Multi-parameter LC sensor circuits

Abstract

A dual-output LC sensor is described. The sensor comprises a capacitor, configured to produce a varying capacitance based on a first physical quantity, such as a pressure, temperature, strain, humidity, gas, and touch. The sensor further comprises a first coil, configured to produce a magnetic field, and a second coil, configured to sense the magnetic field and produce an output signal based on the magnetic field. At least one of the first coil and the second coil is configured to deflect along an axis based on a second physical quantity, such as another pressure, temperature, strain, humidity, gas, and touch. In some embodiments, a readout device can be configured to detect the first and / or second physical quantities by measuring a resonant frequency and / or an amplitude of the output signal.

Description

TITLE: MULTI -PARAMETER LC SENSOR CIRCUITSRELATED APPLICATION

[0001] This application claims benefit of united states provisional patent application serial no. 63 / 726,292 filed November 28, 2024, incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to the field of sensors. Specifically, microelectronic multi-parameter LC sensor circuits for sensing physical quantities such as, but not limited to, temperature, pressure, displacement, and other such characteristics and circuits therefor.BACKGROUND

[0003] Sensors for measuring various parameters such as, but not limited to, pressure, displacement and temperature, are ubiquitous and can be considered fundamental components in many industrial, commercial, scientific, and medical applications. For example, in the medical domain, sensing internal pressure from the heart or the arteries is used for efficient disease management. Changes in pressure may be related to worsening of cardiac condition that can lead to the experience of life-threatening episodes.

[0004] Additionally, real-time monitoring of various parameters, such as the aforementioned parameters, is used in the clinical care of patients affected by chronic conditions. For example, pulmonary pressure is measured to diagnose cardiovascular diseases, bladder pressure can be measured to treat incontinence, and intraocular pressure can be monitored for the diagnosis and management of glaucoma. Development of sensors for medical applications involves the adoption of cost-effective solutions to guarantee size, scalability and performance.

[0005] Lastly, wireless sensors are pervasive components used in a wide range of biomedical, agricultural, industrial, and automotive applications. Accordingly, it is beneficial to have sensors have the ability to measure various parameters and transmit the measured parameters wirelessly and thus can be widely used.SUMMARY

[0006] The following summary is provided to introduce the reader to the more detailed discussion to follow. The summary is not intended to limit or define any claimed or as yetclaimed invention. One or more inventions may reside in any combination or sub-combination of the elements or process steps disclosed in any part of this document including its claims and figures.

[0007] In a first aspect, in accordance with some embodiments, a dual-output LC sensor is provided. The sensor comprises a capacitor, configured to produce a varying capacitance when subjected to a first physical quantity. The sensor additionally comprises a first coil, configured to produce a magnetic field. The sensor further comprises a second coil, configured to sense the magnetic field and produce an output signal based on the magnetic field. Additionally, at least one of the first coil and the second coil is configured to deflect along an axis based on a second physical quantity.

[0008] In some embodiments, the capacitor is configured, when subjected to the first physical quantity, to undergo any combination of: a displacement of at least one electrode of the capacitor, a change in dielectric property of the capacitor, and a change in a charge of the capacitor.

[0009] In some embodiments, the capacitor is configured, when subjected to the first physical quantity, to undergo any combination of: a first displacement of a first electrode relative to a second electrode of the capacitor, a change in a dielectric property of a material between the first electrode and the second electrode, and a change in a relative charge between the first and second electrodes.

[0010] In some embodiments, wherein the first coil and / or the second coil is configured to undergo a second displacement relative to one another when subjected to the second physical quantity.

[0011] In some embodiments the output signal further varies based on a change in capacitance of the capacitor due to the first physical quantity.

[0012] In some embodiments, the first or second physical quantity comprises any combination of: a pressure, a temperature, a strain, a humidity, a gas, and a touch.

[0013] In some embodiments, the sensor can further comprise a bipolar transistor, wherein a base of the bipolar transistor is connected to the second coil and a collector of the bipolar transistor is connected to a resonant circuit formed by the capacitor and the first coil.

[0014] In some embodiments, the second coil can further be operable to transfer the output signal to a readout device.

[0015] In some embodiments, the readout device can comprise a wireless reader, and the second coil is adapted to transmit the output signal wirelessly to the readout device.

[0016] In some embodiments, the readout device can comprise a voltage measurement device, and the readout device is configured to measure the output signal using the voltage measurement device.

[0017] In some embodiments, the sensor is adapted to generate the output signal with a resonant frequency that is related to the first physical quantity so that the readout device is able to detect the first physical quantity by measuring the resonant frequency of the output signal.

[0018] In some embodiments, the sensor is adapted to generate the output signal with an amplitude that is related to the second physical quantity so that the readout device is able to detect the second physical quantity by measuring the amplitude of the output signal

[0019] In some embodiments, the sensor can comprise an inductive pressure sensor. The inductive pressure sensor contains a silicon wafer. The inductive pressure sensor also comprises the first coil, disposed on a first face of the silicon wafer, and the second coil, disposed on an opposite face of the silicon wafer.

[0020] In some embodiments, the inductive pressure sensor can further comprise a first layer of silicon dioxide, disposed between the silicon wafer and the first coil, and a second layer of silicon dioxide, disposed between the silicon wafer and the second coil. At least one of the first and second layer of silicon dioxide can be adapted to deflect under an applied pressure.

[0021] In some embodiments, the inductive pressure sensor can further comprise a vacuum cavity formed within the silicon wafer between the first and second coils.

[0022] In some embodiments, the sensor can further comprise a third coil, configured to produce a second magnetic field and to deflect when subjected to a third physical quantity, a fourth coil, configured to produce a third magnetic field and to deflect when subjected to a fourth physical quantity, and a multiplexer. The second coil can be further configured to sensethe second and third magnetic fields, and the multiplexer can be configured to activate one of the first, third, and fourth coils, such that the second coil can sense only one of the magnetic field, the second magnetic field, and the third magnetic field at a time.

[0023] In some embodiments, the sensor can further comprise a capacitor array. The capacitor array can comprise the capacitor and one or more array capacitors. The one or more array capacitors are configured to produce one or more additional varying capacitances when subjected to one or more additional physical quantities, and a plurality of switches. Each switch of the plurality of switches can be connected to given capacitor which is a unique one of the capacitor and one of the one or more array capacitors. Each switch of the plurality of switches can also be operable to electrically connect the given capacitor to the first coil.

[0024] In another aspect, in accordance with some embodiments, a dual-output LC sensor is provided. The sensor comprises a capacitor, configured to produce a varying capacitance based on a first physical quantity, a first coil, configured to produce a first fixed inductance based on a tap setting, a second coil, configured to produce a second fixed inductance based on the tap setting, and a resistor, configured to produce a varying resistance based on a second physical quantity.

[0025] In some embodiments, the capacitor, when subjected to the first physical quantity, is adapted to undergo any combination of: a displacement of at least one electrode of the capacitor, a change in a dielectric property of the capacitor, and a change in a charge of the capacitor.

[0026] In another aspect, in accordance with some embodiments, a dual-output tuned- amplifier circuit is provided. The circuit comprises a resonant tank. The resonant tank comprises a capacitor configured to produce a varying capacitance and a first inductor. The circuit further comprises a second inductor magnetically coupled to the first inductor, wherein a magnetic coupling between the second inductor and the first inductor is variable, and an amplifier connected to the resonant circuit and the second inductor, configured to produce an output signal. The output signal comprises a varying amplitude based on the magnetic coupling and a varying frequency based on the varying capacitance.

[0027] In some embodiments, the varying capacitance can be produced when the capacitor is subjected to a first physical quantity.

[0028] In some embodiments, the magnetic coupling can vary when one of the inductors are subjected to a second physical quantity.

[0029] In some embodiments, the capacitor, when subjected to the first physical quantity, is adapted to undergo any combination of: a displacement of at least one electrode of the capacitor, a change in a dielectric property of the capacitor, and a change in a charge of the capacitor.

[0030] In some embodiments, the capacitor, when subjected to the first physical quantity, is adapted to undergo any combination of: a first displacement of a first electrode relative to a second electrode of the capacitor, a change in a dielectric property of the material between the first electrode and the second electrode, and a change in a relative charge between the first and second electrodes.

[0031] In some embodiments, wherein one of the inductors, when subjected to the second physical quantity, is adapted to undergo a change in a second displacement of the first inductor relative to the second inductor.

[0032] In some embodiments, the varying frequency can be based on a resonant frequency of the resonant tank.

[0033] In some embodiments, the amplifier can be a transistor.

[0034] In some embodiments, the transistor can be a bipolar junction transistor or a CMOS transistor.

[0035] In some embodiments, the second inductor can be connected to a base of the transistor and the resonant tank can be connected to a collector of the transistor.

[0036] In some embodiments the output signal can be taken at one of the base and the collector of the transistor.

[0037] In some embodiments, when a relative distance between the first inductor and the second inductor is greater than a critical distance, a resonant frequency of the resonant tank is dependent only on the varying capacitance.

[0038] In some embodiments, the circuit can further comprise an inductive pressure sensor. The inductive pressure sensor comprises a silicon wafer, the first inductor, disposedon a first face of the silicon wafer, and the second inductor, disposed on an opposite face of the silicon wafer.

[0039] In some embodiments, the inductive pressure sensor can further comprise a first layer of silicon dioxide, disposed between the silicon wafer and the first inductor, and a second layer of silicon dioxide, disposed between the silicon wafer and the inductor coil. At least one of the first and second layer of silicon dioxide can be adapted to deflect under an applied pressure.

[0040] In some embodiments, the inductive pressure sensor can further comprise a vacuum cavity formed within the silicon wafer between the first and second inductors.

[0041] In some embodiments, the circuit can further comprise a capacitor array, comprising the capacitor and one or more array capacitors. The resonant tank can further comprise the capacitor array. The one or more array capacitors can be configured to produce one or more additional varying capacitances when subjected to one or more additional physical quantities respectively. The circuit can further comprise a plurality of switches, wherein each switch of the plurality of switches is connected to a given capacitor that is a unique one of the capacitor and one of the one or more array capacitors and is operable to electrically connect the given capacitor to the resonant tank.DRAWINGS

[0042] The drawings included herewith are for illustrating various examples of articles, methods, and apparatuses of the present specification and are not intended to limit the scope of what is taught in any way.

[0043] FIG. 1 shows an example LC sensor circuit in accordance with at least one embodiment.

[0044] FIG. 2 shows another example LC sensor circuit in accordance with at least one embodiment.

[0045] FIG. 3 shows an example inductive pressure sensor in accordance with at least one embodiment.

[0046] FIG. 4 shows an experimental setup of the example LC sensor circuit of FIG. 2.

[0047] FIG. 5 shows an example PCB coil.

[0048] FIG. 6 shows a graph of the spectrum for test results obtained using the experimental setup of FIG. 4.

[0049] FIG. 7 shows an example of a moisture sensor in accordance with at least one embodiment.

[0050] FIG. 8a and 8b show graphs of the spectrum for test results obtained using the moisture sensor of FIG. 7.

[0051] FIG. 9 shows an LC sensor array circuit in accordance with at least one embodiment.

[0052] FIG. 10 shows a graph of simulated currents for the circuit of FIG. 1 .

[0053] FIG. 11 shows a graph of simulated spectrums for the circuit of FIG. 1 .

[0054] FIG. 12 shows a graph of a transient response for the circuit of FIG. 1 .

[0055] FIGS. 13a and 13b show 3D models of inductive pressure sensors in accordance with at least one embodiment.

[0056] FIG. 14 shows a graph of displacement vs mutual inductance for the sensor of FIG. 13a.

[0057] FIG. 15 shows a 3D model of an inductive pressure sensor in accordance with at least one embodiment.

[0058] FIG. 16 shows a graph of spectrums for the inductive pressure sensor of FIG. 15.

[0059] FIG. 17 shows graphs of inductance vs frequency for the sensor of FIG. 3 in accordance with at least one embodiment.

[0060] FIG. 18 shows a graph of mutual inductance vs distance for the sensor of FIG. 3 in accordance with at least one embodiment.

[0061] FIG. 19 shows graphs of deflections for the sensor of FIG. 3 in accordance with at least one embodiment.

[0062] FIG. 20 shows a 3D model of a coil of the sensor of FIG. 3 in accordance with at least one embodiment.

[0063] FIG. 21 shows a graph of impedance vs displacement.

[0064] FIG. 22 shows an LC sensor array circuit in accordance with at least one embodiment.

[0065] FIG. 23 shows a sensor circuit in accordance with at least one embodiment.

[0066] FIG. 24 shows a graph of impedance vs displacement for the sensor of FIG. 3 in accordance with at least one embodiment.

[0067] FIG. 25a illustrates several example embodiments of a fabricated inductive pressure sensor in accordance with the teachings herein.

[0068] FIG. 25b is a cross-sectional view of a fabricated sensor showing the layered architecture.

[0069] FIG. 25c shows a top-down view of sensor components prior to full assembly.

[0070] FIG. 25d shows an assembled inductive pressure sensor unit in accordance with the teachings herein.

[0071] FIG. 25e shows an experimental setup for testing the performance of the sensor of FIG. 25d.

[0072] FIG. 25f is a close-up view of the sensor of FIG. 25d interfacing with the test apparatus of FIG. 25e.

[0073] FIG. 25g is a performance graph plotting measured coupling coefficient (k) as a function of the applied force (N).

[0074] FIG. 25h is a graph of the frequency response of the sensor of FIG. 25d under a wide range of applied forces.

[0075] FIG. 25i is a graph plotting membrane displacement (mm) versus applied pressure (N) illustrating mechanical hysteresis of the sensor of FIG. 25d.

[0076] FIG. 25j is a graph of membrane tension (measured as force) versus time over a 15-minute period for the sensor of FIG. 25d.DESCRIPTION OF VARIOUS EMBODIMENTS

[0077] Numerous embodiments are described in this application and are presented for illustrative purposes only. The described embodiments are not intended to be limiting in any sense. The teachings herein are widely applicable to numerous embodiments, as is readilyapparent from the disclosure herein. Those skilled in the art will recognize that the embodiments described herein may be practiced with modification and alteration without departing from the teachings disclosed herein. Although particular features of the teachings herein may be described with reference to one or more particular embodiments or figures, it should be understood that such features are not limited to usage in the one or more particular embodiments or figures with reference to which they are described.

[0078] The terms “an embodiment,” “embodiment,” “embodiments,” “the embodiment,” “the embodiments,” “one or more embodiments,” “some embodiments,” and “one embodiment” mean “one or more (but not all) embodiments of the Applicant’s teachings,” unless expressly specified otherwise.

[0079] The terms “including,” “comprising” and variations thereof mean “including but not limited to,” unless expressly specified otherwise. A listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a,” “an” and “the” mean “one or more,” unless expressly specified otherwise.

[0080] As used herein and in the claims, two or more parts are said to be “coupled”, “connected”, “attached”, “joined”, “affixed”, or “fastened” where the parts are joined or operate together either directly or indirectly (i.e. , through one or more intermediate parts), so long as a link occurs. As used herein and in the claims, two or more parts are said to be “directly coupled”, “directly connected”, “directly attached”, “directly joined”, “directly affixed”, or “directly fastened” where the parts are connected in physical contact with each other. As used herein, two or more parts are said to be “rigidly coupled”, “rigidly connected”, “rigidly attached”, “rigidly joined”, “rigidly affixed”, or “rigidly fastened” where the parts are coupled so as to move as one while maintaining a constant orientation relative to each other. None of the terms “coupled”, “connected”, “attached”, “joined”, “affixed”, and “fastened” distinguish the manner in which two or more parts are joined together.

[0081] Further, although method steps may be described (in the disclosure and I or in the claims) in a sequential order, such methods may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of methodsdescribed herein may be performed in any order that is practical. Further, some steps may be performed simultaneously.

[0082] Some elements herein may be identified by a part number, which is composed of a base number followed by an alphabetical or subscript-numerical suffix (e.g., 112a, or 112i ). Multiple elements herein may be identified by part numbers that share a base number in common and that differ by their suffixes (e.g., 112i, 1122, and 112s). All elements with a common base number may be referred to collectively or generically using the base number without a suffix (e.g., 112).

[0083] As used herein and in the claims, a group of elements are said to ‘collectively’ perform an act where that act is performed by any one of the elements in the group, or performed cooperatively by two or more (or all) elements in the group.

[0084] As used herein and in the claims, a first element is said to be “received” in a second element where at least a portion of the first element is received in the second element unless specifically stated otherwise.

[0085] It should also be noted that, as used herein, the wording “and / or” is intended to represent an inclusive-or. That is, “X and / or Y” is intended to mean X or Y or both X and Y, for example. As a further example, the phrases “X, Y, and / or Z”, “any operable combination of X, Y and Z”, “X, Y, Z or any combination thereof” or “any combination of X, Y and Z” is intended to mean X, Y, Z, X and Y, X and Z, Y and Z, or X, Y and Z.

[0086] It should be noted that terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree may also be construed as including a deviation of the modified term, such as by 1 %, 2%, 5%, 10% or 15%, for example, if this deviation does not negate the meaning of the term it modifies.

[0087] Furthermore, the recitation of numerical ranges by endpoints herein includes all numbers and fractions subsumed within that range (e.g., 1 to 5 includes 1 , 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term “about” which means a variation of up to a certain amount of the number to which reference is being made if the end result is not significantly changed, such as 1 %, 2%, 5%, 10% or 15%, for example.

[0088] As used herein and in the claims, an inductor may be referred to as a “coil” and vice versa. In addition, as used herein and in the claims, an LC circuit may be referred to as a “resonant circuit”, “resonant tank”, ‘tank circuit’ and vice versa.

[0089] Current pressure sensors either rely on wired connections or consist of large components and batteries, resulting in patient discomfort, implantation issues, and surgical complications. There is a need to develop minimally-invasive wireless pressure sensors for continuous monitoring of pressure from different and new anatomical areas in the body. Additionally, typical wireless sensors face power and cost limitations due to the integration of sensing elements, readout electronics, conversion, and wireless transmission stages.

[0090] Among the wide range of pressure measuring methods, resonant sensors have shown superior performance, scalability and ease of fabrication, making them suitable for the development of wireless medical sensors. Resonant (or LC) sensors may be used to alleviate some of these issues. LC sensors are passive sensors that combine two electrical components, a capacitor and an inductor. LC sensors combine a sensing capacitor and two mutually-coupled inductors where one of the inductor coils may be connected to the capacitor and form an LC tank, while the other inductor coil can be used to transmit the resonant frequency of the LC sensors to an external reader device. Changes in a target parameter that has an effect on one of the plates of the capacitor, or in a dielectric property between the plates, can be represented by a change in capacitance of the LC tank and are then translated to a shift in the resonant frequency of the tank. Thus, these sensors can be highly sensitive to specific parameters, including pressure, strain, humidity, temperature, gas, and touch, among others.

[0091] Beside their high sensitivity, LC sensors benefit from not requiring a power source for their operation. Real-time parameter sensing is achieved by remote query via an external reader. Additionally, LC sensors are particular advantageous in applications requiring low cost and minimal invasiveness.

[0092] Conventional LC sensors adopt the capacitor as the sensing element, while a fixed inductor is combined with the capacitor to achieve resonance. Capacitive LC pressure sensors can be used to measure pulmonary artery pressure in cardiac patients. Though such devices are currently used in clinical care, their cost may be higher due to sub-optimalfabrication processes, and their operation relies on the use of bulky external equipment and significant patient compliance. Further device miniaturization can enable access to new diagnostically-relevant anatomical regions, thus creating new opportunities for more effective diagnosis and treatment. Additionally, capacitive pressure sensors can achieve high linearity and sensitivity, but are greatly susceptible to parasitics, noise, and environmental conditions, which limit their accuracy and long-term stability.

[0093] Inductive sensors represent a suitable alternative to implementing sensitive and accurate pressure sensors. Inductive sensors, however, conventionally rely on more complex fabrication processes and result in a relatively large device. In addition, conventional inductive sensors consist of one planar coil or one 3D coil, whose inductance varies with respect to another conductive element in order to measure some parameter. This type of sensor cannot be effectively used in combination with capacitive sensors in LC circuits while discerning between two distinct sensor outputs, since both changes in inductance and capacitance result in a frequency shift.

[0094] In one aspect, in accordance with the teachings herein, there is provided at least one embodiment of novel inductive LC sensors based on a MEMS (micro-electromechanical- systems) inductive link with one flexible coil and one fixed coil. The coils may, in some embodiments, be fabricated on each side of a thinned silicon wafer. Such embodiments may be more easily fabricated in standard microfabrication processes and offer potential for aggressive device scaling and integration with CMOS circuits, leading to lower manufacturing costs and improved performance. Accordingly, at least one of the embodiments described herein may be useful in the development of high-performing injectable sensors for chronic disease management.

[0095] In another aspect, in accordance with the teachings herein, there is provided at least one embodiment of a multi-parameter LC sensor, wherein both the capacitive and inductive components in an LC sensor can be adopted concurrently as sensing components. In some embodiments, dual-parameter readout may be achieved using a tuned amplifier which embeds inductive and capacitive sensors. The use of a single oscillator circuit for two different sensors can be highly beneficial in terms of power consumption and scalability.

[0096] The LC sensors described herein may generally use an inductive sensor consisting of an inductive link, with one moving and one fixed coil. By making one coil movable (e.g., by using a suspended structure), the coil may move, upon an applied pressure or other force, closer to the fixed coil, thus transferring a higher amount power between the coil and leading to variations in voltage amplitude corresponding to the power transfer, with negligible changes in inductance. This scheme exploits the changes in power transferred between a driving coil and a sensing coil, corresponding to a change in the coupling factor between the coils, which varies based on the relative distance of one coil to another. In some embodiments, the inductive link between the coils can be further designed so that the level of transmitted power is linearly proportional to the distance between the coils and hence to the applied pressure.

[0097] In another aspect, at least one of the embodiments described herein may leverage MEMS technology which is generally categorized into four primary approaches: piezoresistive, piezoelectric, capacitive, and inductive. For wireless sensing applications, capacitive and inductive pressure sensors can be used as they can be used in resonant circuits and interrogated wirelessly. Capacitive pressure sensors may be combined with inductors and operated at a specific resonant frequency.

[0098] The capacitor can be fabricated using a MEMS process, but the inductor is conventionally an external component. Thus, it can be difficult to integrate the parts together monolithically. Conventional MEMS inductive sensors are typically based on the use of a medium, such as a metal sheet, that interacts with the magnetic flux between a sensing and driving coil upon application of pressure. The coils are fabricated using standard CMOS layers and encapsulated. A metal sheet or ball may be integrated on top of the coil structure. The resulting fabrication process is generally not compatible with available CMOS processes and are therefore not easily reproducible or scalable. However, in at least one embodiment described herein, a novel monolithic resonant inductive pressure sensor may be used that can be integrated in standard CMOS processes, resulting in highly scalable, miniaturized and cost-effective solutions.

[0099] FIGS. 1 and 2 show example LC sensor circuits 100a and 100b in accordance with embodiments described herein. LC sensor circuit 100b may contain a dual output LC sensor106 that may include a capacitor 102, a first coil 120b, and a second coil 118b. While FIG. 1 shows the LC sensor circuit 100a being used to measure some parameter of tissue, it should be understood that these sensor circuits can be used in other applications.

[0100] FIG. 1 shows an example sensor circuit 100a containing a first resonant circuit 126, a second resonant circuit 124, and a third resonant circuit 114. First resonant circuit 126 contains capacitor 102a, inductor 120a, and an AC voltage source 122 for driving the resonant circuit. Second resonant circuit 124 contains second coil 118a, coupled to first coil 120a, and a relay capacitor 128. Third resonant circuit 114 contains a readout coil 108, a readout capacitor 110, and reader hardware 112. The arrangement shown in circuit 100a may facilitate wireless transfer of sensor data between the first resonant circuit 126, the second resonant circuit 124, and the third resonant circuit 114.

[0101] FIG. 2 shows an example sensor circuit 100b containing a resonant circuit 202 formed by capacitor 102b and first coil 120b. Second coil 118b is inductively coupled to first coil 120b. Circuit 100b is arranged in a modified tuned-amplifier configuration. T ransistor 214, which may be a bipolar junction transistor or a field effect transistor (FET), is used as an amplifier. Resonant circuit 202 and second coil 118b is connected to the amplifier. Specifically, resonant circuit 202 is connected to the collector of transistor 214 and second coil 118b is connected to the base of transistor 214. Bias resistors and bypass capacitors Ri- 3, and Ci ,2 are shown. A switch, SD, is used to damp the energy in the tank at regular intervals and restart the oscillation in the tank. The values for the components of the tuned amplifier may be in accordance with the example values listed in TABLE 1 .TABLE 1 . Example components values for the tuned amplifier shown in FIG. 2

[0102] Referring generally back to both FIGS. 1 and 2, the capacitor 102 is configured to produce a varying capacitance based on (e.g., when subjected to) a first physical quantity. The capacitor 102 may be comprised of a first electrode and a second electrode. The first physical quantity may be an applied pressure, temperature, strain, humidity, touch, gas, or some other physical quantity to be measured. Any capacitor capable of producing a varying capacitance based on the first physical quantity can be used.

[0103] In some embodiments, the first physical quantity may act on the capacitor to affect a displacement of at least one electrode of the capacitor. For example, the first physical quantity may be a pressure or strain against the capacitor, which produces a displacement of the first electrode relative to the second electrode, affecting the capacitance of the capacitor. As an example, the capacitor 102 may be constructed from a pair of parallel plates or interdigitated fingers with a structure containing air gaps or dielectric materials between the plates. The structure may be flexible such that a pressure may cause the parallel plates to move closer to one another, varying the capacitance of the capacitor. In some embodiments, the first physical quantity may affect a dielectric property of the capacitor. For example, the first physical quantity may be a humidity, which changes a hygroscopic dielectric material between the first and second electrodes to produce a varying dielectric constant, thereby affecting the capacitance of the capacitor. In some embodiments, the first physical quantity may affect a charge of the capacitor. For example, a touch from a conductive object such as a human finger may produce a change in the charge of one electrode relative to the other.

[0104] The variation of the capacitance may change the resonance properties of the circuit. For example, in circuit 100a, the resonance frequency of first resonant circuit 126 will vary with the capacitance of capacitor 102a. Similarly, for circuit 100b, the resonance frequency of resonant circuit 202 will vary with the capacitance of capacitor 102b.

[0105] The first coil 120 is configured to produce a magnetic field. Coils 120 and 118 may be coils of any configuration that are capable of producing a magnetic field when a current flows through the coil. For example, coils 120 and 118 may be circular planar coils, square planar coils, or solenoidal coils. The second coil 118 is configured to sense the magnetic fieldproduced by the first coil 120, produce an output signal based on the magnetic field, and transfer a signal to a readout device based on the magnetic field. Second coil 118 may sense the magnetic field, for example, through the current induced in coil 118 by the magnetic field produced by coil 120. In other words, the second coil 118 sensing the magnetic field of coil 120 may arise from the coupling between the coils through mutual inductance. The coupling between the coils may be variable.

[0106] One or both of the first coil 120 and the second coil 118 may be configured to deflect along an axis based on (e.g., when subjected to) a second physical quantity. The second physical quantity may act upon at least one of the first and second coils to produce a displacement of the first coil 120 relative to the second coil 118, or vice versa. The deflection varies the relative distance between the coil, affecting the coupling between the coils, thereby affecting power transfer between the coils. The second physical quantity may be any physical quantity to be sensed, particularly a physical quantity that can produce the requisite displacement such as a pressure or touch applied to one of the coils. In one embodiment, coils 120 and 118 may be constructed as per sensor 300 shown in FIG. 3, which will be described in further detail later. The deflecting coil may deflect away from or towards the other coil along a single axis. In at least one embodiment, both coils may be capable of deflecting. It will be appreciated that the exact selection of which coil deflects does not affect the basic operating principles of the sensor, but only that there is a variable displacement of one coil relative to the other. It will also be appreciated that when the distance between the first coil and the second coil is greater than a critical distance, dcrit, the resonance frequency of the resonant circuit formed by coil 120 and capacitor 102 is independent of the mutual coupling between coils 118 and 120.

[0107] The second coil 118 may further be configured to produce an output signal based on the magnetic field. The output signal may take the form of a current, a voltage, a field, or any other means of providing information / data about the magnetic field. The second coil may further transfer the output signal to a readout device. The transfer may be a wireless transfer or a wired transfer. The readout device may be a wireless reader unit that picks up the wirelessly transmitted signal, or an electronic component that picks up the signal transmitted along a wire.

[0108] As described above, in at least one embodiment, a wireless configuration may be used for reading the output signal. For example, in circuit 100a, a 3-coil wireless inductive link can be formed. Coil 118a senses the magnetic field generated by coil 120a, which induces a corresponding current in resonant circuit 124. Coil 118a may then produce an output signal in the form of a further magnetic field, which can then be picked up by readout coil 108. In other words, the second coil 118a acts as a relay and transmits power from first coil 120a to an external readout coil 108. In at least one embodiment, the coupling between the second coil 118a and the readout coil 108 may be fixed by design. The power level transferred from first coil 120a to readout coil 108 through second coil 118a may then be proportional to a pressure induced single-axis displacement of first coil 120a.

[0109] In at least one embodiment, a wired configuration may be used for detecting the readout signal. As an example, in circuit 100b, second coil 118b produces an output signal in the form of the voltage waveform observed at the base 212 or at the collector 206 of transistor 214. The voltage waveform may have a varying amplitude depending on the coupling between the first coil 120b and second coil 118b and a varying frequency based on the varying capacitance of capacitor 102b. The reader hardware I readout device 112 may be a device configured to observe the voltage at the base 212 or the collector 206. Specifically, the voltages at the collector 206 (Vc) and base 212 (VB) of transistor 214 are coupled to each other through the mutual inductance M between coils 118b and 120b. The small-signal operation of the circuit can be described as follows:where LsAis the inductance of coil 120b, LsBis the inductance of coil 118b, Csis the capacitance of capacitor 102b, Zb= ^ / (l + ST„ ) is the impedance at the base of the B JT, and Cbare the small-signal base-emitter resistance and capacitance of the BJT, respectively, gmis the transconductance of the BJT, and h, hare the currents in the primary and secondary coils, respectively. Thus, the amplitude of VB depends on the distance between the first coil 120b and the second coil 118b. It will be appreciated that for a small range of distances, this relationship may be considered linear.

[0110] The output signal may comprise information about the first physical quantity and / or the second physical quantity. For example, a spectrum of the output signal may be measured, from which information about the first and second physical quantities can be derived. Taking the example of circuit 100a from FIG. 1 , a peak may be observed at a frequency corresponding to the resonance frequency of resonant circuit 126. As the inductance of coil 102a does not change, the resonance frequency of resonant circuit 126 depends on the variable capacitance of capacitor 102a, and the resonant frequency observed is indicative of the capacitance of capacitor 102a. Further, as the capacitance of capacitor 102a depends on a physical quantity such as, but not limited to, a touch, pressure, humidity, or temperature, the resonant frequency observed from the output signal will be indicative of said physical quantity. Similarly, a second physical quantity may produce a change in a relative displacement between coil 120a and 118a which may affect the power transfer from coil 120a to coil 118a. In this way, the amplitude of the output signal may be indicative of the second displacement.

[0111] FIG. 10 shows a graph 1000 of simulation results for transient currents in first coil 120a (1002), second coil 118a (1006), and readout coil 108 (1004). A 1 -V, 50-MHz voltage was applied to the sensing circuit for a range of coefficients of coupling between the coils between 0.05 and 0.2. FIG. 11 shows a graph 1100 of a 24k-point Fast Fourier Transform of the current in the readout coil 108 for different values of the coefficient of coupling between the coils. FIG. 12 shows a graph 1200 of the transient changes of the current in the readout coil 108 for different values of the coupling efficient between the coils.

[0112] As another example, referring back to FIG. 2, the resonance frequency of the resonant circuit 202 may be given by:the impedance looking into the base of the transistor 214 is given by:where sM)2 / Zcis the impedance of the tank circuit at the collector, Zc, reflected back in series with LsA. At resonance, Zc« RsB, which is the series resistance of LsB. The resonantcircuit 202 embeds a capacitive sensor 102b, and an inductive sensor formed by inductor 118b and inductor 120b. A change in the capacitance of capacitor 102b modulates the resonance frequency of the resonant circuit, fr, whereas a change in coupling between the inductors 118b and 120b modulates the amplitude of the voltage at the base, VB(212). Simultaneous measurement of the frequency and amplitude of the sinusoidal wave at VBresults in a dual-parameter LC sensor.

[0113] FIG. 4 shows an example proof-of-concept measurement setup 400 consisting of a PCB. Setup 400 contains a PCB 406 designed and fabricated with the modified tuned amplifier, a trim capacitor Cs(410) for adjusting the capacitance of the LC tank, and an inductive link 402. In this configuration, the coil LSA is fixed in place, and LSB is mounted on an adjustable jig 412, allowing displacement in 10pm increments. The trim capacitor Cs(410) can be adjusted linearly between 25 pF and 600 pF, to vary the resonant frequency of the LC tank. The windings of inductors, LSA and LSB, are aligned in opposite directions to each other. Two identical coils were fabricated on a PCB with their values summarized in TABLE 2. FIG. 5 shows an example PCB coil 500 consisting of 20 turns with a trace width of 0.4 mm and an outer diameter of 27 mm.TABLE 2. PCB coil parameters.

[0114] FIG. 6 shows a plot 600 of the measured spectrum of the base voltage VB for different displacements of the coils between 0 mm and 8 mm in steps of 2 mm and different values of Csbetween 600 pF and 25 pF in 4 steps. The circuit was powered with a supply voltage of VDD = 8V, and the spectrum of the base voltage VB was recorded on an oscilloscope. The circuit consumed a total of 25mW during continuous operation. The capacitance was adjusted from 600pF to 25pF in four steps, with the coil displacement between 0mm and 8mm in steps of 2mm. The average frequency shift due to a change in Csis 2 kHz / pF. The amplitude of the sinusoidal waveform shows an average linear decrease of around 1 dB / mm. The results show a small change in frequency versus displacement in a range between 5 and 15 kHz / mm. This shift is due to small changes in the parasitic coupling capacitance, Cp, between the two coils with distance and changes in inductance in the tank coil due to eddy currents. Due to these frequency shifts, the sensing resolution is 10 pF for a maximum displacement of 8mm. The frequencies and peak values are summarized in TABLE 3.TABLE 3. Corresponding frequencies and peak values for FIG. 6

[0115] To demonstrate the dual parameter sensing operation of the circuit, trim capacitor Cs(410) in setup 400 may be replaced with a soil moisture sensor (e.g., Capacitive Soil Moisture Sensor V1.2). The commercial sensor was modified so that only the capacitive probe was connected to the LC tank. The circuit was tested with the sensor dry and fully submerged in water. The displacement of the inductively coupled coils was varied from 1 mm to 5 mm in 1-mm increments. Both spectra are within an approximate 250 kHz range with each peak separated by around 60 kHz. The frequency peaks occur at a range of 5.5 MHz to 5.80 MHz and 4.33 MHz to 4.56 MHz in dry and wet conditions, respectively. In both conditions, the amplitude changes by an average of around 1.25 dB / mm. In dry conditions, the amplitude decreases from -25.26 dB to -29.15 dB, while in the wet condition, the amplitude changes from -16.94 dB to -23.0 dB with varying coil distances.

[0116] FIG. 7 shows the moisture sensor in dry condition (700a) and fully submerged in water (700b). FIG. 8 shows comparisons of moisture sensors readings corresponding to dry conditions (800a) and the fully submerged in water state (800b) for different displacements of the coils between 1 mm and 5 mm in steps of 1 mm. The corresponding frequencies and peak values for graphs 800a and 800b are shown in TABLE 4.TABLE 4. Corresponding frequencies and peak values of FIG. 8.

[0117] Reference is next made to FIG. 3, which shows an example embodiment of an inductively coupled pressure sensor 300 in accordance with the teachings herein. Sensor 300 may contain a first coil 306 and a second coil 312. Coils 306 and 312 may be used as coils 120 and 118 in circuits 100a and 100b of FIGS. 1 and 2. Coil 306 may be disposed on a first face of a silicon wafer 310, and coil 312 may be disposed on an opposing face of the wafer 310. For example, coils 306, 312 may be patterned on the top and bottom sides of a silicon wafer 310, respectively, as shown in FIG. 3. Coils 306 and 312 may be deposited upon SiO2 layers 302, 316, respectively, which are disposed between the wafer 310 and the coils. A portion of silicon underneath the top coil 306 is etched to form a vacuum cavity 308 within the wafer 310 between the coils 306, 312, thereby allowing the SiO2 membrane 302 to produce a deflection 318 under applied pressure. The displacement of the movable coil may occur only along a single axis. For example, for a planar coil, the axis may be orthogonal to the plane of the coil, with no angular displacement present. In some embodiments, both the first and second layers of silicon dioxide may be operable to produce a deflection.

[0118] The default distance between the coils may be the thickness of the silicon substrate wafer 310 (for e, g., 300pm) and can be adjusted by wafer thinning. As a part of the fabrication process, the bare silicon wafer 310 may be thinned down to approximately 80pm before the micromachining process. The total distance 314 between the coils 306, 312 may be equal to the thickness of the silicon wafer 310, plus the additional thickness of the SiO2 layers 302, 316 and Al layers (which may be approx. 1 -2 pm).

[0119] Coils 306 and 312 may be silicon square spiral coils. The inductance, Ls, of a silicon square spiral coil with N turns is given by the following:where p = (do- di) / (d0+ d / ) is the fill factor and dav= 0.5(do+ df) is the average turn diameter, with d0and dtthe outer and inner diameter of the coil, respectively.

[0120] The mutual inductance between the two coaxial spiral coils is given by:where represents the mutual inductance between the / th and jth turns of the two coils and is given by:whereand r2are the coil radii, d is distance between the coils and K(k) and E(k) are the complete elliptic integrals of the first and second kind, respectively.

[0121] FIG. 17 shows a plot 1700 of the inductance, L, and the self-resonant frequency, fsR, calculated for different coil geometries versus fill factor, p, for various embodiments of pressure sensor 300. Plot 1700 confirms the tradeoff between L and fsR, where a low number of turns for coils 312 and 306 may result in high fsR but low L and vice versa for a high number of turns. The inventors have found that a moderate number of turns (N=6-8) and a p = 0.5- 0.6 may result in optimum coil parameters.

[0122] Excitation of the primary (receiving) coil induces a voltage in the secondary (sensing) coil, which results in a reflected impedance, Zr, at the primary side given as:where Zsis the impedance in the secondary (sensing) coil. At resonance, this impedance is real, and so is the reflected impedance. As the sensing coil is deflected towards the receivingcoil due to applied pressure, the magnitude of the reflected impedance will change due to a change in mutual impedance.

[0123] FIG. 18 shows a plot 1800 of the quadratic relationship between the mutual inductance, M, and distance 314, d, for different embodiments of sensor 300 of FIG. 3, for coils with N = 6, 8, and 10. For a small range of distances, M is approximately linear (F?2> 0.9), with a sensitivity (nH / pm) dependent on the number of turns, as shown in the inset of the figure for a distance 314, d, between 50 and 80 pm, consistent with simulated values shown in FIG. 19. The linear change in M results in a linear change in reflected impedance according to Eq. 8, which can be read at the primary coil. The calculated values of M result in values of the coupling coefficient k = ^[ / ^LpLsof 0.1 for N = 6, 0.125 for N = 8, and 0.16 for N = 10.

[0124] For some embodiments of sensor 300 of FIG. 3, the top deformable plate 302 is separated from a stationary plate 316 by a gap 314 (cf). The radius, thickness, density, and Young’s modulus of the upper plate are denoted by R, tm, p, and E, respectively. Kirchoff’s thin plate theory, including geometrical nonlinearities, were adopted to simulate the mechanical behaviour of the microsensor. The sensor 300 is modeled under the assumption that pressure is homogeneously distributed across the membrane 302. The governing equation for the dynamic transverse deformation of the movable plate 302 (sensing coil) takes the following form:where W represents the plate deformation, t is time, eo is the permittivity of the air, D is the bending rigidity of the plate, and C is the damping coefficient. The external force Q is modeled as a low-frequency sinusoidal pressure wave. TABLE 5, below, shows the specifications of the membrane 302.TABLE 5: Specifications of the pressure-sensing membrane

[0125] FIG. 19 shows a plot 1900 of the deflection 318 of an embodiment of pressuresensing membrane 300 with 1 pm-thick membrane 302 under a range of pressures between 0 and 20 kPa, and a plot 1902 for different membrane thicknesses under maximum pressure 20 kPa. As seen in plot 1900, at the maximum pressure, the deflection at the center of the membrane is 27pm, with a sensitivity of approximately 1 ,3pm / kPa.

[0126] FIG. 20 show an example 3D model 2000 of coils 306, 312 of FIG. 3 in accordance with at least one embodiment. Model 2000 shows a tapered spiral inductor embodiment of the coils. Various embodiments of sensor 300 and constituent components can be designed, modelled, and simulated in the ANSYS Electronics 3D electromagnetic High-Frequency Simulation Software (HFSS).

[0127] The single coil square spiral design, as shown in model 2000, was constrained within a 2mm-by-2mm area operating at the frequency of 775 MHz. For the model of the overall sensor, both the movable primary top coil and stationary bottom coil were resonated at 775 MHz using a fixed lumped capacitor of 0.4 pF. The primary coil was excited differentially using a lumped port with an impedance of 1 MQ. The S-parameters resulting from the 3D model simulation in ANSYS HFSS were utilized to calculate the input impedance. The input impedance, Zin, of a 1 -port network of the primary spiral is given by:(1 + Sn)Zin = Zo _ ' . (10)I1 dllJ where Zois the 50-Q characteristic impedance. The input impedance Zincomprises the real, R and the imaginary component, Xi_. The input impedance was used to determine the inductance of the primary coil at the operating frequency of 300 MHz using the equation:

[0128] Similarly, the quality factor, Q, of the designed inductors were extracted from the calculated inductance and input impedance. The unloaded Q of the parallel resonant circuitused is given below, where the real value of Zin is the peak resistance at the resonance frequency, fsR:

[0129] TABLE 6 reports three design variants that were studied by the inventors. Design A represents a square planar tapered coil. Design B represents a square symmetrical coil with a shorter bridge, and design C represents a conventional square planar coil. The table also reports simulated results of coil inductance L, quality factor Q, and self-resonance frequency, fsR. It can be seen that design A exhibits better overall performance as tapered spiral silicon coils offer higher inductance and quality factors compared to conventional silicon coils due to the lower skin and proximity effects of the center turn.TABLE 6: Comparison of coil designs in HFSS

[0130] L and Q were evaluated at 300 MHz. To ensure consistency with the results, the thickness of the top two metal layers were kept constant at 0.5pm. Additionally, the silicon substrate thickness was fixed at 50pm. Taper factors, twand ts, quantify the adjustment in width, Aw and spacing As per turn, normalized to the maximum width, Wmax and maximum spacing, Smax, respectively.

[0131] As shown in TABLE 6, design A presents the most promising structure in terms of trade-off between L, Q, and fsR. Further optimizations such as a change in the number of turns and the taper factor were conducted to improve its performance. Following furtherenhancement of the coil of design A, tuned to be resonant at a frequency of 775 MHz, improvements to inductance and quality factor were seen, as denoted in TABLE 7. The thickness of the two metal layers and the silicon substrate remained unaltered.TABLE 7: Modification of Design ‘A’ Tapered Square Spiral Inductor

[0132] The optimized tapered spiral inductor was combined with a secondary and identical spiral in the 3D model to observe the changes in parameters as the primary coil experienced displacement. The displacement ranged from 81 pm to 61 m. Errors in the HFSS simulation of design A were minimized by ensuring that the number of solved elements were consistent for each deflection step (e.g., between 70000 and 75000).

[0133] FIG. 24 shows a graph 2400 of the linear relationship between the magnitude of Zm and displacement of the movable coil of FIG. 3, evaluated at 775 MHz. The coil displacement varied from 81 pm to 61 pm. Additionally, a few discrete points do not align with the linearity at 775 MHz due to the modelling errors. Specifically, the mesh size was slightly altered at each displacement level. The increments in displacement are very small, and may have introduced offset in the model, resulting in the outliers. Furthermore, for a deflection range of 20pm, the impedance, Z / n, varied from approximately 2310 Q to 2775 Q, indicating a change of 465 Q over a 20pm. This resulted in an average sensitivity of 23.25 Q / pm. Furthermore, changes in inductance were observed as the coil experienced displacement, however with minimal fluctuations between 49.84nH and 50.1 nH.

[0134] FIG. 21 shows a graph 2100 of the magnitude of input impedance, Z / n, at 780, 775, and 770 MHz, versus of the primary coil displacement. A similar linear trend over a 20pm deflection range can be observed across all of the aforementioned frequency values. The deviation in Z / / 7is relatively small for all three frequencies. These results closely correspond to the results presented in FIG. 24 with reasonable alignment with the linear fit, indicating consistent behaviour.

[0135] Reference is next made to FIGS. 13a and 13b, which show 3D models 1300a and 1300b of example embodiments of inductive pressure sensor 300 of FIG. 3. The 3D models may be analyzed using finite-element-method (FEM) analysis. The models 1300 consist of two equal coils 1302 and 1304 constructed on each face of the silicon substrate and separated by approximately 600pm. Model 1300a shows a low density, 3-turn coil. Model 1300b shows a high density, 10-turn coil. One of the coils may be fixed, whereas the other coil can be displaced along the z-axis toward the fixed coil in response to pressure applied in the z-direction. As the moving coil deflects toward the fixed coil, their mutual inductance increases. An increase in the mutual inductance will translate to a large voltage measured at the secondary (fixed) coil as shown in FIG. 16. The voltage in the secondary is 1.2V at maximum distance between the two coils (no pressure applied) and 5V at minimum distance between the two coils (maximum pressure applied). A linear relationship between voltage and pressure can be determined through calibration. FIG. 14 shows a graph 1400 of the change in mutual inductance between coils 1302 and 1304 versus the distance between coils 1302 and 1304 for a 3-turn coil. FIG. 15 shows a 3D model 1500 of another embodiment of a 10-turn coil, on a smaller footprint than the one shown in FIG. 13b. FIG. 16 shows a graph 1600 of the change in voltage in the secondary coil in response to a change in displacement due to applied pressure at a resonance frequency of 50MHz.

[0136] Reference is next made to FIG. 9, which shows a sensor array circuit 900. Circuit 900 may be considered an extension of circuit 100a of FIG. 1 into an N-element array. Circuit 900 contains an array 918 of integrated MEMS moving coils 904. The excitation of each coil 904 can be controlled by a 1 :N multiplexer 924. Each coil 904 may transmit a signal to the relay coil 916, which may then relay the signal to reader circuit 914. The signal may be a magnetic field that produces a coupling with the relay coil, which may contain information about the displacement of the moving coils 904 and the variable capacitors 902 in the form of an amplitude and a resonant frequency of the signal, respectively. To ensure strong coupling between each coil unit 904 in the array 918 and the relay coil 916, the size of the relay coil 916 may cover the entire area of the array 918.

[0137] In some embodiments, the sensor circuit may use a capacitor array instead of a single capacitor. For example, reference is next made to FIG. 22, which shows an LC sensor circuit 2200 with a capacitor array 2202. Circuit 2200 is similar to circuit 100b of FIG. 2,except the single variable capacitor 102b of circuit 100b is replaced with the capacitor array 2202. The capacitor array can contain a plurality of variable capacitors, the variable capacitors being responsive to one or more additional physical quantities. A plurality of switches 2204, each being connected to a unique one of a capacitor of the capacitor array 2202, can be used to connect each capacitor of the capacitor array 2202 to the resonant tank 2206. Once one of the capacitors 2202 is connected, the resulting circuit becomes equivalent to that of circuit 100b of FIG. 2, and the principle of operation is substantially the same.

[0138] Reference is next made to FIG. 23, which shows an LC sensor circuit 2300. Circuit 2300 contains a variable capacitor 2302, a variable resistor 2304, and a fixed coil 2306. Circuit 2300 may be similar to circuit 100b of FIG. 2, except the movable coil is disconnected, and only a fixed coil 2306 remains connected to the circuit. Fixed coil 2306 is tapped such that two coils are formed, with the inductance of each coil varying with the tap setting. Variable capacitor 2302 may produce a varying capacitance based on a displacement of the electrodes of the capacitor. Variable resistor 2304 may produce a varying resistance based on a further physical quantity such as, but not limited to, an applied pressure, touch, strain, temperature, humidity, or gas, for example. For example, variable resistor 2304 may be a force-sensitive resistor operating on piezo-resistive principles, a temperature-sensitive resistor, or any other suitable type of variable resistor capable of responding to a desired physical quantity.

[0139] Similar to circuit 100b, a change in the capacitance of capacitor 2302 may change the resonance frequency of the resonant circuit 2308. A change in the resistance of resistor 2304 may result in a change of the quality factor of the LC tank, which in turn results in a change in the amplitude of the measured voltage signal, which can be taken at the collector, at the resonance frequency. The fixed coil 2306 may be tapped such that the LC tank forms a Hartley oscillator.

[0140] Referring to FIG. 25a, shown therein are several example embodiments of a fabricated inductive pressure sensor in accordance with the teachings herein. The various sensor geometries and sizes of these inductive pressure sensors highlight consistency in the fabrication method used where the top coil (e.g., sensor membrane) is built on a flexible polyimide (e.g., flexible PCB) and subsequently mounted onto a rigid PCB. The rigid PCB isshown equipped with SMA connectors, demonstrating a practical means of interfacing the sensor for electronic measurements.

[0141] Referring to FIG. 25b, shown therein is a cross-sectional view of a fabricated sensor showing the layered architecture. This view illustrates the spatial relationship between the main components of a top flexible membrane (containing the top coil), a 3D-printed spacer which defines an air gap and sensing range, and a bottom rigid PCB (e.g., FR4 PCB) which provides a fixed base for the bottom coil.

[0142] Referring to FIG. 25c, shown therein is a top-down view of sensor components prior to full assembly, the geometry of the bottom inductive coil fixed on its substrate and the precise placement of the 3D-printed spacer can be seen. This illustrates how the spacer defines the active area and boundary for the flexible membrane that will be placed on top.

[0143] Referring to FIG. 25d, shown therein is an assembled inductive pressure sensor unit in accordance with the teachings herein. Fig. 25d shows the final assembly of the flexible polyimide membrane over the spacer and bottom coil, all mounted on the rigid PCB. The SMA connectors are shown attached, indicating that the sensor is prepared for use (e.g., experimental validation).

[0144] Referring to FIG. 25e, shown therein is an experimental setup for testing the performance of the sensor of FIG. 25d. The experimental setup provides the means to validate the function of the LC sensor. The sensor is shown under test, and a force gauge and a displacement reader are used to apply and measure, respectively, precise force and deflection. A vector network analyzer may also be used to measure the sensor's electrical response in terms of s-parameters, which are used to extract relevant data (e.g., coupling coefficient).

[0145] Referring now to FIG. 25f, shown therein is a close-up view of the sensor of FIG. 25d interfacing with the test apparatus of FIG. 25e. Fig. 25f shows how force is applied to the sensor's flexible top membrane using a 3D-printed screw tip. This allows for the application of a controlled, localized pressure to induce membrane deflection and, consequently, a change in the inductive coupling.

[0146] Referring now to FIG. 25g, shown therein is a performance graph plotting measured coupling coefficient (k) as a function of the applied force (N). This graph demonstrates thesensor's linear response over a test range of 0.5N to 5N. The high coefficient of determination (R2= 0.9843) provides quantitative evidence of this linearity, representing a high-fidelity pressure sensor.

[0147] Referring now to FIG. 25h, shown therein is a graph of the frequency response of the sensor of FIG. 25d under a wide range of applied forces. This graph demonstrates the advantageous feature of the self-resonance frequency of the inductive sensor being minimally dependent on the applied force. This stability is evident as the resonant peaks for all applied forces (from 1.2N to 3.7N) are tightly clustered, simplifying the design of the interrogation electronics. This stability demonstrates that the resonance peak can act as a stable reference, independent of the pressure being measured by the inductive coupling. This characteristic enables the use of a capacitive sensor as part of an LC circuit, whereby the stable resonance peak is used to extract a capacitance measurement. This creates a dual-mode sensor where the capacitance reading is independent to and non-interfering with the pressure reading obtained from the inductive link.

[0148] Referring now to FIG. 25i, shown therein is a graph plotting membrane displacement (mm) versus applied pressure (N) illustrating mechanical hysteresis of the sensor of FIG. 25d. The two distinct curves in this graph are for increasing pressure (bottom line) and for decreasing pressure (top line) and they quantify the "memory" effect of the polyimide membrane. This data can be used to characterize the sensor's repeatability and accuracy over operational cycles.

[0149] Referring now to FIG. 25j, shown therein is a graph of membrane tension (measured as force) versus time over a 15-minute period for the sensor of FIG. 25d. This data is significant for validating the long-term stability and reliability of the sensor. The graph shows a deviation of less than 0.5N over the measured time, demonstrating the sensor's ability to maintain a stable reading after an initial settling period, which is an advantageous feature allowing for use in practical applications.

[0150] The foregoing embodiments and advantages are provided merely as examples and are not to be construed as limiting the claims. Also, the description of the embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.

Claims

CLAIMS:1 . A dual-output LC sensor comprising: a capacitor, configured to produce a varying capacitance when subjected to a first physical quantity; a first coil, configured to: produce a magnetic field; and a second coil, configured to: sense the magnetic field; and produce an output signal based on the magnetic field, wherein at least one of the first coil and the second coil is configured to deflect along an axis when subjected to a second physical quantity.

2. The sensor of claim 1 , wherein the capacitor is configured, when subjected to the first physical quantity, to undergo any combination of: a displacement of at least one electrode of the capacitor, a change in dielectric property of the capacitor, and a change in a charge of the capacitor.

3. The sensor of claim 1 , wherein the capacitor is configured, when subjected to the first physical quantity, to undergo any combination of: a first displacement of a first electrode relative to a second electrode of the capacitor, a change in a dielectric property of a material between the first electrode and the second electrode, and a change in a relative charge between the first and second electrodes.

4. The sensor of any one of claims 1 to 3, wherein the first coil and / or the second coil is configured to undergo a second displacement relative to one another when subjected to the second physical quantity.

5. The sensor of any one of claims 1 to 4, wherein the output signal varies based on the relative displacement of the first and second coils to one another due to the second physical quantity.

6. The sensor of any one of claims 1 to 5, wherein the output signal further varies based on a change in capacitance of the capacitor due to the first physical quantity.

7. The sensor of any one of claims 1 to 6, wherein the first physical quantity comprises any combination of: a pressure, a temperature, a strain, a humidity, a gas, and a touch.

8. The sensor of any one of claims 1 to 7, wherein the second physical quantity comprises any combination of: a pressure, a temperature, a strain, a humidity, and a touch.

9. The sensor of any one of claims 1 to 8, further comprising a bipolar transistor, wherein a base of the bipolar transistor is connected to the second coil and a collector of the bipolar transistor is connected to a resonant circuit formed by the capacitor and the first coil.

10. The sensor of any one of claims 1 to 9, wherein^the second coil is further operable to transfer the output signal to a readout device.11 . The sensor of claim 10, wherein: the readout device comprises a wireless reader; and the second coil is adapted to transmit the output signal wirelessly to the readout device.

12. The sensor of claim 10, wherein: the readout device comprises a voltage measurement device; and the readout device is configured to measure the output signal using the voltage measurement device.

13. The sensor of any one of claims 10 to 12, wherein the sensor is adapted to generate the output signal with a resonant frequency that is related to the first physical quantity so that the readout device is able to detect the first physical quantity by measuring the resonant frequency of the output signal.

14. The sensor of any one of claims 10 to 13, wherein the sensor is adapted to generate the output signal with an amplitude that is related to the second physical quantity so that the readout device is able to detect the second physical quantity by measuring the amplitude of the output signal.

15. The sensor of any one of claims 1 to 14, further comprising an inductive pressure sensor, the inductive pressure sensor comprising:a silicon wafer; the first coil, disposed on a first face of the silicon wafer; and the second coil, disposed on an opposite face of the silicon wafer.

16. The sensor of claim 15, wherein the inductive pressure sensor further comprises: a first layer of silicon dioxide, disposed between the silicon wafer and the first coil; and a second layer of silicon dioxide, disposed between the silicon wafer and the second coil, wherein at least one of the first and second layers of silicon dioxide is adapted to deflect under an applied pressure.

17. The sensor of any one of claims 15 and 16, wherein the inductive pressure sensor further comprises a vacuum cavity formed within the silicon wafer between the first and second coils.

18. The sensor of any one of claims 1 to 17, further comprising: a third coil, configured to produce a second magnetic field and to deflect based when subjected to a third physical quantity; a fourth coil, configured to produce a third magnetic field and to deflect when subjected to a fourth physical quantity; and a multiplexer, wherein: the second coil is further configured to sense the second and third magnetic fields; and the multiplexer is configured to activate one of the first, third, and fourth coils, such that the second coil can sense only one of the magnetic field, the second magnetic field, and the third magnetic field at a time.

19. The sensor of any one of claims 1 to 17, further comprising: a capacitor array, comprising the capacitor and one or more array capacitors, wherein the one or more array capacitors are configured to produce one or more additional varying capacitances when subjected to one or more additional physical quantities; and a plurality of switches,wherein each switch of the plurality of switches is: connected to a given capacitor which is a unique one of: the capacitor and one of the one or more array capacitors; and operable to electrically connect said given capacitor to the first coil.

20. A dual-output LC sensor comprising: a capacitor, configured to produce a varying capacitance based on a first physical quantity; a first coil, configured to produce a first fixed inductance based on a tap setting; a second coil, configured to produce a second fixed inductance based on the tap setting; and a resistor, configured to produce a varying resistance based on a second physical quantity.

21. The sensor of claim 20, wherein the capacitor, when subjected to the first physical quantity, is adapted to undergo any combination of: a displacement of at least one electrode of the capacitor, a change in a dielectric property of the capacitor, and a change in a charge of the capacitor.

22. A dual-output tuned-amplifier circuit, the circuit comprising: a resonant tank comprising: a capacitor configured to produce a varying capacitance; and a first inductor; a second inductor magnetically coupled to the first inductor, wherein a magnetic coupling between the second inductor and the first inductor is variable; and an amplifier connected to the resonant circuit and the second inductor, configured to produce an output signal, the output signal comprising a varying amplitude based on the magnetic coupling and a varying frequency based on the varying capacitance.

23. The circuit of claim 22, wherein the varying capacitance is produced when the capacitor is subjected to a first physical quantity.

24. The circuit of any one of claims 22 to 23, wherein the magnetic coupling varies when one of the first and second inductors is subjected to a second physical quantity.

25. The circuit of any one of claims 22 to 24, wherein the capacitor, when subjected to the first physical quantity, is adapted to undergo any combination of: a displacement of at least one electrode of the capacitor, a change in a dielectric property of the capacitor, and a change in a charge of the capacitor.

26. The circuit of any one of claims 22 to 24, wherein the capacitor, when subjected to the first physical quantity, is adapted to undergo any combination of: a first displacement of a first electrode relative to a second electrode of the capacitor, a change in a dielectric property of a material between the first electrode and the second electrode, and a change in a relative charge between the first and second electrodes.

27. The circuit of any one of claims 22 to 26, wherein one of the inductors, when subjected to the second physical quantity, is adapted to undergo a change in a second displacement of the first inductor relative to the second inductor.

28. The circuit of any one of claims 22 to 27, wherein the varying frequency is based on a resonant frequency of the resonant tank.

29. The circuit of any one of claims 22 to 28, wherein the amplifier is a transistor.

30. The circuit of claim 29, wherein the transistor is a bipolar junction transistor or a CMOS transistor.

31. The circuit of claim any one of claims 29 to 30, wherein the second inductor is connected to a base of the transistor and the resonant tank is connected to a collector of the transistor.

32. The circuit of claim 31 , wherein the output signal is taken at one of the base and the collector of the transistor.

33. The circuit of any one of claims 22 to 32, wherein when a relative distance between the first inductor and the second inductor is greater than a critical distance, a resonant frequency of the resonant tank is dependent only on the varying capacitance.

34. The circuit of any of claims 22 to 33, further comprising an inductive pressure sensor, the inductive pressure sensor further comprising: a silicon wafer; wherein the first inductor is disposed on a first face of the silicon wafer; and wherein the second inductor is disposed on an opposite face of the silicon wafer.

35. The circuit of claim 34, wherein the inductive pressure sensor further comprises: a first layer of silicon dioxide, disposed between the silicon wafer and the first inductor; and a second layer of silicon dioxide, disposed between the silicon wafer and the inductor coil, wherein at least one of the first and second layers of silicon dioxide deflect under an applied pressure.

36. The circuit of any one of claims 34 to 35, wherein the inductive pressure sensor further comprises a vacuum cavity formed within the silicon wafer between the first and second inductors.

37. The circuit of any one of claims 21 to 36, further comprising: a capacitor array, comprising the capacitor and one or more array capacitors, wherein the resonant tank further comprises the capacitor array and the one or more array capacitors are configured to produce one or more additional varying capacitances when subjected to one or more additional physical quantities respectively; and a plurality of switches, wherein each switch of the plurality of switches is: connected to a given capacitor that is a unique one of: the capacitor and one of the one or more array capacitors; and operable to electrically connect said given capacitor to the resonant tank.

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