Sensor device

Abstract

To provide a sensor device for detecting conductivity, capable of improving the sensitivity of an electrical signal for detecting the conductivity.SOLUTION: A sensor device 100 includes: an element 110 changing into effective characteristic impedance Zc2 having a value different from a characteristic impedance Zc1; an output part 120 having an output impedance Zo and capable of generating an electrical signal having an amplitude changing to time to output the electrical signal to the transmission line 111 of the element 110; and a detection part 130 having an input impedance Zi and capable of inputting the electrical signal through the transmission line 111 to detect the conductivity of an object 200 to be detected on the basis of the amplitude size of the electrical signal. The output impedance Zo of the output device 120 is matched to the effective characteristic impedance Zc2 of the element 110; and the input impedance Zi of the detection part 130 is set to a value larger than the effective characteristic impedance Zc2 of the element 110.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sensor device.

Background Art

[0002] Conventionally, devices for detecting the electrical conductivity of a detection target have been proposed in, for example, Patent Documents 1 and 2. This device includes a detection unit having a conductor pattern as a transmission line, and a circuit unit that outputs an electrical signal to the conductor pattern and detects the electrical signal that has passed through the conductor pattern.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in Patent Documents 1 and 2, in order to suppress corrosion of the conductor pattern, a protective layer is formed on the conductor pattern. However, since the conductor pattern does not directly contact the detection target due to the protective layer, there is a possibility that the sensitivity of the electrical signal detected by the circuit unit may decrease. Of course, even if the conductor pattern is not covered with the protective layer, improvement in the sensitivity of the electrical signal is desired.

[0005] In view of the above points, an object of the present invention is to provide a configuration capable of improving the sensitivity of an electrical signal for detecting electrical conductivity in a sensor device for detecting electrical conductivity.

Means for Solving the Problems

[0006] To achieve the above object, in the invention according to claim 1, the sensor device includes an element (110), an output unit (120), and a detection unit (130).

[0007] The element (110) is configured as a transmission line (111) having a characteristic impedance (Zc1), and when the detection target (200) approaches the transmission line, the characteristic impedance changes to an effective characteristic impedance (Zc2) whose value is different from the characteristic impedance.

[0008] The output unit has an output impedance (Zo), generates an electrical signal whose amplitude changes with time, and outputs the electrical signal to the transmission line of the element.

[0009] The detection unit has an input impedance (Zi), inputs an electrical signal via the transmission line, and detects the electrical conductivity of the detection target based on the magnitude of the amplitude of the electrical signal.

[0010] The output impedance of the output unit is matched to the effective characteristic impedance of the element.

[0011] The input impedance of the detection unit is set to a value larger than the effective characteristic impedance of the element.

[0012] According to this, since the output impedance and the effective characteristic impedance are matched, the voltage reflection when the electrical signal is output from the output unit to the transmission line is eliminated. As a result, it is possible to reduce the electrical stress, distortion of the electrical signal, noise generation, etc. when the electrical signal is output from the output unit to the transmission line.

[0013] Also, since the input impedance is set to a value larger than the effective characteristic impedance, the voltage reflection when the electrical signal is input from the transmission line to the detection unit can be increased. As a result, the amplitude of the electrical signal detected by the detection unit can be increased not only by the incident component but also by the reflected component.

[0014] Therefore, in a sensor device for detecting electrical conductivity, the sensitivity of an electrical signal for detecting electrical conductivity can be improved.

[0015] Note that the reference signs in parentheses for each means described in this column and the claims indicate the correspondence with the specific means described in the embodiments described later.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are identical or equivalent to each other are denoted by the same reference numerals in the drawings.

[0018] (First Embodiment) Hereinafter, the first embodiment will be described with reference to the drawings. The sensor device according to this embodiment is a sensor that detects the electrical conductivity of a detection target as a physical quantity. Electrical conductivity is a physical quantity corresponding to the concentration of salts, fertilizers, etc. in the detection target. The sensor device detects the electrical conductivity, for example, based on the Time Domain Transmission method.

[0019] The detection target includes, for example, soil, water, ceramics, concrete, etc. Soil is a base for growing crops and includes soil, sand, clay, etc. Water includes various types of water such as pure water, water containing mineral components, and water in which carbon dioxide gas is dissolved.

[0020] As shown in FIG. 1, the sensor device 100 includes an element 110, an output unit 120, and a detection unit 130.

[0021] The element 110 is a component for detecting the electrical conductivity of the detection target 200. The element is a part that directly contacts the detection target 200. The element 110 is configured as a transmission line 111 having a characteristic impedance Zc1. One end side of the transmission line 111 is connected to the output unit 120. The other end side of the transmission line 111 is connected to the detection unit 130. Hereinafter, "Zc1" may be used as the value of the impedance. The same applies to other impedances other than the characteristic impedance Zc1.

[0022] The characteristic impedance Zc1 is an impedance preset when the sensor device 100 is manufactured. The characteristic impedance Zc1 changes to the effective characteristic impedance Zc2 when the detection target 200 is brought closer to the transmission line 111. That is, the effective characteristic impedance Zc2 is an impedance with a value different from that of the characteristic impedance Zc1.

[0023] The transmission line 111 has, for example, a signal line and a GND line. The signal line and the GND line are metal wirings such as Cu. The transmission line 111 is provided on, for example, a pedestal. The pedestal is, for example, a printed circuit board having one surface. The pedestal may be a flexible board. The transmission line 111 is formed on one surface of the printed circuit board. Note that the transmission line 111 is not limited to the case of being composed of one layer, and the transmission line 111 may be composed of a plurality of layers such as the first layer and the second layer.

[0024] The transmission line 111 is covered with an insulating film, for example. The insulating film is a protective film for protecting the transmission line 111 from corrosion. Note that the above-mentioned effective characteristic impedance Zc2 is the impedance that appears when the transmission line 111 is covered with the insulating film. Also, the transmission line 111 may not be covered with the insulating film. In this case, the effective characteristic impedance Zc2 is the impedance that appears when the transmission line 111 is not covered with the insulating film.

[0025] The output unit 120 is a circuit unit that outputs an electrical signal to the transmission line 111 of the element 110. The output unit 120 has a signal generation circuit 121 that generates an electrical signal and an output impedance Zo.

[0026] The signal generation circuit 121 is configured as, for example, a transient signal generation circuit. The electrical signal is a transient signal whose amplitude changes with time. The electrical signal includes signals such as pulse signals, impulse signals, Sin waves, and triangular waves. Therefore, the signal generation circuit 121 generates one of these transient signals and outputs it to the element 110.

[0027] The output impedance Zo is the impedance when viewed from the element 110 side to the output section 120 side. The output impedance Zo is configured as, for example, a single resistor element. The output impedance Zo may be configured as a circuit section that generates the output impedance Zo.

[0028] The detection section 130 is a circuit section that inputs an electrical signal from the transmission line 111 and detects the electrical conductivity of the soil or water, which is the detection target 200, based on the electrical signal. The detection section 130 has a signal detection circuit 131 that detects the electrical signal and an input impedance Zi.

[0029] The signal detection circuit 131 is configured as, for example, a transient signal detection circuit. The electrical signal detected by the signal detection circuit 131 includes electrical characteristics such as voltage, current, time, frequency, and impedance. The signal detection circuit 131 detects the electrical conductivity of the detection target 200 based on, for example, the magnitude of the amplitude of the voltage included in the electrical signal.

[0030] The detection section 130 is in cooperation with the output section 120. Therefore, the detection section 130 can acquire information on the timing when the electrical signal is output from the output section 120.

[0031] Note that the signal detection circuit 131 may detect the electrical conductivity of the detection target 200 based on the magnitude of the rising slope of the electrical signal in the time domain transmission method. The signal detection circuit 131 acquires, for example, data on the slope of the slope maximum point where the slope of the electrical signal is maximum, and calculates the electrical conductivity based on the slope of the slope maximum point. Also, since the vertical axis of the electrical signal is amplitude and the horizontal axis is time, the magnitude of the rising slope of the electrical signal may be calculated by detecting the time and the magnitude of the amplitude from when the electrical signal starts to rise until it reaches a predetermined amplitude.

[0032] The input impedance Zi is the impedance when viewed from the element 110 side to the detector 130 side. The input impedance Zi is configured as, for example, a single resistor element. The input impedance Zi may be configured as a circuit section that generates the input impedance Zi.

[0033] The sensor device 100 may be configured, for example, as follows. The printed circuit board on which the transmission line 111 is disposed is formed in a rectangular parallelepiped shape. The transmission line 111 extends from one end side of the printed circuit board along the outer edge of the printed circuit board to the other end side, folds back at the other end side of the printed circuit board, and is arranged in a ring shape so as to extend to one end side of the printed circuit board along the outer edge of the printed circuit board. The output unit 120 and the detection unit 130 are provided on one end side of the printed circuit board.

[0034] Alternatively, the transmission line 111 may be provided linearly without a folded portion. In this case, one end side of the output unit 120 and the transmission line 111 is arranged on one end side of the pedestal, and the other end side of the detection unit 130 and the transmission line 111 is arranged on the other end side of the pedestal. In this way, the shape of the pedestal, the pattern of the transmission line 111, and the positions of the output unit 120 and the detection unit 130 can be determined as appropriate.

[0035] In the above configuration, an impedance that simultaneously satisfies two conditions is set so that the sensitivity of the electrical conductivity of the detection target 200 detected by the detection unit 130 is maximized.

[0036] The first condition is that the output impedance Zo of the output unit 120 is matched with the effective characteristic impedance Zc2 of the transmission line 111.

[0037] Here, impedance matching means matching the output impedance Zo of the output unit 120 and the effective characteristic impedance Zc2 when the detection target 200 is brought close to the transmission line 111. Matching the impedance means making the output impedance Zo and the effective characteristic impedance Zc2 equal to the same value, or adjusting the values so that the impedances are of the same order. That is, the output impedance Zo and the effective characteristic impedance Zc2 do not have to be exactly the same, as long as they are values close enough to obtain the effects of the invention. Therefore, matching includes not only the case where Zo = Zc2, but also the case where Zo ≒ Zc2.

[0038] The second condition is that the input impedance Zi of the detection unit 130 is set to a value larger than the effective characteristic impedance Zc2 of the element 110. That is, Zi > Zc2.

[0039] Each impedance Zo, Zc1, Zi is predetermined. In particular, the output impedance Zo and the input impedance Zi are designed in advance corresponding to the values when the characteristic impedance Zc1 changes to the effective characteristic impedance Zc2. Therefore, at the time of manufacturing the sensor device 100, the impedance of the transmission line 111 of the element 110 is the characteristic impedance Zc1, but when the detection target 200 is brought close to the element 110, each impedance Zo, Zc1, Zi satisfies the first condition and the second condition.

[0040] Note that at the time of manufacturing the sensor device 100, the state of the detection target 200 that will actually be detected is unknown. Therefore, for example, an index corresponding to the detection target 200 is prepared, and the characteristic impedance Zc1 is designed for this index.

[0041] Next, the basis for each of the above conditions will be described. First, in the sensor device 100, as shown in FIG. 2, there are two impedance mismatch points, namely point A and point B. Also, since it is desired to maximize the sensitivity of the electrical signal when the detection target 200 is brought close to the element 110, the impedance of the element 110 is considered as the effective characteristic impedance Zc2 instead of the characteristic impedance Zc1.

[0042] At point A, which is the output side of the electrical signal, reflection occurs when the electrical signal is output from the output unit 120 to the transmission line 111 of the element 110. The reflected voltage at point A is expressed by the following equation (1) as the ratio of the output impedance Zo to the effective characteristic impedance Zc2.

[0043]

Equation

[0044] Also, the traveling wave voltage of the electrical signal passing through point A becomes smaller by the amount of the reflected voltage at point A, and is thus expressed by the following equation (2).

[0045]

Equation

[0046] On the other hand, at point B, which is the input side of the electrical signal, reflection occurs when the electrical signal is input from the transmission line 111 of the element 110 to the detection unit 130. The reflected voltage at point B is expressed by the following equation (3) as the ratio of the input impedance Zi to the effective characteristic impedance Zc2.

[0047]

Equation

[0048] At point B, the incident of the electrical signal to the detection unit 130 and the reflection of the electrical signal to the output unit 120 side occur. Therefore, the combined voltage at point B is the combined voltage = traveling wave voltage + reflected voltage. The traveling wave voltage is represented by Equation (2), and the reflected voltage when the traveling wave voltage enters point B is represented by Equation (2) × Equation (3). By adding the two, the combined voltage at point B is represented by the following Equation (4).

[0049] [Number]

[0050] Since the sensitivity of the electrical signal detected by the detection unit 130 is the voltage change when the effective characteristic impedance Zc2 changes due to the electrical conductivity of the detection target 200, it is expressed as Δ combined voltage / ΔZc2.

[0051] Here, let Zc2 = x, Zo = y, Zi = z, and the voltage at point B = Vout. Since we want to find the voltage change with respect to the change in Zc2, differentiating the combined voltage at point B represented by Equation (4) with respect to x (= Zc2) gives the following Equation (5).

[0052] [Number]

[0053] Furthermore, to obtain z (input impedance Zi) such that the sensitivity represented by the above Equation (5) is maximized, differentiating Equation (5) with respect to z gives the following Equation (6).

[0054] [Number]

[0055] Figure 3 is a graph of Equation (5) and Equation (6) with x and y as fixed values and z as a variable. The horizontal axis of Figure 3 is z (input impedance Zi), the left vertical axis is the sensitivity, and the right vertical axis is the sensitivity change rate.

[0056] According to FIG. 3, in the range where z is small, the sensitivity (ΔVout / Δx) increases rapidly. That is, the sensitivity change rate ((ΔVout / Δx) / Δz) also decreases rapidly. However, when z is increased, ΔVout / Δz, that is, the sensitivity, gradually increases. Therefore, by increasing the input impedance Zi, the sensitivity can be increased and stabilized.

[0057] Therefore, as a condition for obtaining the sensitivity of the electrical signal, the input impedance Zi > the effective characteristic impedance Zc2 can be set. This corresponds to the second condition described above. Also, the condition Zi > Zc2 means increasing the voltage reflection when the electrical signal is input from the transmission line 111 to the detection unit 130. As a result, the amplitude of the electrical signal detected by the detection unit 130 is increased not only by the incident component but also by the reflected component, leading to an improvement in sensitivity.

[0058] Subsequently, in order to obtain y (output impedance Zo) such that the sensitivity (ΔVout / Δx) is maximized under the condition Zi > Zc2, differentiating Equation (5) with respect to y gives the following Equation (7).

[0059]

Equation

[0060] FIG. 4 shows graphs of Equation (5) and Equation (6) with x and z as fixed values and y as a variable. The horizontal axis in FIG. 4 is y (output impedance Zo), the left vertical axis is the sensitivity, and the right vertical axis is the sensitivity change rate.

[0061] As shown in Fig. 4, it can be seen that the sensitivity (ΔVout / Δx) has a peak. And when y (output impedance Zo) = x (effective characteristic impedance Zc2), the sensitivity of the electrical signal is maximized. This corresponds to the first condition described above. Also, the condition that the output impedance Zo and the effective characteristic impedance Zc2 are matched means that there is no voltage reflection when the electrical signal is output from the output unit 120 to the transmission line 111. As a result, electrical stress, distortion of the electrical signal, noise generation, etc. when the electrical signal is output from the output unit 120 to the transmission line 111 are reduced.

[0062] Therefore, as a condition for obtaining the sensitivity of the electrical signal, the second condition (Zi > Zc2) can be satisfied, and the output impedance Zo = the effective characteristic impedance Zc2. Here, the equality of the first condition (Zo = Zc2) means matching, and Zo and Zc2 do not necessarily have to be exactly the same. As shown in Fig. 4, since the peak of the sensitivity (ΔVout / Δx) has a width, the value of the effective characteristic impedance Zc2 may also have a range. That is, the output impedance Zo only needs to be within the range of the effective characteristic impedance Zc2 that includes the maximum value of the sensitivity (ΔVout / Δx).

[0063] Subsequently, the results of simulating the difference in sensitivity due to the difference in impedance values will be described. As the detection target 200, pure water and three types of saline water with different salt concentrations were adopted. The three types of salt concentrations are 1 mS / cm, 2 mS / cm, and 3 mS / cm.

[0064] Fig. 5 shows a simulation circuit for simulating the sensitivity. A pulse voltage source was adopted as the signal generation circuit 121 of the output unit 120. Also, the voltage at point B was monitored.

[0065] As the first step of the simulation, the propagation characteristics (S parameters) were measured for each of the four types of detection targets 200 with the element 110 immersed.

[0066] As the second step of the simulation, for each of the four types of S-parameters, the output voltage waveform at point B was simulated for combinations of the output impedance Zo and the input impedance Zi.

[0067] Two patterns were prepared as impedance combinations. In pattern a, the output impedance Zo and the input impedance Zi were set to the same value. Pattern a does not satisfy both the above-mentioned first condition and the second condition.

[0068] In pattern b, the output impedance Zo was matched to the effective characteristic impedance Zc2 when the saline concentration was, for example, 2 mS / cm. Thereby, the first condition is satisfied. Also, in pattern b, the input impedance Zi was set to a value 100 times that of the output impedance Zo. Since the output impedance Zo and the effective characteristic impedance Zc2 are matched, the second condition that the input impedance Zi is larger than the effective characteristic impedance Zc2 is also satisfied.

[0069] Since sensitivity is the magnitude of the change in voltage with respect to the change in electrical conductivity, it can be said that the higher the change in voltage with respect to the change in electrical conductivity, the higher the sensitivity. In this simulation, the change in electrical conductivity corresponds to the difference in saline concentration. Therefore, here, the definition of sensitivity is taken as the difference between the voltage at a saline concentration of 2 mS / cm detected by the detection unit 130 after a certain time has elapsed since the electrical signal was output from the output unit 120 and the voltage at a saline concentration of 3 mS / cm.

[0070] Figure 6 shows the output voltage waveform of pattern a that does not satisfy the conditions. According to Figure 6, the voltage change of pattern a corresponding to the above definition of sensitivity was 40 mV. Figure 7 shows the output voltage waveform of pattern b that satisfies the conditions. According to Figure 7, the voltage change of pattern b corresponding to the above definition of sensitivity was 134 mV.

[0071] Thus, even though pattern b measures the same detection target 200 as pattern a, a sensitivity more than three times that of pattern a was obtained. Therefore, it was found that the sensitivity of the electrical signal can be improved by adjusting the input impedance Zi and the output impedance Zo so as to satisfy the above-described first condition and second condition.

[0072] Here, there is a fact that as the electrical conductivity of the detection target 200 increases, the effective characteristic impedance Zc2 decreases. Further, as the electrical conductivity of the detection target 200 increases, the voltage difference decreases, that is, the sensitivity decreases. Therefore, it is effective to match the effective characteristic impedance Zc2 when the electrical conductivity is high with the output impedance Zo. That is, the value of the output impedance Zo also decreases.

[0073] As described above, since the output impedance Zo decreases, the rise of the electrical signal detected by the detection unit 130 becomes sharp. As a result, the difference in the slope of the electrical signal due to the difference in the electrical conductivity of the detection target 200 decreases.

[0074] Actually, in pattern a of FIG. 6, a difference occurs in the rising slope of the electrical signal due to the difference in the electrical conductivity of the detection target 200. On the other hand, in pattern b of FIG. 7, the difference in the rising slope of the electrical signal is small.

[0075] On the other hand, the propagation time of the electrical signal from point A to point B changes due to the difference in the relative permittivity of the detection target 200. Therefore, the state of the detection target 200 can be detected by detecting the propagation time of the electrical signal. The state of the detection target 200 is, for example, the moisture content of the detection target 200. The moisture content is the ratio of water contained in the detection target 200. In other words, the moisture content is the volume content ratio of water contained in the detection target 200. The moisture content is represented by, for example, the unit of %.

[0076] The propagation time is the time from when the output unit 120 outputs an electrical signal until the amplitude of the electrical signal detected by the detection unit 130 starts to rise. For example, the time from when the output unit 120 outputs an electrical signal until the amplitude of the electrical signal detected by the detection unit 130 reaches a specified value may be defined as the propagation time. Of course, the detection unit 130 acquires the timing at which the output unit 120 outputs an electrical signal from the output unit 120.

[0077] Therefore, due to the small difference in the rising slope of the electrical signal caused by the difference in the electrical conductivity of the detection target 200, an effect can also be obtained that the detection error of the propagation time of the electrical signal can be reduced.

[0078] Next, examples of the values of the output impedance Zo and the input impedance Zi will be described. As shown in FIG. 3, the sensitivity increases and saturates as the input impedance Zi increases. As the sensitivity increases, the voltage amplitude of the electrical signal also increases. For example, the value of the input impedance Zi can be set to 10 times the value of the effective characteristic impedance Zc2. Thereby, the saturation of the sensitivity becomes prominent.

[0079] Also, as shown in FIG. 4, in the range where the output impedance Zo is small, the change in sensitivity is large. That is, the influence degree of the change in sensitivity is high. On the other hand, in the range where the output impedance Zo is large, the change in sensitivity is small. That is, the influence degree of the change in sensitivity is low. Therefore, for example, the output impedance Zo can be set so as to satisfy 0.7×Zc2 < Zo < 1.5×Zc2. Even if a range is provided for the value of the output impedance Zo, since the effect of improving the sensitivity can be obtained, it can be said that the output impedance Zo is matched with the effective characteristic impedance Zc2.

[0080] As described above, in the present embodiment, as the first condition, the output impedance Zo of the output unit 120 is matched with the effective characteristic impedance Zc2 of the transmission line 111. Thereby, it is possible to eliminate or reduce the voltage reflection when the electrical signal is output from the output unit 120 to the transmission line 111. Therefore, since the electrical stress, distortion of the electrical signal, noise generation, etc. when the electrical signal is output from the output unit 120 to the transmission line 111 are reduced, the sensitivity of the electrical signal can be improved.

[0081] Further, as the second condition, the input impedance Zi of the detection unit 130 is set to a value larger than the effective characteristic impedance Zc2 of the element 110. Thereby, the voltage reflection when the electrical signal is input from the transmission line 111 to the detection unit 130 increases. Therefore, since the amplitude of the electrical signal detected by the detection unit 130 can be increased not only by the incident component but also by the reflected component, the sensitivity of the electrical signal can be improved.

[0082] Since the sensor device 100 according to the present embodiment can maximize the sensitivity of the electrical signal, it is possible to improve the situation where the state of the detection target 200 is erroneously detected or cannot be detected due to insufficient sensitivity.

[0083] In recent years, instead of traditional agriculture relying on experience and know-how, data-based agriculture has been favored. In agriculture where crops are planted in soil, soil sensing technology for digitizing the state of the soil has been developed. In such an environment, it becomes possible to highly sensitively detect the electrical conductivity of the soil by the sensor device 100.

[0084] (Second Embodiment) In the present embodiment, mainly the parts different from the first embodiment will be described. In the present embodiment, in the sensor device 100, the output impedance Zo and the input impedance Zi are configured to be variable. That is, the sensor device 100 has a sensitivity adjustment function.

[0085] Specifically, as shown in FIG. 8, the output unit 120 has an output-side variable element 122. The output-side variable element 122 is an element for setting the output impedance Zo of the output unit 120. The output-side variable element 122 is controlled by, for example, the signal generation circuit 121. Alternatively, the output-side variable element 122 may be controlled by another circuit unit provided in the output unit 120. Thereby, the output impedance Zo is variable by the output-side variable element 122.

[0086] Also, as shown in FIG. 8, the detection unit 130 has a detection-side variable element 132. The detection-side variable element 132 is an element for setting the input impedance Zi of the detection unit 130. The detection-side variable element 132 is controlled by, for example, the signal detection circuit 131. Alternatively, the detection-side variable element 132 may be controlled by another circuit unit provided in the detection unit 130. Thereby, the input impedance Zi is variable by the detection-side variable element 132.

[0087] The output-side variable element 122 and the detection-side variable element 132 are composed of, for example, a circuit in which a plurality of resistance elements are connected in parallel. A switch is connected in series to each resistance element, and the combined resistance value can be adjusted by switching the switch. Of course, each variable element 122, 132 may be composed of other circuit configurations. The adjustment of each variable element 122, 132 is performed, for example, when the sensor device 100 is powered on or at regular intervals.

[0088] Alternatively, the adjustment of each variable element 122, 132 can be performed before detecting the electrical conductivity. For example, by automatically adjusting each variable element 122, 132 in a state where the detection target 200 is in contact with the element 110, it is possible to automatically adjust the point at which the sensitivity due to the difference in the detection target 200 is maximized. Alternatively, the sensitivity may be adjustable by the user adjusting each variable element 122, 132.

[0089] Further, by adjusting each of the variable elements 122 and 132, it is possible to correct a sensitivity decrease due to a difference in proximity of the detection target 200 to the element 110. Furthermore, it is possible to correct a sensitivity decrease due to deterioration of the element 110 or the like. Adjustment of each of the variable elements 122 and 132 not only improves the sensitivity but also enables correspondence to applications such as those where the sensitivity is not required and the absolute value of the voltage needs to be suppressed.

[0090] As a modification, although the output unit 120 has the output-side variable element 122, the detection unit 130 may not have the detection-side variable element 132. That is, the output impedance Zo may be a variable value, and the input impedance Zi may be a fixed value.

[0091] As a modification, the output unit 120 may not have the output-side variable element 122, and the detection unit 130 may have the detection-side variable element 132. That is, the output impedance Zo may be a fixed value, and the input impedance Zi may be a variable value.

[0092] (Third Embodiment) In this embodiment, mainly the parts different from the above embodiments will be described. In this embodiment, the sensor device 100 has two systems of elements 110.

[0093] Specifically, as shown in FIG. 9, the element 110 has two systems as transmission lines 111, a first transmission line 111A and a second transmission line 111B. For example, the first transmission line 111A is formed on the surface of the printed circuit board, and the second transmission line 111B is formed on the back surface of the printed circuit board. Alternatively, each of the transmission lines 111A and 111B may be formed on the same surface of the printed circuit board. It is desirable that the wiring patterns of the transmission lines 111A and 111B are the same.

[0094] Here, the output impedance Zo and the input impedance Zi of the two systems of the element 110 can be set to either the same system or different systems.

[0095] When two systems of element 110 are of the same system, in output unit 120, a first output impedance Zo1 with respect to first transmission line 111A and a second output impedance Zo2 with respect to second transmission line 111B are set to the same value. Also, in detection unit 130, a first input impedance Zi1 with respect to first transmission line 111A and a second input impedance Zi2 with respect to second transmission line 111B are set to the same value. Thereby, the two systems of element 110 are configured as the same system.

[0096] Since the two systems of element 110 are configured as the same system, by comparing the detected values of the electrical signals, if there is a difference in the detected values, abnormalities, differences in proximity, etc. can be detected. Also, even if one of the two systems of element 110 is abnormal, the electrical conductivity can be detected by the other, so the robustness of sensor device 100 can be improved.

[0097] When two systems of element 110 are of different systems, in output unit 120, a first output impedance Zo1 with respect to first transmission line 111A and a second output impedance Zo2 with respect to second transmission line 111B are set to different values. Also, in detection unit 130, a first input impedance Zi1 with respect to first transmission line 111A and a second input impedance Zi2 with respect to second transmission line 111B are set to different values. Thereby, the two systems of element 110 are configured as different systems.

[0098] Since the two systems of element 110 are configured as different systems, the applicable range of detection target 200 can be expanded, such as using the more sensitive one of the two systems of element 110. Also, if there is no difference by comparing the detected values of the electrical signals, abnormalities, differences in proximity, etc. can be detected.

[0099] Furthermore, since element 110 has two systems, there is also an advantage that the electrical conductivities of different detection targets 200 can be detected simultaneously.

[0100] (Fourth Embodiment) In this embodiment, mainly the parts different from the above-described embodiments will be described. In this embodiment, as shown in FIG. 10, the output impedance Zo is included in the signal generation circuit 121. In this way, the output unit 120 can be configured by one electronic circuit. Further, the impedance Zi is included in the signal detection circuit 131. In this way, the detection unit 130 can be configured by one electronic circuit.

[0101] Alternatively, as shown in FIG. 11, the circuit for generating the output impedance Zo, the circuit for generating the impedance Zi, the signal generation circuit 121, and the signal detection circuit 131 may be configured as one integrated circuit chip 140. The integrated circuit chip 140 is mounted on, for example, a printed circuit board.

[0102] Note that although the output impedance Zo is included in the signal generation circuit 121, the impedance Zi may not be included in the signal detection circuit 131. Although the output impedance Zo is not included in the signal generation circuit 121, the impedance Zi may be included in the signal detection circuit 131. The circuit for generating the output impedance Zo, the circuit for generating the impedance Zi, the signal generation circuit 121, and the signal detection circuit 131 may each be configured as an individual electronic circuit, or may be configured as one electronic circuit as a whole.

[0103] (Fifth Embodiment) In this embodiment, mainly the parts different from the above-described embodiments will be described. In this embodiment, as shown in FIG. 12, the element 110, the circuit for generating the output impedance Zo, the circuit for generating the impedance Zi, the signal generation circuit 121, and the signal detection circuit 131 are formed on one semiconductor chip 150.

[0104] The transmission line 111 of the element 110 is formed as a conductor pattern of the semiconductor chip 150. The conductor pattern is formed, for example, as MEMS (Micro Electro Mechanical Systems). Thus, the sensor device 100 may be configured as one semiconductor chip 150.

[0105] As a modification, the element 110 and other circuits may be formed on separate semiconductor chips 150.

[0106] (Other embodiments) The configuration of the sensor device 100 shown in each of the above embodiments is an example, and is not limited to the configuration shown above, and other configurations capable of realizing the present invention may be used. For example, the transmission line 111 is not limited to a conductor pattern, and may be composed of metal parts such as a metal bar or a waveguide.

[0107] The technical features of the sensor device disclosed in this specification are shown as follows. (Item 1) An element (110) configured as a transmission line (111) having a characteristic impedance (Zc1), wherein the characteristic impedance changes to an effective characteristic impedance (Zc2) having a value different from the characteristic impedance when the detection target (200) is brought close to the transmission line, An output unit (120) having an output impedance (Zo), generating an electrical signal whose amplitude changes with time, and outputting the electrical signal to the transmission line of the element, A detection unit (130) having an input impedance (Zi), inputting the electrical signal via the transmission line, and detecting the electrical conductivity of the detection target based on the magnitude of the amplitude of the electrical signal, comprising the output impedance of the output unit is matched to the effective characteristic impedance of the element, the input impedance of the detection unit is set to a value larger than the effective characteristic impedance of the element, a sensor device. (Item 2) The output unit includes an output-side variable element (122), The sensor device according to item 1, wherein the output impedance is variable by the output-side variable element. (Item 3) The detection unit includes a detection-side variable element (132), The sensor device according to item 1 or 2, wherein the input impedance is variable by the detection-side variable element. (Item 4) The sensor device according to any one of items 1 to 3, wherein the element has two systems of a first transmission line (111A) and a second transmission line (111B) as the transmission line. (Item 5) In the output unit, a first output impedance (Zo1) with respect to the first transmission line and a second output impedance (Zo2) with respect to the second transmission line are set to the same value, In the detection unit, a first input impedance (Zi1) with respect to the first transmission line and a second input impedance (Zi2) with respect to the second transmission line are set to the same value, The sensor device according to item 4, wherein the two systems are configured as the same system. (Item 6) In the output unit, a first output impedance (Zo1) with respect to the first transmission line and a second output impedance (Zo2) with respect to the second transmission line are set to different values, In the detection unit, a first input impedance (Zi1) with respect to the first transmission line and a second input impedance (Zi2) with respect to the second transmission line are set to different values, The sensor device according to item 4, wherein the two systems are configured as different systems. (Item 7) The element is formed on a semiconductor chip (150), The sensor device according to any one of items 1 to 6, wherein the transmission line of the element is formed as a conductor pattern of the semiconductor chip. (Item 8) The detection target includes at least one of soil and water. The detection unit detects at least one of the electrical conductivity of the soil and the electrical conductivity of the water. The sensor device according to any one of Items 1 to 7.

Description of Reference Numerals

[0108] 100 Sensor device 110 Element 111 Transmission line 120 Output unit 122 Output-side variable element 130 Detection unit 132 Detection-side variable element 150 Semiconductor chip 200 Detection target

Claims

1. An element (110) configured as a transmission line (111) having a characteristic impedance (Zc1), wherein the characteristic impedance changes to an effective characteristic impedance (Zc2) having a value different from the characteristic impedance when a detection target (200) is brought close to the transmission line, An output unit (120) having an output impedance (Zo), generating an electrical signal whose amplitude changes with time, and outputting the electrical signal to the transmission line of the element, A detection unit (130) having an input impedance (Zi), inputting the electrical signal via the transmission line, and detecting the electrical conductivity of the detection target based on the magnitude of the amplitude of the electrical signal, comprising: the output impedance of the output unit is matched to the effective characteristic impedance of the element, the input impedance of the detection unit is set to a value greater than the effective characteristic impedance of the element, a sensor device.

2. the output unit includes an output-side variable element (122), the output impedance is variable by the output-side variable element, the sensor device according to claim 1.

3. the detection unit includes a detection-side variable element (132), the input impedance is variable by the detection-side variable element, the sensor device according to claim 1 or 2.

4. the element has two systems, a first transmission line (111A) and a second transmission line (111B), as the transmission line, the sensor device according to claim 1.

5. the output unit has a first output impedance (Zo1) for the first transmission line and a second output impedance (Zo2) for the second transmission line set to the same value, the detection unit has a first input impedance (Zi1) for the first transmission line and a second input impedance (Zi2) for the second transmission line set to the same value, the two systems are configured as the same system, the sensor device according to claim 4.

6. the output unit has a first output impedance (Zo1) for the first transmission line and a second output impedance (Zo2) for the second transmission line set to different values, The detection unit is configured such that a first input impedance (Zi1) with respect to the first transmission line and a second input impedance (Zi2) with respect to the second transmission line are set to different values. The sensor device according to claim 4, wherein the two systems are configured as different systems. **Claim 7** The element is formed on a semiconductor chip (150). The sensor device according to claim 1, wherein the transmission line of the element is formed as a conductor pattern of the semiconductor chip. **Claim 8** The detection target includes at least one of soil and water. The sensor device according to claim 1, wherein the detection unit detects at least one of the electrical conductivity of the soil and the electrical conductivity of the water.

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