Sensor wire, sensor device, and wire harness

Abstract

Provided are a sensor wire serving as a member capable of sensitively detecting mechanical deformation and environmental changes, and a sensor device and a wire harness including the sensor wire.　A sensor wire 1 comprises a pair of insulated wires 12, 12 each having a conductor and an insulating covering, the pair of insulated wires 12, 12 constituting a two-wire coil 11 wound in a helical shape with the longitudinal axes thereof aligned. Further, a sensor device 2 includes: the sensor wire 1; and a monitoring means 21 for inputting a differential signal to the pair of insulated wires 12, 12 constituting the sensor wire 1 and acquiring a response signal, and monitoring changes in the response signal. Furthermore, the wire harness comprises a target wire comprising at least one wire, and the sensor device 2, wherein the sensor wire 1 constituting the sensor device 2 is disposed in at least a partial region in the longitudinal direction of the target wire, with the central axis thereof oriented in the longitudinal direction.

Description

Sensor wire, sensor device, and wire harness

[0001] The present disclosure relates to a sensor wire, a sensor device, and a wire harness.

[0002] Electric wires are installed or laid in various electrical and electronic devices, transportation equipment, buildings, public facilities, etc., and damage to the wires may occur over long-term use. To prevent damage from seriously affecting the performance of the wire, it is desirable to detect the occurrence of damage early and sensitively. One method for detecting damage to an electric wire is to attach a component that functions as a damage-detecting sensor to the electric wire and inspect the electric wire for damage using the component. For example, Patent Document 1 discloses an electric wire in which a conductive tape or laminated tape is disposed around the outer periphery of a core wire having a conductor and an insulating coating. The conductive tape is wound spirally around the surface of the insulating coating along the axial direction of the core wire, and gaps not occupied by the conductive tape are provided between the spiral turns of the conductive tape. The laminated tape has a substrate formed as a tape-shaped insulator or semiconductor and conductive coating layers formed on both sides of the substrate. When a defect is formed in the electric wire, the damage to the conductive tape changes the characteristic impedance between the conductive tape and the conductor that constitutes the core wire, and the damage to the laminated tape changes the characteristic impedance between the two coating layers included in the laminated tape, so that the formation of a defect in the electric wire can be sensitively detected.

[0003] JP 2021-162449 A

[0004] By attaching a material whose electrical properties change when damaged, such as the conductive tape or laminated tape used in the above-mentioned Patent Document 1, to an electric wire, damage caused by external force or the like can be detected with high sensitivity. However, electric wires may be frequently subjected to deformation due to mechanical loads or changes in the surrounding environment, even if they do not result in irreversible damage. These mechanical deformations and environmental changes may change the operation and characteristics of the electric wire, which may cause the electric wire itself or the equipment to which the electric wire is connected to to fail to perform its intended function. Furthermore, if the effects of mechanical deformations and environmental changes accumulate in an electric wire, they may eventually lead to damage or deterioration of the electric wire. To avoid such situations, it is desirable to be able to sensitively detect mechanical deformations and environmental changes in an electric wire that do not immediately result in damage or deterioration.

[0005] In view of the above, an object of the present invention is to provide a sensor wire as a member capable of sensitively detecting mechanical deformation and environmental changes, and a sensor device and a wire harness including such a sensor wire.

[0006] The sensor wire according to the present disclosure comprises a pair of insulated wires, each having a conductor and an insulating coating covering the outer periphery of the conductor, and the pair of insulated wires form a two-wire coil wound in a spiral shape with their longitudinal axes aligned.

[0007] The sensor device according to the present disclosure includes the sensor wire and a monitoring means that inputs a differential signal to the pair of insulated wires that make up the sensor wire to obtain a response signal and monitors changes in the response signal.

[0008] The wire harness according to the present disclosure includes a target electric wire consisting of at least one electric wire and the sensor device, and the sensor electric wire constituting the sensor device is arranged in at least a partial region along the longitudinal direction of the target electric wire, with its central axis facing the longitudinal direction.

[0009] The sensor wire, sensor device, and wire harness according to the present disclosure are sensor wires that are components capable of sensitively detecting mechanical deformation and environmental changes, and are sensor devices and wire harnesses that include such sensor wires.

[0010] FIG. 1A is a perspective view showing a sensor wire according to an embodiment of the present disclosure. FIG. 1B is a schematic diagram showing a configuration of a sensor device according to an embodiment of the present disclosure. FIGS. 2A and 2B are perspective views showing an example configuration of a wire harness according to an embodiment of the present disclosure. FIG. 2A shows a configuration in which a sensor wire runs parallel to a target wire, and FIG. 2B shows a configuration in which the target wire is inserted into a hollow portion of a two-wire coil. FIGS. 3A and 3B are schematic cross-sectional views showing state changes when a two-wire coil is stretched, with FIG. 3A showing the state before stretching and FIG. 3B showing the state after stretching. FIGS. 4A and 4B are schematic cross-sectional views showing state changes when a liquid is brought into contact with a two-wire coil, with FIG. 4A showing the state before contact with the liquid and FIG. 4B showing the state after contact with the liquid. FIGS. 5A and 5B are schematic cross-sectional views showing state changes associated with melting of a substance in contact with the two-wire coil, with FIG. 5A showing the state before melting and FIG. 5B showing the state after melting. 6A and 6B are schematic cross-sectional views showing the state change due to chemical change of a substance in contact with a two-wire coil. FIG. 6A shows the low-dielectric-constant state before the chemical change, and FIG. 6B shows the high-dielectric-constant state after the chemical change. FIG. 7 shows measurement results showing the change in the reflection coefficient due to elongation of the sensor wire. FIG. 8 shows measurement results showing the change in the reflection coefficient due to bending of the sensor wire. FIG. 9 shows measurement results showing the change in the reflection coefficient of the sensor wire due to elongation caused by heating. FIGS. 10A to 10D show measurement results showing the change in the reflection coefficient due to contact with various substances. FIG. 10A shows the change due to contact with water, FIG. 10B shows the change due to contact with silicone oil, FIG. 10C shows the change due to contact with polyurethane, and FIG. 10D shows the change due to contact with a water-absorbing polymer. FIGS. 11A and 11B show measurement results showing the change in the reflection coefficient of the sensor wire due to contact with a conductive substance. FIG. 11A shows the change due to contact with a liquid substance, and FIG. 11B shows the change due to contact with a solid substance. FIG. 12 shows measurement results showing the change in the reflection coefficient due to heating when a heat-shrinkable tube is placed around the outer periphery of a two-wire coil. 13A and 13B show measurement results showing the change in reflection coefficient due to contact with a substance for the first comparative electric wire and the second comparative electric wire, respectively.

[0011] [Description of the embodiment of the present disclosure] First, the embodiment of the present disclosure will be described.

[0012] [1] The sensor wire of the present disclosure comprises a pair of insulated wires, each having a conductor and an insulating coating covering the outer periphery of the conductor, and the pair of insulated wires form a two-wire coil wound in a spiral shape with their longitudinal axes aligned.

[0013] The sensor wire sensitively detects mechanical deformation and environmental changes applied to the sensor wire and outputs the detected electrical signals. Specifically, by inputting a differential signal to a pair of insulated wires constituting a two-wire coil and acquiring a response signal such as characteristic impedance, the response signal can change to reflect the mechanical deformation and environmental changes applied to the sensor wire. This is because an electric field is generated between adjacent insulated wires along the spiral axis, and the state of this electric field changes with changes in the distance between the insulated wires due to deformation of the two-wire coil and changes in the dielectric constant of materials surrounding the two-wire coil. Changes in the state of the electric field also change the response signal such as characteristic impedance. Therefore, by placing the sensor wire together with a target wire whose effects of mechanical deformation and environmental changes are to be monitored, inputting an inspection signal to the sensor wire, and detecting the response signal, mechanical deformation and environmental changes applied to the assembly of the target wire and the sensor wire can be sensitively detected as changes in the response signal.

[0014] In this sensor wire, a pair of insulated wires are wound in a spiral shape, forming a two-wire coil. This allows for more sensitive detection of mechanical deformation and environmental changes as changes in the response signal than when the wires run parallel to each other in a straight line. This is because the long insulated wires are housed in a predetermined length region, allowing the entire length of the insulated wires to be used as a sensor. Furthermore, the expansion and contraction of the two-wire coil allows for large deformation. Furthermore, because the insulated wires are wound in a spiral shape, when an AC signal is input, a magnetic field may be generated for each individual insulated wire. However, because the two insulated wires are wound in a spiral shape with their longitudinal axes aligned, and the signals input to the two insulated wires are differential signals with opposite polarities, the magnetic fields generated by the two insulated wires cancel each other out. This reduces the likelihood of the magnetic field affecting the detection results of the sensor wire or the operation of the target wire.

[0015] [2] In the above aspect [1], each of the pair of insulated wires may be configured as an enameled wire. This allows the insulating coating of the insulated wire to be thin and the distance between adjacent conductors in the spiral shape to be small, so that deformation of the two-wire coil and changes in the dielectric constant of the material surrounding the two-wire coil are more likely to be reflected as changes in the electric field. As a result, mechanical deformation or environmental changes in the sensor wire are more likely to cause large changes in the response signal.

[0016] [3] In the above aspect [1] or [2], a core may be inserted through the central axis of the two-wire coil. Using a core makes it easier to use the sensor wire as a self-supporting component. Furthermore, using a core makes the two-wire coil less likely to deform under small mechanical loads, such as minute vibrations. This makes it possible to ignore mechanical loads within a range that can be considered normal and selectively detect mechanical loads that should be detected as abnormalities, etc., as changes in the response signal.

[0017] [4] In the above aspect [3], the core material may have flexibility that allows it to bend and deform in accordance with bending of the two-wire coil. In this case, when an external force that bends and deforms the sensor wire is applied, the sensor wire, including the core material, undergoes bending deformation, causing a change in the response signal.

[0018] [5] In the above aspect [3] or [4], the core material may have elasticity that allows it to expand and contract in accordance with the expansion and contraction of the two-wire coil. In this case, when an external force that causes expansion and contraction deformation is applied to the sensor wire, the sensor wire, including the core material, undergoes expansion and contraction deformation, causing a change in the response signal.

[0019] [6] In any one of the above aspects [3] to [5], the core may be configured as a hollow cylinder with both ends open along the central axis of the two-wire coil. A hollow core is more susceptible to deformation, such as bending and expansion, than a solid core. When an external force is applied to the sensor wire, the applied external force can be sensitively reflected in a change in the response signal of the sensor wire. Furthermore, when gas is trapped inside the core, having both ends open makes it easier to avoid a situation in which the response signal changes due to the expansion / contraction of the gas, as in the aspect [7] below. This suppresses changes in the response signal due to temperature changes, enabling the mechanical deformation of the sensor wire to be selectively and predominantly reflected in changes in the response signal.

[0020] [7] Alternatively, in any one of the above aspects [3] to [5], the core material may be configured as a hollow cylinder with both ends closed along the central axis of the two-wire coil, and a gas may be sealed in the hollow portion. In this case, the gas sealed inside the core material expands / contracts in response to temperature changes in the environment in which the sensor wire is placed, and the constituent material of the core material also expands / contracts accordingly. This causes the two-wire coil to expand and contract along with the core material, resulting in a change in the response signal acquired by the sensor wire. In this way, temperature changes in the environment in which the sensor wire is placed can be detected via changes in the response signal.

[0021] [8] Alternatively, in any one of the above aspects [3] to [5], the core material may be configured as a solid body. In this case, the core material is less likely to deform due to a mechanical load or expand / contract due to a temperature change. Therefore, in the sensor wire, the application of a mechanical load or a temperature change is less likely to cause a change in the response signal. Therefore, events that may cause a change in the state of the electric field in the sensor wire other than the application of a mechanical load or a temperature change, such as changes in a material that comes into contact with the sensor wire from the outside, can be detected by the change in the response signal while suppressing the effects of the application of a mechanical load or a temperature change.

[0022] [9] In any one of the above aspects [1] to [8], it is preferable that a medium containing a substance that causes a change in the permittivity of the region surrounding the two-wire coil in response to a change in the environment be disposed on at least one of the inside and outside of the two-wire coil. In this case, when a change occurs in the environment in which the sensor wire is placed, a change in the response signal of the sensor wire occurs due to the change in the permittivity of the region surrounding the two-wire coil and the accompanying change in the state of the electric field. The change in the environment can then be detected based on the change in the response signal.

[0023]

[10] In the aspect [9] above, the change in the dielectric constant may be caused by at least one of a phase transformation and a chemical change of the intermediary material. In many substances, the dielectric constant changes when a phase transformation or a chemical change occurs. By using a substance that undergoes such a phase transformation or a chemical change as the intermediary material, changes in the environment in which the sensor wire is placed can be sensitively detected as changes in the response signal of the sensor wire.

[0024]

[11] In the aspect

[10] above, the intermediate material may be a heat-shrinkable tube having an adhesive on its inner surface that softens or melts when heated, and the heat-shrinkable tube is disposed around the two-wire coil. In this case, when the heat-shrinkable tube is heated, the adhesive becomes more fluid, causing the adhesive to penetrate into gaps and hollow spaces between the insulated wires that make up the spiral shape of the two-wire coil. Furthermore, when the heat-shrinkable tube shrinks, the adhesive is forced toward the inside of the two-wire coil, accelerating these phenomena. When these phenomena occur, the adhesive adheres to the surfaces of the insulated wires that make up the two-wire coil, significantly changing the state of the electric field around the two-wire coil and resulting in a change in the response signal. This change in the response signal allows sensitive detection of temperature increases in the environment in which the sensor wire is placed.

[0025]

[12] The sensor device of the present disclosure includes a sensor wire according to any one of [1] to

[11] above, and a monitoring means for inputting a differential signal to the pair of insulated wires constituting the sensor wire, acquiring a response signal, and monitoring changes in the response signal.

[0026] This sensor device receives a response signal by inputting a differential signal to the sensor wire having the two-wire coil via a monitoring means. When the sensor wire is subjected to mechanical deformation or an environmental change, the response signal changes sensitively via a change in the state of the electric field around the two-wire coil. Therefore, the sensor device can be used as a detection device for detecting the application of a mechanical load or a change in the environment. For example, by arranging the sensor wire along a target electric wire whose effects of mechanical deformation or an environmental change are to be monitored and monitoring the response signal, the sensor device can sensitively detect mechanical deformation or an environmental change when the aggregate of the target electric wire and the sensor wire is subjected to such an event. Because a pair of insulated electric wires constitute the two-wire coil and a differential signal is input to the two-wire coil, the generation of a magnetic field by the two-wire coil is unlikely to occur during measurement by the monitoring means.

[0027]

[13] In the aspect

[12] above, the monitoring means may determine that at least one of mechanical deformation, temperature change, and change in a material in contact with the sensor wire has occurred when a change in the response signal exceeding a reference value occurs. Mechanical deformation, temperature change, and change in a material in contact with the sensor wire are all events that cause a change in the response signal obtained from the sensor wire. By setting a predetermined reference value for the change in the response signal and determining that at least one of these events has occurred when a change in the response signal exceeding the reference value occurs, it is possible to detect the occurrence of such an event at a level that exceeds a predetermined level, such as a level that has a non-negligible impact on the operation of a target electric wire along which the sensor wire is placed, or a level that could lead to irreversible changes in the target electric wire, and to take measures to address the occurrence.

[0028]

[14] In the above aspect

[12] or

[13] , the monitoring means may monitor, as the response signal, a change in the characteristic impedance or reflection coefficient between the pair of insulated wires constituting the sensor wire. The characteristic impedance and reflection coefficient are parameters whose values ​​change and sensitively reflect changes in the state of the electric field due to mechanical deformation of the sensor wire or environmental changes. Therefore, by measuring the characteristic impedance or reflection coefficient of the sensor wire, mechanical deformation and environmental changes in the sensor wire can be sensitively detected.

[0029]

[15] In the aspect

[14] above, the monitoring means may measure the characteristic impedance or reflection coefficient using a time-domain reflectometry or a frequency-domain reflectometry. By employing the time-domain reflectometry or the frequency-domain reflectometry, the area where the change occurs in the characteristic impedance or reflection coefficient in the response signal can be associated with a position along the central axis of the sensor wire through appropriate calculations based on information about the area where the change occurs. Furthermore, the position can be associated with a position where mechanical deformation or an environmental change occurs in the sensor wire. This makes it possible to easily and accurately identify the position where mechanical deformation or an environmental change occurs along the axis of the sensor wire.

[0030]

[16] In any one of the above aspects

[12] to

[15] , the two-wire coil may be impedance-matched with the monitoring means by adjusting the number of turns. By matching the impedance between the two-wire coil and the monitoring means, it is possible to acquire a response signal while reducing the effects of loss and noise, and to detect mechanical deformation and environmental changes in the sensor wire with high accuracy. In the two-wire coil, adjusting the number of turns allows the characteristic impedance to be easily changed and impedance matching with the monitoring means to be achieved.

[0031]

[17] The wire harness of the present disclosure includes a target electric wire consisting of at least one electric wire and any one of the sensor devices

[12] to

[16] above, and the sensor electric wire constituting the sensor device is arranged in at least a partial region along the longitudinal direction of the target electric wire, with its central axis facing the longitudinal direction.

[0032] In this wire harness, a sensor wire having a two-wire coil is arranged along the longitudinal direction of the target electric wire. Therefore, if mechanical deformation or environmental changes occur in the assembly of the target electric wire and the sensor electric wire, the sensor device can sensitively detect them. This makes it possible to detect mechanical deformation or environmental changes that may affect the operation or characteristics of the target electric wire, take these effects into consideration when using the target electric wire, and take measures such as replacing the target electric wire before the mechanical deformation or environmental changes lead to irreversible damage or deterioration of the target electric wire.

[0033]

[18] In the aspect

[17] above, the sensor wire may be arranged alongside the target electric wire. In this case, regardless of the specific configurations of the sensor wire and the target electric wire, the sensor wire can be arranged along the longitudinal direction of the target electric wire, so that the sensor wire can provide various target electric wires with the function of detecting changes such as mechanical deformation and environmental changes.

[0034]

[19] Alternatively, in the aspect

[17] above, the target electric wire may be inserted into a hollow portion of the two-wire coil. In this case, by utilizing the shape of the two-wire coil having a hollow portion, it is possible to construct a wire harness including a sensor electric wire while keeping the space occupied small.

[0035] [Details of the embodiment of the present disclosure] A sensor wire, a sensor device, and a wire harness according to the embodiment of the present disclosure will be described in detail below with reference to the drawings. A sensor device is configured including the sensor wire according to the embodiment of the present disclosure. A wire harness is configured including the sensor device. The sensor wire and the sensor device monitor mechanical deformation and environmental changes, and in a wire harness, the sensor device monitors the target wire to be monitored. In this specification, terms such as linear and spiral that indicate the shape and arrangement of components of a wire include not only a strict geometric concept but also an allowable range of error for the wire.

[0036] <Outline of the Configuration of the Sensor Wire, Sensor Device, and Wire Harness> First, an outline of the configuration of the sensor wire, sensor device, and wire harness according to an embodiment of the present disclosure will be described. Fig. 1A shows a perspective view of an example of the structure of the sensor wire according to an embodiment of the present disclosure. Fig. 1B shows a schematic diagram of an example of the configuration of the sensor device according to an embodiment of the present disclosure. Furthermore, Figs. 2A and 2B show perspective views of an example of the configuration of the wire harness according to an embodiment of the present disclosure. Figs. 2A and 2B each show a different configuration.

[0037] (1) Sensor Wire As shown in Fig. 1A, a sensor wire 1 according to one embodiment of the present disclosure includes a two-wire coil 11. The two-wire coil 11 includes a pair (two) of insulated wires 12, 12. Each insulated wire 12 includes a conductor 12a and an insulating coating 12b that covers the outer periphery of the conductor 12a (see Fig. 3A). The type of insulated wires 12, 12 is not particularly specified, but it is preferable that they be configured as enameled wires.

[0038] In the two-wire coil 11, a pair of insulated electric wires 12, 12 are wound in a spiral shape with their longitudinal axes aligned. In FIG. 1B , the pair of insulated electric wires 12, 12 are schematically shown as thick and thin lines. As shown in FIGS. 1A and 1B , the pair of insulated electric wires 12, 12 are parallel to each other along the central axis of the two-wire coil 11 (the horizontal direction in the figure), forming a spiral structure. Therefore, in a cross section of the two-wire coil 11 cut along the central axis, the two insulated electric wires 12, 12 are alternately arranged (see FIG. 3A ). In the two-wire coil 11, the pair of insulated electric wires 12, 12 are not fixed to each other by, for example, fusing the insulating coating 12 b, and are movable relative to each other.

[0039] The sensor wire 1 further includes, optionally, a core 13. The core 13 is inserted through the central axis of the two-wire coil 11. That is, the core 13 is inserted through the spiral-shaped hollow portion 11a of the two-wire coil 11 along the central axis. The sensor wire 1 includes the core 13, which stably maintains the structure of the two-wire coil 11, which is straightened along the central axis, making the sensor wire 1 easier to handle as a free-standing member. Furthermore, the insertion of the core 13 makes the two-wire coil 11 less susceptible to deformation due to small mechanical loads such as minute vibrations. The core 13 also functions as a base when the pair of insulated wires 12, 12 are wound spirally to form the two-wire coil 11. The core 13 is preferably made of a non-magnetic insulator, but the specific configuration and material of the core 13 are preferably selected depending on the change to be detected by the sensor wire 1, as will be described in detail later.

[0040] Furthermore, although not included in the illustrated embodiment, the sensor wire 1 may include an intermediate material on at least one of the inside and outside of the two-wire coil 11. The intermediate material refers to a substance that causes a change in the dielectric constant in the area surrounding the two-wire coil 11 (the area outside the two-wire coil 11 and inside the hollow portion 11a) due to environmental changes. The environmental changes refer to changes in the temperature of the space in which the sensor wire 1 is placed or changes in the surrounding substances. When the intermediate material is disposed inside the two-wire coil 11, the intermediate material can be filled into the hollow portion 11a of the two-wire coil 11. The core material 13 may also serve as the intermediate material. When the intermediate material is disposed outside the two-wire coil 11, a sheet-shaped intermediate material can be wrapped around the outer periphery of the two-wire coil 11, a tubular intermediate material can be fitted, or other such forms can be used. Specific types of intermediate material will be described later.

[0041] (2) Sensor Device As shown schematically in FIG. 1B , a sensor device 2 according to an embodiment of the present disclosure includes the sensor wire 1 and monitoring means 21 (the core 13 of the sensor wire 1 is omitted in FIG. 1B ). The monitoring means 21 is a device that inputs an AC inspection signal to the sensor wire 1, acquires a response signal, and monitors changes in the response signal. The inspection signal is a differential signal. That is, AC signals of opposite polarities are input to each of the insulated wires 12, 12. By inputting a differential signal to the two-wire coil 11, the insulated wires 12, 12 through which AC currents of opposite polarities flow are arranged alternately along the central axis of the two-wire coil 11 (see FIG. 3A ).

[0042] The monitoring means 21 inputs an inspection signal consisting of a differential signal to the two-wire coil 11 of the sensor wire 1, and the characteristic impedance between the pair of insulated wires 12, 12 can be suitably used as the electrical parameter measured as the response signal. As will be described in detail later, when the sensor wire 1 undergoes mechanical deformation or environmental changes (such as temperature changes or changes in contacting materials), the state of the electric field in the space surrounding the sensor wire 1 changes, resulting in a corresponding change in the value of the characteristic impedance. Therefore, the sensor device 2 measures and monitors the value of the characteristic impedance as a response signal while inputting the inspection signal, and can detect mechanical deformation or environmental changes in the sensor wire 1 based on changes in the value. In addition to the characteristic impedance, other parameters that can be measured as the response signal include reflection coefficient, conductance, capacitance, and the like. These parameters are correlated with the characteristic impedance and reflect changes in the state of the electric field in the space surrounding the sensor wire 1. Measuring the characteristic impedance or reflection coefficient as the response signal is preferred in terms of high detection sensitivity to mechanical deformation and environmental changes.

[0043] The monitoring means 21 may be configured with a measuring device capable of generating a differential signal as an inspection signal and detecting a response signal. For example, an impedance meter or the like may be used to measure characteristic impedance as the response signal. When acquiring the response signal using the monitoring means 21, either a transmission method or a reflection method may be used. From the perspective of ease of measurement, the reflection method is preferable because the response signal can be acquired by connecting a measuring device to only one end. When using the reflection method, it is preferable to connect the measuring device to one end of the two-wire coil 11 and connect a terminating resistor 25 to the other end. In the sensor device 2, impedance matching is preferably performed between the monitoring means 21 and the two-wire coil 11 to reduce loss and noise in the response signal. Impedance matching can be easily achieved by adjusting the number of turns of the two-wire coil 11 (the number of times the insulated wires 12, 12 are wound helically).

[0044] The sensor device 2 can be used alone as a device that detects mechanical deformation and environmental changes. That is, by detecting mechanical deformation and environmental changes applied to the sensor wire 1 itself, the sensor device 2 can be used as an inspection device that detects mechanical loads occurring in the environment in which the sensor wire 1 is installed, as well as changes in temperature and substances present in that environment. Alternatively, the sensor wire 1 may be incorporated into a wire harness together with other wires, and the sensor device 2 may be used as a component that detects mechanical deformation and environmental changes applied to the entire wire harness. A form in which the sensor device 2 is used as a component of this wire harness will be described below.

[0045] (3) Wire Harness As shown in Fig. 2A and Fig. 2B , the wire harness 3 according to the embodiment of the present disclosure includes the sensor device 2 and a target electric wire 31. The target electric wire 31 is an electric wire that is the target of monitoring mechanical deformation and environmental changes by the sensor device 2, and is configured of at least one electric wire. In the illustrated embodiment, the target electric wire 31 includes only one electric wire. When the target electric wire 31 includes multiple electric wires, the multiple electric wires may be bundled with their longitudinal directions aligned.

[0046] In the wire harness 3, the sensor wire 1 constituting the sensor device 2 is arranged in at least a partial region along the longitudinal direction of the target electric wire 31. The sensor wire 1 and the target electric wire 31 are arranged with their axes aligned with each other. In other words, the sensor wire 1 is arranged with its central axis (coil axis) facing the longitudinal direction of the target electric wire 31.

[0047] 2A , the sensor wire 1 is arranged parallel to the target wire 31. By running the sensor wire 1 parallel to the target wire 31 in this manner, a wire harness 3 can be configured, and the target wire 31 can be provided with a monitoring function using the sensor wire 1. Although not shown in the figure, in the wire harness 3 in which the target wire 31 and the sensor wire 1 run parallel to each other, the target wire 31 and the sensor wire 1 are preferably bundled together using an exterior material, tape, or the like so that they do not separate from each other.

[0048] 2B , the target electric wire 31 is inserted into the hollow portion 11a of the two-wire coil 11 that constitutes the sensor electric wire 1. In this case, by utilizing the fact that the two-wire coil 11 has a spiral shape with the hollow portion 11a, the wire harness 3 can be constructed while minimizing the space occupied by the assembly of the two-wire coil 11 and the target electric wire 31. In particular, when the sensor electric wire 1 does not have a core material 13, this form of inserting the target electric wire 31 can be suitably adopted.

[0049] As described above, the sensor device 2 can detect mechanical deformation or environmental changes that occur to the sensor wire 1 through changes in the response signal. In the wire harness 3, the sensor wire 1 is aligned with the target wire 31, and the entire assembly of the sensor wire 1 and the target wire 31 is subjected to mechanical deformation or environmental changes. Therefore, when the sensor device 2 detects that mechanical deformation or environmental changes have occurred to the sensor wire 1, this means that the same type of mechanical deformation or environmental change has also occurred to the target wire 31. In this way, when changes such as mechanical deformation or environmental changes that may affect the characteristics or function of the target wire 31 occur, the sensor wire 1 can be used to detect these changes. Using the detection results, for example, the target wire 31 can be used while taking into consideration the impact that these changes may have on the characteristics and function of the target wire 31. Furthermore, measures such as replacing the target wire 31 can be taken before the effects of mechanical deformation or environmental changes accumulate and cause irreversible damage or deterioration to the target wire 31.

[0050] <Monitoring Changes Using a Sensor Wire> Next, a mechanism for monitoring changes such as mechanical deformation and environmental changes in the sensor wire 1 will be described, along with a configuration of the sensor wire 1 suitable for realizing this mechanism. First, a case where mechanical deformation is applied to the sensor wire 1 will be described in detail. Next, a case where an environmental change, that is, a temperature change or a change in a contacting substance, is applied to the sensor wire 1 will be described. In the description of the case where an environmental change is applied, matters common to the case where a mechanical change is applied will be omitted as appropriate. The following description will be given taking as an example a case where characteristic impedance is measured as a response signal.

[0051] (1) When Mechanical Deformation is Applied As a typical example of mechanical deformation, a case where the sensor wire 1 is stretched along the central axis will be described.

[0052] FIG. 3A shows a schematic cross section of the two-wire coil 11 cut along the central axis for the sensor wire 1 at its natural length without extension. In the figure, a pair of insulated wires 12, 12 constituting the two-wire coil 11 are arranged alternately. A differential signal is input as an inspection signal to the two-wire coil 11, causing the polarities of the pair of insulated wires 12, 12 to differ from each other. In the cross section, the insulated wires 12, 12 with opposite polarities are arranged alternately (polarity is indicated by + and - signs in the figure). When the inspection signal is input to the two-wire coil 11, an electric field is generated in the space surrounding the two-wire coil 11. As shown by the dashed and dotted lines in the figure, electric field lines are generated connecting adjacent insulated wires 12, 12. In the figure, the dashed and dotted lines indicate electric field lines pointing in opposite directions. The density of the electric field lines corresponds to the electric field strength. The magnitude of the characteristic impedance measured as a response signal reflects the state of the electric field generated by the two-wire coil 11. The display format of the diagrams is the same in FIGS. 3B to 6B.

[0053] When the two-wire coil 11 is extended along its central axis from the state shown in Figure 3A , the adjacent insulated wires 12, 12 in the spiral shape of the two-wire coil 11 move away from each other along the central axis of the two-wire coil 11, and the distance between the adjacent insulated wires 12, 12 increases, as shown in Figure 3B . This reduces the density of electric field lines in the space surrounding the two-wire coil 11. In other words, the electric field strength decreases. The increase in the distance between the adjacent insulated wires 12, 12 occurs both between a pair of two insulated wires 12, 12 that are adjacent with their longitudinal axes aligned, and between one insulated wire 12 and the other insulated wire 12 that are adjacent between turns of the spiral when the pair is wound in a spiral shape.

[0054] In the two-wire coil 11, adjacent insulated wires 12, 12 have opposite polarities, so that the adjacent insulated wires 12, 12 behave as a type of capacitor, and the capacitor characteristics affect the characteristic impedance between the pair of insulated wires 12, 12. The characteristics of a capacitor change depending on the distance between the electrodes. In the sensor wire 1 of this embodiment, when the two-wire coil 11 is elongated, the distance between the adjacent insulated wires 12, 12 with opposite polarities increases, and the electric field strength in the space near the two-wire coil 11 weakens, the characteristic impedance measured as a response signal in the sensor wire 1 increases. The greater the amount of elongation of the two-wire coil 11, the greater the increase in the characteristic impedance.

[0055] By utilizing this, the sensor wire 1 can detect mechanical deformation in a direction that stretches the sensor wire 1 itself or the wire harness 3 including the sensor wire 1. For example, in the wire harness 3, when an inspection signal is input to the sensor wire 1 and the characteristic impedance of the response signal obtained changes in an increasing direction exceeding a predetermined reference value, it can be determined that a mechanical load in the direction of stretching is being applied to the sensor wire 1 and the target wire 31. The reference value may be set as the amount of change in the characteristic impedance of the sensor wire 1 that corresponds to the upper limit of allowable stretch of the target wire 31. Applying an excessive mechanical load in the direction of stretching the wire can lead to an abnormality such as a break. Therefore, by detecting the load before a full-scale abnormality occurs in the target wire 31 due to the accumulated effect of the load, countermeasures can be taken early.

[0056] In the sensor wire 1 according to this embodiment, the pair of insulated wires 12, 12 are not arranged with their longitudinal axes aligned and stretched straight, but are wound in a spiral shape to form the two-wire coil 11, which allows for sensitive detection of mechanical deformations such as elongation as changes in the response signal. As will be shown in the examples below, one reason for this is that, because the spiral two-wire coil 11 extends along the central axis, changes in characteristic impedance due to changes in the distance between the insulated wires 12, 12 with opposite polarities can be utilized, as described above. If the pair of insulated wires 12, 12 were arranged with their longitudinal axes stretched straight, such changes in characteristic impedance due to changes in the distance between the insulated wires 12, 12 would be unlikely to occur. Another reason is that the spiral shape increases the actual length (the length along the longitudinal direction of the insulated wires 12, 12 themselves) of the two-wire coil 11, thereby increasing the total amount of change in characteristic impedance throughout the two-wire coil 11. Furthermore, because the two-wire coil 11 can expand and contract reversibly, even if mechanical loads are repeatedly and intermittently applied to the wire harness 3, the application of such loads can be detected each time they are applied. In this respect, it differs from detection members that detect the application of external loads by causing irreversible damage, such as the conductive tape or laminated tape disclosed in Patent Document 1.

[0057] In the two-wire coil 11 constituting the sensor wire 1, a pair of insulated wires 12, 12 are wound in a spiral shape. When an AC test signal is input, the insulated wires 12, 12 may act as an electromagnet and generate a magnetic field. However, because the pair of insulated wires 12, 12 are wound in a spiral shape with their longitudinal axes aligned, and the test signal, which is a differential signal, imparts opposite polarities to the pair of insulated wires 12, 12, the magnetic fields generated by the pair of insulated wires 12, 12 are opposite in direction and cancel each other out. Therefore, the two-wire coil 11 as a whole generates virtually no magnetic field. To effectively suppress the generation of a magnetic field, it is preferable that the core material 13 be made of a nonmagnetic material. Note that when an AC signal is input to a single insulated wire 12 wound in a spiral shape, not only does a magnetic field occur, but the characteristic impedance as a response signal remains almost unchanged even when subjected to mechanical deformation or environmental changes, and the sensor wire does not function (see Test [7] in the Examples).

[0058] As explained above, when the sensor wire 1 is stretched, an inspection signal consisting of a differential signal is input, and the stretch can be detected from a change in the characteristic impedance obtained as a response signal. However, even when mechanical deformation other than stretching is applied to the sensor wire 1, the mechanical deformation can be detected from a change in the response signal via a change in the electric field caused by a change in the distance between the alternating insulated wires 12, 12 in the spiral shape of the two-wire coil 11. For example, when the sensor wire 1 is compressed along the central axis, the distance between adjacent insulated wires 12, 12 in the spiral shape decreases, and the characteristic impedance obtained as a response signal when an inspection signal is input decreases. The greater the amount of compression, the greater the decrease in the response signal.

[0059] Furthermore, when the sensor wire 1 is bent, that is, when the central axis of the two-wire coil 11 is bent from a straight state into an arc, a change occurs in the characteristic impedance obtained as a response signal. This is because the sensor wire 1 is elongated on the outside of the bent shape, increasing the distance between adjacent insulated wires 12, 12, and the sensor wire 1 is compressed on the inside of the bent shape, decreasing the distance between adjacent insulated wires 12, 12. The direction of the change in the response signal depends on the specific compression shape. However, when the pair of insulated wires 12, 12 in the sensor wire 1 are wound relatively tightly, the effect of elongation on the outside of the bent shape is greater, and bending causes an increasing change in the characteristic impedance as a response signal. The amount of change in the response signal increases as the amount of bending increases, that is, as the bending diameter decreases.

[0060] From the viewpoint of sensitively detecting the mechanical deformation of the sensor wire 1 as a change in the response signal, it is preferable that the insulating coating 12b of the insulated wires 12, 12 constituting the two-wire coil 11 be thin. This is because, in the spiral shape of the two-wire coil 11, the shorter the distance between the conductors 12a constituting adjacent insulated wires 12, 12, the greater the change in the electric field due to the mechanical deformation of the two-wire coil 11, resulting in a large change in the characteristic impedance. As will be described later, when detecting environmental changes using the sensor wire 1, the thinner the insulating coating 12b, the more easily changes in the surrounding environment are reflected as changes in the electric field formed by the conductors 12a. The thinner the insulating coating 12b, the better, as long as the insulation properties of the conductors 12a can be maintained. It is most preferable to use enameled wire for each insulated wire 12.

[0061] Furthermore, in the two-wire coil 11, a pair of insulated electric wires 12, 12 wound with their longitudinal axes aligned are preferably wound closely together with small gaps between the turns. This reduces the difference between the distance between the insulated electric wires 12, 12 whose longitudinal axes are aligned (e.g., the distance between the nth and n+1th insulated electric wires from the left in FIG. 3A ; n is a positive odd number) and the distance between adjacent insulated electric wires in adjacent spiral turns (e.g., the distance between the n+1th and n+2th insulated electric wires from the left in FIG. 3A ). This allows for highly uniform changes in characteristic impedance due to mechanical deformation and environmental changes across the entire area of ​​the two-wire coil 11. Furthermore, the high density of the insulated electric wires 12, 12 in the two-wire coil 11 increases the amount of change in characteristic impedance due to mechanical deformation and environmental changes. Preferably, a pair of insulated wires 12, 12 are arranged in close contact with each other and wound in a spiral shape without any gaps between the turns, excluding unavoidable gaps. When the two-wire coil 11 is formed with small gaps between the turns in this manner, mechanical deformations such as elongation and bending that increase the distance between the insulated wires 12, 12 can be detected with high sensitivity through changes in the response signal. However, deformations such as compression that predominantly decrease the distance between the insulated wires 12, 12 may not detect changes in the response signal with high sensitivity. However, in electric wires used in environments where external forces may be applied, such as electric wires for automobiles, mechanical deformations that are likely to occur are elongation and bending, and it is these elongation and bending that are also likely to develop into irreversible damage, such as wire breakage, if repeatedly performed.

[0062] The specific dimensions and shape of the two-wire coil 11 may be determined arbitrarily depending on the type and dimensions of the target electric wires 31 used together, the arrangement in the wire harness 3, the change event to be detected, etc. For example, various parameters related to the dimensions and shape of the two-wire coil 11, such as the outer diameter of the insulated electric wires 12, 12, the coil diameter, the number of coil turns, etc., may be set so that the characteristic impedance is approximately 100 to 300 Ω.

[0063] From the viewpoint of allowing the mechanical deformation of the sensor wire 1 to be reflected significantly in changes in the response signal, it is preferable to not provide the sensor wire 1 with a core 13 and to maintain the two-wire coil 11 in a state in which it is easily deformed. However, from the viewpoint of making the sensor wire 1 more self-supporting and preventing the sensor wire 1 from detecting minute deformations, such as deformations due to normal minute vibrations, it is preferable to insert the core 13 into the hollow portion 11a of the two-wire coil 11. It is preferable to use a core 13 that can deform together with the two-wire coil 11 and the target electric wire 31 to be monitored without excessively interfering with the mechanical deformations of the two-wire coil 11 and the target electric wire 31. In other words, when the sensor wire 1 is used to detect expansion and contraction, the core 13 should be made of a material that is stretchable and can expand and contract in accordance with the expansion and contraction of the two-wire coil 11. When the sensor wire 1 is used to detect bending, the core 13 should be made of a material that is flexible and can bend in accordance with the bending of the two-wire coil 11. Alternatively, a core material 13 having both the stretchability and flexibility may be used.

[0064] An example of a core material 13 that is easily deformed mechanically is one made of a hollow cylinder. A hollow cylinder is more susceptible to deformation due to external forces than a solid body. It is particularly preferable to construct the hollow cylinder from a resin material. To minimize changes in the response signal due to temperature changes in order to primarily detect mechanical deformation using the sensor wire 1, it is preferable to configure the core material 13 as a hollow cylinder with both ends open along the central axis of the two-wire coil 11. As will be described later as an example of detecting temperature changes, if both ends are closed to seal air inside the core material 13, the expansion and contraction of the air will likely cause the expansion and contraction of the two-wire coil 11 in conjunction with the expansion and contraction of the core material 13. To minimize changes in the response signal due to mechanical deformation in order to primarily detect changes in substances in the environment, the core material 13 may be constructed as a material that is less susceptible to deformation, such as a solid body.

[0065] (2) When a Change Occurs in the Contacting Material Environmental changes that can occur to the sensor wire 1 include a temperature change and a change in the material in contact with the two-wire coil 11. First, we will explain the case where the material in contact with the two-wire coil 11 changes. There are two possible cases where the material in contact with the two-wire coil 11 changes: when the type of material in contact with the two-wire coil 11 changes, that is, when a material different from the one that was initially in contact with the two-wire coil 11 comes into contact with the two-wire coil 11; and when the state of the material in contact with the two-wire coil 11 changes. In either case, a change in the dielectric constant of the material present around the two-wire coil 11 occurs, and this occurs through a similar mechanism, in that the dielectric constant of the material present around the two-wire coil 11 changes.

[0066] First, an example will be described in which a liquid comes into contact with the two-wire coil 11. Figures 4A and 4B show schematic cross sections of the two-wire coil 11 cut along its central axis when the two-wire coil 11 comes into contact with a liquid. Figure 4A shows the two-wire coil 11 before contact with the liquid, and is the same as that shown in Figure 3A. Figure 4B shows the state after the liquid L comes into contact with the two-wire coil 11.

[0067] The electric field generated when a test signal is input to the two-wire coil 11 depends on the dielectric constant of the surrounding material; the higher the dielectric constant, the higher the electric field strength. In other words, the density of the electric field lines between adjacent insulated wires 12, 12 increases. In the state before contact with the liquid L shown in FIG. 4A , the two-wire coil 11 is surrounded by and in contact with air. Because air has a relative dielectric constant of approximately 1, the density of the electric field lines is low. In contrast, when the liquid L comes into contact with the two-wire coil 11, as shown in FIG. 4B , the liquid L not only covers the surface of the two-wire coil 11 but also penetrates into the spaces between the adjacent insulated wires 12, 12 due to the spiral shape of the two-wire coil 11. Typical liquid materials have a higher dielectric constant than air. Therefore, contact with the liquid L increases the electric field strength generated by the two-wire coil 11, and as shown in FIG. 4B , the density of the electric field lines between the adjacent insulated wires 12, 12 increases. As a result, the characteristic impedance measured as a response signal in the sensor wire 1 decreases. The longer the area along the central axis of the two-wire coil 11 that is in contact with the liquid L, the greater the decrease in the characteristic impedance.

[0068] Using this, the sensor wire 1 can detect contact of the liquid L with the sensor wire 1 itself or the wire harness 3 including the sensor wire 1. For example, in the wire harness 3, when a response signal obtained by inputting an inspection signal to the sensor wire 1 decreases beyond a predetermined reference value, it can be determined that the liquid L has come into contact with the sensor wire 1 and the target wire 31. The reference value may be defined as the amount of change in the characteristic impedance of the sensor wire 1 corresponding to the upper limit of the allowable amount of contact. When a liquid such as water or oil comes into contact with an electric wire, the performance of the electric wire may be affected, such as by a decrease in insulation due to the conductivity of the electric wire if the liquid is conductive, or by the liquid's deterioration of the electric wire components. In particular, with electric wires for automobiles, water from the external environment or oil from the interior of the automobile, such as engine oil, may enter the contact points with the electric wire due to defective sealing, making it important to detect the intrusion of such water or oil early. In the configuration for detecting mechanical elongation described above, it was preferable to wind the insulated wires 12, 12 in a spiral shape in the two-wire coil 11 without leaving any gaps between the turns. However, in the configuration for detecting contact of the liquid L described here, from the viewpoint of increasing the change in the response signal caused by the liquid L entering between the insulated wires 12, 12 that make up the two-wire coil 11, it is preferable to configure the spiral shape so that some gaps are left between the turns to allow the liquid L to easily enter.

[0069] In cases where the substance in contact with the two-wire coil 11 is a liquid or a solid, changes in the substance can be detected by changes in the characteristic impedance, which serve as a response signal. In the case of a solid substance, as in the case of the liquid substance described above, the response signal of the sensor wire 1 changes due to changes in the dielectric constant of the substance surrounding the two-wire coil 11. However, in the case of a liquid substance, as shown in FIG. 4B , when the substance comes into contact with the two-wire coil 11, it penetrates into the gaps between the insulated wires 12, 12 that make up the two-wire coil 11. However, in the case of a solid substance, it cannot penetrate into the gaps between the insulated wires 12, 12 and only comes into contact with the two-wire coil 11 on its surface (see FIG. 5A ). Therefore, when a substance with a similar dielectric constant comes into contact with the two-wire coil 11, if the substance is solid, the change in the response signal is less likely to be large compared to when the substance is liquid.

[0070] In the embodiment described above, the change in the substance in contact with the two-wire coil 11 is a change from air to another liquid or solid substance. However, a case where the substance in contact with the two-wire coil 11 remains the same but the state of the substance changes will also be described. Examples of changes in the state of a substance include a phase transformation and a chemical change. The dielectric constant of the substance in contact with the two-wire coil 11 changes through a phase transformation or a chemical change, and the distribution of the substance around the two-wire coil 11 also changes, which changes the state of the electric field formed by the two-wire coil 11 and causes a change in the response signal obtained from the sensor wire 1. The change in the state of the substance in contact with the two-wire coil 11 can be detected based on the change in the response signal.

[0071] An example of a phase transformation occurring among changes in the state of the material (contact material) in contact with the two-wire coil 11 is when the contact material melts and changes from solid to liquid. In many materials, the dielectric constants of solids and liquids are different, so a phase transformation from solid to liquid causes a change in the characteristic impedance obtained as a response signal in the sensor wire 1. In addition, when the contact material in contact with the two-wire coil 11 acquires fluidity through melting, the spatial distribution of the contact material changes, as shown in Figures 5A and 5B, and this spatial distribution also causes a change in the characteristic impedance.

[0072] FIG. 5A shows the state of the solid contact material C before it melts, and FIG. 5B shows the state of the contact material C after it melts, using a cross-sectional view of the two-wire coil 11. Before melting, as shown in FIG. 5A, the contact material C is only in contact with the two-wire coil 11 at the solid surface. However, as it melts and acquires fluidity, it penetrates into the gaps between the insulated wires 12, 12 that make up the two-wire coil 11, as shown in FIG. 5B. As a result, the contact material C becomes distributed near the insulated wires 12, 12 that make up the two-wire coil 11, increasing the dielectric constant in the region near the insulated wires 12, 12. As a result, the electric field strength near the two-wire coil 11 increases, and the density of the electric field lines also increases. This reduces the characteristic impedance obtained as a response signal. This mechanism is the same as that described above for the contact of the liquid L with reference to FIGS. 4A and 4B.

[0073] When the contact material C is heated and melted, and then cooled, it returns to a solid state, but the spatial distribution of the molten contact material C, i.e., the state in which it has entered the gaps between the insulated wires 12, 12 that make up the two-wire coil 11, is maintained. In other words, even though the dielectric constant of the contact material C is the same as in the state before melting shown in Figure 5A, the distribution of contact material C near the insulated wires 12, 12 that make up the two-wire coil 11 increases the dielectric constant in the region near the insulated wires 12, 12, which results in a decrease in the characteristic impedance obtained as a response signal.

[0074] Next, among the changes in the state of the substance in contact with the two-wire coil 11, examples of chemical changes include a change in the dielectric constant of the contact substance C due to a chemical reaction between the contact substance C in contact with the two-wire coil 11 and other substances, such as components in the atmosphere in which the contact substance C is placed, or due to decomposition or deterioration. Figures 6A and 6B show cross-sectional views of such cases in which the contact substance C undergoes a chemical change.

[0075] Fig. 6A shows the state of the contact material C before it undergoes a chemical change, and Fig. 6B shows the state after it has undergone the chemical change. Here, it is assumed that the chemical change is a chemical reaction that increases the dielectric constant of the contact material C. As shown in Fig. 6B, when the dielectric constant of the contact material C increases due to a chemical change, the electric field strength formed by the two-wire coil 11 increases, and the density of the electric field lines also increases. This reduces the characteristic impedance obtained as a response signal in the sensor wire 1. Conversely, if the dielectric constant of the contact material C decreases due to a chemical change, the characteristic impedance increases.

[0076] In this way, a chemical change in the contact material C can be detected by a change in the response signal obtained in the sensor wire 1. This detection of a chemical change can be applied when the dielectric constant of the contact material C changes due to a chemical change, or when the conductivity, which is a physical property correlated with the dielectric constant, changes. By detecting a phase transformation or chemical change in the contact material C, it is possible to detect changes in the environment in which the sensor wire 1 itself and the wire harness 3 including the sensor wire 1 are placed.

[0077] The contact material C that comes into contact with the two-wire coil 11 of the sensor wire 1 is assumed to be a material that is present near the sensor wire 1 in the environment in which the sensor wire 1 is placed and that is external to the sensor wire 1. However, it may also be a material that is internal to the sensor wire 1. That is, the sensor wire 1 may be configured with the contact material C incorporated therein in advance. By disposing a material, as the contact material C, whose dielectric constant changes sensitively in response to changes in the environment in which the sensor wire 1 is placed in contact with the two-wire coil 11, when a change in the environment occurs, the change in the dielectric constant of the contact material C can be detected with high sensitivity as a change in the response signal of the sensor wire 1. The intermediate material described above in connection with the outline of the configuration of the sensor wire 1 corresponds to the contact material C that is intentionally incorporated into the sensor wire 1 in this way. As described above, the intermediate material is a material that causes a change in the dielectric constant in the area surrounding the two-wire coil 11 in response to a change in the environment, and the intermediate material is disposed on at least one of the inside and outside of the two-wire coil 11. The phenomenon that causes the change in the dielectric constant of the medium can include a phase transformation and a chemical change of the medium.

[0078] An example of a configuration using an intermediary material is a configuration using a water-absorbent polymer. The water-absorbent polymer is a substance that transforms from a solid state to a gel state upon absorbing water. In the sensor wire 1, a dry water-absorbent polymer may be placed in contact with the two-wire coil 11 by filling the hollow portion 11a of the two-wire coil 11, or by forming it into a sheet or tube and wrapping it around the outer periphery of the two-wire coil 11. In this state, when water is introduced into the space in which the sensor wire 1 is placed and comes into contact with the water-absorbent polymer, the water-absorbent polymer absorbs the water and gels. Compared to the water-absorbent polymer before absorbing water, the water-absorbent polymer often has a higher dielectric constant. Furthermore, as the water-absorbent polymer gels, it swells and comes into close contact with the insulated wires 12, 12 that make up the two-wire coil 11. As a result, the characteristic impedance obtained as a response signal from the sensor wire 1 increases. In this way, by using a water-absorbing polymer as an intermediary material, it is possible to sensitively detect water being introduced into the sensor wire 1 itself or into the space in which the wire harness 3 equipped with the sensor wire 1 is placed.

[0079] Another example of a configuration using an intermediary material is a configuration using a functional material (gas sensing material) that undergoes a chemical reaction upon contact with specific gas molecules. In the sensor wire 1, such gas sensing material may be inserted into the hollow portion 11a of the two-wire coil 11, or formed into a sheet or tube and placed around the two-wire coil 11, thereby bringing the material into contact with the two-wire coil 11. In this state, when gas molecules that cause a chemical reaction in the gas sensing material are introduced into the space in which the sensor wire 1 is placed, the gas sensing material comes into contact with the gas molecules and initiates a chemical reaction. When the dielectric constant or conductivity of the gas sensing material changes due to the chemical reaction, a change occurs in the characteristic impedance obtained as a response signal in the sensor wire 1. By detecting this change, it is possible to detect the introduction of the gas molecules into the space in which the sensor wire 1 is installed. For example, in a hydrogen-powered vehicle, if a sensor wire 1 having a gas sensing material that selectively detects hydrogen as an intermediary material is placed in a location where a hydrogen leak is likely to occur, a hydrogen leak can be detected early.

[0080] (3) When a Temperature Change is Applied Next, a case where a temperature change occurs among environmental changes applied to the sensor wire 1 will be described. In addition to being detected directly through a change in the dielectric constant of the surrounding material due to a temperature change, a temperature change in the sensor wire 1 can also be detected through the mechanical deformation of the two-wire coil 11, which is one of the change phenomena described above, or through a change in the material with which the two-wire coil 11 comes into contact. In many cases, the change in the dielectric constant of a material due to a temperature change that does not involve a phase transformation is small, and when direct detection is performed through a change in the dielectric constant of the surrounding material, the amount of change in the response signal is small. However, by incorporating the mechanical deformation of the two-wire coil 11 or a change in the material with which the two-wire coil 11 comes into contact, the change in the response signal can be made larger.

[0081] An example of a configuration in which temperature changes are detected via mechanical deformation of the two-wire coil 11 is when the sensor wire 1, in which the core 13 is inserted through the two-wire coil 11, is heated, causing the core 13 to expand and elongate along the central axis of the two-wire coil 11. As the core 13 elongates, the two-wire coil 11 also elongates along its central axis. Then, due to a mechanism similar to that described above for the elongation of the two-wire coil 11 due to mechanical load, namely, an increase in the distance between adjacent insulated wires 12, 12 and the resulting change in the electric field state, the characteristic impedance increases as a response signal. The greater the temperature rise and the greater the expansion of the core 13, the greater the increase in the response signal. Conversely, if the sensor wire 1 is cooled, causing the core 13 to contract and the two-wire coil 11 to compress, a decrease in the response signal may occur.

[0082] To sensitively reflect temperature changes as changes in the response signal, it is preferable to use a core material 13 that undergoes significant expansion / contraction in response to temperature changes. An example of such a core material 13 is a hollow cylindrical body with both ends closed, with a gas sealed in the hollow space. When such a core material 13 is heated, the gas inside expands, and the core material 13 is also pushed outward and elongated in the axial direction. By utilizing gas expansion in this way, the amount of elongation of the core material 13 when temperature rises is greater than when the core material 13 is a hollow cylindrical body with both ends open and expands alone, resulting in a larger change in the response signal. The gas sealed in the core material 13 may be air or a gas other than air. The pressure of the sealed gas can be atmospheric pressure, but sealing the gas at a pressure higher than atmospheric pressure can increase the amount of expansion when temperature rises.

[0083] As an example of a mode in which a temperature change is detected via a change in the material with which the two-wire coil 11 comes into contact, a medium that contains a material that causes a change in the dielectric constant in the area surrounding the two-wire coil 11 due to a temperature change may be used as the medium that constitutes the sensor wire 1. Even if the temperature of the gas in the space in which the two-wire coil 11 is placed changes, the change in the dielectric constant is very small. However, a large change in the dielectric constant around the two-wire coil 11 occurs due to a change in state or chemical change in the medium due to temperature, which can be detected as a large change in the response signal.

[0084] An example of such a configuration for detecting temperature changes using an intermediary material is a configuration in which a heat-shrinkable tube is disposed around the two-wire coil 11 as the intermediary material. Here, the heat-shrinkable tube has an inner surface coated with an adhesive made of a material (thermoplastic material) that softens or melts when heated, preferably melts. Heat-shrinkable tubes with such adhesives are widely used as components for insulating and protecting electrical components. In the sensor wire 1, the heat-shrinkable tube is placed around the two-wire coil 11 in an unshrunk (unheated) state. When the sensor wire 1 is heated to a temperature above the temperature at which the adhesive on the inner surface softens or melts and becomes flowable due to an increase in the temperature of the surrounding environment, the adhesive flows and enters the gap between the insulated wires 12, 12 of the two-wire coil 11, as shown in the transition from FIG. 5A to FIG. 5B . The adhesive may also flow into the hollow portion 11a of the two-wire coil 11. In addition, if the temperature rise reaches the temperature at which the heat-shrinkable tube shrinks, the heat-shrinkable tube shrinks, forcing the adhesive toward the inside of the two-wire coil 11 and accelerating its penetration into the spaces between the insulated wires 12 and into the hollow portions 11a. Even if the environmental temperature drops thereafter, the adhesive solidifies while remaining in the gaps between the insulated wires 12 and into the hollow portions 11a, as shown in Figure 5B . In this way, the adhesive seeps into the gaps between the insulated wires 12 and into the hollow portions 11a that make up the two-wire coil 11, thereby reducing the characteristic impedance obtained as a response signal in the sensor wire 1.

[0085] Temperature changes in electric wires for automobiles and the like can affect the functionality of the wire, such as by changing transmission characteristics. Furthermore, large or repeated temperature changes can cause irreversible damage or deterioration to the components of the wire, such as the insulating coating, and to surrounding components. By detecting temperature changes using the sensor wire 1, whether installed alone or in a wire harness 3 that includes the sensor wire 1 together with a target electric wire 31, it becomes possible to take measures against these events.

[0086] (4) Various Forms of Monitoring Using the Sensor Wire As described above, by using the sensor wire 1, environmental changes, such as mechanical deformation, temperature change, and change in a contacting material, can be detected in the sensor wire 1 itself or in the wire harness 3 including the sensor wire 1, based on changes in the response signal obtained when an inspection signal consisting of a differential signal is input. For example, the monitoring means 21 of the sensor device 2 may be configured to determine that one of the following change events has occurred in the sensor wire 1: mechanical deformation, temperature change, or change in a contacting material, when a change exceeding a reference value occurs in the response signal, and then appropriately notify personnel, such as a system administrator, including the sensor wire 1, by issuing an alarm or the like. The reference value of the response signal may be set to correspond to the upper limit of an acceptable range for the occurrence of a change event. Which of the various change events is to be sensitively detected can be determined by selecting the number of turns of the two-wire coil 11, the presence or absence of a core material 13 and an intermediate material, the structure, and the constituent materials, as described above for each form.

[0087] The sensor device 2 may be configured to monitor the intensity of a specific frequency of the response signal when receiving an inspection signal and acquiring a response signal. If a predetermined change occurs in the intensity of the response signal received at that frequency, it may determine that a change event has occurred in the sensor wire 1. Furthermore, the greater the change in the response signal, the greater the degree of change in the change event. Alternatively, an inspection signal over a certain frequency range may be input, and the occurrence and extent of the change event may be determined based on the change in the response signal within that frequency range. Furthermore, by measuring the response signal using the time domain method or the frequency domain method, the area where a change occurs in the response signal can be associated with position information, thereby identifying the location along the central axis of the sensor wire 1 where a change event, such as local deformation or local contact with an external object, has occurred. In the time domain method, the time axis can be converted to a position on the sensor wire 1 based on the propagation speed of the inspection signal. In the frequency domain method, the frequency information can be converted to a position on the sensor wire 1 by performing an inverse Fourier transform on the response signal obtained relative to the frequency axis. Preferably, the time domain method or the frequency domain method may be used. In the sensor device 2, the response signal may be acquired continuously to constantly monitor whether or not a change event has occurred in the sensor wire 1, or the response signal may be acquired intermittently so that when a change event occurs in the sensor wire 1, it can be detected with little delay.

[0088] In the wire harness 3, the sensor wire 1 may be disposed to monitor the occurrence of a change event over the entire longitudinal length of the target electric wire 31, or may be disposed only in a partial region, such as a position where a change event such as mechanical deformation is likely to occur. The wire harness 3 may include only one sensor wire 1, or multiple sensor wires 1 may be disposed along the longitudinal length of the target electric wire 31. For example, if there are multiple discontinuous positions along the longitudinal length of the target electric wire 31 where a change event such as mechanical deformation is likely to occur, a sensor wire 1 may be disposed at each of those positions. When multiple sensor wires 1 are disposed, the multiple sensor wires 1 may be connected in series. In this case, an inspection signal can be input and a response signal can be acquired collectively for a group of multiple serially connected sensor wires 1. Then, based on the behavior of the obtained response signal, it is possible to detect which sensor wire 1 is experiencing a change event. For example, when a response signal is acquired over a certain frequency range, the resulting spectral shape changes depending on which sensor wire 1 is experiencing a change event. Therefore, it is possible to identify which sensor wire 1 is experiencing a change event based on the spectral shape. Alternatively, as described above, by applying the time domain method or frequency domain method, it is possible to identify with high accuracy which sensor wire 1 is experiencing a change event. The multiple sensor wires 1 connected in series may all be of the same type, such as those suitable for detecting mechanical extension, or multiple types of sensor wires 1 having configurations suitable for detecting different change events may be connected. Furthermore, multiple types of sensor wires 1 having configurations suitable for detecting different change events may be arranged in parallel in a single wire harness 3, and the response signal for each sensor wire 1 may be monitored independently.

[0089] Examples are shown below. However, the present invention is not limited to these examples. Here, it was confirmed whether various change events can be detected by the sensor wire.

[0090] [1] Detection of mechanical extension First, the case where the sensor wire is mechanically extended was examined.

[0091] (Test Method) First, a sensor wire was prepared. A hollow, cylindrical silicone tube with both ends open was used as the core material, and two insulated enameled wires with an outer diameter of 0.4 mm were spirally wound around the core material to prepare a two-wire coil. The two-wire coil had an outer diameter of 3 mm, a length of 33 mm, and 42 turns.

[0092] A differential signal was input as an inspection signal to the sensor wire, and the reflection coefficient was measured as a response signal between a pair of insulated wires. A vector network analyzer (VNWA) was used for the measurement. One end of the pair of insulated wires constituting the two-wire coil was connected to one port (port 1) of the VNWA, and the other end was connected to another port (port 2). Then, the reflection coefficient S １１ The measurements were carried out in the frequency range of 1 to 100 MHz, and the evaluation was mainly carried out on the measured value at 10 MHz.

[0093] Here, the characteristic impedance of a pair of insulated wires that make up the sensor wire is Z at a point that is not affected by the change event. ０ , Z at the point affected by the change event Ｌ Then, the reflection coefficient S １１ is expressed by the following equation (1): １１ = (Z Ｌ -Z ０ ) / (Z Ｌ +Z ０ ) (1) In other words, when the characteristic impedance changes at a location affected by a change event, the reflection coefficient also changes. Therefore, in this embodiment, the reflection coefficient is measured as a characteristic instead of the characteristic impedance.

[0094] In this test, to confirm whether mechanical elongation can be detected, the above measurements were performed not only in a state where the sensor wire was at its natural length with no force applied to it, but also in a state where both ends of the sensor wire were pulled to stretch the two-wire coil and the core material together. The elongation amount of the sensor wire was determined so that the length of the two-wire coil (coil length) was 105%, 109%, and 116%, with the natural length of the two-wire coil being 100%.

[0095] (Test Results) Figure 7 shows the measurement results of the reflection coefficient for each coil length. Table 1 below also summarizes the amount of change in the reflection coefficient at 10 MHz.

[0096]

[0097] As shown in Figure 7, in the frequency range lower than the region where the reflection coefficient drops sharply around 50 MHz, the reflection coefficient is higher when the sensor wire is stretched compared to when the sensor wire is not stretched (coil length 100%). Furthermore, the reflection coefficient increases as the amount of stretch increases. This trend is even more clearly shown in Table 1, which summarizes the change in the measured value at 10 MHz. Table 1 shows that the reflection coefficient increases nearly proportionally as the amount of coil stretch increases. These evaluation results confirm that when the sensor wire is mechanically stretched, the stretch can be detected as an increase in the reflection coefficient. The sharp drop in the reflection coefficient around 50 MHz in Figure 7 is due to a resonance phenomenon, and the change in the reflection coefficient can be evaluated at a lower frequency.

[0098] [2] Detection of mechanical bending Next, the case where the sensor wire is mechanically bent was examined.

[0099] (Test Method) The same sensor wire as in Test [1] above was used as the sample, and the same measurements were performed. However, in this case, the sensor wire was bent instead of being stretched. When bending, the two-wire coil and the core material were integrated, and the central axis of the sensor wire was bent into a substantially arc shape, and the reflection coefficient was measured in this state. The amount of bending was set in terms of the bending diameter from 50 mm to 20 mm in 10 mm increments. The smaller the bending diameter, the greater the amount of bending, which means that the bending was more severe.

[0100] (Test Results) Figure 8 shows the measurement results of the reflection coefficient for each bending diameter. The figure is an enlarged view of the area around 10 MHz (the same applies to the following figures). Figure 8 shows that the reflection coefficient is higher when the sensor wire is bent compared to when the sensor wire is not bent (str). There is also a tendency for the reflection coefficient to increase as the bending diameter decreases and the amount of bending increases. These results confirm that when the sensor wire is mechanically bent, the bending can be detected as an increase in the reflection coefficient.

[0101] [3] Detection of elongation due to heating Next, the case where the sensor wire is elongated by heating was examined.

[0102] (Test Method) A sensor wire was prepared as a sample. The sensor wire had the same configuration as that used in the above test [1], except for the configuration of the core material. The core material was a hollow cylindrical silicone tube with both ends sealed. Air was sealed in the sealed space at atmospheric pressure.

[0103] The reflection coefficient of the sensor wire was measured while it was being heated. The measurement method was the same as in Test [1]. During heating, the sensor wire was housed in a silicone pipe, wrapped in aluminum foil, and heated from the outside using a heater. The temperature of the sensor wire during heating was measured using a thermocouple between the silicone pipe and the sensor wire. The reflection coefficient was measured while the sensor wire was heated to temperatures from 22°C (unheated state) to 72°C in 10°C increments.

[0104] (Test Results) Figure 9 shows the measurement results of the reflection coefficient for each heating temperature. This shows that the reflection coefficient is higher when the sensor wire is heated compared to when it is not heated (22°C). Furthermore, the higher the heating temperature, the higher the reflection coefficient. This is thought to be because the air sealed inside the core expands upon heating, stretching the core in the longitudinal direction and thus the entire sensor wire. As confirmed in Test [1] above, elongation of the sensor wire causes an increase in the reflection coefficient. These results confirm that when the sensor wire is heated, a temperature increase can be detected as an increase in the reflection coefficient via the elongation of the sensor wire.

[0105] [4] Detection of Contact of Substances Next, verification was carried out on cases where various substances were brought into contact with the two-wire coil that constitutes the sensor wire.

[0106] (Test Method) A sample sensor wire was fabricated in the same manner as in Test [1], except that the core material was constructed as a solid nylon body, the length of the two-wire coil was 37 mm, and the number of turns was 37. The reflection coefficient of the sensor wire was measured using the same method as in Test [1]. However, in this case, the reflection coefficient was measured by bringing various substances into contact with the two-wire coil that constitutes the sensor wire. The substances that were brought into contact were water (tap water), silicone oil, polyurethane, and water-absorbent polymer.

[0107] When the liquid substances, water and silicone oil, were brought into contact with the two-wire coil, paper was impregnated with each liquid and then wrapped around the outer periphery of the two-wire coil. To vary the size of the contact area of ​​each liquid, the width of the paper (length along the central axis of the two-wire coil) was varied to 5 mm, 10 mm, and 15 mm. When the elastic substance, polyurethane, was brought into contact with the two-wire coil, a sheet of elastic material was wrapped around the outer periphery of the two-wire coil. The width of the sheet was varied to 5 mm, 10 mm, and 15 mm. When the water-absorbent polymer was brought into contact with the two-wire coil, the water-absorbent polymer was first absorbed into a gel, and the gel was then formed into a width of approximately 10 mm and wrapped around the outer periphery of the two-wire coil. Regardless of the substance used, the contact position was the center of the two-wire coil along the central axis.

[0108] (Test Results) Figure 10A shows the reflection coefficient measurement results when water, Figure 10B shows silicone oil, Figure 10C shows polyurethane, and Figure 10D shows water-absorbent polymer, were brought into contact with the two-wire coil that makes up the sensor wire, along with the results when nothing was in contact. Figures 10A to 10C each show the measurement results when the width of the contact area (width of the paper and sheet) was changed. Table 2 below also summarizes the change in reflection coefficient at 10 MHz when silicone oil was brought into contact as a representative example.

[0109]

[0110] 10A to 10D and Table 2, for all materials, contact with the two-wire coil reduces the reflection coefficient compared to when there is no contact. Furthermore, the decrease in reflection coefficient tends to be greater as the width of the contact area and the amount of material in contact with the two-wire coil increase. Bringing a material with a higher dielectric constant than air into contact with the two-wire coil increases the electric field strength formed by the two-wire coil, which is thought to increase the characteristic impedance in the area where contact with the material occurs, thereby decreasing the reflection coefficient. This confirms that when a material comes into contact with the two-wire coil, that contact can be detected as a decrease in the reflection coefficient.

[0111] Compared to the water and silicone oil contacts shown in Figures 10A and 10B, the change in reflection coefficient due to contact with polyurethane shown in Figure 10C is smaller. This is interpreted as meaning that liquid substances such as water and silicone oil have fluidity and can penetrate into the gaps between the insulated wires that make up the two-wire coil, whereas solid substances such as polyurethane, although elastic, cannot penetrate into the gaps between the insulated wires like liquid substances and only come into surface contact with the two-wire coil, thereby minimizing the change in dielectric constant near the two-wire coil. On the other hand, the water-absorbent polymer shown in Figure 10D constitutes a gel-like substance and can penetrate into the gaps between the insulated wires that make up the two-wire coil. Furthermore, because it is gel-like, it has a higher viscosity than a liquid, making it easier to stably maintain its state of penetration into the gaps between the insulated wires. Due to these factors, it is interpreted that the water-absorbent polymer shown in Figure 10D causes a larger change in reflection coefficient compared to the cases shown in Figures 10A to 10C.

[0112] [5] Detection of changes in the state of a material Next, we investigated the case where the state of a material in contact with the two-wire coil changes, especially the case where the conductivity of the material in contact with the two-wire coil changes.

[0113] (Test Method) Using the same sensor wire as in the above test [4] as a sample, the reflection coefficient was measured using the same measurement method as in test [4]. Here, the test was conducted in two ways: when a liquid substance was brought into contact with the two-wire coil that constitutes the sensor wire, and when a solid substance was brought into contact with the two-wire coil.

[0114] When a liquid substance was used, reflection coefficient measurements were performed with paper soaked in the liquid and wrapped around the two-wire coil, as in Test [4] above. The paper width was approximately 10 mm. Water (tap water) and saline solution were used as liquid substances. Salt solution has higher conductivity than water. When the paper was soaked in water and the resistance was measured at a distance of 20 mm, the resistance was approximately 1 to 1.5 MΩ for water and approximately 0.3 to 0.5 MΩ for saline solution. When a solid substance was used, reflection coefficient measurements were performed with a sheet-shaped solid substance wrapped around the two-wire coil. The sheet was 3 mm thick and approximately 20 mm wide. Non-conductive rubber and conductive rubber were used as solid substances. In addition to the non-conductive and conductive rubber samples, preliminary reflection coefficient measurements were also performed using a sample with aluminum foil wrapped around the surface of non-conductive rubber and a sample with polyvinyl chloride (PVC) tape wrapped around the surface of conductive rubber.

[0115] (Test Results) Figure 11A shows the measurement results of the reflection coefficient when a liquid substance is brought into contact with the two-wire coil that constitutes the sensor wire. The measurement results when the liquid brought into contact is water and saline are shown, along with the measurement results when nothing is brought into contact. Table 3 below also summarizes the amount of change in the reflection coefficient at 10 MHz.

[0116]

[0117] 11A and Table 3, the reflection coefficient decreases when the two-wire coil is in contact with water or saline solution compared to when nothing is in contact. The decrease in reflection coefficient is greater when the coil is in contact with saline solution, which is a liquid with higher conductivity than water, than when the coil is in contact with water, which is a liquid with lower conductivity. This result confirms that when the conductivity of the liquid in contact with the two-wire coil changes, the increase in conductivity can be detected as a decrease in the reflection coefficient.

[0118] Furthermore, Figure 11B shows the measurement results of the reflection coefficient when a solid object is in contact with the two-wire coil. The measurement results when the solid object is non-conductive rubber and conductive rubber are shown, along with the measurement results when nothing is in contact. Table 4 below summarizes the change in reflection coefficient at 10 MHz.

[0119]

[0120] According to Figure 11B and Table 4, the reflection coefficient decreases when the two-wire coil is in contact with both non-conductive rubber and conductive rubber, compared to when nothing is in contact. However, as seen in the results of Test [4] above, the change is smaller when the coil is in contact with a liquid than when the coil is in contact with a liquid (Figure 11A). Comparing the change in reflection coefficient when two solid materials are in contact, the decrease in reflection coefficient is greater when the coil is in contact with conductive rubber than when the coil is in contact with non-conductive rubber. These results confirm that, as with liquid materials, when the conductivity of a material in contact with a two-wire coil changes, the increase in conductivity can be detected as a decrease in the reflection coefficient.

[0121] Furthermore, as a preliminary test, we compared the change in reflection coefficient when a two-wire coil was placed in contact with non-conductive rubber, conductive rubber, non-conductive rubber wrapped with aluminum foil to make only the surface conductive, and conductive rubber wrapped with PVC tape to make only the surface non-conductive. A decrease in reflection coefficient occurred with each material, but the amount of decrease varied for each material. The non-conductive rubber wrapped with aluminum foil showed a larger decrease than the non-conductive rubber but significantly smaller than the conductive rubber. The conductive rubber wrapped with PVC tape showed an even smaller decrease than the non-conductive rubber. These results indicate that the decrease in reflection coefficient does not simply reflect the surface conductivity of the material in contact with the two-wire coil. However, they suggest a complex relationship exists between the distribution of conductive and non-conductive materials and the change in reflection coefficient.

[0122] [6] Detection of temperature change using an intermediary material Next, it was verified whether a temperature change could be detected using a heat-shrinkable tube with an adhesive on its inner surface as an intermediary material.

[0123] (Test Method) The same sensor wire as in Test [4] above was used as a sample, and the reflection coefficient was measured using the same measurement method as in Test [4]. Here, the reflection coefficient was measured with a heat-shrinkable tube with adhesive on the inner surface covering the two-wire coil that constitutes the sensor wire. The reflection coefficient was also measured after the heat-shrinkable tube was heated to melt the adhesive and shrink, and then allowed to cool.

[0124] (Test Results) Figure 12 shows the measurement results of the reflection coefficient before and after placing the heat-shrinkable tubing around the two-wire coil and before and after heating. Table 5 below also summarizes the change in reflection coefficient at 10 MHz.

[0125]

[0126] According to Figure 12 and Table 5, when the two-wire coil was simply covered with heat-shrink tubing and before heating, the reflection coefficient only changed slightly compared to before the heat-shrink tubing was placed. Subsequently, the reflection coefficient significantly decreased as the heat-shrink tubing was heated, melting the adhesive and shrinking. As the tubing contracted, the molten adhesive was pushed toward the inside of the two-wire coil and penetrated deeply into the gaps between the insulated wires that make up the two-wire coil. This suggests that the penetration of the adhesive reduced the dielectric constant around the two-wire coil, resulting in a decrease in the reflection coefficient. These results confirm that using adhesive-backed heat-shrink tubing as an intermediary material allows for sensitive detection of temperature increases in the environment in which the sensor wire is placed, as a decrease in the reflection coefficient due to the melting of the adhesive. The change in reflection coefficient was significantly greater than when detecting temperature increases using the thermal expansion of the air inside the core material, as shown in Figure 9. Using an intermediary material allows for more accurate temperature increase detection.

[0127] [7] Configurations other than those using a two-wire coil Finally, we confirmed how sensor wires formed with structures other than a two-wire coil behave in response to environmental changes.

[0128] (Test Method) First, a pair of insulated wires was prepared as a first comparative wire, running parallel to each other without being wound in a spiral shape. Specifically, two insulated wires made of enameled wire with an outer diameter of 0.4 mm, the same as those used to form the two-wire coil in Tests [1] to [6] above, were cut to a length of 100 mm and aligned side by side while maintaining their straightness. The distance between the wires was set to 0 mm.

[0129] A second comparative electric wire was prepared by spirally winding only one insulated electric wire. Specifically, a single insulated electric wire, consisting of the same enameled wire with an outer diameter of 0.4 mm as used to form the two-wire coil in Tests [1] to [6] above, was spirally wound into a single-wire coil. The coil had an outer diameter of 3 mm, a length of 35 mm, and 70 turns. To enable differential signal input, a straight single wire of the same insulated electric wire was run parallel to the single-wire coil, and the assembly of the single-wire coil and the straight single wire was used as the second comparative electric wire.

[0130] The reflection coefficients of the first and second comparative electric wires were measured. As in the above tests [1] to [6], the reflection coefficients were measured by connecting one end of each of the two insulated electric wires constituting each comparative electric wire to port 1 of the VNWA and the other end to port 2. The reflection coefficient S １１ The measurements were carried out with each comparative wire in a state where nothing was in contact with it, and with polyurethane, non-conductive rubber, and conductive rubber. The polyurethane was the same as in the above test [4], and the non-conductive rubber and conductive rubber were the same as in the above test [5], and were arranged in the same way.

[0131] (Test Results) Figure 13A shows the measurement results of the reflection coefficient for the first comparative electric wire, and Figure 13B shows the measurement results for the second comparative electric wire, both in a state where nothing is in contact with the wire and in a state where polyurethane, non-conductive rubber, and conductive rubber are in contact with the wire. Figure 13A shows that the reflection coefficient of the first comparative electric wire, which has a pair of parallel insulated electric wires, decreases when polyurethane, non-conductive rubber, and conductive rubber are in contact with the wire, as in the case of using the two-wire coil shown in Figures 10C and 11B. When comparing the non-conductive rubber and conductive rubber, the result also shows that the decrease in reflection coefficient is greater when conductive rubber is in contact with the wire. However, regardless of the contact with either material, the decrease in reflection coefficient due to contact is smaller than when using the two-wire coil shown in Figures 10C and 11B. Thus, even when using the first comparative electric wire, which has a pair of parallel insulated electric wires, it is possible to detect changes in the dielectric constant due to changes in the surrounding environment as changes in the reflection coefficient, but it does not achieve the same high detection sensitivity as when using the two-wire coil. By spirally winding a pair of insulated wires with aligned longitudinal axes to form a two-wire coil, the actual length of the insulated wires that make up the sensor wire becomes longer, and it is thought that the change in the reflection coefficient due to the change in the surrounding dielectric constant becomes more pronounced.

[0132] On the other hand, Figure 13B shows that the second comparative electric wire with a single-wire coil did not experience any significant change in the reflection coefficient when it was contacted with polyurethane, non-conductive rubber, or conductive rubber. This indicates that simply winding a single insulated electric wire in a spiral shape is not enough to detect changes in the surrounding dielectric constant due to changes in the surrounding environment as a change in the reflection coefficient. As confirmed by these test results, in order to reflect changes in the surrounding dielectric constant in a change in the reflection coefficient, a pair of insulated electric wires must be paired, their longitudinal axes aligned to form a sensor electric wire, and the insulated electric wires with opposite polarities must be arranged side by side. Simply winding a single insulated electric wire in a spiral shape does not form such a structure, and changes in the surrounding dielectric constant cannot be detected as a change in the reflection coefficient.

[0133] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0134] REFERENCE SIGNS LIST 1 sensor wire 11 two-wire coil 11a hollow portion 12 insulated wire 12a conductor 12b insulating coating 13 core material 2 sensor device 21 monitoring means 25 terminating resistor 3 wire harness 31 target wire C contact material L liquid

Claims

1. A sensor wire comprising a pair of insulated wires, each having a conductor and an insulating coating covering the outer circumference of the conductor, the pair of insulated wires constituting a two-wire coil wound in a spiral shape with their longitudinal axes aligned.

2. The sensor wire according to claim 1, wherein each of the pair of insulated wires is configured as an enameled wire.

3. The sensor wire according to claim 1, wherein a core material is inserted through the central axis of the two-wire coil.

4. The sensor wire according to claim 3, wherein the core material has flexibility that allows it to bend and deform in accordance with bending of the two-wire coil.

5. The sensor wire according to claim 3, wherein the core material has elasticity that allows it to expand and contract in accordance with the expansion and contraction of the two-wire coil.

6. The sensor wire according to claim 3, wherein the core material is configured as a hollow cylinder having both ends open along the central axis of the two-wire coil.

7. A sensor wire as described in claim 3, wherein the core material is configured as a hollow cylinder with both ends closed along the central axis of the two-wire coil, and a gas is sealed in the hollow portion.

8. The sensor wire according to claim 3, wherein the core material is configured as a solid body.

9. The sensor wire according to claim 1, wherein an intermediate material containing a substance that causes a change in dielectric constant in the region surrounding the two-wire coil in response to a change in the environment is disposed on at least one of the inside and outside of the two-wire coil.

10. The sensor wire according to claim 9, wherein the change in the dielectric constant is caused by at least one of a phase transformation and a chemical change of the medium material.

11. The sensor wire according to claim 10, wherein the intermediate material is a heat-shrinkable tube having an adhesive on its inner surface that softens or melts when heated, the heat-shrinkable tube being disposed around the outer periphery of the two-wire coil.

12. A sensor device comprising: a sensor wire as claimed in any one of claims 1 to 11; and a monitoring means for inputting a differential signal to the pair of insulated wires constituting the sensor wire, acquiring a response signal, and monitoring changes in the response signal.

13. The sensor device according to claim 12, wherein the monitoring means determines that at least one of mechanical deformation, temperature change, and change in the material in contact with the sensor wire has been applied to the sensor wire when a change exceeding a reference value occurs in the response signal.

14. The sensor device according to claim 12, wherein said monitoring means monitors, as said response signal, a change in characteristic impedance or reflection coefficient between said pair of insulated wires constituting said sensor wire.

15. The sensor apparatus of claim 14, wherein the monitoring means measures the characteristic impedance or reflection coefficient by time domain reflectometry or frequency domain reflectometry.

16. The sensor device according to claim 12, wherein the two-wire coil is impedance-matched to the monitoring means by adjusting the number of turns.

17. A wire harness comprising: a target electric wire composed of at least one electric wire; and a sensor device as described in claim 12, wherein the sensor electric wire constituting the sensor device is arranged in at least a portion of the longitudinal direction of the target electric wire, with its central axis oriented in the longitudinal direction.

18. The wire harness according to claim 17, wherein the sensor wire is arranged next to the target wire.

19. The wire harness as set forth in claim 17, wherein the target electric wire is inserted into a hollow portion of the two-wire coil.

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