Ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscope

Abstract

The invention discloses an ultra-wide-band conformal MIMO antenna suitable for a wireless capsule endoscope, an annular ferrite is adopted as a substrate, an IFA antenna is set to be oval, impedance matching of different resonant modes is controlled through variables in the long-axis direction and the short-axis direction, the annular ferrite material and an improved inverted-F structure are creatively integrated together, and the antenna can be applied to the wireless capsule endoscope. The band width of 120.5% (0.31-1.25 GHz) is realized through excitation and control of multi-mode resonance, industrial, scientific and medical (ISM) frequency bands (433 / 915 MHz) are covered, and a high-performance solution is provided for sub-GHz in-vivo high-definition medical imaging transmission.

Description

Technical Field

[0001] The present application relates to the field of clinical medical auxiliary equipment, and in particular to an ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscopes. Background Art

[0002] UWB antennas must operate in the 3.1-10.6 GHz frequency band, with either a fractional bandwidth exceeding 20% ​​or an absolute bandwidth greater than 0.5 GHz. Currently available UWB-MIMO antennas for WCE typically have narrow bandwidths (fractional bandwidths not exceeding 50%) or operate in frequencies above 1 GHz. Narrow bandwidths contribute little to improving channel capacity. Furthermore, the skin depth effect indicates that implantable antennas operating at high frequencies will suffer from significant path loss. Therefore, UWB-MIMO antennas with lower operating frequencies and greater bandwidths typically perform better.

[0003] The WCEs on the market are usually small in size, with a diameter of less than 15mm and a length of about 30mm. However, both UWB and MIMO technologies require a large space.

[0004] In summary, the current UWB-MIMO antennas used in WCE have not yet achieved an antenna technology that can simultaneously achieve a fractional bandwidth exceeding 100%, operate in low-frequency bands (such as sub-GHz), and be integrated in a small space. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides an ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscopes to solve the problem that the existing antennas suitable for wireless capsule endoscopes have high fractional bandwidth and cannot be integrated into a small space.

[0006] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is: an ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscope, using a ring ferrite as the substrate, and setting the IFA antenna to an elliptical shape, and controlling the impedance matching of different resonant modes by variables in the major axis direction and the minor axis direction.

[0007] The beneficial effects of the present invention are: 1. The antenna provided by this invention controls the impedance matching of different resonant modes by adjusting the variables in the major and minor axis directions, reducing the number of variables required to control impedance matching. By combining an elliptical structure with a coplanar waveguide feed structure to excite and manipulate multiple resonance modes, it achieves a high bandwidth coverage, covering the industrial, scientific, and medical (ISM) frequency band, and facilitating integration with capsule components such as batteries and cameras. 2. Using toroidal ferrite as the substrate introduces a new degree of freedom, magnetic permeability, into the design of implantable antennas.

[0008] Furthermore: it includes a decoupling structure and antenna units connected by the decoupling structure, and is symmetrical along the central axis of the decoupling structure.

[0009] Furthermore: the decoupling structure includes an inverted T-shaped groove and two inverted L-shaped branches.

[0010] The beneficial effects of the above further scheme are: since the coupling between multiple antenna units will affect the performance of the antenna, the introduction of a decoupling structure between the antenna units improves the isolation (from 28 dB to 33 dB), reduces the impact of mutual coupling, improves the performance of the antenna, and provides space for further integration of more units.

[0011] Furthermore: the antenna unit is a semi-elliptical structure, including an upper arm that is concave at the top and convex at the bottom, and a ground plate that is concave at the top.

[0012] Furthermore, the protrusion below the upper arm is aligned with the concave above the grounding plate, and the width of the protrusion below the upper arm is smaller than the width of the concave above the grounding plate.

[0013] Furthermore: a coplanar waveguide feeding unit for multi-frequency resonance is also provided in the antenna unit.

[0014] The beneficial effect of the above further solution is: coplanar waveguide (CPW) feeding is introduced into the semi-elliptical ifa structure, and the introduction of this structure realizes multi-frequency resonance.

[0015] Further: Long axis direction variables include: The first major axis distance a1 is used to represent the longest distance from the center of the semi-ellipse to the outer side of the upper arm; The second major axis distance a2 is used to represent the longest distance from the center of the semi-ellipse to the inner side of the upper arm; The third major axis distance a3 is used to represent the longest distance from the center of the semi-ellipse to the outer side of the ground plate; Minor axis direction variables include: The first minor axis distance b1 is used to represent the shortest distance from the center of the semi-ellipse to the semi-ellipse where the outer side of the upper arm is located; The second minor axis distance b2 is used to represent the shortest distance from the center of the semi-ellipse to the inner side of the upper arm; The third minor axis distance b3 is used to represent the shortest distance from the center of the semi-ellipse to the outer side of the ground plane.

[0016] Furthermore: the first long axis distance a1, the first short axis distance b1 and the maximum operating wavelength of the antenna The relationship is: .

[0017] The beneficial effect of the above further solution is that the impedance matching of multiple resonant modes can be precisely controlled by only 6 variables, thereby reducing the number of variables for controlling impedance matching. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of an ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscopy; Figure 2 An example diagram of the dimensions of an ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscopy; Figure 3 Schematic diagram of the influence of the second major axis distance a2, the third major axis distance a3, the second minor axis distance b2 and the third minor axis distance b3 on impedance matching; Figure 4 This is a schematic diagram of the wireless capsule endoscope model; Figure 5 This is an exploded view of a wireless capsule endoscope; Figure 6 Schematic diagram of the simulation environment and heterogeneous human body model; Figure 7 Schematic diagram for comparison of antenna S parameters between simulation and test; Figure 8 E-plane and H-plane radiation patterns for simulation and testing; Figure 9 This is the simulated 1g average SAR field distribution diagram; Figure 10 Schematic diagram of the antenna's envelope correlation coefficient (ECC), diversity gain (DG), channel capacity (CC), and link margin (LM) results; Among them, 1. Antenna unit; 2. Decoupling structure; 3. Coplanar waveguide feeding unit; 4. Inverted T-slot; 5. Inverted L-shaped branch; 6. Upper arm; 7. Ground plate. DETAILED DESCRIPTION

[0019] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0020] like Figure 1 As shown, this embodiment provides an ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscopes, sets the IFA antenna to an elliptical shape, and controls the impedance matching of different resonant modes by variables in the long axis direction and the short axis direction.

[0021] An ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscope includes a decoupling structure 2 and antenna units 1 connected via the decoupling structure 2 and symmetrically arranged along the central axis of the decoupling structure 2 .

[0022] The decoupling structure 2 includes an inverted T-shaped slot 4 and two inverted L-shaped branches 5 .

[0023] The antenna unit 1 is a semi-elliptical structure, comprising an upper arm 6 that is concave at the top and convex at the bottom, and a ground plate 7 that is concave at the top.

[0024] The protrusion below the upper arm 6 is aligned with the depression above the ground plate 7 , and the width of the protrusion below the upper arm 6 is smaller than the width of the depression above the ground plate 7 .

[0025] The antenna unit 1 is also provided with a coplanar waveguide feeding unit 3 (CPW) for multi-frequency resonance, and the multi-frequency resonance is achieved through the coupling effect IFA structure between the strip line of the coplanar waveguide structure and the ground.

[0026] like Figure 2 As shown, this embodiment provides an example of the size of the ultra-wideband conformal MIMO antenna of the wireless capsule endoscope. Figure 2 In , the variables that can determine the direction of the major axis include: The first major axis distance a1 is used to represent the longest distance from the center of the semi-ellipse to the outer side of the upper arm 6; The second major axis distance a2 is used to represent the longest distance from the center of the semi-ellipse to the inner side of the upper arm 6; The third major axis distance a3 is used to represent the longest distance from the center of the semi-ellipse to the outer side of the ground plate 7; Minor axis direction variables include: The first minor axis distance b1 is used to represent the shortest distance from the center of the semi-ellipse to the outer side of the upper arm 6; The second minor axis distance b2 is used to represent the shortest distance from the center of the semi-ellipse to the inner side of the upper arm 6; The third minor axis distance b3 is used to represent the shortest distance from the center of the semi-ellipse to the outer side of the ground plate 7 .

[0027] Furthermore, Figure 2 The specific dimensions of the ultra-wideband conformal MIMO antenna for wireless capsule endoscopes are also provided. The unfolded dimensions of the antenna are 26.16×5×1.5mm. 3 , for the rest of the distances, see Figure 2 .

[0028] exist Figure 2 In the figure, L represents the length of the metal part of the antenna when it is unfolded, and W represents the width of the metal part of the antenna when it is unfolded; w Indicates the width of the slot on the upper arm of the inverted F antenna; gr hIndicates the height of the slot on the upper arm of the inverted F antenna; c sw represents the line width of the coplanar waveguide center feed line; c h represents the distance between the coplanar waveguide and the floor; c w Indicates the distance between the two sides of the coplanar waveguide; c g represents the floor height at the coplanar waveguide; t1 represents the opening width of the inverted T-slot of the decoupling structure; g w represents the height of the inverted T-slot floor of the decoupling structure; t s represents the height of the closed branch of the inverted T-slot of the decoupling structure; t h represents the height of the upper side of the closed branch of the inverted T-slot of the decoupling structure; l d represents the distance between the two Ls in the decoupling structure and the inverted L structure; l1 represents the width of the two L branches in the decoupling structure and the inverted L structure; l b Indicates the length of the branch of the decoupled inverted L structure; l w represents the branch line width of the decoupled inverted L structure; l h Represents the height of the inverted L structure of the decoupling structure.

[0029] The length of the upper arm 6 of the IFA antenna is generally 0.25 times the working wavelength. The calculation formula is as follows: Where c represents the speed of light, f represents the operating frequency, represents the relative dielectric constant of the substrate, represents the relative magnetic permeability of the substrate; After the IFA antenna is improved to an elliptical shape, the first major axis distance a1, the first minor axis distance b1 and the maximum operating wavelength of the antenna are The relationship is: .

[0030] The second long axis distance a2, the third long axis distance a3, the second short axis distance b2 and the third short axis distance b3 are all used to coordinately achieve impedance matching, and their influence on impedance is as follows: Figure 3 As shown in the figure, the main factors for impedance adjustment in a traditional IFA include the length and width of the upper arm 6, the size of the floor, and the gap between the floor and the upper arm 6. (a2, b2) and (a3, b3) form an impedance matching system: a2 dominates low-frequency impedance matching, b2 mainly affects high-frequency resonance (as shown in the dashed box in the figure), and both a3 and b3 affect the entire bandwidth.

[0031] Preferably, when the antenna is implanted in the wireless capsule endoscope, it is wrapped around the outer surface of the annular ferrite substrate.

[0032] Example 2: This embodiment provides a specific application of the antenna described in Example 1 in a wireless capsule endoscope.

[0033] This embodiment provides a size that meets the expected indicators. The length L of the expanded metal part of the antenna is 26.16 mm, the width W of the expanded metal part of the antenna is 5 mm, and the width gr of the slot on the upper arm of the inverted F antenna is 1. w 2mm, the height of the slot on the upper arm of the inverted F antenna is h The line width c of the coplanar waveguide center feed line is 0.5 mm. w The floor height c of the coplanar waveguide is 2 mm. g The decoupling structure inverted T-slot opening width t1 is 0.8 mm, and the decoupling structure inverted T-slot floor height g is w The height of the closed branch of the inverted T-slot of the decoupling structure is 0.3 mm. s The height of the upper side of the closed branch of the inverted T-slot of the decoupling structure is 0.6 mm. h 0.8mm, decoupling structure inverted L structure two L spacing l d The width l1 of the two L branches of the decoupling structure inverted L structure is 0.4mm, and the length l of the branches of the decoupling structure inverted L structure is 0.1mm. b 0.45mm, the branch line width of the decoupling structure inverted L structure is l w 0.2mm, the height of the decoupling structure is l h The above dimensions are only used as an example for specific applications and experiments, and are not limited to the above single values.

[0034] like Figure 4 and Figure 5 As shown, in this embodiment, a specific wireless capsule endoscope model (WCE) is provided, which includes a 3D printed capsule shell (CapsuleShell) made of biocompatible transparent resin, and a battery, a ferrite-based MIMO antenna, a camera module and a printed circuit board that are tightly arranged and encapsulated in the 3D printed capsule shell.

[0035] The relative dielectric constant of the 3D-printed capsule shell is 3.5, and a clamping structure is designed inside the capsule to help fix each component. The metal structure of the proposed MIMO antenna is symmetrical around the yoz plane and wrapped around the outer surface of the annular ferrite substrate. The ferrite material has a relative dielectric constant of 15, a relative magnetic permeability of 12, a dielectric loss tangent of 0.01, and a magnetic loss tangent of 0.3.

[0036] In this embodiment, Figure 6The simulation environment for the proposed antenna is shown. A homogeneous layered model was used for rapid development in the initial design phase, followed by optimization and final evaluation in a heterogeneous human body model. The data for the homogeneous layered model, such as electromagnetic properties and the thickness of different tissues, was derived from historical medical data. All simulations were performed in CST StudioSuite (CST).

[0037] To simplify the experiment, minced pork was used to simulate human tissue in this experimental environment. Figure 7 As shown in the figure, the test results show that the antenna has a wide bandwidth of 120.5% (0.31-1.25GHz) and an isolation level of more than 33dB. Although the unevenness of the mixed pork causes a slight difference in the reflection coefficient between the two antennas, the consistency between the test and simulation results is within an acceptable range.

[0038] Figure 8 The E-plane and H-plane radiation patterns of the antenna designed in this invention are shown, both simulated and tested, at 433 MHz and 915 MHz. It can be observed that the directivity measured in ground pork closely matches the simulation results. The measured gain differs slightly from the simulation results due to differences in the measurement environment and simulation setup, which is acceptable in a deeply implanted environment.

[0039] To ensure patient safety, implantable antennas are often evaluated for SAR. According to IEEE standards, the SAR value for tissues exceeding 1g (IEEEC-95-1999) must be less than 1.6W / kg. Figure 9 The 1g average SAR distribution is shown: When the input power is 1W, the maximum average SAR values ​​of this antenna evaluated in the stomach and intestine at 1g are 376.4 and 391.9 W / kg at 433MHz, and 309.8 and 314.6 W / kg at 915MHz, respectively. Therefore, the maximum permissible input power is 4.25 and 4.08 mW at 433MHz, and 5.16 and 5.09 mW at 915MHz. In clinical use, the input power of implantable medical devices is typically less than 25μW, far below the maximum permissible power of this antenna, indicating that the SAR values ​​in both operating frequency bands meet the IEEE safety limits.

[0040] Envelope correlation coefficient (ECC), diversity gain (DG), channel capacity (CC) and link margin (LM) are key indicators for evaluating WCEMIMO antenna performance. The detailed calculation method and related parameters are derived from the classical calculation method. Figure 10As shown, the ECC and DG values ​​meet the requirements of MIMO systems in WCE (ECC < 0.5). The calculated CC results reveal that the CC values ​​at 433 MHz and 915 MHz are very close to the ideal 2×2 MIMO CC values. Furthermore, considering the LM with a 20 dB margin, it is shown that the proposed antenna can ensure sufficient signal strength for transmission at a speed of 120 Mbps within a range of 6 meters at 433 MHz and 4 meters at 915 MHz, respectively.

[0041] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An ultra-wideband conformal MIMO antenna suitable for wireless capsule endoscopy, characterized in that: A ring ferrite is used as the substrate, and the IFA antenna is set to an elliptical shape. The impedance matching of different resonant modes is controlled by variables in the major and minor axis directions.

2. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 1, characterized in that: It comprises a decoupling structure (2) and an antenna unit (1) connected via the decoupling structure, and is symmetrical along the central axis of the decoupling structure.

3. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 2, characterized in that: The decoupling structure includes an inverted T-shaped groove (4) and two inverted L-shaped branches (5).

4. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 2, characterized in that: The antenna unit is a semi-elliptical structure, comprising an upper arm (6) that is concave at the top and convex at the bottom, and a ground plate (7) that is concave at the top.

5. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 4, characterized in that: The protrusion below the upper arm (6) is aligned with the concave above the grounding plate (7), and the width of the protrusion below the upper arm (6) is smaller than the width of the concave above the grounding plate.

6. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 2, characterized in that: A coplanar waveguide feeding unit (3) for multi-frequency resonance is also provided in the antenna unit.

7. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 4, characterized in that: Long axis direction variables include: The first major axis distance a1 is used to represent the longest distance from the center of the semi-ellipse to the outer side of the upper arm (6); The second major axis distance a2 is used to represent the longest distance from the center of the semi-ellipse to the inner side of the upper arm (6); The third major axis distance a3 is used to represent the longest distance from the center of the semi-ellipse to the outer side of the ground plate (7); Minor axis direction variables include: The first minor axis distance b1 is used to represent the shortest distance from the center of the semi-ellipse to the outer side of the upper arm (6); The second minor axis distance b2 is used to represent the shortest distance from the center of the semi-ellipse to the inner side of the upper arm (6); The third minor axis distance b3 is used to represent the shortest distance from the center of the semi-ellipse to the outer side of the ground plate (7).

8. The ultra-wideband conformal MIMO antenna for wireless capsule endoscope according to claim 7, characterized in that: The first long axis distance a1, the first short axis distance b1 and the maximum operating wavelength of the antenna The relationship is: 。

Images