Loaded square resonant ring implantable circularly polarized antenna for wireless biomedical applications

Abstract

The present invention designs a loaded square resonator loop implantable circularly polarized antenna for wireless biomedical applications. Adding a meandering structure around the radiation patch can make the surface current of the antenna flow along the meandering structure in a meandering manner, thereby increasing the surface current path of the antenna and reducing the resonant frequency of the antenna. The square complementary split-ring resonator loaded at the center of the loaded square resonator loop radiation patch is an array of metamaterial structures with negative magnetic permeability, which can further enhance the efficiency generated by a single complementary split-ring resonator, reduce the overall size of the antenna, and two orthogonal modes can be excited by adjusting the size of the square complementary split-ring resonator to generate circular polarization characteristics. The volume of the antenna is only 11×11×0.635 mm<supgt;3< / supgt>, and it has the characteristics of miniaturization, circular polarization, wide bandwidth, anti-interference, and excellent biocompatibility. It is applicable to the ISM 2.45 GHz frequency band and meets the requirements of miniaturization and circular polarization operation after being implanted into the human tissue environment.

Description

Technical Field

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

[0002] With the improvement of medical level and the continuous growth of economy, the trend of population aging has become irreversible worldwide, which has brought great pressure to the medical industry. Using wireless technology to carry out telemedicine will be a low-cost and high-efficiency solution. The advantage of wireless biomedical technology is that hospitals and patients can be free from distance restrictions, and doctors can remotely monitor and detect patients' physiological parameters. Compared with traditional diagnosis and treatment methods, wireless biomedical technology can provide comprehensive and accurate data in real time to provide doctors with diagnostic basis. Doctors can analyze and diagnose data more quickly and efficiently, and patients can be examined and treated without going to the hospital in person. In daily life, commonly used wireless biomedical devices include: pacemakers, cochlear implants, cardioversion defibrillators, blood glucose monitors, temperature monitors, retinal implants, etc. Wireless biomedical technology mainly collects human physiological parameters through various sensors, transmits the collected physiological parameters to the analysis system and storage device through the transmission unit, and the doctor makes diagnosis and treatment recommendations based on the original data or analysis data provided by the analysis system. Data transmission between the data acquisition system and the analysis system and storage device needs to be through an implanted antenna. Therefore, the implanted antenna is an important part of the wireless biomedical device and the core device in the data transmission system. Implantable antennas need to be implanted in human organs or tissues. Therefore, comfort is a key factor in implanting human organs or tissues, which requires implantable antennas to have low profile and miniaturization. The electrical characteristics in human organs and tissues are quite different from those in free space, which requires implantable antennas to have broadband characteristics to reduce the impact of the complex human environment on the antenna. This requires linear polarization antennas to have a wider impedance bandwidth and circular polarization antennas to have a wider axial ratio bandwidth. Circular polarization antennas have the advantages of low bit error rate, strong resistance to multipath interference, and strong anti-interference ability. The main methods to achieve circular polarization characteristics are: opening a gap with a specific structure on the radiating patch so that the surface current can meander along the gap, thereby increasing the current path on the antenna surface. Opening a gap with a specific structure on the antenna surface can produce a polarization degenerate mode with a phase difference of 90 degrees, so that the antenna has a circular polarization characteristic; the circular polarization characteristic can be achieved by using the aperture coupling feeding method. This method has a more flexible feeding position, and the floor can well isolate the feed line and the radiating unit; feeding on the diagonal line of the radiating unit and introducing a slice resistor can achieve circular polarization performance; the radiating unit adopts aperture coupling or slotting technology, and circular polarization performance can be achieved by feeding through multiple feeding points. The gap is similar to a resonant structure, and the bandwidth can be widened by being close to the resonant frequency of the radiating unit. 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.Non-patent document 1 discloses a circularly polarized antenna loaded with a complementary open resonant ring. The open resonant ring is loaded at the center of the radiating unit. It is a metamaterial structure with negative magnetic permeability, which reduces the size of the antenna. The circular polarization performance is achieved by adjusting the opening position and size of the open resonant ring. Four C-shaped slots are added around the radiating unit to increase the effective current path and further reduce the size of the antenna. Non-patent document 2 discloses a square ring-shaped circularly polarized implantable antenna. Rectangular slots of different sizes are opened on the four edges of the radiating unit to achieve circular polarization characteristics. A square slot is opened in the center of the radiating patch, and two triangles are added on the diagonals of the square to form a geometric perturbation. The size of the antenna is further reduced by introducing a short-circuit probe.

[0003] Citation list

[0004] Non-patent literature 1:

[0005] Non-patent literature 2: Z. Yang, S. Xiao, L. Zhu, B. Zhang, and H. Tu. Acircularly polarized implantable antenna for 2.4-GHz ISM band biomedical applications [J]. IEEE Antennas Wireless Propag. Lett., 2017, 16: 2554-2557. Summary of the invention

[0006] The purpose of the present invention is to provide an implantable circularly polarized antenna with a square resonant ring for wireless biomedical treatment. The antenna has the characteristics of miniaturization, circular polarization, wide frequency band, anti-interference, excellent biocompatibility, etc. It is convenient to integrate with implantable wireless biomedical devices, is suitable for the ISM 2.45GHz frequency band, and can meet the requirements of wireless biomedical devices for antenna performance.

[0007] The technical solution of the present invention is: a square resonant ring loaded implantable circularly polarized antenna for wireless biomedical treatment, which is composed of a dielectric substrate 1, a square resonant ring loaded radiation patch 2, a lower short-circuit probe 3, an upper short-circuit probe 4, a coaxial connector 5, and a floor 6, and is characterized in that:

[0008] a. The loaded square resonant ring radiation patch 2 is a rectangular groove around the radiation patch, and a left side meandering structure 2-1, an upper side meandering structure 2-2, a right side meandering structure 2-3, and a lower side meandering structure 2-4 are added in the rectangular groove. The left side meandering structure 2-1 is rotated 90 degrees with the dielectric substrate 1 as the center to obtain an upper side meandering structure 2-2, a right side meandering structure 2-3, and a lower side meandering structure 2-4. The left side meandering structure 2-1, an upper side meandering structure 2-2, a right side meandering structure 2-3, and a lower side meandering structure 2-4 are added around the radiation patch. Structure 2-4 can make the antenna surface current meander along the meander structure, thereby increasing the antenna surface current path and reducing the antenna resonant frequency. Adjusting the sizes of the left meander structure 2-1, the upper meander structure 2-2, the right meander structure 2-3, and the lower meander structure 2-4 can further optimize the impedance matching. A square groove is opened in the middle of the square resonant ring radiation patch 2, and the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 are loaded in the square groove. The lower left square The complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 are composed of two square rings and a square patch, which are connected to the loaded square resonant ring radiation patch 2 through three rectangular conduction bands. The angle difference between the three rectangular conduction bands relative to the center of the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 is 90 degrees. The lower left square complementary open resonant ring loaded at the center of the loaded square resonant ring radiation patch 2 The vibration ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 are a metamaterial structure array with negative magnetic permeability, which can further enhance the performance of a single complementary open resonant ring, shift the antenna resonance frequency toward the low frequency direction, and reduce the overall size of the antenna. By adjusting the sizes of the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8, two orthogonal modes can be excited, thereby generating circular polarization characteristics;

[0009] b. The lower short-circuit probe 3 and the upper short-circuit probe 4 are arranged on the lower left side and the upper left side of the loaded square resonant ring radiation patch 2. The lower short-circuit probe 3 and the upper short-circuit probe 4 are symmetrical about the horizontal axis of the antenna dielectric substrate 1. Adding the lower short-circuit probe 3 and the upper short-circuit probe 4 can increase the resonance point, thereby widening the impedance bandwidth of the antenna;

[0010] c. The coaxial connector 5 is located on the diagonal line on the upper right side of the loaded square resonant ring radiation patch 2, the inner core of the coaxial connector 5 is connected to the loaded square resonant ring radiation patch 2, and the outer core of the coaxial connector 5 is connected to the floor 6;

[0011] d. The floor 6 is a square complete metal patch structure without additional slots or gaps, forming a shielding layer between the implantable circularly polarized antenna and the underlying wireless biomedical device electronic components, which can reduce the interference of the implantable circularly polarized antenna to other electronic components and improve the electromagnetic compatibility of the implantable circularly polarized antenna.

[0012] e. The length L of the dielectric substrate 1 is 10 mm to 12 mm, and the width W is 10 mm to 12 mm.

[0013] f. The length L2 of the rectangular groove opened around the loaded square resonant ring radiation patch 2 is 1.3mm~1.5mm, the width W4 is 5.5mm~5.7mm, the width W2 of the left side meandering structure 2-1, the upper side meandering structure 2-2, the right side meandering structure 2-3, and the lower side meandering structure 2-4 is 0.15mm~0.25mm, the distance W3 from the left side of the rectangular groove is 0.25mm~0.3mm, and the distance L1 from the bottom of the rectangular groove is 0.25mm~0.35mm. The width W6 of the square groove in the middle of the loaded square resonant ring radiation patch 2 is 4.9mm~5.1mm, and the lower left square complementary open resonant ring 2-5, upper left square complementary open resonant ring 2-5 loaded in the square groove are The width W12 of the outer square ring of the square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 is 2.2mm~2.3mm, the distance W7 between the outer square ring and the left side of the square groove is 0.1mm~0.2mm, the width W11 of the middle square ring is 1.6mm~1.7mm, the distance W8 between the middle square ring and the outer square ring is 0.1mm~0.2mm, the width W10 of the inner direction patch is 1mm~1.2mm, the distance W9 between the inner direction patch and the middle square ring is 0.1mm~0.2mm, and the width W5 of the three rectangular guide bands connecting two square rings and one square patch is 0.1mm~0.3mm.

[0014] The radius R1 of the short-circuit probe 3 and the short-circuit probe 4 is 0.2mm~0.4mm, the distance R2 between the center of the lower short-circuit probe 3 and the upper short-circuit probe 4 and the center of the dielectric substrate 1 is 5.8mm~6.2mm, the angle a1 between the lower short-circuit probe 3, the upper short-circuit probe 4 and the longitudinal symmetry axis of the dielectric substrate 1 is 40 degrees~50 degrees, and the radius of the lower short-circuit probe 3 and the upper short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

[0015] The distance L0 between the center of the coaxial connector 5 and the transverse symmetry axis of the dielectric substrate 1 is 2.8 mm to 3.2 mm, and the distance W0 between the center of the coaxial connector 5 and the longitudinal symmetry axis of the dielectric substrate 1 is 2.8 mm to 3.2 mm.

[0016] The floor 6 is a complete square metal patch, and the size of the floor 6 is the same as that of the dielectric substrate 1, with a length L of 10 mm to 12 mm and a width W of 10 mm to 12 mm.

[0017] The outer surface of the square resonant ring loaded implantable circularly polarized antenna for wireless biomedical treatment is coated with an ultra-thin biocompatible thin film aluminum oxide which has little effect on the antenna gain and reflection coefficient. The dielectric constant is similar to that of the dielectric substrate 1, the dielectric constant εr is 9.2, the loss tangent tanδ is 0.008, and the coating thickness is 0.02 mm. The human tissue is isolated from the implantable circularly polarized antenna, preventing the human tissue from directly contacting the conductive patch of the antenna, thereby reducing the influence of the human tissue on the performance of the implantable circularly polarized antenna.

[0018] The effect of the present invention is that the present invention designs a square resonant ring implantable circular polarization antenna for wireless biomedical treatment. The meandering structure added around the radiation patch can make the antenna surface current meander along the meandering structure, thereby increasing the antenna surface current path, reducing the antenna resonant frequency, and adjusting the meandering structure size can further optimize the impedance matching. The square complementary open resonant ring loaded at the center of the square resonant ring radiation patch is a metamaterial structure array with negative magnetic permeability, which can further enhance the efficiency generated by a single complementary open resonant ring, shift the antenna resonant frequency toward the low frequency direction, and reduce the overall size of the antenna. By adjusting the size of the square complementary open resonant ring, two orthogonal modes can be excited, thereby generating circular polarization characteristics. The floor is a square complete metal patch structure, without adding slots or gaps, forming a shielding layer between the implantable circular polarization antenna and the lower wireless biomedical device electronic device, which can reduce the interference of the implantable circular polarization antenna to other electronic devices and improve the electromagnetic compatibility performance of the implantable circular polarization antenna. Adding a short-circuit probe can increase the resonance point, thereby widening the impedance bandwidth of the antenna. The implantable circularly polarized antenna has a planar structure and a volume of only 11×11×0.635mm3. It has the characteristics of miniaturization, circular polarization, wide bandwidth, 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

[0019] Figure 1 It is a schematic diagram of the front structure of an embodiment of the present invention.

[0020] Figure 2 It is a schematic diagram of the side structure of an embodiment of the present invention.

[0021] Figure 3 It is a schematic diagram of the back structure of an embodiment of the present invention.

[0022] Figure 4 This is the influence of the width W2 of the meandering structure in the embodiment of the present invention on the antenna impedance bandwidth and axial ratio bandwidth.

[0023] Figure 5 This is the influence of the width W12 of the outer square ring, the width W11 of the middle square ring, and the width W10 of the inner and lateral patches on the antenna impedance bandwidth and axial ratio bandwidth of the square complementary open resonant ring in the embodiment of the present invention.

[0024] Figure 6 Schematic diagram of the implantation depth of the skin layer in an embodiment of the present invention.

[0025] Figure 7 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.

[0026] Figure 8 1 is a simulated and measured impedance bandwidth curve of an embodiment of the present invention.

[0027] Fig. 9 It is the E-plane radiation pattern of the embodiment of the present invention at a frequency of 2.45 GHz.

[0028] Fig.10 This is the H-plane radiation pattern of the embodiment of the present invention at a frequency of 2.45 GHz. DETAILED DESCRIPTION

[0029] The specific implementation mode of the present invention is: Figure 1As shown, a square resonant ring loaded implantable circularly polarized antenna for wireless biomedical treatment is composed of a dielectric substrate 1, a square resonant ring loaded radiation patch 2, a lower short-circuit probe 3, an upper short-circuit probe 4, a coaxial connector 5, and a floor 6. The characteristics are as follows: the square resonant ring loaded radiation patch 2 is a radiation patch with rectangular grooves around it, and a left-side meandering structure 2-1, an upper-side meandering structure 2-2, a right-side meandering structure 2-3, and a lower-side meandering structure 2-4 are added to the rectangular grooves. The left-side meandering structure 2-1 is rotated 90 degrees with the dielectric substrate 1 as the center to obtain the upper-side meandering structure 2-2, the right-side meandering structure 2-3, and the lower-side meandering structure 2-4. The meander structure 2-4 is added around the radiation patch, and the left meander structure 2-1, the upper meander structure 2-2, the right meander structure 2-3, and the lower meander structure 2-4 can make the antenna surface current meander along the meander structure, thereby increasing the antenna surface current path and reducing the antenna resonant frequency. The impedance matching can be further optimized by adjusting the sizes of the left meander structure 2-1, the upper meander structure 2-2, the right meander structure 2-3, and the lower meander structure 2-4. A square groove is opened in the middle of the square resonant ring radiation patch 2, and the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-5 are loaded in the square groove. The resonator ring 2-6, the upper right square complementary open resonant ring 2-7, the lower right square complementary open resonant ring 2-8, the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 are composed of two square rings and a square patch, which are connected to the loaded square resonant ring radiation patch 2 through three rectangular conduction bands. The angle difference between the three rectangular conduction bands relative to the center of the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 is 90 degrees. The lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 loaded at the center of the ring radiation patch 2 are a metamaterial structure array with negative magnetic permeability, which can further enhance the performance generated by a single complementary open resonant ring, shift the antenna resonant frequency toward the low frequency direction, and reduce the overall size of the antenna. By adjusting the sizes of the lower left square complementary open resonant ring 2-5, the upper left square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8, two orthogonal modes can be excited, thereby generating circular polarization characteristics;The lower short-circuit probe 3 and the upper short-circuit probe 4 are arranged on the lower left and upper left sides of the loaded square resonant ring radiation patch 2. The lower short-circuit probe 3 and the upper short-circuit probe 4 are symmetrical about the horizontal axis of the antenna dielectric substrate 1. Adding the lower short-circuit probe 3 and the upper short-circuit probe 4 can increase the resonance point, thereby widening the impedance bandwidth of the antenna; the coaxial connector 5 is located on the diagonal line of the upper right side of the loaded square resonant ring radiation patch 2, the inner core of the coaxial connector 5 is connected to the loaded square 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 additional slots or gaps, forming a shielding layer between the implantable circular polarization antenna and the lower wireless biomedical device electronic device, which can reduce the interference of the implantable circular polarization antenna to other electronic devices and improve the electromagnetic compatibility performance of the implantable circular polarization antenna. ;

[0030] The length L of the dielectric substrate 1 is 10 mm to 12 mm, and the width W is 10 mm to 12 mm.

[0031] The length L2 of the rectangular groove around the loaded square resonant ring radiation patch 2 is 1.3mm~1.5mm, the width W4 is 5.5mm~5.7mm, the width W2 of the left side meandering structure 2-1, the upper side meandering structure 2-2, the right side meandering structure 2-3, and the lower side meandering structure 2-4 is 0.15mm~0.25mm, the distance W3 from the left side of the rectangular groove is 0.25mm~0.3mm, and the distance L1 from the bottom of the rectangular groove is 0.25mm~0.35mm. The width W6 of the square groove in the middle of the loaded square resonant ring radiation patch 2 is 4.9mm~5.1mm, and the lower left square complementary open resonant ring 2-5 and the upper left square complementary open resonant ring 2-5 loaded in the square groove are 0.15mm~0.25mm, and the distance W3 from the left side of the rectangular groove is 0.25mm~0.3mm, and the distance L1 from the lower side of the rectangular groove is 0.25mm~0.35mm. The width W12 of the outer square ring of the square complementary open resonant ring 2-6, the upper right square complementary open resonant ring 2-7, and the lower right square complementary open resonant ring 2-8 is 2.2mm~2.3mm, the distance W7 between the outer square ring and the left side of the square groove is 0.1mm~0.2mm, the width W11 of the middle square ring is 1.6mm~1.7mm, the distance W8 between the middle square ring and the outer square ring is 0.1mm~0.2mm, the width W10 of the inner direction patch is 1mm~1.2mm, the distance W9 between the inner direction patch and the middle square ring is 0.1mm~0.2mm, and the width W5 of the three rectangular guide bands connecting two square rings and one square patch is 0.1mm~0.3mm.

[0032] The radius R1 of the lower short-circuit probe 3 and the upper short-circuit probe 4 is 0.2mm~0.4mm, the distance R2 between the center of the lower short-circuit probe 3 and the upper short-circuit probe 4 and the center of the dielectric substrate 1 is 5.8mm~6.2mm, the angle a1 between the lower short-circuit probe 3, the upper short-circuit probe 4 and the longitudinal symmetry axis of the dielectric substrate 1 is 40 degrees~50 degrees, and the radius of the lower short-circuit probe 3 and the upper short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5.

[0033] The distance L0 between the center of the coaxial connector 5 and the transverse symmetry axis of the dielectric substrate 1 is 2.8 mm to 3.2 mm, and the distance W0 between the center of the coaxial connector 5 and the longitudinal symmetry axis of the dielectric substrate 1 is 2.8 mm to 3.2 mm.

[0034] The floor 6 is a complete square metal patch, and the size of the floor 6 is the same as that of the dielectric substrate 1, with a length L of 10 mm to 12 mm and a width W of 10 mm to 12 mm.

[0035] The outer surface of the square resonant ring loaded implantable circularly polarized antenna for wireless biomedical treatment is coated with an ultra-thin biocompatible thin film aluminum oxide which has little effect on the antenna gain and reflection coefficient. The dielectric constant is similar to that of the dielectric substrate 1, the dielectric constant εr is 9.2, the loss tangent tanδ is 0.008, and the coating thickness is 0.02 mm. The human tissue is isolated from the implantable circularly polarized antenna, preventing the human tissue from directly contacting the conductive patch of the antenna, thereby reducing the influence of the human tissue on the performance of the implantable circularly polarized antenna.

[0036] Embodiment: The specific manufacturing process is as described in the implementation method. Rogers RO3210 dielectric substrate is selected, with dielectric constant εr=10.2, loss tangent tanδ=0.003, thickness H=0.635mm, and coaxial connector adopts standard SMA connector. The length L of the dielectric substrate is 11mm, and the width W is 11mm. Adding a meandering structure around the radiation patch can make the antenna surface current flow along the meandering structure, thereby increasing the antenna surface current path and reducing the antenna resonant frequency. Adjusting the size of the meandering structure can further optimize the impedance matching. The length L2 of the rectangular slot around the square resonant ring radiation patch 2 is 1.4mm, the width W4 is 5.67mm, the width W2 of the left zigzag structure 2-1, the upper zigzag structure 2-2, the right zigzag structure 2-3, and the lower zigzag structure 2-4 is 0.21mm, the distance W3 from the left side of the rectangular slot is 0.27mm, and the distance L1 from the bottom of the rectangular slot is 0.27mm. The square complementary open resonant ring loaded in the center of the square resonant ring radiation patch is a metamaterial structure array with negative magnetic permeability, which can further enhance the performance of a single complementary open resonant ring, shift the antenna resonant frequency to the low frequency direction, and reduce the overall size of the antenna. By adjusting the size of the square complementary open resonant ring, two orthogonal modes can be excited, thereby generating circular polarization characteristics. The width W6 of the middle square slot of the square resonant ring radiation patch 2 is 5mm, the width W12 of the outer square rings of the lower left square complementary open resonant ring 2-5, upper left square complementary open resonant ring 2-6, upper right square complementary open resonant ring 2-7, and lower right square complementary open resonant ring 2-8 loaded in the square slot is 2.22mm, the distance W7 between the outer square ring and the left side of the square slot is 0.14mm, the width W11 of the middle square ring is 1.66mm, the distance W8 between the middle square ring and the outer square ring is 0.14mm, the width W10 of the inner direction patch is 1.1mm, the distance W9 between the inner direction patch and the middle square ring is 0.14mm, and the width W5 of the three rectangular guide strips connecting two square rings and one square patch is 0.14mm. Adding a short-circuit probe can increase the resonance point, thereby widening the impedance bandwidth of the antenna. The radius R1 of the lower short-circuit probe 3 and the upper short-circuit probe 4 is 0.3 mm, the distance R2 between the center of the lower short-circuit probe 3 and the upper short-circuit probe 4 and the center of the dielectric substrate 1 is 6 mm, the angle a1 between the lower short-circuit probe 3 and the upper short-circuit probe 4 and the longitudinal symmetry axis of the dielectric substrate 1 is 46 degrees, and the radius of the lower short-circuit probe 3 and the upper short-circuit probe 4 is equal to the inner core radius of the coaxial connector 5. The distance L0 between the center of the coaxial connector 5 and the transverse symmetry axis of the dielectric substrate 1 is 3 mm, and the distance W0 from the longitudinal symmetry axis of the dielectric substrate 1 is 3 mm.The floor is a square complete metal patch structure, without additional slots or gaps, forming a shielding layer between the implantable circularly polarized antenna and the lower wireless biomedical device electronic device, which can reduce the interference of the implantable circularly polarized antenna to other electronic devices and improve the electromagnetic compatibility performance of the implantable circularly polarized antenna. The floor 6 is a complete square metal patch, and the size of the floor 6 is the same as that of the dielectric substrate 1, with a length L of 11mm and a width W of 11mm. A layer of ultra-thin biocompatible thin film aluminum oxide with little effect on the antenna gain and reflection coefficient is plated on the outer surface of the square resonant ring implantable circularly polarized antenna for wireless biomedical treatment, which has a dielectric constant similar to that of the dielectric substrate 1, with a dielectric constant εr of 9.2, a loss tangent tanδ of 0.008, and a coating thickness of 0.02mm, isolating human tissue from the implantable circularly polarized antenna, preventing direct contact between human tissue and the conductive patch of the antenna, and reducing the influence of human tissue on the performance of the implantable circularly polarized antenna.

[0037] The influence of the width W2 of the meandering structure on the antenna impedance bandwidth and axial ratio bandwidth is analyzed as follows: Figure 4 As shown in the figure, three cases of W2 = 0.15 mm, W2 = 0.21 mm and W2 = 0.25 mm are selected to analyze the antenna performance. Figure 4 It can be seen that as the width W2 of the meandering structure increases, the resonant frequency of the antenna shifts toward the low frequency direction, the resonance degree gradually increases, and the axial ratio coefficient also shifts accordingly. The reason is that the addition of the meandering structure around the radiation patch can make the surface current of the antenna meander along the meandering structure, thereby increasing the surface current path of the antenna and reducing the resonant frequency of the antenna. Adjusting the size of the meandering structure can further optimize the impedance matching. When W2 = 0.21mm, the antenna performance is optimal, and both the impedance bandwidth and the axial ratio bandwidth cover the required ISM2.45GHz frequency band.

[0038] Select the width W12 of the outer square ring of the square complementary open resonant ring, the width W11 of the middle square ring, and the width W10 of the inner and side patches 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: W12 = 2.2mm, W11 = 1.6mm, W10 = 1mm, W12 = 2.22mm, W11 = 1.66mm, W10 = 1.1mm and W12 = 2.3mm, W11 = 1.7mm, W10 = 1.2mm. Figure 5It can be seen that as the size of the square complementary open resonant ring increases, the antenna resonant frequency shifts toward the low frequency direction, the resonance degree first increases and then decreases, and the axial ratio coefficient also shifts toward the low frequency. The reason is that the square complementary open resonant ring loaded at the center of the square resonant ring radiation patch is a metamaterial structure array with negative magnetic permeability, which can further enhance the performance of a single complementary open resonant ring, shift the antenna resonant frequency toward the low frequency direction, and reduce the overall size of the antenna. By adjusting the size of the square complementary open resonant ring, two orthogonal modes can be excited, thereby generating circular polarization characteristics. When W12 = 2.22mm, W11 = 1.66mm, and W10 = 1.1mm, the antenna performance is optimal, and the impedance bandwidth and axial ratio bandwidth both cover the required ISM 2.45GHz frequency band.

[0039] The application environment of the implantable circularly polarized antenna designed by the present invention is mainly the skin layer. The simulation environment is a single-layer skin model of 90mm×90mm×25mm. 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 implantation depth of the skin layer is as follows: Figure 6 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 7 As shown, when the implantation depth H is in the range of 3 mm to 7 mm, the reflection coefficient and axial ratio coefficient of the implantable circularly polarized antenna are relatively stable, and various performances have good robustness, which can well cover the required ISM 2.45 GHz frequency band.

[0040] 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. Figure 8 As shown, the simulated impedance bandwidth of the implantable circularly polarized antenna is 2.26GHz~2.71GHz, the resonant frequency is 2.45GHz, the simulated axial ratio bandwidth is 2.28GHz~2.52GHz, the measured impedance bandwidth is 2.29GHz~2.75GHz, the resonant frequency is 2.46GHz, the resonance degree is significantly increased, the measured axial ratio bandwidth is 2.30GHz~2.56GHz, 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 impedance characteristics and axial ratio characteristics of the implantable circularly polarized antenna are good in the working frequency band, and the resonant frequency and axial ratio coefficient are slightly shifted toward the high frequency direction. The reasons for the frequency shift are mainly caused by 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.

[0041] 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. 9 , Fig.10 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, that is, toward the outside of the human body. The main polarization is left-hand circular polarization. The actual gain value along the Z-axis is -28.8dBi. The difference between the main polarization and the cross polarization is 32.1dBi. It is mainly through adjusting the size of the square complementary open resonant ring that two orthogonal modes can be excited, thereby generating circular polarization characteristics. The antenna has a wider axial ratio beam in the working frequency band and excellent radiation characteristics. It is suitable for the ISM 2.45GHz working frequency band and can meet the needs of complex implant environments.

[0042] Taking into account the safety factors of implantation in human tissue, 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 average SAR value was used to evaluate the safe range of energy absorption by the human body model. After simulation calculation, the maximum average SAR value of the implantable circularly polarized antenna at 2.45GHz for 1-g human tissue is 392.5W / kg, and the maximum average SAR value of 10-g human tissue is 82.7W / kg. In order to meet the safety standards of IEEEC95.1-1999 and IEEEC95.1-2005 for SAR values, the corresponding maximum input powers of the implantable circularly polarized antenna are 3.1mW and 21.6mW respectively. The electromagnetic radiation of the implantable circularly polarized antenna under the above conditions is safe and harmless to human tissue.

Claims

1. A square resonant ring loaded implantable circularly polarized antenna for wireless biomedical treatment, comprising a dielectric substrate (1), a square resonant ring loaded radiation patch (2), a lower short-circuit probe (3), an upper short-circuit probe (4), a coaxial connector (5), and a floor (6), characterized in that: a. The loaded square resonant ring radiation patch (2) is a rectangular groove opened around the radiation patch, and a left-side meandering structure (2-1), an upper meandering structure (2-2), a right-side meandering structure (2-3), and a lower meandering structure (2-4) are added in the rectangular groove; the left-side meandering structure (2-1) is rotated 90 degrees with the dielectric substrate (1) as the center to obtain an upper meandering structure (2-2), a right-side meandering structure (2-3), and a lower meandering structure (2-4); the left-side meandering structure (2-1), an upper meandering structure (2-2), a right-side meandering structure (2-3), and a lower meandering structure (2-4) are added around the radiation patch. The meandering structure (2-4) can make the current on the antenna surface meander along the meandering structure, thereby increasing the current path on the antenna surface and reducing the antenna resonant frequency. The impedance matching can be further optimized by adjusting the sizes of the left meandering structure (2-1), the upper meandering structure (2-2), the right meandering structure (2-3), and the lower meandering structure (2-4). A square slot is opened in the middle of the square resonant ring radiation patch (2), and the lower left square complementary open resonant ring (2-5), the upper left square complementary open resonant ring (2-6), the upper right square complementary open resonant ring (2-7), and the lower right square complementary open resonant ring (2-8) are loaded in the square slot. The lower left square complementary open resonant ring (2-5), the upper left square complementary open resonant ring (2-6), the upper right square complementary open resonant ring (2-7), and the lower right square complementary open resonant ring (2-8) are composed of two square rings and a square patch, and are connected to the loaded square resonant ring radiation patch (2) through three rectangular conduction bands. The angle difference between the three rectangular conduction bands relative to the center of the lower left square complementary open resonant ring (2-5), the upper left square complementary open resonant ring (2-6), the upper right square complementary open resonant ring (2-7), and the lower right square complementary open resonant ring (2-8) is 90 degrees. The lower left square loaded at the center of the loaded square resonant ring radiation patch (2) The complementary open resonant ring (2-5), the upper left square complementary open resonant ring (2-6), the upper right square complementary open resonant ring (2-7), and the lower right square complementary open resonant ring (2-8) are a metamaterial structure array with negative magnetic permeability, which can further enhance the performance of a single complementary open resonant ring, shift the antenna resonance frequency toward the low frequency direction, and reduce the overall size of the antenna. By adjusting the sizes of the lower left square complementary open resonant ring (2-5), the upper left square complementary open resonant ring (2-6), the upper right square complementary open resonant ring (2-7), and the lower right square complementary open resonant ring (2-8), two orthogonal modes can be excited, thereby generating circular polarization characteristics. b. The lower short-circuit probe (3) and the upper short-circuit probe (4) are arranged on the lower left side and the upper left side of the loaded square resonant ring radiation patch (2). The lower short-circuit probe (3) and the upper short-circuit probe (4) are symmetrical about the horizontal axis of the antenna dielectric substrate (1). Adding the lower short-circuit probe (3) and the upper short-circuit probe (4) can increase the resonance point, thereby widening the impedance bandwidth of the antenna; c. The coaxial connector (5) is located on the diagonal line on the upper right side of the loaded square resonant ring radiation patch (2), the inner core of the coaxial connector (5) is connected to the loaded square 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 square complete metal patch structure without additional slots or gaps, forming a shielding layer between the implantable circularly polarized antenna and the underlying wireless biomedical device electronic devices, which can reduce the interference of the implantable circularly polarized antenna to other electronic devices and improve the electromagnetic compatibility of the implantable circularly polarized antenna; e. The dielectric substrate (1) has a length L of 10 mm to 12 mm and a width W of 10 mm to 12 mm; f. The length L2 of the rectangular groove around the loaded square resonant ring radiation patch (2) is 1.3mm~1.5mm, the width W4 is 5.5mm~5.7mm, the width W2 of the left zigzag structure (2-1), the upper zigzag structure (2-2), the right zigzag structure (2-3), and the lower zigzag structure (2-4) is 0.15mm~0.25mm, the distance W3 from the left side of the rectangular groove is 0.25mm~0.3mm, and the distance L1 from the bottom of the rectangular groove is 0.25mm~0.35mm. The width W6 of the square groove in the middle of the loaded square resonant ring radiation patch (2) is 4.9mm~5.1mm, and the lower left square complementary open resonant ring (2-5 ), the width W12 of the outer square ring of the upper left square complementary open resonant ring (2-6), the upper right square complementary open resonant ring (2-7), and the lower right square complementary open resonant ring (2-8) is 2.2mm~2.3mm, the distance W7 between the outer square ring and the left side of the square groove is 0.1mm~0.2mm, the width W11 of the middle square ring is 1.6mm~1.7mm, the distance W8 between the middle square ring and the outer square ring is 0.1mm~0.2mm, the width W10 of the inner direction patch is 1mm~1.2mm, the distance W9 between the inner direction patch and the middle square ring is 0.1mm~0.2mm, and the width W5 of the three rectangular guide bands connecting the two square rings and one square patch is 0.1mm~0.3mm.

2. The square resonant ring implantable circularly polarized antenna for wireless biomedical treatment according to claim 1, characterized in that The radius R1 of the lower short-circuit probe (3) and the upper short-circuit probe (4) is 0.2 mm to 0.4 mm, the distance R2 between the center of the lower short-circuit probe (3) and the center of the upper short-circuit probe (4) and the center of the dielectric substrate (1) is 5.8 mm to 6.2 mm, the angle a1 between the lower short-circuit probe (3), the upper short-circuit probe (4) and the longitudinal symmetry axis of the dielectric substrate (1) is 40 degrees to 50 degrees, and the radius of the lower short-circuit probe (3) and the upper short-circuit probe (4) is equal to the inner core radius of the coaxial connector (5).

3. The square resonant ring implantable circularly polarized antenna for wireless biomedical treatment 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 2.8 mm to 3.2 mm, and the distance W0 between the center of the coaxial connector (5) and the longitudinal symmetry axis of the dielectric substrate (1) is 2.8 mm to 3.2 mm.

4. The square resonant ring implantable circularly polarized antenna for wireless biomedical treatment according to claim 1, characterized in that The floor (6) is a complete square metal patch. The size of the floor (6) is the same as that of the dielectric substrate (1), with a length L of 10 mm to 12 mm and a width W of 10 mm to 12 mm.

5. The square resonant ring implantable circularly polarized antenna for wireless biomedical treatment according to claim 1, characterized in that The outer surface of the square resonant ring implantable circularly polarized antenna for wireless biomedical treatment is coated with an ultra-thin biocompatible thin film aluminum oxide, which has a dielectric constant similar to that of the dielectric substrate (1), a dielectric constant εr of 9.2, a loss tangent tanδ of 0.008, and a coating thickness of 0.02 mm. The invention isolates human tissue from the implantable circularly polarized antenna, prevents direct contact between human tissue and the conductive patch of the antenna, and reduces the influence of human tissue on the performance of the implantable circularly polarized antenna.

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