Method for sensing underwater two-dimensional alternating current flow field by using tubular IPMC sensor

Abstract

The invention discloses a method for sensing an underwater two-dimensional alternating current flow field by using a tubular IPMC sensor. According to the method, a Nafion tube is used for machining a tubular IPMC sensor, the tubular IPMC sensor is subjected to a characterization experiment of underwater one-dimensional alternating current flow field perception, and the tubular IPMC sensor is used for underwater two-dimensional alternating current flow field perception. The method solves the problem that an existing IPMC alternating current flow velocity sensor lacks an effective algorithm and a model, and is of great significance to promotion of application of intelligent flexible materials and development of an underwater sensing technology.

Description

Technical Field

[0001] The present invention relates to the field of sensor sensing technology, and in particular to a method for sensing an underwater two-dimensional alternating current flow field by using a tubular IPMC sensor. Background Art

[0002] IPMC (Ionic Polymer Metal Composites) is a representative ionic EAP (Electro Active Polymer, EAP) smart material. The structure of IPMC is composed of "electrode-ion exchange membrane-electrode". The ion exchange membrane in the middle layer is usually Nafion membrane from DuPont, USA, which contains hydrophobic polymer chains, mobile cations and a certain amount of solvent. The precious metal electrodes on both sides of the ion exchange membrane (common ones are palladium, platinum, gold, etc.) are mostly prepared by surface plating process. When the IPMC material is bent and deformed by external force, the cations and water molecules in the membrane combine to form freely movable hydrated cations. These hydrated cations will migrate according to the bending direction, generating stress gradients, which will cause the charge distribution inside the membrane to change. Inside the membrane, the low-density area expands due to excess positive charge and reduced negative charge, while the high-density area shrinks due to the accumulation of negative charge and insufficient positive charge. This uneven charge distribution leads to charge polarization, forming a potential difference on both sides of the electrode. Due to the presence of metal electrodes, electrical signals can be detected. In addition, the change in potential difference can be used to detect and measure the magnitude or direction of external force. By monitoring the change in potential difference on both sides of the electrode, the external force information applied to the IPMC can be inferred, making IPMC smart materials have application potential in sensors.

[0003] IPMC sensors have the characteristics of soft texture, fast response, simple structure, high sensitivity, strong plasticity, and the ability to operate in complex underwater environments. They can be used to sense and measure underwater flow velocity, and therefore have great application potential in underwater robots, energy collection, environmental monitoring, marine resource development and other fields.

[0004] However, the existing methods of using IPMC sensors for flow velocity sensing are mostly based on the design of flow velocity sensors based on sheet IPMC materials. Therefore, the sensing ability of a single sensor is one-dimensional. Even if it is assembled into a sensor device with multi-dimensional sensing ability, it is difficult to simultaneously meet the requirements of miniaturization, compact structure, high stability, and simple calculation algorithm.

[0005] Flow velocity sensing requires, on the one hand, the sensor device to convert the measured physical quantity into a measurable electrical signal, and on the other hand, it also requires the design and derivation of algorithms and models that match the physical characteristics of the sensor, and the provision of calculation formulas to quantitatively describe the corresponding relationship between the sensor output and input. Currently, many researchers have done a lot of work on the design of the sensor device itself, but there is relatively little work on the related matching algorithms and models.

[0006] In addition, the properties of IPMC materials themselves make IPMC sensors naturally sensitive to external excitation responses. Changing excitation will lead to changing sensor signal outputs, which can fully utilize the advantages of IPMC sensors, but on the other hand, it also makes sensor modeling more complicated, bringing some algorithmic challenges and difficulties. Summary of the invention

[0007] To solve the above problems, the present invention provides a method for sensing an underwater two-dimensional AC flow field using a tubular IPMC sensor, comprising the following steps: Step 1: Use Nafion tube to process tubular IPMC, divide its outer surface electrode into four sub-electrodes along the axial direction, and use the inner surface electrode as a common ground line; the four sub-electrodes are sub-electrode p1, sub-electrode p2, sub-electrode p3, and sub-electrode p4 in the radial direction, wherein sub-electrode p1 and sub-electrode p3, and sub-electrode p2 and sub-electrode p4 are symmetrical along the axis; Step 2: Convert the current output of each sub-electrode into a measurable bipolar voltage signal, namely u1(t), u2(t), u3(t), and u4(t), where t represents the time variable; Step 3: Conduct a characterization experiment of underwater 2D AC flow field perception on the tubular IPMC sensor: calibrate the sensing signals u1(t,v,n), u2(t,v,n), u3(t,v,n), and u4(t,v,n) of each sub-electrode facing the oscillation direction of the water wave at different oscillation frequencies, where v represents the flow velocity, and the positive integer n represents the number of the sub-electrode pn facing the oscillation direction of the water wave, and the value range of n is 1 to 4; Step 4: For each sub-electrode facing the oscillation direction of the water wave, first calculate the frequency response of the output signal of the sub-electrode at different oscillation frequencies, and then use the least squares method to fit a transfer function Hn(s) corresponding to the sub-electrode to describe the corresponding relationship between the output signal of this path and the change of the AC flow rate; Step 5: When using the tubular IPMC sensor for underwater two-dimensional AC flow field perception, first obtain the one-dimensional AC flow velocity vx(t) in the x direction through u1(t), u3(t) and transfer function Hn(s), and obtain the one-dimensional AC flow velocity vy(t) in the y direction through u2(t), u4(t) and transfer function Hn(s) to realize two-dimensional AC flow field perception.

[0008] Further, in step 1, the method of processing tubular IPMC using Nafion tube is: Step 1.1: Use Nafion tube to process into tubular IPMC; Step 1.2: Divide the outer surface electrode into four mutually insulated equal parts along the axial direction of the tubular IPMC to form four sub-electrodes, and an insulating isolation zone is provided between adjacent sub-electrodes. The outer surface metal deposition at the isolation zone position is removed to achieve an insulating effect; Step 1.3: Connect a wire to the entire inner surface electrode as a common ground wire, and connect each of the four sub-electrodes with a wire as a signal wire. Each signal wire and the common ground wire constitute a sensing signal output of the sensor; Step 1.4: The tubular IPMC is encapsulated in a film capsule and placed in a water bath for a predetermined period of time and then taken out, and the tubular IPMC has moisture inside; Step 1.5: Use gelatin resin material to perform biomimetic encapsulation of tubular IPMC.

[0009] Furthermore, after step 1.4, a thin film coating is formed on the surface of the tubular IPMC, and the thickness of the thin film coating is between 20 microns and 50 microns.

[0010] Furthermore, in step three, a characterization experiment of underwater 1D AC flow field perception is conducted on the tubular IPMC sensor, specifically, an underwater vibrating sphere is placed in a static water environment, the vibration direction of which is parallel to the water surface, the tubular IPMC sensor is placed below the water surface, its axis is perpendicular to the water surface, the midpoint of its axis is at the same depth as the center of the sphere, the plane formed by its axis and the vibration direction of the sphere intersects with the sub-electrode surface facing the water wave oscillation direction at the axial midline of the sub-electrode, and the plane also intersects with the sub-electrode surface facing away from the water wave oscillation direction at the axial midline of the sub-electrode; the vibrating sphere generates a dipole source and generates a potential flow in the water, thereby calculating the water flow velocity function v(t)=Asin(2πft)a at the location of the tubular IPMC sensor. 3 / r 3 , A is the vibration amplitude, and f is the vibration frequency.

[0011] Furthermore, the corresponding relationship between the output signals of each sub-electrode and the changes in the AC flow rate is un(s)=Hn(s)v(s), where s represents the Laplace operator; v(s) is obtained by Laplace transforming the water flow velocity function v(t); un(s) is obtained by Laplace transforming the sub-electrode output signal un(t); and n is the sub-electrode number.

[0012] Furthermore, the diameter a of the underwater vibrating sphere is 2 cm, and the center of the sphere is 10 cm away from the water surface; the axis of the tubular IPMC sensor is 10 cm away from the center of the sphere r.

[0013] Furthermore, in step three, the duration of the collected sensor signal is at least 10 seconds, and the sampling frequency is at least 1000 Hz.

[0014] Furthermore, in step four, the frequency response includes the ratio of the output and input amplitudes at different oscillation frequencies and the output and input phase difference, the output refers to the output signal of the sub-electrode, and the input refers to the flow velocity at the location of the sensor, and the output and input in the time domain are fast Fourier transformed to obtain their respective amplitudes and phases.

[0015] Furthermore, in step five, the axis of the tubular IPMC sensor is perpendicular to the plane formed by the x-direction and the y-direction, and the axis and the x-direction form a first plane, which intersects with the surfaces of the sub-electrode p1 and the sub-electrode p3 at their axial midline; the axis and the y-direction form a second plane, which intersects with the surfaces of the sub-electrode p2 and the sub-electrode p4 at their axial midline.

[0016] Furthermore, in step 5, the specific method for calculating vx(t) is as follows: the inverse transfer function H1_inv(s)=1 / H1(s) of the transfer function H1(s) of the sub-electrode p1 is calculated, and then u1(t) is input into the inverse transfer function H1_inv(s) to obtain the one-dimensional AC flow velocity vx1(t) in the x direction. Similarly, the one-dimensional AC flow velocity vx2(t) in the x direction can be obtained through u2(t), and the average value of vx1(t) and vx2(t) is taken as vx(t); The specific method for calculating vy(t) is: calculate the inverse transfer function H2_inv(s) = 1 / H2(s) of the transfer function H2(s) of the sub-electrode p2, and then input u2(t) into the inverse transfer function H2_inv(s) to obtain the one-dimensional AC flow velocity vy2(t) in the y direction. Similarly, the one-dimensional AC flow velocity vy4(t) in the y direction can be obtained through u4(t), and the average value of vy2(t) and vy4(t) is taken as vy(t).

[0017] The beneficial effects of the present invention are: The present invention overcomes the shortcomings of the prior art and utilizes a tubular symmetrical structure to realize the direct two-dimensional isotropic sensing capability of a single IPMC sensor. It quantitatively calibrates and describes the AC flow velocity sensing characteristics of the sensor from the frequency domain dimension, establishes a transfer function model of the sensor, and solves the problem of the lack of effective algorithms and models in the existing IPMC AC flow velocity sensors. This is of great significance for promoting the application of intelligent flexible materials and the development of underwater sensing technology. DETAILED DESCRIPTION

[0018] Before introducing the present invention, a method for preparing an underwater two-dimensional sensing IPMC sensor is first described.

[0019] The preparation method of the underwater two-dimensional sensing IPMC sensor includes the following steps: Step 1.1: Select a Nafion tube and process it into a tubular IPMC.

[0020] The specific processing steps include Step 1~Step 5: Step 1. In the pretreatment stage: Boil the Perma Pure Nafion drying tube (model: TT-110) in 2wt% dilute hydrochloric acid for 1 hour, and then heat it in deionized water for 1 hour to remove impurities and allow the Nafion tube to bend freely.

[0021] Step 2. In the ion adsorption stage: immerse the Nafion tube in a solution of tetraammineplatinum chloride (molecular formula: [Pt(NH3)4]Cl2), and the platinum ions in the platinum complex solution are exchanged with the cations in the Nafion.

[0022] Step 3. In the first chemical plating stage: clean the Nafion tube with deionized water, put it into a 5 wt% sodium borohydride (molecular formula: NaBH4) solution, use a heated magnetic stirrer to increase the temperature of the solution, and add 1 ml of sodium borohydride solution every 15 minutes. Through the reduction reaction, platinum electrodes are formed on the inner and outer surfaces of the Nafion tube.

[0023] Step 4. In the secondary chemical plating stage: In order to precipitate more platinum ions, repeat the acid treatment from Step 1 to Step 3 to the reduction reaction step to complete the secondary deposition of platinum and enhance the conductivity of the platinum electrode.

[0024] Step 5. In the replacement reaction stage: After the reduction reaction is completed, the Nafion tube is cleaned and then placed in dilute hydrochloric acid and boiled in a constant temperature water bath to allow the cations in the Nafion tube to exchange with the hydrogen ions in the hydrochloric acid.

[0025] It should be noted that the electrodes at both ends of the cross section of the tubular IPMC need to be removed to prevent the inner and outer surface electrodes from short-circuiting with each other.

[0026] Step 1.2: Make the sub-electrodes on the outer surface. The specific method is: remove the surface electrode to make an isolation zone, divide the outer electrode into four mutually insulated equal parts along the axial direction of the tubular IPMC, and form four uniform and symmetrical sub-electrodes on the outer surface. It should be noted that, while ensuring sufficient insulation between adjacent sub-electrodes, the width of the isolation zone should be as thin as possible, and the depth of the isolation zone should be as shallow as possible, so as to minimize the impact of this step on the overall material properties and mechanical properties of the tubular IPMC.

[0027] When manufacturing sub-electrodes, a mold can be made using a 3D printing method, and the tubular IPMC can be placed and fixed in the mold. The mold acts as a mask, covering the sub-electrode part while exposing the isolation zone part to be processed, thereby ensuring that the division of the sub-electrode is uniform and symmetrical.

[0028] Step 1.3: Make a common ground wire. Lead a wire to connect the entire inner surface electrode as a common ground wire, lead 4 wires to connect the 4 sub-electrodes on the outer surface as 4 signal wires, each signal line and the common ground wire constitute a sensor signal output of the sensor; in this step, the connection method between the wire and the electrode can be welding or bonding, or other methods that can ensure long-term good conductivity.

[0029] The four signal lines of the sub-electrodes on the outer surface can also be combined in pairs to form multi-channel sensing signal outputs.

[0030] Step 1.4: Film capsule packaging. The tubular IPMC connected with the wires is encapsulated with a polymer film capsule by using a vacuum physical vapor deposition method, and then placed in a high temperature (the high temperature is generally 60-80 degrees Celsius) water bath for a period of time and then taken out to lock sufficient water molecules inside the tubular IPMC encapsulated by the film capsule. The polymer material used for capsule packaging can form a thin film coating on the surface of the tubular IPMC through the vacuum physical vapor deposition process.

[0031] After depositing the thin film, the temperature and duration of the water bath are determined based on the thickness of the film. The thicker the film, the higher the water bath temperature and the longer the immersion time required.

[0032] The thickness of the thin film coating is between 20 microns and 50 microns, which can ensure that the coating has extremely low permeability to water molecules at room temperature, and the permeability of the coating to water molecules will be greatly improved in a high-temperature water bath. The polymer material includes but is not limited to Parylene.

[0033] In this embodiment, the film thickness is 25 microns, the temperature of the high-temperature water bath is 80 degrees Celsius, and it is taken out after immersion for 48 hours. Changing the thickness of the film capsule packaging, the temperature of the high-temperature water bath, and the length of the immersion time will directly change the number of water molecules that enter the tubular IPMC through osmosis, thereby affecting the sensing characteristics of the tubular IPMC.

[0034] Step 1.5: Bionic packaging. The above-processed tubular IPMC is subjected to bionic packaging of the colloidal resin material by injection molding, which plays a role in amplifying water flow excitation. The mold is made by 3D printing or machining, and the tubular IPMC after step 4 is placed and fixed in the center of the mold; the colloidal resin material used for bionic packaging can wrap the tubular IPMC and fill the space inside the tube through the injection molding process, forming the packaging shape of the bionic bullet shell as a whole, and the axis of the packaging shell coincides with the axis of the tubular IPMC, and the main cross-sectional radius is larger than the outer radius of the tubular IPMC. Preferably, the difference between the two radii is about 1-3 mm. In this embodiment, the main cross-sectional radius is about two millimeters larger than the outer radius of the tubular IPMC. The colloidal resin material includes but is not limited to polydimethylsiloxane (PDMS).

[0035] Preferably, the method further comprises step 1.6: using a 3D printing method to manufacture a base of the processed tubular IPMC, wherein the axial direction of the tubular IPMC is perpendicular to the plane of the base. The shape of the base is not limited, as long as it can play a fixing role.

[0036] The method of the present invention is further described below.

[0037] Step 1: According to the aforementioned method, a tubular IPMC is processed using a Nafion tube, and its outer surface electrode is divided into four sub-electrodes that are insulated from each other and orthogonally symmetrically distributed along the axial direction, and form four sensing signal outputs with the inner surface electrode respectively. The inner surface electrode serves as a common ground wire, and the four sub-electrodes are respectively sub-electrode p1, sub-electrode p2, sub-electrode p3, and sub-electrode p4 along the radial direction, wherein sub-electrode p1 and sub-electrode p3, sub-electrode p2 and sub-electrode p4 are symmetrical along the axis, and sub-electrode p1 is adjacent to sub-electrode p2 and sub-electrode p4 respectively.

[0038] Step 2: Use a signal conditioning circuit based on photoelectric coupling and a signal amplification circuit based on an operational amplifier to convert the current output of each sensing signal into a measurable bipolar voltage signal u1(t), u2(t), u3(t), and u4(t), which correspond to sub-electrode p1, sub-electrode p2, sub-electrode p3, and sub-electrode p4, respectively. The t in the voltage signal represents the time variable.

[0039] The signal conditioning circuit and the signal amplification circuit adopt the existing technology. The low-pass cut-off frequency of the RC low-pass filter circuit contained therein is set to 100 Hz, and the output range of the bipolar voltage signal is between positive and negative 5 volts.

[0040] Step 3: Conduct a characterization experiment on the underwater 2D AC flow field perception of the tubular IPMC sensor: calibrate the sensing signals u1(t,v,n), u2(t,v,n), u3(t,v,n), and u4(t,v,n) of each sub-electrode facing the direction of water wave oscillation at different oscillation frequencies, where v represents the flow velocity, and the positive integer n represents the number of the sub-electrode pn facing the direction of water wave oscillation, and the value of n is 1, 2, 3, or 4.

[0041] In this step, the means of achieving water flow oscillation is: placing an underwater vibrating sphere in a static water environment, the vibration direction is parallel to the water surface, the sphere diameter a is 2 cm, the center of the sphere is 10 cm away from the water surface, the sphere is driven by a resonator to vibrate and generate oscillating water waves, and the vibration amplitude A and frequency f can be adjusted; the tubular IPMC sensor is placed below the water surface, its axis is perpendicular to the water surface, the distance r from the center of the sphere is 10 cm, the midpoint of its axis is maintained at the same depth as the center of the sphere, the plane formed by its axis and the vibration direction of the sphere intersects with the sub-electrode surface facing the water wave oscillation direction at the axial midline of the sub-electrode, and the plane also intersects with the sub-electrode surface facing the water wave oscillation direction at the axial midline of the sub-electrode; the vibrating sphere generates a dipole source and generates a potential flow in the water, thereby calculating the flow velocity v(t)=Asin(2πft)a at the sensor location 3 / r 3 , where the true value of the vibration amplitude A is obtained by the laser displacement sensor.

[0042] In this step, the sensing signal needs to be collected after the experimental environment reaches a steady state. The signal duration is at least 10 seconds and the sampling frequency is above 1000 Hz.

[0043] Step 4: Based on the data in the above characterization experiment, for the case where each sub-electrode is facing the direction of water wave oscillation, first calculate the frequency response of the output signal of the sub-electrode at different oscillation frequencies, and then use the least squares method to fit a transfer function Hn(s) corresponding to the sub-electrode, which is used to describe the corresponding relationship un(s)=Hn(s)v(s) of the output signal changing with the AC flow rate, where s represents the Laplace operator, v(s) is obtained by Laplace transforming the water flow velocity function v(t), and un(s) is obtained by Laplace transforming the sub-electrode output signal un(t).

[0044] The frequency response includes the ratio of the output and input amplitudes at different oscillation frequencies and the output and input phase difference. The output refers to the output signal of the sub-electrode, and the input is the flow velocity at the location of the sensor. Fast Fourier transform is performed on the output and input in the time domain to obtain their respective amplitudes and phases.

[0045] Step 5: When using the tubular IPMC sensor to sense the underwater two-dimensional AC flow field, first obtain the one-dimensional AC flow velocity vx(t) in the x direction through u1(t), u3(t) and the transfer function Hn(s), and obtain the one-dimensional AC flow velocity vy(t) in the y direction through u2(t), u4(t) and the transfer function Hn(s), so as to realize the two-dimensional AC flow field sensing. The axis of the tubular IPMC sensor is perpendicular to the plane formed by the x direction and the y direction, and the plane formed by the axis and the x direction intersects with the surface of the sub-electrode p1 and the sub-electrode p3 at the midline of the axial direction, and the plane formed by the axis and the y direction intersects with the surface of the sub-electrode p2 and the sub-electrode p4 at the midline of the axial direction.

[0046] The specific method for calculating vx(t) is: calculate the inverse transfer function H1_inv(s)=1 / H1(s) of the transfer function H1(s) of the sub-electrode p1, and then input the sensing signal u1(t) of the sub-electrode p1 into the inverse transfer function H1_inv(s) to obtain the one-dimensional AC flow velocity vx1(t) in the x direction. Similarly, the one-dimensional AC flow velocity vx2(t) in the x direction can be obtained through u3(t), and the average value of vx1(t) and vx2(t) is taken as vx(t).

[0047] The specific method for calculating vy(t) is: calculate the inverse transfer function H2_inv(s) = 1 / H2(s) of the transfer function H2(s) of the sub-electrode p2, and then input u2(t) into the inverse transfer function H2_inv(s) to obtain the one-dimensional AC flow velocity vy2(t) in the y direction. Similarly, the one-dimensional AC flow velocity vy4(t) in the y direction can be obtained through u4(t), and the average value of vy2(t) and vy4(t) is taken as vy(t).

Claims

1. A method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor, characterized in that: The method comprises the following steps: Step 1: Use Nafion tube to process tubular IPMC, divide its outer surface electrode into four sub-electrodes along the axial direction, and use the inner surface electrode as a common ground line; the four sub-electrodes are sub-electrode p1, sub-electrode p2, sub-electrode p3, and sub-electrode p4 in the radial direction, wherein sub-electrode p1 and sub-electrode p3, and sub-electrode p2 and sub-electrode p4 are symmetrical along the axis; Step 2: Convert the current output of each sub-electrode into a measurable bipolar voltage signal, namely u1(t), u2(t), u3(t), and u4(t), where t represents the time variable; Step 3: Conduct a characterization experiment of underwater 3D DC flow field perception on the tubular IPMC sensor: calibrate the sensing signals u1(t,v,n), u2(t,v,n), u3(t,v,n), and u4(t,v,n) of each sub-electrode facing the oscillation direction of the water wave at different oscillation frequencies, where v represents the flow velocity, and the positive integer n represents the number of the sub-electrode pn facing the oscillation direction of the water wave, and the value range of n is 1~4; Step 4: For each sub-electrode facing the oscillation direction of the water wave, first calculate the frequency response of the output signal of the sub-electrode at different oscillation frequencies, and then use the least squares method to fit a transfer function Hn(s) corresponding to the sub-electrode to describe the corresponding relationship between the output signal of this path and the change of the AC flow rate; Step 5: When using the tubular IPMC sensor for underwater two-dimensional AC flow field perception, first obtain the one-dimensional AC flow velocity vx(t) in the x direction through u1(t), u3(t) and transfer function Hn(s), and obtain the one-dimensional AC flow velocity vy(t) in the y direction through u2(t), u4(t) and transfer function Hn(s) to realize two-dimensional AC flow field perception.

2. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 1, characterized in that: In step 1, the method of processing tubular IPMC using Nafion tube is as follows: Step 1.1: Use Nafion tube to process into tubular IPMC; Step 1.2: Divide the outer surface electrode into four mutually insulated equal parts along the axial direction of the tubular IPMC to form four sub-electrodes, and an insulating isolation zone is provided between adjacent sub-electrodes. The outer surface metal deposition at the isolation zone position is removed to achieve an insulating effect; Step 1.3: Connect a wire to the entire inner surface electrode as a common ground wire, and connect each of the four sub-electrodes with a wire as a signal wire. Each signal wire and the common ground wire constitute a sensing signal output of the sensor; Step 1.4: The tubular IPMC is encapsulated in a film capsule and placed in a water bath for a predetermined period of time and then taken out, and the tubular IPMC has moisture inside; Step 1.5: Use gelatin resin material to perform biomimetic encapsulation on the tubular IPMC.

3. The method for underwater two-dimensional AC flow field sensing using a tubular IPMC sensor according to claim 2 is characterized in that: After step 1.4, a thin film coating is formed on the surface of the tubular IPMC, and the thickness of the thin film coating is between 20 microns and 50 microns.

4. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 2 or 3, characterized in that: In the step 3, a characterization experiment of underwater 3D DC flow field perception is conducted on the tubular IPMC sensor, specifically, an underwater vibrating sphere is placed in a static water environment, the vibration direction is parallel to the water surface, the tubular IPMC sensor is placed below the water surface, its axis is perpendicular to the water surface, the midpoint of its axis is at the same depth as the center of the sphere, the plane formed by its axis and the vibration direction of the sphere intersects with the sub-electrode surface facing the water wave oscillation direction at the axial midline of the sub-electrode, and the plane also intersects with the sub-electrode surface facing away from the water wave oscillation direction at the axial midline of the sub-electrode; the vibrating sphere generates a dipole source and generates a potential flow in the water, thereby calculating the water flow velocity function v(t)=Asin(2πft)a at the location of the tubular IPMC sensor 3 / r 3 , A is the vibration amplitude, and f is the vibration frequency.

5. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 4, characterized in that: The corresponding relationship between the output signals of each sub-electrode and the changes in the AC flow rate is un(s)=Hn(s)v(s), where s represents the Laplace operator; v(s) is obtained by Laplace transforming the water flow velocity function v(t); un(s) is obtained by Laplace transforming the sub-electrode output signal un(t); and n is the sub-electrode number.

6. The method for underwater two-dimensional AC flow field sensing using a tubular IPMC sensor according to claim 4, characterized in that: The diameter a of the underwater vibrating sphere is 2 cm, and the center of the sphere is 10 cm away from the water surface; the axis of the tubular IPMC sensor is 10 cm away from the center of the sphere r.

7. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 2 or 3, characterized in that: In the step three, the duration of the collected sensor signal is at least 10 seconds, and the sampling frequency is at least 1000 Hz.

8. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 2 or 3, characterized in that: In step 4, the frequency response includes the ratio of the output and input amplitudes at different oscillation frequencies and the output and input phase difference. The output refers to the output signal of the sub-electrode, and the input refers to the flow velocity at the location of the sensor. Fast Fourier transform is performed on the output and input in the time domain to obtain their respective amplitudes and phases.

9. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 2 or 3, characterized in that: In step five, the axis of the tubular IPMC sensor is perpendicular to the plane formed by the x-direction and the y-direction. The axis and the x-direction form a first plane, which intersects the surfaces of the sub-electrode p1 and the sub-electrode p3 at their axial midline; the axis and the y-direction form a second plane, which intersects the surfaces of the sub-electrode p2 and the sub-electrode p4 at their axial midline.

10. The method for sensing underwater two-dimensional AC flow field using a tubular IPMC sensor according to claim 2 or 3, characterized in that: In step 5, the specific method for calculating vx(t) is as follows: calculate the inverse transfer function H1_inv(s)=1 / H1(s) of the transfer function H1(s) of the sub-electrode p1, and then input u1(t) into the inverse transfer function H1_inv(s) to obtain the one-dimensional AC flow velocity vx1(t) in the x direction. Similarly, the one-dimensional AC flow velocity vx2(t) in the x direction can be obtained through u2(t), and the average value of vx1(t) and vx2(t) is taken as vx(t); The specific method for calculating vy(t) is: calculate the inverse transfer function H2_inv(s) = 1 / H2(s) of the transfer function H2(s) of the sub-electrode p2, and then input u2(t) into the inverse transfer function H2_inv(s) to obtain the one-dimensional AC flow velocity vy2(t) in the y direction. Similarly, the one-dimensional AC flow velocity vy4(t) in the y direction can be obtained through u4(t), and the average value of vy2(t) and vy4(t) is taken as vy(t).