Flexible radio frequency power divider with extensible characteristic

Abstract

The invention aims to provide a flexible radio frequency power divider with an extensible characteristic, and belongs to the technical field of flexible electronic devices. The extensible flexible radio frequency power divider is of a sandwich-shaped structure, the top layer is a patterned transmission layer, the middle layer is an intrinsic extensible flexible dielectric material, and the reflecting layer is an extensible snakelike linear array. According to the power divider, the maximum main strain in the circuit pattern and the reflecting layer does not exceed 5% under 15% stretching, that is to say, the device cannot be broken under the stretching condition.

Description

Technical Field The present invention belongs to the technical field of flexible electronic devices, and in particular relates to a flexible radio frequency power divider with extensible characteristics. Background Art With the development of flexible electronic technology, material science and artificial intelligence technology, wearable electronic devices are receiving extensive attention from researchers. Through the research and development of wearable electronic devices, real-time monitoring of various internal and external states of the human body, such as physiological state and external electromagnetic environment, can be achieved, which helps to better understand the environment inside and outside the human body and detect and eliminate hidden dangers as early as possible. A power divider is a device that divides an input signal into multiple output signals at a specific ratio. In the field of modern communication technology, power dividers are widely used in signal distribution modules in communication base stations and antenna arrays. They can also be used in T / R components in equipment such as antenna arrays or radars. Power dividers are important structural components in the field of modern radio frequency communications and are also the basic structural part of information transmission circuits in wearable electronic devices. Traditional power dividers are generally printed circuits integrated on a hard substrate, and the other side of the substrate is a metal layer ground plane. This design has the characteristics of low processing cost, high reliability and high integration. However, its hard dielectric substrate, complete metal layer ground plane and non-extensible circuit design limit its ductility. At the same time, the hard substrate occupies a large area, which poses a challenge to the miniaturization design of the device. In recent years, researchers have conducted research on the flexibility of power dividers, such as wearable textile power dividers using textile materials as substrates. [1] , Bendable power divider using etched circuits [2] , Graphene-based surface plasmon flexible power divider [3] However, these devices usually have limited flexibility and can only work on curved surfaces or simple conformal surfaces. [4] When the human body is exercising, the skin at joints and other parts of the body will stretch by 5%-15% while changing shape. Electronic devices that are not stretchable will cause users to feel uncomfortable and may also cause damage to the devices. Therefore, how to design a flexible power divider so that it can maintain its basic original performance when stretched has become a concern for researchers.

[0001] Z. Kou, J. Li, C. Zhang, Z. Chen, Z. Liu and W. Lu, "A Wearable All-Fabric Wilkinson Power Divider for Flexible Radio Frequency Applications," 2024 14th International Symposium on Antennas, Propagation and EM Theory (ISAPE), Hefei, China, 2024, pp. 1-4.

[0002] F. Li, C. Yu and Y. Liu, "Design of Flexible Dual-band Filtering Power Divider with Significant Out-of-band Suppression Performance," 2022 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP), Guangzhou, China, 2022, pp. 1-3.

[0003] Bian Wu et al. "Flexible wideband power divider with high isolation incorporating spoof surface plasmon polaritons transition with graphene flake" 2019 Appl. Phys. Express 12 022008.

[0004] Y. Zhao, K.-Q. Jin, J.-D. Li, K.-K. Sheng, W.-H. Huang, Y.-L. Liu, Flexible and Stretchable Electrochemical Sensors for Biological Monitoring. Adv. Mater. 2023, 2305917. Summary of the Invention Aiming at the problems existing in the background technology, the purpose of the present invention is to provide a flexible RF power divider with extensible characteristics. The extensible flexible RF power divider has a "sandwich" structure, with a patterned transmission layer on the top layer, an intrinsically stretchable flexible dielectric material in the middle layer, and a ground plane composed of an extensible serpentine line array. The flexible power divider of the present invention still has normal electromagnetic performance when stretched to 15%. To achieve the above purpose, the technical solution of the present invention is as follows: A flexible RF power divider with extensible characteristics, which successively includes a patterned transmission layer, a flexible dielectric layer, and a reflection layer from top to bottom; The patterned transmission layer includes an input segment transmission line, two identical one-to-two transmission lines, four identical end transmission lines, and four identical impedance matching regions; Among them, the input segment transmission line is a first rectangular patch. The one-to-two transmission line includes a first straight line and a serpentine line connected to the first straight line. One end of the first straight line is connected to the first rectangular patch. The serpentine line includes several semicircles and several second straight lines, and the semicircles and the second straight lines are connected in sequence, and the opening directions of adjacent two semicircles are opposite. The first straight line and the serpentine line are connected by a quarter circle. The end transmission line includes a 90° bent line and a serpentine line connected to the bent line. The end of the serpentine line in the one-to-two transmission line is connected to one end of the bent line of the end transmission line through a quarter circle. The serpentine line end of the end transmission line is connected to the impedance matching region through a connection region. The connection region is composed of two quarter circles. Among them, the quarter circles in the two connection regions on the same side in the extension direction of the flexible RF power divider have opposite opening directions. The serpentine lines in the one-to-two transmission line and the serpentine lines in the end transmission line are the same; The impedance matching region is composed of a second rectangular patch and a third rectangular patch connected thereto. One end of the second rectangular patch is connected to the serpentine line in the end transmission line through a quarter circle, and the sizes of the second rectangular patch and the third rectangular patch are different; The reflection layer is obtained by arranging a periodic array of reflection units. Each reflection unit is obtained by rotating a semicircle 90°, 180°, and 270° in sequence with one endpoint as the center point, and the whole is in the shape of a "卍". Further, the line width w of the serpentine line is determined by the dielectric constant ε of the selected dielectric substrate r , the thickness h of the flexible RF power divider, and the matched impedance Z 0 ; Among them, ε e is the equivalent dielectric constant. Further, in order to suppress signal crosstalk, the inner diameter of the arc of the serpentine line is generally not less than 1 mm. The width of the second straight line is the same as the line width of the semicircle in the serpentine line, and the length is 1 / 4 of the wavelength of the operating frequency. Furthermore, the length of the second rectangular patch and the third rectangular patch is 1 / 4 wavelength of the working frequency band, and the width should satisfy the matching of the serpentine line circuit impedance and the output impedance. Furthermore, the patterned transmission layer and the reflective layer are made of metal materials, preferably gold, platinum, copper, aluminum, etc.; the flexible dielectric layer can be PDMS, Ecoflex, LCP, etc. Furthermore, the copper foil surfaces of the patterned transmission layer and the reflective layer are locally slightly acid-etched to increase the surface roughness, thereby increasing the peeling resistance between the flexible dielectric layer and the copper foil. Furthermore, the thickness of the patterned transmission layer and the reflection layer are both 18 μm-35 μm; the thickness of the flexible dielectric layer is 0.5 mm-3 mm. Furthermore, the line width of the semicircle in the reflective layer is 0.1-0.15 mm, and the arc radius is 0.8-1.0 mm. In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The stretchable flexible RF power divider proposed in the present invention can evenly distribute the input RF signal into 4 output RF signals. By designing a serpentine line of a special shape and reasonably designing the parameters of the serpentine line, good impedance matching is ensured between the power divider and the input RF signal. At the same time, the design of the serpentine line ensures that the power divider has good ductility, that is, it still has good RF characteristics under stretching. 2. The stretchable flexible RF power divider proposed in the present invention has a patterned reflective layer with good electromagnetic reflection properties through special graphical design. At the same time, the maximum principal strain in the circuit pattern and the reflective layer of the power divider of the present invention does not exceed 5% under a 15% stretching, that is, the device can be achieved without breaking under stretching conditions. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic structural diagram of a flexible radio frequency power divider with extensible characteristics of the present invention. Figure 2 It is a structural schematic diagram of the patterned circuit layer of the present invention. Figure 3 It is a schematic diagram of the reflective unit structure and an electromagnetic energy reflection coefficient diagram of the patterned reflective layer of the present invention. Figure 4 It is a finite element simulation diagram of the serpentine line in the patterned reflection layer and transmission layer of the present invention under tension. Figure 5 The figure is a schematic diagram of the preparation process of the flexible radio frequency power divider of the present invention. Figure 6 These are photos of the actual flexible power divider of the present invention and photos of its flexible application scenarios. Figure 7This is the electromagnetic parameter test result diagram of the flexible power divider of the present invention before and after stretching. Specific Embodiments To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. A flexible radio frequency power divider with extensible characteristics, the structural schematic diagram of which is as Figure 1 shown, from top to bottom are a patterned transmission layer, a flexible dielectric layer and a reflection layer in sequence; The structural schematic diagram of the patterned transmission layer is as Figure 2 shown, including an input segment transmission line, two identical one-to-two transmission lines, four identical end transmission lines and four identical impedance matching regions; Among them, the input segment transmission line is a first rectangular patch, the one-to-two transmission line includes a first straight line and a serpentine line connected to the first straight line. One end of the first straight line is connected to the first rectangular patch. The serpentine line includes a plurality of semicircles and a plurality of second straight lines. Among them, in order to avoid deformation in directions other than the stretching direction, a straight line is added between the serpentine line and the bent line to isolate the strain between the two arc lines; the semicircles and the second straight lines are connected in sequence, and the opening directions of adjacent two semicircles are opposite. The first straight line and the serpentine line are connected by a quarter arc; the end transmission line includes a 90° bent line and a serpentine line connected to the bent line; the end of the serpentine line in the one-to-two transmission line is connected to one end of the bent line of the end transmission line through a quarter arc, and the serpentine line end of the end transmission line is connected to the impedance matching region through the connection region. The connection region is composed of two quarter arcs. Among them, the quarter arcs in the two connection regions on the same side in the extension direction of the flexible radio frequency power divider have opposite opening directions; the serpentine lines in the one-to-two transmission line and the serpentine lines in the end transmission line are the same; The impedance matching region is composed of a second rectangular patch and a third rectangular patch connected thereto. One end of the second rectangular patch is connected to the serpentine line in the end transmission line through a quarter arc, and the sizes of the second rectangular patch and the third rectangular patch are different; The reflection layer is obtained by arranging a periodic array of reflection units. Each reflection unit is obtained by rotating a semicircle 90°, 180° and 270° in sequence with one endpoint as the center point, and the whole is in the shape of a "卍". Figure 3 This is the structural schematic diagram of the reflection unit of the patterned reflection layer of the present invention and the electromagnetic energy reflection coefficient diagram. In the frequency band of 1.8 - 3.5 GHz, a serpentine line with a line width D of 0.1 mm and an arc radius R of 0.8 mm is selected, and its reflection coefficient is greater than 0.92, which can ensure that most of the energy does not leak through the ground plane. At the same time Figure 4The finite element simulation results of the local strain distribution of the serpentine structure of the design under 15% tension are shown. At this tensile strength, the maximum principal strain of the serpentine ground plane is 3.3%, which is lower than the 5% fracture criterion, indicating that the structural parameters will not break under 15% tension. At the same time, the finite element simulation results of the local strain distribution of the serpentine part in the transmission layer under 15% tension are shown. At this tensile strength, the maximum principal strain of the serpentine ground plane is 4.2%, which is also lower than the 5% fracture criterion. Example 1 A method for preparing a flexible radio frequency power divider with extensible characteristics, the preparation process is as follows Figure 5 As shown, the specific steps include: Step 1. Immerse a copper foil with a thickness of 18 μm in an etching solution for 5 seconds for roughening treatment, and then use alcohol to wash away the residual etching solution after taking it out; Step 2: Use a tape-casting process to scrape a semi-molten polydimethylsiloxane (PDMS) precursor on the roughened copper foil surface. Considering the fluidity of the semi-molten PDMS, the distance between the scraper and the copper foil surface is set to 0.7 mm. Step 3: Place the copper foil covered with dielectric material on a hot plate with vacuum adsorption function for curing at 65° C. for 1 hour to obtain a flexible dielectric layer with a relative dielectric constant of 2.5, a dielectric loss of 0.03, and a dielectric substrate layer thickness of 0.4 mm; Step 4: Cover the surface of the copper foil with the flexible dielectric layer obtained in step 3 with a mask, and closely adhere to a layer of solid photosensitive film, and use a photolithography process to sequentially perform development, etching, and exposure to obtain a patterned transmission layer and a reflective layer; Step 5: The two flexible dielectric layers connected to the patterned transmission layer and the reflective layer obtained in step 4 are laminated and cured to obtain the desired flexible RF power divider. Figure 6 The actual photograph of the flexible and stretchable power divider proposed in the present invention is shown. The power divider can ensure the integrity of the device in different states such as stretching, bending, twisting, and folding, that is, the power divider of the present invention has a stretchable characteristic. Figure 7In order to demonstrate the measured electromagnetic characteristics of the flexible and stretchable power divider proposed in the present invention, the feeding end is defined as port 1 and the four output ends are defined as ports 2-5. It can be seen from the figure that within 3.1-3.6GHz, the power divider can achieve a one-to-four uniform energy distribution, and its S11 parameter is lower than -10dB, while the S21, S31, S41, and S51 parameters are all around -8dB to -9dB, which is relatively close to the theoretical ideal value of -7.5dB. The right figure shows the electromagnetic characteristic parameters of the power divider measured at a stretching rate of 13%. When stretched to 13%, the S11 of the power divider proposed in the present invention is lower than -10dB in the range of 3.1-3.6GHz, and has normal working ability. At the same time, the S21-S51 parameters have produced a certain divergence compared with before stretching, but are still in the range of -8dB to -9dB at the center frequency, and diverge to about -7dB to -10dB at the edge of the band. Therefore, it can be judged that the power divider of the invention can still maintain a stable working state at a stretching rate of 13%. The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A flexible radio frequency power divider with extensible characteristics, characterized in that: From top to bottom, there are a patterned transmission layer, a flexible dielectric layer, and a reflective layer in sequence; The patterned transmission layer includes an input segment transmission line, two identical one-to-two transmission lines, four identical end transmission lines, and four identical impedance matching regions; Among them, the input segment transmission line is a first rectangular patch. The one-to-two transmission line includes a first straight line and a serpentine line connected to the first straight line. One end of the first straight line is connected to the first rectangular patch. The serpentine line includes a number of semicircles and a number of second straight lines. The semicircles and the second straight lines are connected in sequence, and the opening directions of adjacent semicircles are opposite. The first straight line and the serpentine line are connected by a quarter circle. The end transmission line includes a 90° bent line and a serpentine line connected to the bent line. The end of the serpentine line in the one-to-two transmission line is connected to one end of the bent line of the end transmission line through a quarter circle. The serpentine line end of the end transmission line is connected to the impedance matching region through a connection region. The connection region is composed of two quarter circles. Among them, the quarter circles in the two connection regions on the same side in the extension direction of the flexible radio frequency power divider have opposite opening directions. The serpentine line in the one-to-two transmission line is the same as the serpentine line in the end transmission line; The impedance matching region is composed of a second rectangular patch and a third rectangular patch connected thereto. One end of the second rectangular patch is connected to the serpentine line in the end transmission line through a quarter circle. The sizes of the second rectangular patch and the third rectangular patch are different; The reflective layer is obtained by arranging a periodic array of reflective units. Each reflective unit is obtained by rotating a semicircle 90°, 180°, and 270° in sequence with one endpoint as the center point, and the whole is in the shape of a "卍".

2. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The line width w of the serpentine line depends on the dielectric constant ε of the selected dielectric substrate. r , it is determined by the thickness h of the flexible RF power divider and the matching impedance Z0.

3. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The inner diameter of the arc of the serpentine line is not less than 1 mm. The width of the second straight line is the same as the line width of the semicircle in the serpentine line, and the length is 1 / 4 wavelength of the working frequency band.

4. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The lengths of the second rectangular patch and the third rectangular patch are 1 / 4 wavelength of the working frequency band, and the width should satisfy the impedance matching between the serpentine line circuit impedance and the output impedance.

5. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The patterned transmission layer and the reflective layer are made of metal materials, and the flexible dielectric layer is PDMS, Ecoflex, or LCP.

6. The flexible radio frequency power divider with extensible characteristics as claimed in claim 5, characterized in that: The metal materials are gold, platinum, copper, or aluminum.

7. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The copper foil surfaces of the patterned transmission layer and the reflective layer are subjected to local micro-etching treatment to increase the surface roughness.

8. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The thicknesses of both the patterned transmission layer and the reflective layer are 18 μm - 35 μm; the thickness of the flexible dielectric layer is 0.5 mm - 3 mm.

9. The flexible radio frequency power divider with extensible characteristics as claimed in claim 1, characterized in that: The line width of the semicircle in the reflective layer is 0.1 - 0.15 mm, and the arc radius is 0.8 - 1.0 mm.

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