LC Wireless Passive Pressure Sensing System with Matching Circuit and Sensor Manufacturing Method

Abstract

The present invention discloses an LC wireless passive pressure sensing system with a matching circuit and a method for manufacturing a sensor. The pressure sensing system includes a resonant micro-pressure sensor and a signal acquisition circuit. The signal acquisition circuit includes a measurement circuit, a signal generator, a mixing circuit, a low-pass filter circuit, a sampling circuit, and a control circuit. The measurement circuit includes a matching capacitor, a measurement inductor, a measurement resistor, and a reference resistor. The resonant micro-pressure sensor includes a first film layer, a second film layer, and an intermediate layer, and the intermediate layer is sandwiched between the first film layer and the second film layer. A first capacitor plate is disposed in the first film layer, and a second capacitor plate is disposed at a position opposite to the first capacitor plate in the second film layer. The first capacitor plate is connected to an inductor wire. A hollow air vent cavity is disposed in the intermediate layer. In the above pressure sensing system, a compact signal acquisition circuit is designed to improve portability, a matching capacitor is provided to increase the wireless induction distance, and an air vent cavity is provided to discharge internal air to improve measurement sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible microsensors, and particularly to an LC wireless passive pressure sensing system with a matching circuit and a method for manufacturing a sensor. Background Art

[0002] With the acceleration of the aging process of China's population, the demand for medical care has become increasingly prominent. As a core indicator for evaluating the normal physiological functions of the human body, internal physiological pressure measurement has become an important research object for promoting the development of precision medicine and high-end medical device technologies. For example, intraocular pressure (IOP) is an important indicator for evaluating glaucoma, and its continuous increase may lead to optic nerve damage and even blindness. Accurate monitoring of IOP is of great significance for the early diagnosis and treatment of glaucoma. Another example is intracranial pressure (ICP), which is a key monitoring indicator for patients with traumatic brain injury. An abnormal increase in ICP (>15 mmHg) may lead to serious complications and even endanger the patient's life. Therefore, the development of highly sensitive implantable pressure sensors for accurately measuring human internal physiological pressure parameters has become the key to improving treatment efficiency and ensuring patient safety.

[0003] Traditional pressure sensors are difficult to meet the usage requirements in the human internal physiological environment due to problems such as large volume, susceptibility to external environmental interference, and inability to perform long-term real-time monitoring. In recent years, flexible wireless passive micro pressure sensors based on LC resonance (LC resonance refers to the phenomenon that the reactances of an inductor and a capacitor cancel each other out at a specific frequency, resulting in the circuit presenting a pure resistive property) have provided a potential solution for such requirements. Such sensors have the advantages of a flexible structure, no need for a power supply, and non-contact connection, and can achieve highly sensitive pressure signal reading in a complex physiological environment. Although some design schemes of passive pressure sensors have been disclosed in the prior art, limited by the signal strength attenuation characteristics of passive devices themselves, most current LC sensing systems still have significant deficiencies in the readout distance and are difficult to meet the actual requirements for long-distance and non-contact reading in clinical or complex physiological scenarios. Therefore, the passive pressure sensors in the prior art methods have the problem that the induction distance is too close to meet the usage requirements. Summary of the Invention

[0004] Embodiments of the present invention provide an LC wireless passive pressure sensing system with a matching circuit and a method for manufacturing a sensor, aiming to solve the problem that the induction distance of the passive pressure sensors in the prior art methods is too close to meet the usage requirements.

[0005] In a first aspect, embodiments of the present invention provide an LC wireless passive pressure sensing system with a matching circuit, which includes a resonant micro pressure sensor and a signal acquisition circuit;

[0006] The signal acquisition circuit includes a measurement circuit, a signal generator, a mixing circuit, a low-pass filter circuit, a sampling circuit, and a control circuit; the measurement circuit includes a matching capacitor, a measurement inductor, a measurement resistor, and a reference resistor;

[0007] One end of the signal generator is grounded, and the other end is connected to one end of the measurement resistor and one input end of the mixing circuit; the other end of the measurement resistor is connected to one end of the measurement inductor, the other end of the measurement inductor is connected to one end of the matching capacitor, the other end of the matching capacitor is connected to one end of the reference resistor and the other input end of the mixing circuit; the other end of the reference resistor is grounded;

[0008] The output end of the mixing circuit is connected to the input end of the low-pass filter circuit, the output end of the low-pass filter circuit is connected to the input end of the sampling circuit, the output end of the sampling circuit is connected to the input end of the control circuit, and the control end of the control circuit is connected to the control input end of the signal generator;

[0009] The resonant micro-pressure sensor includes a first film layer, a second film layer, and an intermediate layer, and the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor plate is arranged in the first film layer, and a second capacitor plate is arranged at a position opposite to the first capacitor plate in the second film layer; the first capacitor plate is connected to an inductor wire; a hollow ventilation cavity is arranged in the intermediate layer; one end of the ventilation cavity penetrates through the side surface of the intermediate layer and is connected to the outside, and the other end of the ventilation cavity extends between the first capacitor plate and the second capacitor plate; the first capacitor plate and the second capacitor plate are combined to form an induction capacitor, and the induction capacitor is connected in series with an equivalent resistor and an equivalent inductor formed by the inductor wire to form a ring-shaped induction circuit, and the equivalent inductor is coupled with the measurement inductor to generate an induction signal; the matching capacitor is matched in real time according to the capacitance value of the induction capacitor.

[0010] In a second aspect, an embodiment of the present invention further provides a sensor manufacturing method, wherein the sensor manufacturing method is used to manufacture the resonant micro-pressure sensor in the LC wireless passive pressure sensing system with a matching circuit as described in the first aspect above; the sensor manufacturing method includes:

[0011] Clean the bottom insulating film and attach a copper metal layer on its upper layer;

[0012] Coat a photoresist layer on the copper metal layer and transfer the sensor layout pattern to the photoresist layer;

[0013] Etch the copper metal layer after developing;

[0014] Attach an upper insulating film to the etched copper metal layer to prepare the first film layer and the second film layer;

[0015] Place the first film layer and the second film layer on both sides of the intermediate layer with a pre-cut ventilation cavity respectively, and bond and press the formed multi-layer structure to obtain the resonant micro-pressure sensor.

[0016] The embodiment of the present invention provides an LC wireless passive pressure sensing system with a matching circuit and a sensor manufacturing method. The pressure sensing system includes a resonant micro-pressure sensor and a signal acquisition circuit; the signal acquisition circuit includes a measurement circuit, a signal generator, a mixing circuit, a low-pass filter circuit, a sampling circuit and a control circuit; the measurement circuit includes a matching capacitor, a measurement inductor, a measurement resistor and a reference resistor; the resonant micro-pressure sensor includes a first film layer, a second film layer and an intermediate layer, and the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor plate is arranged in the first film layer, and a second capacitor plate is arranged at a position opposite to the first capacitor plate in the second film layer; the first capacitor plate is connected to an inductor wire; a hollow ventilation cavity is arranged in the intermediate layer. The above pressure sensing system provides a compact signal acquisition circuit to improve portability, and at the same time sets a matching capacitor to increase the sensing distance; a ventilation cavity is arranged in the resonant micro-pressure sensor to discharge the internal air to improve the measurement sensitivity. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0018] Figure 1 It is a three-dimensional structure diagram of the resonant micro-pressure sensor provided by the embodiment of the present invention;

[0019] Figure 2 It is a side structure diagram of the resonant micro-pressure sensor provided by the embodiment of the present invention;

[0020] Figure 3 It is another side structure diagram of the resonant micro-pressure sensor provided by the embodiment of the present invention;

[0021] Figure 4 It is a planar structure diagram of the spiral microstrip line provided by the embodiment of the present invention;

[0022] Figure 5 It is an application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0023] Figure 6 It is a circuit structure diagram of a passive pressure sensor in the traditional technical method;

[0024] Figure 7 The circuit structure diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0025] Figure 8 The method flow chart of the sensor manufacturing method provided by the embodiment of the present invention;

[0026] Figure 9 The manufacturing process flow chart of the sensor manufacturing method provided by the embodiment of the present invention;

[0027] Figure 10 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0028] Figure 11 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0029] Figure 12 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0030] Figure 13 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0031] Figure 14 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0032] Figure 15 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0033] Figure 16 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0034] Figure 17 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0035] Figure 18 Another application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by the embodiment of the present invention;

[0036] Reference numerals: DDS, signal generator; Mi, mixer circuit; LPF, low-pass filter circuit; ADC, sampling circuit; MCU, control circuit; Cr, matching capacitor; Lr, measuring inductor; Rr, measuring resistor; Rref, reference resistor; Ls, equivalent inductor; Rs, equivalent resistor; Cs, inductive capacitor; 10, first film layer; 30, second film layer; 20, intermediate layer; 11, first capacitor plate; 31, second capacitor plate; 12, inductor wire; 21, ventilation cavity; 101, first insulating layer; 102, second insulating layer; 103, first copper layer; 301, third insulating layer; 302, fourth insulating layer; 13, epoxy resin adhesive layer. Detailed implementation manners

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] It should be understood that when used in this specification and the appended claims, the terms "comprises" and "comprising" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0039] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0040] It should be further understood that the term " / and" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0041] The specific embodiment of the present application discloses an LC wireless passive pressure sensing system with a matching circuit, which includes a resonant micro-pressure sensor and a signal acquisition circuit; the signal acquisition circuit includes a measurement circuit, a signal generator DDS, a mixing circuit Mi, a low-pass filter circuit LPF, a sampling circuit ADC, and a control circuit MCU; the measurement circuit includes a matching capacitor Cr, a measurement inductor Lr, a measurement resistor Rr, and a reference resistor Rref; one end of the signal generator DDS is grounded, and the other end is connected to one end of the measurement resistor Rr and one input end of the mixing circuit Mi; the other end of the measurement resistor Rr is connected to one end of the measurement inductor Lr, the other end of the measurement inductor Lr is connected to one end of the matching capacitor Cr, and the other end of the matching capacitor Cr is connected to one end of the reference resistor Rref and the other input end of the mixing circuit Mi; the other end of the reference resistor Rref is grounded; the output end of the mixing circuit Mi is connected to the input end of the low-pass filter circuit LPF, the output end of the low-pass filter circuit LPF is connected to the input end of the sampling circuit ADC, the output end of the sampling circuit ADC is connected to the input end of the control circuit MCU, and the control end of the control circuit MCU is connected to the control input end of the signal generator DDS to send a drive control signal to the signal generator DDS through the control circuit MCU, so as to drive the signal generator DDS to generate an AC voltage signal. Wherein, the matching capacitor is matched in real time according to the capacitance value of the induction capacitor.

[0042] The LC wireless passive pressure sensing system with a matching circuit proposed in the embodiment of the present invention is composed of a portable signal acquisition circuit and an LC resonant micro-pressure sensor, and the specific circuit structure is as Figure 7 shown, where the signal acquisition circuit includes a measurement circuit, a signal generator DDS, a mixing circuit Mi, a low-pass filter circuit LPF, a sampling circuit ADC, and a control circuit MCU; the control circuit MCU can also be connected to a Bluetooth receiving circuit, so as to send the induction signal obtained by the control circuit MCU to an external terminal (such as a mobile phone, a tablet computer, etc.) through the Bluetooth receiving circuit.

[0043] In recent years, the traditional frequency-sweeping reading circuit proposed by Nopper et al. has been proven effective, but its current source drive mechanism needs to implement signal conversion through a transconductance amplifier, and there are the following inherent defects: on the one hand, multiple signal conversion links will introduce additional transmission losses; on the other hand, the gain-bandwidth product of the transconductance amplifier restricts the high-frequency response ability of the system. To overcome the above problems, the present invention proposes a simplified circuit architecture directly excited by a voltage source (as Figure 7 shown), and its effectiveness is verified through theoretical analysis and simulation.

[0044] Existing LC wireless passive sensing is achieved through near-field mutual inductance coupling between an external readout coil and the inductor of the sensor. Its effective reading distance is very limited and is usually comparable to the size of the sensor inductor. To increase the readout distance of the system, the technical method of this application further introduces a matching capacitor Cr (as shown in Figure 6 ) on the basis of the voltage-driven architecture shown in Figure 7 to adjust the impedance matching state between the readout end and the sensor. This design can effectively improve the signal strength of the LC wireless passive sensing system, thereby increasing the effective readout distance of the sensor.

[0045] To verify the performance differences between the two readout circuit structures formed with and without the addition of the matching capacitor Cr, this study uses ADS (Advanced Design System) software to conduct electromagnetic simulation analysis on the two circuit structures proposed above, focusing on analyzing the frequency response characteristics of the readout circuit under different pressure conditions. First, an LCR sensing readout circuit model is established, and the driving voltage is set to 1V, the inductance Lr = Ls = 0.4 μH, the resistance Rr = Rs = 2.17 Ω, the coupling coefficient k = 0.1, the reference resistance R ref = 2 Ω, and the matching capacitor Cr = Cs. By scanning the inductive capacitor Cs and the matching capacitor Cr, the frequency response curve is obtained, and the scanning parameters are set as shown in Table 1:

[0046] Table 1: Corresponding relationship between the sensor capacitor Cs and pressure

[0047]

[0048] The simulation results are as shown in Figure 12 . Figure 12 In (a), it shows the frequency response curve of the readout circuit without the matching capacitor; Figure 12 In (b), it shows the frequency response curve of the readout circuit after introducing the matching capacitor; Figure 12 In (c), it shows the relationship between the resonant frequency of the LC passive sensor and the externally applied pressure. At the same distance (same coupling coefficient), the maximum value of the output voltage without the matching capacitor differs from the baseline signal by 1.3V, and the maximum value of the output voltage with the matching capacitor differs from the baseline signal by 6.3V, and the signal strength is enhanced by 4.8 times. At the same time, at a short distance (larger coupling coefficient), the wave peak will be split into two from the middle. Therefore, we can obtain the resonant frequency through the average value of the frequencies of the two side wave peaks. As shown in Figure 12 In (b), the average value of the frequencies of the two side wave peaks is basically the same as the resonant frequency without the matching capacitor, with a small deviation. The main error is due to the limitation of the frequency scanning accuracy.

[0049] The above signal acquisition circuit cooperates with the resonant micro-pressure sensor in actual application to sense and obtain pressure signals. The working principle of the resonant micro-pressure sensor is as follows: Figures 1 to 3 As shown, Figure 2 for Figure 1 The structural diagram of the A-A' section, Figure 3 for Figure 1 In the structural diagram of the B-B' section, the resonant micro-pressure sensor includes a first film layer 10, a second film layer 30 and an intermediate layer 20, wherein the intermediate layer 20 is sandwiched between the first film layer 10 and the second film layer 30; a first capacitor sheet 11 is arranged in the first film layer 10, and a second capacitor sheet 31 is arranged in the second film layer at a position opposite to the first capacitor sheet 11; the first capacitor sheet 11 is connected to the inductor 12; a hollow ventilation cavity 21 is arranged in the intermediate layer 20; one end of the ventilation cavity 21 passes through the side of the intermediate layer 20 and is connected to the outside, and the other end of the ventilation cavity 21 extends between the first capacitor sheet 11 and the second capacitor sheet 31; the first capacitor sheet 11 and the second capacitor sheet 31 are combined to form an inductive capacitor Cs, which is connected in series with the equivalent resistor Rs and the equivalent inductor Ls formed by the inductor 12 to form a ring induction circuit, and the equivalent inductor Ls is coupled with the measuring inductor Lr to generate an induction signal.

[0050] like Figure 1 As shown, the resonant micro-pressure sensor is mainly composed of a three-layer sandwich metal pressure-sensitive parallel plate capacitor and a planar spiral inductor, wherein the first film layer 10, the second film layer 30 and the middle layer 20 constitute a three-layer sandwich structure, and the first capacitor plate 11, the second capacitor plate 31 and the inductor line 12 constitute a planar spiral inductor. The first capacitor plate 11 and the second capacitor plate 31 are combined to form a sensing capacitor Cs, and the first capacitor plate 11 serves as the upper plate of the sensing capacitor Cs, and the second capacitor plate 31 serves as the lower plate. When there is no external pressure load, that is, ΔP=0, the upper and lower plates of the capacitor are not deformed and remain parallel, and exhaust is exhausted to the outside through the ventilation cavity 21 to achieve air pressure balance; at this time, the LC resonant frequency remains unchanged, and the device structure is as shown in FIG. Figure 2 When subjected to external pressure load, the upper and lower sensitive electrode membranes are deformed under pressure, and the gap distance of the middle ventilation cavity 21 is reduced, resulting in an increase in the capacitance of the pressure sensor, and then a decrease in the resonant frequency. The device structure is shown in FIG. Figure 3 Based on the above physical changes, pressure-sensitive information can be obtained through the decrease in the resonant frequency of the sensor when it is under pressure.

[0051] The equivalent resistance Rs is the resistance generated by the physical structure of the resonant micro-pressure sensor itself. Since the equivalent resistance Rs here is not a real resistance but is spontaneously generated based on its hardware characteristics, for the purpose of explaining the circuit structure design and the content of the scheme, it is described here as the equivalent resistance Rs; the equivalent inductance Ls is the inductance corresponding to the inductor line 12. In a more specific embodiment, the resistance value of the measurement resistor Rr is equal to that of the equivalent resistance Rs, and the inductance value of the measurement inductor Lr is equal to that of the equivalent inductance Ls. To improve the measurement accuracy, the resistance value of the measurement resistor Rr can be further set to be equal to that of the equivalent resistance Rs, and the inductance value of the measurement inductor Lr can be set to be equal to that of the equivalent inductance Ls.

[0052] In a more specific embodiment, the inductor line 12 is a spiral microstrip line, and the spiral microstrip line spirally extends around the first capacitor plate 11. Specifically, the number of turns of the inductor line 12 is 4 - 8. To improve the reactance application effect of the inductor line 12, the inductor line 12 can be set as a spiral microstrip line, and the spiral microstrip line is also a planar spiral inductor. The specific structure is as Figure 4 shown, where the spiral microstrip line spirally extends around the periphery of the first capacitor plate 11. To make the inductor line 12 have a better application effect, the number of turns of the inductor line 12 can be set to 4 - 8 (the number of turns of the inductor line 12 spirally extending around the first capacitor plate 11). In the optimal embodiment, the number of turns of the inductor line 12 can be set to 6 to balance the matching requirements of high sensitivity and the interface circuit bandwidth.

[0053] In a more specific embodiment, the thicknesses of the first film layer 10 and the second film layer 30 are equal; the first film layer 10 includes a first insulating layer 101, a second insulating layer 102, and a first copper layer 103, and the second film layer 30 includes a third insulating layer 301, a fourth insulating layer 302, and a second copper layer; the first copper layer 103 is sandwiched between the first insulating layer 101 and the second insulating layer 102, and the second copper layer is sandwiched between the third insulating layer 301 and the fourth insulating layer 302; the first copper layer 103 includes the first capacitor plate 11 and the inductor line 12; the second copper layer includes the second capacitor plate 31. Among them, the first capacitor plate 11 and the second capacitor plate 31 are both circular capacitor plates and have the same size. Specifically, the height of the ventilation cavity 21 is 0.45 - 0.6 times the thickness of the first film layer 10.

[0054] Furthermore, the thicknesses of the first film layer 10 and the second film layer 30 can be set to be equal. Specifically, the first film layer 10 and the second film layer 30 can be set to be mirror-symmetrical along the midline of the intermediate layer 20.

[0055] In a more specific embodiment, the thickness of the outer insulating layer in the first film layer 10 is greater than the thickness of the insulating layer close to the second film layer 30; the thickness of the outer insulating layer in the second film layer 30 is greater than the thickness of the insulating layer close to the first film layer 10; the thickness of the first copper layer 103 is less than that of the first insulating layer 101 and the second insulating layer 102, and the thickness of the second copper layer is less than that of the third insulating layer 301 and the fourth insulating layer 302. Further, the radii of both the first capacitor plate 11 and the second capacitor plate 31 are 1.8 - 2.5 mm; the inner diameter of the spiral microstrip line is 5.2 - 7 mm, and the line width and line pitch of the spiral microstrip line are equal.

[0056] In a specific embodiment, the first insulating layer 101 can be set as the outer insulating layer in the first film layer 10, and the fourth insulating layer 302 can be set as the outer insulating layer in the second film layer 30; then the thickness of the first insulating layer 101 is equal to the thickness of the fourth insulating layer; the thickness of the second insulating layer 102 is equal to the thickness of the third insulating layer 301, and the thickness of the first copper layer 103 is equal to the thickness of the second copper layer. Set the thickness of the first insulating layer 101 to be greater than the thickness of the second insulating layer 102. Preferably, the thickness h1 of the first insulating layer 101 can be set to 27.5 μm, the thickness h2 of the first copper layer 103 can be set to 18 μm, the thickness h3 of the second insulating layer 102 can be set to 25 μm, and the radius a of the first capacitor plate 11 can be set to 2.3 mm. On this basis, the inner diameter of the spiral microstrip line is correspondingly set to 5.2 - 7 mm.

[0057] In a specific embodiment, the materials of the first insulating layer 101, the second insulating layer 102, the third insulating layer 301, and the fourth insulating layer 302 can all be set as PI (Polyimide).

[0058] During the deformation of the sensor under pressure, the compression of the gas in the sealed cavity will generate a reaction force on the flexible film, thereby causing a decrease in the overall sensitivity of the sensor. Therefore, the present invention integrates a ventilation channel design in the sensing unit to improve the gas retention effect, and verifies its improvement effect through the establishment of a theoretical model and a finite element simulation model. When the upper and lower flexible films are deformed under external pressure, the air pressure in the closed cavity will increase due to the compression effect. At this time, the internal pressure of the closed cavity P t can be expressed as:

[0059] (1);

[0060] where P 0 is the atmospheric pressure, V 0 is the volume of the sealed cavity when not under pressure ( V 0 =πa2 g ), V t The volume of the cavity after the double-sided film is compressed and deformed can be expressed as:

[0061] (2);

[0062] Where a is the radius of the film, g is the height of the ventilation cavity ，w 0 is the deflection at the center of the film. In the range of small deflections, from equations (1) and (2), we can obtain:

[0063] (3);

[0064] At this time, the pressure difference Δ P’ between the inside and outside of the sensor is:

[0065] (4);

[0066] Therefore, in the sealed cavity sensor, the film is subjected to the reaction of the trapped air inside, and the pressure difference ΔP' between the two sides of the film is smaller than the pressure difference ΔP of the sensor with a ventilation cavity. To verify this theory, a finite element simulation was carried out on a sensor with a sealed cavity of the PI-Cu-PI composite film structure ( h 1 = 27.5 μm, h 2 = 18 μm, h 3 = 25 μm, the radius of the capacitor a = 2.3 mm). The simulation results show that the central deflection of the sensor film is 5.2 μm, and the test results are as shown in Figure 10 in (a), Figure 10 in (a) shows the deflection simulation results of the sensor film when a pressure of 5 kPa is applied under the trapped air effect of the sealed cavity. Similarly, a finite element simulation was carried out on a sensor with a ventilation cavity of the same specification and a width of 1 mm. The simulation results are as shown in Figure 10 in (b), Figure 10 in (b) shows the deflection simulation results of the film under the action of a 5 kPa pressure under the condition of integrated air channels and completely fixed edge constraints. The central deflection of the sensor film is 12.1 μm, which is much larger than that of the sensor with only a sealed cavity shown in Figure 10 in (a), showing higher deformation sensitivity. Considering that in practical applications, the ventilation cavity will cause the edges of the diaphragm to not be fully constrained, the response behavior under semi-constrained boundary conditions was further simulated in this paper. The simulation results show that the central deflection of the film reaches 13.0 μm ( Figure 10In (c)), the error is only 7.4% compared to the fully constrained condition. Figure 10 Figure (c) shows the simulation results of the film deflection under a 5 kPa pressure with an integrated air channel and edge partial constraints. The results indicate that even under non-ideal actual boundary conditions, the theoretical model under full constraints still has good predictive ability and can serve as an effective approximation basis for engineering design. In summary, through theoretical analysis models and finite element simulation, it is verified that the integrated ventilation cavity greatly improves the sensitivity of the sensor.

[0067] The wireless passive pressure sensor designed in this study adopts a PI–Cu–PI multi-layer sandwich flexible film structure to achieve insulation protection, anti-oxidation, and anti-short circuit functions for the metal layer. According to the deformation theory of multi-layer circular films, let the radius of the film be a , under the action of uniform external pressure, the deflection expression at any radius position r is:

[0068] (5);

[0069] where ΔP is the pressure difference between both sides of the film, and D′ is the equivalent bending stiffness.

[0070] Assume that the parallel-plate capacitor film gap of the sensor under no pressure load is g . When the upper and lower layers of the film are pressurized, the equivalent capacitance C g of the intermediate cavity can be expressed by integration using the micro-element method as:

[0071] (6);

[0072] where ε 0 is the vacuum permittivity, and ε r is the relative permittivity.

[0073] It is worth mentioning that due to the use of a multi-layer thin film sensor design in this patent, multiple dielectric layers between the two metals need to be regarded as multiple capacitors in series. When the film deforms under pressure, the spacing of the intermediate cavity capacitor changes; its capacitance value Cg can be calculated using Equation (7). At the same time, the thickness change of the other dielectric layer capacitors can be ignored and can be directly calculated using the traditional parallel-plate capacitor formula. Finally, the expression of the total capacitance Cs of the sensor thin film sensor is:

[0074] (7);

[0075] C i is the capacitance value of the i-th capacitor in multiple capacitors in series.

[0076] In the sensor, a planar spiral structure is adopted to construct an inductance element, and the inductance value of the equivalent inductance generated by it can be approximately calculated by the Wheeler correction model as:

[0077] (8);

[0078] Where μ 0 is the magnetic permeability of free space, n is the number of turns of the planar spiral inductor coil, D ave is the average spiral diameter:

[0079] (9);

[0080] The filling factor ρ is defined as:

[0081] (10);

[0082] Where D out is the outer diameter of the spiral microstrip line, D in is the inner diameter of the spiral microstrip line, x 1, x 2, x 3, x 4 are parameters related to the shape of the planar spiral inductor. In this design, a circular planar spiral inductor is adopted, that is x 1 = 1, x 2 = 2.46, x 3 = 0, x 4 = 0.2.

[0083] The resistance of the sensor is mainly generated in the spiral inductor metal wire. The resonant circuit operates in the high-frequency range. Considering the skin effect, the equivalent resistance of the sensor is:

[0084] (11);

[0085] Where w l is the line width, ρ r is the metal resistivity, t metal is the metal thickness, δ is the skin depth, which can be expressed as:

[0086] (12);

[0087] And the total length l total of the toroidal spiral inductor is:

[0088] (13);

[0089] Wherein s l is the line pitch.

[0090] To verify the above-proposed capacitance theoretical model of the multi-layer thin film structure, we carried out finite element simulation with the same conditions, and the test results are as Figure 11 shown. Figure 11 shows the comparison of the central deflection and capacitance between the FEM (Finite Element Model) model and the theoretical model. The central deflection and capacitance changes obtained from the finite element simulation are very close to the results of the theoretical model. When the pressure increases to 5 kPa, the difference ( Figure 11 in which Erro rave represents the average error between the theoretical model and the actual FEM model) increases slightly, which is mainly due to the non-linear deformation of the thin film under higher pressure. The simulation results verify the effectiveness of the capacitance theoretical model of the multi-layer structure thin film. Since the calculation of inductance and resistance mainly depends on known geometric structures and material parameters, and the theoretical model has been widely verified and has high accuracy, there is no need to conduct additional simulation verification for it in this study.

[0091] Among them, the specific size parameters of the sensor structure in the simulation test are shown in Table 2 as follows:

[0092] Table 2

[0093]

[0094] In this design, a circular metal thin film is selected as the capacitance sensitive unit because it has higher deformation sensitivity under the same boundary conditions. At the same time, due to the manufacturing process constraints of the flexible printed circuit board, the copper thickness of the capacitance thin film is determined to be 18 μm, and the upper and lower PI thin films are 27.5 μm and 25 μm respectively. In addition, in order to obtain better linearity and sensitivity, according to the small deflection theory of the thin film, the central deflection (13 μm) of the thin film is less than 0.2 times the thickness of the first film layer (70.5 μm), and the radius of the capacitance chip is determined to be 2.3 mm.

[0095] The inductance of the pressure sensor was optimized based on the resonance frequency and sensitivity; there is a certain correlation between the sensitivity and resonance frequency of the sensor and the number of turns of the inductance wire, and the relevant test results are as Figure 5 shown. The inner diameter D of the inductance wire inThe radius r is 6 mm, the line width w is 0.254 mm, and the line pitch s is 0.254 mm. Considering the scanning frequency range of the preliminary interface circuit is 0 - 200 MHz and the inevitable errors in the sensor manufacturing process, taking into account the scanning frequency range (0–200 MHz) of the interface circuit, the machining error tolerance, and the balance between device miniaturization and sensitivity improvement, the number of turns n of the spiral microstrip line is finally determined to be 6.

[0096] Table 3 summarizes the key structural parameters of the finally determined sensing unit:

[0097] Table 3

[0098]

[0099] Based on theoretical modeling and simulation analysis, its expected performance is shown in Table 4. The resonant frequency of the sensor is 153.8 MHz, and the sensitivity is −3.27 kHz / Pa;

[0100] Table 4

[0101]

[0102] 1. Theoretical derivation of the circuit without matching capacitor (traditional type)

[0103] Based on electromagnetic simulation verification, an equivalent circuit model as shown in Figure 6 is established to conduct theoretical analysis and derivation of the electrical characteristics of the wireless passive reading system. Let the driving voltage be , and the reference resistance be R ref , then the total input impedance of the system is:

[0104] (14);

[0105] where R r is the measuring resistance of the measuring circuit, L r and L s are the measuring inductance of the measuring circuit and the inductance value of the inductive wire in the sensor respectively, and C s is the capacitance value of the sensor. At this time, the resonant frequency f 0 and the quality factor Q of the sensor are respectively:

[0106] (15);

[0107] (16);

[0108] Substituting Eqs. (15) and (16) into Eq. (14) and arranging, the real and imaginary components of the impedance can be obtained as:

[0109] (17);

[0110] (18);

[0111] 2. Mixing Processing and Signal Demodulation

[0112] In the proposed traditional read circuit architecture, the input excitation voltage V in is mixed with the voltage V ref across the reference resistor. Assuming the mixer gain is k, the output signal can be expressed as:

[0113] (19);

[0114] After filtering out the high-frequency components by a low-pass filter with a gain of B, the output DC signal is:

[0115] (20);

[0116] By defining the parameter , its extreme position and the maximum voltage output can be used to characterize the change in the resonant frequency of the sensor;

[0117] (21);

[0118] By taking the derivative of λ with respect to f and directly setting , the analytical solution f of the maximum value of λ obtained is a very complex expression. Since and are usually small resistors, , to simplify the calculation, the internal resistances and are ignored, and we can obtain:

[0119] (22);

[0120] Finally, by solving the equation , the approximate solution f of the maximum value of λ is:

[0121] (23);

[0122] In summary, through theoretical derivation and simulation verification, the traditional readout architecture based on voltage source excitation proposed in this paper can effectively read the resonant frequency of LC wireless passive sensors. This architecture abandons the traditional transconductance amplifier and its related circuits, significantly simplifies the system structure, and at the same time avoids the limitation of the gain-bandwidth product of the transconductance amplifier, further expanding the working frequency range and signal demodulation efficiency of the system.

[0123] 3. Theoretical Deduction of the Reading Method with a Matching Capacitor (Impedance Matching Optimization)

[0124] The above introduced a traditional reading circuit model of a portable LC resonance frequency based on a voltage source input, which was verified by theory and simulation. In practical applications, the reading circuit is affected by factors such as near-field coupling, high-frequency noise, and circuit parasitic capacitance, resulting in the circuit being able to identify valid signals only within a short distance. Therefore, based on this, the present invention proposes an impedance matching optimization method with a capacitor Cr, hereinafter referred to as IMC (Impedance Matching Circuit), as Figure 7 shown. This method aims to improve the signal strength and extend the reading distance.

[0125] Under the condition of introducing a matching capacitor, the total input impedance Z in of the reading port is

[0126] (24);

[0127] In the formula, ω is the angular frequency, R r is the measurement resistance of the measurement circuit, L r and L s are respectively the measurement inductance of the measurement circuit and the inductance value of the inductive wire in the sensor, C s is the capacitance value of the sensor, and C r is the capacitance value of the matching capacitor. After organizing Z in , we respectively obtain and :

[0128] (25);

[0129] (26);

[0130] According to Equation (20), it can be known that the system output voltage Vout can characterize the resonance frequency shift through the extreme value of the parameter λ. Since there is complexity in directly solving the extreme value of the analytical solution of , this paper uses a method combining theoretical analysis and simulation experiments to conduct characteristic research. The electromagnetic simulation parameters based on ADS (Advanced Design System) are set as: inductance Lr = Ls = 0.4 μH, resistance Rr = Rs = 2.17 Ω, coupling coefficient k = 0.15, reference resistance Rref = 2 Ω, capacitance Cr = Cs = 3.34 pF. The simulation results are as Figure 13 shown, Figure 13 where (a) in it shows the frequency response curve of the mixing phase component cosφ ; Figure 13 where (b) in it shows the frequency response curve of the input impedance modulus |Zin|Figure 13 Figures (c) and (d) therein illustrate the comparison of the frequency response curves of the demodulation parameter λ under the impedance matching optimization structure (IMC) and the traditional structure. Experimental data show that, under the same parameter conditions, after introducing the matching capacitor, λ the value increases from 0.01 to 0.158, with an increase of 15.8 times. Further analysis of the cosφ characteristic shows that there are three characteristic peaks, and the corresponding frequencies can be obtained by solving the equation φ = 0:

[0131] (27);

[0132] Since when, the input impedance ∣ Zin ∣ reaches a maximum value due to the mutual cancellation of the inductive reactance and the capacitive reactance, resulting in the final λ not showing a peak; while at ω 1,2 at λ a significant resonance peak appears. Therefore, in the long-distance transmission scenario, the traditional method cannot effectively extract the sensor signal due to near-field coupling, parasitic parameters, and noise interference, while the introduction of the matching capacitor can effectively improve the reading distance by enhancing the signal amplitude.

[0133] To evaluate the signal strength and the improvement effect of the reading distance of the reading circuit after introducing the matching capacitor (IMC), the embodiments of this application evaluate the signal strength and the reading distance of the reading circuit with and without the matching capacitor (traditional reading method). The experiment uses the same-sized reading coil and LC wireless passive pressure sensor for testing. First, the LC pressure sensor is tested without the matching capacitor, and the distance between the sensor and the reading coil is 10 mm. Figure 14 shows the relationship between the frequency and the output voltage. The resonance frequency drops from 153 MHz to 136.98 MHz, and the sensitivity of the LC pressure sensor is about -3.2 kHz / Pa, with an error of only -2% from the theoretical predicted value. The signal strength without the matching capacitor differs from the baseline signal by about 40 mV. Affected by factors such as system noise fluctuation, ADC resolution, and system delay, the maximum distance of the reading system without the matching capacitor is about 10 mm.

[0134] Subsequently, the reading circuit with the matching capacitor (IMC) structure is tested, and the test results are as Figures 15 to 18 shown. To compare the circuit enhancement effect, the distance between the sensor and the reading coil is also set to 10 mm; Figure 15 illustrates the relationship between the pressure and the resonance frequency at a reading distance of 10 mm under the IMC architecture; Figure 16 illustrates the sensitivity linear fitting curves under the IMC and the traditional reading circuit architectures at a distance of 10 mm; Figure 17Schematically shows the frequency response curve when the reading distance is 16 mm under the introduced matching capacitor (IMC) structure, showing the maximum effective reading distance of the system; Figure 18 Schematically shows the comparison of the pressure-frequency (single-peak) response curves between the two reading methods of the matching capacitor (IMC) and the non-matching capacitor (traditional structure). When the sensor capacitance changes, we adjust the matching capacitor to restore symmetry. As shown in the figure, at the same distance, the signal intensity with the matching capacitor differs from the baseline signal by approximately 400 mV, a 10-fold increase, indicating that the output signal intensity can be enhanced with the matching capacitor. At close range, the peak will split into two from the middle. Therefore, we can identify the frequencies corresponding to the maximum signal intensities of the two peak signals to obtain the resonance frequency. As shown in the figure, the left peak, the right peak, and the average value between the peaks have the same frequency response trend as that of the non-matching capacitor (traditional method). The sensitivity obtained through the average value between the peaks is approximately 3.26 kHz / Pa, with an error of -0.18% from the theoretically predicted value. This error is caused by the difficulty in fully balancing the matching capacitor and the sensor capacitance and the unstable air pressure.

[0135] To verify the enhancement of the reading distance, we increased the distance between the sensor and the reading coil. During the increase, the two peaks approached each other until they merged into the same peak, and the distance at this time was the reading distance of the strongest signal. Consistent with the above experimental setup, the maximum reading distance obtained was 16 mm, which is 1.6 times that of the non-matching capacitor reading system. At the same time, the trend of the frequency response characteristic curve is consistent with that without the matching capacitor, and the sensor pressure sensitivity is -3.2 kHz / Pa, with an error of only -2% from the theoretically predicted value. These results indicate that the test results of this circuit system are consistent with the theoretical model and can effectively improve the reading distance.

[0136] The embodiment of the present application also discloses a method for manufacturing a sensor, wherein the method for manufacturing the sensor is used to manufacture the resonant micro-pressure sensor in the LC wireless passive pressure sensing system with a matching circuit as described in the above embodiment; as Figure 8 shown, the method for manufacturing the sensor includes steps S1 to S5.

[0137] S1. Clean the bottom insulating film and attach a copper metal layer on its upper layer.

[0138] First, clean the bottom insulating film and attach a copper metal layer on its upper layer. The specific processing steps are as Figure 9 shown in (a) and (b) in.

[0139] S2. Coat a photoresist layer on the copper metal layer and transfer the sensor layout pattern to the photoresist layer.

[0140] A photoresist layer is coated on a 18-μm-thick copper layer, and the sensor layout pattern is transferred onto the photoresist layer on the upper layer of the copper layer. Among them, the bottom insulating film is a 25-μm-thick polyimide film. The specific processing steps are as Figure 9 shown in (c) of

[0141] S3. After development, the copper layer is etched.

[0142] The copper layer is developed and etched to form a circular capacitive electrode and a circular spiral inductance structure. The specific processing steps are as Figure 9 shown in (d) and (e) of

[0143] S4. An upper insulating film is laminated on the etched copper layer to prepare a first film layer and a second film layer.

[0144] The photoresist on the etched copper layer is removed. The specific processing steps are as Figure 9 shown in (f) of

[0145] By changing the sensor layout pattern, a first copper layer including a first capacitive plate and an inductor wire and a second copper layer including only a second capacitive plate can be obtained respectively, and thus the first film layer and the second film layer are prepared correspondingly. Among them, the specific processing steps for obtaining the first film layer are as Figure 9 shown in (g) of

[0146] S5. The first film layer and the second film layer are respectively placed on both sides of the intermediate layer with a pre-cut ventilation cavity, and the combined multi-layer structure is bonded and pressed to obtain the resonant micro-pressure sensor.

[0147] The first film layer and the second film layer are respectively laminated on both sides of the intermediate layer with a pre-cut ventilation cavity to form a multi-layer structure, and the multi-layer structure is bonded and pressed to obtain the resonant micro-pressure sensor. The specific processing steps are as Figure 9 shown in (h) of

[0148] The present invention relates to the technical field of sensors, and in particular to a flexible wireless passive pressure sensor reading system and a sensor manufacturing method based on LC resonance. The application fields of the flexible pressure sensor mainly include healthcare, in vitro diagnosis, patient monitoring, precision drug delivery, implantable medical devices, and Internet of Things applications.

[0149] In the field of medical devices, the high-sensitivity characteristics of sensors enable them to accurately monitor physiological pressures inside the human body, such as intraocular pressure (IOP) and intracranial pressure (ICP). This provides doctors with accurate disease diagnoses and treatment plans, helping to improve the quality and effectiveness of medical services. Especially in scenarios that require long-term monitoring, the passive and wireless characteristics of sensors allow them to be in-situ monitored through implantation, providing continuous and reliable data support for patients.

[0150] In addition, this sensor can also be widely applied in the field of the Internet of Things (IoT) for scenarios with limited wired connections such as environmental monitoring and home control. Its high-precision and low-power consumption characteristics give it significant advantages in the large-scale deployment of IoT sensing nodes, providing strong technical support for the popularization and development of IoT applications.

[0151] In summary, the present invention has broad application prospects in the fields of healthcare, in vitro diagnosis, patient monitoring, precision drug delivery, implantable medical devices, and IoT applications, providing an important driving force for technological progress and industrial development in related fields.

[0152] In the embodiments of the present invention, there is provided an LC wireless passive pressure sensing system with a matching circuit and a method for manufacturing a sensor. The pressure sensing system includes a resonant micro-pressure sensor and a signal acquisition circuit; the signal acquisition circuit includes a measurement circuit, a signal generator, a mixing circuit, a low-pass filter circuit, a sampling circuit, and a control circuit; the measurement circuit includes a matching capacitor, a measurement inductor, a measurement resistor, and a reference resistor; the resonant micro-pressure sensor includes a first film layer, a second film layer, and an intermediate layer, and the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor plate is provided in the first film layer, and a second capacitor plate is provided at a position opposite to the first capacitor plate in the second film layer; the first capacitor plate is connected to an inductor wire; a hollow ventilation cavity is provided in the intermediate layer. The above pressure sensing system provides a compact signal acquisition circuit to improve portability, and at the same time sets a matching capacitor to increase the sensing distance; a ventilation cavity is provided in the resonant micro-pressure sensor to discharge the internal air to improve the measurement sensitivity.

[0153] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An LC wireless passive pressure sensing system with a matching circuit, characterized in that It includes a resonant micro-pressure sensor and a signal acquisition circuit; The signal acquisition circuit includes a measurement circuit, a signal generator, a mixing circuit, a low-pass filter circuit, a sampling circuit and a control circuit; the measurement circuit includes a matching capacitor, a measurement inductor, a measurement resistor and a reference resistor; One end of the signal generator is grounded, and the other end is connected to one end of the measurement resistor and one input end of the mixing circuit; the other end of the measurement resistor is connected to one end of the measurement inductor, the other end of the measurement inductor is connected to one end of the matching capacitor, and the other end of the matching capacitor is connected to one end of the reference resistor and the other input end of the mixing circuit; the other end of the reference resistor is grounded; The output end of the mixing circuit is connected to the input end of the low-pass filter circuit, the output end of the low-pass filter circuit is connected to the input end of the sampling circuit, the output end of the sampling circuit is connected to the input end of the control circuit, and the control end of the control circuit is connected to the control input end of the signal generator; The resonant micro-pressure sensor includes a first film layer, a second film layer and an intermediate layer, and the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor plate is arranged in the first film layer, and a second capacitor plate is arranged at a position opposite to the first capacitor plate in the second film layer; the first capacitor plate is connected to an inductor wire; a hollow ventilation cavity is arranged in the intermediate layer; one end of the ventilation cavity penetrates the side surface of the intermediate layer and is connected to the outside, and the other end of the ventilation cavity extends between the first capacitor plate and the second capacitor plate; the first capacitor plate and the second capacitor plate are combined to form an induction capacitor, and the induction capacitor, an equivalent resistor and an equivalent inductor formed by the inductor wire are connected in series to form a ring-shaped induction circuit, and the equivalent inductor is coupled with the measurement inductor to generate an induction signal; the matching capacitor is matched in real time according to the capacitance value of the induction capacitor; The resistance value of the measurement resistor is equal to that of the equivalent resistor, and the inductance value of the measurement inductor is equal to that of the equivalent inductor.

2. The LC wireless passive pressure sensing system with a matching circuit according to claim 1, characterized in that, The inductor wire is a spiral microstrip line, and the spiral microstrip line spirally extends around the first capacitor plate.

3. The LC wireless passive pressure sensing system with a matching circuit according to claim 2, characterized in that, The number of turns of the inductor wire is 4-8.

4. The LC wireless passive pressure sensing system with a matching circuit according to claim 3, characterized in that, The thicknesses of the first film layer and the second film layer are equal; the first film layer includes a first insulating layer, a second insulating layer and a first copper layer, and the second film layer includes a third insulating layer, a fourth insulating layer and a second copper layer; the first copper layer is sandwiched between the first insulating layer and the second insulating layer, and the second copper layer is sandwiched between the third insulating layer and the fourth insulating layer; The first copper layer includes the first capacitor plate and the inductor wire; the second copper layer includes the second capacitor plate.

5. The LC wireless passive pressure sensing system with a matching circuit according to claim 4, characterized in that, Both the first capacitor plate and the second capacitor plate are circular capacitor plates and have the same size.

6. The LC wireless passive pressure sensing system with a matching circuit according to claim 5, characterized in that The height of the ventilation cavity is 0.45-0.6 times the thickness of the first film layer.

7. The LC wireless passive pressure sensing system with a matching circuit according to claim 6, characterized in that, The thickness of the outer insulating layer in the first film layer is greater than the thickness of the insulating layer close to the second film layer; the thickness of the outer insulating layer in the second film layer is greater than the thickness of the insulating layer close to the first film layer; the thickness of the first copper layer is less than that of the first insulating layer and the second insulating layer, and the thickness of the second copper layer is less than that of the third insulating layer and the fourth insulating layer.

8. The LC wireless passive pressure sensing system with a matching circuit according to claim 7, characterized in that, The radii of the first capacitor plate and the second capacitor plate are both 1.8 - 2.5 mm; The inner diameter of the spiral microstrip line is 5.2 - 7 mm, and the line width of the spiral microstrip line is equal to the line pitch.

9. A method for manufacturing a sensor, characterized in that, The sensor manufacturing method is used to manufacture the resonant micro-pressure sensor in the LC wireless passive pressure sensing system with a matching circuit as described in any one of claims 1 - 8; The sensor manufacturing method includes: Cleaning the bottom insulating film and attaching a metal copper layer on its upper layer; Coating a photoresist layer on the metal copper layer and transferring the sensor layout pattern onto the photoresist layer; Etching the metal copper layer after developing; Laminating an upper insulating film on the etched metal copper layer to prepare the first film layer and the second film layer; Placing the first film layer and the second film layer on both sides of the intermediate layer with a pre-cut ventilation cavity respectively, and bonding and pressing the combined multi-layer structure to obtain the resonant micro-pressure sensor.

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