Implantable circularly polarized antenna based on graphene ring-loop sector-loaded patch

Abstract

The present invention discloses an implantable circularly polarized antenna based on a graphene annular loop sector-loaded patch. The radiation patch and the floor material of the antenna are both multi-layer graphene films. The use of multi-layer graphene films to process the antenna can improve the performance of the antenna, effectively reduce losses and improve transmission efficiency. By adding four sector-loaded patches to the annular loop, the design size of the antenna can be effectively reduced. Rectangular branches of the same size and interlaced with each other are added between the four sector-loaded patches to form an interdigitated capacitor structure, thereby reducing the resonant frequency of the implantable antenna. By slitting the conduction band and adding rectangular open-circuit protrusions, geometric perturbations are generated, resulting in circular polarization characteristics. The volume of the antenna is only 5.5×5.5×0.635mm 3 It has the characteristics of wide frequency band, circular polarization, miniaturization, anti-interference, good biocompatibility, etc. It is suitable for the WMTS 1.43GHz frequency band and can meet the working requirements after being implanted in complex environments.

Description

Technical Field

[0001] The invention relates to the technical field of implantable antennas, and in particular to an implantable circularly polarized antenna based on a graphene annular loop sector-shaped loading patch, which is suitable for a circularly polarized implantable biomedical device in the WMTS 1.43 GHz frequency band. Background Art

[0002] With the emergence of social problems such as the surge in the number of sub-healthy people and the prominence of the aging population, mobile medical care has attracted much attention. Wireless human area network is a key technology for realizing mobile medical care. Its role is to communicate human physiological information with hospitals, home networks and big data platforms through the network. Implantable medical devices such as intracranial pressure monitoring, subcutaneous blood glucose monitoring, artificial retinas, etc. are specific ways to assist or expand medical diagnosis and treatment. Implantable antennas transmit human physiological information to the Internet of Things or big data platforms through the network, providing decision-making basis for professionals to implement diagnosis and treatment and care. Implantable antennas are the core components of implantable medical devices. Their working environment is special, especially the electrical characteristics of human tissue have a great impact on implantable antennas. When designing implantable antennas, the performance requirements of antenna size, bandwidth, low power consumption and anti-interference should be fully considered. After the antenna is implanted into the human body, it will move or rotate with the movement of the human body. If it is a linearly polarized antenna, polarization mismatch will occur due to the change in the angle between the implantable antenna and the external antenna, thus affecting the communication quality. Circularly polarized antennas can suppress polarization mismatches caused by antennas in different tissue environments and movements, thereby reducing the demand for polarization characteristics of external linearly polarized antennas, while also reducing multipath interference and bit error rates. However, designing a circularly polarized implantable antenna requires taking into account multiple requirements such as circular polarization, miniaturization, electromagnetic interference and compatibility, working bandwidth and frequency, and biocompatibility. Designing an implantable circularly polarized antenna with excellent performance is challenging. The main methods for miniaturizing implantable antennas are to extend the current path to increase electrical dimensions, change the structure of the dielectric substrate, use a high dielectric constant dielectric substrate, and use loading technology to increase active networks. Non-patent document 1: A circularly polarized square ring implantable antenna operating in the 915MHz frequency band is disclosed. First, four square patches are added inside the square ring to produce a slow wave effect, thereby miniaturizing the antenna. Two short-circuit probes are added to the square patches to increase the bandwidth of the resonance point. By adjusting the positions of the short-circuit probes and the coaxial connector, two orthogonal components with equal amplitudes and a phase difference of 180 degrees are generated, thereby producing circular polarization characteristics. The size of the antenna is 13mm×13mm×1.27mm. Non-patent document 2: A small circularly polarized ring implantable antenna is disclosed. The antenna radiation unit consists of a ring and a middle circular patch. A rectangular groove is opened on the ring to extend the current path on the antenna surface, thereby reducing the size of the antenna. Two protruding branches are added to the inside of the ring to excite two degenerate modes with a phase difference of 90 degrees and equal amplitudes, thereby producing circular polarization characteristics. The size of the antenna is π×(5.5mm)2 ×1.27mm. The conductivity of graphene materials is 50 times that of ordinary materials. The honeycomb structure of graphene can produce a higher carrier density and has excellent conductivity. At the same time, the conductivity of graphene materials is dynamically adjustable. Graphene materials have attracted widespread attention in the fields of mechanics, optics, electricity, and thermal engineering due to their unique properties and advantages. The use of graphene materials in printed antennas can greatly improve the performance of antennas, achieve efficient dynamic adjustment, high transparency, improve transmission efficiency and reduce losses, meet the miniaturization requirements of antennas in ingestible wireless communication systems, and greatly increase communication distances. Domestic and foreign scholars' research on graphene materials in the field of antennas mainly focuses on terahertz antennas, reconfigurable antennas, filtering antennas, flexible antennas, and wearable antennas. There is relatively little research on graphene in implantable antennas.

[0003] Citation list

[0004] Non-patent literature 1: Xu LJ, Guo YX, Wu W..Miniaturized circularly polarizedloop antenna for bio-medical applications[J]. IEEE Transactions on Antennasand Propagation, 2015, 63(3):922-930.

[0005] Non-patent literature 2: Li R., Guo YX, Zhang B., et al. A miniaturized circularlypolarized implantable annular-ring antenna [J]. IEEE Antennas and WirelessPropagation Letters, 2017, 16: 2566-2569. Summary of the invention

[0006] The purpose of the present invention is to provide an implantable circularly polarized antenna based on a graphene annular loop sector-loaded patch, which has the characteristics of wide frequency band, circular polarization, miniaturization, anti-interference, good biocompatibility, etc., is easy to be integrated into an implantable wireless biomedical device, is suitable for the WMTS 1.43GHz frequency band, and can meet the working requirements after being implanted in human tissue.

[0007] The technical solution of the present invention is: an implantable circularly polarized antenna based on a graphene annular loop sector-loaded patch, which is composed of a dielectric substrate 1, a graphene annular loop loaded radiation patch 2, a short-circuit probe 3, a short-circuit probe 4, a coaxial connector 5, and a graphene floor 6; the graphene annular loop loaded radiation patch 2 and the graphene floor 6 are both made of multilayer graphene film, and the multilayer graphene film material has good electrical conductivity. Using the multilayer graphene film to process the antenna can improve the performance of the antenna, effectively reduce the loss and improve the transmission efficiency; the characteristics are:

[0008] a. The graphene annular loop loaded radiation patch 2 is composed of an annular loop 2-1, a fan-shaped loaded patch 2-2, a fan-shaped loaded patch 2-3, a fan-shaped loaded patch 2-4, a fan-shaped loaded patch 2-5 and a central circular slotted patch 2-6. The annular loop 2-1 is located outside the graphene annular loop loaded radiation patch 2. The fan-shaped loaded patch 2-2, the fan-shaped loaded patch 2-3, the fan-shaped loaded patch 2-4 and the fan-shaped loaded patch 2-5 are connected to the annular loop 2-1 through four conducting strips. By adding the fan-shaped loaded patch 2-2, the fan-shaped loaded patch 2-3, the fan-shaped loaded patch 2-4 and the fan-shaped loaded patch 2-5 to the annular loop 2-1, the design size of the antenna can be effectively reduced. Rectangular branches of the same size and interlaced with each other are added between the patch 2-4 and the fan-shaped loading patch 2-5 to form an interdigitated capacitor structure, which increases the coupling capacitance per unit length and reduces the resonant frequency of the implantable antenna. A slit is opened on the left and right conductive strips, and two rectangular open-circuit protrusions are added on the inner sides of the fan-shaped loading patch 2-2 and the fan-shaped loading patch 2-4 and inserted into the central circular slotted patch 2-6. Geometric perturbations are generated by slitting the conductive strips and adding rectangular open-circuit protrusions, thereby forming orthogonal components with equal amplitudes and a phase difference of 90 degrees in space, thereby generating circular polarization characteristics. The central circular slotted patch 2-6 is located at the center of the graphene ring loop loading radiation patch 2. An X-shaped slit is opened in the middle of the central circular slotted patch 2-6 to adjust the antenna impedance matching and improve the axial ratio performance.

[0009] b. The short-circuit probe 3 and the short-circuit probe 4 are arranged on the sector-shaped loading patch 2-2 and the sector-shaped loading patch 2-4 in the graphene ring loop loading radiation patch 2. The short-circuit probe 3 and the short-circuit probe 4 are symmetrical about the longitudinal axis of the antenna dielectric substrate 1. Adding the short-circuit probe 3 and the short-circuit probe 4 can increase the resonance point and further broaden the impedance bandwidth of the implantable antenna;

[0010] c. The coaxial connector 5 is located on the fan-shaped loading patch 2-4 in the graphene ring loop loaded radiation patch 2, the inner core of the coaxial connector 5 is connected to the graphene ring loop loaded radiation patch 2, and the outer core of the coaxial connector 5 is connected to the graphene floor 6;

[0011] d. The graphene floor 6 adopts a complete circular structure to form a shielding layer in the implantable wireless biomedical device, which can reduce the interference of the implantable antenna to other electronic components of the wireless biomedical device and improve the electromagnetic compatibility of the implantable antenna.

[0012] The thickness of the multilayer graphene film is 0.01 mm to 0.03 mm, and the radius R of the dielectric substrate 1 is 8 It is 4.8mm~5.7mm.

[0013] The inner radius R of the annular loop 2-1 of the graphene annular loop loaded with the radiation patch 2 is 3 is 4.5mm~5mm, and the thickness of the annular loop 2-1 is W 8 The width W of the upper and lower connecting conductors between the annular loop and the fan-shaped loading patch is 0.2mm~0.3mm. 7 0.5mm~0.9mm, length L 1 The length L of the left and right connecting conductors between the annular loop and the fan-shaped loading patch is 0.5mm~0.6mm. 2 The length of the gap between the left and right connecting guides is 0.5mm to 0.9mm. 10 2.2mm~2.4mm, width W 1 The inner radius R of the fan-shaped loading patch is 0.5mm~0.9mm. 1 1.4mm~1.8mm, outer radius R 4 The length L of the interlaced rectangular branches between the fan-shaped loading patches is 4.1mm~4.3mm. 1 0.5mm~0.6mm, width W 6 The distance between the rectangular branches is 0.1mm to 0.2mm. 5 0.1mm~0.3mm, the distance L from the rectangular branch to the fan-shaped edge 9 The length L of two rectangular open-circuit protrusions is 0.1mm to 0.2mm, and the inner side of the fan-shaped loading patch 2-4 is increased. 7 0.4mm~0.5mm, width W 2 The length L of the rectangular gap between the central circular slotted patch 2-6 and the rectangular open protrusion is 0.9mm~1mm. 5 0.5mm~0.9mm, width W 3 0.5mm~0.9mm, the width W of the X-shaped gap of the central circular slit patch 2-6 4 The length of the rectangle in the four directions of the X-shaped gap is L 8 0.5mm~0.6mm, the length L of the rectangle in the middle of the X-shaped gap 4 It is 0.8mm~1.2mm.

[0014] The distance R between the short-circuit probe 3 and the short-circuit probe 4 and the center of the dielectric substrate 1 is 6 is 3.2 mm to 3.5 mm, and the angle a between the center of the short-circuit probe 3 and the center of the short-circuit probe 4 and the vertical symmetry axis of the dielectric substrate 1 is 1 5 to 15 degrees, short-circuit probe 3, short-circuit probe 4 radius R 5 The radius of the short-circuit probe 3 and the short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

[0015] The distance R between the coaxial connector 5 and the center of the dielectric substrate 1 is 7 The angle a between the center of the coaxial connector 5 and the horizontal symmetry axis of the dielectric substrate 1 is 3 mm to 3.3 mm. 2 It is 16 to 24 degrees.

[0016] The outer surface of the implantable circularly polarized antenna of the ring loop sector loading patch is coated with a layer of biocompatible aluminum oxide with a thickness of 0.03 mm and a dielectric constant of ε r The angle of the antenna is 9.2, and the loss tangent tanδ is 0.008, which isolates the implantable circularly polarized antenna from human tissue and increases the biocompatibility of the implantable circularly polarized antenna.

[0017] The effect of the present invention is that the present invention designs an implantable circularly polarized antenna based on a graphene annular loop sector-loaded patch. The graphene annular loop loaded radiation patch and the graphene floor are both made of multilayer graphene film. The multilayer graphene film material has good electrical conductivity. The use of multilayer graphene film to process the antenna can improve the performance of the antenna, effectively reduce the loss and improve the transmission efficiency. By adding four sector-loaded patches to the annular loop, the design size of the antenna can be effectively reduced. Rectangular branches of the same size and interlaced with each other are added between the four sector-loaded patches to form an interdigitated capacitor structure, which increases the coupling capacitance per unit length and reduces the resonant frequency of the implantable antenna. Geometric perturbations are generated by slitting the conduction band and adding rectangular open-circuit protrusions, thereby forming orthogonal components with equal amplitudes and a phase difference of 90 degrees in space, generating circular polarization characteristics. An X-shaped gap is opened in the middle of the central circular slit patch to adjust the antenna impedance matching and improve the axial ratio performance. The graphene floor adopts a complete circular structure to form a shielding layer in the implantable wireless biomedical device, which can reduce the interference of the implantable antenna to other electronic devices of the wireless biomedical device and improve the electromagnetic compatibility performance of the implantable antenna. The implantable circularly polarized antenna is a planar structure with a volume of only 5.5×5.5×0.635mm 3 It has the characteristics of wide frequency band, circular polarization, miniaturization, anti-interference, good biocompatibility, etc. It is suitable for the WMTS 1.43GHz frequency band and can meet the working requirements after being implanted in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the front structure of an embodiment of the present invention.

[0019] Figure 2 It is a schematic diagram of the side structure of an embodiment of the present invention.

[0020] Figure 3 It is a schematic diagram of the back structure of an embodiment of the present invention.

[0021] Figure 4 is the length L of the interlaced rectangular branches between the fan-shaped loading patches in the embodiment of the present invention. 1 , Width W 6 Impact on antenna impedance bandwidth and axial ratio bandwidth.

[0022] Figure 5 is the length L of the rectangular open-circuit protrusion inside the fan-shaped loading patch of the embodiment of the present invention 7 , Width W 2 Impact on antenna impedance bandwidth and axial ratio bandwidth.

[0023] Figure 6 is the width W of the X-shaped gap in the embodiment of the present invention 4 , the rectangular length L of the X-shaped gap in four directions 8 , the length of the rectangle in the middle of the X-shaped gap 4 Impact on antenna impedance bandwidth and axial ratio bandwidth.

[0024] Figure 7 This is the influence of the thickness T of the multilayer graphene film on the antenna performance in the embodiment of the present invention.

[0025] Figure 8 It is a schematic diagram of the implantation environment and position of an embodiment of the present invention.

[0026] Fig. 9 This is the effect of the implantation depth on the antenna impedance bandwidth according to the embodiment of the present invention.

[0027] Fig.10 1 is a simulated and measured impedance bandwidth curve of an embodiment of the present invention.

[0028] Fig.11 It is the E-plane radiation pattern of the embodiment of the present invention at a frequency of 1.43 GHz.

[0029] Fig.12 This is the H-plane radiation pattern of the embodiment of the present invention at a frequency of 1.43 GHz. DETAILED DESCRIPTION

[0030] The specific implementation mode of the present invention is: Figure 1As shown, the implantable circularly polarized antenna based on the graphene annular loop sector-loaded patch is composed of a dielectric substrate 1, a graphene annular loop loaded radiation patch 2, a short-circuit probe 3, a short-circuit probe 4, a coaxial connector 5, and a graphene floor 6; the graphene annular loop loaded radiation patch 2 and the graphene floor 6 are both made of multi-layer graphene film, and the multi-layer graphene film material has good conductivity. Using the multi-layer graphene film to process the antenna can improve the performance of the antenna, effectively reduce the loss and improve the transmission efficiency; it is characterized in that: the graphene annular loop loaded radiation patch 2 is composed of an annular loop 2-1, a sector-loaded patch 2-2, a sector-loaded patch 2-3, a sector-loaded patch 2-4, a sector-loaded patch 2-5 and a center The antenna is composed of a circular slotted patch 2-6, the ring loop 2-1 is located outside the graphene ring loop loaded radiation patch 2, the fan-shaped loaded patch 2-2, the fan-shaped loaded patch 2-3, the fan-shaped loaded patch 2-4, and the fan-shaped loaded patch 2-5 are connected to the ring loop 2-1 through four conduction bands, and the design size of the antenna can be effectively reduced by adding the fan-shaped loaded patch 2-2, the fan-shaped loaded patch 2-3, the fan-shaped loaded patch 2-4, and the fan-shaped loaded patch 2-5 to the ring loop 2-1. Rectangular branches of the same size and interlaced with each other are added between the fan-shaped loaded patch 2-2, the fan-shaped loaded patch 2-3, the fan-shaped loaded patch 2-4, and the fan-shaped loaded patch 2-5 to form an interdigitated capacitor structure, thereby increasing the coupling capacitance per unit length and reducing the capacitance. The resonant frequency of the low implantable antenna is reduced, a gap is opened on the left and right conductive strips, and two rectangular open-circuit protrusions are added on the inner sides of the fan-shaped loading patch 2-2 and the fan-shaped loading patch 2-4, and inserted into the central circular slotted patch 2-6. The geometric perturbation is generated by the conductive strip slits and the addition of the rectangular open-circuit protrusions, thereby forming orthogonal components with equal amplitudes and a phase difference of 90 degrees in space, thereby generating circular polarization characteristics. The central circular slotted patch 2-6 is located at the center of the graphene ring loop loaded radiation patch 2, and an X-shaped gap is opened in the middle of the central circular slotted patch 2-6, which can adjust the antenna impedance matching and improve the axial ratio performance; the short-circuit probes 3 and 4 are arranged in the fan-shaped loading patch in the graphene ring loop loaded radiation patch 2. On the sheet 2-2 and the fan-shaped loading patch 2-4, the short-circuit probe 3 and the short-circuit probe 4 are symmetrical about the longitudinal axis of the antenna dielectric substrate 1. Adding the short-circuit probe 3 and the short-circuit probe 4 can increase the resonance point and further broaden the impedance bandwidth of the implantable antenna; the coaxial connector 5 is located on the fan-shaped loading patch 2-4 in the graphene ring loop loaded radiation patch 2, the inner core of the coaxial connector 5 is connected to the graphene ring loop loaded radiation patch 2, and the outer core of the coaxial connector 5 is connected to the graphene floor 6; the graphene floor 6 adopts a complete circular structure to form a shielding layer in the implantable wireless biomedical device, which can reduce the interference of the implantable antenna to other electronic devices of the wireless biomedical device and improve the electromagnetic compatibility performance of the implantable antenna.

[0031] The thickness of the multilayer graphene film is 0.01 mm to 0.03 mm, and the radius R of the dielectric substrate 1 is 8 It is 4.8mm~5.7mm.

[0032] The inner radius R of the annular loop 2-1 of the graphene annular loop loaded with the radiation patch 2 is 3 is 4.5mm~5mm, and the thickness of the annular loop 2-1 is W 8 The width W of the upper and lower connecting conductors between the annular loop and the fan-shaped loading patch is 0.2mm~0.3mm. 7 0.5mm~0.9mm, length L 1 The length L of the left and right connecting conductors between the annular loop and the fan-shaped loading patch is 0.5mm~0.6mm. 2 The length of the gap between the left and right connecting guides is 0.5mm to 0.9mm. 10 2.2mm~2.4mm, width W 1 The inner radius R of the fan-shaped loading patch is 0.5mm~0.9mm. 1 1.4mm~1.8mm, outer radius R 4 The length L of the interlaced rectangular branches between the fan-shaped loading patches is 4.1mm~4.3mm. 1 0.5mm~0.6mm, width W 6 The distance between the rectangular branches is 0.1mm to 0.2mm. 5 0.1mm~0.3mm, the distance L from the rectangular branch to the fan-shaped edge 9 The length L of two rectangular open-circuit protrusions is 0.1mm to 0.2mm, and the inner side of the fan-shaped loading patch 2-4 is increased. 7 0.4mm~0.5mm, width W 2 The length L of the rectangular gap between the central circular slotted patch 2-6 and the rectangular open protrusion is 0.9mm~1mm. 5 0.5mm~0.9mm, width W 3 0.5mm~0.9mm, the width W of the X-shaped gap of the central circular slit patch 2-6 4 The length of the rectangle in the four directions of the X-shaped gap is L 8 0.5mm~0.6mm, the length L of the rectangle in the middle of the X-shaped gap 4 It is 0.8mm~1.2mm.

[0033] The distance R between the short-circuit probe 3 and the short-circuit probe 4 and the center of the dielectric substrate 1 is 6 is 3.2 mm to 3.5 mm, and the angle a between the center of the short-circuit probe 3 and the center of the short-circuit probe 4 and the vertical symmetry axis of the dielectric substrate 1 is 15 to 15 degrees, short-circuit probe 3, short-circuit probe 4 radius R 5 The radius of the short-circuit probe 3 and the short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

[0034] The distance R between the coaxial connector 5 and the center of the dielectric substrate 1 is 7 The angle a between the center of the coaxial connector 5 and the horizontal symmetry axis of the dielectric substrate 1 is 3 mm to 3.3 mm. 2 It is 16 to 24 degrees.

[0035] The outer surface of the implantable circularly polarized antenna of the ring loop sector loading patch is coated with a layer of biocompatible aluminum oxide with a thickness of 0.03 mm and a dielectric constant of ε r The angle of the antenna is 9.2, and the loss tangent tanδ is 0.008, which isolates the implantable circularly polarized antenna from human tissue and increases the biocompatibility of the implantable circularly polarized antenna.

[0036] Example: The specific manufacturing process is as described in the embodiment. Rogers RO3210 dielectric substrate is selected, and the dielectric constant ε r =10.2, loss tangent tanδ=0.003, thickness H=0.635mm, and the coaxial connector adopts a standard SMA connector. The graphene ring loop loaded radiation patch 2 and the graphene floor 6 are both made of multilayer graphene film. The multilayer graphene film material has good conductivity. Using multilayer graphene film to process the antenna can improve the performance of the antenna, effectively reduce the loss and improve the transmission efficiency. The thickness of the multilayer graphene film is 0.03mm, and the radius R of the dielectric substrate 1 is 8 The design size of the antenna can be effectively reduced by adding four sector-shaped loading patches to the ring loop. Adding rectangular branches of the same size and interlaced with each other between the four sector-shaped loading patches to form an interdigitated capacitor structure can increase the coupling capacitance and reduce the resonant frequency of the implantable antenna. The inner circle radius R of the ring loop 2-1 of the graphene ring loop loaded with the radiation patch 2 3 is 4.78 mm, and the thickness of the annular loop 2-1 is W 8 The width W of the upper and lower connecting conductive strips between the annular loop and the fan-shaped loading patch is 0.22 mm. 7 0.7mm, length L 1 The length L of the left and right connecting conductors between the ring loop and the fan-shaped loading patch is 0.58 mm. 2 The length of the gap between the left and right connecting conductors is L 10 2.33mm, width W 1 The inner radius R of the fan-shaped loading patch is 0.7 mm. 1 1.6mm, outer radius R 4The length L of the interlaced rectangular branches between the fan-shaped loading patches is 4.2 mm. 1 0.58mm, width W 6 is 0.15mm, the distance between the rectangular branches is W 5 is 0.15mm, the distance L from the rectangular branch to the fan edge 9 The length L of the two rectangular open-circuit protrusions added to the inner side of the sector loading patch 2-4 is 0.15mm. Geometric perturbations are generated by slits in the conduction band and by adding rectangular open-circuit protrusions, thereby forming orthogonal components with equal amplitudes and a phase difference of 90 degrees in space, producing circular polarization characteristics. 7 0.42mm, width W 2 The length L of the rectangular gap between the central circular slotted patch 2-6 and the rectangular open protrusion is 0.96 mm. 5 0.7mm, width W 3 The width W of the X-shaped gap in the center circular slot patch 2-6 is 0.7mm. 4 The rectangular length L of the X-shaped gap in four directions is 0.16mm. 8 0.54mm, the length L of the rectangle in the middle of the X-shaped gap 4 The distance R between the short-circuit probe 3 and the short-circuit probe 4 and the center of the dielectric substrate 1 is 1 mm. 6 is 3.3 mm, and the angle a between the center of the short-circuit probe 3 and the center of the short-circuit probe 4 and the vertical symmetry axis of the dielectric substrate 1 is 1 The radius of short-circuit probe 3 and short-circuit probe 4 is R 5 The addition of short-circuit probes 3 and 4 can increase the resonance point and further broaden the impedance bandwidth of the implantable antenna. The distance R between the coaxial connector 5 and the center of the dielectric substrate 1 is 7 is 3.1 mm, and the angle a between the center of the coaxial connector 5 and the horizontal symmetry axis of the dielectric substrate 1 is 2 It is 18 degrees.

[0037] Select the length L of the interlaced rectangular branches between the fan-shaped loading patches 1 , Width W 6 Analyze the impact on antenna impedance bandwidth and axial ratio bandwidth, such as Figure 4 As shown, select L 1 =0.5mm, W 6 =0.1mm, L 1 =0.58mm, W 6 =0.15mm and L 1 =0.6mm, W 6 =0.2mm, the antenna performance is analyzed in these three cases. Figure 4It can be seen that as the size of the interlaced rectangular branches between the sector-loaded patches increases, the resonant frequency of the implantable circularly polarized antenna shifts toward the low-frequency direction, the resonance degree increases, and the optimal frequency point of the axial ratio performance also moves toward the low-frequency direction. The reason is that the addition of rectangular branches of the same size and interlaced with each other forms an interdigitated capacitor structure, which increases the coupling capacitance per unit length, thereby increasing the propagation constant and reducing the resonant frequency of the implantable antenna to around 1.43 GHz. When L 1 =0.58mm, W 6 When =0.15mm, the implantable antenna can achieve good performance, and both the impedance bandwidth and the axial ratio bandwidth cover the required WMTS 1.43GHz frequency band.

[0038] Select the length L of the rectangular open protrusion inside the fan-shaped loading patch 7 , Width W 2 Analyze the impact on antenna impedance bandwidth and axial ratio bandwidth, such as Figure 5 As shown, select L 7 =0.4mm, W 2 =0.9mm, L 7 =0.42mm, W 2 =0.96mm and L 7 =0.5mm, W 2 =1mm, the antenna performance is analyzed in these three cases. Figure 5 It can be seen that the resonant frequency and resonance degree of the implantable antenna change little, and the minimum value of the axial ratio performance gradually decreases, indicating that the change in the size of the rectangular open-circuit protrusion has little effect on the impedance matching of the antenna, and the axial ratio performance is greatly affected by the rectangular open-circuit protrusion. The reason is that the addition of the rectangular open-circuit protrusion produces geometric perturbations, which can make the current alternate along the X-axis and Y-axis directions, forming orthogonal components in space. Adjusting the size of the rectangular open-circuit protrusion can make the amplitude of the current components along the X-axis and Y-axis directions equal, forming orthogonal components with a phase difference of 90 degrees and equal amplitude in space, thereby producing circular polarization characteristics. When L 7 =0.58mm, W 2 When =0.15mm, the implantable antenna can achieve good performance, and both the impedance bandwidth and the axial ratio bandwidth cover the required WMTS 1.43GHz frequency band.

[0039] Select the width W of the X-shaped gap 4 , the rectangular length L of the X-shaped gap in four directions 8 , the length of the rectangle in the middle of the X-shaped gap 4 Analyze the impact on antenna impedance bandwidth and axial ratio bandwidth, such as Figure 6 As shown, select W 4 =0.1mm, L 8=0.5mm, L 4 =0.8mm, W 4 =0.16mm, L 8 =0.54mm, L 4 =1mm and W 4 =0.2mm, L 8 =0.6mm, L 4 =1.2mm, the antenna performance is analyzed in these three cases. Figure 6 It can be seen from the figure that the resonant frequency of the implantable antenna shifts toward the high frequency direction, the resonance degree gradually increases, the best frequency point of the axial ratio performance also moves toward the high frequency direction, and the minimum value of the axial ratio performance gradually decreases. The reason is that the introduction of the X-shaped gap can adjust the antenna impedance matching and improve the axial ratio performance. 4 =0.16mm, L 8 =0.54mm, L 4 When =1mm, the implantable antenna can achieve good performance, and both the impedance bandwidth and axial ratio bandwidth cover the required WMTS 1.43GHz frequency band.

[0040] Select the thickness T of the multilayer graphene film as 0.02mm, 0.03mm, and 0.04mm, and analyze the effect of the thickness of the multilayer graphene film on the antenna performance. Figure 7 As shown in the figure, it can be seen that with the increase of the thickness of the multilayer graphene film, the resonance degree of the implantable circularly polarized antenna continues to increase, the resonant frequency offset does not change much, the optimal frequency point of the axial ratio performance changes little, and the minimum value of the axial ratio performance also decreases accordingly. It can be seen that the impedance matching and axial ratio performance of the implantable circularly polarized antenna are significantly improved. The reason is that with the increase of the thickness of the multilayer graphene film, the conductivity of the multilayer graphene film is gradually enhanced, so that the loss of the multilayer graphene film is continuously reduced, and the impedance matching and axial ratio performance of the implantable circularly polarized antenna are improved. When the thickness T of the multilayer graphene film is selected as 0.03mm, the performance of the implantable circularly polarized antenna meets the working requirements of the WMTS 1.43GHz frequency band.

[0041] The implantable antenna designed by the present invention is mainly used in the skin layer. In actual application, the implantable antenna will enter the muscle layer or fat layer due to the movement of the human body. Therefore, the designed antenna is placed in the skin layer, fat layer and muscle layer for simulation testing. Figure 8 As shown in Figure 2, the impact of implanting different human tissue layers on the antenna impedance bandwidth and axial ratio bandwidth is shown in Figure 2. Fig. 9As shown in the figure, when the antenna is implanted in the fat layer, the antenna resonant frequency shifts toward the high frequency direction compared to the skin layer, and the axial ratio performance is seriously deteriorated because the relative dielectric constant of the fat layer is much smaller than that of the skin layer. When the antenna is implanted in the muscle layer, the antenna resonant frequency shifts toward the low frequency direction, the impedance bandwidth can meet the working requirements, and the axial ratio performance deteriorates to a certain extent because the dielectric constant of the muscle layer is larger than that of the skin layer.

[0042] The implantable circularly polarized antenna is placed in a simulated human tissue environment, and the impedance bandwidth of the antenna is tested using a vector network analyzer. The axial ratio bandwidth of the antenna is tested indirectly by using an in vitro antenna. The simulation results of the impedance bandwidth and axial ratio bandwidth are consistent with the test results. Fig.10 As shown in the figure, the simulated impedance bandwidth of the implantable antenna is 1.35GHz~1.47GHz, the resonant frequency is 1.43GHz, the simulated axial ratio bandwidth is 1.37GHz~1.46GHz, the measured impedance bandwidth is 1.37GHz~1.46GHz, the resonant frequency is 1.44GHz, the resonance degree is reduced, the measured axial ratio bandwidth is 1.39GHz~1.45GHz, the axial ratio bandwidth can cover the working frequency, the measured and simulated results are consistent, the implantable circularly polarized antenna has a wide working bandwidth, and the impedance characteristics and axial ratio characteristics within the working frequency band are good. The center of the resonant frequency and axial ratio bandwidth is slightly offset in the high-frequency direction. The offset is caused by processing test errors, bubbles between the implantable antenna and the simulated human tissue, and differences in the electrical parameters of the test environment and the human tissue.

[0043] The E-plane and H-plane radiation patterns of the antenna at the 1.43 GHz frequency point are tested to verify the radiation characteristics of the antenna. The measured patterns are as follows: Fig.11 , Fig.12 As shown in the figure, it can be seen that the main polarization of the implantable circularly polarized antenna is left-hand circular polarization, and the maximum left-hand gain value is -29dBic. The main guide band slits and the addition of rectangular open-circuit protrusions produce geometric perturbations, thereby producing left-hand circular polarization characteristics. The antenna has good radiation characteristics within the working frequency band, and the axial ratio beam is wider. It is suitable for the WMTS 1.43GHz working frequency band and can meet the needs of complex implant environments.

[0044] A comprehensive analysis was conducted on the safety of implantable circularly polarized antennas. The input power of the implantable circularly polarized antenna was set to 1W, and the distribution of the average SAR value of the human body was analyzed. After simulation calculation, the maximum 1- / 10-gSAR value of the implantable circularly polarized antenna at 1.43GHz was 264.3 / 29.6W / kg. It was calculated that in order to meet the FCC and IEEE safety standards for SAR values, the maximum allowable input power of the intake antenna is 5.48mW and 43.6mW. The electromagnetic radiation of the implantable circularly polarized antenna under the above conditions is safe and harmless to human tissue.

Claims

1. An implantable circularly polarized antenna based on a graphene annular loop sector-loaded patch, comprising a dielectric substrate (1), a graphene annular loop-loaded radiation patch (2), a first short-circuit probe (3), a second short-circuit probe (4), a coaxial connector (5), and a graphene floor (6); the graphene annular loop-loaded radiation patch (2) and the graphene floor (6) are both made of multilayer graphene film, which has good electrical conductivity. Using the multilayer graphene film to process the antenna can improve the performance of the antenna, effectively reduce the loss and improve the transmission efficiency; the characteristics are: a. The graphene annular loop loaded radiation patch (2) is composed of an annular loop (2-1), a first fan-shaped loading patch (2-2), a second fan-shaped loading patch (2-3), a third fan-shaped loading patch (2-4), a fourth fan-shaped loading patch (2-5) and a central circular slotted patch (2-6); the annular loop (2-1) is located outside the graphene annular loop loaded radiation patch (2); the first fan-shaped loading patch (2-2), the second fan-shaped loading patch (2-3), the third fan-shaped loading patch (2-4) and the fourth fan-shaped loading patch (2-5) are connected to the annular loop (2-1) through four conducting strips; by adding the first fan-shaped loading patch (2-2), the second fan-shaped loading patch (2-3), the third fan-shaped loading patch (2-4) and the fourth fan-shaped loading patch (2-5) to the annular loop (2-1), the design size of the antenna can be effectively reduced; in the first fan-shaped loading patch (2 -2), rectangular branches of the same size and interlaced with each other are added between the second fan-shaped loading patch (2-3), the third fan-shaped loading patch (2-4), and the fourth fan-shaped loading patch (2-5) to form an interdigitated capacitance structure, thereby increasing the coupling capacitance per unit length and reducing the resonant frequency of the implantable antenna. A slit is opened on the left and right conducting bands, and two rectangular open-circuit protrusions are added on the inner sides of the first fan-shaped loading patch (2-2) and the third fan-shaped loading patch (2-4) and inserted into the interior of the central circular slotted patch (2-6). By opening the conducting band slits and adding the rectangular open-circuit protrusions, geometric perturbations are generated, thereby forming orthogonal components with equal amplitudes and a phase difference of 90 degrees in space, thereby generating circular polarization characteristics. The central circular slotted patch (2-6) is located at the center of the graphene ring loop loading radiation patch (2). An X-shaped slit is opened in the middle of the central circular slotted patch (2-6) to adjust the antenna impedance matching and improve the axial ratio performance. b. The first short-circuit probe (3) and the second short-circuit probe (4) are arranged on the first sector-shaped loading patch (2-2) and the third sector-shaped loading patch (2-4) in the graphene ring loop loaded radiation patch (2); the first short-circuit probe (3) and the second short-circuit probe (4) are symmetrical about the longitudinal axis of the antenna dielectric substrate (1); adding the first short-circuit probe (3) and the second short-circuit probe (4) can increase the resonance point and further broaden the impedance bandwidth of the implantable antenna; c. The coaxial connector (5) is located on the third sector-shaped loading patch (2-4) in the graphene annular loop loaded radiation patch (2), the inner core of the coaxial connector (5) is connected to the graphene annular loop loaded radiation patch (2), and the outer core of the coaxial connector (5) is connected to the graphene floor (6); d. The graphene floor (6) adopts a complete circular structure to form a shielding layer in the implantable wireless biomedical device, which can reduce the interference of the implantable antenna to other electronic devices of the wireless biomedical device and improve the electromagnetic compatibility of the implantable antenna; The inner radius R3 of the annular loop (2-1) of the graphene annular loop loaded radiation patch (2) is 4.5 mm to 5 mm, the thickness W8 of the annular loop (2-1) is 0.2 mm to 0.3 mm, the width W7 of the upper and lower connecting conductive strips between the annular loop and the fan-shaped loading patch is 0.5 mm to 0.9 mm, the length L1 is 0.5 mm to 0.6 mm, the length L2 of the left and right connecting conductive strips between the annular loop and the fan-shaped loading patch is 0.5 mm to 0.9 mm, and the length L2 of the gap between the left and right connecting conductive strips is 0.5 mm to 0.9 mm. 10 The inner radius R1 of the fan-shaped loading patch is 1.4 mm to 1.8 mm, the outer radius R4 is 4.1 mm to 4.3 mm, the length L1 of the rectangular branches staggered between the fan-shaped loading patches is 0.5 mm to 0.6 mm, the width W6 is 0.1 mm to 0.2 mm, the distance W5 between the rectangular branches is 0.1 mm to 0.3 mm, the distance L9 from the rectangular branches to the fan edge is 0.1 mm to 0.2 mm, and the inner radius R2 of the fan-shaped loading patch (2-4) is 1.4 mm to 1.8 mm, the outer radius R4 is 4.1 mm to 4.3 mm, the length L1 of the rectangular branches staggered between the fan-shaped loading patches is 0.5 mm to 0.6 mm, the width W6 is 0.1 mm to 0.2 mm, the distance W5 between the rectangular branches is 0.1 mm to 0.3 mm, and the distance L9 from the rectangular branches to the fan edge is 0.1 mm to 0.2 mm. The length L7 of the two rectangular open protrusions added on the side is 0.4mm~0.5mm, and the width W2 is 0.9mm~1mm. The length L5 of the rectangular gap corresponding to the central circular slit patch (2-6) and the rectangular open protrusion is 0.5mm~0.9mm, and the width W3 is 0.5mm~0.9mm. The width W4 of the X-shaped gap of the central circular slit patch (2-6) is 0.1mm~0.2mm. The rectangular length L8 in the four directions of the X-shaped gap is 0.5mm~0.6mm, and the length L4 of the rectangle in the middle of the X-shaped gap is 0.8mm~1.2mm.

2. The implantable circularly polarized antenna of the graphene-based ring-loop sector-loaded patch according to claim 1, characterized in that The thickness of the multilayer graphene film is 0.01 mm to 0.03 mm, and the radius R8 of the dielectric substrate (1) is 4.8 mm to 5.7 mm.

3. The implantable circularly polarized antenna of the graphene-based ring-loop sector-loaded patch according to claim 1, characterized in that The distance R6 between the first short-circuit probe (3) and the second short-circuit probe (4) and the center of the dielectric substrate (1) is 3.2 mm to 3.5 mm, the angle a1 between the center of the first short-circuit probe (3) and the second short-circuit probe (4) and the vertical symmetry axis of the dielectric substrate (1) is 5 to 15 degrees, the radius R5 of the first short-circuit probe (3) and the second short-circuit probe (4) is 0.2 mm to 0.4 mm, and the radius of the first short-circuit probe (3) and the second short-circuit probe (4) is equal to the inner core radius of the coaxial connector (5).

4. The implantable circularly polarized antenna of the graphene-based ring-loop sector-loaded patch according to claim 1, characterized in that The distance R7 between the coaxial joint (5) and the center of the dielectric substrate (1) is 3 mm to 3.3 mm, and the angle a2 between the center of the coaxial joint (5) and the horizontal symmetry axis of the dielectric substrate (1) is 16 to 24 degrees.

5. The implantable circularly polarized antenna of the graphene-based ring-loop sector-loaded patch according to claim 1, characterized in that The outer surface of the implantable circularly polarized antenna of the ring loop sector loading patch is coated with a layer of biocompatible aluminum oxide with a thickness of 0.03 mm and a dielectric constant of ε r The angle of the antenna is 9.2, and the loss tangent tanδ is 0.008, which isolates the implantable circularly polarized antenna from human tissue and increases the biocompatibility of the implantable circularly polarized antenna.

Images