LC wireless passive pressure sensing system with matching circuit and sensor manufacturing method

Abstract

The invention discloses an LC wireless passive pressure sensing system with a matching circuit and a sensor manufacturing method. The pressure sensing system comprises a resonant micro-pressure sensor and a signal acquisition circuit, the signal acquisition circuit comprises a measuring circuit, a signal generator, a frequency mixing circuit, a low-pass filter circuit, a sampling circuit and a control circuit; the measuring circuit comprises a matching capacitor, a measuring inductor, a measuring resistor and a reference resistor; the resonant micro-pressure sensor comprises a first film layer, a second film layer and a middle layer, wherein the middle layer is clamped between the first film layer and the second film layer; a first capacitor sheet is arranged in the first film layer, and a second capacitor sheet is arranged at a position, opposite to the first capacitor sheet, in the second film layer; the first capacitor sheet is connected with the inductance wire; a hollow ventilation cavity is formed in the middle layer. According to the pressure sensing system, the compact signal acquisition circuit is designed to improve the portability, and the matching capacitor is arranged to improve the wireless sensing distance; a vent cavity is provided to exhaust internal air to improve measurement sensitivity.

Description

Technical Field

[0001] The invention relates to the technical field of flexible micro sensors, and in particular to an LC wireless passive pressure sensing system with a matching circuit and a sensor manufacturing method. Background Art

[0002] With the acceleration of the aging process of my country'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, the measurement of internal physiological pressure has become an important research object to promote the development of precision medicine and high-end medical device technology. For example, intraocular pressure (IOP) is an important indicator for evaluating glaucoma, and its continued increase may cause damage to the optic nerve or even blindness. Accurate monitoring of intraocular pressure is of great significance for the early diagnosis and treatment of glaucoma. For another example, intracranial pressure (ICP) is a key monitoring indicator for patients with traumatic brain injury. Its abnormal increase (>15 mmHg) may lead to serious complications or even endanger the patient's life. Therefore, the development of highly sensitive implantable pressure sensors for accurately measuring the internal physiological pressure parameters of the human body has become the key to improving treatment efficiency and ensuring patient safety.

[0003] Traditional pressure sensors are difficult to meet the use requirements in the human body's internal physiological environment due to their large size, susceptibility to external environmental interference, and inability to monitor in real time for a long time. In recent years, flexible wireless passive micro pressure sensors based on LC resonance (LC resonance is the phenomenon that the reactance of inductance and capacitance cancel each other out at a specific frequency, resulting in a purely resistive circuit) have provided a potential solution to such needs. This type of sensor has the advantages of flexible structure, no need for power supply, and contactless connection, and can achieve high-sensitivity pressure signal reading in complex physiological environments. Although some passive pressure sensor design solutions have been disclosed in the prior art, most of the current LC sensing systems are still significantly insufficient in terms of readout distance due to the signal strength attenuation characteristics of the passive device itself, and it is difficult to meet the actual needs of long-distance, non-contact reading in clinical or complex physiological scenarios. Therefore, the passive pressure sensor in the prior art method has the problem that the sensing distance is too close and does not meet the use requirements. Summary of the invention

[0004] The embodiments of the present invention provide an LC wireless passive pressure sensing system with a matching circuit and a sensor manufacturing method, aiming to solve the problem that the sensing distance of the passive pressure sensor in the prior art method is too short to meet the use requirements.

[0005] In a first aspect, an embodiment of the present invention provides 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 measuring circuit, a signal generator, a mixing circuit, a low-pass filtering circuit, a sampling circuit and a control circuit; the measuring circuit includes a matching capacitor, a measuring inductor, a measuring resistor and a reference resistor; One end of the signal generator is grounded, and the other end is connected to one end of the measuring resistor and an input end of the mixing circuit; the other end of the measuring resistor is connected to one end of the measuring inductor, the other end of the measuring 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; The output end of the frequency mixing circuit is connected to the input end of the low-pass filtering circuit, the output end of the low-pass filtering 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, wherein the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor sheet is arranged in the first film layer, and a second capacitor sheet is arranged in the second film layer at a position opposite to the first capacitor sheet; the first capacitor sheet is connected to the inductor; a hollow ventilation cavity is arranged in the intermediate layer; one end of the ventilation cavity passes through the side of the intermediate layer and is connected to the outside, and the other end of the ventilation cavity extends between the first capacitor sheet and the second capacitor sheet; the first capacitor sheet and the second capacitor sheet are combined to form an inductive capacitor, and the inductive capacitor is connected in series with the equivalent resistor and the equivalent inductor formed by the inductor to form a ring induction circuit, and the equivalent inductor is coupled with the measuring inductor to generate an induction signal; the matching capacitor performs real-time matching according to the capacitance value of the inductive capacitor.

[0006] 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 a resonant micro-pressure sensor in an LC wireless passive pressure sensing system with a matching circuit as described in the first aspect above; the sensor manufacturing method comprises: Cleaning the bottom insulating film and attaching a metal copper layer on top of it; Coating a photoresist layer on the metal copper layer and transferring a sensor layout pattern onto the photoresist layer; After developing, etching the metal copper layer; Laying an upper insulating film on the metal copper layer to be etched to prepare a first film layer and a second film layer; The first film layer and the second film layer are respectively placed on both sides of the middle layer with the ventilation cavity cut in advance, and the combined multi-layer structure is bonded and pressed to obtain the resonant micro-pressure sensor.

[0007] 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, the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor sheet is arranged in the first film layer, and a second capacitor sheet is arranged in the second film layer at a position opposite to the first capacitor sheet; the first capacitor sheet is connected to the inductor line; a hollow ventilation cavity is arranged in the intermediate layer. The above-mentioned pressure sensing system provides a compact signal acquisition circuit to improve portability, and a matching capacitor is arranged to increase the sensing distance; a ventilation cavity is arranged in the resonant micro-pressure sensor to discharge internal air to improve measurement sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0009] Figure 1 A three-dimensional structural diagram of a resonant micro-pressure sensor provided in an embodiment of the present invention; Figure 2 A side structural diagram of a resonant micro-pressure sensor provided in an embodiment of the present invention; Figure 3 Another side structural diagram of the resonant micro-pressure sensor provided by an embodiment of the present invention; Figure 4 A planar structural diagram of a spiral microstrip line provided by an embodiment of the present invention; Figure 5 An application effect diagram of an LC wireless passive pressure sensing system with a matching circuit provided in an embodiment of the present invention; Figure 6 It is a circuit structure diagram of a passive pressure sensor in a traditional technical method; Figure 7 A circuit structure diagram of an LC wireless passive pressure sensing system with a matching circuit provided in an embodiment of the present invention; Figure 8 A method flow chart of a sensor manufacturing method provided by an embodiment of the present invention; Fig. 9 A manufacturing process flow chart of a sensor manufacturing method provided by an embodiment of the present invention; Fig.10Another application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.11 Another application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.12 Another application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.13 The following is an application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.14 Another application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by the embodiment of the present invention; Fig.15 Another application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.16 A further application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.17 Another subsequent application effect diagram of the LC wireless passive pressure sensing system with matching circuit provided by an embodiment of the present invention; Fig.18 A subsequent application effect diagram of the LC wireless passive pressure sensing system with a matching circuit provided by an embodiment of the present invention; 1. Reference numerals: DDS, signal generator; Mi, mixing circuit; LPF, low-pass filter circuit; ADC, sampling circuit; MCU, control circuit; Cr, matching capacitor; Lr, measurement inductor; Rr, measurement resistor; Rref, reference resistor; Ls, equivalent inductor; Rs, equivalent resistor; Cs, sensing capacitor; 10, first film layer; 30, second film layer; 20, middle layer; 11, first capacitor sheet; 31, second capacitor sheet; 12, inductor line; 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 DESCRIPTION

[0010] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0011] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0012] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0013] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0014] 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 an 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, and the other end of the measurement inductor Lr is connected to the matching One end of the capacitor Cr, 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 mixer circuit Mi; the other end of the reference resistor Rref is grounded; the output end of the mixer 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, so as to send a driving control signal to the signal generator DDS through the control circuit MCU, thereby driving the signal generator DDS to generate an AC voltage signal. Wherein, the matching capacitor performs real-time matching according to the capacitance value of the inductive capacitor.

[0015] The LC wireless passive pressure sensing system with 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. The specific circuit structure is as follows: Figure 7As shown, 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 that the sensing signal obtained by the control circuit MCU is sent to an external terminal (such as a mobile phone, a tablet computer, etc.) through the Bluetooth receiving circuit.

[0016] In recent years, the traditional sweep-frequency reading circuit proposed by Nopper et al. has been proven to be effective, but its current source driving mechanism requires a transconductance amplifier to achieve signal conversion, which has the following inherent defects: on the one hand, the multi-stage signal conversion link will introduce additional transmission loss; on the other hand, the gain-bandwidth product of the transconductance amplifier restricts the high-frequency response capability of the system. In order to overcome the above problems, the present invention proposes a simplified circuit architecture based on direct voltage source excitation (such as Figure 7 The effectiveness of this paper is verified through theoretical analysis and simulation.

[0017] Existing LC wireless passive sensing is achieved through near-field mutual inductance coupling between an external readout coil and the sensor inductor, and its effective reading distance is very limited, usually comparable to the size of the sensor inductor. In order to improve the system reading distance, the technical method of this application is Figure 6 Based on the voltage drive architecture shown in the figure, a matching capacitor Cr (such as Figure 7 As shown in Figure 2, it is used 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.

[0018] In order to verify the performance difference between the two reading circuit structures formed without adding matching capacitor Cr and adding matching capacitor Cr, this study uses ADS (Advanced Design System) software to perform electromagnetic simulation analysis on the two circuit structures proposed above, focusing on analyzing the frequency response characteristics of the reading circuit under different pressure conditions. First, the LCR sensor reading circuit model is established and the driving voltage is set. 1V, inductance Lr=Ls=0.4μH, resistance Rr=Rs=2.17Ω, coupling coefficient k=0.1, reference resistance R ref =2Ω, matching capacitor Cr=Cs, and the frequency response curve is obtained by scanning the sensing capacitor Cs and the matching capacitor Cr. The scanning parameter settings are shown in Table 1: Table 1: Correspondence between sensor capacitance Cs and pressure

[0019] The simulation results are as follows Fig.12 As shown, Fig.12 (a) shows the frequency response curve of the reading circuit without matching capacitors; Fig.12 (b) shows the frequency response curve of the reading circuit after the matching capacitor is introduced; Fig.12 (c) shows the relationship between the resonant frequency of the LC passive sensor and the external applied pressure. At the same distance (same coupling coefficient), the maximum output voltage differs from the baseline signal by 1.3V when there is no matching capacitor, and the maximum output voltage differs from the baseline signal by 6.3V when there is a matching capacitor, and the signal strength is enhanced by 4.8 times. At the same time, at a close distance (larger coupling coefficient), the peak will be split in half from the middle, so we can get the resonant frequency by the average frequency of the peaks on both sides. Fig.12 As shown in (b), the frequency average of the peaks on both sides is basically consistent with the resonant frequency when there is no matching capacitor, with a small deviation. The main error comes from the limitation of frequency scanning accuracy.

[0020] 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.

[0021] like Figure 1As 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.

[0022] The equivalent resistance Rs is the resistance generated by the physical structure of the resonant micro-pressure sensor. Since the equivalent resistance Rs here is not a real resistance, but is spontaneously generated based on its hardware characteristics, it is described as the equivalent resistance Rs for the purpose of explaining the circuit structure design and the content of the solution; the equivalent inductance Ls is the inductance formed by the inductance line 12. In a more specific embodiment, the resistance value of the measuring resistance Rr is equal to the equivalent resistance Rs, and the inductance value of the measuring inductance Lr is equal to the equivalent inductance Ls. In order to improve the measurement accuracy, the resistance value of the measuring resistance Rr can be further set to be equal to the resistance value of the equivalent resistance Rs, and the inductance value of the measuring inductance Lr can be set to be equal to the inductance value of the equivalent inductance Ls.

[0023] In a more specific embodiment, the inductor 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 12 is 4-8. In order to improve the reactance application effect of the inductor 12, the inductor 12 can be set to a spiral microstrip line, which is also a planar spiral inductor. The specific structure is as follows: Figure 4 As shown, the spiral microstrip line is spirally extended around the periphery of the first capacitor plate 11. In order 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 extended 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 take into account the matching requirements of high sensitivity and interface circuit bandwidth.

[0024] In a more specific embodiment, the thickness 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 sheet 11 and the inductor line 12; the second copper layer includes the second capacitor sheet 31. The first capacitor sheet 11 and the second capacitor sheet 31 are both circular capacitor sheets 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.

[0025] Furthermore, the thickness of the first film layer 10 and the second film layer 30 may be set to be equal. Specifically, the first film layer 10 and the second film layer 30 may be set to be mirror-symmetrical along the center line of the intermediate layer 20 .

[0026] 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 the first insulating layer 101 and the second insulating layer 102, and the thickness of the second copper layer is less than the third insulating layer 301 and the fourth insulating layer 302. Further, the radius of the first capacitor plate 11 and the second capacitor plate 31 are both 1.8-2.5mm; the inner diameter of the spiral microstrip line is 5.2-7mm, and the line width and line spacing of the spiral microstrip line are equal.

[0027] In a specific embodiment, the first insulating layer 101 can be set as the insulating layer on the outside of the first film layer 10, and the fourth insulating layer 302 can be set as the insulating layer on the outside of 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. The thickness of the first insulating layer 101 is set to be greater than the thickness of the second insulating layer 102. Preferably, the thickness of the first insulating layer 101 can be set to h1=27.5μm, the thickness of the first copper layer 103 can be set to h2=18μm, the thickness of the second insulating layer 102 can be set to h3=25μm, and the radius of the first capacitor plate 11 can be set to a=2.3mm. On this basis, the inner diameter of the spiral microstrip line is set to 5.2-7mm.

[0028] 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 may all be PI (polyimide).

[0029] Since the compression of the gas in the sealed cavity will produce a reaction force on the flexible membrane during the deformation of the sensor under pressure, which will lead to a decrease in the overall sensitivity of the sensor. Therefore, the present invention integrates a ventilation channel design in the sensor unit to improve the gas retention effect, and verifies its improvement effect by establishing a theoretical model and a finite element simulation model. When the upper and lower flexible membranes are deformed by external pressure, the air pressure in the closed cavity will increase due to the compression effect. At this time, the pressure inside the closed cavity is P t It can be expressed as: (1); in P 0 is the atmospheric pressure, V 0 is the volume of the sealed chamber when it is not pressurized ( V 0 =πa 2 g ), V t The cavity volume after the double-sided membrane is compressed and deformed can be expressed as: (2);

[0030] in a is the film radius, g is the height of the ventilation cavity ，w 0 is the central disturbance of the film. In the small deflection range, from equations (1) and (2), we can get: (3); At this time, the pressure difference between the inside and outside of the sensor Δ P’ for: (4); Therefore, in the sealed cavity sensor, the film is reacted by the trapped air inside, and the pressure difference ΔP' on both sides of the film is smaller than the pressure difference ΔP with a vented cavity. To verify this theory, the PI-Cu-PI composite film structure ( h 1 =27.5 μm, h 2 = 18 μm, h 3 = 25 μm, capacitor radius a= 2.3mm) sealed chamber sensor was simulated by finite element method. The simulation results showed that the center deflection of the sensor film was 5.2μm. The test results are as follows Fig.10 As shown in (a), Fig.10 (a) shows the simulation result of the deflection of the sensor film under the air trapping effect of the sealed cavity when a pressure of 5kPa is applied. Similarly, the finite element simulation of the same specification ventilated cavity sensor with a width of 1mm is performed, and the simulation results are shown in Fig.10 As shown in (b), Fig.10 (b) shows the simulation results of the film deflection under 5kPa pressure under the condition of integrated air channel and completely fixed edge constraint. The center deflection of the sensor film is 12.1μm, which is much larger than Fig.10 The sensor with only a sealed cavity shown in (a) shows higher deformation sensitivity. Considering that the vented cavity will cause the edge of the diaphragm to be unable to be fully constrained in practical applications, this paper further simulates the response behavior under semi-constrained boundary conditions. The simulation results show that the central disturbance of the film reaches 13.0μm ( Fig.10 (c)), the error is only 7.4% compared with the fully constrained condition. Fig.10 (c) shows the simulation results of the membrane deflection under 5kPa pressure with integrated air channels and edge constraints. This result shows that even when the actual boundary conditions are not ideal, the fully constrained theoretical model still has good predictive ability and can be used as an effective approximate basis for engineering design. In short, the integrated ventilation cavity has greatly improved the sensitivity of the sensor through theoretical analysis models and finite element simulations.

[0031] The wireless passive pressure sensor designed in this study adopts a PI-Cu-PI multilayer sandwich flexible membrane structure to achieve insulation protection, anti-oxidation and anti-short circuit functions for the metal layer. According to the deformation theory of multilayer circular membrane, the diaphragm radius is a , under uniform external pressure, at any radius position r The disturbance expression at is: (5); Among them, ΔP is the pressure difference on both sides of the diaphragm, and D′ is the equivalent bending stiffness.

[0032] Assume that the parallel plate capacitor film gap of the sensor under no pressure load is g When the upper and lower membranes are compressed, the equivalent capacitance of the middle cavity is C g It can be expressed by differential method integration as: (6); in, ε 0 is the dielectric constant of vacuum, ε r is the relative dielectric constant.

[0033] It is worth mentioning that since this patent adopts a multi-layer thin film sensor design, it is necessary to regard the multiple dielectric layers between the two metals as multiple capacitors in series. When the film is deformed by pressure, the spacing of the middle cavity capacitor changes; its capacitance value Cg can be calculated using formula (7). At the same time, the thickness change of the capacitance of other dielectric layers can be ignored and can be directly calculated using the traditional flat plate capacitor formula. Finally, the total capacitance Cs of the sensor film sensor is expressed as: (7); C i is the capacitance value of the i-th capacitor among multiple capacitors connected in series.

[0034] The sensor uses a planar spiral structure to construct the inductor element, and the inductance value of the equivalent inductance generated by it can be approximately calculated by the Wheeler correction model as follows: (8); in μ 0 is the magnetic permeability of free space, n is the number of turns of the planar spiral inductor, D ave is the average spiral diameter: (9); Fill Factor ρ Defined as: (10); in 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 It is a parameter related to the shape of the planar spiral inductor. This design uses a circular planar spiral inductor, that is, x 1 = 1, x 2 = 2.46, x 3 = 0, x 4 = 0.2.

[0035] The resistance of the sensor is mainly generated in the spiral inductor metal wire. The resonant circuit works in the high frequency range. Considering the skin effect, the equivalent resistance of the sensor is: (11); in 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: (12); The total length of the toroidal spiral inductor is l total for: (13); in s l Is the line distance.

[0036] In order to verify the theoretical model of multilayer film structure capacitor proposed above, we conducted finite element simulation under the same conditions. The test results are as follows: Fig.11 shown. Fig.11 The comparison of the center disturbance and capacitance between the FEM (Finite Element Model) model and the theoretical model is shown in the figure. The center disturbance and capacitance changes obtained from the finite element simulation are very close to the results of the theoretical model. When the pressure increases to 5kPa, the difference ( Fig.11 Erro rave The average error between the theoretical model and the actual FEM model) increased slightly, which is mainly due to the nonlinear deformation of the film under higher pressure. The simulation results verify the validity of the theoretical model of multilayer film capacitors. Since the calculation of inductance and resistance mainly depends on the known geometric structure and material parameters, the theoretical model has been widely verified and has high accuracy, so no additional simulation verification is required in this study.

[0037] Among them, the specific size parameters of the sensor structure in the simulation test are shown in Table 2: Table 2

[0038] In this design, a circular metal film is selected as the capacitor 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 capacitor film is determined to be 18 μm, and the upper and lower PI 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 film, the central disturbance of the film (13 μm) is less than 0.2 times the thickness of the first film layer (70.5 μm), and the radius of the capacitor sheet is determined to be 2.3 mm.

[0039] The inductance of the pressure sensor is optimized based on the resonant frequency and sensitivity. The sensitivity and resonant frequency of the sensor are related to the number of turns of the inductor. The relevant test results are as follows: Figure 5 As shown. The inner diameter D of the inductor in The line width w is 6 mm, the line width w is 0.254 mm, and the line spacing s is 0.254 mm. Since the scanning frequency range of the preliminary interface circuit is 0-200MHz and there are inevitable errors in the sensor manufacturing process, the number of turns of the spiral microstrip line n=6 is finally determined by comprehensively considering the scanning frequency range of the interface circuit (0–200MHz), the tolerance of processing errors, and the balance between device miniaturization and sensitivity improvement.

[0040] Table 3 summarizes the key structural parameters of the final sensor unit: Table 3

[0041] Based on theoretical modeling and simulation analysis, the 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; Table 4

[0042] 1. Theoretical derivation of circuit without matching capacitor (traditional type) Based on electromagnetic simulation verification, the following Figure 6 The equivalent circuit model shown in the figure is used to theoretically analyze and derive the electrical characteristics of the wireless passive reading system. Assume that the driving voltage is , the reference resistance is R ref , then the total input impedance of the system for: (14); Where R r is the measured resistance of the measuring circuit, L r and L s are the measured inductance of the measuring circuit and the inductance of the inductor in the sensor, C sis the capacitance value of the sensor. At this time, the resonant frequency of the sensor f 0 And the quality factor Q are: (15); (16); Substituting equations (15) and (16) into equation (14), we can get the real and imaginary components of the impedance as follows: (17); (18); 2. Mixing processing and signal demodulation In the proposed conventional read circuit architecture, the input excitation voltage V in The voltage across the reference resistor V ref Mixing is performed. Assuming the mixer gain is k, the output signal can be expressed as: (19); After filtering out the high-frequency components through a low-pass filter with a gain of B, the output DC signal is: (20); By defining parameters , its extreme value position and the maximum voltage output can be used to characterize the change of the sensor's resonant frequency; (twenty one); Derivative f through λ, and directly let , the analytical solution f for the maximum value of λ is a very complex expression, because and Usually a small resistor, To simplify the calculation, the internal resistance is ignored. and , we can get: (twenty two); Finally, by solving the equation , the approximate solution f for the maximum value of λ is: (twenty three); 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 the LC wireless passive sensor. This architecture abandons the traditional transconductance amplifier and its related circuits, significantly simplifies the system structure, avoids the limitation of the gain-bandwidth product of the transconductance amplifier, and further expands the system's operating frequency range and signal demodulation efficiency.

[0043] 3. Theoretical derivation of the reading method with matching capacitor (impedance matching optimization) The above introduces a portable LC resonant frequency traditional reading circuit model based on voltage source input, and is verified by theory and simulation. In practical applications, the reading circuit will be affected by factors such as near-field coupling, high-frequency noise, and circuit parasitic capacitance, resulting in the circuit only being able to recognize valid signals within a short distance. Therefore, on this basis, the present invention proposes an impedance matching optimization method with capacitor Cr, hereinafter referred to as IMC (Impedance Matching Circuit), such as Figure 7 This method is designed to increase signal strength and extend the reading distance.

[0044] With the introduction of matching capacitors, the total input impedance Z of the reading port is in for: (twenty four); Where ω is the angular frequency, R r is the measured resistance of the measuring circuit, L r and L s are the measured inductance of the measuring circuit and the inductance of the inductor in the sensor, C s is the capacitance value of the sensor, C r is the capacitance value of the matching capacitor. in Afterwards, we obtained and : (25); (26); According to equation (20), the system output voltage Vout can be characterized by the extreme value of parameter λ to represent the resonant frequency deviation. The analytical solution of the extreme value is complex. This paper uses a combination of theoretical analysis and simulation experiments to study the characteristics. The electromagnetic simulation parameters based on ADS (Advanced Design System) are set as follows: 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, and the simulation results are as follows: Fig.13 As shown, Fig.13 (a) shows the mixing phase component cosφ Frequency response curve of Fig.13 (b) shows the frequency response curve of the input impedance modulus |Zin|. Fig.13(c) and (d) in the figure show the comparison of the frequency response curves of the demodulation parameter λ under the impedance matching optimization structure (IMC) and the traditional structure. The experimental data show that under the same parameter conditions, after the introduction of matching capacitors λ The value increased from 0.01 to 0.158, an increase of 15.8 times. Further analysis of the cosφ characteristic shows that it has three characteristic peaks. By solving the equation φ=0, the corresponding frequency can be obtained: (27); because When the input impedance ∣ Zin ∣ Because the inductive reactance and the capacitive reactance cancel each other out and reach the maximum value, the final λ No peak was observed; ω 1,2 Department λ 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 matching capacitors will effectively increase the reading distance by enhancing the signal amplitude.

[0045] In order to evaluate the effect of improving the signal strength and reading distance of the reading circuit after introducing the matching capacitor (IMC), the embodiment of the present application evaluates the signal strength and reading distance of the reading circuit with the matching capacitor (IMC) and without the matching capacitor (traditional reading method). The experiment uses the same size of reading coil and LC wireless passive pressure sensor for testing. First, the LC pressure sensor is tested with no matching capacitor. The distance between the sensor and the reading coil is 10mm. Fig.14 The relationship between frequency and output voltage is shown. The resonant frequency drops from 153MHz to 136.98MHz, and the sensitivity of the LC pressure sensor is about -3.2kHz / Pa, which is only -2% different from the theoretical prediction. The signal strength of the unmatched capacitor is about 40mV different from the baseline signal. Affected by factors such as system noise fluctuations, ADC resolution, and system delay, the maximum distance of the readout system without matching capacitors is about 10mm.

[0046] Then the readout circuit with the matched capacitor (IMC) structure was tested. The test results are as follows: Figures 15 to 18 As shown, in order to compare the circuit enhancement effect, the distance between the sensor and the readout coil is also set to 10 mm; Fig.15 The relationship between pressure and resonant frequency at a reading distance of 10mm under the IMC architecture is shown; Fig.16 The sensitivity linear fitting curves of IMC and traditional reading circuit architecture at a distance of 10 mm are shown; Fig.17 The frequency response curve at a reading distance of 16 mm with the introduction of an IMC structure is shown, showing the maximum effective reading distance of the system; Fig.18The pressure-frequency (single peak) response curves of the two reading methods, matched capacitor (IMC) and non-matched capacitor (traditional structure), are compared. When the sensor capacitance changes, we adjust the matched capacitor to restore symmetry. As shown in the figure, at the same distance, the signal strength with matched capacitor is about 400mV different from the baseline signal, which is 10 times higher, indicating that the output signal strength can be enhanced when there is a matched capacitor. At close distances, the peak will be divided into two from the middle, so we can get the resonant frequency by identifying the frequencies corresponding to the maximum signal strength of the two peaks. As shown in the figure, the left side is the front, the right side is the peak, and the peak-to-peak average has the same frequency response trend as the non-matched capacitor (traditional method). The sensitivity is about 3.26kHz / Pa obtained by the peak-to-peak average, which is -0.18% from the theoretical prediction. This error is caused by the difficulty in achieving complete balance between the matched capacitor and the sensor capacitor and the unstable air pressure.

[0047] In order to verify the enhancement of the readout distance, we increase the distance between the sensor and the reading coil. During the increase, the two peaks approach each other until they merge into the same peak. The distance at this time is the readout distance of the strongest signal. Consistent with the above experimental setup, the maximum readout distance is 16mm, which is 1.6 times the distance of the unmatched capacitor readout system. At the same time, the trend of the frequency response characteristic curve is consistent with that of the unmatched capacitor, and the sensor pressure sensitivity is -3.2kHz / Pa, which is only -2% different from the theoretical prediction. These results show that the test results of this circuit system are consistent with the theoretical model and can effectively improve the readout distance.

[0048] The present application also discloses a sensor manufacturing method, wherein the sensor manufacturing method is used to manufacture a resonant micro-pressure sensor in an LC wireless passive pressure sensing system with a matching circuit as described in the above embodiment; Figure 8 As shown, the sensor manufacturing method includes steps S1 to S5.

[0049] S1. Clean the bottom insulating film and attach a metal copper layer on the top.

[0050] First, the bottom insulating film is cleaned and a metal copper layer is attached to the top. The specific processing steps are as follows: Fig. 9 As shown in (a) and (b) in .

[0051] S2, coating the metal copper layer to form a photoresist layer and transferring the sensor layout pattern onto the photoresist layer.

[0052] A photoresist layer is formed on the 18 μm thick metal copper layer, and the sensor layout pattern is transferred to the photoresist layer on the metal copper layer; wherein the bottom insulating film is a polyimide film with a thickness of 25 μm. The specific processing steps are as follows: Fig. 9 As shown in (c) in .

[0053] S3, etching the metal copper layer after developing.

[0054] The metal copper layer is developed and etched to form a circular capacitor electrode and a ring-shaped spiral inductor structure. The specific processing steps are as follows: Fig. 9 As shown in (d) and (e) in the figure.

[0055] S4, coating an upper insulating film on the etched metal copper layer to prepare a first film layer and a second film layer.

[0056] Remove the photoresist on the metal copper layer after etching. The specific processing steps are as follows: Fig. 9 As shown in (f) in the figure. Furthermore, an upper insulating film is attached to the metal copper layer to form a three-layer composite structure of PI-Cu-PI; the upper insulating film can be a 27.5μm thick polyimide-based protective layer (CVL), and the surface of the device is covered with a polyimide-based protective layer film in combination with an epoxy resin adhesive layer to effectively achieve anti-oxidation and circuit insulation protection, that is, the peripheral area of ​​the metal copper layer is coated with an epoxy resin adhesive layer.

[0057] By changing the sensor layout pattern, a first copper layer including a first capacitor sheet and an inductor line and a second copper layer including only a second capacitor sheet can be obtained, thereby preparing a first film layer and a second film layer accordingly. The specific processing steps for processing the first film layer are as follows: Fig. 9 As shown in (g) in FIG. 1 , the specific process of obtaining the second film layer is similar.

[0058] S5. Place the first film layer and the second film layer on both sides of the middle layer with the ventilation cavity cut in advance, and bond and press the combined multilayer structure to obtain the resonant micro-pressure sensor.

[0059] The first film layer and the second film layer are respectively attached to both sides of the middle layer with the ventilation cavity cut in advance, so as to form a multi-layer structure, and the multi-layer structure is bonded and pressed to obtain a resonant micro-pressure sensor. The specific processing steps are as follows: Fig. 9 As shown in (h) in .

[0060] The present invention relates to the field of sensor technology, and in particular to a flexible wireless passive pressure sensor reading system based on LC resonance and a sensor manufacturing method. The application fields of the flexible pressure sensor mainly include medical care, in vitro diagnosis, patient monitoring, precise drug delivery, implantable medical devices and Internet of Things applications.

[0061] In the field of medical devices, the high sensitivity of sensors enables them to accurately monitor physiological pressures inside the human body, such as intraocular pressure (IOP) and intracranial pressure (ICP). This provides doctors with accurate diagnosis and treatment plans for the disease, 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 implanted for in-situ monitoring, providing patients with continuous and reliable data support.

[0062] In addition, the sensor can also be widely used in the field of the Internet of Things, for use in scenarios with limited wired connections such as environmental monitoring and home control. Its high precision and low power consumption make it have significant advantages in the large-scale deployment of IoT sensor nodes, providing strong technical support for the promotion and development of IoT applications.

[0063] In summary, the present invention has broad application prospects in the fields of medical care, in vitro diagnosis, patient monitoring, precision drug delivery, implantable medical devices and Internet of Things applications, and provides an important impetus for technological progress and industrial development in related fields.

[0064] In the embodiment of the present invention, an LC wireless passive pressure sensing system with a matching circuit and a sensor manufacturing method are provided, 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, the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor sheet is arranged in the first film layer, and a second capacitor sheet is arranged in the second film layer at a position opposite to the first capacitor sheet; the first capacitor sheet is connected to the inductor line; a hollow ventilation cavity is arranged in the intermediate layer. The above-mentioned pressure sensing system provides a compact signal acquisition circuit to improve portability, and a matching capacitor is arranged to increase the sensing distance; a ventilation cavity is arranged in the resonant micro-pressure sensor to discharge internal air to improve measurement sensitivity.

[0065] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on 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 measuring circuit, a signal generator, a mixing circuit, a low-pass filtering circuit, a sampling circuit and a control circuit; the measuring circuit includes a matching capacitor, a measuring inductor, a measuring resistor and a reference resistor; One end of the signal generator is grounded, and the other end is connected to one end of the measuring resistor and an input end of the mixing circuit; the other end of the measuring resistor is connected to one end of the measuring inductor, the other end of the measuring 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; The output end of the frequency mixing circuit is connected to the input end of the low-pass filtering circuit, the output end of the low-pass filtering 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, wherein the intermediate layer is sandwiched between the first film layer and the second film layer; a first capacitor sheet is arranged in the first film layer, and a second capacitor sheet is arranged in the second film layer at a position opposite to the first capacitor sheet; the first capacitor sheet is connected to the inductor; a hollow ventilation cavity is arranged in the intermediate layer; one end of the ventilation cavity passes through the side of the intermediate layer and is connected to the outside, and the other end of the ventilation cavity extends between the first capacitor sheet and the second capacitor sheet; the first capacitor sheet and the second capacitor sheet are combined to form an inductive capacitor, and the inductive capacitor is connected in series with the equivalent resistor and the equivalent inductor formed by the inductor to form a ring induction circuit, and the equivalent inductor is coupled with the measuring inductor to generate an induction signal; the matching capacitor performs real-time matching according to the capacitance value of the inductive capacitor.

2. The LC wireless passive pressure sensing system with matching circuit according to claim 1, characterized in that: The resistance value of the measuring resistor is equal to the equivalent resistor, and the inductance value of the measuring inductor is equal to the equivalent inductance.

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

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

5. The LC wireless passive pressure sensing system with matching circuit according to claim 4, characterized in that: The first film layer and the second film layer have the same thickness; 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 sheet and the inductor line; the second copper layer includes the second capacitor sheet.

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

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

8. The LC wireless passive pressure sensing system with matching circuit according to claim 7, 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 the first insulating layer and the second insulating layer, and the thickness of the second copper layer is less than the third insulating layer and the fourth insulating layer.

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

10. A sensor manufacturing method, characterized in that: The sensor manufacturing method is used to manufacture a resonant micro-pressure sensor in an LC wireless passive pressure sensing system with a matching circuit as described in any one of claims 1 to 9; the sensor manufacturing method comprises: Cleaning the bottom insulating film and attaching a metal copper layer on top of it; Coating a photoresist layer on the metal copper layer and transferring a sensor layout pattern onto the photoresist layer; After developing, etching the metal copper layer; Laying an upper insulating film on the metal copper layer to be etched to prepare a first film layer and a second film layer; The first film layer and the second film layer are respectively placed on both sides of the middle layer with the ventilation cavity cut in advance, and the combined multi-layer structure is bonded and pressed to obtain the resonant micro-pressure sensor.

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