Transparent and flexible electronic skin and method of making same

Abstract

The invention provides a transparent and flexible electronic skin with three-dimensional sensing capability. The electronic skin includes: a substrate; a transparent and flexible electric field sensor disposed on the substrate; a control circuit disposed on the substrate; and a transparent and flexible protective layer encapsulating the electric field sensor and the control circuit. The electric field sensor comprises a transmitter electrode; one or more receiver electrodes; and a dielectric layer disposed between the transmitter electrode and the receiver electrode. The control circuit is connected to the electric field sensor and is configured to drive the transmitter electrode to transmit a reference signal to establish a quasi-static electric near field; and processing one or more measurement signals received by the one or more receiver electrodes, respectively, each measurement signal being indicative of a distortion of the quasi-static electrical near field due to proximity of an object.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application No. 18 / 492,808, filed on October 24, 2023, and the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] The present invention generally relates to electronic skin technology. More specifically, the present invention relates to a transparent and flexible electronic skin with three-dimensional sensing capabilities. Background Art

[0003] Three-dimensional sensing capabilities are essential for human-machine interaction and machine perception in a three-dimensional world. In recent years, with the popularity of topics such as the metaverse and teleoperated robots, 3D spatial perception has become increasingly essential. However, conventional skin electronics are limited to collecting two-dimensional spatial data only through physical contact.

[0004] In recent years, the field of 3D gesture recognition has made rapid progress. Some existing wearable devices can rely on inertial sensors, strain / stress sensors, ultrasound or electrocardiogram signals to detect the movement of fingers in space. These devices are generally limited in recognizing gestures of different ranges and dynamically tracking the movement of fingers in space. Other strategies based on image analysis, magnetic fields, radar technology or electrostatic principles also face their own challenges, such as complex processing algorithms, large device size, high power consumption, sensitivity to changes in the working environment, etc. Summary of the invention

[0005] One object of the present invention is to provide a transparent and flexible electronic skin that has three-dimensional sensing capability, simpler processing algorithms, compact size, low power consumption, and adaptability to various working environments. Another object of the present invention is to provide a method for manufacturing a transparent and flexible electronic skin suitable for mass production.

[0006] According to one aspect of the present invention, a transparent and flexible electronic skin is provided, which is inspired by the active sensing system of long-jawed fish (Mormyroidea). The transparent and flexible electronic skin comprises: a transparent and flexible substrate; a transparent and flexible electric field sensor disposed on the substrate. The electric field sensor comprises: a transparent and flexible transmitter electrode; and one or more transparent and flexible receiver electrodes. The electronic skin also comprises a control circuit disposed on the substrate and connected to the electric field sensor, and a transparent and flexible protective layer encapsulating the electric field sensor and the control circuit. The control module is configured to: drive the transmitter electrode to transmit a reference signal to establish a quasi-static electric near field around the electric field sensor; and process one or more measurement signals received by one or more receiver electrodes, each measurement signal indicating a distortion of the quasi-static electric near field due to an object approaching the corresponding receiver electrode.

[0007] According to another aspect of the present invention, a method for manufacturing a transparent and flexible electronic skin is provided. The method includes: molding a transparent and flexible material to form a patterned transparent and flexible substrate; dispensing a conductive transparent gel on the patterned transparent and flexible substrate to form a transmitter electrode; forming a control circuit on the patterned transparent and flexible substrate; molding a transparent and flexible material to form a patterned transparent and flexible dielectric layer; dispensing a conductive transparent gel on the patterned transparent and flexible dielectric layer to form one or more receiver electrodes; attaching the dielectric layer to the substrate so that the transmitter electrode is separated from the one or more receiver electrodes by the dielectric layer to form an electric field sensor; and encapsulating the control circuit and the electric field sensor with a transparent and flexible material.

[0008] By using biogel as electrode material and silicone polymer as substrate / dielectric layer, the electronic skin provided by the present invention has excellent stretchability and light transmittance. This unique feature enables seamless integration with existing surfaces such as screens without significantly reducing brightness. In addition, the electric field sensor in the provided electronic skin exhibits excellent performance in 3D sensing even when immersed in water. Through actual evaluations involving PCs, robots and drones, the huge application potential of the present invention has been demonstrated in scenarios of human-computer interaction (such as touch screens), virtual-reality spaces (such as the metaverse) and robotic applications (such as remote robot control) that require three-dimensional operation and perception. In addition, the feasibility of large-scale production through printing technology greatly reduces manufacturing costs.

[0009] Although the use of biogel as an electrode does not match the performance of conventional metal electrodes, it can enhance the stretchability of the device and eliminate issues regarding metal fatigue. The provided electronic skin is lightweight, transparent, and wireless. In addition, when human skin is used as a grounding system, the overall performance of the electronic skin attached to human skin can be significantly enhanced. In addition, the provided electronic skin exhibits excellent underwater performance, indicating great potential for underwater applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Various aspects of the present disclosure may be readily understood by referring to the following detailed description of the accompanying drawings. The illustrations may not necessarily be drawn to scale. That is, for clarity of discussion, the sizes of various features may be arbitrarily increased or decreased. Due to manufacturing processes and tolerances, there may be differences between the artistic reproductions in the present disclosure and the actual devices. Common reference numerals are used throughout the drawings and detailed description to indicate the same or similar elements.

[0011] Figure 1 A photograph showing a transparent and flexible electronic skin according to one embodiment of the present invention.

[0012] Figure 2A and 2B Schematic exploded views showing the sensing part and the circuit part of the electronic skin respectively.

[0013] Figure 3 An equivalent circuit model of an electric field sensor according to an embodiment of the present invention is shown.

[0014] Figure 4A shows a high frequency square wave voltage signal used by the control circuit to drive the transmitter electrode; and Figure 4B The voltage signals received by the receiver electrodes are shown.

[0015] Figure 5 Graphs showing capacitance and received voltage versus distance obtained by placing a target at various distances from the electric field sensor in the electronic skin.

[0016] Figure 6 An exemplary electrode design according to one embodiment of the present invention is shown.

[0017] Figure 7 Some key parameters of the electronic skin according to an embodiment of the present invention are shown.

[0018] Figure 8 FIG. 1 is a functional block diagram of the control circuit 130 according to an embodiment of the present invention.

[0019] Fig. 9 A schematic flow chart of a method for manufacturing a transparent and flexible electronic skin according to an embodiment of the present invention is shown.

[0020] Fig.10 The light transmittance of the electronic skin provided by the present invention is shown.

[0021] Fig.11 The capacitance change during the stretching of the electronic skin by 25% from its original length is shown.

[0022] Fig.12 Performance of the electronic skin after more than 8,000 folding and unfolding cycles.

[0023] Fig.13 It shows how to use electronic skin to collect and process sensing signals generated by the proximity of a user's finger to obtain the three-dimensional spatial coordinates of the finger within a predefined interaction space.

[0024] Fig.14 It shows the sensing signals received by the electronic skin and the calculated finger movement trajectory when the five letters "CITYU" are written in the predefined interaction space using a finger. DETAILED DESCRIPTION

[0025] In the following description, details of the present invention are set forth as preferred embodiments. It will be apparent to those skilled in the art that modifications, including additions and / or substitutions, may be made without departing from the scope and spirit of the present invention. Certain details may be omitted so as not to obscure the present invention; however, this disclosure is written to enable those skilled in the art to practice the teachings herein without undue experimentation.

[0026] According to various aspects of the present invention, a transparent and flexible electronic skin with three-dimensional sensing capabilities is provided, which is inspired by the active sensing system of long-jawed fish. Long-jawed fish are a superfamily of weakly electric fish that can use electric fields to detect prey hidden in underwater sediments. These fish generate weak electric fields through electric organs on their tails, and then sense the electric field distortion caused by the target through electroreceptors throughout the body.

[0027] Figure 1 A photograph showing a transparent and flexible electronic skin 100 according to one embodiment of the present invention is shown. The electronic skin 100 may be divided into a sensing part 101 and a circuit part 102. Figure 2A and 2B Schematic exploded views of the sensing part and the circuit part are shown respectively. As shown in the figure, the electronic skin 100 includes: a transparent and flexible substrate 110; a transparent and flexible electric field sensor 120; a control circuit 130; and a transparent and flexible protective layer 140 for encapsulating the electric field sensor and the control circuit to protect the electric field sensor and the control circuit from external environmental factors such as moisture or dust.

[0028] Figure 2A and2B A close-up view of the sensing portion 101 and the circuit portion 102 of the electric field sensor 120 is shown respectively. As shown, the electric field sensor 120 is disposed on the substrate 110 and is covered by the protective layer 140. That is, the electric field sensor 120 is arranged between the substrate 110 and the protective layer 140. The electric field sensor 120 includes a transparent and flexible transmitter electrode 121; one or more transparent and flexible receiver electrodes 122; and a transparent and flexible dielectric layer 123 arranged between the transmitter electrode and the receiver electrode.

[0029] Preferably, the substrate 110, the dielectric layer 123 and the protective layer 140 are made of silicone polymers, such as polydimethylsiloxane (PDMS). The electrodes may be made of a conductive transparent gel, such as a biogel containing NaCl and having an ionic conductivity of 34.3 S / m.

[0030] The control circuit 130 is disposed on the substrate 110 and connected to the electric field sensor 120. The control circuit 130 is configured to drive the transmitter electrode 121 to transmit a reference signal to establish a quasi-static electric near field around the electric field sensor 120; and process one or more measurement signals respectively received by one or more receiver electrodes 122. Each measurement signal indicates a distortion of the quasi-static electric near field (i.e., the reference signal) caused by an object (e.g., a finger) approaching the corresponding receiver electrode.

[0031] Figure 3 The equivalent circuit model of the electric field sensor is shown in FIG. The transmitter (Tx) and receiver (Rx) electrodes of the electric field sensor together with the dielectric layer in between form a capacitor with a capacitance value C 传感器 A parallel plate capacitor having a capacitance denoted by C is formed between the object (or target) to be detected or sensed (e.g., a human hand) and the receiver electrode. 手 The capacitance formed by the two electrodes and the system ground is C RG and C Ta When using an external power supply, it is assumed that the system ground is equivalent to the earth ground. The capacitance between the target to be sensed and the earth ground is C HG When using battery power, there is a gap between the system ground and the earth ground, represented by C GND For simplicity, C is omitted from the model. GND and C HG Given a driving signal V applied to the Tx electrode Tx , the received signal V received by the Rx electrode Rx It can be expressed as:

[0032] This received signal V RxDepends on the capacitance C 传感器 and C 手 , these capacitance values ​​can be estimated using the flat plate capacitor formula C = ε·ε0·S / d, where ε is the relative dielectric constant, ε0 is the vacuum dielectric constant, S is the effective area and d is the distance.

[0033] In some embodiments, the transmitter electrode can be driven by a control circuit with a high frequency square wave signal with an amplitude of about 3V (eg Figure 4A The frequency of the square wave signal can be in the range of 44k to 115kHz.

[0034] When the hand approaches the sensor, C 手 increases (in the plate capacitor formula, S increases and d decreases), which results in the received signal V Rx Reduce (such as Figure 4B Capacitance and received voltage vs. distance ( Figure 5 ) can be obtained by placing the target at various distances from the sensor. According to equation (1), when C 手 When the variation range is fixed, in order to obtain a larger response, that is, to make V Rx The change of C 传感器 The value should be close to C RG +C 手 And C RG +C 手 Should be as small as possible.

[0035] The performance of the electronic skin can be affected by various factors, such as the power source (USB or battery), whether there is a grounded shield underneath, whether it is connected to the skin, etc. When the device is powered by a battery, C HG and C GND , resulting in a decrease in device performance. For example, when the electronic skin is directly attached to human skin, no matter what type of power supply is used, its performance is significantly reduced because the capacitance formed by the Rx electrode and the skin is added as a non-negligible term to the denominator of equation (1). To solve this problem, the electronic skin 100 may further include a grounding pad 150 configured to electrically connect the system ground of the electronic skin 100 to the earth ground.

[0036] Figure 6 An exemplary electrode design according to one embodiment of the present invention is shown. As shown, each of the transmitter electrode and the receiver electrode can have a grid pattern formed with conductive grid lines. The receiver electrode 122 can include four peripheral receiver electrodes 601 to 604 located at four peripheral areas of the electric field sensor, respectively; and a central receiver electrode 605 located at the central area of ​​the electric field sensor.

[0037] Figure 7 Some key parameters of the electronic skin are shown. Preferably, the total conductive area of ​​the transmitter electrodes (expressed as A Tx wire , that is, the total area of ​​the conductive grid lines) and the total electrode area of ​​the transmitter electrodes (expressed as A Tx ) is equal to or less than 8.1%. Preferably, the total conductive area of ​​the receiver electrodes (expressed as A Rx wire , i.e. the total area of ​​the conductive grid lines) and the total electrode area of ​​the receiver electrodes (denoted as A Rx ) is equal to or less than 12.4%. The thickness of the dielectric layer (denoted as d) may be in the range of 0.75 mm to 0.85 mm. Preferably, the thickness of the dielectric layer is equal to 0.8 mm.

[0038] Typically, the thickness of the substrate is 0.4 mm, the thickness of the dielectric layer is 0.6 to 0.8 mm, the thickness of the biogel trace is 0.2 mm and the width is 0.2 mm. The total thickness of the electronic skin is about 1 mm.

[0039] Furthermore, the orientation of the conductive gridlines of the transmitter electrodes differs substantially by 45° from the orientation of the conductive gridlines of the receiver electrodes. In other words, the conductive gridlines of the transmitter electrodes are arranged with an inclination angle substantially equal to 45° relative to the conductive gridlines of the receiver electrodes.

[0040] Figure 8 1 shows a functional block diagram of a control circuit 130 according to one embodiment of the present invention. The control circuit may include: a signal driver 801, which is configured to drive a transmitter (Tx) electrode to transmit a reference signal; and an analog-to-digital converter 802, which is configured to convert one or more measurement signals received from a receiver (Rx) electrode into one or more digital signals, respectively. The control circuit may further include a microprocessor 803, which is configured to: process one or more digital signals to respectively calculate one or more distances of an object relative to one or more receiver electrodes; and analyze one or more calculated distances to determine the position / gesture data of the object. The control circuit may further include a wireless communication unit 804, which is configured to send the position / gesture data to a remote device 805, such as a mobile phone. In some embodiments, the wireless communication unit 804 is a low-power Bluetooth (BLE) communication module.

[0041] In some embodiments, the distance of the object relative to each of the one or more receiver electrodes is calculated by processor 803 based on a least squares multilateration algorithm.

[0042] Preferably, the electronic skin may further include a lithium-ion battery 806; a capacitive touch switch 807 for switching the connection between the battery 806 and the control unit; and a low dropout regulator (LDO) 808 for regulating the voltage of the battery to a fixed DC voltage of the control circuit.

[0043] The electronic skin may further include a wireless charger receiver 809 configured to receive electromagnetic energy from the wireless charger transmitter 810 and convert the received electromagnetic energy into a DC voltage to charge the lithium-ion battery 806 .

[0044] Fig. 9 A schematic flow chart of a method for manufacturing a transparent and flexible electronic skin according to an embodiment of the present invention is shown. As shown in the figure, the method comprises:

[0045] S901: Molding a transparent and flexible material with a mold to form a patterned transparent and flexible substrate.

[0046] S902: dispensing a conductive transparent gel on a patterned transparent and flexible substrate to form an emitter electrode;

[0047] S903: forming a control circuit on the patterned transparent and flexible substrate;

[0048] S904: molding a transparent and flexible material with a mold to form a patterned transparent and flexible dielectric layer;

[0049] S905: dispensing a conductive transparent gel on the patterned transparent and flexible dielectric layer to form one or more receiver electrodes;

[0050] S906: attaching a dielectric layer to the substrate so that the transmitter electrode is separated from the one or more receiver electrodes by the dielectric layer to form an electric field sensor; and

[0051] S907: Encapsulate the control circuit and the electric field sensor with a transparent and flexible material.

[0052] In some embodiments, a photocurable 3D printer (Creality HalotBox, Shenzhen Chuangxiang 3D Technology Co., Ltd.) with resin (polyacrylate) can be used to make a mold with a pattern to form a patterned transparent and flexible substrate / dielectric layer.

[0053] In some embodiments, silicone polymers, such as PDMS (Sylgard 184, Dow Corning, 20:1) can be used for transparent and flexible operations. In step S901 / S904, PDMS is introduced into the mold and cured at 100°C for 30 minutes to obtain a patterned transparent and flexible substrate / dielectric layer. In step S907, PDMS is used to encapsulate the control circuit and electric field sensor and cured overnight at room temperature.

[0054] In some embodiments, the conductive transparent gel can be prepared by dissolving sodium chloride, citric acid, sodium citrate, and glycerol in deionized water to form a first solution; and dissolving gelatin powder (300-g Bloom) in the first solution to form the conductive transparent gel.

[0055] In one embodiment, the weight ratio of sodium chloride, citric acid, sodium citrate, glycerol and deionized water in the first solution is substantially equal to 10:1:10:60:80. The weight ratio of the first solution and the gelatin powder is substantially equal to 4:1. For example, a conductive transparent gel can be prepared by dissolving 1g of sodium chloride, 0.1g of citric acid, 1g of sodium citrate and 6g of glycerol in 8ml of deionized water, mixing on a stirrer for 20 minutes, after which 4g of gelatin powder should be added and heated in an oven at 75°C for 4 hours to completely dissolve the gelatin. After cooling, the liquid will turn into a gel due to the physical cross-linking of the gelatin chains and the chemical cross-linking of the citrate ions with the gelatin chains. When using the biogel, it only needs to be heated to return it to a liquid state, which will cause it to be squeezed out of the needle when dispensing, and when the temperature drops to room temperature, the gel will return to a gel-like state and adhere to the substrate.

[0056] In step S902 / S905, the biogel is placed in a cartridge. The biogel is then heated to 50°C and injected / dispensed into the electrode pattern channels on the PDMS substrate / dielectric layer by a printing or dispensing process to form transmitter / receiver electrodes.

[0057] In some embodiments, the control circuit is formed on the patterned transparent and flexible substrate by transfer printing a conductive trace pattern from a donor substrate to the patterned transparent and flexible substrate; and attaching electronic components on the patterned transparent and flexible substrate to form the control circuit.

[0058] Performance Evaluation

[0059] Fig.10The light transmittance of the electronic skin provided by the present invention is shown. As shown in the figure, the electronic skin exhibits a light transmittance of greater than 80% in the range of 410nm to 1000nm. This high level of transparency allows the electronic skin to be used as a transparent 3D sensing and gesture recognition layer. For example, the electronic skin can be applied directly on a display or infrared sensor without blocking any line of sight. In addition, the transparency of the electronic skin allows it to be integrated into existing devices as a nearly invisible surface layer without changing the aesthetics of the device.

[0060] Fig.11 The capacitance change during the stretching of the electronic skin provided by the present invention from its original length to 25% is shown. Fig.12 The device was shown to have no significant change in performance after more than 8,000 folding and unfolding. Because conductive biogel is used to make the electrodes, there is no fatigue effect like metals that wear out over time. This means that the electronic skin can be stretched and bent repeatedly without suffering any damage.

[0061] The electronic skin provided by the present invention can be used for gesture recognition and finger position tracking. Fig.13 As shown, the electronic skin can be used to collect and process sensing signals generated by the proximity of the user's finger to obtain the three-dimensional spatial coordinates of the finger within a predefined interaction space. Fig.14 The figure shows the sensing signals received by the electronic skin and the calculated finger movement trajectory when the five letters "CITYU" are written in the predefined interaction space using a finger. The electronic skin is very suitable for 3D modeling, AR / VR, wearable devices and other applications that need to operate in three-dimensional space.

[0062] For example, electronic skin can also be used to enable robots or drones to more effectively perceive their surroundings and provide a more comprehensive solution for 3D object detection and distance measurement. For example, a robotic arm can use electronic skin to judge the distance between objects or whether it has grasped an object. A drone can use electronic skin to determine if there are obstacles such as cables in its path.

[0063] In underwater applications, the electronic skin can act as a gesture recognition sensor in turbid water to help divers communicate effectively when vision is obstructed. This technology can also be used to monitor marine life and study collective animal behavior in the wild. This technology can help us understand and protect marine ecosystems and the species that inhabit them.

[0064] The foregoing description of the present invention has been provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations will be apparent to those skilled in the art.

[0065] The embodiment was chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated.

Claims

1. A transparent and flexible electronic skin with three-dimensional sensing capability, characterized in that: include: Transparent and flexible substrate; A transparent and flexible electric field sensor disposed on the substrate and comprising: Transparent and flexible emitter electrodes; and one or more transparent and flexible receiver electrodes; a control circuit disposed on the substrate and connected to the electric field sensor; and a transparent and flexible protective layer encapsulating the electric field sensor and the control circuit; and The control circuit is configured to: driving the transmitter electrode to transmit a reference signal to establish a quasi-static electric near field around the electric field sensor; and One or more measurement signals respectively received by the one or more receiver electrodes are processed, each measurement signal being indicative of a distortion of the quasi-static electric near field due to an object approaching a corresponding receiver electrode.

2. The transparent and flexible electronic skin according to claim 1, characterized in that: The one or more receiver electrodes include: a central receiver electrode located at a central region of the electric field sensor; and Four peripheral receiver electrodes are respectively located at four peripheral areas of the electric field sensor.

3. The transparent and flexible electronic skin according to claim 1, characterized in that: The transparent and flexible substrate is made of polydimethylsiloxane.

4. The transparent and flexible electronic skin according to claim 1, characterized in that: The transparent and flexible protective layer is made of polydimethylsiloxane.

5. The transparent and flexible electronic skin according to claim 1, characterized in that: The transparent and flexible dielectric layer is made of polydimethylsiloxane.

6. The transparent and flexible electronic skin according to claim 1, characterized in that: The transparent and flexible transmitter and receiver electrodes are made of a conductive transparent gel.

7. The transparent and flexible electronic skin according to claim 6, characterized in that: The conductive transparent gel contains sodium ions.

8. The transparent and flexible electronic skin according to claim 1, characterized in that: The control circuit comprises: a signal driver configured to drive the transmitter electrode to transmit the reference signal; and An analog-to-digital converter is configured to convert the one or more measurement signals into one or more digital signals, respectively.

9. The transparent and flexible electronic skin according to claim 8, characterized in that: The control circuit further comprises a microprocessor, wherein the microprocessor is configured to: processing the one or more digital signals to respectively calculate one or more distances of the object relative to the one or more receiver electrodes; as well as The one or more calculated distances are analyzed to determine position / gesture data for the object.

10. The transparent and flexible electronic skin according to claim 9, characterized in that: The control circuit also includes a wireless communication unit configured to transmit the position / gesture data to a remote device.

11. The transparent and flexible electronic skin according to claim 10, characterized in that: The distance of the object relative to the one or more receiver electrodes is calculated by the processor based on a least squares multilateration algorithm.

12. The transparent and flexible electronic skin according to claim 1, characterized in that: Also includes a lithium-ion battery for supplying power to the control unit; and A wireless charging unit is configured to receive electromagnetic energy and convert the received electromagnetic energy into a DC voltage to charge the lithium-ion battery.

13. A method for manufacturing a transparent and flexible electronic skin, characterized in that: include: molding a transparent and flexible material to form a patterned transparent and flexible substrate; dispensing a first conductive transparent gel on the patterned transparent and flexible substrate to form a transmitter electrode; forming a control circuit on the patterned transparent and flexible substrate; molding the transparent and flexible material to form a patterned transparent and flexible dielectric layer; dispensing a second conductive transparent gel on the patterned transparent and flexible dielectric layer to form one or more receiver electrodes; attaching the dielectric layer to the substrate such that the transmitter electrode is spaced apart from the one or more receiver electrodes by the dielectric layer to form an electric field sensor; as well as The control circuit and the electric field sensor are encapsulated with the transparent and flexible material.

14. The method according to claim 13, characterized in that The control circuit is formed on the patterned transparent and flexible substrate by: transfer printing a conductive trace pattern from a donor substrate to the patterned transparent and flexible substrate; as well as Electronic components are attached to the patterned transparent and flexible substrate to form the control circuit.

15. The method according to claim 13, characterized in that Each of the first and second conductive transparent gels is prepared by: dissolving sodium chloride, citric acid, sodium citrate, and glycerol in deionized water to form a first solution; as well as Gelatin powder is dissolved in the first solution to form the conductive transparent gel.

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