A small implantable rectenna

Abstract

The present invention belongs to the field of biomedical telemetry, and relates to a small implantable rectifier antenna, comprising: a dielectric substrate, an antenna radiating unit, a floor, a rectifier circuit, a short-circuit probe, and a feeding coaxial probe, wherein: the dielectric substrate comprises a first layer of dielectric substrate, a second layer of dielectric substrate, and a third layer of dielectric substrate, the antenna radiating unit is located on the lower surface of the first layer of dielectric substrate, the floor is located on the lower surface of the second layer of dielectric substrate, the rectifier circuit is located on the lower surface of the third layer of dielectric substrate, the antenna radiating unit is electrically connected to the rectifier circuit through the feeding coaxial probe, the rectifier circuit is connected to the floor through the short-circuit probe, and the antenna radiating unit and the rectifier circuit share the floor. The antenna radiating unit forms a bending curve structure by loading multiple bending gaps, which effectively expands the bandwidth of the rectifier antenna. The present invention has the advantages of small size and high rectification efficiency under low power input, can be implanted in the human body, and can also be applied to the field of wireless energy transmission in biomedicine.

Description

Technical Field

[0001] The invention belongs to the field of biomedical telemetry and relates to a small implantable rectenna. Background Art

[0002] With the continuous advancement of biomedical engineering and personalized healthcare, implantable medical devices have made great progress in the past few decades and are moving towards commercial scale. Implantable medical devices can send human physiological data information to external medical devices, so that doctors can diagnose and treat remotely. Currently, it has been widely used in medical devices including pacemakers, defibrillators, cochlear implants, bladder pressure monitoring devices, neurostimulators, etc. However, traditional biomedical implantable devices are powered by internal batteries. When the battery is exhausted, it needs to be replaced through surgery, which adds unnecessary trouble and pain to patients.

[0003] Therefore, the power supply of biomedical equipment is more inclined to practical, effective, non-invasive and safe wireless energy transmission methods. Implantable rectennas for wireless energy transmission have gradually become a research hotspot in recent years. Implantable rectennas can receive external radio frequency signals and convert them into DC energy to power implanted medical devices. In order to better receive radio frequency energy, it is necessary to design high-efficiency rectennas. The rectenna consists of two parts: a receiving antenna and a rectifier circuit. It takes up a large space and will increase the size of the implantable medical device. The current implantable rectennas mainly have problems such as low rectification efficiency and large size. Summary of the invention

[0004] In view of the shortcomings of the existing implantable rectenna, the present invention provides a small implantable rectenna.

[0005] The present invention is implemented by the following technical solutions:

[0006] A small implantable rectifying antenna comprises: a dielectric substrate, an antenna radiation unit, a floor, a rectifying circuit, a short-circuit probe and a feeding coaxial probe, wherein:

[0007] The dielectric substrate comprises a first dielectric substrate, a second dielectric substrate and a third dielectric substrate, the antenna radiation unit is located on the lower surface of the first dielectric substrate, the floor is located on the lower surface of the second dielectric substrate, the rectifier circuit is located on the lower surface of the third dielectric substrate, the antenna radiation unit is electrically connected to the rectifier circuit through a feeding coaxial probe, the rectifier circuit is connected to the floor through a short-circuit probe, and the antenna radiation unit and the rectifier circuit share the floor.

[0008] Preferably, the antenna radiation unit includes a fifth fan-ring patch, namely: a first fan-ring patch, a second fan-ring patch, a third fan-ring patch, a fourth fan-ring patch and a fifth fan-ring patch, wherein: the center angles of the first fan-ring patch, the second fan-ring patch, the third fan-ring patch and the fourth fan-ring patch are all 60 degrees, and the center angle of the fifth fan-ring patch is 120 degrees.

[0009] Preferably, the first fan-shaped annular patch, the second fan-shaped annular patch, the third fan-shaped annular patch and the fourth fan-shaped annular patch form a bending curve structure by loading a plurality of bending gaps.

[0010] Preferably, the radial width of the bending curve structure is 0.2 mm, and the axial width is 0.15 mm.

[0011] Preferably, the first sector ring patch is connected to a matching branch at the end away from the center of the circle, for adjusting the impedance matching of the antenna.

[0012] Preferably, the third sector ring patch is connected to a curved branch to extend the effective path of the current.

[0013] Preferably, the width of the curved branch is 0.2 mm, and the angle between the end of the curved branch and the radial line of the edge of the third sector annular patch is 42 degrees.

[0014] Preferably, the rectifier circuit adopts a double voltage rectifier structure, including: a matching network, a DC blocking capacitor, a filter capacitor, a rectifier diode, a load resistor and 7 microstrip lines, and the microstrip lines are connected through a matching network, a DC blocking capacitor or a filter capacitor.

[0015] Preferably, the radius of the feeding coaxial probe is 0.35 mm, and the radius of the short-circuit probe is 0.3 mm.

[0016] Preferably, the floor is circular with a radius of 4 mm.

[0017] The present invention includes the following beneficial effects:

[0018] (1) The meandering structure of the present invention is conducive to extending the effective path of the current and reducing the size of the antenna; by adjusting the size of the bent branches and the gaps, the two resonance points can be brought closer to each other, thereby expanding the bandwidth of the rectenna; the rectifier circuit is integrated on the back of the rectenna and is designed as an integrated whole with the rectenna, thereby reducing the volume occupied by the rectenna.

[0019] (2) The present invention has the advantages of small size and high rectification efficiency under low power input, can be implanted in the human body, and can also be applied to the field of wireless energy transmission in biomedicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1Schematic diagram of a small implantable rectenna in one embodiment of the present invention, wherein: (a) is a radiation unit diagram of the small implantable rectenna, (b) is a bottom view of the small implantable rectenna, and (c) is a side view of the small implantable rectenna;

[0021] Figure 2 A simulation diagram of a three-layer human tissue model of a small implantable rectenna in one embodiment of the present invention;

[0022] Figure 3 A reflection coefficient S11 curve diagram of a small implantable rectenna in one embodiment of the present invention;

[0023] Figure 4 The gain patterns of the small implantable rectenna in the XOZ and YOZ planes at a frequency of 915 MHz in one embodiment of the present invention;

[0024] Figure 5 This is a simulation diagram of the rectifying efficiency and output DC voltage of a small implantable rectifying antenna in one embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0026] like Figure 1 As shown in (a) to (c), a small implantable rectifying antenna comprises: a dielectric substrate 1, an antenna radiating unit 2, a floor 3, a rectifying circuit 4, a short-circuit probe 5 and a feeding coaxial probe 6, wherein:

[0027] The dielectric substrate 1 includes a first dielectric substrate 1A, a second dielectric substrate 1B and a third dielectric substrate 1C, the antenna radiation unit 2 is located on the lower surface of the first dielectric substrate 1A, the floor 3 is located on the lower surface of the second dielectric substrate 1B, and the rectifier circuit 4 is located on the lower surface of the third dielectric substrate 1C. The antenna radiation unit 2 is electrically connected to the rectifier circuit 4 through a feeding coaxial probe 6, the rectifier circuit 4 is connected to the floor 3 through a short-circuit probe 5, and the antenna radiation unit 2 and the rectifier circuit 4 share the floor 3.

[0028] In a preferred embodiment, the antenna radiation unit 2 has a radius of 4 mm and is composed of fan-shaped patches 21, 22, 23, 24, and 25. The central angles of the fan-shaped patches 21, 22, 23, and 24 are all 60 degrees, and the central angle of the fan-shaped patch 25 is 120 degrees. The interface between the antenna radiation unit 2 and the feeding coaxial probe 6 is located on the fan-shaped patch 21. The fan-shaped patch 21 is etched with three curved gaps near the center end to form a zigzag structure. The radial width of the zigzag structure is w1=0.2 mm, and the axial width is s1=0.15 mm. The fan-shaped patch 21 is connected to a matching branch 26 at the end away from the center to adjust the impedance matching of the antenna.

[0029] The fan-shaped patch 21 is electrically connected to the fan-shaped patch 22. The fan-shaped patch 22 is etched with multiple curved slots to form a zigzag structure. The radial width of the zigzag structure is w1 = 0.2 mm, and the axial width is s1 = 0.15 mm. The curved slot 28 on the fan-shaped patch 22 can tune the resonance point of the antenna. The angle between the end of the curved slot 28 and the radial line of the edge of the fan-shaped patch 22 is a1 = 24 degrees.

[0030] The fan-shaped patch 22 is electrically connected to the fan-shaped patch 25 in the counterclockwise direction. The central angle of the fan-shaped patch 25 is 120 degrees. The inner radius of the fan-shaped patch 25 is 0.6 mm, which can adjust the impedance matching of the antenna. The fan-shaped patch 25 is electrically connected to the fan-shaped patch 24 in the counterclockwise direction. The fan-shaped patch 24 is similar in structure to the fan-shaped patch 22. The curved slot 29 on the fan-shaped patch 24 can tune the resonance point of the antenna. The angle between the end of the curved slot 29 and the radial line of the edge of the fan-shaped patch 24 is a2 = 55 degrees.

[0031] The fan ring patch 24 is electrically connected to the fan ring patch 23 in the counterclockwise direction. The fan ring patch 23 is a zigzag structure. The radial width of the zigzag structure is w1 = 0.2 mm, and the axial width is s1 = 0.15 mm. The fan ring patch 23 is electrically connected to the curved branch 27, the width of the curved branch 27 is w1 = 0.2 mm, and the angle between the end and the radial line of the edge of the fan ring patch 23 is a3 = 42 degrees.

[0032] The antenna radiation unit of the present invention is etched with a plurality of curved gaps in order to form a meandering structure, extend the effective current path, and achieve a miniaturized antenna.

[0033] The rectifier circuit 4 adopts a double voltage rectifier structure, including a matching network, a DC blocking capacitor, a filter capacitor, a rectifier diode, a load resistor and a plurality of microstrip lines. The antenna radiation unit 2 is connected to the input microstrip line 41 of the rectifier circuit 4 through a feeding coaxial probe 6. The microstrip line 41 is a square structure with a side length of 1 mm. The microstrip line 41 is connected to the matching network through microstrip lines 42 and 43. The matching network is composed of inductance elements L1 and L2. The microstrip line 43 is connected to the microstrip line 47 through the inductance element L2. The microstrip line 42 is connected to the microstrip line 44 through the inductance element L1.

[0034] After passing through the matching network, microstrip line 44 is connected to microstrip line 45 via DC blocking capacitor C1, and microstrip line 45 is connected to microstrip line 46 and microstrip line 47 respectively via rectifier diode D1 in SOT23-3 package. The left end of microstrip line 46 is connected to microstrip line 47 via filter capacitor C2, and the right end of microstrip line 46 is connected to microstrip line 47 via load resistor R1. Microstrip line 47 is connected to floor 3 via short-circuit probe 5, and DC voltage is output across load resistor R1.

[0035] The inductance values ​​of the inductor components L1 and L2 are 24nH and 4.7nH respectively. The capacitance values ​​of the capacitor components C1 and C2 are 100pF and 330pF respectively, and the load resistor R1 is 7.5KΩ. Both are packaged in 0603. The rectifier diode uses a Schottky diode in a SOT23-3 package, model HSMS-2852, which contains two diodes.

[0036] The radius of the feeding coaxial probe 6 is 0.35 mm, and the radius of the short-circuit probe 5 is 0.3 mm.

[0037] The radius of the floor 3 is 4 mm, and it remains intact except for the area where the feeding coaxial probe 6 passes, which can reduce the influence of the bottom rectifying circuit components on the antenna performance.

[0038] The dielectric substrate 1 is made of Rogers Ro3210, with a radius of 4 mm, a thickness of 0.635 mm, a relative dielectric constant of 10.2, and a loss tangent of 0.003.

[0039] The present invention uses a dielectric substrate with a high dielectric constant, which can reduce the resonant frequency of the antenna, thereby reducing the size of the antenna. A layer of dielectric substrate is covered on the surface of the antenna radiation unit to prevent the antenna from directly contacting the human body tissue.

[0040] The simulation of the small implantable rectenna of the present invention in a three-layer human tissue model is described below.

[0041] Small implantable rectennas were placed in a three-layer tissue model that simulates the human body, e.g. Figure 2As shown, from top to bottom are the skin layer, fat layer, and muscle layer, with thicknesses of 4mm, 4mm, and 50mm respectively. The antenna is placed at a position of dp=4mm below the muscle layer, and the distance from the edges of the model is 50mm. Because the electromagnetic properties of human tissue change with frequency, the relative dielectric constant and conductivity of the three-layer tissue model need to be set at the center frequency of 915MHz. The small implantable rectifier antenna operates at 902-928MHz in the ISM band. When the frequency is 915MHz, the relative dielectric constants of the skin layer, fat layer, and muscle layer are 41.3, 5.46, and 55 respectively, and the conductivity is 0.87S / m, 0.051S / m, and 0.948S / m respectively.

[0042] The reflection coefficient S11 of a small implantable rectenna placed in a three-layer tissue model, e.g. Figure 3 As shown, Figure 3 The reflection coefficient S11 is shown in the figure when the third dielectric substrate 1C containing the rectifier circuit is not added and the third dielectric substrate 1C containing the rectifier circuit is added. When the third dielectric substrate 1C containing the rectifier circuit is not added, the -10dB impedance bandwidth of the antenna is 0.79-1.11GHz (33.7%), and after the third dielectric substrate 1C containing the rectifier circuit is added, the -10dB impedance bandwidth of the antenna is 0.83-1.03GHz (21.5%), both covering 902-928MHz in the ISM band.

[0043] The small implantable rectenna is placed in a three-layer tissue model, and the radiation patterns in the XOZ and YOZ planes at 915MHz are shown in Figure 2. Figure 4 As shown, the small implantable rectenna has a peak gain of -28.9dBi at 915MHz.

[0044] The rectification efficiency and output DC voltage curve of the rectification circuit of the small implantable rectenna at different powers, such as Figure 5 As shown, the conversion efficiency of the rectifying antenna from AC to DC can reach up to 81%, and the rectification efficiency can reach 50% when the input power is -15dBm. Therefore, the present invention can achieve a relatively high rectification efficiency at low input power.

[0045] The small implantable rectifier antenna of the present invention integrates the receiving antenna and the rectifier circuit into an integrated design, effectively reducing the volume occupied by the rectifier antenna; the antenna radiation unit is etched with multiple curved gaps to form a meandering structure, extending the effective current path, thereby reducing the size of the antenna; by adjusting the size of the curved branches, the two resonance points can be brought closer to each other, thereby expanding the bandwidth of the antenna.

[0046] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited by the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A small implantable rectenna, characterized in that: include: Dielectric substrate, antenna radiation unit, floor, rectifier circuit, short-circuit probe and feeding coaxial probe, wherein: The dielectric substrate comprises a first dielectric substrate, a second dielectric substrate and a third dielectric substrate, the antenna radiation unit is located on the lower surface of the first dielectric substrate, the floor is located on the lower surface of the second dielectric substrate, the rectifier circuit is located on the lower surface of the third dielectric substrate, the antenna radiation unit is electrically connected to the rectifier circuit through a feeding coaxial probe, the rectifier circuit is connected to the floor through a short-circuit probe, and the antenna radiation unit and the rectifier circuit share the floor; The antenna radiation unit includes a fifth fan-shaped ring patch, which are: a first fan-shaped ring patch, a second fan-shaped ring patch, a third fan-shaped ring patch, a fourth fan-shaped ring patch and a fifth fan-shaped ring patch, wherein: the center angles of the first fan-shaped ring patch, the second fan-shaped ring patch, the third fan-shaped ring patch and the fourth fan-shaped ring patch are all 60 degrees, and the center angle of the fifth fan-shaped ring patch is 120 degrees; The first fan ring patch, the second fan ring patch, the third fan ring patch and the fourth fan ring patch form a bending curve structure by loading a plurality of bending gaps; The third sector ring patch is connected to a bent branch to extend the effective path of the current.

2. The small implantable rectenna according to claim 1, characterized in that: The radial width of the bending curve structure is 0.2 mm, and the axial width is 0.15 mm.

3. The small implantable rectenna according to claim 1, characterized in that: A matching branch is connected to the end of the first sector ring patch away from the center of the circle, which is used to adjust the impedance matching of the antenna.

4. The small implantable rectenna according to claim 1, characterized in that: The width of the bent branch is 0.2 mm, and the angle between the end of the bent branch and the radial line of the edge of the third sector annular patch is 42 degrees.

5. The small implantable rectenna according to claim 1, characterized in that: The rectifier circuit adopts a double voltage rectifier structure, including: a matching network, a DC blocking capacitor, a filter capacitor, a rectifier diode, a load resistor and 7 microstrip lines. The microstrip lines are connected through a matching network, a DC blocking capacitor or a filter capacitor.

6. The small implantable rectenna according to claim 1, characterized in that: The radius of the feed coaxial probe is 0.35mm and the radius of the short-circuit probe is 0.3mm.

7. The small implantable rectenna according to claim 1, characterized in that: The floor is circular with a radius of 4mm.

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