Ion capacitive pressure sensor based on three-dimensional structure electrode and preparation method thereof

Abstract

The present invention discloses an ion capacitive pressure sensor based on a three-dimensional structure electrode and a preparation method thereof, wherein the sensor comprises a first electrode, an elastic microstructure and a second electrode arranged in sequence from top to bottom; the first electrode and the second electrode are both three-dimensional flexible electrodes, the three-dimensional flexible electrode is formed by stacking conductive fibers in a non-compact manner, and the conductive fibers construct a conductive path with a three-dimensional structure inside the three-dimensional flexible electrode; the elastic microstructure adopts a polyurethane sponge, and pores capable of accommodating a portion of the conductive fibers are distributed in a non-uniform manner on the upper and lower surfaces of the elastic microstructure, and the pores are interwoven and connected with each other. The present invention adopts a flexible three-dimensional structure as an electrode, which significantly increases the number of ion double-layer capacitors formed between the electrode and the dielectric ion layer, increases the amplitude of the capacitance signal, and thus increases the sensitivity of the capacitive pressure sensor.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to an ion capacitive pressure sensor based on a three-dimensional structure electrode and a preparation method thereof. Background Art

[0002] like Figure 1 The figure shows the schematic diagram of the principle structure of the existing ion capacitive pressure sensor, which consists of two PI-Au electrodes and an open-cell polyurethane sponge (PU)-IL composite foam. The open-cell polyurethane sponge (PU)-IL foam is sandwiched between two PI-Au electrodes. Figure 2 The sensing mechanism of the pressure sensor is given. The ion-type flexible pressure sensor uses the electric double layer (EDL) capacitance generated on the nanoscale interface between the electrode and the ionic electrolyte to achieve pressure sensing. As can be seen from the figure, a large number of positive and negative ion pairs are distributed on the porous structure filled with ions inside the electrode interface. Under the action of external pressure, the contact area between the electrode and the porous structure increases, and more charges accumulate at the contact interface. The capacitance of the sensor increases due to the accumulation of more charges, so the capacitance signal can reflect the contact area and the pressure applied to the device. Figure 3 The sensitivity of the ion capacitive pressure sensor in the pressure range of 114 kPa is given. As can be seen from the figure, the maximum sensitivity is 9280 kPa in the pressure range of 5 kPa-10 kPa. −1 However, when the pressure exceeds 10 kPa, the sensitivity and linearity of the sensor drop sharply, that is, the sensing performance of the ion capacitive pressure sensor in the medium and high pressure range needs to be improved urgently.

[0003] Sensitivity (S) is the most basic performance parameter of a pressure sensor. It refers to the ratio of the external load to the sensor output capacitance, and reflects the response accuracy of the capacitive pressure sensor to the external force signal.

[0004] For capacitive pressure sensors, their sensitivity is generally expressed as:

[0005]

[0006] Where 𝐶0—initial capacitance before load is applied (pF) ∆𝐶—capacitance change before and after load is applied (pF) 𝑃—load (kPa)

[0007] According to the classic EDL model, the inductive capacitance of the interface EDL can be expressed as:

[0008]

[0009] Where, UAC—unit capacitance density (μF / cm 2)𝐴—Contact area between ion layer and electrode layer (cm 2 )

[0010] In the ion-type capacitive pressure sensor, the electrode layer and the sensing layer of the device will partially contact in the initial stage, which is generally called the initial contact area 𝐴0, which will produce an initial capacitance value 𝐶0. From the sensor sensitivity formula 𝑆 = 𝛿(∆𝐶𝐶0⁄ ) / 𝛿𝑃, it can be seen that low 𝐶0, that is, low 𝐴0, is beneficial for obtaining high-sensitivity devices. Therefore, in this field, people are often more concerned about the ratio of the change in contact area to the initial contact area, that is, ∆𝐴 / 𝐴0. Without considering the deviation caused by the packaging process, 𝐴0 is still only related to the structure of the device sensing layer. Therefore, for the convenience of understanding, some researchers directly expressed the rate of change of the contact area at the interface between the electrode layer and the sensing layer during the device's force deformation process as:

[0011] Where 𝜓 is a geometric parameter that depends only on the surface morphology of the material.

[0012] P——External load (kPa)

[0013] 𝐸——Young’s modulus of the elastic body (kPa)

[0014] Therefore, for a specific surface structure (i.e., 𝜓 is a constant), in order to obtain a highly sensitive pressure sensor, the flexible structure of the sensor requires a smaller elastic modulus 𝐸 and as small an initial contact area 𝐴0 as possible between the electrode and the ion layer. The change in contact area △𝐴 is also an important parameter that affects the sensor's ability to sense force signals.

[0015] At present, there are still some problems with conventional flexible capacitive pressure sensors. For example, the use of a flat two-dimensional electrode structure limits the number of ionic double-layer capacitance structures formed between the electrode and the dielectric ion layer, thereby limiting the sensitivity and range of the ionic double-layer capacitance sensor device, which has reached its maximum sensitivity in the pressure range of 5kPa-10kPa. However, when the pressure exceeds 10kPa, the sensitivity and linearity of the sensor drop sharply, which greatly limits the application scope of the flexible capacitive pressure sensor. That is, the sensing performance of ionic capacitive pressure sensors in the medium and high pressure range needs to be improved urgently. Summary of the invention

[0016] In view of the shortcomings of the prior art, the present invention provides an ion capacitive pressure sensor based on a three-dimensional structure electrode and a preparation method thereof. The present invention sets the electrode as a three-dimensional structure, and sets an open hole structure on the substrate. When the electrode and the substrate are in contact with each other under pressure, the amplitude of the capacitance signal is increased by increasing the number of ion double-layer capacitances formed between the electrode and the dielectric ion layer, thereby improving the sensitivity of the capacitive pressure sensor.

[0017] The technical means adopted by the present invention are as follows:

[0018] An ionic capacitive pressure sensor based on a three-dimensional structure electrode comprises a first electrode, an elastic microstructure and a second electrode arranged in sequence from top to bottom;

[0019] The first electrode and the second electrode are both three-dimensional flexible electrodes, and the three-dimensional flexible electrode is formed by stacking conductive fibers in a non-compact manner, and the conductive fibers construct a conductive path with a three-dimensional structure inside the three-dimensional flexible electrode;

[0020] The elastic microstructure adopts polyurethane sponge, and pores capable of accommodating some conductive fibers to penetrate deeply are distributed in a non-uniform manner on the upper and lower surfaces of the elastic microstructure, and the pores are interwoven and connected with each other. A mixed solution of 1-butyl-3-methylimidazolium iodide and saturated NaCl with an ion concentration of 15% is adsorbed on the surface of the elastic microstructure.

[0021] Furthermore, the ionic capacitive pressure sensor further includes a first packaging layer disposed above the first electrode and a second packaging layer disposed below the second electrode.

[0022] Furthermore, the first electrode and the second electrode include a substrate and conductive fibers, the substrate is an open-cell polyurethane foam sponge, the conductive fibers are prepared by subjecting the substrate to PVD conductive treatment and electroplated metal thickening treatment, and the metal types are nickel and copper.

[0023] Furthermore, in the dielectric ion layer open-cell polyurethane sponge-ionic solution composite foam, the mass ratio of polyurethane sponge to ionic solution is 1:10.

[0024] The present invention also discloses a method for preparing the ionic capacitive pressure sensor based on the three-dimensional structure electrode as described above, comprising the following steps:

[0025] The polyurethane sponge is washed with deionized water, placed in a centrifuge to remove excess water, and then cut into the required size;

[0026] Prepare 30 ml of saturated NaCl solution;

[0027] Using the dilution equation method, the ionic liquid of 1-butyl-3-methylimidazolium iodide with an ion concentration of 99% was diluted with a saturated NaCl solution to finally obtain a mixed ion solution with an ionic liquid concentration of 15%;

[0028] The cut polyurethane sponge is fully immersed in a mixed ion solution and loaded with ions, thereby obtaining an elastic microstructure;

[0029] The elastic microstructure is sandwiched between two three-dimensional flexible electrodes, and after being wrapped with a 0.05 mm TPU film, the opening is sealed by heat sealing machine to obtain a sensor. Copper wires are used as test electrodes on the upper and lower sides of the sensor to lead out the performance test system. Compared with the prior art, the present invention has the following advantages:

[0030] 1. The three-dimensional structure used in the sensor of the present invention has a three-dimensional conductive network built inside. These networks are interwoven by conductive fibers from microscopic to macroscopic scales, forming a continuous conductive path located in different planes, and have the characteristics of a three-dimensional structure with a large specific surface area and high porosity. Compared with a flat electrode, under the same external pressure, the conductive fiber structure inside the three-dimensional structure can form double electric layer (EDL) capacitors located in different planes when in contact with the dielectric ion layer, significantly increasing the amount of ionic double electric layer (EDL) capacitors formed between the electrode and the dielectric ion layer, and generating μF / cm on a macro scale. 2 Ultra-high capacitance, much higher than the common nF / cm 2 The traditional ionic capacitive pressure tactile sensor based on flat electrodes can effectively resist the interference of environmental capacitance noise (pF / cm 2 It has the advantages of high sensitivity and high signal-to-noise ratio.

[0031] 2. The present invention improves the sensitivity of the pressure sensor while increasing the amplitude of the capacitance signal, so that the sensor device has ultra-high sensitivity within a large pressure range.

[0032] 3. The present invention uses a three-dimensional structure of flexible porous electrodes and a high-porosity open-cell polyurethane sponge. The compressible soft medium that combines the sponge and the ionic liquid serves as the dielectric ion layer. Its highly matched elastic modulus solves the problem that the soft medium of the traditional thickness-controlled capacitive sensor is difficult to compress and has poor mechanical deformation. Due to the limited thickness change and the limitation of the flat two-dimensional electrode structure, the sensitivity is sharply reduced in the low pressure range (0-10kPa). BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 It is a schematic diagram of the structure of an existing ion capacitive pressure sensor.

[0035] Figure 2 Schematic diagram of the sensing mechanism of an existing ion capacitive pressure sensor.

[0036] Figure 3 It is the sensitivity of the existing ion capacitive pressure sensor within the pressure range of 114 kPa.

[0037] Figure 4 Schematic diagram of the structure of an ion capacitive pressure sensor based on a three-dimensional structure electrode in an embodiment of the present invention.

[0038] Figure 5 Schematic diagram of the sensing mechanism of the ionic capacitive pressure sensor based on the three-dimensional structure electrode in an embodiment of the present invention.

[0039] Figure 6 4 is an equivalent circuit diagram of an ionic capacitive pressure sensor based on a three-dimensional structure electrode in an embodiment of the present invention.

[0040] Figure 7 Schematic diagram of a sensor performance testing platform in an embodiment of the present invention.

[0041] Figure 8 Response time of the ionic capacitive pressure sensor based on the three-dimensional structure electrode in the embodiment of the present invention.

[0042] Fig. 9 It is the sensitivity of the ion capacitive pressure sensor based on the three-dimensional structure electrode in the embodiment of the present invention within the pressure range of 180 kPa.

[0043] In the figure: 1. first packaging layer; 2. first electrode; 3. elastic microstructure; 4. second electrode; 5. second packaging layer. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0045] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein are implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0046] like Figure 4 As shown, the present invention discloses an ion capacitive pressure sensor based on a three-dimensional structure electrode, comprising a first electrode, an elastic microstructure and a second electrode arranged in sequence from top to bottom, wherein the elastic microstructure has non-uniform openings so that when subjected to vertical pressure, the first electrode and the second electrode can partially penetrate into the open structure to generate double electric layers located in different planes.

[0047] Specifically, the ion capacitive pressure sensor of the three-dimensional structure electrode in this embodiment is composed of two three-dimensional flexible porous electrodes, the materials of the first electrode 2 and the second electrode 4 on the elastic microstructure 3, in this embodiment, is based on polyurethane foam sponge, which is prepared by PVD conductive treatment and thickening treatment such as electrodeposition of metal nickel and copper. The metal on the surface of its internal network structure ensures its good conductivity while improving the flexibility and elasticity of the sensor, and the open-cell polyurethane sponge-ion solution composite foam is sandwiched between the two three-dimensional flexible electrodes. The sensor is wrapped with a 0.05mm TPU film, and the opening is sealed by heat sealing machine. The upper and lower sides are welded with copper wires on the copper side of the flexible polyimide (PI) copper electrode lead-out part, and the test electrode is connected to the performance test system. The ion capacitive flexible pressure sensor uses the double electric layer (EDL) capacitance generated on the nanoscale interface between the electrode and the ionic electrolyte to realize pressure sensing. By introducing a three-dimensional flexible porous electrode, its internal special pore structure directly increases the surface area A of the electrode, that is, under the same external pressure, more double electric layer capacitance is formed on the electrode surface. Compared with the flat electrode, the conductive fiber framework inside the three-dimensional structure can significantly increase the amount of ionic double-layer capacitance formed between the electrode and the dielectric ion layer when in contact with the dielectric ion layer, generating μF / cm 2 Ultra-high capacitance, much higher than the common nF / cm 2 The traditional ionic capacitive pressure tactile sensor based on flat electrodes can effectively resist the interference of environmental capacitance noise (pF / cm 2 magnitude), with the advantages of high sensitivity and high signal-to-noise ratio. While increasing the amplitude of the capacitance signal, the sensitivity of the pressure sensor is also increased, making the sensing device have ultra-high sensitivity over a large pressure range. At the same time, the three-dimensional structured flexible porous electrode and the compressible soft medium combined with the high-porosity open-cell polyurethane (PU) foam and ionic liquid are used as the dielectric ion layer. Its highly matched elastic modulus enables its fast response recovery time of 16.7ms, while solving the problem of a sharp decrease in sensitivity in the low pressure range (0-10kPa) due to limited thickness changes and limitations of the flat two-dimensional structure electrodes. The sensing mechanism is as follows Figure 5 As shown in the figure, it can be seen that a large number of positive and negative ion pairs are distributed on the interface of the elastic porous structure (polyurethane foam) filled with ions inside - the electrode. The special pore structure inside the three-dimensional flexible porous electrode is interwoven by conductive ligaments from microscopic to macroscopic scales. Before the pressure is applied, due to the high porosity of the elastic porous structure (polyurethane foam) and the three-dimensional flexible electrode conductive polyurethane foam, the tips of the ion-attached elastic microstructure ligaments have almost no contact with the conductive ligaments of the three-dimensional flexible electrode, resulting in an extremely low initial capacitance (C0) of pF / cm 2level. As the pressure gradually increases, the conductive ligaments with certain strength and elasticity interweave with the ion-attached elastic porous structure, the contact area begins to increase, the double electric layer (EDL) capacitance increases, and the output capacitance increases. As the pressure further increases, some of the ligament tips of the ion-attached elastic porous structure and the free positive and negative ion pairs penetrate into the internal pores of the three-dimensional flexible structure to produce double electric layer (EDL) capacitances located in different planes. That is, under the same external pressure, more EDL structures are formed on the electrode surface, which directly increases the volume of EDL interface capacitance formed by the contact between the electrode and the dielectric ion layer, thereby generating a significant change in the capacitance signal. Therefore, the capacitance signal can reflect the contact area and the pressure applied to the device.

[0048] In this embodiment, the three-dimensional flexible porous electrode is used as a combined electrode structure. Figure 6 As shown in the figure, the upper and lower three-dimensional structure of the flexible porous electrode contacts with the positive and negative charges in the polyurethane sponge to form many parallel C EDL capacitor, the capacitor is connected through a variable contact resistor (R CONT ) in series.

[0049] Use Figure 7 The test device shown is used to perform a performance test on the sensor given in this embodiment. Specifically, the LCR instrument terminal is connected to the copper wires at both ends of the sensor; the LCR instrument measurement mode is set to CP-D, the frequency is 1kHz, the voltage is 1V, and calibration is performed; a digital pressure gauge and an LCR tester are used to build a performance test system for data analysis and display. The digital pressure gauge provides the pressure required for the pressure sensor test, and its resolution is 0.1N. A 2cm*2cm acrylic plate is glued to the bottom of the digital pressure gauge with hot melt adhesive as the force application area, which overlaps with the PI film on the upper surface of the device, and the force area is 4cm 2 , i.e. 0.0004m 2 . The pressure applied = pressure / pressure area (P=F / S).

[0050] The sensitivity within the pressure range of 180 kPa is shown in the attached figure. Figure 8 The ionic capacitive pressure sensing device with flexible three-dimensional structure electrode has a sensitivity of 44679 kPa in the low pressure range (0-10 kPa). -1 , which far exceeds the sensitivity of previously reported sensors in any pressure range. When the external pressure continues to increase, the sensitivity of the ionic capacitive pressure sensor device with flexible three-dimensional structure electrodes continues to rise, reaching 99840.19 kPa in the pressure range of 10-37.5 kPa. -1 , in the pressure range of 37.5-95kPa, the sensitivity rises sharply to 198160kPa -1This is an extremely high value, which is unique in the history of ion capacitive flexible pressure sensors. As the external pressure continues to increase, the remaining gaps in the flexible three-dimensional structure electrodes and the polyurethane sponge gradually saturate with the increase in pressure, and the sensitivity decreases slightly. In the pressure range of 97.5-140kPa, the sensitivity is still 46100kPa -1 Compared with the sensor devices reported in the current literature, the maximum sensitivity of the ion capacitive pressure sensor device with flexible three-dimensional structure electrode is better than the existing ion capacitive sensor and is the highest value among similar devices reported so far.

[0051] The present invention also discloses a method for preparing the ionic capacitive pressure sensor based on the three-dimensional structure electrode as described above, comprising the following steps:

[0052] First, the polyurethane sponge was cleaned with deionized water and placed in a centrifuge to remove excess water. The speed was set to 1000 rpm. This process was repeated several times to remove impurities on the surface of the polyurethane sponge. The sponge was naturally dried and cut into the required size. The polyurethane sponge was cut to a size of 2cm*2cm*0.3cm as the framework. The three-dimensional structure electrode was cut to a size of 2cm*2cm*0.4cm, one on each side.

[0053] Next, prepare 30 ml of saturated NaCl solution (water: sodium chloride ratio is 1 ml: 0.359 g) to obtain 30 ml of saturated NaCl solution with a concentration of 35.9%. Use the dilution equation method:

[0054]

[0055] (Wherein, C1 and C2 are the initial and final solution concentrations, respectively, and V1 and V2 are the initial and final solution volumes, respectively). Use saturated NaCl solution to dilute the ionic liquid of 1-butyl-3-methylimidazolium iodide (easily soluble in water) with an ion concentration of 99% (C1=99%). Take 0.5ml of 1-butyl-3-methylimidazolium iodide with an ion concentration of 99%, that is, V1=0.5ml. Dilute to a mixed ion solution with a concentration of 15% (C2=15%), and calculate that V2=3.3ml, that is, add 2.8ml of saturated NaCl solution, and finally obtain a mixed ion solution with an ionic liquid concentration of 15%.

[0056] Again, the polyurethane sponge cut out to a size of 2cm*2cm*0.3cm was fully soaked in a mixed ion solution with an ionic liquid concentration of 15%, and then placed in an ion cleaning machine for five minutes. Ions were loaded during the soaking and shaking process to serve as the ion layer in the ion pressure sensor.

[0057] Then, the polyurethane sponge soaked in the mixed ion solution was taken out, and the mass ratio of polyurethane sponge to ion solution was 1:10 (1:10 is the best ratio for the performance of polyurethane sponge as a dielectric ion layer). In order to avoid the influence of external environmental factors on the experimental data, the sensor device was wrapped with a 0.05mm TPU film, and the opening was sealed by heat sealing machine. The upper and lower sides were welded with copper wires on the copper side of the flexible polyimide (PI) copper electrode lead-out part as the test electrode lead-out. .

[0058] Finally, by building the Figure 7 The sensor performance test platform is used to perform basic pressure sensing performance tests on the sensor performance.

[0059] The present invention adopts a flexible three-dimensional structure as an electrode, which significantly increases the amount of ionic double-layer capacitance formed between the electrode and the dielectric ion layer, so that the sensor device has ultra-high sensitivity in a large range, and at the same time solves the problem that the sensitivity of the flexible pressure sensor device decreases with increasing pressure.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ionic capacitive pressure sensor based on a three-dimensional structure electrode, characterized in that: It includes a first electrode, an elastic microstructure and a second electrode arranged in sequence from top to bottom; The first electrode and the second electrode are both three-dimensional flexible electrodes, and the three-dimensional flexible electrode is formed by stacking conductive fibers in a non-compact manner, and the conductive fibers construct a conductive path with a three-dimensional structure inside the three-dimensional flexible electrode; The elastic microstructure adopts polyurethane sponge, and pores capable of accommodating some conductive fibers to penetrate deeply are distributed in a non-uniform manner on the upper and lower surfaces of the elastic microstructure, and the pores are interwoven and connected with each other. A mixed solution of 1-butyl-3-methylimidazolium iodide with an ion concentration of 15% and saturated NaCl is adsorbed on the surface of the elastic microstructure, and a compressible soft medium combining the sponge and the ionic liquid is used as a dielectric ion layer; The conductive fiber contacts the dielectric ion layer to form a double-layer capacitor located in different planes, increasing the amount of ionic double-layer capacitor formed between the electrode and the dielectric ion layer, generating μF / cm 2 Ultra-high capacitance.

2. The ionic capacitive pressure sensor based on three-dimensional structure electrode according to claim 1, characterized in that: The ion capacitive pressure sensor further includes a first packaging layer disposed above the first electrode and a second packaging layer disposed below the second electrode.

3. The ionic capacitive pressure sensor based on three-dimensional structure electrode according to claim 1, characterized in that: The first electrode and the second electrode include a substrate and conductive fibers, wherein the substrate is an open-cell polyurethane foam sponge, and the conductive fibers are prepared by subjecting the substrate to PVD conductive treatment and electroplated metal thickening treatment, wherein the metal types are nickel and copper.

4. The ionic capacitive pressure sensor based on three-dimensional structure electrode according to claim 3, characterized in that: The mass ratio of polyurethane sponge to ionic solution in the dielectric ionic layer open-cell polyurethane sponge-ionic solution composite foam is 1:

10.

5. A method for preparing an ionic capacitive pressure sensor based on a three-dimensional structure electrode as claimed in claim 1, characterized in that: The following steps are involved: The polyurethane sponge is washed with deionized water, placed in a centrifuge to remove excess water, and then cut into the required size; Prepare 30 ml of saturated NaCl solution; Using the dilution equation method, the ionic liquid of 1-butyl-3-methylimidazolium iodide with an ion concentration of 99% was diluted with a saturated NaCl solution to finally obtain a mixed ion solution with an ionic liquid concentration of 15%; The cut polyurethane sponge is fully immersed in a mixed ion solution and loaded with ions, thereby obtaining an elastic microstructure; The elastic microstructure is sandwiched between two three-dimensional flexible electrodes and wrapped with a 0.05 mm TPU film. The opening is then sealed with a heat sealer to obtain a sensor. Copper wires are used as test electrodes on the upper and lower sides of the sensor to lead into a performance test system.

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