Implantable small circularly polarized antenna loaded with octagonal complementary split ring resonator

Abstract

The present invention designs an implantable small circularly polarized antenna loaded with an octagonal complementary open resonant ring. Adding a symmetrical C-shaped structure around the radiation patch loaded with the octagonal complementary open resonant ring can effectively extend the current path on the antenna surface and reduce the antenna resonant frequency. Adjusting the size of the T-slot and the L-slot can optimize the impedance matching. Adding two semi-hexagonal patches at the open end of the L-slot can increase the capacitance distribution per unit length and reduce the size of the antenna. The electrical length of the octagonal complementary open resonant ring structure is much smaller than the signal wavelength at resonance, thereby shifting the antenna resonant frequency to a low frequency and further reducing the size of the antenna. The volume of the antenna is only 8.5×8.5×0.635mm 3 It has the characteristics of wide bandwidth, miniaturization, circular polarization, anti-interference, and excellent biocompatibility. It is suitable for the ISM 2.45GHz frequency band and meets the miniaturization and circular polarization working requirements after being implanted in the human tissue environment.

Description

Technical Field

[0001] The invention relates to the technical field of implantable antennas, and in particular to an implantable small circularly polarized antenna loaded with an octagonal complementary open resonant ring, which is suitable for an implantable circularly polarized wireless biomedical device in the ISM 2.45 GHz frequency band. Background Art

[0002] Wireless biomedicine can provide high-quality medical services within a limited medical budget and has become one of the focuses of global attention. Implantable medical devices are the core components of wireless biomedicine. They can continuously monitor the body's metabolic level without considering the patient's physiological state and without the intervention of doctors, providing doctors with comprehensive diagnosis and treatment information. For example, implantable medical devices can be used for blood glucose monitoring of diabetic patients. The traditional method is mainly to obtain data through finger blood sampling. The disadvantage of this method is that it brings pain to patients, and the test results cannot objectively reflect the overall trend and change direction related to eating habits. The implantable blood glucose monitoring device can detect blood glucose concentration in real time and transmit the test data to an in vitro receiving device to provide a basis for doctors' diagnosis. Implantable medical devices are usually composed of sensors, antennas, batteries, processors, etc. Among them, implantable antennas are key components to ensure that implantable medical devices can communicate reliably. The performance, size, power consumption, anti-interference ability, and biocompatibility of implantable antennas will affect the working performance of implantable medical devices. Therefore, designing implantable antennas is a complex and challenging task. The main methods to reduce the design size of implantable antennas are: using a high dielectric constant substrate, but high dielectric constant materials will lead to a decrease in antenna gain and impedance bandwidth. When selecting high dielectric constant materials, bandwidth, gain and size should be considered comprehensively; short-circuit loading technology, adding a short-circuit probe or short-circuit plate between the radiation patch and the floor, reducing the size of the antenna while ensuring that the antenna radiation characteristics remain unchanged; meander technology, opening slots of different forms and sizes on the surface of the radiation patch, so that the surface current flows along the direction of the slot, thereby extending the current path on the antenna surface, reducing the resonant frequency, and realizing the miniaturization of the antenna; fractal technology, the fractal structure can achieve the filling of the surface of the radiation unit, and increasing the iteration order can extend the current path, thereby reducing the antenna resonant frequency. The main methods to achieve anti-interference capabilities are multiple-input multiple-output technology, polarization diversity technology and circular polarization technology, among which circular polarization technology has the characteristics of reducing bit error rate, reducing polarization mismatch and suppressing multipath interference. In order to collect human physiological parameters, stable and reliable information transmission is required between the implantable system and the external receiving device. Circularly polarized antennas can overcome the limitation of antenna placement angle, ensure reliable information transmission between implantable devices and external devices, and reduce the loss caused by multipath effects. Circularly polarized antennas usually adopt single feed form, and dual feed or multi-feed will increase the volume of the antenna. Introducing geometric perturbations can produce circular polarization characteristics, such as adding cross slots in the middle of the antenna, cutting off part of the shape at the diagonal of the patch, adding strip slots on the diagonal of the patch, etc.; circular polarization performance can be achieved through aperture coupling or adding gaps to the ring structure; using slow wave structure to increase the propagation constant per unit length can also produce circular polarization characteristics.The complementary open resonant ring is a geometrically coupled structure. By exchanging the gap part and the metal part, a complementary open resonant structure can be obtained. The complementary open resonant structure is a metamaterial structure with negative magnetic permeability. Its dielectric constant is much smaller than the wavelength at resonance. The circular polarization performance of the antenna can be achieved by adjusting the position and size of the open resonant ring. The use of complementary open resonant rings can meet the miniaturization and circular polarization design requirements of the antenna. Summary of the invention

[0003] The purpose of the present invention is to provide an implantable small circularly polarized antenna loaded with an octagonal complementary open resonant ring. The antenna has the characteristics of wide bandwidth, miniaturization, circular polarization, anti-interference, excellent biocompatibility, etc., is easy to be integrated into an implantable wireless biomedical device, is suitable for the ISM 2.45GHz frequency band, and can meet the working requirements after being implanted in human tissue.

[0004] The technical solution of the present invention is: an implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring, which is composed of a dielectric substrate 1, a radiation patch 2 loaded with an octagonal complementary open resonant ring, a short-circuit probe 3, a short-circuit probe 4, a coaxial connector 5, and a floor 6, and is characterized in that:

[0005] a. The loaded octagonal complementary open resonant ring radiation patch 2 is formed by slotting around the radiation patch to form a symmetrical C-shaped structure 2-1, a symmetrical C-shaped structure 2-2, a symmetrical C-shaped structure 2-3, and a symmetrical C-shaped structure 2-4. The symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 are formed by opening a T-shaped slot and an L-shaped slot around the radiation patch. The two right angles of the L-shaped slot are connected by an isosceles right triangle transition. Two semi-hexagonal patches are added to the open end of the L-shaped slot. The symmetrical C-shaped structure 2-1 is rotated 90 degrees around the dielectric substrate 1 to obtain a symmetrical C-shaped structure 2-2, a symmetrical C-shaped structure 2-3, and a symmetrical C-shaped structure 2-4. Adding symmetrical C-shaped structures 2-1, symmetrical C-shaped structures 2-2, symmetrical C-shaped structures 2-3, and symmetrical C-shaped structures 2-4 around the radiation patch can effectively extend the current path on the antenna surface, reduce the antenna resonant frequency, and adjust the T-shaped The size of the slot and the L-shaped slot can optimize impedance matching. Adding two semi-hexagonal patches at the open end of the L-shaped slot can increase the capacitance distribution per unit length, further increase the propagation constant, and reduce the size of the antenna. An octagonal complementary open resonant ring structure 2-5 is set in the center of the radiation patch. The octagonal complementary open resonant ring structure 2-5 is to open two octagonal slots in the center of the radiation patch to form an octagonal ring and an octagonal patch. The octagonal ring and the octagonal patch are respectively connected to the radiation patch through rectangular conduction bands. The octagonal complementary open resonant ring structure 2-5 is a metamaterial structural unit with a negative dielectric constant. Its electrical length is much smaller than the signal wavelength at resonance, so that the antenna resonant frequency is shifted to a low frequency, further reducing the size of the antenna. By adjusting the opening position and size of the octagonal complementary open resonant ring structure 2-5, two orthogonal modes can be excited, and the two modes have a phase difference of 90 degrees and equal amplitudes, thereby producing circular polarization characteristics;

[0006] b. The short-circuit probe 3 and the short-circuit probe 4 are arranged on the lower left and upper left sides of the octagonal complementary open resonant ring structure 2-5 in the octagonal complementary open resonant ring radiation patch 2. The short-circuit probe 3 and the short-circuit probe 4 are symmetrical about the horizontal axis of the antenna dielectric substrate 1. Adding the short-circuit probe 3 and the short-circuit probe 4 can reduce the size of the antenna while ensuring that the antenna radiation characteristics remain unchanged;

[0007] c. The coaxial connector 5 is located on the upper right side of the octagonal complementary open resonant ring structure 2-5 in the loaded octagonal complementary open resonant ring radiation patch 2, the inner core of the coaxial connector 5 is connected to the loaded octagonal complementary open resonant ring radiation patch 2, and the outer core of the coaxial connector 5 is connected to the floor 6;

[0008] d. The floor 6 is a square complete metal patch structure without adding gaps or slots, which can form a shielding layer between the implanted antenna and the underlying electronic devices, effectively reducing the interference of the implanted antenna to other electronic devices and improving the electromagnetic compatibility of the implanted antenna.

[0009] The length L of the dielectric substrate 1 is 8 mm to 9 mm, and the width W is 8 mm to 9 mm.

[0010] The length L5 of the transverse rectangular groove of the T-shaped groove of the symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 in the loaded octagonal complementary open resonant ring radiation patch 2 is 0.1mm~0.3mm, the width W8 is 4.6mm~4.8mm, the length L1 of the longitudinal rectangular groove is 0.9mm~1.1mm, the width W7 is 0.1mm~0.3mm, the length L2 of the upper rectangular branch of the C-shaped structure is 0.2mm~0.4mm, the width W4 is 2.2mm~2.4mm, the width W6 of the middle rectangular branch of the C-shaped structure is 0.2mm~0.4mm, the transverse rectangular groove length L3 of the L-shaped groove is 0.4mm~0.6mm, the two right angles of the L-shaped groove are connected by an isosceles right triangle transition, the right angle side length W2 of the right triangle is 0.3mm~0.5mm, and the distance between the two right triangles is 0. The distance from W3 is 1.6mm~1.8mm, two semi-hexagonal patches are added at the open end of the L-shaped groove, the radius R1 of the semi-hexagonal patch is 0.2mm~0.4mm, and an octagonal complementary open resonant ring structure 2-5 is arranged in the center of the radiation patch, the radius R5 of the octagonal patch is 0.7mm~0.9mm, the outer ring radius R3 of the octagonal ring is 1.7mm~1.9mm, the inner ring radius R4 is 1.3mm~1.5mm, the outer ring radius R2 of the outer octagonal groove is 2mm~2.2mm, the right rectangular guide band width L7 connecting the octagonal ring is 0.2mm~0.4mm, the angle a2 between the central axis of the right rectangular guide band and the horizontal axis of the dielectric substrate 1 is 8 degrees~12 degrees, the left rectangular guide band width L6 connecting the octagonal patch is 0.5mm~0.7mm, and the angle a1 between the central axis of the left rectangular guide band and the horizontal axis of the dielectric substrate 1 is 6 degrees~10 degrees.

[0011] The distance L8 between the center of the short-circuit probe 3, the short-circuit probe 4 and the center of the dielectric substrate 1 is 2.2mm~2.4mm, the angle a3 between the short-circuit probe 3, the short-circuit probe 4 and the longitudinal symmetry axis of the dielectric substrate 1 is 25 degrees~35 degrees, the radius R6 of the short-circuit probe 3, the short-circuit probe 4 is 0.2mm~0.4mm, and the radius of the short-circuit probe 3, the short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

[0012] The distance L0 between the center of the coaxial connector 5 and the transverse symmetry axis of the dielectric substrate 1 is 1.8 mm to 2.2 mm, and the distance W0 between the center of the coaxial connector 5 and the longitudinal symmetry axis of the dielectric substrate 1 is 1.8 mm to 2.2 mm.

[0013] The dimensions of the floor 6 are consistent with those of the dielectric substrate 1 , with a length L of 8 mm to 9 mm and a width W of 8 mm to 9 mm.

[0014] The outer surface of the implantable small circular polarization antenna loaded with the octagonal complementary open resonant ring is coated with a layer of biocompatible coating material aluminum oxide with insulating properties, which has a dielectric constant similar to that of the dielectric substrate 1, and the dielectric constant ε r The loss tangent tanδ is 9.2, the loss tangent tanδ is 0.008, and the coating thickness is 0.03 mm, which isolates human tissue from the implantable small circularly polarized antenna, prevents the human tissue from directly contacting the implantable small circularly polarized antenna and causing a short circuit, and reduces the influence of human tissue on the performance of the implantable small circularly polarized antenna.

[0015] The effect of the present invention is that the present invention designs an implantable small circularly polarized antenna loaded with an octagonal complementary open resonant ring. Adding a symmetrical C-shaped structure around the octagonal complementary open resonant ring radiation patch can effectively extend the antenna surface current path and reduce the antenna resonant frequency. Adjusting the size of the T-shaped slot and the L-shaped slot can optimize the impedance matching. Adding two semi-hexagonal patches at the opening end of the L-shaped slot can increase the capacitance distribution per unit length, further increase the propagation constant, and reduce the size of the antenna. The octagonal complementary open resonant ring structure is a metamaterial structural unit with a negative dielectric constant. Its electrical length is much smaller than the signal wavelength at resonance, so that the antenna resonant frequency is shifted to a low frequency, further reducing the size of the antenna. By adjusting the opening position and size of the octagonal complementary open resonant ring structure, two orthogonal modes can be excited, and the phase difference of these two modes is 90 degrees and the amplitude is equal, thereby generating circular polarization characteristics. The floor is a square complete metal patch structure, without adding gaps or slots, and can form a shielding layer between the implanted antenna and the lower electronic device, effectively reducing the interference of the implanted antenna to other electronic devices and improving the electromagnetic compatibility of the implanted antenna. Adding a short-circuit probe can reduce the size of the antenna while ensuring that the antenna radiation characteristics remain unchanged. The implantable circularly polarized antenna has a planar structure and the volume of the antenna is only 8.5×8.5×0.635mm 3 It has the characteristics of wide bandwidth, miniaturization, circular polarization, anti-interference, and excellent biocompatibility. It is suitable for the ISM 2.45GHz frequency band and meets the miniaturization and circular polarization working requirements after being implanted in the human tissue environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the front structure of an embodiment of the present invention.

[0017] Figure 2 It is a schematic diagram of the side structure of an embodiment of the present invention.

[0018] Figure 3 It is a schematic diagram of the back structure of an embodiment of the present invention.

[0019] Figure 4 This is the influence of the width W8 of the transverse rectangular groove and the length L2 of the longitudinal rectangular groove of the T-slot in the symmetrical C-shaped structure of the embodiment of the present invention on the antenna impedance bandwidth and axial ratio bandwidth.

[0020] Figure 5 This is the influence of the outer ring radius R3, the inner ring radius R4, and the radius R5 of the octagonal patch of the embodiment of the present invention on the antenna impedance bandwidth and the axial ratio bandwidth.

[0021] Figure 6 The figure shows the influence of the angle a1 between the central axis of the left rectangular conductive strip and the horizontal axis of the dielectric substrate and the angle a2 between the central axis of the right rectangular conductive strip and the horizontal axis of the dielectric substrate on the antenna impedance bandwidth and the axial ratio bandwidth in the embodiment of the present invention.

[0022] Figure 7 Schematic diagram of the implantation depth of the skin layer in an embodiment of the present invention.

[0023] Figure 8 This is the influence of different implantation depths H on the antenna impedance bandwidth and axial ratio bandwidth according to the embodiment of the present invention.

[0024] Fig. 9 1 is a simulated and measured impedance bandwidth curve of an embodiment of the present invention.

[0025] Fig.10 It is the E-plane radiation pattern of the embodiment of the present invention at a frequency of 2.45 GHz.

[0026] Fig.11 This is the H-plane radiation pattern of the embodiment of the present invention at a frequency of 2.45 GHz. DETAILED DESCRIPTION

[0027] The specific implementation mode of the present invention is: Figure 1As shown, an implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring is composed of a dielectric substrate 1, a radiation patch 2 loaded with an octagonal complementary open resonant ring, a short-circuit probe 3, a short-circuit probe 4, a coaxial connector 5, and a floor 6. It is characterized in that: the radiation patch 2 loaded with an octagonal complementary open resonant ring is grooved around the radiation patch to form a symmetrical C-shaped structure 2-1, a symmetrical C-shaped structure 2-2, a symmetrical C-shaped structure 2-3, and a symmetrical C-shaped structure 2-4. The symmetrical C-shaped structures 2-1, symmetrical C-shaped structures 2-2, symmetrical C-shaped structures 2-3, and symmetrical C-shaped structures 2-4 are formed by opening T-shaped grooves and L-shaped grooves around the radiation patch, and the two right angles of the L-shaped groove are formed by isosceles right-angle triangles. Angular transition connection, two half-hexagonal patches are added to the open end of the L-shaped slot, the symmetrical C-shaped structure 2-1 is rotated 90 degrees with the dielectric substrate 1 as the center to obtain the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4, and the symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 are added around the radiation patch to effectively extend the current path on the antenna surface and reduce the antenna resonant frequency. Adjusting the size of the T-shaped slot and the L-shaped slot can optimize the impedance matching. Adding two half-hexagonal patches at the open end of the L-shaped slot can increase the capacitance distribution per unit length, further increase the propagation constant, and reduce the size of the antenna. An octagonal complementary open resonant ring structure 2-5 is provided. The octagonal complementary open resonant ring structure 2-5 is formed by opening two octagonal grooves in the center of the radiation patch to form an octagonal ring and an octagonal patch. The octagonal ring and the octagonal patch are respectively connected to the radiation patch through rectangular guide bands. The octagonal complementary open resonant ring structure 2-5 is a metamaterial structural unit with a negative dielectric constant. Its electrical length is much smaller than the signal wavelength at resonance, thereby shifting the antenna resonant frequency to a low frequency and further reducing the size of the antenna. By adjusting the opening position and size of the octagonal complementary open resonant ring structure 2-5, two orthogonal modes can be excited, and the two modes have a phase difference of 90 degrees and equal amplitudes, thereby producing Circular polarization characteristics; the short-circuit probe 3 and the short-circuit probe 4 are arranged on the lower left and upper left sides of the octagonal complementary open resonant ring structure 2-5 in the octagonal complementary open resonant ring radiation patch 2, and the short-circuit probe 3 and the short-circuit probe 4 are symmetrical about the horizontal axis of the antenna dielectric substrate 1. Adding the short-circuit probe 3 and the short-circuit probe 4 can reduce the size of the antenna while ensuring that the antenna radiation characteristics remain unchanged; the coaxial connector 5 is located on the upper right side of the octagonal complementary open resonant ring structure 2-5 in the octagonal complementary open resonant ring radiation patch 2, the inner core of the coaxial connector 5 is connected to the octagonal complementary open resonant ring radiation patch 2, and the outer core of the coaxial connector 5 is connected to the floor 6;The floor 6 is a square complete metal patch structure without adding gaps or slots, which can form a shielding layer between the implanted antenna and the underlying electronic devices, effectively reducing the interference of the implanted antenna to other electronic devices and improving the electromagnetic compatibility of the implanted antenna. ;

[0028] The length L of the dielectric substrate 1 is 8 mm to 9 mm, and the width W is 8 mm to 9 mm.

[0029] The length L5 of the transverse rectangular groove of the T-shaped groove of the symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 in the loaded octagonal complementary open resonant ring radiation patch 2 is 0.1mm~0.3mm, the width W8 is 4.6mm~4.8mm, the length L1 of the longitudinal rectangular groove is 0.9mm~1.1mm, the width W7 is 0.1mm~0.3mm, the length L2 of the upper rectangular branch of the C-shaped structure is 0.2mm~0.4mm, the width W4 is 2.2mm~2.4mm, the width W6 of the middle rectangular branch of the C-shaped structure is 0.2mm~0.4mm, the transverse rectangular groove length L3 of the L-shaped groove is 0.4mm~0.6mm, the two right angles of the L-shaped groove are connected by an isosceles right triangle transition, the right angle side length W2 of the right triangle is 0.3mm~0.5mm, and the distance between the two right triangles is 0. The distance from W3 is 1.6mm~1.8mm, two semi-hexagonal patches are added at the open end of the L-shaped groove, the radius R1 of the semi-hexagonal patch is 0.2mm~0.4mm, and an octagonal complementary open resonant ring structure 2-5 is arranged in the center of the radiation patch, the radius R5 of the octagonal patch is 0.7mm~0.9mm, the outer ring radius R3 of the octagonal ring is 1.7mm~1.9mm, the inner ring radius R4 is 1.3mm~1.5mm, the outer ring radius R2 of the outer octagonal groove is 2mm~2.2mm, the right rectangular guide band width L7 connecting the octagonal ring is 0.2mm~0.4mm, the angle a2 between the central axis of the right rectangular guide band and the horizontal axis of the dielectric substrate 1 is 8 degrees~12 degrees, the left rectangular guide band width L6 connecting the octagonal patch is 0.5mm~0.7mm, and the angle a1 between the central axis of the left rectangular guide band and the horizontal axis of the dielectric substrate 1 is 6 degrees~10 degrees.

[0030] The distance L8 between the center of the short-circuit probe 3, the short-circuit probe 4 and the center of the dielectric substrate 1 is 2.3mm~2.5mm, the angle a3 between the short-circuit probe 3, the short-circuit probe 4 and the longitudinal symmetry axis of the dielectric substrate 1 is 25 degrees~35 degrees, the radius R6 of the short-circuit probe 3, the short-circuit probe 4 is 0.2mm~0.4mm, and the radius of the short-circuit probe 3, the short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

[0031] The distance L0 between the center of the coaxial connector 5 and the transverse symmetry axis of the dielectric substrate 1 is 1.8 mm to 2.2 mm, and the distance W0 between the center of the coaxial connector 5 and the longitudinal symmetry axis of the dielectric substrate 1 is 1.8 mm to 2.2 mm.

[0032] The dimensions of the floor 6 are consistent with those of the dielectric substrate 1 , with a length L of 8 mm to 9 mm and a width W of 8 mm to 9 mm.

[0033] The outer surface of the implantable small circular polarization antenna loaded with the octagonal complementary open resonant ring is coated with a layer of biocompatible coating material aluminum oxide with insulating properties, which has a dielectric constant similar to that of the dielectric substrate 1, and the dielectric constant ε r The loss tangent tanδ is 9.2, the loss tangent tanδ is 0.008, and the coating thickness is 0.03 mm, which isolates human tissue from the implantable small circularly polarized antenna, prevents the human tissue from directly contacting the implantable small circularly polarized antenna and causing a short circuit, and reduces the influence of human tissue on the performance of the implantable small circularly polarized antenna.

[0034] 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 length L of the dielectric substrate 1 is 8.5mm, and the width W is 8.5mm. Adding symmetrical C-shaped structure 2-1, symmetrical C-shaped structure 2-2, symmetrical C-shaped structure 2-3, and symmetrical C-shaped structure 2-4 around the radiation patch can effectively extend the current path on the antenna surface and reduce the antenna resonant frequency. Adjusting the size of the T-shaped slot and the L-shaped slot can optimize the impedance matching. Adding two semi-hexagonal patches at the open end of the L-shaped slot can increase the capacitance distribution per unit length, further increase the propagation constant, and reduce the size of the antenna. The length L5 of the transverse rectangular groove of the T-shaped groove loaded with the symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 in the octagonal complementary open resonant ring radiation patch 2 is 0.2mm, the width W8 is 4.7mm, the length L1 of the longitudinal rectangular groove is 1mm, the width W7 is 0.2mm, the length L2 of the upper rectangular branch of the C-shaped structure is 0.3mm, the width W4 is 2.3mm, the width W6 of the middle rectangular branch of the C-shaped structure is 0.3mm, the transverse rectangular groove length L3 of the L-shaped groove is 0.5mm, the two right angles of the L-shaped groove are connected by an isosceles right triangle transition, the right angle side length W2 of the right triangle is 0.4mm, the distance W3 between the two right triangles is 1.7mm, and two semi-hexagonal patches are added at the open end of the L-shaped groove, and the radius R1 of the semi-hexagonal patch is 0.27mm. An octagonal complementary open resonant ring structure 2-5 is set at the center of the radiation patch. The octagonal complementary open resonant ring structure 2-5 is a metamaterial structural unit with a negative dielectric constant. Its electrical length is much smaller than the signal wavelength at resonance, so that the antenna resonant frequency shifts to a low frequency, further reducing the size of the antenna. By adjusting the opening position and size of the octagonal complementary open resonant ring structure 2-5, two orthogonal modes can be excited, and the phase difference between the two modes is 90 degrees and the amplitude is equal, thereby producing circular polarization characteristics. The radius R5 of the octagonal patch is 0.8 mm, the outer ring radius R3 of the octagonal ring is 1.8 mm, the inner ring radius R4 is 1.4 mm, the outer ring radius R2 of the outer octagonal groove is 2.1 mm, the right rectangular conductive band width L7 connecting the octagonal ring is 0.3 mm, the angle a2 between the central axis of the right rectangular conductive band and the horizontal axis of the dielectric substrate 1 is 10 degrees, the left rectangular conductive band width L6 connecting the octagonal patch is 0.6 mm, and the angle a1 between the central axis of the left rectangular conductive band and the horizontal axis of the dielectric substrate 1 is 8 degrees. Adding short-circuit probes 3 and 4 can reduce the size of the antenna while ensuring that the antenna radiation characteristics remain unchanged. The distance L8 between the center of the short-circuit probe 3 and the center of the dielectric substrate 1 is 2.4 mm, the angle a3 between the short-circuit probe 3 and the longitudinal symmetry axis of the dielectric substrate 1 is 30 degrees, the radius R6 of the short-circuit probe 3 and the short-circuit probe 4 is 0.3 mm, and 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.The distance L0 from the center of the coaxial connector 5 to the transverse symmetry axis of the dielectric substrate 1 is 2 mm, and the distance W0 from the longitudinal symmetry axis of the dielectric substrate 1 is 2 mm. The floor 6 is a square complete metal patch structure without adding gaps or slots, which can form a shielding layer between the implanted antenna and the underlying electronic devices, effectively reducing the interference of the implanted antenna to other electronic devices and improving the electromagnetic compatibility of the implanted antenna. The size of the floor 6 is consistent with that of the dielectric substrate 1, with a length L of 8.5 mm and a width W of 8.5 mm. The outer surface of the implantable small circularly polarized antenna loaded with an octagonal complementary open resonant ring is coated with a layer of alumina, a biocompatible coating material with insulating properties, which has a dielectric constant similar to that of the dielectric substrate 1, and a dielectric constant ε. r The loss tangent tanδ is 9.2, the loss tangent tanδ is 0.008, and the coating thickness is 0.03 mm, which isolates human tissue from the implantable small circularly polarized antenna, prevents the human tissue from directly contacting the implantable small circularly polarized antenna and causing a short circuit, and reduces the influence of human tissue on the performance of the implantable small circularly polarized antenna.

[0035] The influence of the width W8 of the transverse rectangular groove and the length L2 of the longitudinal rectangular groove of the T-shaped slot in the symmetrical C-shaped structure on the antenna impedance bandwidth and axial ratio bandwidth is analyzed as follows: Figure 4 As shown, the antenna performance is analyzed by selecting three cases: W8 = 4.6 mm, L2 = 0.2 mm, W8 = 4.7 mm, L2 = 0.3 mm, and W8 = 4.8 mm, L2 = 0.4 mm. Figure 4 It can be seen that as the size of the T-slot in the symmetrical C-shaped structure increases, the resonant frequency of the antenna shifts to the low frequency direction, and the frequency point with the best axial ratio performance also shifts to the low frequency direction. The reason is that adding a symmetrical C-shaped structure can effectively extend the current path on the antenna surface and reduce the antenna resonant frequency. Adjusting the size of the T-slot and L-slot can optimize the impedance matching. When W8 = 4.7mm and L2 = 0.3mm, the antenna performance is optimal, and both the impedance bandwidth and the axial ratio bandwidth cover the required ISM 2.45GHz frequency band.

[0036] The outer ring radius R3 of the octagonal ring, the inner ring radius R4, and the radius R5 of the octagonal patch are selected to analyze the impact on the antenna impedance bandwidth and axial ratio bandwidth. Figure 5 As shown, the antenna performance is analyzed by selecting three cases: R3 = 1.7mm, R4 = 1.3mm, R5 = 0.7mm, R3 = 1.8mm, R4 = 1.4mm, R5 = 0.8mm and R3 = 1.9mm, R4 = 1.5mm, R5 = 0.9mm. Figure 5It can be seen that with the increase of the outer ring radius R3 of the octagonal ring, the inner ring radius R4, and the radius R5 of the octagonal patch, the antenna resonant frequency shifts to the low frequency direction, and the frequency point with the best axial ratio performance also shifts to the low frequency. The reason is that the octagonal complementary open resonant ring structure is a metamaterial structural unit with a negative dielectric constant. Its electrical length is much smaller than the signal wavelength at resonance, which shifts the antenna resonant frequency to the low frequency and further reduces the size of the antenna. When R3 = 1.8mm, R4 = 1.4mm, and R5 = 0.8mm, the antenna performance is optimal, and the impedance bandwidth and axial ratio bandwidth both cover the required ISM 2.45GHz frequency band.

[0037] The included angle a1 between the center axis of the rectangular conductive strip on the left and the horizontal axis of the dielectric substrate and the included angle a2 between the center axis of the rectangular conductive strip on the right and the horizontal axis of the dielectric substrate are selected to analyze the influence on the antenna impedance bandwidth and axial ratio bandwidth. Figure 6 As shown in the figure, the antenna performance is analyzed by selecting three cases: a1 = 6°, a2 = 8°, a1 = 8°, a2 = 10°, and a1 = 10°, a2 = 12°. Figure 6 It can be seen that with the change of the angle a1 between the center axis of the left rectangular conductive strip and the horizontal axis of the dielectric substrate, and the angle a2 between the center axis of the right rectangular conductive strip and the horizontal axis of the dielectric substrate, the resonance point of the antenna does not change much, the resonance degree increases first and then decreases, and the best point of the axial ratio performance also changes accordingly. The reason is that by adjusting the opening position and size of the octagonal complementary open resonant ring structure, two orthogonal modes can be excited, and the phase difference of these two modes is 90 degrees and the amplitude is equal, thus producing circular polarization characteristics. When a1=8° and a2=10°, the antenna performance is optimal, and the impedance bandwidth and axial ratio bandwidth both cover the required ISM 2.45GHz frequency band.

[0038] The application environment of the implantable circularly polarized antenna designed in the present invention is mainly the skin layer. The simulation environment is a single-layer skin model of 160mm×160mm×12mm. The antenna is placed in the center of the single-layer skin model. The distance between the upper layer of the skin model and the upper surface of the antenna is H. The schematic diagram of the implanted skin layer depth is as follows: Figure 7 As shown in Figure 2, the influence of different implantation depths H on the antenna impedance bandwidth and axial ratio bandwidth is shown in Figure 2. Figure 8 As shown in the figure, with the increase of implantation depth, the resonance point of the implantable circularly polarized antenna shifts toward the low frequency direction, and the resonance degree gradually decreases. It can still cover the required ISM 2.45GHz frequency band well. The axial ratio performance changes greatly, but these three implantation depths can still maintain the radiation of circularly polarized waves.

[0039] The implantable circularly polarized antenna was placed in a solution simulating human skin for testing. The skin solution included 58.2% deionized water, 5.1% diethylene glycol monobutyl ether, and 36.7% polyethylene glycol octylphenyl ether. The impedance bandwidth of the antenna was tested using a vector network analyzer, and the circular polarization characteristics of the antenna were tested indirectly by using an in vitro linearly polarized dipole antenna. The simulation results of the impedance bandwidth and axial ratio bandwidth were compared with the test results. Fig. 9 As shown in the figure, the simulated impedance bandwidth of the implantable circularly polarized antenna is 2.35GHz~2.62GHz, the resonant frequency is 2.45GHz, the simulated axial ratio bandwidth is 2.38GHz~2.47GHz, the measured impedance bandwidth is 2.31GHz~2.59GHz, the resonant frequency is 2.43GHz, the resonance degree has increased to a certain extent, the measured axial ratio bandwidth is 2.36GHz~2.51GHz, the axial ratio bandwidth can cover the required operating frequency, the simulation results are slightly different from the test results, and good resonance can be achieved in the ISM band. The implantable circularly polarized antenna has a wide working bandwidth, good impedance characteristics and axial ratio characteristics within the working frequency band, the resonant frequency and axial ratio bandwidth centers are slightly shifted toward the low frequency direction, and the resonance degree is increased. The reasons for the frequency offset are mainly the processing test errors of the implantable antenna, the influence of bubbles between the coaxial cable and the simulated human tissue on the antenna test, and the difference in the dielectric constant of the simulated test environment.

[0040] The E-plane and H-plane radiation patterns of the implantable circularly polarized antenna at 2.45 GHz were tested to verify the radiation characteristics of the antenna. The measured patterns are as follows: Fig.10 , Fig.11 As shown. From the radiation pattern, it can be seen that the antenna has good directivity. The maximum radiation direction of the implantable circularly polarized antenna is along the Z-axis. The main polarization is right-hand circular polarization. The actual gain value along the Z-axis is -21.2dBi. The difference between the main polarization and the cross polarization is 29.6dBi. It is mainly through adjusting the opening position and size of the octagonal complementary open resonant ring structure that two orthogonal modes can be excited. The phase difference between these two modes is 90 degrees and the amplitude is equal, thus producing 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 ISM2.45GHz working frequency band and can meet the needs of complex implant environments.

[0041] Taking into account the safety factors of implantation in the human body, a comprehensive analysis is conducted on the safety of the implantable circularly polarized antenna. A 1W input signal is provided to the implantable circularly polarized antenna, and the average SAR value is used to evaluate the safe range of energy absorption by the human body model. After simulation calculation, the maximum 1-g human tissue maximum average SAR value of the implantable circularly polarized antenna at 2.45GHz is 213.8W / kg, and the maximum 10-g human tissue maximum average SAR value is 41.2W / kg. It can be calculated that in order to meet the FCC and IEEE safety standards for SAR values, the maximum input energy of the implantable circularly polarized antenna is 8.1mW. The electromagnetic radiation of the implantable circularly polarized antenna under the above conditions is safe and harmless to human tissue.

Claims

1. An implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring is composed of a dielectric substrate 1, a radiation patch loaded with an octagonal complementary open resonant ring 2, a short-circuit probe 3, a short-circuit probe 4, a coaxial connector 5, and a floor 6, and is characterized by: a. The loaded octagonal complementary open resonant ring radiation patch 2 is formed by slotting around the radiation patch to form a symmetrical C-shaped structure 2-1, a symmetrical C-shaped structure 2-2, a symmetrical C-shaped structure 2-3, and a symmetrical C-shaped structure 2-4. The symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 are formed by opening a T-shaped slot and an L-shaped slot around the radiation patch. The two right angles of the L-shaped slot are connected by an isosceles right triangle transition, and an L-shaped slot opening end is added. Two half-hexagonal patches, the symmetrical C-shaped structure 2-1 is rotated 90 degrees with the dielectric substrate 1 as the center to obtain the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4, and an octagonal complementary open resonant ring structure 2-5 is set in the center of the radiation patch. The octagonal complementary open resonant ring structure 2-5 is to open two octagonal grooves in the center of the radiation patch to form an octagonal ring and an octagonal patch. The octagonal ring and the octagonal patch are respectively connected to the radiation patch through rectangular guide bands; b. The short-circuit probe 3 and the short-circuit probe 4 are arranged on the lower left and upper left sides of the octagonal complementary open resonant ring structure 2-5 in the octagonal complementary open resonant ring radiation patch 2, and the short-circuit probe 3 and the short-circuit probe 4 are symmetrical about the horizontal axis of the antenna dielectric substrate 1; c. The coaxial connector 5 is located on the upper right side of the octagonal complementary open resonant ring structure 2-5 in the loaded octagonal complementary open resonant ring radiation patch 2, the inner core of the coaxial connector 5 is connected to the loaded octagonal complementary open resonant ring radiation patch 2, and the outer core of the coaxial connector 5 is connected to the floor 6; d. The floor 6 is a complete square metal patch structure without adding gaps or grooves; The length L5 of the transverse rectangular groove of the T-shaped groove of the symmetrical C-shaped structure 2-1, the symmetrical C-shaped structure 2-2, the symmetrical C-shaped structure 2-3, and the symmetrical C-shaped structure 2-4 in the loaded octagonal complementary open resonant ring radiation patch 2 is 0.1mm~0.3mm, the width W8 is 4.6mm~4.8mm, the length L1 of the longitudinal rectangular groove is 0.9mm~1.1mm, the width W7 is 0.1mm~0.3mm, the length L2 of the upper rectangular branch of the C-shaped structure is 0.2mm~0.4mm, the width W4 is 2.2mm~2.4mm, the width W6 of the middle rectangular branch of the C-shaped structure is 0.2mm~0.4mm, the transverse rectangular groove length L3 of the L-shaped groove is 0.4mm~0.6mm, the two right angles of the L-shaped groove are connected by an isosceles right triangle transition, the right angle side length W2 of the right triangle is 0.3mm~0.5mm, and the distance between the two right triangles is 0. The distance from W3 is 1.6mm~1.8mm, two semi-hexagonal patches are added at the open end of the L-shaped groove, the radius R1 of the semi-hexagonal patch is 0.2mm~0.4mm, and an octagonal complementary open resonant ring structure 2-5 is arranged in the center of the radiation patch, the radius R5 of the octagonal patch is 0.7mm~0.9mm, the outer ring radius R3 of the octagonal ring is 1.7mm~1.9mm, the inner ring radius R4 is 1.3mm~1.5mm, the outer ring radius R2 of the outer octagonal groove 2 is 2mm~2.2mm, the right rectangular guide band width L7 connecting the octagonal ring is 0.2mm~0.4mm, the angle a2 between the central axis of the right rectangular guide band and the horizontal axis of the dielectric substrate 1 is 8 degrees~12 degrees, the left rectangular guide band width L6 connecting the octagonal patch is 0.5mm~0.7mm, and the angle a1 between the central axis of the left rectangular guide band and the horizontal axis of the dielectric substrate 1 is 6 degrees~10 degrees.

2. The implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring according to claim 1, characterized in that The length L of the dielectric substrate 1 is 8 mm to 9 mm, and the width W is 8 mm to 9 mm.

3. The implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring according to claim 1, characterized in that The distance L8 between the center of the short-circuit probe 3, the short-circuit probe 4 and the center of the dielectric substrate 1 is 2.2mm~2.4mm, the angle a3 between the short-circuit probe 3, the short-circuit probe 4 and the longitudinal symmetry axis of the dielectric substrate 1 is 25 degrees~35 degrees, the radius R6 of the short-circuit probe 3, the short-circuit probe 4 is 0.2mm~0.4mm, and the radius of the short-circuit probe 3, the short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

4. The implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring according to claim 1, characterized in that The distance L0 between the center of the coaxial connector 5 and the transverse symmetry axis of the dielectric substrate 1 is 1.8 mm to 2.2 mm, and the distance W0 between the center of the coaxial connector 5 and the longitudinal symmetry axis of the dielectric substrate 1 is 1.8 mm to 2.2 mm.

5. The implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring according to claim 1, characterized in that The dimensions of the floor 6 are consistent with those of the dielectric substrate 1 , with a length L of 8 mm to 9 mm and a width W of 8 mm to 9 mm.

6. The implantable small circular polarization antenna loaded with an octagonal complementary open resonant ring according to claim 1, characterized in that The outer surface of the implantable small circular polarization antenna loaded with the octagonal complementary open resonant ring is coated with a layer of biocompatible coating material aluminum oxide with insulating properties, and the dielectric constant ε r The loss tangent tanδ is 9.2, the loss tangent tanδ is 0.008, and the coating thickness is 0.03mm.

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