Sensor device
The sensor device addresses misalignment and limited detection range issues by using a configuration with point-symmetric power supply ports and optimized antenna elements, enhancing detection range and sensitivity.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2025-04-21
- Publication Date
- 2026-07-23
AI Technical Summary
Existing sensor devices face issues with reduced detection accuracy due to misalignment and limited detection range, particularly when measuring biological information, as they require precise mounting against arterial sites.
The sensor device incorporates a configuration with two antennas arranged to sandwich a ground, featuring point-symmetric power supply ports and a specific winding of antenna elements to enhance current flow and electromagnetic field distribution, expanding the detection range and maintaining accuracy even with positional misalignment.
This configuration allows for a wider detection range and improved sensitivity by synchronizing current phases and reinforcing electromagnetic fields, thereby reducing the impact of misalignment on detection accuracy.
Smart Images
Figure JP2025015332_23072026_PF_FP_ABST
Abstract
Description
Sensor device
[0001] The present disclosure relates to a sensor device.
[0002] Patent Document 1 discloses a sensor device for measuring biological information. The sensor device disclosed in Patent Document 1 transmits radio waves from an antenna to a measurement site and receives reflected waves of the radio waves reflected from the measurement site, thereby detecting the pulse wave of an artery.
[0003] Japanese Patent Application Laid-Open No. 2019-154861
[0004] When using the sensor device disclosed in Patent Document 1, it is necessary to abut the antenna against a portion corresponding to the artery. For this reason, if a misalignment occurs in the mounting position of the sensor device, the detection accuracy may decrease. Further, in the sensor device disclosed in Patent Document 1, there is no disclosure regarding the detection range of the antenna, and it is not possible to expect an expansion of the detection range.
[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a sensor device capable of expanding the detection range of an antenna.
[0006] The sensor device according to the present disclosure includes a ground provided on a substrate, a first antenna and a second antenna provided on the substrate and arranged so as to sandwich the ground from one end side and the other end side of the ground, a first power supply port provided on the first antenna and connected to one end portion of the ground, and a second power supply port provided on the second antenna and connected to the other end portion of the ground. The first power supply port and the second power supply port are arranged to be point-symmetrical to each other with respect to the center of the ground.
[0007] According to the present disclosure, the detection range of the antenna can be expanded. For this reason, even if a misalignment occurs in the mounting position of the sensor device, a decrease in the detection accuracy of the antenna can be suppressed.
[0008] This is a plan view of the sensor device according to Embodiment 1. This is a cross-sectional view taken along the line II-II in Figure 1. This is a diagram showing the distribution of current and the distribution of the electromagnetic field. This is a plan view of the sensor device according to Embodiment 2. This is a plan view of the sensor device according to Embodiment 3. This is a plan view of the sensor device according to Embodiment 4. This is a plan view of the sensor device according to Embodiment 5. Figures 8A to 8D are comparative diagrams showing the position of the power supply port, the flow of current at the end of the ground, and the direction of the magnetic field.
[0009] To provide a more detailed explanation of this disclosure, the forms for implementing this disclosure will be described below with reference to the attached drawings.
[0010] Embodiment 1. The sensor device 100 according to Embodiment 1 will be described with reference to Figures 1 to 3.
[0011] First, the configuration of the sensor device 100 according to Embodiment 1 will be explained using Figures 1 and 2. Figure 1 is a plan view of the sensor device 100 according to Embodiment 1. Figure 2 is a cross-sectional view taken along the line II-II in Figure 1.
[0012] The sensor device 100 shown in Figure 1 detects, for example, the distance (including changes in distance) between the object to be detected and the antennas 21 and 22 using the antennas 21 and 22. Furthermore, when such a sensor device 100 is used as a biological information measuring device, the sensor device 100 can detect changes in the shape of the living body that is the object to be detected, or changes in the shape of organs inside that body. In this case, the sensor device 100 can be attached to the living body itself or to the clothing that the living body is wearing.
[0013] As shown in Figures 1 and 2, the sensor device 100 includes a substrate 11, a first ground 12, a second ground 13, a plurality of through-holes 14, a first antenna 21, a second antenna 22, a plurality of through-holes 23, and a copper foil pattern 24.
[0014] The substrate 11 has a front surface 11a and a back surface 11b. The front surface 11a and the back surface 11b are surfaces located on opposite sides of the substrate 11 in the thickness direction. The ground 12 and antennas 21 and 22 are provided on the front surface 11a. The ground 13 is provided on the back surface 11b. The grounds 12 and 13 are conductive plates formed of a conductive material, such as gold or copper.
[0015] The ground 12, when viewed from the surface 11a side of the substrate 11, is, for example, rectangular. The ground 12 may also be square or circular. The ground 12 has ends 12a and 12b that face each other in its short-side direction (also called the short-side direction). The ends 12a and 12b extend along the long-side direction (also called the longitudinal direction) of the ground 12. That is, end 12a is one end on the short-side side of the ground 12, and end 12b is the other end on the other short-side side. The long-side direction and short-side direction of the ground 12 indicate the length direction of the ground 12.
[0016] In Figures 1 and 2, the ends 12a and 12b are shown as opposing long sides in the short-side direction of the ground 12, but the ends 12a and 12b may also be shown as opposing short sides in the long-side direction of the ground 12.
[0017] Ground 13 is positioned opposite ground 12, sandwiching the substrate 11 in its thickness direction. Ground 12 and ground 13 are electrically connected by a plurality of through-holes 14.
[0018] The through-hole 14 is a through-hole that penetrates the substrate 11 in the thickness direction. The through-hole 14 is made of a conductive material, such as gold or copper. One end of the through-hole 14 is electrically connected to the ground 12, and the other end of the through-hole 14 is electrically connected to the ground 13.
[0019] In addition, the sensor device 100 according to Embodiment 1 described above is configured to have grounds 12 and 13 on the front surface 11a and back surface 11b of the substrate 11, respectively, but the ground 13 may also be configured to be provided as a ground layer inside the substrate 11.
[0020] Antennas 21 and 22 are both antennas used for both transmitting and receiving. Antennas 21 and 22 are positioned to sandwich the ground 12 in the direction of their shorter sides. Antenna 21 is positioned opposite the end 12a of the ground 12. Antenna 22 is positioned opposite the end 12b of the ground 12.
[0021] Antenna 21 has one or more antenna elements 21a, 21b. Antenna 22 also has one or more antenna elements 22a, 22b. The number of antenna elements in antenna 21 and the number of antenna elements in antenna 22 are preferably the same, as determined from the current distribution in the ground 12. Figure 1 shows an example where antenna 21 has two antenna elements 21a, 21b, and antenna 22 has two antenna elements 22a, 22b.
[0022] Antenna elements 21a and 21b are, for example, made by winding a wire into a square coil. Antenna elements 21a and 21b are electrically conductive to each other. Antenna elements 21a and 21b are arranged in a straight line along the long side of the ground 12. Antenna element 21a is located at one end of the long side of the ground 12. Antenna element 21b is located at the other end of the long side of the ground 12. Note that antenna elements 21a and 21b may also be made by winding a wire into a rectangular or circular coil.
[0023] One copper foil pattern 24 is provided on the back surface 11b of the substrate 11 so as to face the antenna elements 21a and 21b. One through-hole 23 provides electrical conductivity between the antenna element 21a and the copper foil pattern 24, and between the antenna element 21b and the copper foil pattern 24.
[0024] Antenna element 21a has a feed port 21c for the entire antenna 21. The feed port 21c is electrically connected between the end 12a of the ground 12 and the inner end of the antenna element 21a. The outer end of antenna element 21a is electrically connected to the copper foil pattern 24 via a through hole 23. The inner end of antenna element 21b is electrically connected to the copper foil pattern 24 via a through hole 23. The outer end of antenna element 21b is electrically connected to the end 12a of the ground 12 and is also grounded. The feed port 21c is the first feed port.
[0025] Therefore, in antenna element 21a, the current supplied from the end 12a of the ground 12 via the power supply port 21c flows in a coil shape from the inner end to the outer end. Next, in antenna element 21b, the current supplied from the outer end of antenna element 21a flows in a coil shape from the inner end to the outer end. In this way, the antenna 21 can transmit an electromagnetic field as a measurement signal from antenna elements 21a and 21b toward the object to be detected by current flowing from antenna element 21a to antenna element 21b. As a result, the antenna 21 can detect the distance to the object to be detected by receiving the reflected wave (reflected signal) of the electromagnetic field from the object to be detected by antenna elements 21a and 21b.
[0026] Furthermore, the antenna elements 22a and 22b are, for example, made by winding a wire into a square coil. The antenna elements 22a and 22b are electrically conductive to each other. The antenna elements 22a and 22b are arranged in a straight line along the long side of the ground 12. Antenna element 22a is located on the other end of the long side of the ground 12. Antenna element 22b is located on the one end of the long side of the ground 12. Note that the antenna elements 22a and 22b may also be made by winding a wire into a rectangular or circular coil. It is preferable that the antenna elements 21a and 21b and the antenna elements 22a and 22b have the same coil shape.
[0027] The other copper foil pattern 24 is provided on the back surface 11b of the substrate 11 so as to face the antenna elements 22a and 22b. The other through-hole 23 provides electrical conductivity between the antenna element 22a and the copper foil pattern 24, and between the antenna element 22b and the copper foil pattern 24, respectively.
[0028] Antenna element 22a has a feed port 22c for the entire antenna 22. The feed port 22c is electrically connected between the end 12b of the ground 12 and the inner end of antenna element 22a. The outer end of antenna element 22a is electrically connected to the copper foil pattern 24 via a through hole 23. The inner end of antenna element 22b is electrically connected to the copper foil pattern 24 via a through hole 23. The outer end of antenna element 22b is electrically connected to the end 12a of the ground 12 and is also grounded. Note that the feed port 22c is a second feed port.
[0029] Therefore, in antenna element 22a, the current supplied from end 12b of the ground 12 via the power supply port 22c flows in a coil shape from the outer end to the inner end. Next, in antenna element 22b, the current supplied from the inner end of antenna element 22a flows in a coil shape from the inner end to the outer end. In this way, the antenna 22 can transmit an electromagnetic field as a measurement signal from antenna elements 22a and 22b toward the object to be detected by current flowing from antenna element 22a to antenna element 22b. As a result, the antenna 22 can detect the distance to the object to be detected by receiving the reflected wave (reflected signal) of the electromagnetic field from the object to be detected by antenna elements 22a and 22b.
[0030] In this configuration, the feed port 21c of antenna 21 and the feed port 22c of antenna 22 are arranged point-symmetrically with respect to the center of ground 12. Therefore, the current supplied to ground 12 flows close to the ends 12a and 12b and along their length. However, the arrangement of the feed ports 21c and 22c point-symmetrically with respect to the center of ground 12 also includes arrangement that is approximately point-symmetrical. The arrangement of the feed ports 21c and 22c point-symmetrically with respect to the center of ground 12 does not have to be strictly point-symmetrical; it is sufficient that the current supplied to ground 12 flows close to the ends 12a and 12b and along their length.
[0031] Next, the operation and effects of the sensor device 100 according to Embodiment 1 will be explained using Figure 3. In Figure 3, E1 indicates the electromagnetic field generated by antenna 21, and E2 indicates the electromagnetic field generated by antenna 22. Also, the arrow on the ground 12 in Figure 3 indicates the direction of current flow supplied to the ground 12.
[0032] As shown in Figure 3, the sensor device 100 has antennas 21 and 22 on both sides of the short side of the substrate 11, allowing the current supplied to the ground 12 to flow over a wide area in the ground 12. Therefore, the sensor device 100 can expand the range of electromagnetic fields E1 and E2 generated by the antennas 21 and 22 to correspond to the current flow area. As a result, the sensor device 100 can expand the detection range of the antennas 21 and 22 to the entire ground 12. Thus, even if there is a misalignment in the mounting position of the sensor device 100, a decrease in detection accuracy can be suppressed.
[0033] Furthermore, the sensor device 100 is configured such that the power supply port 21c of antenna 21 and the power supply port 22c of antenna 22 are point-symmetric with respect to the center of the ground 12, allowing the current supplied to the ground 12 to flow along its length, close to the ends 12a and 12b. In this case, the parts of the ground 12 that connect to the power supply ports 21c and 22c at the ends 12a and 12b become the parts through which the most current flows.
[0034] Therefore, the electromagnetic field E1 from antenna 21 extends from the feed port 21c toward the center of ground 12. Its generated area is triangular in shape, with the feed port 21c side as the base and the center of ground 12 as the apex. Similarly, the electromagnetic field E2 from antenna 22 extends from the feed port 22c toward the center of ground 12. Its generated area is triangular in shape, with the feed port 22c side as the base and the center of ground 12 as the apex.
[0035] As a result, the sensor device 100 can distribute the current supplied to the ground 12 over a wider area in the ground 12, thereby expanding the detection range. Therefore, even if the sensor device 100 is misaligned in its mounting position, a decrease in detection accuracy can be suppressed.
[0036] Furthermore, by devising the way the wires are wound around the antennas 21 and 22, the sensor device 100 can set the direction of the current flowing to the ground 12 to one direction. Specifically, as shown in Figure 3, the sensor device 100 can allow current to flow from one end of the long side of the ground 12 to the other end, in other words, from the antenna element 21a, 22b side to the antenna element 21b, 22a side of the ground 12.
[0037] Therefore, the sensor device 100 can synchronize the phase of the current flowing along end 12a with the phase of the current flowing along end 12b. As a result, in the sensor device 100, the electromagnetic field E1 generated by antenna 21 and the electromagnetic field E2 generated by antenna 22 reinforce each other, making it possible to respond to small changes in distance or shape of the object being detected. Thus, the sensor device 100 can improve its detection sensitivity.
[0038] As described above, the sensor device 100 according to Embodiment 1 includes a ground 12 provided on a substrate 11, antennas 21 and 22 provided on the substrate 11 and arranged to sandwich the ground 12 from one end and the other end, a power supply port 21c provided on antenna 21 and connected to end 12a of the ground 12, and a power supply port 22c provided on antenna 22 and connected to end 12b of the ground 12. The power supply ports 21c and 22c are arranged to be point-symmetric with respect to the center of the ground 12. As a result, the sensor device 100 can expand the detection range of antennas 21 and 22. As a result, even if there is a positional shift in the mounting position of the sensor device 100, a decrease in the detection accuracy of antennas 21 and 22 can be suppressed.
[0039] Embodiment 2. The sensor device 200 according to Embodiment 2 will be described with reference to Figure 4. Figure 4 is a plan view of the sensor device 200 according to Embodiment 2. Components having the same function as those described in the above-described embodiments are denoted by the same reference numerals, and their descriptions are omitted.
[0040] The sensor device 200 according to Embodiment 2 shown in Figure 4 has specific dimensions added to the configuration of the sensor device 100 according to Embodiment 1 shown in Figure 1, in order to achieve miniaturization and weight reduction.
[0041] When the antenna elements 21a, 21b, 22a, and 22b are formed by winding a conducting wire in a coil shape forming a square, the length L1 of each of the four sides of the antenna elements 21a, 21b, 22a, and 22b is set to be equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200. In this way, the sensor device 200 can electrically reduce the antenna elements 21a, 21b, 22a, and 22b by defining the length L1 of one side of the antenna elements 21a, 21b, 22a, and 22b. Therefore, the sensor device 200 can operate the antenna elements 21a, 21b, 22a, and 22b sensitively even with respect to small distance changes or shape changes in the detected object.
[0042] Further, the sensor device 200 may set the length L2 of the substrate 11 to be equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200. For this reason, the sensor device 200 can reduce the size and weight of the entire device. Note that the length L2 of the substrate 11 is the length of the substrate 11 along the direction in which the antennas 21 and 22 sandwich the ground 12.
[0043] For example, when the operating frequency used by the sensor device 200 is 100 MHz in the VHF band, the length equal to or less than 1 / 10 of one wavelength of the operating frequency is 30 cm or less. That is, the lengths L1 and L2 are 30 cm or less.
[0044] However, the meaning that the length L1 is equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200 also includes the case where the length L1 is approximately equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200. The fact that the length L1 is equal to or less than 1 / 10 of one wavelength of the operating frequency does not necessarily mean that it is strictly less than 1 / 10 of one wavelength of the operating frequency, as long as the antenna elements 21a, 21b, 22a, and 22b are electrically reduced.
[0045] Also, the meaning that the length L2 is equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200 includes the case where the length L2 is approximately equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200. That the length L2 is equal to or less than 1 / 10 of one wavelength of the operating frequency used by the sensor device 200 does not necessarily mean that it is strictly less than 1 / 10 of one wavelength of the operating frequency, as long as the size and weight of the entire device can be reduced.
[0046] As described above, in the sensor device 200 according to the second embodiment, the antenna 21 includes one or more antenna elements 21a and 21b, and the antenna 22 includes one or more antenna elements 22a and 22b. Each side of the square coil-shaped antenna elements 21a, 21b, 22a, and 22b has a length equal to or less than 1 / 10 of one wavelength of the operating frequency. Therefore, the sensor device 200 can be reduced in size and weight.
[0047] Embodiment 3. The sensor device 300 according to Embodiment 3 will be described with reference to FIG. 5. FIG. 5 is a plan view of the sensor device 300 according to Embodiment 3. Components having the same functions as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.
[0048] The sensor device 300 according to Embodiment 3 shown in FIG. 5 is obtained by adding a circuit unit 30 that acquires and outputs the reflected signals detected by the antennas 21 and 22 on the ground 12 with respect to the sensor device 100 according to Embodiment 1 shown in FIG. 1. The reflected signals detected by the antennas 21 and 22 are, for example, signals indicating the distance to the detected object or signals indicating the size of the detected object.
[0049] The circuit unit 30 is provided on the ground 12. The circuit unit 30 includes an analog circuit 31, a digital circuit 32, a storage unit 33, and an output circuit 34. The ground 12 serves as the ground for both the antennas 21 and 22 and the circuit unit 30.
[0050] The analog circuit 31 receives the reflected signals transmitted from antennas 21 and 22. The analog circuit 31 also transmits the received reflected signals to the digital circuit 32. The digital circuit 32 performs A / D conversion on the reflected signals transmitted from the analog circuit 31. The digital circuit 32 also transmits the A / D converted reflected signals to the storage unit 33.
[0051] The memory unit 33 stores the A / D converted reflected signal transmitted from the digital circuit 32. The output circuit 34 outputs the reflected signal stored in the memory unit 33 to the outside of the sensor device 300.
[0052] Note that the sensor device 300 does not necessarily have a memory unit 33. In this case, the output circuit 34 outputs the A / D converted reflected signal transmitted from the digital circuit 32 to the outside of the sensor device 300 without storing it.
[0053] As described above, the sensor device 300 according to Embodiment 3 includes a circuit unit 30 provided on the ground 12 that acquires and processes the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 and outputs it. Therefore, the sensor device 300 can integrate the antennas 21 and 22 and the circuit unit 30 on a single substrate 11.
[0054] Embodiment 4. The sensor device 400 according to Embodiment 4 will be described with reference to Figure 6. Figure 6 is a plan view of the sensor device 400 according to Embodiment 4. Components having the same function as those described in the above embodiments are denoted by the same reference numerals, and their descriptions are omitted.
[0055] The sensor device 300 according to Embodiment 3 shown in Figure 5 includes a circuit unit 30 that acquires and processes reflected signals detected by antennas 21 and 22 and outputs them. In contrast, the sensor device 400 according to Embodiment 4 shown in Figure 6 includes a circuit unit 40 that acquires and processes reflected signals detected by antennas 21 and 22 and outputs them, as well as removing noise within those reflected signals.
[0056] The circuit unit 40 is connected to ground 12. The circuit unit 40 includes an analog circuit 31, a digital circuit 32, a storage unit 33, an output circuit 34, and a variable matching circuit 41. The variable matching circuit 41 is electrically connected between the analog circuit 31 and the digital circuit 32.
[0057] Here, if the distance between antennas 21 and 22 and the object being detected changes, the input impedance of antennas 21 and 22 changes. This input impedance corresponds to the reflection coefficient of antennas 21 and 22 and may become noise in the detected reflected signal (reflected electromagnetic field). A high reflection coefficient results in poor impedance matching and can lead to signal loss. The reflection coefficient of antennas 21 and 22 is the ratio of the incident electromagnetic wave propagating towards the object being detected within antennas 21 and 22 to the reflected electromagnetic wave reflected from the object being detected within antennas 21 and 22.
[0058] The variable matching circuit 41 works to suppress noise in the detected reflected signal by impedance matching the changing input impedance. The variable matching circuit 41 is, for example, a circuit having a diode.
[0059] As described above, in the sensor device 400 according to Embodiment 4, the circuit unit 40 is connected to the antennas 21 and 22 respectively and has a variable matching circuit 41 that impedance matches the input impedance acquired from the antennas 21 and 22. Therefore, the sensor device 400 can remove noise in the reflected signal.
[0060] Embodiment 5. The sensor device 500 according to Embodiment 5 will be described with reference to Figures 7 and 8. Components having the same function as those described in the above-described embodiments are denoted by the same reference numerals, and their descriptions are omitted.
[0061] First, the configuration of the sensor device 500 according to Embodiment 5 will be explained using Figure 7. Figure 7 is a plan view of the sensor device 500 according to Embodiment 5.
[0062] The sensor device 100 according to Embodiment 1 shown in Figure 1 sets the direction of the current flowing to the ground 12 in one direction by devising the way the wires in the antennas 21 and 22 are wound. In contrast, the sensor device 500 according to Embodiment 5 shown in Figure 7 sets the direction of the current flowing to the ground 12 in one direction by providing a circuit section 50 that acquires the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 with the same amplitude and opposite phase, and outputs them.
[0063] The circuit unit 50 is connected to ground 12. The circuit unit 50 includes a digital circuit 32, a storage unit 33, an output circuit 34, a variable matching circuit 41, phase shift circuits 51a and 51b, and matching circuits 52a and 52b.
[0064] The matching circuit 52a is electrically connected to the feed port 21c of the antenna 21. The phase shift circuit 51a is electrically connected to the matching circuit 52a and the variable matching circuit 41. The matching circuit 52b is electrically connected to the feed port 22c of the antenna 22. The phase shift circuit 51b is electrically connected to the matching circuit 52b and the variable matching circuit 41. The variable matching circuit 41 has a digital circuit 32, a memory unit 33, and an output circuit 34 connected in series in that order.
[0065] Specifically, the phase shift circuits 51a and 51b output the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 with a phase difference of 180 degrees. That is, the phase of the reflected signal output from phase shift circuit 51a and the phase of the reflected signal output from phase shift circuit 51b are shifted by 180 degrees from each other.
[0066] For example, one of the phase shift circuits 51a, 51a may be a -90 degree phase shift circuit and the other may be a +90 degree phase shift circuit. Alternatively, one of the phase shift circuits 51a, 51b may be a 0 degree phase shift circuit and the other may be a 180 degree phase shift circuit.
[0067] At this time, the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 are reflected waves from the same electromagnetic field, and therefore have the same amplitude and phase at the power supply ports 21c and 22c.
[0068] However, the statement that the phase shift circuits 51a and 51b output the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 with a phase difference of 180 degrees also includes outputting with a phase difference of approximately 180 degrees. The statement that the phase shift circuits 51a and 51b output the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 with a phase difference of 180 degrees does not strictly mean that they output with a phase difference of 180 degrees; it is sufficient as long as the direction of the current flowing on the ground 12 can be set to one direction.
[0069] The matching circuits 52a and 52b are circuits for matching the impedance from the power supply ports 21c and 22c.
[0070] Although the sensor device 500 is equipped with two phase shift circuits 51a and 51b, it may be replaced with a single phase shift circuit that receives both the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22.
[0071] Furthermore, the impedances at the input and output terminals of the phase shift circuits 51a and 51b are often 50Ω. In this case, the sensor device 500 may provide the variable matching circuit 41 not between the phase shift circuits 51a and 51b, but between the phase shift circuit 51a and the matching circuit 52a or the power supply port 21c, and between the phase shift circuit 51b and the matching circuit 52b or the power supply port 22c.
[0072] Next, the reason why the direction of the current flowing over the ground 12 is unidirectional will be explained using Figure 8. Figures 8A to 8D in Figure 8 are comparative diagrams showing the positions of each power supply port 21c, 22c, the current flow at the ends 12a, 12b of the ground 12, and the direction of the magnetic field at each antenna element 21a, 21b, 22a, 22b. The configuration shown in Figure 8B corresponds to the configurations of the sensor devices 100 to 500 according to Embodiments 1 to 5. The configurations shown in Figures 8A, 8C, and 8D are comparative examples showing configurations to the configurations of the sensor devices 100 to 500 according to Embodiments 1 to 5. The arrows shown in Figures 8A to 8D indicate the direction of current flow supplied from antennas 21 and 22 to the ground 12.
[0073] As shown in the configurations from Figures 8A to 8D, the direction of the current flowing on the ground 12 is determined by the position of each power supply port 21c, 22c and the phase difference of the power supply potential at those power supply ports 21c, 22c.
[0074] In the configuration shown in Figure 8A, the feed port 21c of antenna 21 and the feed port 22c of antenna 22 are positioned symmetrically with respect to the center of ground 12. The feed phase of feed port 21c is 0 degrees, and the feed phase of feed port 22c is also 0 degrees. Therefore, the feed phase difference between them is 0 degrees. The direction of the current flowing through end 12a and the direction of the current flowing through end 12b are opposite to each other.
[0075] In the configuration shown in Figure 8B, the feed port 21c of antenna 21 and the feed port 22c of antenna 22 are positioned symmetrically with respect to the center of ground 12. The feed phase of feed port 21c is 0 degrees, and the feed phase of feed port 22c is 180 degrees. Therefore, the feed phase difference between them is 180 degrees. The direction of the current flowing through end 12a and the direction of the current flowing through end 12b are the same.
[0076] In the configuration shown in Figure 8C, the feed port 21c of antenna 21 and the feed port 22c of antenna 22 are positioned so as not to be point-symmetric with respect to the center of ground 12. Furthermore, the feed phase of feed port 21c is 0 degrees, and the feed phase of feed port 22c is also 0 degrees. Therefore, the feed phase difference between them is 0 degrees. The direction of the current flowing through end 12a and the direction of the current flowing through end 12b are the same.
[0077] In the configuration shown in Figure 8D, the feed port 21c of antenna 21 and the feed port 22c of antenna 22 are positioned at locations that are not point-symmetric with respect to the center of ground 12. The feed phase of feed port 21c is 0 degrees, and the feed phase of feed port 22c is 180 degrees. Therefore, the feed phase difference between them is 180 degrees. The direction of the current flowing through end 12a and the direction of the current flowing through end 12b are opposite to each other.
[0078] Furthermore, as shown in the configurations in Figures 8A to 8D, the direction of the magnetic field formed by each antenna element 21a, 21b, 22a, and 21b is determined by the position of the power supply ports 21c and 22c and the feeding phase at the power supply ports 21c and 22c. In other words, even with antennas 21 and 22 that have the same winding method, the direction of the magnetic field changes when the position of the power supply ports 21c and 22c and the feeding phase at the power supply ports 21c and 22c change. In the sensor device 500 according to Embodiment 5, as shown in Figure 3, the detection sensitivity is improved by determining the position of the power supply ports 21c and 22c and the feeding phase at the power supply ports 21c and 22c so that the change in the magnetic field is greatest above the ground 12.
[0079] In Figures 8A to 8D, the × marks indicate that the electric field formed by antenna elements 21a, 21b, 22a, and 21b is directed from the front side of the paper to the back side. The ● marks indicate that the electric field formed by antenna elements 21a, 21b, 22a, and 21b is directed from the back side of the paper to the front side.
[0080] In the configuration shown in Figure 8A, the direction of the magnetic field formed by the antenna elements 21a and 21b is the same as the direction of the magnetic field formed by the antenna elements 21a and 21b.
[0081] In the configuration shown in Figure 8B, the direction of the magnetic field formed by the antenna elements 21a and 21b is opposite to the direction of the magnetic field formed by the antenna elements 21a and 21b.
[0082] In the configuration shown in Figure 8C, the direction of the magnetic field formed by the antenna elements 21a and 21b is opposite to the direction of the magnetic field formed by the antenna elements 21a and 21b.
[0083] In the configuration shown in Figure 8D, the direction of the magnetic field formed by the antenna elements 21a and 21b is the same as the direction of the magnetic field formed by the antenna elements 21a and 21b.
[0084] As described above, in the sensor device 500 according to Embodiment 5, the circuit unit 50 is connected to the power supply ports 21c and 22c, respectively, and has phase shift circuits 51a and 51b that output the reflected signal detected by antenna 21 and the reflected signal detected by antenna 22 with a phase difference of 180 degrees. Therefore, the sensor device 500 can set the direction of the current flowing to ground 12 to one direction. As a result, the sensor device 500 can improve the detection sensitivity.
[0085] Within the scope of this disclosure, it is possible to freely combine the embodiments, modify any component in each embodiment, or omit any component in each embodiment.
[0086] The sensor device according to this disclosure is suitable for use in sensor devices and the like because it expands the detection range of the antenna by arranging the first power supply port and the second power supply port so that they are point-symmetric with respect to the center of the ground.
[0087] 11 Substrate, 11a Front surface, 11b Back surface, 12 Ground, 12a, 12b Edge, 13 Ground, 14 Through-hole, 21 Antenna, 21a, 21b Antenna element, 21c Feed port, 22 Antenna, 22a, 22b Antenna element, 22c Feed port, 23 Through-hole, 24 Copper foil pattern, 30 Circuit section, 31 Analog circuit, 32 Digital circuit, 33 Memory section, 34 Output circuit, 40 Circuit section, 41 Variable matching circuit, 50 Circuit section, 51a, 51b Phase shift circuit, 52a, 52b Matching circuit, 100, 200, 300, 400, 500 Sensor device, E1, E2 Electromagnetic field, L1 Length of one side of the antenna element, L2 Length of the substrate.
Claims
1. A sensor device comprising: a ground provided on a substrate; a first antenna and a second antenna provided on the substrate and arranged to sandwich the ground from one end and the other end; a first power supply port provided on the first antenna and connected to one end of the ground; and a second power supply port provided on the second antenna and connected to the other end of the ground, wherein the first power supply port and the second power supply port are arranged to be point-symmetric with respect to the center of the ground.
2. The sensor device according to claim 1, wherein the first antenna and the second antenna each have one or more antenna elements, and the length of one side of the square, coil-shaped antenna element is 1 / 10 or less of the wavelength of the operating frequency.
3. The sensor device according to claim 1 or 2, characterized in that it comprises a circuit unit provided in the ground that acquires and processes the signal detected by the first antenna and the signal detected by the second antenna and outputs them.
4. The sensor device according to claim 3, characterized in that the circuit section is connected to the first antenna and the second antenna, respectively, and has a variable matching circuit that impedance matches the input impedances obtained from the first antenna and the second antenna.
5. The sensor device according to claim 3 or 4, characterized in that the circuit section is connected to the first power supply port and the second power supply port, respectively, and has a phase shift circuit that outputs the signal detected by the first antenna and the signal detected by the second antenna with a phase difference of 180 degrees.