A flexible piezoelectric sensor and its signal detection method

Abstract

The present 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 tape. The signal detection method comprises attaching the flexible piezoelectric sensor to a human body and a sheep, wherein the flexible piezoelectric sensor acquires signal data generated at the test location, obtains the signal data through a processing module, performs signal preprocessing based on an improved filtering method, obtains a data set of valid signals with specific patterns, and then transmits the data to a back-end via wireless transmission to achieve accurate recognition of different behaviors. The present invention has the advantages of a simple preparation process, compact size, good flexibility, ease of use, and stable performance. It can detect signals such as heartbeat and respiration in humans and animals in complex environments.

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 rely primarily on behavioral and body posture observations, but these methods lack scientific evidence and are difficult to accurately assess an individual's health status. Therefore, developing sensing devices that can detect behavioral characteristics in humans and animals to improve 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 enable them to convert mechanical pressure into electrical signals. These sensors exploit the piezoelectric effect, whereby when pressure or force is applied, charge separation occurs within a crystal, generating a potential difference. Flexible piezoelectric sensors offer numerous advantages, including compactness, low power consumption, high sensitivity, fast response, good flexibility, and ease of integration and installation. Consequently, they have found widespread application in diverse fields, including robotics, healthcare testing, virtual reality, and smart homes.

[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 accurate signal detection in a variety of environments and conditions. At the same time, the sensors need to be sufficiently durable and reliable to withstand long-term stress and environmental factors. Furthermore, signal processing and analysis methods need to be further improved to enhance detection accuracy and real-time performance. Therefore, it is essential to provide a flexible piezoelectric sensor and a signal detection method thereof. 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] Wires are respectively provided on the upper side of the second electrode layer and the lower side of the first electrode layer through conductive metal glue.

[0009] Preferably, 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 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, stirred continuously at a constant temperature, and residual small bubbles in the precursor solution were removed by ultrasonic treatment to prepare a PTB precursor solution with a certain mass fraction.

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

[0013] The supporting glass slide 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 slide. The zinc oxide-alkali-free glass fiber composite piezoelectric fiber was quickly placed on the supporting glass slide 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 was used, the polydimethylsiloxane reagent was heated and stirred, and then dimethyl diethyl silicate and tin octoate were added. After standing to degas, it was placed in a blast drying oven for drying. The protective layer PDT reagent was mechanically stirred, and after vacuum treatment to remove bubbles, uniform glue and spin coating, the protective layer PDT reagent was evenly coated on one side of the flexible composite piezoelectric film layer, and 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 interior of the PDT protective layer by cooling laser induced graphene technology (CLIGS), 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;

[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 conductive wires 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 encapsulated based on polyurethane tape and PDMS mold. After the encapsulation is completed, 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]

[0026] Where, 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 and voltage intensity response model of the flexible piezoelectric sensor is used to convert the force applied to the sensor into voltage intensity output. The specific model formula is:

[0028]

[0029] Where 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] Acquire signal data through the processing module, perform signal preprocessing based on the improved filtering method, and 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 as follows:

[0035] Select a flexible piezoelectric sensor of appropriate size and shape and attach it to the appropriate part of the object being measured. For sheep monitoring, select a 45mm×45mm flexible piezoelectric sensor and attach it to the sheep's body, including the horizontal position near 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 area. After attachment, return the sheep to the flock;

[0036] For human body detection, a flexible piezoelectric sensor with a size of 20mm×30mm is selected and attached to the omohyoid muscle position of the neck, the position near the armpits on both sides of the chest, or the horizontal position below 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, and the original noisy signal is discretely transformed. The approximation parameters and characteristic parameters are obtained using a low-pass algorithm and a high-pass algorithm respectively. The two coefficient groups are sampled to obtain the post-processed approximation parameter sequence and 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, starting from the second layer, recombining the processed approximation parameters and characteristic parameters to restore the denoised signal, up-sampling the sampled approximation parameter sequence and characteristic parameter group to restore them to the same length as the original signal, and then using the synthesis function corresponding to the decomposition, adding the up-sampled approximation parameters and characteristic parameters to obtain the final valid 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] Where, is the number of decomposition levels, is the standard deviation of the noise, and its estimated value is

[0044] , IMAD is the median value of all high-frequency inherent coefficient amplitudes, and N is the signal length;

[0045] The improved filtering threshold function is:

[0046] Where, is the improved filtering threshold set, represents the symbolic function, is the original coefficient, 、 is the regulating factor.

[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. 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 polyurethane tape. The signal detection method comprises attaching the flexible piezoelectric sensor to a human body or sheep, acquiring signal data through a processing module, performing signal preprocessing based on an improved filtering method to obtain a dataset of valid signals with specific patterns, and then transmitting the data to a backend via wireless transmission to achieve accurate recognition of different behaviors. The present invention has the advantages of a simple preparation process, compact size, good flexibility, ease of use, and stable performance. It can detect signals such as heartbeat and respiration in humans and animals 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 following briefly introduces the drawings required for use in the embodiments. 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 any creative work.

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

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

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

[0053] Figure 4A microscopic morphology of the 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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0060] The purpose of the present invention is to provide a flexible piezoelectric sensor with a simple preparation process, small size and good flexibility, easy use and stable performance, which can detect human and animal heartbeat, breathing and other signals 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 This is a schematic diagram of the structure of a flexible piezoelectric sensor provided by 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] Wires 5 are respectively provided on the upper side of the second electrode layer 2 and the lower side of the first electrode layer 7 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 underside 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 its surface and is composed of an iron-titanium electric polymer copolymer PTB 3 and a nano-scale zinc oxide-alkali-free glass fiber composite (Z-NGFF) piezoelectric fiber 4. 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 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 piezoelectric fiber 4 include nano-zinc oxide and alkali-free glass fiber.

[0066] The preparation method of the flexible composite piezoelectric film layer is as follows:

[0067] PVDF-TrFE powder and nano-barium titanate powder were dissolved in EDMF solution, stirred continuously at a constant temperature, and residual small bubbles in the precursor solution were removed by ultrasonic treatment to prepare a PTB precursor solution with a certain mass fraction.

[0068] Dissolve nano zinc oxide powder in isopropyl alcohol, add alkali-free glass fiber after it is completely dissolved, and stir mechanically and automatically at high temperature to fully mix, then place in a drying oven to dry and stand to obtain zinc oxide-alkali-free glass fiber composite piezoelectric fiber;

[0069] The supporting glass slide 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 slide. The zinc oxide-alkali-free glass fiber composite piezoelectric fiber was quickly placed on the supporting glass slide 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.

[0070] The protective layer PDT is made based on polydimethylsiloxane-dimethyl diethyl silicate-tin octoate, and the preparation method is as follows:

[0071] A certain mass ratio of polydimethylsiloxane: dimethyl diethyl silicate: tin octoate materials was used, the polydimethylsiloxane reagent was heated and stirred, and then dimethyl diethyl silicate and tin octoate were added. After standing to degas, it was placed in a blast drying oven for drying. The protective layer PDT reagent was mechanically stirred, and after vacuum treatment to remove bubbles, uniform glue and spin coating, the protective layer PDT reagent was evenly coated on one side of the flexible composite piezoelectric film layer, and placed in a drying oven for drying and standing to complete the preparation of the PDT protective layer.

[0072] The second electrode layer is transferred to the interior of the PDT protective layer by cooling laser induced graphene technology (CLIGS), 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;

[0073] 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;

[0074] The upper side of the second electrode layer and the lower side of the first electrode layer are adhered to the conductive wires by means of conductive metal glue, and are solidified by constant temperature drying;

[0075] The first electrode layer and the second electrode layer are made of 99.99% pure silver electrode.

[0076] The conductive metal material glue includes conductive silver paste and pure silver wire;

[0077] It should be noted that the present invention provides an embodiment, using cooled laser-induced graphene (CLIGS) technology as an example. The first and second electrode layers are deposited on a square polyimide film (SPI) using the cooled laser-induced graphene technology by laser scanning. The graphene is then attached to a carrier glass sheet and heated at 80°C for 10 minutes. The SPI film measures 40 mm x 40 mm, and thicknesses of 0.06 mm, 0.08 mm, and 0.10 mm have been tested. The FSPI substrate is adhered beneath the first electrode layer, while a PDT protective layer is applied above the second electrode layer.

[0078] The flexible square polyimide substrate is adhered to the lower side of the first electrode layer, and placed in a drying oven to dry and let it stand to complete the substrate attachment of the flexible piezoelectric sensor. The flexible piezoelectric sensor attached to the substrate is completely encapsulated based on polyurethane tape and PDMS mold. After the encapsulation is completed, polarization is performed to obtain the final flexible piezoelectric sensor.

[0079] For the sake of convenience, based on the above content, the present invention provides a preparation process of a flexible piezoelectric sensor as follows:

[0080] 1. Preparation of PTB precursor solution: PVDF-TrFE powder (MW = 180000) and nano-barium titanate powder were dissolved in EDMF solution. The mixture was stirred magnetically at 90°C and 500 rpm for 8 hours. Ultrasonic treatment was repeated 3 times for 15 minutes to remove small bubbles in the precursor solution. A PTB precursor solution with a mass fraction of 15% was prepared.

[0081] 2. Preparation of Z-NGFF piezoelectric fibers: Dissolve nano-zinc oxide powder with a diameter of 50 nm in 95% isopropyl alcohol. After the nano-ZnO is completely dissolved, add GFF fibers with a size of 20 mm × 20 mm and magnetically stir at 90°C for 2 hours to mix thoroughly. Then, place the mixture in a drying oven at a constant temperature of 80°C and let it dry for 12 hours to obtain Z-NGFF piezoelectric fibers. The alkali-free glass fiber composite material (GFF) is made of 60% silica, 15% alumina, 15% calcium oxide, and 10% boron oxide to ensure that the fiber has good electrical insulation and mechanical strength.

[0082] 3. Fabrication of a flexible composite piezoelectric film layer (PTB@Z-NGFF): The loading glass slide was cleaned with a 70% ethanol solution and dried in a drying oven for 15 minutes. After drying, the PTB precursor solution was rotated on the loading glass slide (900 rpm, 20 seconds). The Z-NGFF piezoelectric fiber was then quickly placed on the glass slide so that it was completely covered with the PTB precursor solution. Finally, the entire structure was placed on a constant temperature hot plate and annealed at 90°C for 1 hour to obtain the PTB@Z-NGFF flexible composite piezoelectric film layer.

[0083] 4. Preparation of the PDT protective layer: Using a mass ratio of PDMS:DDS:TO = 1:0.2:0.1, the PDMS reagent (viscosity 60,000 mPa·s) was heated to 40°C and stirred for 1 hour. DDS and TO were then added. The mixture was allowed to stand for degassing and then dried in a forced air drying oven to complete the preparation. The PDT protective layer reagent was then mechanically stirred for 3 minutes and vacuum-treated to remove bubbles. The PDT protective layer reagent was evenly applied to one side of the sensor body using a spin coater set at 200 rpm for 30 seconds. The reagent was then placed in a drying oven at a constant temperature of 80°C and dried for 2 hours to complete the application above the second electrode layer arranged from bottom to top.

[0084] 5. Electrode fabrication: Transfer the electrode layer to the PDT protective layer and attach the electrodes to both ends of the PTB@Z-NGFF, and on the outer sides of the first and second electrode layers, respectively. Then, adhere the 49-silver electrode (99.99%) material to both ends of the flexible composite piezoelectric film layer, and use conductive metal glue to adhere wires on the outer sides of the first and second electrode layers, respectively. Lead out the wires and dry them at a constant temperature. The size of the first and second electrode layers is 20 mm × 20 mm.

[0085] 6. Attaching 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 sensor substrate attachment;

[0086] 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 and the thickness within 6mm. The FPZG piezoelectric film is polarized (voltage: 1.5kV, temperature: 25℃, polarization time: 6 hours).

[0087] After polarization treatment, the piezoelectric constant in some directions of FPZG will become 0, and its piezoelectric equation is:

[0088]

[0089] 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. 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, so d 32 can be ignored, and the simplified piezoelectric equation is:

[0090]

[0091] 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;

[0092] The output charge Q of the piezoelectric film of a flexible piezoelectric sensor with a size of l×w×t is:

[0093]

[0094] Where, 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;

[0095] The pressure and voltage intensity response model of the flexible piezoelectric sensor is used to convert the force applied to the sensor into voltage intensity output. The specific model formula is:

[0096]

[0097] Where 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.

[0098] 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 the surface is smooth. 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 These are the 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.

[0099] The present invention also provides a signal detection method for a flexible piezoelectric sensor, comprising:

[0100] Step 100: attaching flexible piezoelectric sensors to the human body and the sheep;

[0101] Step 200: The flexible piezoelectric sensor acquires signal data generated at the test position, obtains the signal data through a processing module, and performs signal preprocessing based on an improved filtering method to obtain a data set of effective signals with a specific pattern;

[0102] Step 300: Send it to the backend via wireless transmission to achieve accurate recognition of different behaviors.

[0103] By sensing the movement of a specific part, the FPZG sensor generates a voltage signal, which is recorded by a data acquisition system to obtain sufficient data sets for subsequent parameter analysis. During movement, the periodic deformation of the detection part mechanically stretches the FPZG piezoelectric film, generating a corresponding electrical signal.

[0104] In step 100, flexible piezoelectric sensors are attached to the human body and the sheep, specifically:

[0105] If you want to measure the motion signal of sheep, you can use FPZG sensor for detection, specifically:

[0106] Select an appropriately sized FPZG sensor (45mm x 45mm) and ensure its shape and size are suitable for the sheep's body area (chest, abdomen). Place the FPZG sensor where it can effectively detect behavioral cues.

[0107] The FPZG sensor is placed on the sheep's neck. Placing the FPZG sensor on the sheep's chest allows for better adhesion, enabling the recording of deflection changes associated with respiratory movements. Placing the flexible piezoelectric sensor on the sheep's abdomen also allows for recording deflection changes. The abdomen is easier to secure the sensor to than the chest. Before placement, the wool between the sheep and the sensor attachment site must be removed.

[0108] The FPZG sensor is connected to the sensing circuit of the microcontroller and the WIFI module to realize wireless transmission of the acquired data.

[0109] By sensing the corresponding behavior of the sheep's body parts, the FPZG sensor generates a voltage signal, which is recorded by the data acquisition system. In particular, during breathing, the periodic deformation of the sheep's chest wall mechanically stretches 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 threshold was set to 2mV, and the data recording time was 10 minutes per complete set.

[0110] If you want to measure the motion signal of the human body, you can use the FPZG sensor for detection, specifically:

[0111] Select a FPZG sensor of appropriate size (20mm x 30mm) and ensure that its shape and size are suitable for the part of the human body where it will be applied (chest, neck, abdomen, elbow, etc.).

[0112] The FPZG sensor is placed on the part of the human body where behavioral signals can be effectively detected, and records the flexural changes caused by the behavior.

[0113] The FPZG sensor is connected to the sensing circuit of the microcontroller and the WiFi module to realize wireless transmission of the acquired data.

[0114] By sensing the movement of human body parts, the FPZG sensor generates a voltage signal, which is recorded by the data acquisition system. Specifically, during breathing, the periodic deformation of the sensing part mechanically stretches the FPZG piezoelectric film, generating a corresponding electrical signal. For the human body, a 50Hz sampling frequency, a 20ms sampling interval, a 5mV lower signal threshold, and a 10-minute data recording period are used for a complete set of data.

[0115] like Figure 8 As shown, in step 300, signal preprocessing is performed based on the improved filtering method, specifically:

[0116] During the collection, transmission and subsequent signal acquisition of signal data, various interference signals are often mixed in. Certain characteristic points of the signal may be masked by these interferences, thereby 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 all levels; then estimates each coefficient and calculates the threshold of the current coefficient; then estimates the optimal threshold and then performs threshold processing on the coefficients, and according to the calculated threshold, sets the coefficients less than the threshold to zero or reduces them; finally, the processed coefficients are reconstructed to obtain the denoised signal. The denoising operation is as follows:

[0117] Step 301: Collect the original noisy signal captured by the FPZG sensor and extract the characteristic signal from it. Taking into account the characteristics of the signal, based on the statistical properties and model of the signal, the IFM method can dynamically adjust the filter parameters according to the changes in the signal to achieve noise suppression.

[0118] Step 302: The original signal is discretely transformed, and approximation parameters and characteristic parameters are obtained using a low-pass algorithm and a high-pass algorithm, respectively. The two coefficient groups are sampled to obtain a post-processed approximation parameter sequence and a characteristic parameter sequence. Selecting the appropriate number of decomposition levels is a key step in the IFM method. As the number of decomposition levels increases, the difference between signal and noise becomes increasingly pronounced, further facilitating their separation. Based on the IFM method, the decomposition level is set to five.

[0119] Step 303: Define a threshold judgment function. Estimate each transformed feature parameter group and process it using a threshold function to suppress or remove noise components.

[0120] 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 coefficients smaller than the threshold to zero, and retains the other coefficients. The soft threshold function sets the coefficients with an absolute value smaller than the threshold to zero and shrinks the coefficients with an absolute value greater than the threshold. When using the IFM method for noise reduction, the decomposition layer is selected as 5 layers, and reconstruction starts from the second layer. The improved filter threshold is as follows:

[0121]

[0122] Where, is the number of decomposition levels, is the standard deviation of the noise, and its estimated value is

[0123] , IMAD is the median value of all high-frequency inherent coefficient amplitudes, and N is the signal length;

[0124] Step 304: Reconstruct the signal, starting from the second layer. Recombining the processed approximation parameters and characteristic parameters to restore the denoised signal. Upsampling the sampled approximation parameter sequence and characteristic parameter group to restore them to the same length as the original signal. Then, using the synthesis function corresponding to the decomposition, adding the upsampled approximation parameters and characteristic parameters to obtain the final valid denoised signal.

[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] Where, is the improved filtering threshold set, represents the symbolic function, is the original coefficient, 、 It is an adjustment factor. By changing the value of the factor, the threshold function also changes accordingly, thereby compensating for the problem of breakpoints under the hard threshold and improving the deviation problem of the soft threshold function in the part greater than the threshold.

[0127] 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.

[0128] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A flexible piezoelectric sensor, characterized in that: From top to bottom, it includes: protective layer PDT, second electrode layer, flexible composite piezoelectric film layer, first electrode layer, flexible square polyimide substrate and 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 glue; 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 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; 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, stirred continuously at a constant temperature, and residual small bubbles in the precursor solution were removed by ultrasonic treatment to prepare a PTB precursor solution with a certain mass fraction. Dissolve nano zinc oxide powder in isopropyl alcohol, add alkali-free glass fiber after it is completely dissolved, and stir mechanically and automatically at high temperature to fully mix, then place in a drying oven to dry and stand to obtain zinc oxide-alkali-free glass fiber composite piezoelectric fiber; The supporting glass slide 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 slide. The zinc oxide-alkali-free glass fiber composite piezoelectric fiber was quickly placed on the supporting glass slide 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.

2. 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 was used, the polydimethylsiloxane reagent was heated and stirred, and then dimethyl diethyl silicate and tin octoate were added. After standing to degas, it was placed in a blast drying oven for drying. The protective layer PDT reagent was mechanically stirred, and after vacuum treatment to remove bubbles, uniform glue and spin coating, the protective layer PDT reagent was evenly coated on one side of the flexible composite piezoelectric film layer, and placed in a drying oven for drying and standing to complete the preparation of the PDT protective layer.

3. The flexible piezoelectric sensor according to claim 1, characterized in that: The second electrode layer is transferred to the interior 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 conductive wires 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.

4. 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 placed in a drying oven to dry and let it stand to complete the substrate attachment of the flexible piezoelectric sensor. The flexible piezoelectric sensor attached to the substrate is completely encapsulated based on polyurethane tape and PDMS mold. After the encapsulation is completed, polarization is performed to obtain the final flexible piezoelectric sensor.

5. 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: Where, 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 and voltage intensity response model of the flexible piezoelectric sensor is used to convert the force applied to the sensor into voltage intensity output. The specific model formula is: Where 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.

6. A signal detection method for a flexible piezoelectric sensor, characterized in that: The flexible piezoelectric sensor according to any one of claims 1 to 5, wherein the signal detection method comprises: Attaching flexible piezoelectric sensors to humans and sheep; Acquire signal data through the processing module, perform signal preprocessing based on the improved filtering method, and 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.

7. The method according to claim 6, characterized in that Attaching flexible piezoelectric sensors to human bodies and sheep, specifically: Select a flexible piezoelectric sensor of appropriate size and shape and attach it to the appropriate part of the object being measured. For sheep monitoring, select a 45mm×45mm flexible piezoelectric sensor and attach it to the sheep's body, including the horizontal position near 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 area. After attachment, return the sheep to the flock; For human body detection, a flexible piezoelectric sensor with a size of 20mm×30mm is selected and attached to the omohyoid muscle position of the neck, the position near the armpits on both sides of the chest, or the horizontal position below the abdomen near the navel.

8. The method according to claim 6, 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, and the original noisy signal is discretely transformed. The approximation parameters and characteristic parameters are obtained using a low-pass algorithm and a high-pass algorithm respectively. 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, starting from the second layer, recombining the processed approximation parameters and characteristic parameters to restore the denoised signal, up-sampling the sampled approximation parameter sequence and characteristic parameter group to restore them to the same length as the original signal, and then using the synthesis function corresponding to the decomposition, adding the up-sampled approximation parameters and characteristic parameters to obtain the final valid signal after denoising.

9. The method according to claim 8, 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: Where, is the number of decomposition levels, is the standard deviation of the noise, and its estimated value is , IMAD is the median value of all high-frequency inherent coefficient amplitudes, N is the signal length; the improved filtering threshold function is: Where, is the improved filtering threshold set, represents the symbolic function, is the original coefficient, 、 is the regulating factor.

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