Antenna device and detection device

Abstract

To provide an antenna device capable of obtaining sufficient radiation characteristics even when arranged in a state of being close to a metal member, and a detection device.SOLUTION: The antenna device includes an annular substrate including a first surface, a second surface, and an opening penetrating between the first surface and the second surface, an annular antenna element provided on the first surface and surrounding the opening, a first feed line provided on the first surface and including a feed terminal connected to the antenna element, a second feed line provided on the second surface and including a connection terminal connected to a communication unit, the second feed line including an overlapping portion that overlaps a first portion of the first feed line in plan view, and a through hole that penetrates the substrate and connects the first feed line and the overlapping portion of the second feed line.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an antenna device and a detection device. [Background technology]

[0002] Conventionally, there has been a fastening strength detection device characterized by comprising a main body formed in a cylindrical shape through the center of which the shaft of a fastening means can be inserted and which is fastened together with the fastened object by the fastening means, a detection means for detecting the state of distortion of the main body, a transmission unit for wirelessly transmitting the detection value detected by the detection means, a short bar of an appropriate length extending circumferentially around the outer surface of a peripheral wall portion that forms the cylindrical shape of the main body or around an imaginary plane that surrounds the outside of the peripheral wall, and an antenna that is arranged within the outer surface of the peripheral wall portion or the imaginary plane that surrounds the outside of the peripheral wall portion and is formed in a linear or band-like shape with an appropriate length (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-173543 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the antenna of conventional fastening strength detection devices is installed on the peripheral wall, which is the side of the main body, if the antenna is placed close to the metal member, such as when it is installed on top of the metal member inserted into the shaft portion of the fastening means (fastening mechanism), sufficient radiation characteristics may not be obtained and the detected value may not be able to be transmitted wirelessly.

[0005] Therefore, an object of the present invention is to provide an antenna device and a detection device that can obtain sufficient radiation characteristics even when placed in close proximity to a metal member. [Means for solving the problem]

[0006] An antenna device according to an embodiment of the present disclosure includes: an annular substrate having a first surface and a second surface and an opening penetrating between the first surface and the second surface; an annular antenna element provided on the first surface and surrounding the opening; a first feed line provided on the first surface and having a feed terminal connected to the antenna element; a second feed line provided on the second surface and having a connection terminal connected to a communication unit, the second feed line having an overlapping portion that overlaps with a first portion of the first feed line in a planar view; and a through hole penetrating the substrate and connecting the first feed line to the overlapping portion of the second feed line. [Effects of the Invention]

[0007] It is possible to provide an antenna device and a detection device that can obtain sufficient radiation characteristics even when placed in close proximity to a metal member. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a detection device according to an embodiment. [Figure 2A] 1A and 1B are diagrams illustrating an example of a state in which a detection device according to an embodiment is used; [Figure 2B] 1A and 1B are diagrams illustrating an example of a state in which a detection device according to an embodiment is used; [Figure 2C] 10A and 10B are diagrams illustrating an example of the configuration of a nut and a bell washer. [Figure 3] FIG. 2 is a diagram illustrating a disassembled state of the detection device according to the embodiment. [Figure 4] FIG. 2 is a diagram illustrating an example of a configuration of a circuit board unit of the detection device according to the embodiment. [Figure 5A] FIG. 2 is a diagram illustrating an example of a configuration of an upper surface side of a wiring substrate of the detection device according to the embodiment. [Figure 5B] FIG. 2 is a diagram illustrating an example of a configuration of a lower surface side of a wiring substrate of the detection device according to the embodiment. [Figure 6] 5A and 5B are diagrams illustrating an example of a method for adjusting the operating frequency and impedance of an antenna element of the detection device according to the embodiment. [Figure 7] 1A and 1B are diagrams illustrating an example of circularly polarized waves of an antenna device according to an embodiment. [Figure 8A] FIG. 10 is a diagram showing an example of the amplitude distribution of the #1 component and the #2 component with respect to frequency. [Figure 8B] FIG. 10 is a diagram illustrating an example of the phase distribution of the #1 component and the #2 component with respect to frequency. [Figure 9A] 1A and 1B are diagrams illustrating an example of the configuration of an antenna device according to an embodiment that can radiate left-handed circularly polarized waves. [Figure 9B] 1A and 1B are diagrams illustrating an example of the configuration of an antenna device according to an embodiment that can radiate left-handed circularly polarized waves. [Figure 10A] FIG. 10 is a diagram illustrating an example of the configuration of an antenna device according to a first modified example of the embodiment. [Figure 10B] FIG. 10B is an enlarged view of a part of FIG. 10A. [Figure 11A] 10 is a diagram showing an example of the configuration of the upper surface side of a wiring substrate of an antenna device according to a first modified example of the embodiment. FIG. [Figure 11B] 10 is a diagram showing an example of the configuration of the lower surface side of the wiring substrate of the antenna device according to the first modified example of the embodiment. FIG. [Figure 12A] 10A and 10B are diagrams illustrating an example of a simulation result of the frequency characteristics of the VSWR of a detection device including the antenna device according to the first modified example of the embodiment. [Figure 12B] This shows the frequency characteristics of the gain of left-handed circularly polarized waves in the +Z direction when the rock bolt is perpendicular to the mounting surface of the fixed part. [Figure 13A] FIG. 10 is a diagram showing an example of a simulation result of a radiation pattern (directivity) in the ZX plane of a detection device including an antenna device according to a first modified example of the embodiment. [Figure 13B] FIG. 10 is a diagram showing an example of a simulation result of a radiation pattern (directivity) in the ZY plane of a detection device including an antenna device according to a first modified example of the embodiment. [Figure 14] FIG. 10 is a diagram illustrating an example of the configuration of an antenna device according to a second modified example of the embodiment. [Figure 15A] 10 is a diagram showing an example of the configuration of the upper surface side of a wiring substrate of an antenna device according to a second modified example of the embodiment. FIG. [Figure 15B]10 is a diagram showing an example of the configuration of the lower surface side of the wiring substrate of the antenna device according to the second modified example of the embodiment. FIG. [Figure 16] FIG. 10 is a diagram illustrating an example of the configuration of an antenna device according to a third modified example of the embodiment. [Figure 17A] FIG. 10 is a diagram showing an example of the configuration of the upper surface side of a wiring substrate of an antenna device according to a third modified example of the embodiment. [Figure 17B] FIG. 10 is a diagram showing an example of the configuration of the lower surface side of the wiring substrate of the antenna device according to the third modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments to which the antenna device and the detection device of the present disclosure are applied will be described. In the following, the same elements will be given the same reference numerals, and duplicated descriptions may be omitted.

[0010] In the following description, an XYZ coordinate system is defined. The direction parallel to the X axis (X direction), the direction parallel to the Y axis (Y direction), and the direction parallel to the Z axis (Z direction) are perpendicular to one another. Planar view refers to viewing from an XY plane. For ease of explanation, the +Z direction is referred to as the upper side and the −Z direction is referred to as the lower side, but this does not represent a universal vertical relationship. In the following description, the length, width, thickness, etc. of each part may be exaggerated to make the configuration easier to understand. The detection device of the embodiment is disk-shaped in plan view. Therefore, in the following description, the radial direction refers to the radial direction of the disk shape of the detection device.

[0011] <Embodiment> <Outline of the detection device 100> 1 is a diagram showing an example of the configuration of a detection device 100 according to an embodiment. The detection device 100 is fixed to a structure with a bolt portion of a fastening mechanism inserted into a through-hole 123 of a flexure body 120 housed in a case 110, and the fastening mechanism and a fastened member abut against the lower and upper surfaces of a main body portion of the flexure body 120 that protrudes upward and downward from the case 110. The lower and upper surfaces of the main body portion of the flexure body 120 protrude in the -Z direction and the +Z direction, respectively, beyond the case 110.

[0012] The detection device 100 may be used in two ways, for example, when the fastening mechanism abuts against the lower surface of the main body of the strain element 120 and the fastened member abuts against the upper surface of the main body, or when the fastened member abuts against the lower surface of the main body of the strain element 120 and the fastening mechanism abuts against the upper surface of the main body. The detection device 100 detects the axial fastening force applied to the bolt when the fastening mechanism fastens the detection device 100 to the fastened member. The detection device 100 outputs a strain detection signal indicating the axial fastening force to the outside via wireless communication.

[0013] <Usage state of the detection device 100> 2A and 2B are diagrams showing an example of a state in which the detection device 100 is in use. Fig. 2A is a perspective view, and Fig. 2B is a view seen from the +X direction side. Figs. 2A and 2B show the fixing part 10, the fastening mechanism 20, and a washer 30. The washer 30 is an example of a fastened member.

[0014] As shown in FIG. 2B, the fastening mechanism 20 includes a lock bolt 21, a lock nut 22, and a bell washer 23. The lock bolt 21 is an example of a bolt portion. As an example, the detection device 100 is provided between the bell washer 23 and a washer 30. Here, explanation will be made using FIG. 2C in addition to FIGS. 2A and 2B. FIG. 2C is a diagram showing an example of the configuration of the lock nut 22 and the bell washer 23.

[0015] The fixed part 10 is a part of a structure such as a building, a road, a tunnel, or a bridge pier, or a member fixedly attached to a structure. Here, as an example, a form will be described in which the fixed part 10 is the inner wall of a tunnel and is a member made of concrete.

[0016] Washer 30 is a flat metal member that is placed on mounting surface 11 of fixed part 10 and fixed by screwing together lock bolt 21, nut 22, and bell washer 23 of fastening mechanism 20. Lock bolt 21 has a threaded bolt shaft, and is embedded in fixed part 10 to reinforce it, for example. Washer 30 has a through-hole through which the bolt shaft passes.

[0017] The fixed part 10 is connected to the ground. That is, the fixed part 10 is connected to the ground. The lock bolt 21 is buried in the fixed part 10 and is therefore connected to the ground. The washer 30 is connected to the lock bolt 21 and is therefore connected to the ground.

[0018] A lock bolt 21 is inserted through the through hole of the washer 30, the through hole 123 of the strain body 120 of the detection device 100 (see FIG. 1), and the through hole of the bell washer 23. The lock bolt 21 is screwed onto the bolt shaft of the lock bolt 21 from the tip side of the lock bolt 21. If the fixing part 10 is a wall part of a building or the like, has a surface opposite to the mounting surface 11, and has a through hole connecting the mounting surface 11 and the opposite surface, a bolt may be inserted into the through hole from the opposite surface side instead of the lock bolt 21, and fastened with the lock bolt nut 22. In this case, the head of the bolt is located on the surface opposite to the mounting surface 11.

[0019] 2B, when the lock bolt 21 and the nut 22 are fastened, the washer 30 and the detection device 100 are fixed to the fixing part 10. At this time, the lower surface of the main body of the strain element 120 of the detection device 100 abuts against the upper surface 31 of the washer 30, and the upper surface of the main body abuts against the lower surface of the bell washer 23.

[0020] Therefore, a fastening axial force in the axial direction (Z direction) of the bolt shaft of lock bolt 21 is applied to the main body of flexure body 120. Only the lower surface of the main body of flexure body 120 of detection device 100 abuts on upper surface 31 of washer 30, and the lower surface of case 110 does not abut on it. Furthermore, only the upper surface of main body 121 of flexure body 120 abuts on the lower surface of bell washer 23, and the upper surface of case 110 does not abut on it. With this configuration, flexure body 120 can reliably withstand the fastening axial force applied from bell washer 23.

[0021] As a result, strain is generated in the strain element 120 according to the tightening torque of the flexure nut 22. The strain generated in the strain element 120 is detected by a plurality of strain sensors provided on the strain element 120 of the detection device 100. The strain can be detected based on the strain (change in the resistance value of the strain detection element) detected by each of the plurality of strain sensors. A strain detection signal representing the strain is emitted to the outside of the case 110 by the communication unit of the detection device 100. An RFID reader / writer (hereinafter referred to as RFID-R / W) can determine the tightening state of the flexure nut 22 based on the voltage value represented by the strain detection signal received from the detection device 100.

[0022] Furthermore, there is a possibility that the lock bolt 21 is attached at an angle to the mounting surface 11 of the fixed part 10. In other words, there is a possibility that the lock bolt 21 is attached in an inclined state to the mounting surface 11 of the fixed part 10.

[0023] In such a case, the hemispherical convex outer surface 22A (see Figure 2C) of the lock nut 22 stably abuts against the hemispherical concave inner surface 23A (see Figure 2C) of the bell washer 23 in response to the tilt, so that the detection device 100 can be stably fixed even when the lock bolt 21 is tilted relative to the mounting surface 11.

[0024] The detection device 100 may use a wireless communication method such as RFID (Radio Frequency Identifier) ​​or LPWA (Low Power Wide Area-network). For example, in the case of a 920 MHz band RFID, when an RFID-R / W of the RFID communicates with the detection device 100 from the +Z direction, the radio waves transmitted from the RFID-R / W are received by the antenna element and circuit board of the detection device 100, and all circuits and strain sensors operate using the power received, and a strain detection signal is returned as backscatter from the antenna element and circuit board to the RFID-R / W.

[0025] Here, since the antennas of many commercially available RFID-R / Ws are circularly polarized, if the antenna element of the detection device 100 is also circularly polarized in the same rotation direction, communication can be performed in a good state with minimal polarization loss. Also, even if the antenna of the RFID-R / W is linearly polarized, if the antenna of the detection device 100 is circularly polarized, communication can be performed regardless of the angle of the detection device 100 in the XY plane.

[0026] For this reason, the antenna element of the detection device 100 is required to have the following characteristics: Resonate at approximately 920 MHz and ensure a sufficiently low VSWR. Satisfy the 920 MHz RFID frequency band (7 MHz from 916 MHz to 923 MHz). Have a gain comparable to that of a dipole antenna (the gain of a dipole antenna is 2.15 dBi). Be able to emit circularly polarized radio waves. In this embodiment, an antenna device 100A and a detection device 100 are provided that include an antenna element 160 that satisfies these performance requirements.

[0027] <Configuration of the detection device 100> Fig. 3 is a diagram showing the detection device 100 in an exploded state. The right side of Fig. 3 shows an enlarged view of the flexure element 120 and the strain sensor 130. Fig. 4 is a diagram showing an example of the configuration of the circuit board unit 140 of the detection device 100. Fig. 5A is a diagram showing an example of the configuration of the upper surface side of the wiring board 150 of the detection device 100. Fig. 5B is a diagram showing an example of the configuration of the lower surface side of the wiring board 150 of the detection device 100. Since Fig. 5B shows the configuration of the lower surface side of the wiring board 150, the Y direction is opposite to that of Fig. 5A.

[0028] The detection device 100 includes a case 110 , a strain generator 120 , a strain sensor 130 , a wiring board 150 , an antenna element 160 , feeder lines 170 A and 170 B, a through hole 175 , and a circuit section 180 .

[0029] Of these components of the detection device 100, the wiring board 150, the antenna element 160, the feed lines 170A and 170B, and the through-hole 175 form an antenna device 100A.

[0030] Among these components of the detection device 100, the wiring board 150, the antenna element 160, the feeder lines 170A and 170B, the through-hole 175, and the circuit section 180 form a circuit board section 140.

[0031] In the detection device 100, the lower side (-Z direction side) is an example of the first side, and the upper side (+Z direction side) is an example of the second side. The direction connecting the first side and the second side is the up-down direction.

[0032] Case 110 is an example of a housing. Wiring board 150 is an example of a board. Power feed line 170A is an example of a first power feed line, and power feed line 170B is an example of a second power feed line. Circuit unit 180 is an example of a communication unit.

[0033] <Case 110> The case 110 has a lower case 110L and an upper case 110U. Because the detection device 100 performs wireless communication, the case 110 is formed of a dielectric material such as resin. The case 110 has a circular ring shape in a plan view. The case 110 houses at least a portion of the main body 121 of the flexure element 120, a protrusion 122 provided on the side of the main body 121, and the circuit board part 140. The reason that the case 110 houses at least a portion of the main body 121 of the flexure element 120 is because the lower and upper ends of the main body 121 protrude from the case 110.

[0034] <Lower case 110L> The lower case 110L has a lower surface 111L and an opening 112L. The lower surface 111L is the lower surface of the detection device 100, and is also the lower surface of the case 110. However, the lower surface 121A of the strain generating element 120 protrudes downward more than the lower surface 111L. The lower case 110L is, for example, the lower half of the case 110 in the up-down direction.

[0035] The lower case 110L has an opening 112L (see FIG. 3) in the center. The opening 112L is a circular opening in a plan view, and has an opening shape that matches the planar shape of the lower end of the main body 121 of the strain element 120.

[0036] The lower case 110L, together with the upper case 110U, forms an accommodation section, which is a space for accommodating the flexure body 120. The lower end of the main body 121 of the flexure body 120 is inserted into the opening 112L. The size and shape of the opening 112L in a plan view are adjusted so that, when the lower end of the main body 121 of the flexure body 120 is inserted, there is almost no gap between the opening 112L and the outer surface 121C of the lower end of the main body 121. In addition, an O-ring 115L is provided between the opening 112L of the lower case 110L and the flexure body 120, ensuring waterproofing and dustproofing.

[0037] Furthermore, the lower case 110L has a wall surrounding the opening 112L. This wall has a shape that matches the outer circumferential shape of the lower one of the two convex portions 122 of the flexure element 120, and by engaging with the linear portion of the outer periphery of the convex portion 122, it prevents the flexure element 120 from rotating relative to the lower case 110L in a plan view.

[0038] The lower case 110L also accommodates the circuit board unit 140 radially outward of the portion where the flexure element 120 is disposed. In this state, the flexure element 120 is accommodated in an opening in the center of the circuit board unit 140.

[0039] <Upper case 110U> The upper case 110U has the same shape as the lower case 110L in a plan view, and has an upper surface 111U and an opening 112U. As an example, the upper case 110U is the upper half of the case 110 in the vertical direction, and has a configuration in which the lower case 110L is turned upside down. The upper surface 111U is the upper surface of the detection device 100, and is also the upper surface of the case 110. However, the upper surface 121B of the strain generating body 120 protrudes upward more than the upper surface 111U.

[0040] Although a configuration in which the upper case 110U is the upper half of the case 110 in the up-down direction will be described here, the case 110 may be divided at any position in the up-down direction as long as it can accommodate the circuit board unit 140 and the portion of the main body 121 of the strain element 120 other than the upper and lower ends when the upper case 110U and the lower case 110L are combined. Also, the case 110 is not limited to a configuration in which it is divided into upper and lower parts, and may be divided, for example, along a diameter passing through the center of a circle in a plan view.

[0041] The opening 112U is formed in the same position as the opening 112L of the lower case 110L in a plan view, and has the same opening shape. The upper end of the main body 121 of the flexure element 120 is inserted into the opening 112U. The size and shape of the opening 112U in a plan view are adjusted so that, when the upper end of the main body 121 of the flexure element 120 is inserted, there is almost no gap between the opening 112U and the outer surface 121C of the upper end of the main body 121. In addition, an O-ring 115U is provided between the opening 112U of the upper case 110U and the flexure element 120, ensuring waterproof and dustproof properties.

[0042] Additionally, upper case 110U has a wall surrounding opening 112U. This wall has a shape that matches the outer circumferential shape of upper convex portion 122 of two convex portions 122 of flexure element 120, and by engaging with the linear portion of the outer periphery of convex portion 122, it prevents flexure element 120 from rotating relative to upper case 110U in plan view.

[0043] The upper case 110U also accommodates the circuit board unit 140 radially outward of the portion where the flexure element 120 is disposed. In this state, the flexure element 120 is accommodated in an opening in the center of the circuit board unit 140.

[0044] With the strain body 120 and the circuit board unit 140 mounted inside the lower case 110L, the upper case 110U is fixed to the lower case 110L as shown in FIG. 1 by inserting screws 118 (see FIG. 3) into the screw holes and fastening the screws 118 to the screw holes of the lower case 110L via O-rings 116 (see FIG. 3) for ensuring waterproofing and dustproofing. At this time, an O-ring 117 is sandwiched between the outer periphery of the lower case 110L and the outer periphery of the upper case 110U, thereby sealing and ensuring waterproofing and dustproofing. At this time, the recesses on the outer periphery of the wiring board 150 of the circuit board unit 140 engage with the screw holes of the lower case 110L, so that the circuit board unit 140 is fixed in place while housed in the case 110 and does not shift.

[0045] In the case 110 as described above, the lower surface 121A of the main body 121 of the flexure body 120 is exposed from the opening 112L of the lower case 110L, and the upper surface 121B of the main body 121 of the flexure body 120 is exposed from the opening 112U of the upper case 110U. Therefore, with regard to the flexure body 120, the case 110 exposes the lower end portion (the portion on the lower surface 121A side) and the upper end portion (the portion on the upper surface 121B side) of the main body 121, and houses the rest of the parts.

[0046] <Strain body 120> The flexure element 120 has a main body 121, two protrusions 122, and a through-hole 123. The flexure element 120 is preferably made of a metal material such as stainless steel.

[0047] Main body 121 is a portion surrounding through-hole 123, and has lower surface 121A located at the lower end, upper surface 121B located at the upper end, and outer surface 121C. Lower surface 121A is an example of a first end surface, and upper surface 121B is an example of a second end surface. Of main body 121, the lower end portion on the lower side where lower surface 121A is located is an example of a first end portion, and the upper end portion on the upper side where upper surface 121B is located is an example of a second end portion. Main body 121 is a cylindrical portion, and has through-hole 123 that is circular in plan view provided in the center.

[0048] A lower end of main body 121 is inserted through opening 112L of lower case 110L, and lower surface 121A protrudes downward beyond lower surface 111L of lower case 110L. An upper end of main body 121 is inserted through opening 112U of upper case 110U, and upper surface 121B protrudes upward beyond upper surface 111U of upper case 110U.

[0049] The outer surface 121C is the outer side surface of the cylindrical main body 121, and is provided with two protrusions 122 in the center in the Z direction. The two protrusions 122 are provided spaced apart in the up-down direction in the center in the Z direction of the outer surface 121C.

[0050] Strain sensors 130 are provided in a portion of the outer surface 121C between the two protrusions 122. As an example, eight strain sensors 130 are provided, including four strain sensors 130 for detecting strain in the Z-axis direction and four strain sensors 130 for detecting strain in the X- or Y-direction. The eight strain sensors 130 are provided at four locations at 90-degree intervals around the circumferential direction of the outer surface 121C, with one strain sensor 130 for detecting strain in the Z-axis direction and one strain sensor 130 for detecting strain in the X- or Y-direction paired together. The portion of the outer surface 121C where the strain sensors 130 are provided may be a flat surface. The four flat surfaces are provided at equal intervals around the circumferential direction of the outer surface 121C. That is, the four flat surfaces are provided at 90-degree intervals around the circumferential direction of the outer surface 121C.

[0051] Convex portion 122 protrudes outward from outer surface 121C in plan view, and is located above lower surface 121A and below upper surface 121B in the vertical direction. Therefore, outer surface 121C is located above and below two convex portions 122, and outer surface 121C is also located between two convex portions 122.

[0052] The protrusions 122 are annular portions that protrude radially outward from the outer surface 121C, and part of the outer periphery is chamfered at, for example, four locations at 90-degree intervals to prevent rotation inside the lower case 110L and the upper case 110U. The lower case 110L and the upper case 110U engage with the chamfered portions, thereby fixing the protrusions 122 so as not to rotate inside the case 110. Furthermore, the two protrusions 122 abut against the inner walls of the lower case 110L and the upper case 110U in the Z direction, thereby preventing the flexure element 120 from shifting in the Z direction inside the case 110. Furthermore, the protrusions 122 are larger than the openings 112L and 112U of the lower case 110L and the upper case 110U, and therefore the flexure element 120 can be prevented from falling off from the openings 112L or 112U.

[0053] The through hole 123 penetrates the center of the main body 121 in a plan view so as to connect the lower surface 121A and the upper surface 121B. The lock bolt 21 of the fastening mechanism 20 is inserted through the through hole 123, and therefore the through hole 123 has an opening size that matches the planar size of the lock bolt 21. The through hole 123 is a cylindrical hole, and connects the lower surface 121A and the upper surface 121B of the strain element 120.

[0054] As an example, as shown in FIG. 2B, when washer 30 is in contact with lower surface 121A of strain body 120 and fastening mechanism 20 is in contact with upper surface 121B, a fastening axial force is applied in the direction penetrating through hole 123 (Z direction), and strain body 120 is compressed in the up-down direction, causing strain as outer surface 121C of strain body 120 flexes and bulges outward, generating strain.

[0055] <Strain sensor 130> The strain sensor 130 is provided on the outer surface 121C of the main body 121 of the flexure body 120, in a portion between the two protrusions 122. The strain sensor 130 has one or more strain detection elements and detects the strain of the flexure body 120. For example, each strain detection element uses a strain resistance element whose resistance value changes depending on the amount of strain. Four strain detection elements may be provided and connected in a bridge configuration.

[0056] The strain detection elements may be formed on the outer surface 121C by printing a composite resistor containing cermet or a composite resistor whose binder is synthetic resin. In this case, the strain detection elements can be easily and reliably formed at predetermined installation positions on the outer surface 121C. In particular, since the printing, drying, and curing of the strain detection elements can be performed collectively on the multiple flexure bodies 120 while the multiple flexure bodies 120 are arranged side by side, the strain detection elements can be easily and reliably formed on the multiple flexure bodies 120.

[0057] Furthermore, for example, the strain detection element may be mounted on a rigid or flexible substrate and then attached to the outer surface 121C together with the rigid or flexible substrate. In this case, too, the strain detection element can be easily and reliably installed at a predetermined installation position on the outer surface 121C. Note that the portion of the outer surface 121C where the strain detection element is provided is preferably flat.

[0058] <Wiring board 150> As an example, wiring board 150 is a wiring board conforming to FR-4 (Flame Retardant type 4) standards. Wiring board 150 has an annular shape in a plan view and is housed in lower case 110L. In FIGS. 5A and 5B, the point where two dashed lines intersect at right angles represents the center of the annular shape of wiring board 150. Wiring board 150 is parallel to the XY plane. The lower surface of wiring board 150 is an example of a first surface, and the upper surface is an example of a second surface.

[0059] The wiring substrate 150 has an annular shape with an opening 150A in the center, and six circular openings, for example, are provided along the circumferential direction, and eight notches are provided along the circumferential direction on the outer periphery. The openings 150A penetrate between the lower surface (first surface) and the upper surface (second surface). The diameter of the openings 150A is set to be slightly larger (for example, 1 mm larger) than the diameter of the convex portions 122 of the strain generating element 120.

[0060] The six circular openings and eight notches on the outer periphery are provided to avoid the 14 protrusions of the lower case 110L that have the 14 screw holes. The wiring board 150 is fixed in the lower case 110L by thermal caulking, with the six circular openings and eight notches engaging with the 14 protrusions of the lower case 110L and with four protrusions 113L protruding in the +Z direction from the top surface of the lower case 110L passing through the four through holes 151 of the wiring board 150. Two of the four protrusions 113L of the lower case 110L are provided on each of the -Y and +Y direction sides of the opening 112L. Two of the four through holes 151 of the wiring board 150 are provided on each of the -Y and +Y direction sides of the opening 150A.

[0061] For example, wiring board 150 does not have an inner layer. Antenna element 160 is provided over the entire lower surface (see FIG. 5B) of wiring board 150. Antenna element 160 is made of copper foil, for example.

[0062] <Antenna element 160> Antenna element 160 is formed on the lower surface of wiring substrate 150 (see FIG. 5B). Antenna element 160 has an annular shape with an inner radius a and an outer radius b, and the outer periphery at the position of outer radius b is located radially inward of the outer periphery of wiring substrate 150. Antenna element 160 can be produced, for example, by patterning copper foil formed on the lower surface of wiring substrate 150.

[0063] Antenna element 160 is annular, and has a notch 161 at the end of its outer periphery on the −X direction side. Notch 161 is an example of a first notch formed by linearly cutting out part of the circular arc of the circular outer periphery of antenna element 160 parallel to the Y direction. Notch 161 is formed on the underside of annular wiring board 150 to provide a space for arranging feeder line 170A.

[0064] Furthermore, antenna element 160 has eleven cutouts on its outer periphery so as to avoid seven of the eight cutouts on the outer periphery of wiring substrate 150 and the areas around four through holes 151. The eleven cutouts of antenna element 160 are formed along the circumferential direction in parts of the outer periphery of antenna element 160 where cutouts 161 are not formed.

[0065] As an example, antenna element 160 is an antenna element for a ring patch antenna. Because washer 30, which is larger than antenna element 160 in a plan view, is located below antenna element 160, washer 30 serves as the ground layer of the patch antenna. In other words, antenna element 160 is capacitively coupled with washer 30 to form a patch antenna.

[0066] Here, the wireless communication system of the communication unit included in the circuit unit 180 that supplies power to the antenna element 160 can be various, such as RFID or LPWA, but here, an RFID system will be described as an example.

[0067] In such a case, the antenna element 160 is required to have, as an example, a sufficiently low VSWR, satisfy the RFID frequency band of 920 MHz, obtain a gain equivalent to that of a dipole antenna, and be capable of emitting circularly polarized radio waves, as described above.

[0068] <Power supply line 170A> The feed line 170A is provided on the lower surface of the wiring board 150 at a position where the notch 161 of the antenna element 160 is formed and the outer edge of the antenna element 160 is offset radially inward. The feed line 170A has a feed terminal 171A, a bent portion 172A, and an end portion 173A. The feed line 170A forms a microstrip line (MSL) with the washer 30 as the ground layer.

[0069] The power feeding terminal 171A is connected to the antenna element 160 and is a feeding point that feeds power to the antenna element 160. The power feeding terminal 171A is connected to the antenna element 160 at the end of the notch 161 in the -Y direction.

[0070] The power supply line 170A is an L-shaped line that extends from the power supply terminal 171A in the −X direction, bends in the +Y direction at a bent portion 172A, and extends to an end portion 173A. The bent portion 172A is located near the outer periphery of the wiring board 150.

[0071] The portion between bent portion 172A and end portion 173A is parallel to the Y direction, and therefore parallel to notch 161. The portion between bent portion 172A and end portion 173A being parallel to notch 161 means that it is parallel to the edge of notch 161. The edge of notch 161 is a side that is cut out linearly in the outer periphery of antenna element 160 in notch 161 parallel to the Y direction.

[0072] The portion between bent portion 172A and end portion 173A has the desired impedance characteristics by being parallel to the edge of cutout portion 161. Note that the portion between bent portion 172A and end portion 173A only needs to extend along the edge of cutout portion 161, and does not need to be strictly parallel to the edge of cutout portion 161 as long as the desired impedance characteristics are obtained. The portion between bent portion 172A and end portion 173A extending along the edge of cutout portion 161 includes such a configuration that is not strictly parallel. The portion between bent portion 172A and end portion 173A is an example of a straight portion extending along cutout portion 161.

[0073] End 173A is located on the +Y-direction end side of notch 161 in the Y direction. A portion between bent portion 172A and end 173A overlaps a portion between bent portion 172B and end 173B of feed line 170B in a plan view, and is connected to the portion between bent portion 172B and end 173B by a plurality of through holes 175 that penetrate wiring substrate 150 in the thickness direction (Z direction). The portion between bent portion 172A and end 173A is an example of a first portion. The overlapping of the portion between bent portion 172A and end 173A and the portion between bent portion 172B and end 173B and the connection by through holes 175 can reduce copper loss in feed lines 170A and 170B formed by microstrip lines, reducing power supply loss and ultimately contributing to improving the radiation efficiency of antenna element 160.

[0074] <Power Supply Line 170B> The feed line 170B is provided at an end on the −X direction side of the upper surface of the wiring substrate 150. The feed line 170B has a connection terminal 171B, a bent portion 172B, and an end portion 173B. The feed line 170B forms a microstrip line (MSL) with the washer 30 as the ground layer.

[0075] Connection terminal 171B is connected to circuit section 180, and is a terminal through which power is output from circuit section 180 when antenna element 160 radiates radio waves. Connection terminal 171B is provided at a position overlapping with antenna element 160 in a plan view.

[0076] The power supply line 170B is an L-shaped line that extends from the connection terminal 171B in the −X direction, bends in the −Y direction at a bent portion 172B, and extends to an end portion 173B.

[0077] The portion between the bent portion 172B and the end 173B is parallel to the Y direction and overlaps with the portion between the bent portion 172A and the end 173A of the feeder line 170A. The portion between the bent portion 172B and the end 173B is an example of an overlapping portion. The width in the X direction and the length in the Y direction of the portion between the bent portion 172B and the end 173B are equal to the width in the X direction and the length in the Y direction of the portion between the bent portion 172A and the end 173A, respectively. The portion between the bent portion 172B and the end 173B overlaps with the portion between the bent portion 172A and the end 173A of the feeder line 170A in a state where they are aligned. Therefore, in a plan view, the position of the bent portion 172B is equal to the position of the end 173A, and the position of the end 173B is equal to the position of the bent portion 172A.

[0078] The portion between the bent portion 172B and the end portion 173B is connected to the portion between the bent portion 172A and the end portion 173A by a plurality of through holes 175 that penetrate the wiring board 150 in the thickness direction (Z direction).

[0079] <Length and Impedance Characteristics of Feed Lines 170A and 170B> The length in a plan view of the section along the feed lines 170A and 170B from the feed terminal 171A to the connection terminal 171B is set to λe / 4, where λe is the electrical length of the wavelength of the radio wave at the operating frequency of the antenna element 160.

[0080] As an example, the impedance of the power supply terminal 171A with respect to the washer 30 is 1100 Ω, and the impedance of the connection terminal 171B with respect to the circuit unit 180 is 50 Ω. Details of these values ​​will be described later using simulation results. Since the connection terminal 171B is connected to the circuit unit 180 including the communication unit, the impedance is set to 50 Ω to match the impedance of the circuit unit 180. The power supply lines 170A and 170B have a characteristic impedance that converts the impedance of the power supply terminal 171A (1100 Ω) into the impedance of the connection terminal 171B (50 Ω). As described above, such a characteristic impedance can be achieved by appropriately setting the line width in a plan view of the section along the power supply lines 170A and 170B from the power supply terminal 171A to the connection terminal 171B.

[0081] <Through hole 175> The through hole 175 penetrates the wiring board 150 in the thickness direction (Z direction) and connects the portion between the bent portion 172A and the end portion 173A of the power feed line 170A and the portion between the bent portion 172B and the end portion 173B of the power feed line 170B. A plurality of through holes 175 are provided, and are provided at equal intervals in the Y direction, for example. The plurality of through holes 175 are formed, for example, at the center of the width in the X direction between the portion between the bent portion 172A and the end portion 173A of the power feed line 170A and the portion between the bent portion 172B and the end portion 173B of the power feed line 170B.

[0082] The multiple through holes 175 are provided in a section from the vicinity of the bent portions 172A and 172B to the vicinity of the ends 173A and 173B in a plan view. Therefore, the portion of the feed line 170A between the bent portion 172A and the end 173A and the portion of the feed line 170B between the bent portion 172B and the end 173B are connected by the through holes 175 from the end on the −Y direction side to the end on the +Y direction side.

[0083] The portion between bent portion 172A and end portion 173A of feed line 170A and the portion between bent portion 172B and end portion 173B of feed line 170B are connected by a plurality of through holes 175, thereby reducing signal transmission loss in feed lines 170A and 170B and enabling a reduction in the VSWR of antenna device 100A. Note that it is sufficient to provide at least one through hole 175 as long as there is no problem in realizing the impedance characteristics of feed lines 170A and 170B and in reducing the VSWR.

[0084] <Circuit section 180> The circuit unit 180 is connected to the connection terminal 171B of the power supply line 170B, and is also connected to the strain sensor 130 via wiring (not shown). The circuit unit 180 incorporates a control unit that generates a strain detection signal that indicates the degree of strain of the strain element 120 based on the output of the strain sensor 130, and a communication unit that performs wireless communication using the antenna element 160. The detection device 100 is a passive device that operates without a power source such as a battery, and the circuit unit 180 does not have a memory.

[0085] The communication unit generates DC power by rectifying a signal received from the RFID-R / W via the antenna element 160, and supplies the generated power to the control unit to operate it. The control unit generates a strain detection signal indicating the degree of strain of the strain-generating body 120 and transmits it to the communication unit. The communication unit radiates the strain detection signal as backscatter through the antenna element 160. The radiated strain detection signal is received by the RFID-R / W. As mentioned above, there are various wireless communication methods for the communication unit, such as RFID and LPWA, but here we will explain the RFID form as an example.

[0086] In the above description, the detection device 100 is a passive device that does not have a battery, but the present invention is not limited to this. The detection device 100 may be configured to include at least one of a battery and a memory.

[0087] <How to adjust the operating frequency (resonant frequency) and impedance of the antenna element 160> 6 is a diagram illustrating an example of how to adjust the operating frequency and impedance of the antenna element 160. The distance e is the distance between the antenna element 160 and the washer 30 in the vertical direction.

[0088] Here, as an example, we will explain the case where the detection device 100 is fastened to the fixed part 10, which is the inner wall of a concrete tunnel, using a lock bolt 21, a locking nut 22, and a bell washer 23, as shown in Figure 2B.

[0089] The inner radius a (see FIG. 5B) of the antenna element 160 is determined by the diameter of the convex portion 122 of the flexure body 120 of the detection device 100. In other words, the inner radius a is restricted by the dimensions of the convex portion 122 of the flexure body 120 of the detection device 100.

[0090] Therefore, in order to adjust the resonant frequency of the antenna element 160 to a desired value (approximately 920 MHz), the outer radius b (see FIG. 5B) that is not subject to the above-mentioned constraints is adjusted. Therefore, the outer diameter (2b) of the antenna element 160 is an outer diameter that corresponds to the wavelength of the radio wave at the operating frequency of the antenna element 160.

[0091] Connection terminal 171B of power feed line 170B is connected to circuit unit 180, which includes a communication unit. If the high-frequency input / output impedance of circuit unit 180 is 50 Ω, which is typical for high-frequency circuits, the impedance at connection terminal 171B of power feed line 170B also needs to be 50 Ω.

[0092] Here, since the size of wiring board 150 in a plan view is smaller than washer 30, the high-frequency ground (reference potential point) of power feed lines 170A and 170B is washer 30. Therefore, the characteristic impedance of these microstrip lines is determined by the width of the microstrip line, the distance e between wiring board 150 and washer 30 shown in Fig. 5, and the relative dielectric constant of the dielectric (case or air) contained therebetween.

[0093] Furthermore, since the antenna element 160 is also smaller in size than the washer 30, the ground (reference potential point) of the ring patch antenna including the antenna element 160 is the washer 30. The circuit section 180 on the surface of the wiring board 150 operates with the antenna element 160 as its reference potential point.

[0094] Therefore, if antenna element 160 is designed to resonate in the desired 920 MHz band, it is possible to configure an antenna in which washer 30 serves as a ground and antenna element 160 functions as a radiating element, i.e., a ring patch antenna. An example of various dimensions considered is shown below. When the radius of central opening 150A of wiring board 150 is 33 mm, spacing e shown in FIG. 6 is 9 mm, and case 110 is made of PBT with glass filler, antenna element 160 shown in FIG. 5B has an inner radius a of 33.5 mm, an outer radius b of approximately 54 mm, and a length c from the center of antenna element 160 to the edge of cutout 161 in a plan view of approximately 42 mm. The wiring board 150 is made of FR-4 and has a thickness of 0.8 mm.

[0095] Here, in antenna element 160 (ring patch antenna) without feed line 170B of FIG. 5A or feed line 170A of FIG. 5B, the input impedance at feed terminal 171A of FIG. 5B (the impedance of feed terminal 171A with washer 30 as the reference) was calculated to be approximately 1100 Ω by electromagnetic field simulation. To convert this high impedance to 50 Ω at connection terminal 171B, the characteristic impedance Z0 of feed lines 170A and 170B is set to the value shown in the following equation (1), and the length (the length from connection terminal 171B to feed terminal 171A) is set to approximately λe / 4. Note that λe is the wavelength on wiring board 150 when detection device 100 is installed as shown in FIG. 2B, and is the electrical length of the wavelength of radio waves at the operating frequency of antenna element 160 (for example, 920 MHz).

[0096]

number

[0097] The feeder lines 170A and 170B that satisfied these conditions had a width of about 2 mm and a length (length from connection terminal 171B to feed terminal 171A) of about 68 mm, which corresponds to about λe / 4.

[0098] Fig. 7 is a diagram illustrating an example of circular polarization of the antenna device 100A. Fig. 7 shows the antenna element 160 and the feed lines 170A and 170B as viewed from above (the +Z direction side). In Fig. 7, the wiring board 150 and the through-hole 175 of the antenna device 100A are omitted. The antenna element 160 is represented simply as a ring electrode, and the feed lines 170A and 170B are represented as a single microstrip line. The antenna element 160 represented as a ring electrode has an area ΔS X The cutout 161 is formed by cutting out only the area ΔS X The power supply lines 170A and 170B are arranged in this portion.

[0099] With this configuration, the resonance mode degenerated in antenna element 160 is separated into a #1 component parallel to the Y-axis and a #2 component parallel to the X-axis. The #1 component occurs at the diameter of the annular ring of antenna element 160, while the #2 component occurs at the portion where notch 161 is located. Because the radial length of the portion where notch 161 is located is shorter than the diameter of the annular ring of antenna element 160 where the #1 component occurs, the resonance frequency f1 of the #1 component is lower than the resonance frequency f2 of the #2 component.

[0100] 8A is a diagram showing an example of the amplitude distribution of the #1 component and the #2 component with respect to frequency. FIG. 8B is a diagram showing an example of the phase distribution of the #1 component and the #2 component with respect to frequency. The area ΔS of the portion cut out by the cutout portion 161 of the antenna element 160 is xIf this is appropriate, as shown in Fig. 8A, the amplitudes of the #1 and #2 components will be equal at frequency f0, which is intermediate between f1 and f2, and the phase difference will be 90°, resulting in the generation of circularly polarized waves. As shown in Fig. 8B, the phase of the #1 component will lag behind the phase of the #2 component by 90°, resulting in the emission of right-hand circularly polarized (RHCP) radio waves in the +Z direction. In other words, by providing cutout portion 161, it becomes possible to efficiently emit circularly polarized radio waves.

[0101] The above is true when the polarization of the antenna of the detection device 100 is right-handed circularly polarized, but if left-handed circularly polarized (LHCP) is required, the configuration shown in FIG. 9A or 9B can be used. FIGS. 9A and 9B are diagrams illustrating an example of the configuration of an antenna device 100A capable of radiating left-handed circularly polarized waves. Similar to FIG. 7, FIGS. 9A and 9B show the antenna element 160 and feed lines 170A and 170B, but omit the wiring board 150 and through-hole 175. The antenna element 160 and feed lines 170A and 170B are also shown in simplified form. Note that FIG. 9A also shows a circuit section 180.

[0102] In Fig. 9A, feed terminal 171A and connection terminal 171B are arranged left-right reversely to those in Fig. 8. In this case, the position of circuit unit 180 is also different from that in Fig. 5A, and is located on the -Y side of the center of antenna element 160 in the Y direction. To make feed terminal 171A and connection terminal 171B left-right reversed to those in Fig. 8, feed line 170A and feed line 170B are arranged left-right reversely, and circuit unit 180 is positioned to match connection terminal 171B and on the -Y side of the center of antenna element 160 in the Y direction.

[0103] 9B, notches 162 are provided on both sides in the Y direction of the antenna element 160. The area of ​​the portion cut out by each notch 162 is ΔS Y / 2. The notch 162 is an example of a second notch formed by linearly cutting out a part of the circular arc of the circular outer periphery of the antenna element 160 in a direction parallel to the X direction. As an example, one notch 162 is provided on the -Y direction side and one on the +Y direction side. Each notch 162 is provided at a position that differs by 90 degrees from the position of the notch 161 with respect to the center of the annular shape of the antenna element 160.

[0104] The total area ΔS of the portions cut out by the two cutout portions 162 Y (=2×ΔS Y / 2) is the area ΔS of the portion cut out by the cutout portion 161 X is greater than (ΔS Y >ΔS X This means that the length in the X direction from the outer periphery of the annular shape of antenna element 160 to the end edge of notch 162 is twice as long as the length in the Y direction from the outer periphery of the annular shape of antenna element 160 to the end edge of notch 162.

[0105] With two such notches 162, the #1 component is generated in the Y direction between the two notches 162, while the #2 component is generated in the X direction at the portion where the notch 161 is located. Since the length of the antenna element 160 in the radial direction (Y direction) of the portion where the two notches 162 are located is shorter than the length of the antenna element 160 in the radial direction (X direction) of the portion where the notch 161 is located, the resonant frequency f1 of the #1 component is higher than the resonant frequency f2 of the #2 component. In this case, the phase of the #2 component lags behind the phase of the #1 component by 90°, resulting in the emission of left-handed circularly polarized (LHCP) radio waves in the +Z direction. The choice of which configuration to use, FIG. 9A or FIG. 9B, can be made based on the actual mechanical structure, component layout, and the like.

[0106] Instead of the two notches 162, a notch having an area of ​​ΔS Y Even if one notch 162 is provided, the relationship between the #1 component and the #2 component remains the same. X and the total area ΔS of the portion cut out by the cutout portion 162Y By adjusting the magnitude of the polarity, it is possible to select whether to emit left-handed circularly polarized waves or right-handed circularly polarized waves.

[0107] <First Modification> Fig. 10A is a diagram showing an example of the configuration of an antenna device 100AM1 according to a first modified example of the embodiment. Fig. 10B is a diagram showing an enlarged portion of Fig. 10A. Fig. 11A is a diagram showing an example of the configuration of the upper surface side of the wiring board 150 of the antenna device 100AM1. Fig. 11B is a diagram showing an example of the configuration of the lower surface side of the wiring board 150 of the antenna device 100AM1. Since Fig. 11B shows the configuration of the lower surface side of the wiring board 150, the Y direction is opposite to that of Fig. 11A.

[0108] Antenna device 100AM1 includes wiring board 150, antenna element 160, feed lines 170AM1 and 170BM1, and through hole 175. Antenna device 100AM1 has a configuration in which feed lines 170A and 170B of antenna device 100A of the embodiment are replaced with feed lines 170AM1 and 170BM1. Furthermore, in antenna device 100AM1 of the first modified embodiment, antenna element 160 has two notches 162 in addition to notch 161, and therefore can radiate left-handed circularly polarized radio waves in the +Z direction.

[0109] The circuit board part 140M1 of the first modified example of the embodiment includes a wiring board 150, an antenna element 160, feed lines 170AM1 and 170BM1, a through hole 175, and a circuit part 180. Since the feed line 170BM1 is easier to see than the feed line 170AM1 in Figures 10A, 10B, 11A, and 11B, the configuration of the feed line 170BM1 will be described first.

[0110] The feed line 170BM1 is provided at an end on the −X direction side of the upper surface of the wiring substrate 150. The feed line 170BM1 has a connection terminal 171B, a bent portion 172B, an end 173B, and a widened portion 170BW. The feed line 170BM1 forms a microstrip line (MSL) with the washer 30 as the ground layer.

[0111] Widened portion 170BW is a portion obtained by widening the width in the X direction of the portion between bent portion 172B and end portion 173B, and is provided in a portion extending from a portion slightly on the -Y direction side of bent portion 172B to end portion 173B. Widened portion 170BW is widened so as to protrude in the -X direction relative to the portion between bent portion 172B and end portion 173B other than widened portion 170BW. Therefore, the outer edge on the +X direction side in a plan view of the portion between bent portion 172B and end portion 173B is composed of a single edge extending in the Y direction.

[0112] The feed line 170AM1 has a feed terminal 171A, a bent portion 172A, an end portion 173A, and a widened portion 170AW. The feed line 170AM1 forms a microstrip line (MSL) with the washer 30 as the ground layer.

[0113] Widened portion 170AW is a portion obtained by widening the width in the X direction of the portion between bent portion 172A and end portion 173A. It is provided from a position slightly on the +Y direction side of bent portion 172A to end portion 173A. Widened portion 170AW is widened so as to protrude in the -X direction relative to the portion between bent portion 172A and end portion 173A other than widened portion 170AW. Therefore, the outer edge on the +X direction side in a plan view of the portion between bent portion 172A and end portion 173A is composed of a single edge extending in the Y direction.

[0114] The width in the X direction and the length in the Y direction of the widened portion 170AW are equal to the width in the X direction and the length in the Y direction of the widened portion 170BW in plan view, respectively. The widened portion 170AW is provided at a position where it is aligned with and overlaps the widened portion 170BW in plan view. The widened portion 170AW is an example of a first portion of the feed line 170AM1. The widened portion 170BW is an example of an overlapping portion of the feed line 170BM1.

[0115] The multiple through holes 175 are provided along the edge extending in the Y direction on the −X direction side of the widened portions 170AW and 170BW. That is, the multiple through holes 175 are provided at equal intervals in the Y direction on the end side on the −X direction side of the X direction width of the widened portions 170AW and 170BW. In other words, the multiple through holes 175 are provided offset toward the −X direction from the center of the X direction width of the widened portions 170AW and 170BW.

[0116] In this way, by providing the multiple through holes 175 offset toward the -X direction from the center of the width of the widened portions 170AW and 170BW in the X direction, a minute loop antenna as shown by the dashed arrow in Fig. 10B is constructed by the widened portions 170AW and 170BW and the multiple through holes 175. The minute loop antenna is a single-turn loop antenna, and detects the magnetic field in the vicinity of the washer 30, thereby enhancing the reception and emission of radio waves in the antenna device 100AM1.

[0117] <Simulation of a detection device including the antenna device 100AM1> 12A is a diagram showing an example of a simulation result of the frequency characteristic of the VSWR (Voltage Standing Wave Ratio) of a detection device including the antenna device 100AM1. In the simulation, as the reflection characteristic of the detection device including the antenna device 100AM1, the VSWR of the antenna element 160 as seen from the connection terminal 171B (see FIG. 11A) was calculated in a state where the detection device is fastened to the fixing part 10 using the lock bolt 21, the nut 22, and the bell washer 23, as shown in FIG. 2B. In the simulation, the operating frequency (resonance frequency) of the antenna element 160 was set to 920 MHz.

[0118] FIG. 12A shows the frequency characteristics of the VSWR in the detection device 100 when the lock bolt 21 is perpendicular to the mounting surface 11 of the fixed part 10 as shown in FIG. 2B. FIG. 12B shows the frequency characteristics of the gain of left-handed circularly polarized waves in the +Z direction when lock bolt 21 is perpendicular to mounting surface 11 of fixed portion 10.

[0119] As shown in Figure 12A, the VSWR was 2 or less in the range of 915 MHz to 924 MHz. In the wide band of 9 MHz including 920 MHz, the VSWR was low, and good results were obtained. The 9 MHz band including 920 MHz includes the RFID band (7 MHz: 916 MHz to 923 MHz) and is wider than the RFID band.

[0120] Furthermore, the gain of left-handed circularly polarized waves in the +Z direction was 3.11 dBi at 916 MHz, 3.77 dBi at 920 MHz, and 3.21 dBi at 923 MHz, as shown in Figure 12B. We were able to confirm that there was a gain of more than 3 dBi within the RFID band, which is greater than the gain of the dipole antenna commonly used in RFID tags.

[0121] 13A and 13B are diagrams showing examples of simulation results of radiation patterns (directivity) in the ZX and ZY planes, respectively. As shown in Fig. 13A and 13B, it was confirmed that left-handed circularly polarized waves (LHCP) were emitted in the +Z direction.

[0122] In the first modified example, the configuration has been described in which the widened portions 170AW and 170BW are widened so as to protrude in the -X direction, but the widened portions 170AW and 170BW may also be widened so as to protrude in the +X direction.

[0123] In the first modified example, the widened portions 170AW and 170BW are widened so as to protrude in the -X direction, and the multiple through holes 175 are offset in the -X direction from the center of the X-direction width of the widened portions 170AW and 170BW. However, the through holes 175 may be offset in the +X direction from the center of the X-direction width of the widened portions 170AW and 170BW. It is preferable that the widened portions 170AW and 170BW and the multiple through holes 175 form a minute loop antenna.

[0124] <Second Modification> Fig. 14 is a diagram showing an example of the configuration of an antenna device 100AM2 according to a second modified example of the embodiment. Fig. 15A is a diagram showing an example of the configuration of the upper surface side of the wiring board 150 of the antenna device 100AM2. Fig. 15B is a diagram showing an example of the configuration of the lower surface side of the wiring board 150 of the antenna device 100AM2. In Fig. 15B, the Y direction is opposite to that of Fig. 15A in order to show the configuration of the lower surface side of the wiring board 150.

[0125] The antenna device 100AM2 includes a wiring board 150, an antenna element 160, a feed line 170BM2, and a through hole 175. The antenna device 100AM2 has a configuration in which the feed line 170A of the antenna device 100A of the embodiment is omitted and the feed line 170B is replaced with a feed line 170BM2. Furthermore, in the antenna device 100AM2 of the second modified embodiment, the antenna element 160 has two notches 162 in addition to the notch 161, and therefore can radiate left-handed circularly polarized radio waves in the +Z direction.

[0126] The circuit board section 140M2 of the second modified example of the embodiment includes a wiring board 150, an antenna element 160, a feed line 170BM2, a through hole 175, and a circuit section 180.

[0127] The feed line 170BM2 is provided at an end on the −X direction side of the upper surface of the wiring substrate 150. The feed line 170BM2 has a connection terminal 171B, a bent portion 172B, and an end portion 173B. The feed line 170BM2 forms a microstrip line (MSL) with the washer 30 as the ground layer.

[0128] The portion of feed line 170BM2 between bent portion 172B and end portion 173B extends from bent portion 172B in the −Y direction, then bends in the +X direction and extends to end portion 173B. End portion 173B overlaps with the end portion of the edge of cutout portion 161 on the −Y direction side in plan view. End portion 173B is connected to the edge of cutout portion 161 of antenna element 160 by at least one through hole 175. The number of through holes 175 may be determined depending on the area of ​​the overlapping portion between end portion 173B and antenna element 160, and at least one is sufficient.

[0129] When the lengths of connection terminal 171B and end portion 173B are set to approximately λe / 4, the high impedance of end portion 173B can be converted to 50 Ω at connection terminal 171B. Antenna element 160 operates as a ring patch antenna with washer 30 as the ground, and radiates left-handed circularly polarized radio waves in the +Z direction.

[0130] <Third Modification> Fig. 16 is a diagram showing an example of the configuration of an antenna device 100AM3 according to a third modified example of the embodiment. Fig. 17A is a diagram showing an example of the configuration of the upper surface side of the wiring board 150 of the antenna device 100AM3. Fig. 17B is a diagram showing an example of the configuration of the lower surface side of the wiring board 150 of the antenna device 100AM3. In Fig. 17B, the Y direction is opposite to that of Fig. 17A in order to show the configuration of the lower surface side of the wiring board 150.

[0131] The antenna device 100AM3 includes a wiring board 150, an antenna element 160, feed lines 170AM3 and 170BM3, and a through hole 175. The antenna device 100AM3 has a configuration in which the feed lines 170A and 170B of the antenna device 100A of the embodiment are replaced with feed lines 170AM3 and 170BM3. In the antenna device 100AM3 of the third modified example of the embodiment, the antenna element 160 has two notches 162 in addition to the notch 161, and therefore can radiate left-handed circularly polarized radio waves in the +Z direction.

[0132] The circuit board section 140M3 of the third modified example of the embodiment includes a wiring board 150, an antenna element 160, feed lines 170AM3 and 170BM3, a through hole 175, and a circuit section 180.

[0133] The feed line 170AM3 has a feed terminal 171A, a bent portion 172A, and an end portion 173A. The portion of the feed line 170AM3 between the bent portion 172A and the end portion 173A extends from the bent portion 172A in the +Y direction, bends in the +X direction just before the end portion 173A, and extends to the end portion 173A. The end portion 173A is located just before the end of the edge of the notch 161 on the +Y direction side in plan view. There is a gap in the X direction between the end portion 173A and the edge of the notch 161. The end portion 173A overlaps with the end portion 173B of the feed line 170BM3 in plan view. The end portion 173A is an example of a first portion of the feed line 170AM3. The end portion 173B is an example of an overlapping portion of the feed line 170BM3. The feed line 170AM3 constitutes a microstrip line (MSL) with the washer 30 as the ground layer.

[0134] The feed line 170BM3 is provided at an end on the −X direction side of the upper surface of the wiring substrate 150. The feed line 170BM3 has a connection terminal 171B and an end 173B. The end 173B is located on the −X direction side of the connection terminal 171B. The feed line 170BM3 is a short, straight line extending in the X direction. The end 173B overlaps with the end 173A of the feed line 170A in a plan view. The feed line 170BM3 forms a microstrip line (MSL) with the washer 30 as the ground layer.

[0135] End 173B is connected to end 173A of feeder line 170A by at least one through hole 175. The number of through holes 175 may be determined depending on the area of ​​the overlapping portion of ends 173A and 173B, and at least one is sufficient.

[0136] If the length of the portion along feed lines 170A and 170B between feed terminal 171A and connection terminal 171B is set to approximately λe / 4, the high impedance of feed terminal 171A can be converted to 50 Ω at connection terminal 171B. Antenna element 160 operates as a ring patch antenna with washer 30 as the ground, and radiates left-handed circularly polarized radio waves in the +Z direction.

[0137] <Effects> Antenna device 100A of the present disclosure includes: an annular wiring board 150 having a first surface and a second surface and an opening 150A penetrating between the first surface and the second surface; an annular antenna element 160 provided on the first surface and surrounding the opening 150A; a feed line 170A provided on the first surface and having a feed terminal 171A connected to antenna element 160; a feed line 170B provided on the second surface and having a connection terminal 171B connected to circuit section 180, wherein feed line 170B has an overlapping portion that overlaps with a first portion of feed line 170A in a planar view; and a through hole 175 that penetrates wiring board 150 and connects the first portion of feed line 170A to the overlapping portion of feed line 170B. In this way, since the annular antenna element 160 is provided on the first surface of the annular wiring board 150 and surrounds the opening 150A, sufficient radiation characteristics can be obtained even when the antenna element 160 is placed close to a metal member. In addition, the antenna element 160 can emit circularly polarized radio waves.

[0138] Therefore, even if the antenna device 100A is placed in close proximity to a metal member such as the washer 30, it is possible to provide an antenna device 100A that can obtain sufficient radiation characteristics.

[0139] Furthermore, the circuit unit 180 may be connected to the second surface, and the antenna element 160 may overlap the position where the circuit unit 180 is located in a plan view. The circuit unit 180 can operate using the antenna element 160 as a reference potential point, and the operation of the circuit unit 180 becomes stable.

[0140] Furthermore, antenna element 160 may have cutout 161, which is a part of the annular arc cut out in a straight line, and feed line 170A may have a straight portion extending along cutout 161. This makes it possible to more efficiently radiate circularly polarized radio waves, and provides antenna device 100A that has sufficient radiation characteristics even when placed in close proximity to a metal member such as washer 30.

[0141] Furthermore, antenna element 160 may have cutout 162, which is a linear cutout of a portion of the annular arc. Depending on the size of cutouts 161 and 162, left-handed circularly polarized waves or right-handed circularly polarized waves can be selected, and antenna device 100A can be provided that can emit left-handed circularly polarized waves or right-handed circularly polarized waves, and that can obtain sufficient radiation characteristics even when placed close to a metal member such as washer 30.

[0142] Furthermore, notch 161 and notch 162 may be provided at positions that are 90 degrees apart from the center of the annular shape of antenna element 160. Depending on the size of notch 161 and 162, left-handed circularly polarized waves or right-handed circularly polarized waves can be selected, and it is possible to provide antenna device 100A that can emit left-handed circularly polarized waves or right-handed circularly polarized waves and that can obtain sufficient radiation characteristics even when placed close to a metal member such as washer 30.

[0143] Furthermore, through hole 175 may connect the first portion of feed line 170A and the overlapping portion of feed line 170B at their ends in the line width direction. A minute loop antenna is constructed in a cross section including feed line 170A, feed line 170B, and through hole 175, thereby enhancing the reception and radiation of radio waves in antenna device 100A.

[0144] Furthermore, the length of the section along feed line 170A and feed line 170B from feed terminal 171A of feed line 170A to connection terminal 171B of feed line 170B may be λe / 4, where λe is the electrical length of the wavelength of a radio wave at the operating frequency of antenna element 160. The high impedance of feed terminal 171A can be converted to the desired impedance (for example, 50Ω) of connection terminal 171B, and antenna device 100A with good operating characteristics can be obtained.

[0145] Furthermore, the outer diameter of antenna element 160 may be an outer diameter corresponding to the wavelength of radio waves at the operating frequency of antenna element 160. By adjusting the outer diameter of antenna element 160, the operating frequency of antenna element 160 can be set, and antenna device 100A can be provided that has sufficient radiation characteristics even when placed close to a metal member such as washer 30.

[0146] Another antenna device 100AM2 of the present disclosure includes an annular wiring board 150 having a first surface, a second surface, and an opening 150A penetrating between the first surface and the second surface, an annular antenna element 160 provided on the first surface and surrounding the opening 150A, a feed line 170BM2 provided on the second surface and having a connection terminal 171B connected to a circuit unit 180, and a through hole 175 penetrating the wiring board 150 and connecting the feed line 170BM2 and the antenna element 160. As described above, since the antenna device 100AM2 includes an annular antenna element 160 provided on the first surface of the annular wiring board 150 and surrounding the opening 150A, sufficient radiation characteristics can be obtained even when the antenna device is disposed in close proximity to a metal member.

[0147] Therefore, even if the antenna device 100A is placed in close proximity to a metal member such as the washer 30, it is possible to provide an antenna device 100A that can obtain sufficient radiation characteristics.

[0148] The detection device 100 of the present disclosure includes the above-mentioned antenna device 100A, a main body 121 having a first end and a second end, a flexure body 120 having a through hole 123 penetrating the main body 121 in a direction connecting a first side (lower side) where the first end is located and a second side (upper side) where the second end is located, and through which a lock bolt 21 of a fastening mechanism 20 is inserted, the flexure body 120 being inserted into an opening 150A of a wiring board 150, a strain sensor 130 that detects strain on the flexure body 120 due to a fastening axial force applied by the fastening mechanism 20 in the extension direction of the through hole 123, a circuit section 180 that is connected to a feeder line 170B and the strain sensor 130 and performs wireless communication, and a case 110 that houses at least a portion of the main body 121 of the flexure body 120. In this way, since the antenna element 160 is provided on the first surface of the annular wiring board 150 and includes an annular antenna element 160 surrounding the opening 150A, sufficient radiation characteristics can be obtained even when the antenna element 160 is placed close to a metal member.

[0149] Therefore, even when the detector 100 is placed in close proximity to a metal member such as the washer 30, it is possible to provide a detector 100 that can obtain sufficient radiation characteristics.

[0150] The above describes exemplary embodiments of the antenna device and detection device of the present disclosure, but the present disclosure is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

[0151] The following additional notes are provided regarding the above-described embodiments. (Appendix 1) an annular substrate having a first surface and a second surface and an opening extending therethrough between the first surface and the second surface; an annular antenna element provided on the first surface and surrounding the opening; a first feed line provided on the first surface and having a feed terminal connected to the antenna element; a second feed line provided on the second surface and having a connection terminal connected to a communication unit, the second feed line having an overlapping portion that overlaps with a first portion of the first feed line in a plan view; a through hole that passes through the substrate and connects the first portion of the first feed line and the overlapping portion of the second feed line; An antenna device comprising: (Appendix 2) the communication unit is connected to the second surface; 2. The antenna device according to claim 1, wherein the antenna element overlaps with a position where the communication unit is disposed in a plan view. (Appendix 3) the antenna element has a first cutout portion formed by linearly cutting out a part of the annular arc, 3. The antenna device according to claim 1, wherein the first feed line has a straight portion extending along the first cutout portion. (Appendix 4) 4. The antenna device according to claim 3, wherein the antenna element has a second cutout portion in which a portion of the annular arc is cut out in a linear manner. (Appendix 5) 5. The antenna device according to claim 4, wherein the first notch and the second notch are provided at positions that are 90 degrees apart from each other with respect to the center of the annular shape of the antenna element. (Appendix 6) the first portion of the first feed line has a line width different from that of a portion of the first feed line other than the first portion, 6. The antenna device according to claim 1, wherein the overlapping portion of the second feed line has a different line width from a portion of the second feed line other than the overlapping portion. (Appendix 7) a line width of the first portion of the first feed line is wider than a line width of a portion of the first feed line other than the first portion; 7. The antenna device according to claim 6, wherein the line width of the overlapping portion of the second feed line is wider than the line width of a portion of the second feed line other than the overlapping portion. (Appendix 8) 8. The antenna device according to claim 7, wherein the line width of the first portion of the first feed line is equal to the line width of the overlapping portion of the second feed line. (Appendix 9) 9. The antenna device according to claim 6, wherein the through hole connects the first portion of the first feed line and the overlapping portion of the second feed line at their ends in the line width direction. (Appendix 10) 10. The antenna device according to claim 1, wherein a length of a section along the first feed line and the second feed line from the feed terminal of the first feed line to the connection terminal of the second feed line is λe / 4, where λe is the electrical length of a wavelength of radio waves at the operating frequency of the antenna element. (Appendix 11) 11. The antenna device according to any one of claims 1 to 10, wherein the outer diameter of the antenna element corresponds to the wavelength of radio waves at the operating frequency of the antenna element. (Appendix 12) an annular substrate having a first surface and a second surface and an opening extending therethrough between the first surface and the second surface; an annular antenna element provided on the first surface and surrounding the opening; a power supply line provided on the second surface and having a connection terminal connected to a communication unit; a through hole that penetrates the substrate and connects a feed line and the antenna element; An antenna device comprising: (Appendix 13) An antenna device according to any one of Supplementary Notes 1 to 12; a strain generating element having a main body having a first end and a second end, and a through hole penetrating the main body in a direction connecting a first side on which the first end is located and a second side on which the second end is located, wherein a bolt portion of a fastening mechanism is inserted into the through hole, and the main body is inserted into the opening of the substrate; a strain sensor that detects a strain of the strain-generating body due to a fastening axial force applied in the extending direction of the through hole by the fastening mechanism; the communication unit connected to the second power supply line and the strain sensor and configured to perform wireless communication; a case that accommodates at least a portion of the main body of the strain generating body; A detection device comprising: [Explanation of symbols]

[0152] 10 Fixed part 11 Mounting surface 20 Fastening mechanism 21 Rock bolt (an example of a bolt) 22 Komanat 23 Bell Washer 30 washer 100 Detection device 100A, 100AM1, 100AM2, 100AM3 antenna equipment 110 cases 120 Strain body 121 Main body 123 Through Hole 130 Strain Sensor 140, 140M1, 140M2, 140M3 Circuit board section 150 Wiring board (example of board) 150A opening 160 antenna elements 161 Notch (example of first notch) 162 Notch (example of second notch) 170A, 170AM1, 170AM3 power feeder lines (examples of the first power feeder line) 170B, 170BM1, 170BM2, 170BM3 feeder lines (examples of second feeder lines) 170AW Widened section 170BW widening section 171A power supply terminal 171B connection terminal 172A Bend section 172B Bent part 173A End 173B End 175 through hole 180 Circuit section (example of communication section)

Claims

1. an annular substrate having a first surface and a second surface and an opening extending therethrough between the first surface and the second surface; an annular antenna element provided on the first surface and surrounding the opening; a first feed line provided on the first surface and having a feed terminal connected to the antenna element; a second feed line provided on the second surface and having a connection terminal connected to a communication unit, the second feed line having an overlapping portion that overlaps with a first portion of the first feed line in a plan view; a through hole that passes through the substrate and connects the first portion of the first feed line and the overlapping portion of the second feed line; An antenna device comprising:

2. the communication unit is connected to the second surface; The antenna device according to claim 1 , wherein the antenna element overlaps a position where the communication unit is disposed in a plan view.

3. the antenna element has a first cutout portion formed by linearly cutting out a part of the annular arc, The antenna device according to claim 1 , wherein the first feed line has a straight portion extending along the first cutout portion.

4. The antenna device according to claim 3 , wherein the antenna element has a second cutout portion formed by linearly cutting out a portion of the annular arc.

5. The antenna device according to claim 4 , wherein the first notch and the second notch are provided at positions that are different by 90 degrees with respect to the center of the annular shape of the antenna element.

6. the first portion of the first feed line has a line width different from that of a portion of the first feed line other than the first portion, The antenna device according to claim 1 , wherein the overlapping portion of the second feed line has a line width different from that of the portion of the second feed line other than the overlapping portion.

7. a line width of the first portion of the first feed line is wider than a line width of a portion of the first feed line other than the first portion; The antenna device according to claim 6 , wherein the overlapping portion of the second feed line has a line width wider than a line width of the portion of the second feed line other than the overlapping portion.

8. 8. The antenna device according to claim 7, wherein a line width of the first portion of the first feed line and a line width of the overlapping portion of the second feed line are equal.

9. The antenna device according to claim 6 , wherein the through hole connects the first portion of the first feed line and the overlapping portion of the second feed line at end portions in a line width direction.

10. 2. The antenna device according to claim 1, wherein a length of a section along the first feed line and the second feed line from the feed terminal of the first feed line to the connection terminal of the second feed line is λe / 4, where λe is the electrical length of a wavelength of a radio wave at an operating frequency of the antenna element.

11. 2. The antenna device according to claim 1, wherein the outer diameter of the antenna element corresponds to the wavelength of radio waves at the operating frequency of the antenna element.

12. an annular substrate having a first surface and a second surface and an opening extending therethrough between the first surface and the second surface; an annular antenna element provided on the first surface and surrounding the opening; a power supply line provided on the second surface and having a connection terminal connected to a communication unit; a through hole that penetrates the substrate and connects a feed line and the antenna element; An antenna device comprising:

13. The antenna device according to claim 1; a strain generating element having a main body having a first end and a second end, and a through hole penetrating the main body in a direction connecting a first side on which the first end is located and a second side on which the second end is located, wherein a bolt portion of a fastening mechanism is inserted into the through hole, and the main body is inserted into the opening of the substrate; a strain sensor that detects a strain of the strain-generating body due to a fastening axial force applied in the extending direction of the through hole by the fastening mechanism; a communication unit connected to the second power supply line and the strain sensor and configured to perform wireless communication; a case that accommodates at least a portion of the main body of the strain generating body; A detection device comprising:

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