A miniaturized dual-band circularly polarized flexible implantable antenna

Abstract

This invention provides a miniaturized dual-band circularly polarized flexible implantable antenna, comprising: a dielectric substrate and a cover layer, the cover layer being located on top of the dielectric substrate; a radiating surface is printed on the top of the dielectric substrate, and a ground plane is printed on the bottom of the dielectric substrate; the radiating surface and the ground plane are connected via a short-circuit probe and a coaxial feed center line; the radiating surface is connected to the coaxial feed center probe; the short-circuit probe and the coaxial feed center line are symmetrically distributed about the center of the dielectric substrate; and the cover layer is located on top of the radiating surface. This invention provides a miniaturized dual-band circularly polarized flexible implantable antenna with a simple structure, convenient installation, small size, low profile, and large channel capacity.

Description

Technical Field

[0001] This invention relates to the field of antennas, and in particular to a miniaturized dual-frequency circularly polarized flexible implantable antenna. Background Technology

[0002] With the improvement of living standards and a relatively stable international situation, the aging population problem is becoming increasingly serious in countries around the world, inevitably increasing the demand for healthcare services. my country has now become the world's second-largest economy, and the quality of life for its people has significantly improved, leading to higher expectations for the healthcare service industry. Utilizing wireless biomedical devices to improve the service level of the healthcare industry is a major trend in the current and future development of the industry. Currently, wireless medical technology faces many design challenges but has broad application prospects, thus attracting increasing attention from scholars both domestically and internationally. Mobile medical devices utilize wireless communication technology to improve medical services, including telemedicine, appointment platforms, and mobile hospital information solutions. Currently, research teams both domestically and internationally have begun to develop a theoretical framework for implantable antennas. The Industrial, Scientific, and Medical (ISM) band, whose main communication frequency bands include 433.1-434.8 MHz, 868-868.6 MHz, 902-928 MHz, 2.4-2.48 GHz, and 5.725-5.875 GHz, offers advantages such as wide available bandwidth and large channel capacity. Therefore, it is common for implantable medical devices to have terminal antennas covering the ISM band. Implantable antennas can be surgically implanted into tissues such as the scalp or heart, or they can be bent and placed into capsule devices for ingestion by the patient. For miniaturized implantable antennas, researchers from various countries have proposed several different solutions, such as inverted-F antennas (PIFA), slot antennas, and fractal structure antennas. The paper "Design and in Vitro Test of a Differentially Fed Dual-Band Implantable Antenna Operating at MICS and ISM Bands" designs a capacitively loaded circularly polarized antenna operating at 2.4 GHz with dimensions of 10 mm × 10 mm × 1.27 mm. This antenna has a relatively high profile and limited channel capacity. The paper "Coplanar Waveguide-Fed Dual-Band Implantable Antenna Operating at MICS and ISM Bands" also proposes a capacitively loaded circularly polarized antenna operating at 2.4 GHz with dimensions of 10 mm × 10 mm × 1.27 mm, but it has a relatively large size and a high profile.The three antennas mentioned above have the same dimensions but different radiation characteristics due to their different radiating surface structures. They all suffer from large planar dimensions and high profiles. Therefore, designing a dual-band circularly polarized implantable antenna with a simple structure, small size, low profile, and large channel capacity is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a miniaturized dual-frequency circularly polarized flexible implantable antenna with simple structure, convenient installation, small size, low profile, and large channel capacity.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] A miniaturized dual-band circularly polarized flexible implantable antenna includes: a dielectric substrate and a cover layer, wherein the cover layer is located on top of the dielectric substrate;

[0006] The top of the dielectric substrate is printed with a radiating surface, and the bottom of the dielectric substrate is printed with a ground plane. The radiating surface and the ground plane are connected by a short-circuit probe and a coaxial feed center line. The radiating surface and the coaxial feed center probe are connected. The short-circuit probe and the coaxial feed center line are symmetrically distributed about the center of the dielectric substrate. The cover layer is located on top of the radiating surface.

[0007] The radiating surface has a first T-shaped groove, a second T-shaped groove, a third T-shaped groove, and a fourth T-shaped groove sequentially formed along its edge in a clockwise direction with the top center as the center. The center of the radiating surface has a cross-shaped groove. The short-circuit probe solder joints and the coaxial feed center line solder joints of the radiating surface are symmetrically distributed about the top center of the radiating surface. The short-circuit probe solder joints are connected to the short-circuit probes, and the coaxial feed center line solder joints are connected to the coaxial feed center line.

[0008] The ground plane has a cross-shaped groove at its center. The short-circuit probe solder joints and the coaxial feed grounding port are symmetrically distributed about the bottom center of the ground plane. The short-circuit probe solder joints are connected to the short-circuit probes, and the coaxial feed grounding port is connected to the coaxial feed center line.

[0009] Optionally, the first T-shaped groove is formed by two mutually perpendicular rectangles of equal width forming a T shape. The first T-shaped groove, the second T-shaped groove, the third T-shaped groove, and the fourth T-shaped groove are identical and do not communicate with each other.

[0010] Optionally, the radiating cross-shaped groove is formed by two identical rectangles perpendicular to each other, the width of the rectangle is the same as the width of the rectangle in the first T-shaped groove, and the two ends of the rectangle of the radiating cross-shaped groove face the center of the two adjacent T-shaped grooves that are not connected. The radiating cross-shaped groove is not connected to the first T-shaped groove, the second T-shaped groove, the third T-shaped groove and the fourth T-shaped groove.

[0011] Optionally, the ground plane cross-shaped groove is composed of two identical rectangles that are perpendicular to each other, the width of the rectangles is the same as the width of the rectangles in the radiating surface cross-shaped groove, and the orientation of the rectangles in the ground plane cross-shaped groove is the same as the orientation of the rectangles in the radiating surface cross-shaped groove.

[0012] The length of the cross-shaped groove on the radiating surface is 5:11 compared to the length of the cross-shaped groove on the ground plane.

[0013] Optionally, the dielectric substrate and the cover layer are made of polyimide flexible material with a relative permittivity of 10.2.

[0014] Optionally, both the radiating surface and the ground plane are circular metal patches, and both the short-circuit probe and the coaxial feed centerline are metal cylinders.

[0015] According to specific embodiments provided by the present invention, the following technical effects are disclosed: The present invention provides a miniaturized dual-band circularly polarized flexible implantable antenna, which adopts a coaxial feeding structure, making installation convenient, and further reduces the antenna volume by utilizing short-circuit probes; by using slot loading technology to uniformly and symmetrically open T-shaped slots and cross-shaped slots on the radiating surface, a novel symmetrical structure is designed, enabling the antenna to achieve dual-band circular polarization characteristics. The actual impedance bandwidth of the antenna is 0.88-0.98 GHz and 2.27-2.53 GHz, with relative bandwidths reaching 10.75% and 10.83% respectively, relative to its operating bandwidth of 0.902-0.928 GHz and 2.4-2.48 GHz, achieving dual-band wideband. The wideband allows the center frequency to operate stably within the bandwidth, reducing the impact of the complex human tissue environment on antenna performance. The return loss of the antenna at the center frequency reaches -11.8 dB and -31.4 dB respectively. The antenna exhibits good circular polarization characteristics, with a voltage standing wave ratio (VSWR) of less than 2.3 dB throughout its entire operating bandwidth. The axial ratio bandwidths are 0.87-1.05 GHz and 2.37-2.57 GHz, respectively; the effective axial ratio bandwidths are 0.88-0.98 GHz and 2.37-2.53 GHz, respectively, representing 10.75% and 6.53% of the effective axial ratio bandwidth, respectively. The dielectric substrate and capping layer utilize flexible polyimide material with a dielectric constant of 10.2, making the antenna easier to bend and achieving good implantation results, while avoiding direct contact between the radiating surface and human tissue. The center frequency of the antenna is tuned by adjusting the dimensions of the four T-slots on the radiating surface, the cross-shaped slot on the radiating surface, and the cross-shaped slot on the ground plane, achieving dual-band characteristics. Circular polarization is achieved by adjusting the positions of the feed point and the short-circuit probe. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the radiation surface structure according to an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of the ground plane structure according to an embodiment of the present invention;

[0019] Figure 3 This is a cross-sectional structural diagram of an embodiment of the present invention;

[0020] Figure 4 This is a return loss curve of the antenna in three layers of tissue—skin, fat, and muscle—at a frequency of 0.9 GHz, according to an embodiment of the present invention.

[0021] Figure 5 This is a 3dB axial ratio curve of the antenna in the three layers of skin, fat and muscle at a frequency of 0.9 GHz in an embodiment of the present invention.

[0022] Figure 6 This is a diagram showing the amplitude distribution of the radiating surface current of the antenna in the three layers of skin, fat, and muscle at a frequency of 0.9 GHz in an embodiment of the present invention.

[0023] Figure 7 This is a diagram showing the amplitude distribution of the radiating surface current of the antenna in the three layers of skin, fat, and muscle at a frequency of 2.4 GHz, according to an embodiment of the present invention.

[0024] Figure 8 This is a radiation pattern of the antenna in the three layers of skin, fat, and muscle at a frequency of 0.9 GHz in an embodiment of the present invention.

[0025] Figure 9 This is a radiation pattern of the antenna in the three layers of skin, fat, and muscle at a frequency of 2.4 GHz in an embodiment of the present invention.

[0026] Reference numerals: 1. Dielectric substrate; 2. Cover layer; 3. Radiation surface; 4. First T-groove; 5. Second T-groove; 6. Third T-groove; 7. Fourth T-groove; 8. Cross-shaped groove on the radiation surface; 9. Short-circuit probe solder joint on the radiation surface; 10. Coaxial feed center line solder joint on the radiation surface; 11. Short-circuit probe solder joint on the ground plane; 12. Coaxial feed grounding port on the ground plane; 13. Cross-shaped groove on the ground plane; 14. Ground plane; 15. Short-circuit probe; 16. Coaxial feed center line. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The purpose of this invention is to provide a miniaturized dual-frequency circularly polarized flexible implantable antenna with simple structure, convenient installation, small size, low profile, and large channel capacity.

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 3 As shown, a miniaturized dual-band circularly polarized flexible implantable antenna includes: a dielectric substrate 1 and a cover layer 2, wherein the cover layer 2 is located on top of the dielectric substrate 1;

[0031] The top of the dielectric substrate 1 is printed with a radiating surface 3, and the bottom of the dielectric substrate 1 is printed with a ground plane 14. The radiating surface 3 and the ground plane 14 are connected by a short-circuit probe 15 and a coaxial feed center line 16. The radiating surface 3 is connected to the coaxial feed center probe. The short-circuit probe 15 and the coaxial feed center line 16 are symmetrically distributed about the center of the dielectric substrate 1. The cover layer 2 is located on top of the radiating surface 3.

[0032] The radiating surface 3 has a first T-shaped groove 4, a second T-shaped groove 5, a third T-shaped groove 6 and a fourth T-shaped groove 7 sequentially formed along its edge in a clockwise direction with the top center as the center. The center of the radiating surface 3 has a radiating surface cross-shaped groove 8. The short-circuit probe solder joint 9 and the coaxial feed center line solder joint 10 of the radiating surface 3 are symmetrically distributed about the top center of the radiating surface 3. The short-circuit probe solder joint 9 of the radiating surface 3 is connected to the short-circuit probe 15, and the coaxial feed center line solder joint 10 of the radiating surface is connected to the coaxial feed center line 16.

[0033] The ground plane 14 has a cross-shaped groove 13 at its center. The ground plane short-circuit probe solder joint 11 and the ground plane coaxial feed grounding port 12 are symmetrically distributed about the bottom center of the ground plane 14. The ground plane short-circuit probe solder joint 11 is connected to the short-circuit probe 15, and the ground plane coaxial feed grounding port 12 is connected to the coaxial feed center line 16.

[0034] The first T-shaped groove 4 is composed of two mutually perpendicular rectangles of equal width forming a T shape. The first T-shaped groove 4, the second T-shaped groove 5, the third T-shaped groove 6 and the fourth T-shaped groove 7 are identical and do not communicate with each other.

[0035] The radiating surface cross-shaped groove 8 is composed of two identical rectangles that are perpendicular to each other, and the width of the rectangle is the same as the width of the rectangle in the first T-shaped groove 4. The two ends of the rectangle of the radiating surface cross-shaped groove 8 face the center of the two adjacent T-shaped grooves that are not connected. The radiating surface cross-shaped groove 8 is not connected to the first T-shaped groove 4, the second T-shaped groove 5, the third T-shaped groove 6 and the fourth T-shaped groove 7.

[0036] The ground plane cross-shaped groove 13 is composed of two identical rectangles that are perpendicular to each other, and the width of the rectangle is the same as the width of the rectangle in the radiation surface cross-shaped groove 8. The rectangle of the ground plane cross-shaped groove 13 is oriented in the same direction as the rectangle of the radiation surface cross-shaped groove 3.

[0037] The length of the radial cross-shaped groove 8 is 5:11 with the length of the ground plane cross-shaped groove 13.

[0038] The dielectric substrate 1 and the cover layer 2 are made of polyimide flexible material with a relative permittivity of 10.2.

[0039] Both the radiating surface 3 and the ground plane 14 are circular metal patches, and both the short-circuit probe 15 and the coaxial feed center line 16 are metal cylinders.

[0040] One embodiment of the present invention is as follows:

[0041] The dielectric substrate 1 and the capping layer 2 are cylindrical in shape and are made of biocompatible flexible polyimide with a relative permittivity of 10.2. The planar dimensions of the dielectric substrate 1 and the capping layer 2 are π × 4.72 mm. 2 The cross-sectional thicknesses are 0.625 mm and 0.254 mm, respectively.

[0042] like Figure 1 As shown, four identical T-shaped slots are cut clockwise from the top of the radiating surface 3. The first T-shaped slot 4 has a horizontal rectangular slot size of 3.0mm × 0.4mm and a vertically open rectangular slot size of 2.3mm × 0.4mm. A radiating surface cross-shaped slot 8 is cut from the center of the radiating surface 3. The two rectangular slots that form the radiating surface cross-shaped slot 8 are perpendicular to each other and have the same size of 4.0mm × 0.4mm. The two ends of the rectangular cross-shaped slot of the radiating surface 3 face the center of the two adjacent T-shaped slots that are not connected. The vertex of the rectangular slot axis of symmetry of the radiating surface cross-shaped slot 8 is 2.7mm away from the edge of the radiating surface 3.

[0043] like Figure 2As shown, a cross-shaped groove 13 is cut out from the center of the ground plane 14. The two rectangular grooves that make up the cross-shaped groove 13 are perpendicular to each other and have the same size of 8.8mm × 0.4mm. The rectangular orientation of the cross-shaped groove 13 is the same as that of the cross-shaped groove of the radiation surface 3. The vertex of the symmetry axis of the rectangular groove of the cross-shaped groove 13 is 0.3mm away from the edge of the ground plane 14.

[0044] like Figure 1 As shown, the center of the short-circuit probe solder joint 9 on the radiating surface is 0.8 mm from the x-axis and 4.0 mm from the y-axis, with a radius of 0.15 mm; the center of the coaxial feed centerline solder joint 10 on the radiating surface is 0.7 mm from the x-axis and 4.0 mm from the y-axis; the radius of the coaxial feed centerline 16 is 0.2 mm; as... Figure 2 As shown, the center of the ground plane coaxial feed grounding port 12 is 0.7 mm from the x-axis, 4.0 mm from the y-axis, and has a radius of 0.3 mm. The coaxial feed centerline 16 is not in contact with the ground plane coaxial feed grounding port 12.

[0045] First, cut out the first T-shaped slot 5, the second T-shaped slot 5, the third T-shaped slot 6, and the fourth T-shaped slot 7 of the same size in sequence evenly and symmetrically at the top of the radiating surface 3 to obtain dual-frequency operating characteristics; then, cut out the cross-shaped slot 88 of the central radiating surface to obtain circular polarization characteristics for the antenna; finally, cut out the ground plane cross-shaped slot 13 on the ground plane 14 to optimize the impedance matching of the antenna.

[0046] Figure 4 and Figure 5 The figures show the return loss curves and axial ratio curves of the antenna in this embodiment at a frequency of 0.9 GHz in three layers of tissue: skin, fat, and muscle. Figure 4 It can be seen that the antenna achieves a return loss of less than -10dB in the 0.88-0.98GHz and 2.27-2.53GHz frequency bands, realizing dual-band wideband performance; from Figure 5 It can be seen that the antenna's axial ratio is less than 3dB in the 0.87-1.05GHz and 2.37-2.53GHz frequency bands, achieving dual-band circular polarization. Since the antenna operates within human tissue, the complex tissue environment can cause a reduction or shift in the antenna's actual bandwidth, resulting in the center frequency being outside the bandwidth and thus affecting antenna performance. However, this antenna achieves a wide bandwidth, effectively preventing the center frequency from being outside the bandwidth. Furthermore, the antenna's circular polarization characteristic reduces the impact of polarization mismatch on communication quality, enabling the antenna to operate stably in the 0.902-0.928GHz and 2.4-2.48GHz frequency bands.

[0047] Figure 6The figure shows the current amplitude distribution of the antenna in the three layers of skin, fat and muscle at a frequency of 0.9 GHz. It can be seen from the figure that the current path is increased by opening the T-slot and adding the short-circuit probe 15, which effectively reduces the size of the antenna.

[0048] Figure 7 The figure shows the current amplitude distribution of the antenna in the three layers of skin, fat and muscle at a frequency of 2.4 GHz in this embodiment. It can be seen from the figure that by opening the T-shaped slot, the radiation at the 2.4 GHz frequency point is mainly concentrated near the closed rectangular slot of the T-shaped slot.

[0049] Figure 8 This is the radiation pattern of the antenna in this embodiment in the three layers of skin, fat and muscle at a frequency of 0.9 GHz. In the figure, E refers to the electric field and H refers to the magnetic field. It can be seen from the figure that the radiation pattern of the antenna in this embodiment has an approximately omnidirectional characteristic, which meets the engineering requirements.

[0050] Figure 9 This is the radiation pattern of the antenna in this embodiment in the three layers of skin, fat and muscle at a frequency of 2.4 GHz. In the figure, E refers to the electric field and H refers to the magnetic field. It can be seen from the figure that the radiation pattern of the antenna in this embodiment has an approximately omnidirectional characteristic, which meets the engineering requirements.

[0051] This invention provides a miniaturized dual-band circularly polarized flexible implantable antenna. It employs a coaxial feed structure for easy installation and utilizes short-circuit probes to further reduce the antenna's size. Through slot loading technology, a novel symmetrical structure is designed by uniformly and symmetrically opening T-shaped slots and cross-shaped slots on the radiating surface, enabling the antenna to achieve dual-band circular polarization characteristics. The antenna's actual impedance bandwidth is 0.88-0.98 GHz and 2.27-2.53 GHz, with relative bandwidths reaching 10.75% and 10.83% respectively. Compared to its operating bandwidths of 0.902-0.928 GHz and 2.4-2.48 GHz, it achieves dual-band wideband performance. This wideband allows the center frequency to operate stably within the bandwidth, reducing the impact of the complex human body environment on antenna performance. The return loss at the center frequency reaches -11.8 dB and -31.4 dB respectively, while the voltage standing wave ratio (VSWR) is less than 2.3 dB throughout the entire operating bandwidth. The axial ratio bandwidths are 0.87-1.05. The effective axial ratio bandwidths are 0.88-0.98 GHz and 2.37-2.57 GHz, respectively, with relative effective axial ratio bandwidths of 10.75% and 6.53%, exhibiting good circular polarization characteristics. The dielectric substrate and cover layer are made of flexible polyimide material with a dielectric constant of 10.2, making the antenna easier to bend and achieving good implantation results, while avoiding direct contact between the radiating surface and human tissue to prevent harm to the human body. The center frequency of the antenna is tuned by adjusting the size of the four T-slots on the radiating surface, the cross-shaped slot on the radiating surface, and the cross-shaped slot on the ground plane to obtain dual-frequency characteristics. The circular polarization characteristics of the antenna are achieved by adjusting the position of the feed point and the short-circuit probe.

[0052] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A miniaturized dual-frequency circularly polarized flexible implantable antenna, characterized in that, include: A dielectric substrate and a cover layer, wherein the cover layer is located on top of the dielectric substrate; The top of the dielectric substrate is printed with a radiating surface, and the bottom of the dielectric substrate is printed with a ground plane. The radiating surface and the ground plane are connected by a short-circuit probe and a coaxial feed center line. The radiating surface and the coaxial feed center probe are connected. The short-circuit probe and the coaxial feed center line are symmetrically distributed about the center of the dielectric substrate. The cover layer is located on top of the radiating surface. The radiating surface has a first T-shaped groove, a second T-shaped groove, a third T-shaped groove, and a fourth T-shaped groove sequentially formed along its edge in a clockwise direction with the top center as the center. The center of the radiating surface has a cross-shaped groove. The short-circuit probe solder joints and the coaxial feed center line solder joints of the radiating surface are symmetrically distributed about the top center of the radiating surface. The short-circuit probe solder joints are connected to the short-circuit probes, and the coaxial feed center line solder joints are connected to the coaxial feed center line. The first T-shaped groove is composed of two mutually perpendicular rectangles of equal width forming a T shape. The first T-shaped groove, the second T-shaped groove, the third T-shaped groove, and the fourth T-shaped groove are identical and do not communicate with each other. The radiating cross-shaped groove is formed by two identical rectangles perpendicular to each other. The width of the rectangle is the same as the width of the rectangle in the first T-shaped groove. The two ends of the rectangle of the radiating cross-shaped groove face the center of the two adjacent T-shaped grooves that are not connected. The radiating cross-shaped groove is not connected to the first T-shaped groove, the second T-shaped groove, the third T-shaped groove, and the fourth T-shaped groove. A cross-shaped groove is formed in the center of the ground plane. The short-circuit probe solder joints and the coaxial feed grounding port of the ground plane are symmetrically distributed about the bottom center of the ground plane. The short-circuit probe solder joints are connected to the short-circuit probes, and the coaxial feed grounding port of the ground plane is connected to the coaxial feed center line. The ground plane cross-shaped groove is composed of two identical rectangles that are perpendicular to each other, the width of which is the same as the width of the rectangle in the radiating surface cross-shaped groove, and the orientation of the rectangle in the ground plane cross-shaped groove is the same as the orientation of the rectangle in the radiating surface cross-shaped groove.

2. The miniaturized dual-frequency circularly polarized flexible implantable antenna according to claim 1, characterized in that, The length of the cross-shaped groove on the radiating surface is 5:11 compared to the length of the cross-shaped groove on the ground plane.

3. The miniaturized dual-frequency circularly polarized flexible implantable antenna according to claim 1, characterized in that, The dielectric substrate and the cover layer are made of flexible polyimide material with a relative permittivity of 10.

2.

4. The miniaturized dual-frequency circularly polarized flexible implantable antenna according to claim 1, characterized in that, Both the radiating surface and the ground plane are circular metal patches, and both the short-circuit probe and the coaxial feed center line are metal cylinders.

Images