Preparation method and application of wireless drift-free pressure sensor

Abstract

The invention provides a preparation method and application of a wireless drifting-free pressure sensor, and relates to the technical field of flexible electronic sensors. A 1-vinyl-3-butylimidazolium trifluoromethanesulfonimide salt monomer and a cross-linking agent triethylene glycol divinyl ether are mixed in proportion, the polyelectrolyte film is prepared through an ultraviolet curing one-step method, ion migration and liquid leakage are inhibited, and dielectric loss is reduced. The sensor adopts a capacitor parallel discrete structure, each capacitor is independently coupled with an inductance coil, and signal crosstalk is avoided; the torque sensor realizes torque analysis through double-capacitor array points and vector calculation, and the sensitivity is high. The sensor adapts to a biomedical scene through a laser cutting flexible electrode and a sandwich packaging process, can be applied to tooth orthodontics, has the characteristics of high signal-to-noise ratio and no drift, supports high-frequency wireless transmission, and is suitable for high-voltage and high-precision biomechanical monitoring and industrial touch sensing.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible electronic sensors, and in particular to a method for preparing a wireless drift-free pressure sensor based on a creep-free, low-dielectric-loss polyelectrolyte and its application in high-voltage testing (such as orthodontic pressure and biomechanical torque monitoring). Background Art

[0002] As an important part of flexible electronics, flexible pressure sensing technology has played an important role in the fields of human-computer interaction, health testing and virtual reality. Passive wireless flexible devices, as a device that converts pressure stimulation into electrical signals, can be implanted in the human body or applied on the skin of a robot to achieve effective information interaction. In health testing, the accuracy and quality of the signal are of great significance for the detection of some diseases, and drift-free and low-noise signals are required to feedback real perception. In addition, existing inductor-capacitor wireless devices are very mature, and some wireless tags are used in the field of logistics, including object identification and temperature sensing. However, some devices require multiple signals for simultaneous feedback, and some devices will have crosstalk when used at the same time, so the structural design of inductors and capacitors is very important.

[0003] The capacitor elements of existing inductive-capacitive wireless pressure devices usually use air dielectrics, ordinary dielectric elastomers, etc. However, due to the limited capacitance change (1pF order), the sensing range of the device is very narrow (10kPa), especially in some high-voltage testing fields, such as orthodontic pressure testing, kneecap pressure monitoring, etc. (0.1-1MPa order), it is necessary to introduce ionized dielectric materials to make the capacitor change range (1nF order). There is another problem with the existing commonly used ionized capacitor dielectrics, that is, the material (ion gel) will leak and creep during testing, which will lead to signal drift. In addition, since it is rich in free ions, it will further increase the dielectric loss of the device, and then the quality factor of the device will be small, resulting in large signal noise in the time domain test.

[0004] In addition, some devices with multiple sensor elements have unreasonable series and parallel designs, and the inductor is shared with multiple capacitors, which will cause crosstalk in the device signals. For example, the signal change of the A array point interferes with the signal transmission of the B array point. Therefore, these devices are difficult to use in real life. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method and application of a wireless drift-free pressure sensor, which uses a polyelectrolyte material with low dielectric loss to solve the problems of signal drift, large dielectric loss, serious creep phenomenon, and inductance-capacitance crosstalk in the prior art. The present invention adopts a polyelectrolyte material with low dielectric loss, and through the selection of appropriate monomers and crosslinking agents for photocuring polymerization, problems such as liquid leakage and creep of the material under high pressure are avoided, and the stability, reliability, and sensitivity of the sensor are greatly improved.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] Based on the above object, in the first aspect, the present invention provides a preparation method of a wireless drift-free pressure sensor, including the following steps:

[0008] Step 1: Prepare a polyelectrolyte film with low dielectric loss:

[0009] Mix a monomer containing ionic groups and a crosslinking agent according to a mass ratio to form a homogeneous transparent solution;

[0010] In an environment isolated from water and oxygen, add an initiator and cure to form a polyelectrolyte film by ultraviolet light irradiation;

[0011] Step 2: Process a flexible electrode:

[0012] Use laser cutting to process a polyimide-copper substrate to prepare a circular electrode array or a rectangular electrode array;

[0013] Step 3: Package the sensor:

[0014] Perform plasma treatment on the surface of the polydimethylsiloxane encapsulation layer and the polyimide of the polyimide-copper electrode and then bond them; place the polyelectrolyte film on the electrode, turn the electrode on the other side of the polydimethylsiloxane encapsulation layer over and place it on top of the polyelectrolyte film. The sensing area of the device has a sandwich-like structure of electrode-polyelectrolyte-electrode. The two electrodes are distributed on both sides of the polyelectrolyte film, and it is formed into a sealed sensing unit by hot pressing and sealing.

[0015] As a further aspect of the present invention, the preparation of the low dielectric loss polyelectrolyte film includes the following steps: preparing a premixed solution by mixing 1-vinyl-3-butylimidazolium trifluoromethanesulfonate and triethylene glycol divinyl ether at a mass ratio of 5:1 to 10:1 to obtain a basic mixture; dispersing a photoinitiator by adding 1% to 2% of the photoinitiator ethyl 2,4,6-trimethylbenzoyl phenylphosphinate to the basic mixture and stirring on a magnetic stirrer at a speed of 500 - 800 rpm for 1 - 2 minutes to form a homogeneous transparent solution; assembling a film-forming device by quantitatively pouring the solution onto a polyethylene substrate in an inert gas environment, controlling the liquid layer thickness with 100-μm-thick PDMS spacers arranged on both sides, and then covering with an upper polyethylene film to form a sealed sandwich structure; and photo-curing and forming by using an ultraviolet light source with a wavelength of 365 nm to cure for 1 hour at an irradiation intensity of 20 mW / cm 2 to finally obtain a polyelectrolyte film with a thickness of 100 - 200 μm.

[0016] As a further aspect of the present invention, when laser cutting a polyimide-copper substrate, set the power to 20 W and the laser scanning speed to 120 mm / s. The prepared lead wire width is 200 μm. The prepared circular electrode array or rectangular electrode array, where the circular electrode array is a pressure sensor and the rectangular electrode array is a torque sensor.

[0017] As a further aspect of the present invention, when bonding after plasma treatment of the surface of the polydimethylsiloxane encapsulation layer and the polyimide of the polyimide-copper electrode, set the power to 50 W and the time to 30 s. After treatment, press repeatedly to ensure the bonding strength between the electrode and the encapsulation layer; when folding and encapsulating, place the device on a hot stage, set the hot stage temperature to 80 °C, and hot press for 10 minutes.

[0018] As a further aspect of the present invention, the dielectric loss tangent of the polyelectrolyte film in the frequency band of 0.001 - 1.5 GHz is between 0.01 and 0.1, the creep rate under a pressure of 300 kPa for 10 hours is < 0.7%, and there is no liquid leakage.

[0019] As a further aspect of the present invention, after curing to form the polyelectrolyte film, performance optimization is also included. By crosslinking, the imidazole cation is locked in the polymer main chain to inhibit liquid leakage and achieve:

[0020] Dielectric loss < 0.1 (in the frequency band of 0.001 - 1.5 GHz), which is one order of magnitude lower than that of the ion gel;

[0021] Creep rate < 0.7% (under a constant pressure of 300 kPa for 10 hours);

[0022] No liquid leakage, and the mechanical stability is improved.

[0023] As a further aspect of the present invention, the sensor prepared by this preparation method adopts an anti-crosstalk design, has a capacitive parallel discrete structure, each capacitor is independently coupled to an inductance coil, and the crosstalk error between each capacitor is <1%, avoiding signal crosstalk (the crosstalk error is >20% in the series design, and <1% in this design).

[0024] As a further aspect of the present invention, the pressure sensor is: single capacitor and single inductance coupling; the torque sensor is: double capacitors and double independent inductance couplings, eliminating electrical crosstalk of signals through parallel design, and obtaining the overall torque through vector calculation.

[0025] In a second aspect, the present invention provides a wireless drift-free pressure sensor, which is prepared based on the preparation method of the above-mentioned wireless drift-free pressure sensor. The wireless drift-free pressure sensor includes:

[0026] A capacitive dielectric, which is a polyelectrolyte film;

[0027] A capacitive parallel discrete structure, wherein each capacitor is independently coupled to an inductance coil;

[0028] A pressure sensing unit, which is a circular electrode pair and a single inductance coil; and a torque sensing unit, which is a double rectangular electrode pair and double independent inductance coils.

[0029] As a further aspect of the present invention, the sensitivity of the pressure sensor is segmented as follows:

[0030] 0 - 100 kPa: -1 MHz / kPa;

[0031] 100 - 500 kPa: -0.08 MHz / kPa;

[0032] 500 - 1000 kPa: -0.02 MHz / kPa;

[0033] The noise ≤ 0.5 MHz, and the noise level is one order of magnitude smaller than that of the wireless device prepared by ionic gel (4 MHz).

[0034] In a third aspect, the present invention provides an application of the above-mentioned wireless drift-free pressure sensor, which is used for dual-modal monitoring of pressure and torque in orthodontics, and realizes the analysis of mechanical parameters through the resonance frequency-pressure calibration formula and the torque vector algorithm.

[0035] As a further aspect of the present invention, when realizing the analysis of mechanical parameters through the resonance frequency-pressure calibration formula and the torque vector algorithm, it includes:

[0036] Attaching the sensor to the inner side of the invisible dental aligner, and inversely inferring the pressure value through the change of the resonance frequency;

[0037] The double-array torque sensor calculates torque through the formula:

[0038] T = F 1 ·d 1 -F 2 ·d 2

[0039] where T is the torque, F 1 , F 2 is the force exerted by the dental brace on both sides of the tooth, and d 1 , d 2 is the distance from both sides of the torque sensor to the center line respectively.

[0040] As a further solution of the present invention, the pressure monitoring range of the sensor is 0.1 - 1 MPa, the torque monitoring range is 0.1 - 60 N·mm, and the signal-to-noise ratio under 140 kPa high pressure is 49 dB, which is one order of magnitude higher than that of the commonly used ionic gel (the signal-to-noise ratio is only 8.6 dB).

[0041] As a further solution of the present invention, when the sensor is attached to the inner side of the invisible dental brace and orthodontic pressure is detected, P = F·A -1 , where P is the pressure during orthodontic pressure detection, A is the surface area of the pressure sensor, and F is the force exerted by the dental brace on the tooth surface.

[0042] As a further solution of the present invention, in the application of the wireless drift-free pressure sensor, during data acquisition, a network analyzer (frequency resolution 1 kHz) is used to monitor the resonant frequency in real time, and wireless dynamic measurement is realized by combining pre-stored calibration data.

[0043] Compared with the prior art, a preparation method and application of a wireless drift-free pressure sensor proposed by the present invention have significant advantages in high-pressure sensing, signal stability, anti-interference ability and actual application scenarios, and have the following beneficial effects:

[0044] 1. The present invention realizes a breakthrough in material properties, realizes low dielectric loss and no liquid leakage characteristics, reduces the dielectric loss by one order of magnitude. By using a photocurable polyelectrolyte, cations are locked in the polymer backbone through chemical cross-linking to reduce the migration of free ions. The polyelectrolyte material adopted by the present invention has significant low dielectric loss characteristics, significantly reduces the dielectric loss, minimizes the energy loss of the sensor at high frequencies, and thus improves the response speed and measurement accuracy of the sensor.

[0045] 2. The present invention realizes wide-range high-voltage measurement. Through the photocuring crosslinking technology, the polyelectrolyte film has stronger mechanical stability and high-voltage resistance, can effectively prevent liquid leakage and creep phenomena, ensure stability under long-term use, and the high dielectric constant and mechanical stability of the polyelectrolyte enable the capacitance change magnitude to reach 1 nF, support high-voltage scenarios, enhance the anti-fatigue performance, and are suitable for dynamic high-voltage monitoring.

[0046] 3. The present invention adopts an anti-crosstalk design. Through the parallel discrete structure of capacitance and inductance, each capacitance unit independently couples a dedicated inductance coil, and the crosstalk error is less than 1%. It avoids the signal crosstalk of the traditional series design. The low-dielectric-loss material combined with the discrete design supports high-frequency wireless transmission, enhances the high-frequency signal stability, and realizes multi-array point synchronous and precise monitoring through the anti-crosstalk design, thereby improving the accuracy and stability of the sensor.

[0047] 4. By optimizing the structural design and material selection of the sensor, the sensitivity of the sensor in different pressure ranges is significantly improved, and the noise level is one order of magnitude lower than that of the traditional ion gel sensor, ensuring high-precision measurement results and being suitable for biomechanical monitoring.

[0048] 5. The sensor prepared by the preparation method of the present invention is particularly suitable for the field of orthodontics, can realize orthodontic monitoring, can be used to monitor pressure and torque in real time, and helps orthodontists adjust more precise treatment plans according to real-time data. The pressure sensor can measure the force applied by the invisible braces to the teeth in real time, and deduce the pressure value by the resonance frequency shift to guide the optimization of orthodontic force. The torque sensor can monitor the torsional moment, avoid the risk of root resorption caused by overcorrection, and can be applied to wireless mechanical monitoring of high-pressure parts such as knees and spines, support high-precision data acquisition in sports medicine and rehabilitation engineering, and realize passive wireless detection of high-pressure contact force in the industrial field (such as flexible robot tactile sensing).

[0049] In summary, the preparation method and application of the wireless and drift-free pressure sensor of the present invention, through the low-dielectric-loss polyelectrolyte material and anti-crosstalk structure design, solve the problems of narrow high-voltage range, signal drift, large noise and multi-array point interference of traditional wireless pressure sensors, and realize high-precision and high-stability wireless mechanical sensing in the fields of biomedicine, industrial monitoring, etc., with remarkable technological advancement and market application potential.

[0050] These aspects or other aspects of the present application will be more clearly understood in the following description of the embodiments. It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. Brief Description of the Drawings

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the related art, the following will briefly introduce the drawings required for the description of the exemplary embodiments or the related art. The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0052] Figure 1 It is a schematic structural diagram of a polyelectrolyte reaction monomer and a crosslinking agent in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0053] Figure 2 It is a schematic diagram of the polyelectrolyte reaction process in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0054] Figure 3 It is a schematic diagram of the creep test of the polyelectrolyte in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0055] Figure 4 It is a schematic diagram of the comparison of the dielectric losses of the polyelectrolyte and a common ion gel in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0056] Figure 5 It is a schematic structural diagram of a wireless pressure and torque sensor in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0057] Figure 6 It is a schematic diagram of the electrode-coil of a wireless pressure and torque sensor in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0058] Figure 7 It is a schematic diagram of the change of the resonant frequency of a wireless pressure sensor with pressure or torque in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0059] Figure 8 It is a schematic diagram of the change of the resonant frequency of a torque sensor with pressure or torque in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0060] Figure 9 It is a schematic diagram of the constant pressure test of a wireless sensor of the polyelectrolyte and a common ion gel in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0061] Figure 10 It is a schematic diagram of the crosstalk test of the change of the resonant frequency of a torque sensor with the torque applied at position 1 in the preparation method of a wireless drift-free pressure sensor according to an embodiment of the present invention.

[0062] Figure 11 Schematic diagram of crosstalk test of resonant frequency of torque sensor varying with torque applied at position 2 in the preparation method of a wireless non-drift pressure sensor according to an embodiment of the present invention.

[0063] Figure 12 Schematic diagram of application of a wireless pressure and torque sensor prepared by the preparation method of a wireless non-drift pressure sensor according to an embodiment of the present invention in the field of orthodontics. Detailed implementation manners

[0064] Next, in combination with the accompanying drawings and specific implementation manners, the present application will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be combined arbitrarily to form new embodiments.

[0065] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further details the embodiments of the present invention in combination with specific embodiments and with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0066] It should be noted that all the expressions using "first" and "second" in the embodiments of the present invention are used to distinguish two non-identical entities or non-identical parameters with the same name. It can be seen that "first" and "second" are only for the convenience of expression and should not be construed as a limitation on the embodiments of the present invention. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units inherently includes other steps or units.

[0067] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0068] The flowcharts shown in the accompanying drawings are only illustrative examples and do not necessarily include all the contents and operations / steps, nor do they necessarily need to be executed in the described order. For example, some operations / steps can also be decomposed, combined, or partially merged. Therefore, the actual execution order may change according to the actual situation.

[0069] Next, in combination with the accompanying drawings, some implementation manners of the present application will be described in detail. On the premise of no conflict, the following-described embodiments and the features in the embodiments can be combined with each other.

[0070] To solve the problems of signal drift, large dielectric loss, serious creep phenomenon, and inductance-capacitance crosstalk existing in the prior art, the present invention proposes a preparation method of a wireless drift-free pressure sensor based on a creep-free low-dielectric-loss polyelectrolyte and its application in high-pressure tests (such as orthodontic pressure and biomechanical torque monitoring). By using a polyelectrolyte material with low dielectric loss and performing photocuring polymerization by selecting appropriate monomers and crosslinking agents, problems such as liquid leakage and creep of the material under high pressure are avoided, and the stability, reliability, and sensitivity of the sensor are greatly improved.

[0071] See Figure 1 and Figure 2 As shown in

[0072] Step 1: Prepare a low-dielectric-loss polyelectrolyte film:

[0073] (1) Raw material ratio: Mix a monomer containing ionic groups (1-vinyl-3-butylimidazolium trifluoromethanesulfonate) and a crosslinking agent (triethylene glycol divinyl ether) in a mass ratio of 5:1 to 10:1 to obtain a solution, add 1% - 2% of the solution mass of a photoinitiator (ethyl 2,4,6-trimethylbenzoyl phenylphosphinate), and stir on a magnetic stirrer at a speed of 500 - 800 rpm for 1 - 2 minutes to form a homogeneous transparent solution;

[0074] (2) Photocuring polymerization: Under an inert gas environment, quantitatively pour the solution onto a polyethylene substrate, control the liquid layer thickness through 100-μm-thick PDMS spacers arranged on both sides, then cover the upper polyethylene film to form a sealed sandwich structure, and irradiate it with ultraviolet light (wavelength 365 nm, intensity 20 mW / cm 2 ) for 1 hour to cure and form a polyelectrolyte film with a thickness of 100 - 200 μm;

[0075] Step 2: Process flexible electrodes:

[0076] Use laser to cut a polyimide-copper substrate, set the power to 20 W and the laser scanning speed to 120 mm / s. The width of the prepared lead wire is 200 μm, the diameter of the prepared circular (pressure sensor) electrode is 2 mm, and the length of the prepared rectangular (torque sensor) electrode is 3.2 mm and the width is 1.6 mm;

[0077] Step 3: Package the sensor:

[0078] Perform plasma treatment (power 50 W, time 30 s) on the surface of the polyimide of the polydimethylsiloxane (PDMS) packaging layer and the polyimide-copper (PI-Cu) electrode to improve the bonding strength;

[0079] Place the polyelectrolyte film on the electrode, fold the electrode on the other side of the polydimethylsiloxane encapsulation layer and place it on top of the polyelectrolyte film. The sensing area of the device has a sandwich-like structure of electrode-polyelectrolyte-electrode. The two electrodes are distributed on both sides of the polyelectrolyte film. Seal and form it by hot pressing at 80 °C for 10 minutes to form a sealed sensing unit.

[0080] In the present invention, flexible encapsulation and biocompatibility are adopted to adapt to complex application scenarios. Using flexible electrodes and encapsulation processes, through laser cutting of polyimide-copper electrodes (line width 200 μm) combined with PDMS encapsulation, the bending radius of the device is achieved to be <5 mm, adapting to the curved surface fitting of teeth, joints, etc.; plasma treatment (50 W, 30 s) improves the adhesion strength between PDMS and the electrode, and the water vapor transmission rate after encapsulation is <1 g / (m 2 ·day), ensuring long-term use stability. The present invention also has biocompatibility. The encapsulated device passes the ISO 10993-5 cytotoxicity test and is suitable for long-term implantation or attachment to human tissues (such as the oral cavity, skin).

[0081] In this embodiment, see Figure 3 As shown, the dielectric loss tangent of the polyelectrolyte film in the frequency band of 0.001-1.5 GHz is between 0.01 and 0.1, and the creep rate under a pressure of 300 kPa for 10 hours is <0.7%, with relatively small changes and being relatively stable. Among them, after curing to form the polyelectrolyte film, performance optimization is also included. By cross-linking, imidazole cations are locked in the polymer backbone to inhibit liquid leakage, achieving: dielectric loss <0.1 (in the frequency band of 0.001-1.5 GHz), which is one order of magnitude lower than that of ion gels; creep rate <0.7% (under a constant pressure of 300 kPa for 10 hours); no liquid leakage, and the mechanical stability is improved.

[0082] See Figure 4 As shown, compared with commonly used ion gels, the dielectric loss of this polyelectrolyte is one order of magnitude smaller in the field of high-frequency wireless sensing: in the 2 GHz band, the loss tangent of commonly used ion gels is in the order of 0.1, while the loss tangent of the polyelectrolyte is in the order of 0.01.

[0083] In this embodiment, the sensor prepared by this preparation method adopts an anti-crosstalk design, has a capacitive parallel discrete structure, each capacitor is independently coupled with an inductance coil, and the crosstalk error between each capacitor is <1%, avoiding signal crosstalk (when in series design, the crosstalk error >20%, and in this design <1%).

[0084] In this embodiment, the pressure sensor is: single-capacitor and single-inductor coupling; the torque sensor is: double-capacitor and double-independent-inductor coupling. The signal electrical crosstalk is eliminated through a parallel design, the overall torque is obtained through vector calculation, and the device structure is designed such that the capacitors are in parallel and discrete, and the inductors are independently coupled to the capacitors respectively, so that the signal of one device does not interfere with the other device, achieving accurate sensing.

[0085] Among them, when processing the flexible electrodes and packaging the sensors, refer to Figure 5 As shown, after obtaining the polyelectrolyte elastomer, circular and rectangular thin films are obtained by laser cutting. Then, the polyimide-copper flexible material is cut using an appropriate power and speed of a laser cutting machine. The width of the cut electrode line is 200 microns to avoid ablation of the surface due to excessive power. Cut into the following shape, the PDMS encapsulation layer and the polyimide surface are treated with plasma for adhesion, and adhered to the polydimethylsiloxane (PDMS) encapsulation layer. The polyelectrolyte material is placed on the circular or rectangular electrode, and then the PDMS intermediate layer is placed around the polyelectrolyte material. Finally, it is folded along the center line and heated on an 80°C hot stage for 10 minutes to obtain a sample. The device for wireless orthodontic testing is obtained through such sandwich stacking and folding. Among them, during sandwich stacking and folding, the polyelectrolyte material is placed on the circular or rectangular electrode, and then the PDMS intermediate layer is placed around the polyelectrolyte material. Finally, it is folded along the center line and heated on an 80°C hot stage for 10 minutes to obtain a sample.

[0086] The sensitivities of the pressure and torque sensors are as Figure 7 and Figure 8 shown. For the pressure sensor, there is only one capacitive element, and the resonant frequency of the device changes under different pressures. The change slope within 1 MPa is -1 MHz kPa -1 , -0.08 MHz kPa -1 , -0.02 MHz kPa -1 . For the torque sensor, the device has two array points. The force measured is multiplied by the center line to obtain the torque, and combined with the array point direction, the overall torque is obtained through vector calculation. The change slopes of the resonant frequencies at the two positions with respect to torque are respectively, position 1: -14 MHz (N·mm) -1 , -3 MHz (N·mm) -1 ; position 2: -120 MHz (N·mm) -1 , -2 MHz (N·mm) -1 .

[0087] Refer to Figure 9As shown, the wireless device prepared from this polyelectrolyte material features low noise and a high signal-to-noise ratio: compared with common ion gels, when under a high pressure of 140 kPa, the signal of this device remains stable for 10 minutes without signal drift, and the signal change exceeds 100 MHz, with its noise only being 0.5 MHz; while the wireless device prepared from common ion gels will cause the signal to continuously drift downward, with the overall change being less than 50 MHz and its noise being 4 MHz, which affects signal transmission.

[0088] In this embodiment, the parallel design of the two capacitors and the inductor of the torque sensor of the present invention enables the device signals at the two array points to have no electrical crosstalk. The inductor is separated into two parts and each part is connected to a capacitor; one part of the inductor will not affect the signal of the other capacitor. If it is a series design, when one of the capacitive sensors is pressed, the signal of the other capacitor will also change, resulting in crosstalk. The data is as Figure 10 and Figure 11 shown. When different torques are applied at position 1, the resonant frequency at position 1 changes significantly, while due to mechanical crosstalk, the change in the resonant frequency at position 2 is weak. Vice versa.

[0089] The preparation method of the wireless drift-free pressure sensor of the present invention involves polymerizing a sample by ultraviolet irradiation for 1 hour by selecting a suitable monomer (1-vinyl-3-butylimidazolium trifluoromethanesulfonate) and a crosslinking agent (triethylene glycol divinyl ether). The imidazolium cation is locked on the polymer backbone to prevent liquid leakage of the material and reduce the dielectric loss of the material. Crosslinking modification further improves the mechanical properties of the material, enabling no creep to be detected during testing at the 100 kPa level. When preparing the polyelectrolyte film, the thickness is 150 μm, the dielectric loss is 0.008 (2 GHz), and the creep rate at 300 kPa for 10 hours is 0.66%. It can achieve a breakthrough in material properties and has the characteristics of low dielectric loss and no liquid leakage. By using a photocurable polyelectrolyte (such as the copolymerization of 1-vinyl-3-butylimidazolium trifluoromethanesulfonate and a crosslinking agent), the cation is locked on the polymer backbone through chemical crosslinking to reduce the migration of free ions. In the high-frequency band of 0.001 - 1.5 GHz, the dielectric loss tangent (tanδ) is reduced to 0.01 - 0.1 (for traditional ion gels, it is 0.1 - 1), significantly reducing the dielectric loss and improving the quality factor (Q value) of the device, thereby reducing signal noise (noise ≤ 0.5 MHz, and the signal-to-noise ratio is 49 under a high pressure of 140 kPa, with the signal-to-noise ratio increasing by one order of magnitude), achieving a one-order-of-magnitude reduction in dielectric loss. The crosslinked network structure effectively prevents the leakage of ionic liquids, and the creep rate of the material at 300 kPa for 10 hours is < 0.7%, ensuring long-term stability, eliminating signal drift (drift rate < 0.3% / min), and effectively suppressing liquid leakage and creep.

[0090] An embodiment of the present invention also provides a wireless drift-free pressure sensor, which is prepared based on the above-mentioned preparation method of the wireless drift-free pressure sensor. The wireless drift-free pressure sensor includes:

[0091] A capacitive dielectric, which is a polyelectrolyte thin film;

[0092] A capacitive parallel discrete structure, wherein each capacitor is independently coupled to an inductance coil;

[0093] A pressure sensing unit, which is a circular electrode pair and a single inductance coil; and a torque sensing unit, which is a double rectangular electrode pair and a double independent inductance coil.

[0094] Among them, the sensitivity of the pressure sensor is segmented as follows:

[0095] 0 - 100 kPa: -1 MHz / kPa;

[0096] 100 - 500 kPa: -0.08 MHz / kPa;

[0097] 500 - 1000 kPa: -0.02 MHz / kPa;

[0098] Noise ≤ 0.5 MHz, and the noise level is one order of magnitude smaller than that of the wireless device (4 MHz) prepared by ion gel.

[0099] Among them, the torque sensor is a double-capacitor dot design, and the sensitivities are -14 MHz / (N·mm) and -120 MHz / (N·mm) respectively. The mechanical crosstalk error is eliminated through vector calculation.

[0100] In an embodiment of the present invention, the present invention provides an application of the above-mentioned wireless drift-free pressure sensor for dual-mode monitoring of pressure and torque in orthodontics. The mechanical parameter analysis is realized through the resonance frequency-pressure calibration formula and the torque vector algorithm, including:

[0101] Attach the sensor to the inner side of the invisible dental brace, and infer the pressure value by the change of the resonance frequency;

[0102] The double-dot torque sensor passes through the formula:

[0103] T = F 1 ·d 1 -F 2 ·d 2

[0104] Calculate the torque, where T is the torque, F 1 , F 2 is the force exerted by the dental brace on both sides of the tooth, d 1 , d 2It is the distance from both sides of the torque sensor to the center line respectively.

[0105] In this embodiment, the pressure monitoring range of the sensor is 0.1 - 1 MPa, the torque monitoring range is 0.1 - 60 N·mm, and the signal-to-noise ratio is 49 dB under a high pressure of 140 kPa, which is one order of magnitude higher than that of common ionic gels (the signal-to-noise ratio is only 8.6 dB). Among them, the pressure sensor can measure the force exerted by the invisible braces on the teeth in real time (0.1 - 0.5 MPa), and deduce the pressure value by the resonance frequency shift. When detecting orthodontic pressure, P = F·A -1 , where P is the pressure during orthodontic pressure detection, A is the surface area of the pressure sensor, F is the force exerted by the braces on the tooth surface, to guide the optimization of orthodontic force. The torque sensor can monitor the torsional moment (0.1 - 20 N·mm) to avoid the risk of root resorption caused by overcorrection.

[0106] It is applied to wireless mechanical monitoring of high-pressure parts such as knees and spines, supporting high-precision data acquisition in sports medicine and rehabilitation engineering; realizing passive wireless detection of high-pressure contact forces in the industrial field (such as flexible robot tactile sensing).

[0107] The present invention can improve the high-pressure sensing ability, covering the range of 0.1 - 1 MPa. The high dielectric constant and mechanical stability of the polyelectrolyte enable the capacitance change magnitude to reach 1 nF (only 1 pF for traditional air medium), supporting high-pressure scenarios (such as orthodontics and joint pressure monitoring), and realizing wide-range high-pressure measurement. The sensitivity of the pressure sensor is optimized in sections:

[0108] 0 - 100 kPa: -1 MHz / kPa (high sensitivity);

[0109] 100 - 500 kPa: -0.08 MHz / kPa (medium-pressure linear response);

[0110] 500 - 1000 kPa: -0.02 MHz / kPa (high-pressure stable region).

[0111] The capacitance change rate of the material is <2% after 1000 cycles of cyclic loading (300 kPa pressure), which is suitable for dynamic high-pressure monitoring and enhances the fatigue resistance.

[0112] Adopting a parallel discrete structure of capacitance and inductance, each capacitance unit is independently coupled to a dedicated inductance coil, avoiding signal crosstalk in the traditional series design (the crosstalk error <1%, >20% in the series design). For example:

[0113] The torque sensor adopts a double-capacitance array point and an independent inductance. Through the formula:

[0114] T = F 1 ·d 1 -F 2·d 2

[0115] Among them, T is the torque, F 1 , F 2 is the force exerted by the dental appliance on both sides of the tooth, d 1 , d 2 is the distance from both sides of the torque sensor to the center line respectively.

[0116] The calculation formula for the pressure P during orthodontic pressure detection is:

[0117] P = F·A -1

[0118] In the formula, P is the pressure during orthodontic pressure detection, A is the surface area of the pressure sensor, F is the force exerted by the dental appliance on the tooth surface, A, d 1 , d 2 can be adjusted and designed according to different tooth sizes, F, F 1 , F 2 is the resonant frequency of the wireless device that needs to be monitored by a network analyzer. By Figure 8 and Figure 8 The change relationship of is used to inversely deduce the torque of the orthodontic pressure.

[0119] Combined with the parallel design of inductance and capacitance to eliminate electrical interference, the torque measurement error is <3%, and the low-dielectric-loss material combined with the discrete design supports high-frequency (0.001 - 1.5 GHz) wireless transmission, ensuring the stability of high-frequency signals.

[0120] In this embodiment, in the application of the wireless drift-free pressure sensor, during data acquisition, a network analyzer (frequency resolution 1 kHz) is used to monitor the resonant frequency in real time, and wireless dynamic measurement is achieved by combining pre-stored calibration data.

[0121] See Figure 12 As shown, the pressure sensor and torque sensor of the present invention are applied to tooth orthodontics, and can test the orthodontic stress and torque of invisible dental appliances on teeth. The usage method is as follows: The prepared device is adhered to the inner side of the dental appliance. Orthodontic pressure detection is applicable to the test of tooth protrusion. The force exerted by the dental appliance on the tooth divided by the dot area is regarded as its orthodontic pressure; for torque testing, the dental appliance needs to exert a torsional force on the tooth, and the torque of one side dot is calculated by multiplying the distance from the center to the dot. Since the torque forces of the two side dots are in opposite directions, the overall torque received by the teeth during orthodontics is obtained by subtraction.

[0122] In the present invention, high precision and low noise are achieved, which is applicable to biomechanical monitoring and has a high signal-to-noise ratio (SNR is 49 dB at 140 kPa pressure). The reduction of dielectric loss reduces the signal noise to 0.5 MHz (4 MHz for traditional ion gel devices). The minimum detectable frequency change is 0.2 MHz (corresponding to a resolution of 0.1 kPa) at 100 kPa pressure. The sensor response time is <10 ms, supporting real-time monitoring of transient pressure fluctuations during orthodontics or dynamic torque changes during joint movement.

[0123] Therefore, through the design of low dielectric loss polyelectrolyte materials and anti-crosstalk structures, the present invention solves the problems of narrow high-pressure range, signal drift, large noise, and multi-site interference of traditional wireless pressure sensors, achieving high-precision and high-stability wireless mechanical sensing in the fields of biomedicine, industrial monitoring, etc., and having significant technological advancement and market application potential.

[0124] The above are exemplary embodiments disclosed by the present invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments disclosed by the present invention as defined by the claims. The functions, steps, and / or actions of the method claims according to the disclosed embodiments herein do not need to be executed in any specific order. In addition, although the elements disclosed by the embodiments of the present invention can be described or claimed in individual form, they can also be understood as plural unless explicitly limited to the singular.

[0125] It should be understood that, as used herein, unless the context clearly supports an exception, the singular form "a" is also intended to include the plural form. It should also be understood that "and / or" as used herein refers to any and all possible combinations of one or more of the associated listed items. The serial numbers of the disclosed embodiments of the present invention above are only for description and do not represent the superiority or inferiority of the embodiments.

[0126] Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the embodiments disclosed by the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features between the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as above, which are not provided in detail for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present invention shall be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for preparing a wireless drift-free pressure sensor, characterized in that: The method comprises the following steps: Step 1: Preparation of low dielectric loss polyelectrolyte film: The monomer containing the ionic group and the cross-linking agent are mixed in a mass ratio to form a homogeneous transparent solution; In a water-proof and oxygen-proof environment, an initiator is added and the film is cured by ultraviolet light to form a polyelectrolyte film; Step 2: Processing flexible electrodes: Laser cutting of polyimide-copper substrate to prepare circular electrode array or rectangular electrode array; Step 3: Encapsulate the sensor: The polyimide surface of the polydimethylsiloxane encapsulation layer and the polyimide-copper electrode are plasma treated and then bonded; a polyelectrolyte film is placed on the electrode, and the electrode on the other side of the polydimethylsiloxane encapsulation layer is folded and placed on the top of the polyelectrolyte film. The device sensing area presents a sandwich structure of electrode-polyelectrolyte-electrode, and two electrodes are distributed on both sides of the polyelectrolyte film. The device is sealed by hot pressing to form a sealed sensing unit.

2. The method for preparing a wireless drift-free pressure sensor according to claim 1, characterized in that: The preparation of a low dielectric loss polyelectrolyte film comprises the following steps: preparing a premixed solution, mixing 1-vinyl-3-butyl imidazole trifluoromethanesulfonyl imide salt and triethylene glycol divinyl ether in a mass ratio of 5:1 to 10:1 to obtain a basic mixed solution; dispersing a photoinitiator, adding 1% to 2% of the total mass of a photoinitiator 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester to the basic mixed solution, stirring on a magnetic stirrer at a speed of 500 to 800 rpm for 1 to 2 minutes to form a homogeneous transparent solution; assembling a film forming device, in an inert gas environment, quantitatively pouring the solution onto a polyethylene substrate, controlling the thickness of the liquid layer by 100 μm thick PDMS spacers arranged on both sides, and then covering an upper polyethylene film to form a sealed sandwich structure; and photocuring molding, using an ultraviolet light source with a wavelength of 365 nm at 20 mW / cm 2 The film was cured for 1 hour under the irradiation intensity, and finally a polyelectrolyte film with a thickness of 100-200 μm was obtained.

3. The method for preparing a wireless drift-free pressure sensor according to claim 2, characterized in that: When using laser cutting of polyimide-copper substrate, the power is set to 20W, the laser scanning speed is 120mm / s, the prepared lead line width is 200μm, and the prepared circular electrode array or rectangular electrode array is a pressure sensor, and the rectangular electrode array is a torque sensor.

4. The method for preparing a wireless drift-free pressure sensor according to claim 3, characterized in that: When bonding the polydimethylsiloxane encapsulation layer and the polyimide surface of the polyimide-copper electrode after plasma treatment, set the power to 50 W and the time to 30 s. Press repeatedly after treatment to ensure the bonding strength between the electrode and the encapsulation layer. When folding the package, place the device on a hot stage, set the hot stage temperature to 80 ° C, and heat press for 10 minutes.

5. The method for preparing a wireless drift-free pressure sensor according to claim 2, characterized in that: The dielectric loss tangent of the polyelectrolyte film in the frequency band of 0.001-1.5 GHz is 0.01-0.1, the creep rate is less than 0.7% in 10 hours under a pressure of 300 kPa, and there is no liquid leakage.

6. The method for preparing a wireless drift-free pressure sensor according to claim 1, characterized in that: The sensor prepared by the preparation method adopts an anti-crosstalk design and has a capacitor parallel discrete structure. Each capacitor is independently coupled to an inductor coil, and the crosstalk error between the capacitors is less than 1%.

7. The method for preparing a wireless drift-free pressure sensor according to claim 3, characterized in that: The pressure sensor is a single capacitor and a single inductor coupled; the torque sensor is a dual capacitor and dual independent inductor coupled. The parallel design eliminates the electrical crosstalk of the signal, and the overall torque is obtained through vector calculation.

8. A wireless drift-free pressure sensor, characterized in that: The wireless drift-free pressure sensor is prepared based on the preparation method of the wireless drift-free pressure sensor according to any one of claims 1 to 7, and the wireless drift-free pressure sensor comprises: A capacitor medium, wherein the capacitor medium is a polyelectrolyte film; A discrete capacitor parallel structure, where each capacitor is independently coupled to an inductor coil; A pressure sensing unit, which is a circular electrode pair and a single inductor coil; and The torque sensing unit comprises a double rectangular electrode pair and a double independent inductor coil.

9. An application of the wireless drift-free pressure sensor as claimed in claim 8, characterized in that: The dual-mode monitoring of pressure and torque in orthodontics is used to realize mechanical parameter analysis through the resonant frequency-pressure calibration formula and the torque vector algorithm; wherein, the mechanical parameter analysis is realized by the following steps: Attach the sensor to the inside of the invisible braces and infer the pressure value through the change of resonant frequency; The dual-point torque sensor is measured by the formula: T=F1·d1-F2·d2 Calculate the torque, where T is the torque, F1, F2 are the forces applied by the braces on both sides of the tooth, and d1, d2 are the distances from the center line on both sides of the torque sensor.

10. The use of the wireless drift-free pressure sensor according to claim 9, characterized in that: The pressure monitoring range of the sensor is 0.1-1MPa, the torque monitoring range is 0.1-60N·mm, and the signal-to-noise ratio is 49dB under a high pressure of 140kPa.

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