contacting the thermistor material and a second region that is electrically connected to circuitry on or in the substrate. In Aspect 3, the subject matter of Aspect 1 can optionally include, wherein the thermistor connector is separated from the heating element by a second thermal insulator barrier having a lower thermal conductivity man the substrate.

In Aspect 4, the subject matter of one or more of Aspects 1 -3 can optionally include, wherein at least a portion of the heating element is in electrical contact with the thermistor material, and further comprising: a temperature sensor circuit, including a first input electrically coupled to the at least one thermistor connector, and including a second input electrically coupled to at least one of the first or second terminals of the heating element.

In Aspect 5, the subject matter of Aspect 4 can optionally include, comprising a flow detector circuit, coupled to the temperature sensor circuit, the flow detector circuit including circuitry to detect an indication of flow using sensed temperature information from at least one of the first and second nodes and an indication of power provided to the heating element of at least one of the first and second nodes.

In Aspect 5, the subject matter of one or more of Aspects 2-5 can optionally include, wherein the at least one thermistor connector includes at least two thermistor connectors, including: a first thermistor connector, including a first region contacting the thermistor material and a second region that is electrically connected to circuitry on or in the substrate; and a second thermistor connector, separated from the first thermistor connector, the second thermistor connector including a first region contacting the thermistor material and a second region that is electrically connected to circuitry on or in the substrate.

In Aspect 7, the subject matter of one or more of Aspects 1-6 can optionally include, a duct, cone, funnel, coupler, flow concentrator, flow spreader, or other flow guide, coupled to the substrate, to guide the fluid flow passing by the first node and passing by the second node.

In Aspect 8, the subject matter of one or more of Aspects 1-7 can optionally include, a flex circuit or leaded package, coupled to the substrate, to position the substrate with respect to the fluid flow passing by the first node and the second node.

In Aspect 9, the subject matter of one or more of Aspects 1-8 can optionally include, at least one flow ramp, upstream or downstream of at least one of the first and second nodes, to provide a transition between an upper surface of the substrate and at least one of the first and second nodes.

In Aspect 10, the subject matter of one or more of Aspects 1-9 can optionally include, a combined temperature sensor/heater third node, at least a portion of which is located on and projects above an upper surface of the substrate; and a combined temperature sensor/heater fourth node, at least a portion of which is located on and projects above an upper surface of the same substrate; and wherein the first node, the second node, the third node, and the fourth node are arranged in a Wheatstone bridge configuration.

In Aspect 11, the subject matter of Aspect 10 can optionally include, wherein at least a portion of the first node and the fourth node are located on one or more respective ramps facing in an upstream direction of the fluid flow, and at least a portion of the second node and the third node are located on ramps facing in a downstream direction of the fluid flow or with a barrier between the second node and third node and a direction of the fluid flow.

In Aspect 12, the subject matter of one or more of Aspects 10-11 can optionally include, a supply or other reference voltage circuit configured to provide a voltage to a parallel combination of (1) a series combination of the first node and the second node and (2) a series combination of the third node and the fourth node.

In Aspect 13, the subject matter of Aspects 12 can optionally include, a voltage sensing amplifier with a first input coupled to an interconnection between the first node and the second node and a second input coupled to an interconnection between the third node and the fourth node.

In Aspect 14, the subject matter of one or more of Aspects 1-13 can optionally include, at least one humidity sensor located on the same substrate as the first node and the second node.

In Aspect 15, the subject matter of one or more of Aspects 1-14 can optionally include, in which at least one of the first node and the second node is operated in at least one of a constant temperature mode, a constant power mode, a constant voltage mode, or a constant current mode.

Aspect 16 includes subject matter (such as a method, means for performing acts, machine readable medium including instructions that when performed by a machine cause the machine to performs acts, or an apparatus configured to perform) for measuring an air or other gaseous or liquid or other fluid flow or temperature, the subject matter comprising providing a substrate; a combined temperature sensor/heater first node, at least a portion of which is integrated with and projects above an upper surface of the substrate; and a combined temperature sensor/heater second node, at least a portion of which is formed with and projects above an upper surface of the same substrate, and wherein the first and second nodes are arranged and integrated with the substrate to permit the fluid flow passing by the first node to also pass by the second node; the subject matter further including heating the first node; determining a resistance between a first contact and a second contact of the second node; and determining the flow or temperature using the determined resistance.

In Aspect 17, the subject matter of Aspect 16 can optionally include, wherein heating one of the first and second nodes includes: generating a constant voltage between first and second contacts of the first node.

In Aspect 18, the subject matter of Aspect 16 can optionally include, wherein heating one of the first and second nodes includes: generating a constant current between first and second contacts of the first node.

In Aspect 19, the subject matter of one or more of Aspects 16-18 can optionally include, wherein heating the first node includes generating a heat pulse, and wherein determining a resistance between a first contact and a second contact of the second node includes determining a maximum change in the resistance between the first contact and the second contact of the second node, the subject matter comprising: determining a time of flight of the heat pulse between the first node and the second node, wherein determining the flow or temperature using the determined resistance includes determining the flow using the determined time of flight.

In Aspect 20, the subject matter of one or more of Aspects 16-19 can optionally include, determining a humidity of the air or other gas including determining a change in a capacitance of a material between portions of a humidity sensor. Each of the non-limiting aspects or examples described herein may stand on its own, or may be combined in various permutations or combinations with one or more of the other examples.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as "aspects" or "examples." Such examples may include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls.

In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," 'Ή but not A," and "A and B," unless otherwise indicated. In this document, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, mat is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Method examples described herein may be machine or computer- implemented at least in part. Some examples may include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods may include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code may include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code may be tangibly stored on one or more volatile, non- transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media may include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact discs and digital video discs), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments may be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less man all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments may be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.