Method for poling of porous piezoelectret materials

Abstract

This invention provides a polarization method for a porous piezoelectric electret material. The porous piezoelectric electret material includes a porous polymer film, a first electrode, and a second electrode, with the porous polymer film disposed between the first and second electrodes. This invention identifies the minimum and maximum thickness pores among multiple pores in the porous piezoelectric electret material to be polarized. Based on the Poisson breakdown voltage curve obtained from the Townsend model, the gas pressure inside the pores is adjusted in order of decreasing or increasing thickness, and an optimal breakdown voltage is applied synchronously and continuously for polarization. This ensures that pores of different thicknesses can be polarized at the same voltage value, thereby avoiding the need to apply higher polarization voltages to polarize pores that deviate from the optimal breakdown thickness, and the risk of breaking down the porous polymer film due to applying higher polarization voltages.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric electret materials technology, and in particular to a polarization method for porous piezoelectric electret materials. Background Technology

[0002] Piezoelectric materials are materials that generate a potential difference between two electrodes when subjected to pressure, thereby enabling the conversion between mechanical and electrical signals. They have wide applications in the field of sensors. Space charge electret materials with non-uniform mechanical properties and non-uniform charge distribution exhibit the piezoelectric effect and are therefore called piezoelectric electrets.

[0003] Typically, piezoelectric electrets are nonpolar electret polymer porous membranes with a porous structure. The pores are filled with gas. By applying a strong electric field, the gas inside the pores undergoes breakdown discharge, causing the inner surface of the pores to carry positive and negative charges respectively, thus obtaining a non-uniform charge distribution.

[0004] Please see Figure 1-2 , Figure 1 This is a U-shaped Poisson breakdown voltage curve obtained from the Townsend model, showing the breakdown voltage relationship between different pd (the product of gas pressure and pore thickness) values ​​in air when polarizing gases with different compositions within the pores. The curve shows that there exists an optimal gas pressure-thickness product (pd) (the bottom region of the U-shaped curve), within which the required voltage to break down the gas within the pores is relatively low.

[0005] Therefore, under normal pressure, the optimal breakdown voltage of a porous polymer material corresponds to an optimal pore breakdown thickness. However, the pore thickness in actual piezoelectric electret materials is generally significantly different. This means that when polarizing the porous polymer material under normal pressure, it is often necessary to increase the breakdown voltage to achieve the breakdown of the deviated pores. Here, pore thickness refers to the pore thickness in the direction perpendicular to the electrode.

[0006] Figure 2Curve II in the figure shows the relationship between the polarization voltage applied to a porous piezoelectric electret material with a certain gas composition at atmospheric pressure and the corresponding polarization amount. The polarization of the porous piezoelectric electret material exhibits threshold behavior, meaning that when the gas composition and pressure within the pores are determined, there exists a minimum breakdown voltage and a maximum breakdown voltage corresponding to the polarization voltage required to break down the gas within a pore of a certain thickness. When the polarization voltage is lower than the minimum breakdown voltage, the gas in the pore cannot be broken down, and the polarization amount is 0. When the polarization voltage exceeds the minimum breakdown voltage, the pore is broken down. Under the applied polarization voltage V, the polarization amount is linearly related to the polarization voltage, i.e., where k is a material parameter, and V is greater than or equal to 1.

[0007] Therefore, when the polarization voltage V is reached, although the hole can be broken down, the polarization amount P is low, close to 0 (because it is equal to or close to 0). As the polarization voltage V continues to increase, the polarization amount P also increases linearly. While maintaining the applied polarization voltage V, the polarization amount P will continue to increase with the polarization voltage V.

[0008] However, when the applied polarization voltage V is greater than the maximum breakdown voltage corresponding to the sample, the porous polymer material will also be broken down at the same time as the pore, resulting in material damage and unusability.

[0009] Therefore, in the prior art, in order to polarize more of the gas in the pores and increase the polarization amount in the pores of polymer materials, the gas in the pores is generally broken down by increasing the voltage so that a certain amount of charge can be captured in the pores to achieve polarization.

[0010] However, increasing the polarization by increasing the voltage increases the complexity of the equipment and the cost of preparing piezoelectric electret materials. It also increases the risk of the piezoelectric electret materials being directly broken down and damaged. Summary of the Invention

[0011] Therefore, it is necessary to provide a method for polarizing porous piezoelectric electret materials using the optimal breakdown voltage, so as to reduce the risk of the piezoelectric electret materials being directly broken down and damaged.

[0012] This invention provides a polarization method for a porous piezoelectric electret material, the porous piezoelectric electret material comprising a porous polymer film, a first electrode, and a second electrode, wherein the porous polymer film is disposed between the first electrode and the second electrode, and the polarization method includes the following steps:

[0013] The thickness of multiple pores in the porous polymer film is confirmed along the direction from the first electrode to the second electrode to obtain the first thickness corresponding to the largest pore and the second thickness corresponding to the smallest pore;

[0014] The first pressure corresponding to the gas breaking down in the largest pore at the lowest breakdown voltage is determined based on the first thickness, and the second pressure corresponding to the gas breaking down in the smallest pore at the lowest breakdown voltage is determined based on the second thickness; wherein, the lowest breakdown voltage is the minimum voltage value in the U-shaped Poisson breakdown voltage curve obtained by breaking down a component gas in multiple pores of different thicknesses in the porous polymer film according to the Townsend model;

[0015] The polymer porous membrane is de-aired or inflated in a closed space so that the pressure in the largest pore reaches the first pressure; or the polymer porous membrane is inflated or de-aired in a closed space so that the pressure in the smallest pore reaches the second pressure.

[0016] The porous polymer film reaching the first pressure is polarized by applying the optimal breakdown voltage corresponding to the gas in the pores; or the porous polymer film reaching the second pressure is polarized by applying the optimal breakdown voltage corresponding to the gas in the pores; wherein the optimal breakdown voltage is the sum of the breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve at normal pressure and the lowest breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve at the first pressure or the second pressure, i.e.

[0017] The porous polymer film, which reaches the first pressure within the pores, is continuously polarized according to the optimal breakdown voltage, and the sealed space is gradually inflated to the second pressure so that all the pores within the porous polymer film located between the largest pore and the smallest pore are sequentially polarized; or the porous polymer film, which reaches the second pressure within the pores, is continuously polarized according to the optimal breakdown voltage, and the sealed space is gradually evacuated to the first pressure so that all the pores within the porous polymer film located between the smallest pore and the largest pore are sequentially polarized;

[0018] The optimal breakdown voltage is continuously applied to the porous polymer film, and the first or second pressure in the sealed space is gradually restored to normal pressure.

[0019] Stop applying the optimal breakdown voltage to the porous polymer film to complete the polarization of the porous piezoelectric electret material.

[0020] Furthermore, the formula for the Poisson breakdown voltage curve corresponding to the Townsend model is:

[0021] Where A and B are gas-related constants, and γ is the second ionization coefficient.

[0022] Furthermore, the U-shaped Poisson breakdown voltage curves of the gases with different components at normal pressure correspond to a minimum pore thickness at the lowest breakdown voltage. Therefore, the step of evacuating or inflating the polymer porous membrane in a sealed space to make the pressure in the largest pore reach the first pressure; or evacuating or inflating the polymer porous membrane in a sealed space to make the pressure in the smallest pore reach the second pressure includes:

[0023] When the first thickness is less than the minimum hole thickness, the sealed space will be inflated so that the pressure inside the maximum hole reaches the first pressure.

[0024] Alternatively, when the first thickness is less than the minimum hole thickness, the sealed space will be inflated so that the pressure inside the minimum hole reaches the second pressure.

[0025] Alternatively, when the second thickness is greater than the minimum hole thickness, the sealed space will be evacuated so that the pressure inside the minimum hole reaches the second pressure.

[0026] Alternatively, when the second thickness is greater than the minimum hole thickness, the sealed space will be evacuated so that the pressure inside the maximum hole reaches the first pressure.

[0027] Alternatively, when the first thickness is greater than the minimum hole thickness and the second thickness is less than the minimum hole thickness, the sealed space will be evacuated so that the pressure inside the maximum hole reaches the first pressure.

[0028] Alternatively, when the first thickness is greater than the minimum hole thickness and the second thickness is less than the minimum hole thickness, the sealed space will be inflated so that the pressure inside the minimum hole reaches the second pressure.

[0029] Furthermore, the hole is a closed hole, wherein the hole can be regular or irregular, and the thickness of the hole is between these two types.

[0030] Furthermore, the hole is an open hole, wherein the thickness of the hole is between [a certain value].

[0031] Furthermore, the porous polymer film may be, but is not limited to, made of one or more of PTFE, PP, PCTEF, PVDF, E-TFE, Teflon AF, FEP, PFA, P(VDF-TRFE), PI, PET, PE, COC, and PDMS.

[0032] Furthermore, depending on the composition of the gas within the cavity, the optimal breakdown voltage during polarization is between 100V and 20KV, and the pressure within the cavity is between these values.

[0033] Furthermore, when the gas inside the cavity is air, the minimum voltage that breaks down the air inside the cavity under normal pressure is 327 volts, and the optimal cavity thickness is [value missing].

[0034] Compared to existing technologies, the present invention offers the following advantages: By identifying the minimum and maximum thickness pores among the multiple pores in the porous piezoelectric electret material to be polarized, and by adjusting the internal air pressure of the multiple pores in order of their thickness from largest to smallest or smallest to largest according to the Poisson breakdown voltage curve obtained from the Townsend model, the optimal breakdown voltage is applied synchronously and continuously to polarize the pores. This ensures that multiple pores of different thicknesses can be polarized at the same voltage value, thereby avoiding the phenomenon that higher polarization voltages are required to polarize other pores that deviate from the optimal pore breakdown thickness, as well as the risk of breaking down the porous polymer film due to applying higher polarization voltages. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the Poisson breakdown voltage curve obtained based on the Townsend model.

[0036] Figure 2 This is a schematic diagram showing the relationship between polarization voltage and polarization amount under normal pressure and regulated pressure.

[0037] Figure 3 This is a flowchart illustrating a specific implementation of the polarization method of the present invention.

[0038] Figure 4 This is a schematic diagram of the device for polarizing porous piezoelectric electret materials according to the present invention.

[0039] Figure 5 This is a schematic diagram of a scanning electron microscope image of a porous polymer film.

[0040] Figure 6 This is a schematic diagram of a porous polymer film with regular open pores. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. It is understood that the accompanying drawings are provided for reference and illustration only, and are not intended to limit the present invention. The connection relationships shown in the accompanying drawings are only for clear description and do not limit the connection method.

[0042] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component, or there may be an intervening component. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be noted that, unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral connection; as a mechanical connection or an electrical connection; or as a connection within two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0043] It should also be noted that in the description of this invention, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0044] Please see Figure 1-4 This invention provides a polarization method for a porous piezoelectric electret material 10, wherein the porous piezoelectric electret material 10 includes a porous polymer film 11, a first electrode 12, and a second electrode 13, wherein the porous polymer film 11 is disposed between the first electrode 12 and the second electrode 13, and the polarization method includes the following steps:

[0045] The thickness of multiple pores in the porous polymer film 11 is confirmed along the direction from the first electrode 12 to the second electrode 13 to obtain the first thickness corresponding to the largest pore and the second thickness corresponding to the smallest pore (S10).

[0046] The first pressure corresponding to the gas breaking down in the largest pore at the lowest breakdown voltage is determined based on the first thickness, and the second pressure corresponding to the gas breaking down in the smallest pore at the lowest breakdown voltage is determined based on the second thickness; wherein, the lowest breakdown voltage is the minimum voltage value in the U-shaped Poisson breakdown voltage curve obtained by breaking down a component gas in multiple pores of different thicknesses in the porous polymer film 11 according to the Townsend model (S20).

[0047] The polymer porous membrane 11 is de-aired or inflated in a sealed space 25 so that the pressure in the largest pore reaches the first pressure; or the polymer porous membrane 11 is inflated or de-aired in a sealed space 25 so that the pressure in the smallest pore reaches the second pressure (S30).

[0048] The porous polymer film 11 reaching the first pressure is polarized by applying the optimal breakdown voltage corresponding to the gas in the pores; or the porous polymer film 11 reaching the second pressure is polarized by applying the optimal breakdown voltage corresponding to the gas in the pores; wherein the optimal breakdown voltage is the sum of the breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve at normal pressure and the lowest breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve at the first pressure or the second pressure, i.e. (S40).

[0049] The porous polymer film 11, which reaches the first pressure within the pores, is continuously polarized according to the optimal breakdown voltage, and the sealed space 25 is gradually inflated to the second pressure so that all the pores within the porous polymer film 11 located between the largest pore and the smallest pore are sequentially polarized; or the porous polymer film 11, which reaches the second pressure within the pores, is continuously polarized according to the optimal breakdown voltage, and the sealed space 25 is gradually evacuated to the first pressure so that all the pores within the porous polymer film 11 located between the smallest pore and the largest pore are sequentially polarized (S50).

[0050] The optimal breakdown voltage is continuously applied to the porous polymer film 11 and the first or second pressure in the sealed space 25 is gradually restored to normal pressure (S60).

[0051] Stop applying the optimal breakdown voltage to the porous polymer film 11 to complete the polarization of the porous piezoelectric electret material 10 (S70).

[0052] Furthermore, under normal pressure, since the U-shaped Poisson breakdown voltage curves of the gases of different components correspond to a minimum pore thickness corresponding to the lowest breakdown voltage, the step of evacuating or inflating the polymer porous membrane in a sealed space to make the pressure in the largest pore reach the first pressure; or evacuating or inflating the polymer porous membrane in a sealed space to make the pressure in the smallest pore reach the second pressure (S30) includes:

[0053] When the first thickness is less than the minimum hole thickness, the sealed space will be inflated so that the pressure inside the maximum hole reaches the first pressure.

[0054] Alternatively, when the first thickness is less than the minimum hole thickness, the sealed space will be inflated so that the pressure inside the minimum hole reaches the second pressure.

[0055] Alternatively, when the second thickness is greater than the minimum hole thickness, the sealed space will be evacuated so that the pressure inside the minimum hole reaches the second pressure.

[0056] Alternatively, when the second thickness is greater than the minimum hole thickness, the sealed space will be evacuated so that the pressure inside the maximum hole reaches the first pressure.

[0057] Alternatively, when the first thickness is greater than the minimum hole thickness and the second thickness is less than the minimum hole thickness, the sealed space will be evacuated so that the pressure inside the maximum hole reaches the first pressure.

[0058] Alternatively, when the first thickness is greater than the minimum hole thickness and the second thickness is less than the minimum hole thickness, the sealed space will be inflated so that the pressure inside the minimum hole reaches the second pressure.

[0059] In other words, when the porous polymer film has multiple pores with different thickness values, the thickness distribution of all the pores in the porous polymer film can be categorized into the following three cases:

[0060] The first scenario is that the thickness of some of the holes is greater than the minimum hole thickness, meaning that the thickness of the portion of the holes is located to the right of the minimum hole thickness in the U-shaped Poisson breakdown voltage curve; and the thickness of some of the holes is less than the minimum hole thickness, meaning that the thickness of the portion of the holes is located to the left of the minimum hole thickness in the U-shaped Poisson breakdown voltage curve.

[0061] The second scenario is that the thickness of all the holes is greater than the minimum hole thickness, meaning that the thickness of all the holes is located to the right of the minimum hole thickness in the U-shaped Poisson breakdown voltage curve.

[0062] The third scenario is that the thickness of all the holes is less than the minimum hole thickness, meaning that the thickness of all the holes is located to the left of the minimum hole thickness in the U-shaped Poisson breakdown voltage curve.

[0063] Furthermore, in all three cases described above, polarization can be performed from the first thickness to the second thickness, or from the second thickness to the first thickness.

[0064] Furthermore, this application also provides a device having the sealed space 25 for polarizing the porous piezoelectric electret material 10. The device includes a housing 21, a vacuum device 22, an inflation device 23, and a polarization power supply 24. The housing 21 contains the sealed space 25 for placing the porous piezoelectric electret material 10 to be polarized. The vacuum device 22 and the inflation device 23 are respectively connected to the sealed space 25 for vacuuming or inflating the sealed space 25.

[0065] The polarization power supply 24 is used to electrically connect to the porous piezoelectric electret material 10 placed in the sealed space 25, and to apply a voltage to the porous piezoelectric electret material 10 to polarize it when the air pressure in the pore with the maximum thickness in the porous piezoelectric electret material 10 in the sealed space 25 reaches the first air pressure or the air pressure in the pore with the minimum thickness reaches the second air pressure.

[0066] The air extraction device 22 and the air inflation device 23 are respectively provided with control valves 26 between them and the sealed space 25. The control valves 26 are used to control the connection or disconnection between the air extraction device 22 and the air inflation device 23 and the sealed space 25.

[0067] Furthermore, the first electrode 12 and the second electrode 13 are respectively disposed on opposite sides of the porous polymer film 11, and the thickness of the pore is the thickness of the pore along the plane direction perpendicular to the plane where the first electrode 12 or the second electrode 13 is located.

[0068] When confirming the thickness of the plurality of pores in the porous polymer film 11, the thickness of the pores can be estimated by using the relevant parameters used in preparing the porous polymer film 11 and by combining the properties of the raw materials used.

[0069] Furthermore, the size of the pores formed in the porous polymer film 11 can be scanned and the thickness of the pores can be measured using a scanning electron microscope.

[0070] Since each of the porous polymer films 11 has multiple pores, the efficiency of measuring the thickness of the pores by scanning with a scanning electron microscope is not very high. Therefore, preferably, the thickness of the pores can also be analyzed and measured by ImageJ image processing software.

[0071] Furthermore, the housing 21 can be opened and closed. When the housing 21 is opened, it is convenient to put the porous piezoelectric electret material 10 into the housing 21 or to take the porous piezoelectric electret material 10 out of the housing 21. When the housing 21 is closed, the sealed space 25 is formed to regulate the air pressure and polarize the porous piezoelectric electret material 10 in the housing 21.

[0072] Furthermore, the formula for the Poisson breakdown voltage curve corresponding to the Townsend model is as follows:

[0073] Where A and B are gas-related constants, and γ is the second ionization coefficient.

[0074] According to the Poisson breakdown voltage curve formula corresponding to the Townsend model mentioned above, when the composition of the gas filling the hole is different, the breakdown voltage corresponding to the hole of the same thickness under the same conditions will also be different.

[0075] For example, when the gas inside the hole is air, the minimum voltage that breaks down the air inside the hole under normal pressure is 327 volts, and the corresponding optimal hole thickness is [value missing].

[0076] Based on the properties of the gas inside the pores, the thickness of the optimal pore corresponding to the optimal breakdown voltage under normal pressure can be determined, and the effective pore thickness within the porous polymer film 11 can be divided into a first pore that is greater than the optimal pore and a second pore that is less than the optimal pore, using this thickness as a dividing point.

[0077] In one embodiment, when polarizing the porous polymer film 11, the porous polymer film 11 can be first evacuated to the first pressure corresponding to the first thickness according to the first thickness, and when the pressure in the pores corresponding to the first thickness reaches the first pressure, the optimal breakdown voltage is applied to the first pores so that the pores corresponding to the first thickness are polarized.

[0078] After completing the polarization of the first pore, the optimal breakdown voltage is maintained on the porous polymer film 11 and the sealed space 25 is gradually filled with gas so that the gas pressure in the sealed space 25 gradually reaches the second pressure corresponding to the second pore, so that the product of the pressure in the pore between the first thickness and the second thickness and the thickness corresponding to the pore satisfies the optimal breakdown voltage at a certain time, so that the pores between the first thickness and the second thickness are polarized sequentially. Then, the pressure in the sealed space 25 is restored from the second pressure to normal pressure, and finally the voltage applied to the porous piezoelectric electret material 10 is disconnected to complete the polarization of the porous piezoelectric electret material 10.

[0079] In another embodiment, when polarizing the porous polymer film 11, the porous polymer film 11 can be first inflated to the second pressure corresponding to the second thickness, and when the pressure in the pores corresponding to the second thickness reaches the second pressure, the optimal breakdown voltage is applied to the second pores so that the pores corresponding to the second thickness are polarized.

[0080] After completing the polarization of the second pore, the optimal breakdown voltage is maintained on the porous polymer film 11 and the sealed space 25 is gradually evacuated so that the air pressure in the sealed space 25 gradually reaches the first pressure corresponding to the first pore, so that the product of the pressure in the pore between the second thickness and the first thickness and the thickness corresponding to the pore satisfies the optimal breakdown voltage at a certain point in time, so that the pores between the second thickness and the first thickness are polarized sequentially. Then, the pressure in the sealed space 25 is restored from the first pressure to normal pressure, and finally the voltage applied to the porous piezoelectric electret material 10 is disconnected to complete the polarization of the porous piezoelectric electret material 10.

[0081] By controlling the air pressure change in the pores according to the direction from the first thickness to the second thickness, all the pores in the porous polymer film 11 can be effectively polarized at the optimal breakdown voltage. This avoids the need to adjust the breakdown voltage according to the pores of different thicknesses when polarizing multiple pores in the porous polymer film 11, which would result in a larger workload and higher power consumption, as well as safety hazards caused by higher polarization voltage.

[0082] By adjusting the internal pressure of different pores so that all pores can be polarized under the optimal breakdown voltage, this method not only avoids frequent adjustments to the polarization voltage and effectively reduces the polarization voltage required for breakdown of pores deviating from the specified voltage at normal pressure, but also has the advantage of completing the polarization of all pores at once. In addition, the polarization method provided in this application also reasonably reduces the higher equipment performance requirements and equipment complexity that would otherwise be required when the polarization device 24 uses a higher polarization voltage, and improves the safety of the operator when polarizing the porous piezoelectric electret material 10 by using a relatively lower polarization voltage.

[0083] Therefore, the polarization method provided in this application, when applying the optimal polarization voltage, can not only effectively reduce the polarization voltage corresponding to the breakdown of the largest or smallest hole, but also effectively increase the polarization amount of the porous piezoelectric electret material 10, thereby making the porous piezoelectric electret material 10 have better sensitivity.

[0084] Wherein, represents the minimum polarization voltage corresponding to the hole that deviates the farthest from the U-shaped Poisson breakdown voltage curve under normal pressure. That is to say, under normal pressure, the minimum polarization voltage corresponding to the largest hole is, and the minimum polarization voltage corresponding to the smallest hole is. When it is greater than, it is, and when it is greater than, it is.

[0085] Since porous polymer materials need to be polarized to trap charges in the pores in order to have piezoelectric properties, polarization is the key to determining whether the porous polymer film 11 has piezoelectric properties.

[0086] However, possessing piezoelectric properties does not necessarily indicate the level of piezoelectric sensitivity. The standard for measuring the level of piezoelectric sensitivity is the polarization of the porous polymer film 11.

[0087] More specifically, the polarization level can be determined by the amount of charge captured within the pores. The polarization of the porous piezoelectric electret material 10 has a saturation value, meaning that at the optimal breakdown voltage Vp, the gas within the pores will be broken down, causing the captured charge to reach saturation.

[0088] However, when the applied polarization voltage is lower than the minimum breakdown voltage, the polarization voltage is insufficient to break down the gas inside the hole, and the charge will not be captured inside the hole. Therefore, the porous piezoelectric electret material 10 corresponding to the hole does not have piezoelectricity.

[0089] However, when the applied polarization voltage is higher than the minimum breakdown voltage, the gas inside the pore will be broken down. At this time, the polarization of the porous piezoelectric electret material 10 is linearly related to the polarization voltage, and the specific relationship is as follows:

[0090] Where P represents the polarization amount, k is a parameter of the material used to prepare the porous polymer film 11, V represents the actual applied polarization voltage, and represents the minimum breakdown voltage. represents the polarization voltage at which the polarization amount reaches saturation (i.e., ).

[0091] However, the charge trapped on the inner surface of the hole also generates an electric field, which, if it exceeds the hole's breakdown electric field, will cause reverse breakdown of the hole when the polarization voltage is removed.

[0092] The amount of polarization P (residual polarization) after the polarization voltage V is removed has a saturation value. The polarization voltage corresponding to this saturation value is the saturation polarization voltage. That is, when the porous polymer film 11 is polarized with a polarization voltage greater than V, the amount of polarization in the porous polymer film will theoretically reach a value greater than the saturation value when the applied polarization voltage is removed.

[0093] Although the polarization P increases linearly with the application of polarization voltage V (see...) Figure 3 (The dashed part in the middle), but it cannot continue to increase the residual polarization P of the sample. The reason is that the charge trapped on the inner surface of the hole itself will also generate an electric field. If the electric field exceeds the breakdown electric field of the hole, the removal of the polarization voltage V will cause the electric field formed in the hole to break down in the reverse direction, causing the polarization P in the hole to return to the saturation value.

[0094] Therefore, after completing the polarization of all the pores, this application does not first cancel the applied optimal polarization voltage, but first restores the porous piezoelectric electret material 10 to normal pressure before disconnecting the applied optimal polarization voltage. By restoring the pressure in the pores within the porous polymer film 11 to normal pressure, the pores can be restored to a relatively high polarization voltage corresponding to normal pressure, thereby improving the breakdown strength of the pores. This avoids applying a polarization voltage exceeding the optimal breakdown voltage to polarize the pores and immediately disconnecting the polarization voltage after completing the polarization, which would cause the charge trapped in the pores to generate an electric field that would cause the pores to break down in the reverse direction. This would result in at least a partial cancellation of the charge trapped in the porous piezoelectric electret material 10, thereby reducing the polarization amount P of the porous piezoelectric electret material 10 and thus affecting the piezoelectric sensitivity of the porous piezoelectric electret material 10.

[0095] Therefore, the polarization method provided in this application, compared with existing polarization methods, can ensure that the charge captured in each hole does not exceed its corresponding saturation value, that is, when the optimal breakdown voltage is applied, the hole will not experience reverse breakdown, thereby improving the piezoelectric sensitivity of the porous piezoelectric electret.

[0096] Please refer to the following: Figure 2 The polarization method provided in this application reduces the polarization breakdown voltage of the hole by decreasing the pressure inside the hole when the hole with the maximum thickness is polarized or increasing the pressure inside the hole with the minimum thickness, thereby achieving the desired polarization breakdown voltage. Figure 2 The polarization-polarization voltage curve shown shifts from curve II to curve I (including the dashed part in curve I) to increase the polarization of the porous piezoelectric electret material.

[0097] Figure 2 In the figure, curve I (shown by the thick line segment) represents the polarization amount obtained by the porous piezoelectric electret material 10 corresponding to the polarization method described in this application when the pore pressure inside it is adjusted and the optimal breakdown voltage corresponding to more than twice the saturation breakdown voltage is applied.

[0098] The specific corresponding relationship is:

[0099] At this time, the breakdown strength of the pores decreases, which can break down the gas in all the pores and achieve a higher polarization, thereby making the porous polymer film 11 have a higher polarization and thus improving the polarization efficiency, thereby obtaining the porous piezoelectric electret material 10 with higher sensitivity.

[0100] Curve II (shown by the thin line segment) is the polarization amount versus polarization voltage curve of the porous piezoelectric electret material 10 without adjusting the pore pressure (i.e., at normal pressure).

[0101] When the optimal breakdown voltage corresponding to the gas pressure in the pore is applied, only a portion of the gas in the pore can be broken down, but not all of the gas in the pore. Therefore, the pores corresponding to the unbroken gas do not capture the charge, resulting in a relatively low polarization of the porous piezoelectric electret material 10.

[0102] Furthermore, disconnecting the applied polarization voltage after polarization causes the electric field formed by the charge trapped in the partially broken-down pores to cause reverse breakdown, further canceling at least part of the charge trapped in the pores, resulting in a further reduction in the polarization of the porous piezoelectric electret material 10.

[0103] Specifically, such as Figure 2 As shown, therefore, in curve II, when the optimal polarization voltage is applied to polarize the porous polymer film 11, the polarization of the porous polymer film does not reach saturation, so reverse breakdown will not occur when the polarization voltage is removed.

[0104] The specific corresponding relationship is:

[0105] Please see Figure 5-6 In one embodiment, the hole is a closed hole, wherein the hole can be regular or irregular, and the thickness of the hole is between [a certain range].

[0106] Furthermore, the pores can be irregular closed pores with inconsistent thicknesses obtained by directly stretching the polymer.

[0107] The holes can also be closed holes of uniform or inconsistent thickness obtained through processing methods such as MEMS, CNC, compression molding, and injection molding.

[0108] For the closed pores, after the sealed space 25 is evacuated or inflated, the air pressure inside the pores and the air pressure outside the porous polymer film 11 need a certain amount of time to reach equilibrium through the permeation and exchange of gas molecules inside and outside the pores. Therefore, the porous piezoelectric electret material 10 for the closed pores will deform under the action of evacuation or inflation, and the deformation will recover when the air pressure is balanced.

[0109] To ensure that the pressure inside the hole is balanced with the pressure inside the sealed space 25, this can be confirmed by monitoring the deformation of the porous piezoelectric electret. That is, the pressure inside the hole can be balanced with the pressure inside the sealed space 25 by monitoring the distance between the first electrode 12 and the second electrode 13.

[0110] Furthermore, since the thickness change of the porous piezoelectric electret material 10 will cause the corresponding capacitance to change, the capacitance change of the porous piezoelectric electret material 10 can also be monitored to further confirm whether the pressure in the pores and the pressure in the sealed space 25 are consistent and balanced.

[0111] Specifically, when the sealed space 25 is inflated, before the pressure in the pores of the porous piezoelectric electret material 10 reaches equilibrium with the pressure inside the sealed space 25, the porous piezoelectric electret material 10 is compressed due to the increased pressure inside the sealed space 25, resulting in a thinner material. At this time, the capacitance of the porous piezoelectric electret material 10 will increase rapidly. Subsequently, as gas molecules permeate into the pores, the capacitance will continuously decrease and will no longer change when the pressure inside the pores reaches equilibrium with the pressure inside the sealed space 25.

[0112] In another embodiment, the hole is an open hole, wherein the thickness of the hole is between [a certain value].

[0113] Specifically, the holes can also be open holes with consistent or inconsistent thicknesses obtained through processing methods such as MEMS, CNC, compression molding, and injection molding.

[0114] Since the open hole is connected to the sealed space 25 when it is placed inside the sealed space 25, the pressure inside the hole and the pressure inside the sealed space 25 quickly reach equilibrium when the porous piezoelectric electret material 10 with the open hole is evacuated or inflated. Therefore, the monitoring of the thickness of the porous piezoelectric electret material 10 can be omitted, and the pressure of the hole can be determined directly by monitoring the pressure value inside the sealed space 25.

[0115] Furthermore, the porous polymer film 11 may be, but is not limited to, made of one or more of PTFE, PP, PCTEF, PVDF, E-TFE, Teflon AF, FEP, PFA, P(VDF-TRFE), PI, PET, PE, COC, and PDMS.

[0116] Based on the usage and performance requirements of the porous piezoelectric electret material 10, one or more of the above-mentioned polymers can be selected to prepare the porous polymer film 11 to meet the different requirements of the porous piezoelectric electret material 10.

[0117] Please refer to the following: Figure 1 Depending on the composition of the gas inside the hole, the optimal breakdown voltage during polarization is between 100V and 20KV, and the pressure inside the hole is between these values.

[0118] Specifically, such as Figure 1As shown, it displays U-shaped Poisson breakdown voltage curves for air, oxygen, helium, neon, nitrogen, hydrogen, and carbon dioxide, obtained according to the Townsend model, representing the breakdown of gases within multiple pores of varying thicknesses in the porous polymer film 11. It should be noted that: Figure 1 The horizontal axis is pd, which is the air pressure multiplied by the thickness.

[0119] In the specification and claims of this application, the terms "comprising / including" and "having / including" and variations thereof are used to specify the presence of the stated features, values, steps or components, but do not exclude the presence or addition of one or more other features, values, steps, components or combinations thereof.

[0120] Some features of the present invention are described in different embodiments for clarity; however, these features may also be described in combination in a single embodiment. Conversely, some features of the present invention are described only in a single embodiment for brevity; however, these features may also be described individually or in any suitable combination in different embodiments.

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of poling a porous structured piezoelectret material, characterized in that, The porous piezoelectric electret material includes a porous polymer film, a first electrode, and a second electrode. The porous polymer film is disposed between the first electrode and the second electrode. The polarization method includes the following steps: The thickness of multiple pores in the porous polymer film is confirmed along the direction from the first electrode to the second electrode to obtain the first thickness corresponding to the largest pore and the second thickness corresponding to the smallest pore; The minimum breakdown voltage is determined based on this first thickness. The first pressure corresponding to the gas breaking down the largest hole, and the second thickness determining the minimum breakdown voltage. The second pressure corresponding to the gas breaking down within the smallest hole; wherein, the lowest breakdown voltage It is the minimum voltage value in the U-shaped Poisson breakdown voltage curve obtained according to the Townsend model, which is the breakdown voltage of a certain component gas in multiple pores of different thicknesses in the porous polymer film. The porous polymer film is de-aired or inflated in a sealed space so that the pressure in the largest pore reaches the first pressure; or the porous polymer film is inflated or de-aired in a sealed space so that the pressure in the smallest pore reaches the second pressure. Apply the optimal breakdown voltage corresponding to the gas within the pores to the porous polymer film that has reached the first pressure. Polarization; or applying the optimal breakdown voltage corresponding to the gas within the pores to the porous polymer film reaching the second pressure. Polarization is performed; wherein, the optimal breakdown voltage The breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve under normal pressure. The lowest breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve under the first or second pressure. The sum of ; The porous polymer film, which continuously reaches the first pressure within the pores, is subjected to the optimal breakdown voltage. Polarization is performed and the sealed space is gradually inflated to the second pressure so that all the pores in the porous polymer film located between the largest and smallest pores are sequentially polarized; or the porous polymer film in the pores is continuously subjected to the second pressure according to the optimal breakdown voltage. Polarization is performed and the sealed space is gradually evacuated to the first pressure so that all the pores in the porous polymer film located between the smallest pore and the largest pore are sequentially polarized; The optimal breakdown voltage is continuously applied to the porous polymer film. And gradually restore the first or second pressure in the sealed space to normal pressure; Stop applying the optimal breakdown voltage to the porous polymer film. To complete the polarization of the porous piezoelectric electret material; the Poisson breakdown voltage curve formula corresponding to the Townsend model is: Where A and B are gas-related constants, and γ is the second ionization coefficient.

2. The polarization method for porous piezoelectric electret materials according to claim 1, characterized in that, The lowest breakdown voltage corresponding to the U-shaped Poisson breakdown voltage curve of the gas with different components at atmospheric pressure. Having a minimum hole thickness Therefore, the step involves evacuating or inflating the porous polymer film in a sealed space so that the pressure inside the largest pore reaches the first pressure. Alternatively, the porous polymer film may be inflated or deflated within a sealed space to achieve the second pressure within the smallest pore, including: When the first thickness is less than the minimum hole thickness At that time, the sealed space will be inflated so that the pressure inside the largest hole reaches the first pressure; Alternatively, when the first thickness is less than the minimum hole thickness At that time, the sealed space will be inflated so that the pressure inside the smallest hole reaches the second pressure; Alternatively, when the second thickness is greater than the minimum hole thickness At that time, the sealed space will be evacuated so that the pressure inside the smallest hole reaches the second pressure. Alternatively, when the second thickness is greater than the minimum hole thickness At that time, the sealed space will be evacuated so that the pressure inside the largest hole reaches the first pressure. Alternatively, when the first thickness is greater than the minimum hole thickness When, and the second thickness is less than the minimum hole thickness At that time, the sealed space will be evacuated so that the pressure inside the largest hole reaches the first pressure. Alternatively, when the first thickness is greater than the minimum hole thickness When, and the second thickness is less than the minimum hole thickness At that time, the sealed space will be inflated so that the pressure inside the smallest hole reaches the second pressure.

3. The polarization method for porous piezoelectric electret materials according to claim 1, characterized in that, The hole is a closed hole, wherein the hole is irregular in shape, and the thickness of the hole is between [a certain value]. between.

4. The polarization method for porous piezoelectric electret materials according to claim 1, characterized in that, The hole is an open hole, wherein the thickness of the hole is between between.

5. The polarization method for porous piezoelectric electret materials according to claim 1, characterized in that, The porous polymer film is made of one or more of the following: PTFE, PP, PCTEF, PVDF, E-TFE, Teflon AF, FEP, PFA, P(VDF-TRFE), PI, PET, PE, COC, and PDMS.

6. The polarization method for porous piezoelectric electret materials according to claim 1, characterized in that, Depending on the composition of the gas within the cavity, the optimal breakdown voltage during polarization is between 100V and 20KV, and the pressure within the cavity is between [missing information]. between.

7. The polarization method for the porous piezoelectric electret material according to claim 6, characterized in that, When the gas inside the cavity is air, the minimum voltage required to break down the air inside the cavity under normal pressure is 327 volts, and the optimal cavity thickness is... .

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