Flexible piezoelectric sensor and signal detection method thereof

Abstract

The invention provides a flexible piezoelectric sensor and a signal detection method thereof. The flexible piezoelectric sensor comprises a protective layer PDT, a second electrode layer, a flexible composite piezoelectric film layer, a first electrode layer, a flexible square polyimide substrate and a polyurethane adhesive tape. The signal detection method comprises the steps that the flexible piezoelectric sensor is attached to a human body and a sheep, the flexible piezoelectric sensor obtains signal data generated at a test position, the signal data are obtained through the processing module, signal preprocessing is carried out based on an improved filtering method, and a data set with a specific rule of effective signals is obtained. And then the information is sent to a rear end through wireless transmission, so that accurate identification of different behaviors is realized. The invention has the advantages of simple preparation process, small size, good flexibility, convenience in use, stable performance and the like, and can realize detection of heartbeat, respiration and other signals of human bodies and animals in a complex environment.

Description

Technical Field

[0001] The present invention relates to the field of piezoelectric sensing technology, and in particular to a flexible piezoelectric sensor and a signal detection method thereof. Background Art

[0002] Traditional health management methods mainly rely on the observation of behavior and body shape, which lacks scientific basis and is difficult to accurately judge the health status of individuals. Therefore, developing sensor devices that can detect the behavioral characteristics of humans and animals to improve the level of health management has become a current research hotspot and focus.

[0003] Among them, flexible piezoelectric sensors have attracted widespread attention due to their soft and bendable properties, which can convert mechanical pressure into electrical signals. This sensor uses the piezoelectric effect, that is, when pressure or force is applied, charge separation occurs inside the crystal, resulting in an electric potential difference. Flexible piezoelectric sensors have many advantages, such as small size and light weight, low power consumption, high sensitivity, fast response speed, good flexibility, easy integration and installation, etc. Therefore, they have been widely used in many fields, including robotics, medical health testing, virtual reality, smart home, etc.

[0004] However, flexible piezoelectric sensors still face many challenges in practical applications. For example, the sensitivity and stability of flexible piezoelectric sensors need to be improved to ensure that signals can be accurately detected in various environments and conditions. At the same time, the sensor needs to have sufficient durability and reliability to withstand long-term stress and environmental factors. In addition, signal processing and analysis methods also need to be further improved to improve the accuracy and real-time performance of detection. Therefore, it is very necessary to provide a flexible piezoelectric sensor and its signal detection method. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, an object of the present invention is to provide a flexible piezoelectric sensor and a signal detection method thereof.

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

[0007] The present invention provides a flexible piezoelectric sensor, which comprises, from top to bottom, a protective layer PDT, a second electrode layer, a flexible composite piezoelectric film layer, a first electrode layer, a flexible square polyimide substrate and a polyurethane tape;

[0008] The upper side of the second electrode layer and the lower side of the first electrode layer are respectively provided with conductive wires through conductive metal material glue.

[0009] Preferably, the flexible composite piezoelectric film layer comprises an iron-titanium electric polymer copolymer PTB and a zinc oxide-alkali-free glass fiber composite piezoelectric fiber, wherein the iron-titanium electric polymer copolymer PTB is arranged on both the upper and lower sides of the zinc oxide-alkali-free glass fiber composite piezoelectric fiber, the components of the iron-titanium electric polymer copolymer PTB include alkali-treated PVDF-TrFE and nano-barium titanate, and the components of the zinc oxide-alkali-free glass fiber composite piezoelectric fiber include nano-zinc oxide and alkali-free glass fiber;

[0010] The preparation method of the flexible composite piezoelectric film layer is as follows:

[0011] PVDF-TrFE powder and nano-barium titanate powder were dissolved in EDMF solution, and the mixture was stirred continuously under constant temperature. The remaining small bubbles in the precursor solution were removed by ultrasonic treatment to prepare a PTB precursor solution with a certain mass fraction.

[0012] Dissolve the nano zinc oxide powder in isopropanol, add alkali-free glass fiber after it is completely dissolved, and stir it mechanically and automatically at high temperature to fully mix it, put it into a drying oven to dry and stand, and obtain zinc oxide-alkali-free glass fiber composite piezoelectric fiber;

[0013] The supporting glass sheet was cleaned with an ethanol solution and placed in a drying oven for drying and disinfection. The PTB precursor solution was spin-coated on the supporting glass sheet. The zinc oxide-alkali-free glass fiber composite piezoelectric fiber was quickly placed on the supporting glass sheet so that it was completely wrapped by the PTB precursor solution. It was placed on a constant temperature heating plate for high temperature annealing to obtain a flexible composite piezoelectric film layer.

[0014] Preferably, the protective layer PDT is made based on polydimethylsiloxane-dimethyl diethyl silicate-tin octoate, and the preparation method is:

[0015] A certain mass ratio of polydimethylsiloxane: dimethyl diethyl silicate: tin octoate materials is used, the polydimethylsiloxane reagent is heated and stirred, and then dimethyl diethyl silicate and tin octoate are added. After standing to degas, it is placed in a blast drying oven for drying, and the protective layer PDT reagent is mechanically stirred, and after vacuum treatment to remove bubbles, uniform glue and spin coating, the protective layer PDT reagent is evenly coated on one side of the flexible composite piezoelectric film layer, and the layer is placed in a drying oven for drying and standing to complete the preparation of the PDT protective layer.

[0016] Preferably, the second electrode layer is transferred to the inside of the PDT protective layer by cooling laser induced graphene technology (CLIGS), liquid bridge transfer method or hot pressure transfer method, and the second electrode layer is attached to the upper side of the flexible composite piezoelectric film layer;

[0017] The first electrode layer is attached to the lower side of the flexible composite piezoelectric film layer by transferring the electrode layer through cooling laser induced graphene technology, liquid bridge transfer method or hot pressing transfer method;

[0018] The upper side of the second electrode layer and the lower side of the first electrode layer are adhered to the wire by means of conductive metal glue, and are solidified by constant temperature drying;

[0019] The conductive metal material glue includes conductive silver paste and pure silver wire.

[0020] Preferably, the flexible square polyimide substrate is adhered to the lower side of the first electrode layer, placed in a drying oven for drying and standing, completing the substrate attachment of the flexible piezoelectric sensor, and the flexible piezoelectric sensor attached to the substrate is completely packaged based on polyurethane tape and PDMS mold. After packaging, polarization is performed to obtain the final flexible piezoelectric sensor.

[0021] Preferably, the piezoelectric equation of the flexible piezoelectric sensor is:

[0022]

[0023] Where, d 31 is the piezoelectric coefficient in the stretching direction, w refers to the width of the piezoelectric film of the flexible piezoelectric sensor, l refers to the length of the piezoelectric film of the flexible piezoelectric sensor, t refers to the thickness of the piezoelectric film of the flexible piezoelectric sensor, and tw refers to the cross-sectional area of ​​the piezoelectric film of the flexible piezoelectric sensor;

[0024] The output charge Q of the piezoelectric film of a flexible piezoelectric sensor with a size of l×w×t is:

[0025] Q=S(d 31 T1+d 33 T3)E P-T / Z

[0026] In the formula, E P-T / Z represents the elastic modulus of the piezoelectric film of the flexible piezoelectric sensor, and S represents the area of ​​the piezoelectric film of the flexible piezoelectric sensor;

[0027] The pressure magnitude and voltage intensity response model of the flexible piezoelectric sensor is used to convert the magnitude of the force applied to the sensor into a voltage intensity output. The specific model formula is:

[0028]

[0029] Wherein, ε is the relative dielectric constant of the piezoelectric film of the flexible piezoelectric sensor, ε0 is the dielectric constant of vacuum, and d is the thickness of the piezoelectric film of the flexible piezoelectric sensor.

[0030] The present invention also provides a signal detection method for a flexible piezoelectric sensor, comprising:

[0031] Attaching flexible piezoelectric sensors to humans and sheep;

[0032] The signal data is acquired through the processing module, and the signal preprocessing is performed based on the improved filtering method to obtain a data set with specific rules of effective signals;

[0033] It is then sent to the back end via wireless transmission to achieve accurate identification of different behaviors.

[0034] Preferably, the flexible piezoelectric sensor is attached to the human body and the sheep, specifically:

[0035] Select flexible piezoelectric sensors of appropriate size and shape and attach them to appropriate parts of the object to be measured. For sheep monitoring, select flexible piezoelectric sensors of 45mm×45mm size and attach them to the sheep's body parts, including the horizontal position close to the chest cavity, the sheep's ear artery, the area between the fourth and sixth ribs, or the center of the abdomen and the area around the midline of the abdomen. Make sure to remove the wool around the attachment site, and put the sheep back to the flock after attachment;

[0036] For human body detection, a flexible piezoelectric sensor of 20 mm × 30 mm size is selected and attached to the omohyoid muscle of the neck, the armpits on both sides of the chest, or the horizontal position under the abdomen near the navel.

[0037] Preferably, the signal preprocessing is performed based on the improved filtering method, specifically:

[0038] The original noisy signal collected by the flexible piezoelectric sensor is obtained, the original noisy signal is discretely transformed, the approximation parameter and the characteristic parameter are obtained respectively by using a low-pass algorithm and a high-pass algorithm, and the two coefficient groups are sampled to obtain a post-processed approximation parameter sequence and a characteristic parameter sequence;

[0039] Define a threshold judgment function, estimate each transformed feature parameter group, and use the threshold function to process it to suppress or remove the noise component;

[0040] Reconstruct the signal, start from the second layer, recombine the processed approximation parameters and feature parameters, restore the denoised signal, upsample the sampled approximation parameter sequence and feature parameter group, restore them to the same length as the original signal, and then use the synthesis function corresponding to the decomposition to add the upsampled approximation parameters and feature parameters to obtain the final effective signal after denoising.

[0041] Preferably, when performing noise reduction, the number of decomposition layers is selected to be 5, and reconstruction starts from the second layer, wherein the improved filtering threshold is:

[0042]

[0043] In the formula, i is the number of decomposition levels, σ is the standard deviation of the noise, and its estimated value is IMAD is the median value of all high-frequency self-contained coefficient amplitudes, and N is the signal length;

[0044] The improved filtering threshold function is:

[0045]

[0046] Where λ is the set improved filtering threshold, sign() represents the sign function, and w x,y is the original coefficient, and α and β are adjustment factors.

[0047] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0048] The present invention provides a flexible piezoelectric sensor and a signal detection method thereof, wherein the flexible piezoelectric sensor comprises: a protective layer PDT, a second electrode layer, a flexible composite piezoelectric film layer, a first electrode layer, a flexible square polyimide substrate and a polyurethane tape; the signal detection method comprises attaching the flexible piezoelectric sensor to the human body and sheep, obtaining signal data through a processing module, performing signal preprocessing based on an improved filtering method, obtaining a data set with a specific rule of effective signals, and then transmitting it to the back end through wireless transmission to realize accurate recognition of different behaviors. The present invention has the advantages of simple preparation process, small size and good flexibility, easy use and stable performance, and can realize the detection of human and animal heartbeat, breathing and other signals in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0050] Figure 1 A schematic diagram of the structure of a flexible piezoelectric sensor provided in an embodiment of the present invention;

[0051] Figure 2 A schematic diagram of the axis of a piezoelectric crystal provided by an embodiment of the present invention;

[0052] Figure 3 A schematic diagram of the preparation process of a flexible piezoelectric sensor provided in an embodiment of the present invention;

[0053] Figure 4 A microscopic morphology of a flexible composite piezoelectric film layer provided in an embodiment of the present invention;

[0054] Figure 5 A microscopic morphology of a PTB layer provided in an embodiment of the present invention;

[0055] Figure 6 A schematic diagram of the response time of the flexible piezoelectric sensor provided in an embodiment of the present invention;

[0056] Figure 7 Stress-strain curves of the PTB@Z-NGFF composite piezoelectric film, the composite piezoelectric film containing only zinc oxide, and the pure PVDF-TrFE piezoelectric film of the flexible piezoelectric sensor provided in an embodiment of the present invention;

[0057] Figure 8 A schematic flow chart of a signal preprocessing method provided by an embodiment of the present invention.

[0058] Figure numerals: 1. protective layer PDT; 2. second electrode layer; 3. iron-titanium electric polymer copolymer PTB; 4. nano-scale zinc oxide-alkali-free glass fiber composite piezoelectric fiber; 5. wire; 6. conductive metal material glue; 7. first electrode layer; 8. flexible square polyimide substrate; 9. polyurethane tape. DETAILED DESCRIPTION

[0059] 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 only 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.

[0060] The purpose of the present invention is to provide a flexible piezoelectric sensor with the advantages of simple preparation process, small size and good flexibility, easy use and stable performance, which can detect signals such as heartbeat and breathing of human and animals in complex environments.

[0061] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] Figure 1 A schematic diagram of the structure of a flexible piezoelectric sensor provided in an embodiment of the present invention. The present invention provides a flexible piezoelectric sensor (FPZG), which includes, from top to bottom: a protective layer PDT 1, a second electrode layer 2, a flexible composite piezoelectric film layer (PTB@Z-NGFF), a first electrode layer 7, a flexible square polyimide substrate (FSPI) 8 and a polyurethane tape (PT) 9;

[0063] The upper side of the second electrode layer 2 and the lower side of the first electrode layer 7 are respectively provided with wires 5 through conductive metal material glue 6 .

[0064] The polyurethane tape, with a thickness ranging from 0.012 mm to 0.035 mm, is located on the lower side of a flexible square polyimide substrate and is composed of polyamic acid and a curing agent in a ratio of 1:0.6.

[0065] The flexible composite piezoelectric film layer has a micro-nano structure on the surface, and is composed of an iron-titanium electric polymer copolymer PTB 3 and a nano-grade zinc oxide-alkali-free glass fiber composite material (Z-NGFF) piezoelectric fiber 4, wherein the iron-titanium electric polymer copolymer PTB 3 is arranged on both the upper and lower sides of the zinc oxide-alkali-free glass fiber composite material piezoelectric fiber 4, the components of the iron-titanium electric polymer copolymer PTB 3 include alkalized PVDF-TrFE and nano-barium titanate, and the components of the zinc oxide-alkali-free glass fiber composite material piezoelectric fiber 4 include nano-zinc oxide and alkali-free glass fiber;

[0066] The zinc oxide-alkali-free glass fiber composite material is made of 60% silicon dioxide, 15% aluminum oxide, 15% calcium oxide, and 10% boron oxide, ensuring that the fiber has good electrical insulation and mechanical strength.

[0067] The preparation method of the flexible composite piezoelectric film layer is as follows:

[0068] PVDF-TrFE powder and nano-barium titanate powder were dissolved in EDMF solution, and the mixture was stirred continuously under constant temperature. The remaining small bubbles in the precursor solution were removed by ultrasonic treatment to prepare a PTB precursor solution with a certain mass fraction.

[0069] Dissolve the nano zinc oxide powder in isopropanol, add alkali-free glass fiber after it is completely dissolved, and stir it mechanically and automatically at high temperature to fully mix it, put it into a drying oven to dry and stand, and obtain zinc oxide-alkali-free glass fiber composite piezoelectric fiber;

[0070] The supporting glass sheet was cleaned with an ethanol solution and placed in a drying oven for drying and disinfection. The PTB precursor solution was spin-coated on the supporting glass sheet. The zinc oxide-alkali-free glass fiber composite piezoelectric fiber was quickly placed on the supporting glass sheet so that it was completely wrapped by the PTB precursor solution. It was placed on a constant temperature heating plate for high temperature annealing to obtain a flexible composite piezoelectric film layer.

[0071] The protective layer PDT is made based on polydimethylsiloxane-dimethyl diethyl silicate-tin octoate, and the preparation method is as follows:

[0072] A certain mass ratio of polydimethylsiloxane: dimethyl diethyl silicate: tin octoate materials is used, the polydimethylsiloxane reagent is heated and stirred, and then dimethyl diethyl silicate and tin octoate are added. After standing to degas, it is placed in a blast drying oven for drying, and the protective layer PDT reagent is mechanically stirred, and after vacuum treatment to remove bubbles, uniform glue and spin coating, the protective layer PDT reagent is evenly coated on one side of the flexible composite piezoelectric film layer, and the layer is placed in a drying oven for drying and standing to complete the preparation of the PDT protective layer.

[0073] The second electrode layer is transferred to the inside of the PDT protective layer by cooling laser induced graphene technology (CLIGS), liquid bridge transfer method or hot pressure transfer method, and the second electrode layer is attached to the upper side of the flexible composite piezoelectric film layer;

[0074] The first electrode layer is attached to the lower side of the flexible composite piezoelectric film layer by transferring the electrode layer through cooling laser induced graphene technology, liquid bridge transfer method or hot pressing transfer method;

[0075] The upper side of the second electrode layer and the lower side of the first electrode layer are adhered to the wire by means of conductive metal glue, and are solidified by constant temperature drying;

[0076] The materials of the first electrode layer and the second electrode layer are 99.99% pure silver electrode as the electrode layer material;

[0077] The conductive metal material glue includes conductive silver paste and pure silver wire;

[0078] It should be noted that the present invention provides an embodiment, taking the cooling laser induced graphene technology (CLIGS) as an example, the first electrode layer and the second electrode layer are laser scanned on a square polyimide film (SPI) by the cooling laser induced graphene technology to attach graphene, the SPI film is first attached to the supporting glass sheet and heated at 80°C for 10 minutes to complete the attachment, the size of the SPI film is 40mm×40mm, and after testing, the thickness is selected to be 0.06mm, 0.08mm, and 0.10mm. The FSPI substrate is adhered to the bottom of the first electrode layer, and the PDT protective layer is applied on the top of the second electrode layer.

[0079] The flexible square polyimide substrate is adhered to the lower side of the first electrode layer, and is placed in a drying oven to dry and stand to complete the substrate attachment of the flexible piezoelectric sensor. The flexible piezoelectric sensor attached to the substrate is completely packaged based on polyurethane tape and PDMS mold. After packaging, polarization is performed to obtain the final flexible piezoelectric sensor.

[0080] For the convenience of explanation, based on the above contents, the present invention provides a preparation process of a flexible piezoelectric sensor as follows:

[0081] 1. Preparation of PTB precursor solution: PVDF-TrFE powder (MW = 180000) and nano-barium titanate powder were dissolved in EDMF solution, magnetically stirred at 90 ° C and 500 rpm for 8 h, and ultrasonic treatment was repeated 3 times for 15 minutes to remove the remaining small bubbles in the precursor solution, and a PTB precursor solution with a mass fraction of 15% was prepared;

[0082] 2. Prepare Z-NGFF piezoelectric fiber; dissolve nano zinc oxide powder with a diameter of 50nm in 95% isopropanol, wait for the nano ZnO to be completely dissolved, add GFF fiber with a size of 20mm×20mm and stir it magnetically at 90℃ for 2h to make it fully mixed, then put it into a drying oven and dry it at a constant temperature of 80℃ for 12h to obtain Z-NGFF piezoelectric fiber, wherein the alkali-free glass fiber composite material (GFF) is made of 60% silicon dioxide, 15% aluminum oxide, 15% calcium oxide, and 10% boron oxide to ensure that the fiber has good electrical insulation and mechanical strength;

[0083] 3. Preparation of flexible composite piezoelectric film layer (PTB@Z-NGFF): Use 70% ethanol solution to clean the loading glass slide and put it in a drying oven to dry for 15 minutes. After drying, rotate the PTB precursor solution on the loading glass slide (900rpm, 20s), and then quickly place the Z-NGFF piezoelectric fiber on the glass slide so that it is completely wrapped by the PTB precursor solution. Finally, place the entire body on a constant temperature heating plate and anneal at 90℃ for 1h to obtain the PTB@Z-NGFF flexible composite piezoelectric film layer;

[0084] 4. Preparation of PDT protective layer: Take the mass ratio of PDMS: DDS: TO = 1: 0.2: 0.1, heat the PDMS reagent (viscosity 60000 mPa·s) to 40°C and stir for 1 hour, then add DDS and TO, let it stand for degassing and put it in a blast drying oven to complete the preparation, then mechanically stir the PDT protective layer reagent for 3 minutes, and vacuum treat to remove bubbles, set the glue and spin coater (200 rpm, 30 seconds), and evenly apply the PDT protective layer reagent on one side of the sensor body, put it in a drying oven and dry it at a constant temperature of 80°C for 2 hours to complete the coating on the second electrode layer set from bottom to top.

[0085] 5. Electrode production: transfer the electrode layer to the PDT protective layer and attach the electrodes to both ends of PTB@Z-NGFF, and on the outer sides of the first electrode layer and the second electrode layer respectively, then adhere the 49-silver electrode (99.99%) material to both ends of the flexible composite piezoelectric film layer, and use conductive metal material glue to adhere the wires on the outer sides of the first electrode layer and the second electrode layer respectively, lead out the wires, and dry them at a constant temperature. The size of the first electrode layer and the second electrode layer is 20mm×20mm;

[0086] 6. Attachment of the sensor substrate; adhere the FSPI substrate located on the side surface of the sensor body to the bottom of the first electrode layer arranged from bottom to top and place it in a drying oven at a constant temperature of 80° C. for 2 hours to complete the attachment of the sensor substrate;

[0087] 7. Sensor packaging: Use PT and PDMS molds to completely encapsulate the sensor body to obtain a flexible piezoelectric sensor (FPZG), and make the sensor area within 22mm×22mm, the thickness within 6mm, and the FPZG piezoelectric film polarized (voltage is 1.5kV, temperature is 25℃, and polarization time is 6 hours).

[0088] After polarization treatment, the piezoelectric constant in some directions of FPZG becomes 0, and its piezoelectric equation is:

[0089]

[0090] The FPZG piezoelectric film has only one pair of electrode surfaces perpendicular to the C-axis, so the electric displacement D3 is only obtained in the C-axis direction, and the piezoelectric coefficients corresponding to the shear stresses T4, T5, and T6 are all 0. When the substrate structure is flexible, it is believed that the force applied to the FPZG piezoelectric film will cause it to deform along the tensile direction, and the stress T3 in the thickness direction is zero, and d 31 Approximately d 32 10 times, therefore, d 32 can be ignored, and the simplified piezoelectric equation is:

[0091]

[0092] Where, d 31 is the piezoelectric coefficient in the stretching direction, w refers to the width of the piezoelectric film of the flexible piezoelectric sensor, l refers to the length of the piezoelectric film of the flexible piezoelectric sensor, t refers to the thickness of the piezoelectric film of the flexible piezoelectric sensor, and tw refers to the cross-sectional area of ​​the piezoelectric film of the flexible piezoelectric sensor;

[0093] The output charge Q of the piezoelectric film of a flexible piezoelectric sensor with a size of l×w×t is:

[0094] Q=S(d 31 T1+d 33 T3)E P-T / Z

[0095] In the formula, E P-T / Z represents the elastic modulus of the piezoelectric film of the flexible piezoelectric sensor, and S represents the area of ​​the piezoelectric film of the flexible piezoelectric sensor. According to the above principle, when the shape of the FPZG piezoelectric film is determined, the amount of charge formed on its surface is proportional to the pressure it receives;

[0096] The pressure magnitude and voltage intensity response model of the flexible piezoelectric sensor is used to convert the magnitude of the force applied to the sensor into a voltage intensity output. The specific model formula is:

[0097]

[0098] Wherein, ε is the relative dielectric constant of the piezoelectric film of the flexible piezoelectric sensor, ε0 is the dielectric constant of vacuum, and d is the thickness of the piezoelectric film of the flexible piezoelectric sensor.

[0099] The schematic diagram of the piezoelectric crystal axis of the prepared FPZG is shown in Figure 2 The preparation process is as shown in Figure 3 As shown, Figure 4 This is the microscopic morphology of the prepared Z-NGFF. Figure 4 a characterizes that the single fiber is clearly visible and has a smooth surface. Figure 4 b. Figure 4 c and Figure 4 d Characterization of the surface morphology of the flexible composite piezoelectric film layer of PTB@Z-NGFF. The effective components have a good combination with NGFF. Figure 5 The microscopic morphology of the prepared PTB layer shows that the relevant components are evenly distributed to form a continuous piezoelectric phase. Figure 6 This is the response time diagram of the prepared FPZG. The response time and recovery time of the device are 21ms and 42ms respectively, which has an ultra-fast response time. Figure 7 It is the stress-strain curve diagram of the PTB@Z-NGFF composite piezoelectric film of the flexible piezoelectric sensor, the composite piezoelectric film containing only zinc oxide, and the pure PVDF-TrFE piezoelectric film.

[0100] The present invention also provides a signal detection method for a flexible piezoelectric sensor, comprising:

[0101] Step 100: attaching flexible piezoelectric sensors to the human body and the sheep;

[0102] Step 200: The flexible piezoelectric sensor acquires signal data generated at the test position, acquires the signal data through a processing module, performs signal preprocessing based on an improved filtering method, and obtains a data set with a specific rule of effective signals;

[0103] Step 300: Send it to the back end via wireless transmission to achieve accurate identification of different behaviors.

[0104] By sensing the movement of a specific part, the FPZG sensor generates a voltage signal, which is recorded by the data acquisition system to obtain sufficient data sets for subsequent parameter analysis. During the movement, the periodic deformation of the detection part will mechanically stretch the FPZG piezoelectric film, thereby generating a corresponding electrical signal.

[0105] In step 100, the flexible piezoelectric sensors are attached to the human body and the sheep, specifically:

[0106] If you want to measure the movement signal detection of sheep, you can use FPZG sensor for detection, specifically:

[0107] Choose a suitable size (45mm×45mm) FPZG sensor, and make sure its shape and size are suitable for the sheep's body part (chest, abdomen). Place the FPZG sensor on the sheep's body where the behavioral signal can be effectively detected.

[0108] The FPZG sensor is placed on the sheep's neck. The FPZG sensor is placed on the sheep's chest to achieve better adhesion to record the flexural changes of respiratory movements. The flexible piezoelectric sensor is placed on the sheep's abdomen to record the flexural changes. Compared with the chest, the abdomen is easier to fix the sensor. Before placement, the wool on the sheep's body and the sensor attachment area needs to be removed.

[0109] The FPZG sensor is connected to the sensing circuit of the microcontroller and the WIFI module to achieve wireless transmission of the acquired data.

[0110] By sensing the corresponding behavior of the sheep's body parts, the FPZG sensor generates a voltage signal and records it through the data acquisition system. In particular, during breathing, the periodic deformation of the sheep's chest wall will mechanically stretch the FPZG sensor, thereby generating a corresponding electrical signal. The core of the FPZG sensor patch consists of a three-layer structure, similar to a spring-damper mechanical system, which can significantly reduce the noise generated during movement. The FPZG sensor patch can accurately respond to behavioral signals under static and dynamic conditions. For sheep, a sampling frequency of 100Hz was selected, the sampling interval was set to 10ms, the signal lower limit threshold was set to 2mV, and the data recording time was 10min for a complete set.

[0111] If you want to measure the motion signal detection of the human body, you can use the FPZG sensor for detection, specifically:

[0112] Choose a suitable size (20mm×30mm) FPZG sensor, making sure its shape and size are suitable for the body part where it will be applied (chest, neck, abdomen, elbow, etc.).

[0113] The FPZG sensor is placed on the part of the human body where the behavioral signals can be effectively detected, recording the flexural changes caused by the behavior.

[0114] The FPZG sensor is connected to the sensing circuit of the microcontroller and the WiFi module to achieve wireless transmission of the acquired data.

[0115] By sensing the movement of human body parts, the FPZG sensor generates a voltage signal and records it through the data acquisition system. In particular, during breathing, the periodic deformation of the detection part will mechanically stretch the FPZG piezoelectric film, thereby generating a corresponding electrical signal. For the human body, a 50Hz sampling frequency is selected, the sampling interval is set to 20ms, the signal lower limit threshold is set to 5mV, and the data recording time is 10min for a complete set.

[0116] like Figure 8 As shown, in step 300, signal preprocessing is performed based on the improved filtering method, specifically:

[0117] Various interference signals are often mixed in during the collection, transmission and subsequent signal acquisition of signal data. Some characteristic points of the signal may be masked by these interferences, thus affecting the signal quality. Further signal preprocessing is required to eliminate the interference of noise. By performing threshold processing on the function coefficients of the signal, the improved filtering method (IFM) is selected to dynamically adjust the threshold according to the local characteristics of the signal to improve the noise reduction effect and remove the noise component. The IFM method first decomposes the signal to obtain coefficients at each level; then estimates each coefficient and calculates the threshold of the current coefficient; then estimates the optimal threshold and then performs threshold processing on the coefficient, and sets the coefficients less than the threshold to zero or reduce them according to the calculated threshold; finally, the processed coefficients are reconstructed to obtain the denoised signal. The denoising operation is as follows:

[0118] Step 301: Collect the original noisy signal captured by the FPZG sensor and extract the characteristic signal from it. Taking the characteristics of the signal into consideration, based on the statistical characteristics and model of the signal, the IFM method can dynamically adjust the filter parameters according to the change of the signal to achieve noise suppression.

[0119] Step 302: Discretely transform the original signal, and use the low-pass algorithm and the high-pass algorithm to obtain the approximation parameters and characteristic parameters respectively. Sampling the two coefficient groups obtains the post-processed approximation parameter sequence and characteristic parameter sequence. Selecting the appropriate number of decomposition layers is a key step in the IFM method. As the number of decomposition layers increases, the difference between the signal and the noise becomes more and more obvious, which is more conducive to the separation between the two. Based on the IFM method, the decomposition layer is set to 5 layers.

[0120] Step 303: Define a threshold judgment function. Estimate each transformed feature parameter group and use the threshold function to process it to suppress or remove the noise component.

[0121] The threshold function is usually divided into hard threshold and soft threshold. The hard threshold function compares the absolute value of the coefficient with the threshold, sets the coefficient less than the threshold to zero, and retains the other coefficients. The soft threshold function sets the coefficient with an absolute value less than the threshold to zero, and shrinks the coefficient with an absolute value greater than the threshold. When the IFM method is used for noise reduction, the decomposition layer is selected as 5 layers, and reconstruction starts from the second layer. The improved filter threshold after improvement is as follows:

[0122]

[0123] In the formula, i is the number of decomposition levels, σ is the standard deviation of the noise, and its estimated value is IMAD is the median value of all high-frequency self-contained coefficient amplitudes, and N is the signal length;

[0124] Step 304: Reconstruct the signal, starting from the second layer. Recombine the processed approximation parameters and characteristic parameters to restore the denoised signal. Upsample the sampled approximation parameter sequence and characteristic parameter group to restore them to the same length as the original signal. Then use the synthesis function corresponding to the decomposition to add the upsampled approximation parameters and characteristic parameters to obtain the final effective signal after denoising.

[0125] There is a constant error between the high-frequency coefficients before and after denoising of the soft threshold function, which causes the loss of mutations or spike signals. The improved IFM method is expressed as:

[0126]

[0127] Where λ is the set improved filtering threshold, sign() represents the sign function, and w x,y is the original coefficient, α and β are adjustment factors. By changing the value of the factor, the threshold function also changes accordingly, thereby compensating for the breakpoint problem under the hard threshold and improving the deviation problem of the soft threshold function in the part greater than the threshold.

[0128] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0129] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A flexible piezoelectric sensor, characterized in that: From top to bottom, it includes: a protective layer PDT, a second electrode layer, a flexible composite piezoelectric film layer, a first electrode layer, a flexible square polyimide substrate and a polyurethane tape; The upper side of the second electrode layer and the lower side of the first electrode layer are respectively provided with conductive wires through conductive metal material glue.

2. The flexible piezoelectric sensor according to claim 1, characterized in that: The flexible composite piezoelectric film layer includes an iron-titanium electric polymer copolymer PTB and a zinc oxide-alkali-free glass fiber composite piezoelectric fiber, wherein the iron-titanium electric polymer copolymer PTB is arranged on both the upper and lower sides of the zinc oxide-alkali-free glass fiber composite piezoelectric fiber, the components of the iron-titanium electric polymer copolymer PTB include alkalized PVDF-TrFE and nano-barium titanate, and the components of the zinc oxide-alkali-free glass fiber composite piezoelectric fiber include nano-zinc oxide and alkali-free glass fiber; The preparation method of the flexible composite piezoelectric film layer is as follows: PVDF-TrFE powder and nano-barium titanate powder were dissolved in EDMF solution, and the mixture was stirred continuously under constant temperature. The remaining small bubbles in the precursor solution were removed by ultrasonic treatment to prepare a PTB precursor solution with a certain mass fraction. Dissolve the nano zinc oxide powder in isopropanol, add alkali-free glass fiber after it is completely dissolved, and stir it mechanically and automatically at high temperature to fully mix it, put it into a drying oven to dry and stand, and obtain zinc oxide-alkali-free glass fiber composite piezoelectric fiber; The supporting glass sheet was cleaned with an ethanol solution and placed in a drying oven for drying and disinfection. The PTB precursor solution was spin-coated on the supporting glass sheet. The zinc oxide-alkali-free glass fiber composite piezoelectric fiber was quickly placed on the supporting glass sheet so that it was completely wrapped by the PTB precursor solution. It was placed on a constant temperature heating plate for high temperature annealing to obtain a flexible composite piezoelectric film layer.

3. The flexible piezoelectric sensor according to claim 1, characterized in that: The protective layer PDT is made based on polydimethylsiloxane-dimethyl diethyl silicate-tin octoate, and the preparation method is as follows: A certain mass ratio of polydimethylsiloxane: dimethyl diethyl silicate: tin octoate materials is used, the polydimethylsiloxane reagent is heated and stirred, and then dimethyl diethyl silicate and tin octoate are added. After standing to degas, it is placed in a blast drying oven for drying, and the protective layer PDT reagent is mechanically stirred, and after vacuum treatment to remove bubbles, uniform glue and spin coating, the protective layer PDT reagent is evenly coated on one side of the flexible composite piezoelectric film layer, and the layer is placed in a drying oven for drying and standing to complete the preparation of the PDT protective layer.

4. The flexible piezoelectric sensor according to claim 1, characterized in that: The second electrode layer is transferred to the inside of the PDT protective layer by cooling laser induced graphene technology, liquid bridge transfer method or hot pressing transfer method, and the second electrode layer is attached to the upper side of the flexible composite piezoelectric film layer; The first electrode layer is attached to the lower side of the flexible composite piezoelectric film layer by transferring the electrode layer through cooling laser induced graphene technology, liquid bridge transfer method or hot pressing transfer method; The upper side of the second electrode layer and the lower side of the first electrode layer are adhered to the wire by means of conductive metal glue, and are solidified by constant temperature drying; The conductive metal material glue includes conductive silver paste and pure silver wire.

5. The flexible piezoelectric sensor according to claim 1, characterized in that: The flexible square polyimide substrate is adhered to the lower side of the first electrode layer, and is placed in a drying oven to dry and stand to complete the substrate attachment of the flexible piezoelectric sensor. The flexible piezoelectric sensor attached to the substrate is completely packaged based on polyurethane tape and PDMS mold. After packaging, polarization is performed to obtain the final flexible piezoelectric sensor.

6. The flexible piezoelectric sensor according to claim 1, characterized in that: The piezoelectric equation of the flexible piezoelectric sensor is: Where, d 31 is the piezoelectric coefficient in the stretching direction, w refers to the width of the piezoelectric film of the flexible piezoelectric sensor, l refers to the length of the piezoelectric film of the flexible piezoelectric sensor, t refers to the thickness of the piezoelectric film of the flexible piezoelectric sensor, and tw refers to the cross-sectional area of ​​the piezoelectric film of the flexible piezoelectric sensor; The output charge Q of the piezoelectric film of a flexible piezoelectric sensor with a size of l×w×t is: Q=S(d 31 T1+d 33 T3)E P-T / Z In the formula, E P-T / Z represents the elastic modulus of the piezoelectric film of the flexible piezoelectric sensor, and S represents the area of ​​the piezoelectric film of the flexible piezoelectric sensor; The pressure magnitude and voltage intensity response model of the flexible piezoelectric sensor is used to convert the magnitude of the force applied to the sensor into a voltage intensity output. The specific model formula is: Wherein, ε is the relative dielectric constant of the piezoelectric film of the flexible piezoelectric sensor, ε0 is the dielectric constant of vacuum, and d is the thickness of the piezoelectric film of the flexible piezoelectric sensor.

7. A signal detection method for a flexible piezoelectric sensor, characterized in that: include: Attaching flexible piezoelectric sensors to humans and sheep; The signal data is acquired through the processing module, and the signal preprocessing is performed based on the improved filtering method to obtain a data set with specific rules of effective signals; It is then sent to the back end via wireless transmission to achieve accurate identification of different behaviors.

8. The method according to claim 7, characterized in that Attaching flexible piezoelectric sensors to human body and sheep, specifically: Select flexible piezoelectric sensors of appropriate size and shape and attach them to appropriate parts of the object to be measured. For sheep monitoring, select flexible piezoelectric sensors of 45mm×45mm size and attach them to the sheep's body parts, including the horizontal position close to the chest cavity, the sheep's ear artery, the area between the fourth and sixth ribs, or the center of the abdomen and the area around the midline of the abdomen. Make sure to remove the wool around the attachment site, and put the sheep back to the flock after attachment; For human body detection, a flexible piezoelectric sensor of 20 mm × 30 mm size is selected and attached to the omohyoid muscle of the neck, the armpits on both sides of the chest, or the horizontal position under the abdomen near the navel.

9. The method according to claim 7, characterized in that: Signal preprocessing is performed based on the improved filtering method, specifically: The original noisy signal collected by the flexible piezoelectric sensor is obtained, the original noisy signal is discretely transformed, the approximation parameter and the characteristic parameter are obtained respectively by using a low-pass algorithm and a high-pass algorithm, and the two coefficient groups are downsampled to obtain the post-processed approximation parameter sequence and characteristic parameter sequence; Define a threshold judgment function, estimate each transformed feature parameter group, and use the threshold function to process it to suppress or remove the noise component; Reconstruct the signal, start from the second layer, recombine the processed approximation parameters and feature parameters, restore the denoised signal, upsample the sampled approximation parameter sequence and feature parameter group, restore them to the same length as the original signal, and then use the synthesis function corresponding to the decomposition to add the upsampled approximation parameters and feature parameters to obtain the final effective signal after denoising.

10. The method according to claim 9, characterized in that When performing signal preprocessing, the number of decomposition layers is selected to be 5, and reconstruction starts from the second layer. The improved filtering threshold is: In the formula, i is the number of decomposition levels, σ is the standard deviation of the noise, and its estimated value is IMAD is the median value of all high-frequency intrinsic coefficient amplitudes, and N is the signal length; The improved filtering threshold function is: Where λ is the set improved filtering threshold, sign() represents the sign function, and w x,y is the original coefficient, and α and β are adjustment factors.

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