Sensor system, seat, and sensor unit

Abstract

This sensor system includes: a power supply device which has a power transmission antenna disposed in a vehicle; a cushion body which constitutes a part of a seat disposed in the vehicle and comprises a dielectric material; a sensor which is provided to the seat; and a power reception antenna circuit which is disposed inside the cushion body, receives transmission power from the power transmission antenna, and outputs power to be supplied to the sensor.

Description

Sensor system, seat, and sensor unit

[0001] This disclosure relates to a sensor system, a seat, and a sensor unit. This application claims priority to Japanese Patent Application No. 2024-047856, filed on March 25, 2024, and incorporates by reference all of the contents of said Japanese application.

[0002] In recent years, in vehicles such as passenger cars, sensors that detect interior conditions such as the temperature inside the vehicle are often installed to improve the interior comfort of the vehicle. Supplying power to such sensors via a wired connection can lead to complex wiring and can be a factor in increasing costs and weight. Therefore, wireless power supply to the sensors has been considered. For example, Patent Literature 1 discloses a technology related to a wireless power supply system that transmits power via radio waves.

[0003] Special Publication No. 2011-525098

[0004] The sensor system of the embodiment includes a power supply device having a power transmitting antenna arranged inside a vehicle, a cushion body made of a dielectric material that forms part of a seat arranged inside the vehicle, a sensor provided on the seat, and a power receiving antenna circuit arranged inside the cushion body that receives transmitted power from the power transmitting antenna and outputs power that is provided to the sensor.

[0005] FIG. 1 is a side view showing an example of a vehicle equipped with a sensor system according to an embodiment. FIG. 2 is a diagram showing the relationship between the sensor system and various parts of the vehicle. FIG. 3 is a block diagram showing an example of the configuration of a sensor unit. FIG. 4 is a perspective view of a headrest according to the first embodiment. FIG. 5 is a cross-sectional view of the headrest. FIG. 6A is a cross-sectional view of the sensor unit. FIG. 6B is a view of the sensor unit with the cover removed, viewed from the X1 direction. FIG. 7 is a cross-sectional view of a sensor unit according to a modified example. FIG. 8 is a perspective view of a sensor unit according to another modified example. FIG. 9 is a cross-sectional view of a headrest according to a second embodiment. FIG. 10 is a diagram for explaining the position of a rectenna relative to the headrest. FIG. 11A is a graph showing changes in rectenna gain when the distance L is changed. FIG. 11B is a graph showing changes in rectenna gain when the width W is changed. FIG. 12 is a diagram for explaining the thickness of an insulating layer in a cushion body model. FIG. 13 is a graph showing changes in rectenna gain when the thickness of the insulating layer is changed. FIG. 14A is a graph showing directional characteristics of Comparative Example 1. Fig. 14B is a graph showing the directional characteristics of Example 1. Fig. 15 is a cross-sectional view of a headrest according to Comparative Example 2. Fig. 16A is a graph showing the directional characteristics of Comparative Example 2. Fig. 16B is a graph showing the directional characteristics of Example 2.

[0006] [Problem to be Solved by the Present Disclosure] When wirelessly powering a sensor, a power receiving antenna circuit is required to receive the transmitted power and provide power to the sensor. The size of the antenna element of this power receiving antenna circuit depends on the wavelength of the radio waves to be received. The frequency of the radio waves transmitted by wireless power supply is 920 GHz to several GHz. The length of the antenna element for receiving these radio waves may be approximately 150 mm. Furthermore, the placement of the antenna element may be limited by the position of the power transmitting antenna. The interior of a vehicle is relatively small, and considering the placement restrictions, it may be difficult to appropriately place the antenna element inside the vehicle.

[0007] It is possible to reduce the length of the antenna element and thereby miniaturize the power receiving antenna circuit. However, this can cause the antenna element to become omnidirectional, resulting in a problem of reduced received power. Therefore, the present disclosure aims to provide a technology that can increase the received power of a power receiving antenna circuit.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to increase the received power of a power receiving antenna circuit.

[0009] [Description of the embodiment of the present disclosure] First, the contents of the embodiment will be listed and described. [Outline of the embodiment]

[0010] (1) A sensor system according to an embodiment of the present disclosure includes a power supply device having a power transmitting antenna disposed within a vehicle, a cushion body made of a dielectric material that forms part of a seat disposed within the vehicle, a sensor provided on the seat, and a power receiving antenna circuit disposed within the cushion body that receives transmitted power from the power transmitting antenna and outputs power that is provided to the sensor.

[0011] According to the above configuration, the power receiving antenna circuit is disposed inside the cushion. Therefore, the power receiving antenna circuit receives radio waves that are emitted from the power transmitting antenna and pass through the cushion. Here, the surface of the cushion, which constitutes part of the seat, is generally convexly curved, and the cushion is made of a dielectric material. Therefore, radio waves incident on the cushion are refracted so as to be concentrated toward the interior of the cushion. In other words, the cushion functions like a dielectric lens. Therefore, by appropriately positioning the power receiving antenna circuit inside the cushion so as to increase the gain of radio waves that pass through the cushion, the received power of the power receiving antenna circuit can be increased. The sensor system may further include a transmitter that wirelessly transmits the output of the sensor. The inclusion of the transmitter allows the sensor output to be output to an external device.

[0012] (2) In the sensor system of (1), the cushion may have a main body and an internal space provided inside the main body for accommodating the power receiving antenna circuit, in which case the power receiving antenna circuit can be easily disposed inside the cushion.

[0013] (3) In the sensor system of (2), when the main body has a first surface facing the power transmitting antenna and a second surface facing the first surface, the internal space may be provided closer to the second surface. In this case, by providing the internal space closer to the second surface, a greater thickness of the main body of the cushion body interposed between the power transmitting antenna and the power receiving antenna circuit can be ensured. As a result, the received power of the power receiving antenna circuit can be more effectively increased.

[0014] (4) In the sensor system of (2) or (3), an insulating layer having a dielectric loss tangent lower than that of the dielectric material may be provided between the inner surface of the internal space and the outer surface of the power receiving antenna circuit. In this case, the provision of the insulating layer can reduce power loss due to the dielectric loss tangent of the cushion body.

[0015] (5) In the sensor system of (4), the thickness of the insulating layer may be 0.01λ or more and 0.04λ or less, where λ is the wavelength of the radio waves emitted from the power transmitting antenna. If the thickness of the insulating layer is less than 0.02λ, the power loss due to the cushion becomes relatively large, resulting in a decrease in the received power of the power receiving antenna circuit. If the thickness of the insulating layer is more than 0.05λ, the effect of reducing power loss due to the cushion becomes saturated, and the thickness of the insulating layer becomes unnecessarily large. By setting the thickness of the insulating layer to 0.02λ or more and 0.05λ or less, power loss due to the cushion can be effectively reduced.

[0016] (6) In the sensor system of (4) or (5), the insulating layer may include a polystyrene foam layer. In this case, the insulating layer can be provided by interposing polystyrene foam between the wall of the internal space and the power receiving antenna circuit.

[0017] (7) In the sensor system of (4) or (5), the insulating layer may include an air layer. In this case, the insulating layer can be provided by providing a gap between the inner surface of the internal space and the power receiving antenna circuit.

[0018] (8) In addition, the sensor system according to any one of (4) to (7) may further include a resin case that is housed in the internal space and defines the insulating layer by housing the power receiving antenna circuit therein. In this case, housing the power receiving antenna circuit in the resin case makes it possible to easily provide an insulating layer between the inner surface of the internal space and the power receiving antenna circuit.

[0019] (9) In the sensor system of (1), if the power receiving antenna circuit includes an antenna element and an antenna substrate on which the antenna element is mounted, the antenna substrate may be a flexible substrate. In this case, the antenna substrate can be deformed according to the shape of the cushion. Therefore, the antenna substrate deformed so as to increase the received power of the power receiving antenna circuit can be placed inside the cushion.

[0020] (10) In the sensor system according to any one of (1) to (9), the part of the seat may include a headrest. In this case, if the power transmitting antenna is disposed on the ceiling side of the vehicle, the power receiving antenna circuit and the power transmitting antenna can be disposed close to each other.

[0021] (11) Another embodiment is a seat disposed in a vehicle, the seat including a sensor, a cushion body made of a dielectric material, and a power receiving antenna circuit disposed inside the cushion body, receiving transmitted power from a power transmitting antenna disposed in the vehicle, and outputting the power to be provided to the sensor.

[0022] (12) Another embodiment is a sensor unit provided in a seat arranged in a vehicle, the sensor unit including a sensor, a power receiving antenna circuit that receives transmitted power from a power transmitting antenna arranged in the vehicle and outputs power to be provided to the sensor, and a resin case that has an internal storage space for storing the power receiving antenna circuit and is arranged inside a cushion made of a dielectric material that constitutes part of the seat.

[0023] According to the above configuration, the resin case that houses the power receiving antenna circuit and is placed inside the cushion body is provided, so the power receiving antenna circuit can be placed inside the cushion body made of a dielectric material, thereby increasing the received power of the power receiving antenna circuit.

[0024] (13) In the sensor unit of (12), if the power receiving antenna circuit has an antenna substrate, the sensor unit may further include a support member that is provided on the inner surface of the housing space and supports the antenna substrate at a position where a predetermined gap is provided between the antenna substrate and the inner surface. In this case, an insulating layer including an air layer can be provided between the antenna substrate and the resin case, thereby reducing power loss due to the cushioning body.

[0025] (14) In the sensor unit of (13), the support member may further include a circuit board accommodated in the accommodation space, a support post provided on the inner surface of the resin case for supporting the circuit board against the inner surface, and a wire for electrically connecting the antenna board and the circuit board. In this case, the antenna board can be supported by the circuit board, the support post, and the wire.

[0026] (15) The sensor unit of (12) may further include a line that physically connects the sensor to the resin case that is separate from the sensor and supplies power from the resin case to the sensor. In this case, since the sensor and the resin case are separate via the line, the sensor can be disposed outside the cushion body while the power receiving antenna circuit is disposed inside the cushion body.

[0027] [Details of the embodiment] Preferred embodiments will be described below with reference to the drawings. Note that at least some of the embodiments described below may be combined in any manner. [Overall configuration] Fig. 1 is a side view showing an example of a vehicle equipped with a sensor system according to an embodiment. In Fig. 1, a portion of the vehicle 1 is cut away to show the interior of the passenger compartment 1a. In Fig. 1, the vehicle 1 is a vehicle (passenger car) including an electric vehicle, an internal combustion engine vehicle, a hybrid vehicle, etc.

[0028] The sensor system 4 provided in the vehicle 1 is a system that detects the condition inside the vehicle cabin 1a using sensors arranged inside the vehicle cabin 1a. The sensor system 4 has a power supply device 6 and multiple sensor units 8. Note that the sensor system 4 may have only one sensor unit 8. When the sensor system 4 has multiple sensor units 8, the sensor units 8 can be arranged at multiple locations inside the vehicle cabin 1a. The power supply device 6 is installed on the ceiling surface 1a1 inside the vehicle cabin 1a. The power supply device 6 has a power transmission antenna 6a. The power supply device 6 wirelessly supplies power to the multiple sensor units 8 by emitting power supply radio waves from the power transmission antenna 6a inside the vehicle cabin 1a.

[0029] Each of the multiple sensor units 8 includes a sensor that detects the condition inside the vehicle interior 1a. The sensor unit 8 has a function of wirelessly transmitting output information indicating the output of the sensor. The sensor unit 8 also has a function of receiving radio waves for power supply from the power supply device 6 and converting the radio waves into electric power. The sensor unit 8 is configured to operate using the electric power supplied from the power supply device 6. Therefore, the sensor unit 8 can be powered and operated without being connected to other external devices via a wire. The configuration of the sensor unit 8 will be described in detail later.

[0030] The plurality of sensor units 8 are provided in the plurality of seats 10 in the vehicle interior 1a. Each of the plurality of seats 10 has a seat portion 11 including a seat portion and a backrest portion, and a headrest 12. In this embodiment, the sensor unit 8 is provided in the headrest 12. The headrest 12 has the sensor unit 8 built in. In other words, the headrest 12 can also be said to be a sensor in the sensor system 4.

[0031] The vehicle 1 includes a power supply 14 and an ECU (Electronic Control Unit) 16. The power supply 14 is, for example, a secondary battery, and may include a lead-acid battery, a lithium-ion battery, a nickel-metal hydride battery, or a capacitor. The power supply 14 supplies power to the power feeding device 6. The power supply 14 also supplies power to each component of the vehicle 1. The power supply 14 may also store power generated by an alternator or a motor. The ECU 16 has a function of performing processing related to the control of each component of the vehicle 1. As will be described later, the processing includes processing that uses output information from the sensor unit 8.

[0032] 2 is a diagram showing the relationship between the sensor system 4 and each part of the vehicle 1. As shown in FIG. 2, the power supply 14 is connected to the power feeding device 6. The power feeding device 6 is supplied with power from the power supply 14. The power feeding device 6 generates a power feeding signal based on the power supplied from the power supply 14 and supplies the signal to the power transmitting antenna 6a. The power transmitting antenna 6a emits the power feeding signal as a power feeding radio wave and transmits it to the multiple sensor units 8.

[0033] The sensor units 8 detect the state inside the vehicle interior 1 a using the power obtained by receiving the power supply radio waves and wirelessly transmit output information indicating the output of the sensors. The sensor units 8 receive the power supply radio waves inside the headrest 12.

[0034] The vehicle 1 further includes a receiver 18. The receiver 18 is disposed in the passenger compartment 1a. The receiver 18 receives output information transmitted from the plurality of sensor units 8 and provides the output information to the ECU 16. When the output information is provided to the ECU 16, the ECU 16 controls the state of the passenger compartment 1a based on the output information. For example, the ECU 16 controls an air conditioner installed in the vehicle 1 based on the output information.

[0035] 3 is a block diagram showing an example of the configuration of the sensor unit 8. As shown in FIG. 3, the sensor unit 8 includes a rectenna 20, a power control circuit 22, a sensor 24, and a transmitter 26.

[0036] The rectenna 20 has a receiving antenna 20a and a rectifier circuit 20b. The receiving antenna 20a receives radio waves for power supply from the power supply device 6. The receiving antenna 20a provides an electrical signal generated by the received radio waves to the rectifier circuit 20b. The rectifier circuit 20b rectifies the electrical signal provided by the receiving antenna 20a, converts it into DC power, and outputs the converted DC power. In other words, the rectenna 20 constitutes a receiving antenna circuit that receives transmitted power from the transmitting antenna 6a and outputs the power. The DC power output by the rectifier circuit 20b is provided to the power control circuit 22.

[0037] Power control circuit 22 has the function of converting the DC power provided from rectenna 20 to a predetermined voltage and providing the converted power to sensor 24 and transmitter 26. Power control circuit 22 also has the function of storing or discharging the DC power provided from rectenna 20 and controlling the power provided to sensor 24 and transmitter 26. Power control circuit 22 may provide power to sensor 24 and transmitter 26 continuously, or may provide power to sensor 24 and transmitter 26 periodically.

[0038] As described above, the sensor 24 is a sensor for detecting conditions inside the vehicle compartment 1a. More specifically, the sensor 24 includes a temperature sensor, a humidity sensor, an acceleration sensor, an illuminance sensor, etc. The sensor 24 has a function of detecting conditions inside the vehicle compartment 1a, such as temperature, humidity, acceleration (vibration), and illuminance. When DC power is supplied from the power control circuit 22, the sensor 24 provides an output indicating the results of the detection of the conditions inside the vehicle compartment 1a to the transmitter 26.

[0039] The transmitter 26 has a transmission antenna 26a. The transmitter 26 has a function of performing wireless communication with the receiver 18 on the vehicle 1 side via the transmission antenna 26a. The transmitter 26 wirelessly transmits the output provided from the sensor 24 as output information. When DC power is provided from the power control circuit 22, the transmitter 26 establishes a communication connection with the receiver 18 and starts wireless transmission of the output information.

[0040] For example, when the main switch of the vehicle 1 is turned on, the power supply device 6 starts wirelessly supplying power to the plurality of sensor units 8. As a result, the plurality of sensor units 8 receive transmitted power from the power supply device 6. When power is supplied from the power supply device 6, the sensors 24 of each of the plurality of sensor units 8 start detecting the condition inside the vehicle interior 1a and outputting the detection results. Furthermore, the transmitter 26 establishes a communication connection with the receiver 18 and starts wirelessly transmitting output information. Note that when DC power is supplied, the transmitter 26 starts wirelessly transmitting the output information, and may continue transmitting while power is being supplied.

[0041] The output information transmitted by the transmitter 26 is received by the receiver 18 and provided to the ECU 16. The ECU 16 obtains information indicating the state of the vehicle interior 1 a from the output information. The ECU 16 performs control related to the state of the vehicle interior 1 a based on the obtained information indicating the state of the vehicle interior 1 a.

[0042] [Regarding the headrest 12 according to the first embodiment] Figure 4 is a perspective view of the headrest 12 according to the first embodiment. In the following description, in each drawing, three mutually orthogonal directions are referred to as the X direction, the Y direction, and the Z direction. As shown in Figure 1, one of the X directions is referred to as the X1 direction, and the opposite direction of the X1 direction is referred to as the X2 direction. One of the Y directions is referred to as the Y1 direction, and the opposite direction of the Y1 direction is referred to as the Y2 direction. One of the Z directions is referred to as the Z1 direction, and the opposite direction of the Z1 direction is referred to as the Z2 direction. The X direction is the front-to-rear direction, the Y direction is the left-to-right direction, and the Z direction is the up-down direction. The Z1 direction is the upward direction, the X1 direction is the direction toward the front of the vehicle 1, and the Y1 direction is the direction toward the left when viewed from a passenger facing the front of the vehicle 1.

[0043] The headrest 12 is a rounded, pillow-shaped member. The top surface 12a and bottom surface 12b of the headrest 12 are substantially parallel to the Y direction. The top surface 12a, the front surface 12c on the X1 side, the rear surface 12d on the X2 side, the left surface 12e on the Y1 side, and the right surface 12f on the Y2 side of the headrest 12 are convexly curved. The term "convexly curved surface" as used herein refers to a surface that is convexly curved as a whole. Even if the cross-sectional contour shape between a pair of opposing sides among the four sides defining the surface is linear, the cross-sectional contour shape between the remaining pair of sides may be convexly curved. The shape of the headrest 12 is not limited to the shape shown in FIG. 4 as long as it functions as a headrest.

[0044] Fig. 5 is a cross-sectional view of the headrest 12. Fig. 5 shows a cross section parallel to the X-Z plane. The outline shape of the cross section of the headrest 12 parallel to the X-Z plane has a trapezoidal shape in which each side is expanded outward by a convex curve. As shown in Figs. 4 and 5, the headrest 12 includes a sensor unit 8, a frame 28, a cushion body 32, and a cover 34.

[0045] The frame 28 is a gate-shaped member made of steel pipes or the like. The frame 28 has a frame main body 28b disposed inside the headrest 12 and a pair of protrusions 28a protruding from the lower surface 12b. The pair of protrusions 28a are inserted into the upper end of the backrest of the seat portion 11 of the seat 10. In this way, the headrest 12 is fixed to the upper end of the backrest.

[0046] The cushion body 32 is a member made of, for example, a dielectric material. In this embodiment, polyurethane is used as the dielectric material. The cushion body 32 has elasticity. The cushion body 32 is a buffer member when the occupant's head comes into contact with the headrest 12. The cushion body 32 forms the overall shape of the headrest 12. Therefore, the cushion body 32 is a rounded, pillow-shaped member. The top, front, rear, left, and right surfaces of the cushion body 32 have convex curved surfaces. The cover 34 covers the outer surface of the cushion body 32.

[0047] 5 , the cushion body 32 has a main body 36, a first internal space 38, and a second internal space 40. The main body 36 is a member made of polyurethane and forms the overall shape of the cushion body 32. The internal spaces 38, 40 are spaces provided inside the main body 36.

[0048] The frame main body 28b is housed in the first internal space 38. The first internal space 38 is formed in a shape corresponding to the outer shape of the frame main body 28b. The inner surface of the first internal space 38 abuts against the frame main body 28b. This restricts movement of the frame main body 28b within the first internal space 38. Therefore, the frame main body 28b is held inside the cushion body 32. In other words, the cushion body 32 is held by the frame main body 28b.

[0049] The second internal space 40 accommodates the sensor unit 8. In this embodiment, the sensor unit 8 has one surface parallel to the Y-Z plane. This surface is rectangular with long and short sides. Therefore, the sensor unit 8 has a rectangular parallelepiped shape. Therefore, the second internal space 40 is formed in a rectangular parallelepiped shape according to the outer shape of the sensor unit 8. Furthermore, the inner surface 40a of the second internal space 40 abuts against the sensor unit 8. This restricts the movement of the sensor unit 8 within the second internal space 40. Therefore, the sensor unit 8 is held inside the cushion body 32. Note that in this embodiment, the sensor unit 8 is held inside the cushion body 32 with the short side aligned along the Z direction and the long side aligned along the Y direction, as shown in FIG. 4 . Furthermore, the internal spaces 38, 40 may be spaces formed by hollowing out the material of the main body portion 36, or may be spaces formed by making a slit in the material of the main body portion 36, placing the frame main body 28b and the sensor unit 8 in the slit, and elastically expanding the slit.

[0050] The second internal space 40 is provided closer to the lower surface 36b of the main body 36. The second internal space 40 is also provided lower than the vertical center of the main body 36. Therefore, the sensor unit 8 is held closer to the lower surface 36b inside the main body 36. The sensor unit 8 is also held lower than the vertical center inside the main body 36.

[0051] [Regarding the sensor unit 8] Fig. 6A is a cross-sectional view of the sensor unit 8. Fig. 6A shows a cross section parallel to the XY plane when the sensor unit 8 is disposed in the headrest 12. In other words, Fig. 6A explains each part of the sensor unit 8 based on each direction when a circuit board 44, a bottom surface 46a1, etc., which will be described later, are disposed along the YZ plane.

[0052] 6A , in addition to the rectenna 20, the sensor unit 8 includes a circuit board 44 and a resin case 46. The resin case 46 is a rectangular parallelepiped member formed using ABS resin, POM resin, polystyrene foam, or the like. The resin case 46 includes a case body 46a and a lid 46b. The resin case 46 forms the outer shape of the sensor unit 8. Therefore, when the sensor unit 8 is housed in the second internal space 40, the resin case 46 comes into contact with the inner surface 40a of the second internal space 40. The rectenna 20 and the circuit board 44 are housed inside the resin case 46. In other words, the space inside the resin case 46 is a housing space that houses the rectenna 20 and the circuit board 44.

[0053] The circuit board 44 is a rigid board on which the power control circuit 22, sensor 24, and transmitter 26 are mounted. The circuit board 44 has a rectangular plate shape. The circuit board 44 is fixed to the bottom surface 46a1 by support posts 48. The bottom surface 46a1 is the inner surface of the case body 46a and faces the X1 direction. The bottom surface 46a1 has a rectangular shape. The bottom surface 46a1 also extends along the YZ plane. The support posts 48 are provided to protrude from the bottom surface 46a1 of the case body 46a. The support posts 48 support the circuit board 44 against the bottom surface 46a1. At this time, the circuit board 44 is supported so as to extend along the YZ plane. A predetermined distance is provided between the case body 46a (bottom surface 46a1) and the circuit board 44. A predetermined distance is also provided between the cover surface 46b1 of the lid 46b and the circuit board 44. The cover surface 46b1 is the inner surface of the cover 46b and faces in the X2 direction. The cover surface 46b1 has a rectangular shape and is aligned along the YZ plane.

[0054] 6B is a view of the sensor unit 8 when the lid 46b is removed, as viewed from the X1 direction. As shown in FIG. 6B, the rectenna 20 has an antenna substrate 50, a power receiving antenna 20a, and a circuit chip 52. The circuit chip 52 is a circuit chip that includes a rectifier circuit 20b. The antenna substrate 50 is a rectangular, rigid substrate. The antenna substrate 50 is disposed along the YZ plane. The power receiving antenna 20a and the circuit chip 52 are mounted on a first surface 50a of the antenna substrate 50. The first surface 50a is the surface of the antenna substrate 50 that faces the lid 46b and faces the X1 direction.

[0055] The power receiving antenna 20a includes an antenna element 20a1 and a pair of lines 20a2. The antenna element 20a1 and the pair of lines 20a2 are metal foils, such as copper foils, patterned on the first surface 50a. The antenna element 20a1 has a C-shaped loop. Therefore, the power receiving antenna 20a of this embodiment constitutes a loop antenna. When the sensor unit 8 is placed inside the headrest 12, the center C of the antenna element 20a1 is located at the center of the headrest 12 in the Y direction. As a result, the antenna element 20a1 is located at the center of the headrest 12 in the Y direction. The pair of lines 20a2 connect both ends of the antenna element 20a1 to the circuit chip 52.

[0056] The power receiving antenna 20a of the rectenna 20 of this embodiment is a relatively small, high-impedance loop antenna. The impedance of the power receiving antenna 20a is designed to match the impedance of the rectifier circuit 20b. In this way, the rectenna 20 of this embodiment is made compact by employing a small, high-impedance loop antenna. For example, the diameter of the antenna element 20a1 of the rectenna 20 of this embodiment is several tens of millimeters. However, because the antenna element 20a1 is small, the rectenna 20 is omnidirectional.

[0057] The circuit chip 52 is connected to the power control circuit 22 mounted on the circuit board 44. The antenna board 50 and the circuit board 44 are electrically connected by a pair of wires 54. The pair of wires 54 connect the circuit chip 52 and the power control circuit 22 of the circuit board 44.

[0058] The ends of the pair of wires 54 on the antenna substrate 50 side are fixed to the edge of the first surface 50a of the antenna substrate 50 on the Y1 direction side. The ends of the pair of wires 54 on the circuit substrate 44 side are fixed to the edge of the board surface 44a of the circuit board 44 on the Y2 direction side. In this way, the pair of wires 54 connect the edge of the antenna substrate 50 and the edge of the circuit board 44.

[0059] Furthermore, the pair of wires 54 support the antenna board 50 so that it does not come into contact with the resin case 46. In other words, the circuit board 44, the support posts 48, and the pair of wires 54 constitute a support member 47. The support member 47 supports the antenna board 50 so that it does not come into contact with the resin case 46. The support member 47 provides a predetermined gap between the first surface 50a of the antenna board 50 and the cover surface 46b1. A predetermined gap is also provided between the second surface 50b of the antenna board 50 and the bottom surface 46a1. The second surface 50b is the surface of the antenna board 50 that faces the case body 46a and faces in the X2 direction.

[0060] As a result, an insulating layer 56 ( FIG. 6A ) is provided between the rectenna 20 (power receiving antenna circuit) and the inner surface 40 a of the second internal space 40. This insulating layer 56 is an air layer. In this manner, the resin case 46 is housed in the second internal space 40, and the insulating layer 56 is defined by housing the rectenna 20 inside. Since the system 4 of the present embodiment includes the resin case 46, housing the rectenna 20 in the resin case 46 makes it possible to easily provide the insulating layer 56 between the inner surface 40 a of the second internal space 40 and the rectenna 20.

[0061] As described above, the insulating layer 56 is an air layer. Therefore, the insulating layer 56 has a lower dielectric tangent than polyurethane, which is the material of the cushion body 32. For this reason, it is possible to reduce the loss of received power of the rectenna 20 caused by the dielectric tangent of the cushion body 32, compared to when the rectenna 20 and the main body 36 of the cushion body 32 are in direct contact with each other, for example.

[0062] Furthermore, when the wavelength of the radio waves emitted from the power transmitting antenna 6a is λ, the thickness t of the insulating layer 56 may be set to 0.02λ or more and 0.05λ or less. The thickness t includes the thickness t1 between the first surface 50a and the cover surface 46b1 and the thickness t2 between the second surface 50b and the bottom surface 46a1. The insulating layer 56 is present at least on the outer surfaces (the first surface 50a and the second surface 50b) of the antenna substrate 50. If the thickness t is less than 0.02λ, the power loss due to the cushion body 32 becomes relatively large, resulting in a decrease in the received power of the rectenna 20. If the thickness t is greater than 0.05λ, the effect of reducing power loss due to the cushion body 32 becomes saturated, the thickness of the resin case 46 becomes unnecessarily large, and it becomes difficult to properly position the resin case 46 within the headrest 12. By setting the thickness t to 0.02λ or more and 0.05λ or less, power loss due to the cushion body 32 can be effectively reduced. Furthermore, the resin case 46 can be made relatively compact, facilitating appropriate placement within the headrest 12 .

[0063] According to the above configuration, the rectenna 20 (power receiving antenna circuit) is disposed inside the cushion body 32. Therefore, the rectenna 20 receives radio waves that are radiated from the power transmitting antenna 6a and pass through the cushion body 32. Here, the surface of the cushion body 32 of the headrest 12 is a convex curved surface as a whole, and the cushion body 32 is made of a dielectric material. Therefore, radio waves incident on the cushion body 32 are refracted so as to be concentrated toward the inside of the cushion body 32. In other words, the cushion body 32 functions like a dielectric lens. As a result, by appropriately setting the position of the rectenna 20 inside the cushion body 32 so that the gain of radio waves that pass through and reach the cushion body 32 is high, the received power of the rectenna 20 can be increased.

[0064] Furthermore, with the above configuration, the received power of the rectenna 20 can be increased, which makes it possible to reduce the power transmitted by the power feeding device 6 and improve the power consumption of the vehicle 1 equipped with the present system 4. Furthermore, interference with wireless communication systems other than the present system 4 can be reduced.

[0065] Furthermore, since the cushion body 32 of this embodiment has the main body portion 36 and the second internal space 40 , the sensor unit 8 including the rectenna 20 can be easily disposed inside the cushion body 32 .

[0066] Furthermore, in this embodiment, the power transmitting antenna 6a is provided directly above the headrest 12 on the ceiling surface 1a1. Therefore, the upper surface 36a (first surface) of the main body 36 is located on the power transmitting antenna 6a side. The lower surface 36b (second surface) of the main body 36 faces the upper surface 36a. The second internal space 40 is provided closer to the lower surface 36b than to the upper surface 36a. This ensures that the main body 36 has a greater thickness between the power transmitting antenna 6a and the rectenna 20. As a result, the received power of the rectenna 20 can be more effectively increased. Furthermore, because the cushion body 32 of this embodiment constitutes the headrest 12, which is part of the seat 10, the rectenna 20 and the power transmitting antenna 6a can be positioned close to each other.

[0067] In the present embodiment, the insulating layer 56 is an air layer. However, the insulating layer 56 only needs to have a dielectric loss tangent lower than that of polyurethane, which is the material of the cushion body 32. Therefore, the insulating layer 56 may be, for example, a polystyrene foam layer. A polystyrene foam layer has a dielectric loss tangent lower than that of polyurethane. Therefore, even when the insulating layer 56 is a polystyrene foam layer, the loss of received power of the rectenna 20 caused by the dielectric loss tangent of the cushion body 32 can be reduced.

[0068] 7, when the insulating layer 56 is a polystyrene foam layer, the insulating layer 56 can be composed of a first member 56a and a second member 56b. The first member 56a and the second member 56b are members formed of polystyrene foam. The first member 56a is disposed on the X2 side of the rectenna 20 and abuts against the second surface 50b of the antenna substrate 50. The second member 56b is disposed on the X1 side of the rectenna 20 and abuts against the first surface 50a of the antenna substrate 50. The rectenna 20 and the circuit board 44 are sandwiched and held between the first member 56a and the second member 56b.

[0069] In this case, the insulating layer 56 contacts the inner surface 40a of the second internal space 40 and the rectenna 20. Therefore, the sensor unit 8 having the insulating layer 56 can be configured without using the above-described resin case 46. In this way, by omitting the resin case 46, the configuration of the sensor unit 8 can be simplified.

[0070] In addition, the resin case 46 of the sensor unit 8 of this embodiment has been exemplified as housing the rectenna 20 and the sensor 24. However, the sensor 24 may be provided outside the resin case 46. For example, as shown in FIG. 8 , the sensor unit 8 may include a line 60 connecting the sensor 24 to the resin case 46. The resin case 46 houses the rectenna 20 and the circuit board 44. The power control circuit 22 and the transmitter 26, other than the sensor 24, are mounted on the circuit board 44. The line 60 is a line for supplying power from the resin case 46 side to the sensor 24 and for providing the output of the sensor 24 to the resin case 46 side.

[0071] In this case, the sensor 24 and the resin case 46 are separate bodies. The sensor 24 and the resin case 46 are physically connected via the line 60. Therefore, the rectenna 20 can be disposed inside the cushion body 32, while the sensor 24 can be disposed outside the cushion body 32. This allows the sensor 24 to be disposed in an environment more suitable for detecting the state inside the vehicle interior 1a, thereby improving the accuracy of the sensor 24.

[0072] [Headrest 12 According to Second Embodiment] Figure 9 is a cross-sectional view of a headrest 12 according to a second embodiment. This embodiment differs from the first embodiment in that the antenna substrate 50 included in the rectenna 20 is an FPC (Flexible Printed Circuit) and the rectenna 20 is curved. Furthermore, the sensor unit 8 of this embodiment includes a resin case 62 that houses the circuit board 44, and differs from the first embodiment in that the rectenna 20 and the resin case 62 containing the circuit board 44 are separate bodies.

[0073] In this embodiment, the second internal space 40 is provided closer to the upper surface 36a of the main body 36. The second internal space 40 is also curved to follow the shape of the upper surface 36a. Therefore, the rectenna 20 is held closer to the upper surface 36a inside the main body 36. The rectenna 20 is also held above the frame main body 28b (frame 28). Furthermore, the antenna substrate 50 of the rectenna 20 is curved to follow the shape of the upper surface 36a in accordance with the shape of the second internal space 40.

[0074] An insulating layer 56 is provided between the rectenna 20 and the inner surface 40a of the second internal space 40. The insulating layer 56 is a polystyrene foam layer. The insulating layer 56 is composed of a first member 56a and a second member 56b, both made of polystyrene foam. The rectenna 20 is sandwiched and held between the first member 56a and the second member 56b. The first member 56a and the second member 56b are curved to follow the shape of the upper surface 36a in accordance with the shape of the second internal space 40. Therefore, the first member 56a and the second member 56b hold the antenna substrate 50 while bending the antenna substrate 50.

[0075] As described above, the sensor unit 8 of this embodiment includes the resin case 62 that houses the circuit board 44. The resin case 62 is housed in the third internal space 41. The third internal space 41 is a space provided on the rear surface 36d side of the main body 36. The third internal space 41 is exposed at the rear surface 36d. Therefore, the resin case 62 housed in the third internal space 41 is also exposed. This allows the sensor 24 mounted on the circuit board 44 to be placed in an environment more suitable for detecting conditions inside the vehicle interior 1a. As a result, the accuracy of the sensor 24 is improved.

[0076] Resin case 62 and rectenna 20 are connected by lines 64. DC power output by rectenna 20 is applied via lines 64 to each component mounted on circuit board 44.

[0077] In this embodiment, because the antenna substrate 50 is an FPC, it is possible to deform the antenna substrate 50 according to the shape of the cushion body 32 (main body 36). Therefore, the antenna substrate 50 deformed so as to increase the received power of the rectenna 20 can be placed inside the cushion body 32. Furthermore, in this embodiment, because the rectenna 20 is held closer to the upper surface 36a of the main body 36, it can be placed closer to the power transmitting antenna 6a.

[0078] [Others] In the above embodiments, the sensor unit 8 is provided only in the headrest 12 of the seat 10, but the sensor unit 8 may be provided inside a cushion that constitutes part of the seat 10. More specifically, the sensor unit 8 may be provided in the seat portion or backrest portion of the seat 10 that is included in the seat portion 11 that has a cushion made of a dielectric material.

[0079] Furthermore, while the above embodiments have exemplified cases in which sensor unit 8 is provided near the top and bottom of cushion body 32, sensor unit 8 may simply be disposed inside main body 36 of cushion body 32, thereby increasing the reception power of rectenna 20. Furthermore, while the above embodiments have exemplified cases in which main body 36 of cushion body 32 is formed from polyurethane, a dielectric material other than polyurethane may also be used.

[0080] In the first embodiment described above, the antenna substrate 50 of the rectenna 20 is arranged along the Y-Z plane, but the antenna substrate 50 may be arranged along the X-Y plane or the X-Z plane. In this case, as in the first embodiment, the received power of the rectenna 20 can be increased. Furthermore, in each of the above embodiments, the power receiving antenna 20a of the rectenna 20 constitutes a loop antenna, but the power receiving antenna 20a may be another antenna, such as a dipole antenna or a planar antenna.

[0081] [Verification Tests] Next, verification tests conducted on the effects of this system 4 will be described. The test method involved constructing a model of the headrest 12 and rectenna 20 provided in this system 4, and performing computer simulations to determine and evaluate the numerical values ​​to be evaluated. The four tests conducted are described below. Test 1: Verification of the optimal position of the rectenna 20 relative to the headrest 12 Test 2: Verification of the thickness of the insulating layer 56 Test 3: Evaluation of the directional characteristics of the rectenna 20 according to the first embodiment Test 4: Evaluation of the directional characteristics of the rectenna 20 according to the second embodiment

[0082] [Regarding Test 1] In Test 1, a model of the headrest 12 according to the first embodiment was used to determine the change in gain of the rectenna 20 when the relative position of the rectenna 20 with respect to the headrest 12 was changed. In Test 1, the gain was determined when power was supplied by radio waves with a frequency of 920 MHz. Note that the power transmitting antenna 6a was positioned directly above the headrest 12 in the Z direction.

[0083] Fig. 10 is a diagram illustrating the position of the rectenna 20 relative to the headrest 12. In Fig. 10, distance L is the distance in the Z direction from the upper surface 12a (upper surface 36a) to the center C of the antenna element 20a1. Width W is the dimension of the headrest 12 (cushion body 32) in the Y direction. Note that the diameter D of the antenna element 20a1 of the rectenna 20 was set to 40 mm, and the maximum dimension of the headrest 12 in the X direction was set to 30 mm.

[0084] In Test 1, the change in gain of rectenna 20 when the distance L and width W were changed was determined by simulation. When the distance L was changed, the width W was set to 150 mm. The position of rectenna 20 in the X direction was set as follows. First, rectenna 20 was placed at the center of headrest 12 in the X direction, and the distance L at which the gain of rectenna 20 was maximized was determined. Then, the distance L was fixed, and the position of rectenna 20 in the X direction at which the gain of rectenna 20 was maximized was determined. This determined position was used as the reference position of rectenna 20 in the X direction, and the distance L and width W were changed. When the width W was changed, the distance L was set to 130 mm.

[0085] Fig. 11A is a graph showing the change in gain of the rectenna 20 when the distance L is changed. In Fig. 11A, the horizontal axis represents the distance L, and the vertical axis represents the gain. In Fig. 11A, graph g1 shows the change in gain of the Y-direction component in the Z-axis direction. Graph g2 shows the change in gain of the X-direction component in the Z-axis direction. Graph g3 shows the gain of the rectenna 20 when there is no cushion body 32 around it. The position of the rectenna 20 when there is no cushion body 32 around it is the same as the position of the rectenna 20 disposed within the headrest 12 of the first embodiment.

[0086] 11A, when the distance L is 80 mm or more, the gain in the Y direction is higher than the gain of the rectenna 20 alone. Also, when the distance L is less than 130 mm, the gain in the X direction is lower than the gain of the rectenna 20 alone. However, when the distance L is greater than 130 mm, the gain in the X direction is higher than the gain of the rectenna 20 alone.

[0087] 11B is a graph showing the change in gain of rectenna 20 when width W is changed. In FIG. 11B, the horizontal axis represents width W, and the vertical axis represents gain. In FIG. 11B, graph g4 shows the change in gain in the Y direction. Graph g5 shows the change in gain in the X direction. Graph g6 shows the gain when rectenna 20 alone is placed in the same position.

[0088] In Test 1, as shown in Figure 11B, when the width W is 100 mm or more, the gain in the Y direction is higher than the gain of the rectenna 20 alone. Also, when the width W is less than 150 mm, the gain in the X direction is lower than the gain of the rectenna 20 alone. However, when the width W is greater than 150 mm, the gain in the X direction is higher than the gain of the rectenna 20 alone.

[0089] From these, it can be seen that the gain (received power) of the rectenna 20 can be increased by placing the rectenna 20 inside the headrest 12 (cushion body 32). Furthermore, it can be seen that the gain of the rectenna 20 can be further increased if the distance L is greater than 130 mm. It can also be seen that the gain of the rectenna 20 can be further increased if the width W is greater than 150 mm.

[0090] [Regarding Test 2] In Test 2, a pseudo cushion body model was used to determine the change in gain of rectenna 20 when the thickness t of insulating layer 56 was changed. In Test 2, the thickness t of the portion of insulating layer 56 facing the outer surfaces (first surface 50 a and second surface 50 b) of antenna substrate 50 was changed.

[0091] FIG. 12 is a diagram illustrating the thickness t of the insulating layer 56 within the cushion body model. The cushion body model R includes a main body 100 and an internal space 140. The main body 100 corresponds to the main body 36 of the headrest 12. The main body 100 has a cubic shape with sides measuring 200 mm. The internal space 140 corresponds to the second internal space 40 of the headrest 12. The internal space 140 accommodates the rectenna 20. The insulating layer 56 is provided between the rectenna 20 (the antenna substrate 50 thereof) and the inner surface 140a of the internal space 140. In Test 2, the insulating layer 56 was an air layer. In Test 2, the resin case 46 was omitted, as shown in FIG. 12, and only the insulating layer 56 (air layer) was present between the inner surface 140a and the first surface 50a (second surface 50b) of the antenna substrate 50. In this example, the frequency of the radio wave for power supply from the power transmission antenna 6a is set to 920 MHz.

[0092] Figure 13 is a graph showing the change in gain of rectenna 20 when the thickness t of insulating layer 56 is changed. In Figure 13, the horizontal axis represents the thickness t of insulating layer 56, and the vertical axis represents the gain. The dashed line in Figure 13 indicates the gain level for rectenna 20 alone. The gain for rectenna 20 alone is 1.21.

[0093] As shown in Figure 13, when the thickness t is 0 (when the cushion body 32 and the rectenna 20 are in contact), the gain is 0.25 dBi. However, as the thickness t increases, the gain increases and gradually approaches the gain of the rectenna 20 alone. When the thickness t is 4 mm, the gain is approximately 1 dBi. Furthermore, when the thickness t exceeds 10 mm, the gain becomes sufficiently close to the gain of the rectenna 20 alone. In other words, when the thickness t exceeds 10 mm, the gain becomes saturated. Therefore, it can be said that if the thickness t is 4 mm or more and 10 mm or less, the loss of received power of the rectenna 20 due to the cushion body 32 can be reduced.

[0094] Here, if the wavelength of the power supply radio wave is λ and the thickness t is expressed as 0.012λ, since the power supply frequency is 920 MHz, 4 mm is expressed as 0.012λ. Similarly, 10 mm is expressed as 0.04λ. In other words, the results of Test 2 show that power loss due to the cushion body 32 can be effectively reduced by setting the thickness t to be equal to or greater than 0.01λ and equal to or less than 0.04λ.

[0095] [Regarding Test 3] In Test 3, a model of the headrest 12 according to the first embodiment was used, and the rectenna 20 (sensor unit 8) when the distance L was 35 mm, the width W was 180 mm, and the thickness t of the insulating layer 56 was 2 mm was used as Example 1, and the rectenna 20 when there was no cushion body 32 around it was used as Comparative Example 1, and the directional characteristics of the two were compared. The position of the rectenna 20 when there was no cushion body 32 around it was the same as the position of the rectenna 20 in Example 1.

[0096] Fig. 14A is a graph showing the directional characteristics of Comparative Example 1. Fig. 14B is a graph showing the directional characteristics of Example 1. Arrow Z in Figs. 14A and 14B indicates the Z1 direction, and arrow X indicates the X1 direction. Figs. 14A and 14B show the directional characteristics of a polarized component along the X direction in the X-Z plane (hereinafter also referred to as the X-axis component), and the directional characteristics of a polarized component along the Y direction in the X-Z plane (hereinafter also referred to as the Y-axis component).

[0097] In Fig. 14A, graph g7 shows the directional characteristics of the Y-axis component, and graph g8 shows the directional characteristics of the X-axis component. Graph g7 and graph g8 overlap. In Fig. 14B, graph g9 shows the directional characteristics of the Y-axis component, and graph g10 shows the directional characteristics of the X-axis component.

[0098] As shown in Fig. 14B, the directional characteristics of Example 1 are improved in the Z1 direction compared to the directional characteristics of Comparative Example 1. That is, the directional characteristics of Example 1 are improved in the direction toward the power transmitting antenna 6a. More specifically, in Fig. 14B, the gain in the Z1 direction of the X-axis component is improved by about 3 dB compared to the gain of Comparative Example 1 (Fig. 14A). Also, in Fig. 14B, the gain in the Z1 direction of the Y-axis component is improved by about 1 dB compared to the gain of Comparative Example 1.

[0099] The above results show that the received power of rectenna 20 is increased in Example 1. In addition, as shown in FIG. 14B, it can be seen that rectenna 20 according to Example 1 is capable of receiving both the X-axis component and the Y-axis component.

[0100] [Regarding Test 4] In Test 4, the rectenna 20 when using the model of the headrest 12 according to the second embodiment was designated as Example 2, and the rectenna 20 without a curved shape was designated as Comparative Example 2, and the directional characteristics of both were compared.

[0101] Fig. 15 is a cross-sectional view of a headrest 12 according to Comparative Example 2. The sensor unit 8 shown in Fig. 15 differs from the sensor unit 8 of the second embodiment shown in Fig. 9 only in that the rectenna 20 is planar along the XY plane and does not have a curved shape.

[0102] FIG. 16A is a graph showing the directional characteristics of Comparative Example 2. FIG. 16B is a graph showing the directional characteristics of Example 2. In FIGS. 16A and 16B, arrow Z indicates the Z1 direction, and arrow X indicates the X1 direction. As shown in FIG. 16B, the directional characteristics of Example 2 are improved in the Z1 direction compared to the directional characteristics of Comparative Example 2. That is, the directional characteristics of Example 2 are improved in the direction toward the power transmitting antenna 6a. More specifically, in FIG. 16B, the gain in the Z1 direction is improved by about 1 dB compared to the gain of Comparative Example 2 ( FIG. 16A ). Also, in FIG. 16B, the gain of Example 2 is improved compared to the gain of Comparative Example 2 ( FIG. 16A ) in a range of 60 degrees on both sides of the Z1 direction.

[0103] From the above results, it can be seen that in Example 2, the received power of the rectenna 20 is increased over a wide range in the front-to-rear direction.

[0104] [Conclusion] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the meaning described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0105] REFERENCE SIGNS LIST 1 vehicle 1a vehicle interior 1a1 ceiling surface 4 sensor system 6 power supply device 6a power transmitting antenna 8 sensor unit 10 seat 11 seat portion 12 headrest 12a upper surface 12b lower surface 12c front surface 12d rear surface 12e left surface 12f right surface 14 power supply 16 ECU 18 receiver 20 rectenna (power receiving antenna circuit) 20a power receiving antenna 20a1 antenna element 20a2 line 20b rectifier circuit 22 power control circuit 24 sensor 26 transmitter 26a transmitting antenna 28 frame 28a protrusion 28b frame main body 32 cushion body 34 cover 36 main body portion 36a upper surface 36b lower surface 36d rear surface 38 first internal space 40 Second internal space 40a Inner surface 41 Third internal space 44 Circuit board 44a Board surface 46 Resin case 46a Case body 46a1 Bottom surface 46b Lid 46b1 Lid surface 47 Support member 48 Support 50 Antenna board 50a First surface 50b Second surface 52 Circuit chip 54 Wire 56 Insulating layer 56a First member 56b Second member 60 Line 62 Resin case 64 Line 100 Main body 140 Internal space 140a Inner surface C Center D Diameter L Distance W Width g1, g2, g3, g4, g5, g6, g7, g8, g9, g10 Graph t, t1, t2 Thickness

Claims

1. A sensor system comprising: a power supply device having a power transmitting antenna arranged inside a vehicle; a cushion made of a dielectric material that forms part of a seat arranged inside the vehicle; a sensor provided on the seat; and a power receiving antenna circuit that is arranged inside the cushion and receives transmitted power from the power transmitting antenna and outputs power to be given to the sensor.

2. The sensor system according to claim 1, wherein the cushion body has a main body portion and an internal space provided inside the main body portion and accommodating the power receiving antenna circuit.

3. The sensor system according to claim 2, wherein the main body has a first surface on the side of the power transmitting antenna and a second surface opposite the first surface, and the internal space is provided closer to the second surface.

4. The sensor system according to claim 2 or 3, further comprising an insulating layer between the inner surface of the internal space and the outer surface of the power receiving antenna circuit, the insulating layer having a dielectric loss tangent lower than that of the dielectric material.

5. The sensor system according to claim 4, wherein the thickness of the insulating layer is 0.01λ or more and 0.04λ or less, where λ is the wavelength of the radio waves emitted from the power transmitting antenna.

6. The sensor system according to claim 4 or claim 5, wherein the insulating layer includes a polystyrene foam layer.

7. The sensor system according to claim 4 or claim 5, wherein the insulating layer includes an air layer.

8. The sensor system according to any one of claims 4 to 7, further comprising a resin case housed in the internal space and defining the insulating layer by housing the power receiving antenna circuit therein.

9. The sensor system according to claim 1, wherein the power receiving antenna circuit has an antenna element and an antenna substrate on which the antenna element is mounted, and the antenna substrate is a flexible substrate.

10. The sensor system of any one of claims 1 to 9, wherein the portion of the seat includes a headrest.

11. A seat to be placed in a vehicle, comprising: a sensor; a cushion body made of a dielectric material; and a power receiving antenna circuit that is placed inside the cushion body, receives transmitted power from a power transmitting antenna placed in the vehicle, and outputs power to be given to the sensor.

12. A sensor unit provided in a seat arranged in a vehicle, comprising: a sensor; a power receiving antenna circuit that receives transmitted power from a power transmitting antenna arranged in the vehicle and outputs power to be given to the sensor; and a resin case that has an internal storage space for accommodating the power receiving antenna circuit and is arranged inside a cushion made of a dielectric material that constitutes part of the seat.

13. The sensor unit according to claim 12, wherein the power receiving antenna circuit has an antenna board, and further comprises a support member that is provided on the inner surface of the storage space and supports the antenna board at a position where a predetermined gap is provided between the antenna board and the inner surface.

14. The sensor unit described in claim 13, wherein the support member further comprises: a circuit board accommodated in the accommodation space; a support provided on the inner surface of the resin case for supporting the circuit board against the inner surface; and a wire for electrically connecting the antenna board and the circuit board.

15. The sensor unit according to claim 12, further comprising a line that physically connects the sensor to the resin case that is separate from the sensor and supplies power from the resin case to the sensor.

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