Fabric-based wearable tunable filter structures and methods of making

Abstract

The application discloses a kind of wearable fabric-based tunable filter and its preparation method, belong to microwave device technical field, containing impedance matching conversion part of SSPP structure, classic SSPP trench, additional path for regulating and controlling SSPP dispersion characteristics, upper bias circuit for realizing high-frequency isolation, lower bias circuit such as metal structure, fabric substrate and load on fabric SSPP OECT.By direct current biasing to OECT, the dispersion characteristics and operating frequency of SSPP can be changed accordingly, so as to obtain dynamic adjustable filtering characteristics, in addition, by reasonably setting the length combination of additional path, the frequency tunable characteristics of multiple states can be realized.The application provides an effective solution for the frequency interference problem faced by wearable communication system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of microwave devices, and relates to a fabric-based wearable tunable filter structure and a preparation method. BACKGROUND

[0002] With the rapid development of medical, security, sports science and other fields, the importance of wearable technology and system is increasingly prominent. Generally speaking, the functions of wearable system include measuring physiological, vital signs or sports data of human body and transmitting them to communication nodes. With the increasing demand for monitoring and transmitting various signals, multi-band communication is an indispensable part of today's wearable devices. One problem that cannot be ignored for multi-band communication devices is the interference between different frequency signal channels. Generally speaking, for traditional rigid communication systems, this problem can be solved by designing frequency tunable antennas or tunable filters, while for wearable systems, more factors need to be considered, such as the influence of human motion on shape change, wearing comfort, etc. Some research teams try to solve this problem from the perspective of wearable antennas. For example, using frequency tunable antennas can reduce the interference of other channels, but narrowband antennas are easily affected by human motion, leading to the problem of frequency shift. In addition, wideband wearable antennas can reduce the influence caused by the human body, but cannot solve the problem of channel interference. For this problem, the ideal choice is to design a wearable tunable filter, which has the advantages of being insensitive to deformation and wearing comfortably.

[0003] Under such demand guidance, the advantages of surface plasmon polaritons (SSPP) stand out. SSPP has excellent field localization, which makes it less sensitive to device deformation and can well ensure the stability of the device under human body deformation. Using this characteristic, in recent work, SSPP has been applied to wearable systems as a transmission line (X. Tian, P. M. Lee, Y. J. Tan, et al. Wireless body sensor networks based on metamaterial textiles. Nat. Electron. 2019, 2, 243-251.). In this document, SSPP structure is used for signal transmission, which improves the transmission efficiency by nearly 30 dB compared with the transmission of radio waves in free space, further proving the advantages of SSPP in wearable systems. On the other hand, using fabric or textile materials to design and prepare microwave devices will give the microwave devices the advantages of lightness, thinness, flexibility and many others. For wearable devices, fabric substrates are easier to integrate with clothes. Therefore, preparing SSPP on fabric and changing its dispersion characteristics by using control means to change the working frequency of SSPP is a good way to realize wearable tunable filter, which has important significance for solving the frequency interference phenomenon of wearable systems.

[0004] However, there are still many problems to be solved in order to realize the wearable tunable filter based on SSPP. So far, most of the tunable SSPPs are realized by integrating rigid lumped elements, and the high temperature required by the soldering process is easy to damage the fabric substrate, resulting in sample processing failure. In addition, the soldered lumped devices are easy to be desoldered when the human body deforms, causing the lumped device to be open. In recent years, organic electrochemical transistors (OECT) have attracted more and more attention, and the advantage of high planar integration makes it have a unique advantage in the preparation of flexible devices. In a recent report, researchers used OECT to prepare a metasurface and proved that the working frequency of OECT can reach 3.8GHz (G.E. Bonacchini, F.G. Omenetto. Reconfigurable microwave metadevices based on organic electrochemical transistors. Nat. Electron. 2021, 4, 424-428.), which provides a basis for the design and preparation of tunable devices based on OECT in the microwave band. SUMMARY

[0005] Technical problem: In view of the frequency interference problem of wearable systems, combining the advantages of strong field localization of SSPP structure, small deformation interference and high planar integration of OECT without high temperature soldering, a wearable tunable filter is designed. The specific invention content includes the structure design of using OECT to control the working frequency of SSPP, the bias circuit design, the integration of the conductive pattern on the fabric substrate and the integration of OECT.

[0006] Technical scheme: In order to achieve the above invention purpose, a wearable tunable filter based on fabric of the present application adopts the following technical scheme:

[0007] The filter includes an impedance matching conversion part (1) of a co-planar waveguide and a surface plasmon structure SSPP structure, a surface plasmon groove structure, a groove structure additional path for controlling the dispersion characteristics of the SSPP, an upper bias circuit for realizing high frequency isolation, a lower bias circuit, a fabric substrate, and an organic electrochemical transistor loaded between the surface plasmon groove structure and the groove structure additional path and the upper bias circuit; The filter is divided into three parts from left to right, of which the left and right are impedance matching conversion parts, and the middle part is in order from top to bottom as upper bias circuit, groove structure additional path, surface plasmon groove structure, lower bias circuit; The three ends of the organic electrochemical transistor are connected to the surface plasmon groove structure, the groove structure additional path and the upper bias circuit, respectively.

[0008] The impedance matching conversion part is divided into upper, middle and lower parts, the upper and lower parts are symmetrical horn opening shapes, the middle part is a gradually changing guide band with a wide outer part and a narrow inner part, and a groove structure is arranged on the guide band; the upper bias circuit has four spring-shaped structures, and the lower part of the spring-shaped structures is located beside the gap between the groove structure additional path and the artificial surface plasmon groove structure; the lower bias circuit has one spring-shaped structure, and the upper part of the spring-shaped structure is connected to the artificial surface plasmon groove structure.

[0009] The impedance matching conversion part, the artificial surface plasmon groove structure, the groove structure additional path, the upper bias circuit and the lower bias circuit are all metal patterns transferred to the fabric base by copper cloth processing, and the organic electrochemical transistor is prepared first and then coated with ionic gel between the artificial surface plasmon SSPP groove structure, the groove structure additional path and the upper bias circuit by using the dispensing technology.

[0010] The organic electrochemical transistor comprises a first PEDOT:PSS and a second PEDOT:PSS, and the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) PEDOT:PSS is coated on the gate and between the source and the drain of the organic electrochemical transistor by ionic gel.

[0011] The ionic gel is prepared by water bath stirring of polyvinyl alcohol, sodium poly(p-phenylene sulfonate), ethylene glycol, sorbitol and deionized water in a mass ratio of 1:3.3:1.2:0.8:10.

[0012] The fabric base (6) is selected according to the selection basis of small loss and a loss tangent less than 1x10 -2 .

[0013] The preparation method of the wearable and adjustable filter based on the fabric comprises the following steps:

[0014] Step 1: modeling simulation, determining the structure parameters of the metal pattern composed of the impedance matching conversion part, the artificial surface plasmon groove structure, the groove structure additional path, the upper bias circuit and the lower bias circuit, and the structure and property parameters of the fabric base;

[0015] Step 2: processing of the metal pattern, integrating the metal part onto the fabric base;

[0016] Step 3: preparing the organic electrochemical transistor;

[0017] Step 4: printing the organic electrochemical transistor to complete the device preparation.

[0018] The fabric substrate in step 1 is selected from polyester material, and the thickness, relative dielectric constant and loss tangent of the polyester material are 0.42 mm, 1.801 and 2.21 x 10 -3 .

[0019] In step 2, the metal pattern is processed by the method of cutting first and then transferring, that is, the copper cloth is processed by using a laser cutting machine first, and then transferred to the fabric substrate by using a heat release tape.

[0020] In step 4, the printing of the organic electrochemical transistor uses the dispensing function of the printer, and during the printing process, the heating function of the printer is turned on to prevent the first PEDOT:PSS, the second PEDOT:PSS and the ion gel from diffusing on the fabric substrate.

[0021] Invention principle: The OECT based on PEDOT:PSS is a depletion-mode organic electrochemical transistor, which works in the “on” state when the applied gate voltage is zero. With the increase of the gate voltage, cations are injected into the polymer to compensate for the sulfonic acid group of PSS, thereby effectively de-doping the conjugated backbone of PEDOT, making the channel close. The trench structure of SSPP and the additional path can be regarded as the source and drain of the OECT, and the PEDOT:PSS printed thereon will be doped by the ion gel under the control of the applied voltage, realizing the switching state. From the perspective of the characteristics of the SSPP unit, it is equivalent to change the equivalent length of the SSPP trench structure, when the OECT is turned on, the equivalent length increases, when the OECT is turned off, the additional path is invalid, and the equivalent length decreases. Correspondingly, the working frequency of the SSPP changes. Further, through the selection of different lengths of additional paths, multi-state frequency regulation can be realized.

[0022] Beneficial effects: Compared with the prior art, the wearable adjustable filter based on fabric of the present application integrates the OECT of the regulation material into the device by dispensing, without the need for welding process, which ensures its applicability on the fabric substrate, so that the filter has high planar integration and high wearing comfort. In addition, the filter of the present application utilizes the SSPP structure, which retains the advantages of strong field localization and small influence of human body deformation of the typical SSPP structure. Through ingenious structural design, the working frequency of the SSPP can be controlled by the direct current bias voltage loaded on the OECT, thereby obtaining the dynamic adjustable filtering characteristics. The present application provides an effective solution to the frequency interference problem faced by wearable communication systems. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of the overall structure of the wearable adjustable filter based on fabric;

[0024] Figure 2is a schematic diagram of a fabric-based wearable tunable filter regulating unit part metal structure;

[0025] Figure 3 is a schematic diagram of a fabric-based wearable tunable filter DC bias circuit parameter;

[0026] Figure 4 is a simulation and actual measurement result diagram of a fabric-based wearable tunable filter.

[0027] In the figure: impedance matching conversion part 1, artificial surface plasmon groove structure 2, groove structure additional path 3, upper bias circuit 4, lower bias circuit 5, fabric substrate 6, organic electrochemical transistor 7, first additional path 31, second additional path 32, first PEDOT:PSS 71, second PEDOT:PSS 72, ion gel 73. DETAILED DESCRIPTION

[0028] The structure and performance of the present application will be further described below in conjunction with the drawings.

[0029] Figure 1 is a schematic diagram of the overall structure of a fabric-based wearable tunable filter. It includes the impedance matching conversion part 1 of the co-planar waveguide and the SSPP structure, the artificial surface plasmon groove structure 2, the groove structure additional path 3 for regulating the dispersion characteristics of the SSPP, the upper bias circuit 4 for realizing high-frequency isolation, the lower bias circuit 5, the fabric substrate 6, and the organic electrochemical transistor 7 loaded between the fabric SSPP groove structure 2, the groove structure additional path 3 and the upper bias circuit 4. The specific numerical values of the parameters therein are l1=20mm, l2=100mm, w1=40mm, w2=10mm, w3=4mm, H=8mm, p=25mm, d=2mm, s=0.25mm.

[0030] The impedance matching conversion part 1, the artificial surface plasmon groove structure 2, the groove structure additional path 3, the upper bias circuit 4, and the lower bias circuit 5 are all metal structures processed from copper cloth and transferred to the fabric substrate 6. The organic electrochemical transistor 7 is first prepared and then coated onto the SSPP structure using dispensing technology.

[0031] The first PEDOT:PSS 71 is the PEDOT:PSS adhered to the gate of the organic electrochemical transistor, the second PEDOT:PSS 72 is the PEDOT:PSS spanning between the source and drain of the organic electrochemical transistor 7, and the ion gel 73 is the ion gel structure of the OECT.

[0032] Figure 2This is a schematic diagram of the metal structure of the control unit of a wearable adjustable filter based on fabric. The first additional path 31 and the second additional path 32 are two additional paths of different lengths. The specific parameter values ​​are H1 = 3mm, H2 = 8mm, g = 3mm, and H = 8mm.

[0033] Figure 3 This is a schematic diagram of the DC bias circuit parameters for a wearable adjustable filter based on fabric. OECT requires a DC bias for adjustment; however, the presence of the DC bias circuit can affect the propagation of SSPP. To reduce the impact of the DC bias circuit on high-frequency SSPP waves, the parameters of the bias circuit were optimized. The optimized parameters are h. t1 =3mm,l t1 =6mm,l t2 =19.75mm,l t3 =10mm,l t4 =6mm,g t1 =5mm,w t1 =24mm,w t2 =4mm,l b1 =25mm,l b2 =10mm,l b3 =20.25mm,l b4 =9.5mm,w b1 =8mm, the line width of the bias circuit is 1mm.

[0034] The design and fabrication of a wearable tunable filter based on fabric according to the present invention includes the following steps:

[0035] Step 1: Modeling and Simulation. The element dispersion characteristics of SSPP are simulated using the characteristic mode model in CST. An appropriate operating frequency is selected to determine... Figure 2 The structural parameters of the SSPP trench structure 2, such as period and duty cycle, are determined. Next, frequency domain simulation using CST is used to optimize the SSPP structure and determine... Figure 1 The structure and physical properties of the coplanar waveguide and SSPP structure impedance matching conversion part 1, the trench structure additional path for controlling the dispersion characteristics of SSPP 3, the upper bias circuit for achieving high-frequency isolation 4, the lower bias circuit 5, and the fabric substrate 6 are described. The parameters of the fabric substrate 6 depend on the selected fabric material. In this invention, polyester material is used, with a thickness, relative permittivity, and loss tangent of 0.42 mm, 1.801, and 2.21 × 10⁻⁶ mm, respectively. -3 .

[0036] Step 2: Fabrication of metal pattern. In this invention, the impedance matching transition part 1, the artificial surface plasmonic slot structure 2, the slot structure additional path 3, the upper biasing circuit 4, and the lower biasing circuit 5 of the metal pattern are fabricated by cutting and transferring method. The detailed operation is as follows: the.dxf model of the simulated CST parameter model is exported and imported into CADlaser, the.ud5 model is exported by using CADlaser software, the copper cloth is cut and attached to the heat release tape by using a laser cutting machine, and then the unnecessary metal part is removed. Next, the copper cloth is attached to the fabric substrate 6 by using the adhesive on the copper cloth, and finally, the heat release tape is removed after heating, obtaining the metal pattern on the heat release tape, including the impedance matching transition part 1 of the coplanar waveguide and the SSPP structure, the SSPP slot structure 2, the slot structure additional path 3 for regulating the dispersion characteristics of the SSPP, the upper biasing circuit 4 for realizing high-frequency isolation, and the lower biasing circuit 5.

[0037] Step 3: Preparation of organic electrochemical transistor OECT, structure of OECT, including first PEDOT:PSS 71, second PEDOT:PSS 72, and ionic gel 73. PEDOT:PSS can be purchased directly. The preparation process of ionic gel is as follows: weigh 1 g of white granular material polyvinyl alcohol, weigh 3.3 g of amber oil liquid sodium poly (p-phenylene sulfonate) PSS, 1.2 g of colorless viscous liquid ethylene glycol, and 0.8 g of white powder sorbitol. Put the above-mentioned substances into a 15 mL sample bottle, and add 10 g of deionized water. Mix them in a mass ratio of 1:3.3:1.2:0.8:10, add a magnetic rotor with appropriate diameter, and continuously stir at 90°C for 1 hour with a constant temperature water bath stirrer to prepare the electrolyte of the gel organic electrochemical transistor.

[0038] Step 4: Printing OECT. First, use a dispensing machine to print PEDOT:PSS on the OECT gate and between the source and drain. The first PEDOT:PSS 71 on the gate and the second PEDOT:PSS 72 between the source and drain. During the printing process, turn on the heating function of the printer to prevent PEDOT:SS from spreading on the fabric. Then, print the prepared ionic gel 73.

[0039] Step 5: After the fabric-based wearable tunable filter is prepared according to the method of the present application, SMA joints are welded at both ends of the device to serve as a feed source for radio frequency signals. The positive electrode of the OECT is connected to the top end of the upper bias circuit 4, which can be divided into four DC bias signals, and the negative electrode is connected to the bottom end of the lower bias circuit 5. By controlling the voltage of the four bias signals respectively, the switching state of the four OECTs can be realized. As shown in Figure 4 the switching state of the OECTs on the frequency regulation effect of the SSPP transmission line is simulated and tested. The four OECT units are divided into two groups, and as the control configuration changes, the simulation results of the cutoff frequency of the SSPP change from 4.4 to 3.5 and then to 2.7 GHz, and the corresponding experimental results change from 3.7 to 3.25 and then to 2.45 GHz. Although there is some deviation, a significant frequency regulation effect is obtained.

[0040] The parts of the present application not described in detail are known to those skilled in the art. The embodiments of the present application are described above in conjunction with the drawings, but the present application is not limited to the specific embodiments described above, and the above-described embodiments are merely illustrative and not limiting. Those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these are all within the protection of the present application.

Claims

1. A fabric-based wearable tunable filter, characterized by: The filter comprises an impedance matching conversion part (1) of a coplanar waveguide and a surface artificial plasma structure SSPP structure, a surface artificial plasma groove structure (2), a groove structure additional path (3) for regulating the dispersion characteristics of the SSPP, an upper bias circuit (4) for realizing high-frequency isolation, a lower bias circuit (5), a fabric substrate (6), and an organic electrochemical transistor (7) loaded between the surface artificial plasma groove structure (2), the groove structure additional path (3), and the upper bias circuit (4). The filter is divided into three parts from left to right, wherein the left and right parts are the impedance matching conversion part (1), and the middle part is sequentially arranged from top to bottom as the upper bias circuit (4), the groove structure additional path (3), the surface artificial plasma groove structure (2), and the lower bias circuit (5). The three ends of the organic electrochemical transistor (7) are connected to the surface artificial plasma groove structure (2), the groove structure additional path (3), and the upper bias circuit (4) respectively. The lower bias circuit (5) has a spring-shaped structure, and the upper part of the spring-shaped structure is connected to the surface artificial plasma groove structure (2).

2. The fabric-based wearable tunable filter of claim 1, wherein: The impedance matching conversion part (1) is divided into upper, middle, and lower parts, the upper and lower parts are symmetrically shaped like a horn opening, and the middle part is a gradually changing guide strip with a wide outer part and a narrow inner part, and the guide strip is provided with a groove structure. The upper bias circuit (4) has four spring-shaped structures, and the lower parts of the spring-shaped structures are located beside the gap between the groove structure additional path (3) and the surface artificial plasma groove structure (2).

3. The fabric-based wearable tunable filter of claim 1, wherein: The impedance matching conversion part (1), the surface artificial plasma groove structure (2), the groove structure additional path (3), the upper bias circuit (4), and the lower bias circuit (5) are all metal patterns transferred to the fabric substrate (6) by copper cloth processing, and the organic electrochemical transistor (7) is prepared first and then coated with an ionic gel (73) between the surface artificial plasma SSPP groove structure (2), the groove structure additional path (3), and the upper bias circuit (4) by using a dispensing technology.

4. The fabric-based wearable tunable filter of claim 1, wherein: The organic electrochemical transistor (7) comprises a first PEDOT:PSS (71) and a second PEDOT:PSS (72), and a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) PEDOT:PSS is coated on the gate of the organic electrochemical transistor (7) and between the source and the drain by using the ionic gel (73).

5. The fabric-based wearable tunable filter of claim 4, wherein: The ionic gel (73) is prepared by water bath stirring of polyvinyl alcohol, poly sodium p-styrenesulfonate, ethylene glycol, sorbitol, and deionized water in a mass ratio of 1:3.3:1.2:0.8:

10.

6. The fabric-based wearable tunable filter of claim 1, wherein: The fabric base (6) is selected according to small loss and tan δ less than 1×10 -2 .

7. A method of making a fabric-based wearable tunable filter as claimed in claim 1, characterized by: The method comprises the following steps: Step 1: modeling simulation, determining the structure parameters of the metal pattern composed of the impedance matching conversion part (1), the surface artificial plasma groove structure (2), the groove structure additional path (3), the upper bias circuit (4), and the lower bias circuit (5), and the structure and property parameters of the fabric substrate (6); Step 2: processing of the metal pattern, integrating the metal part onto the fabric substrate (6). Step 3: Preparation of organic electrochemical transistor (7); Step 4: Printing of organic electrochemical transistor (7) to complete the device preparation.

8. The method of making a fabric-based wearable tunable filter of claim 7, wherein: The fabric base (6) in Step 1 is made of polyester material, and the thickness, relative dielectric constant and loss tangent of the polyester material are 0.42 mm, 1.801 and 2.21 x 10 -3 , respectively.

9. The method of making a fabric-based wearable tunable filter of claim 7, wherein: The processing of the metal pattern in Step 2 uses a cut-and-transfer method. First, the copper cloth is processed using a laser cutting machine, and then transferred to the fabric substrate (6) using a heat-releasing tape.

10. The method of claim 7, wherein: In Step 4, the printing of the organic electrochemical transistor (7) uses the dispensing function of the printer. During the printing process, the heating function of the printer is turned on to prevent the first PEDOT:PSS (71), the second PEDOT:PSS (72), and the ionic gel (73) from spreading on the fabric substrate (6).

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