Electromagnetic shield

Abstract

This electromagnetic shield (10) is provided with a plurality of substrates (11) each having one or more conductors (12). The substrates (11) that are adjacent to each other are supported so that the distance between the conductors (12) changes due to disturbances naturally present around the substrates.

Description

Electromagnetic shielding

[0001] The present disclosure relates to electromagnetic shielding.

[0002] There are concerns about information leakage due to interception of electromagnetic waves. For example, there are concerns about eavesdropping on communications via electromagnetic waves of a specific frequency used for wireless communications, and eavesdropping on internal device information (for example, images displayed on a monitor if the device has one) via electromagnetic waves of a specific frequency unintentionally emitted by electronic devices (so-called electromagnetic noise) (so-called TEMPEST).

[0003] One known countermeasure against the information leakage is to install electromagnetic shields on the walls and windows of a building to reduce the leakage of electromagnetic waves to the outside. A conventional electromagnetic shield is disclosed in, for example, Patent Document 1.

[0004] Japanese Patent Application Laid-Open No. 2017-188516

[0005] The electromagnetic shield disclosed in Patent Document 1 uses an elastic structure to enable transmission or blocking of electromagnetic waves. In the electromagnetic shield disclosed in Patent Document 1, when the elastic structure is not elastically deformed, electromagnetic waves from a radio wave transmitter are blocked. On the other hand, when the elastic structure is elastically deformed, electromagnetic waves from the radio wave transmitter are transmitted. Therefore, in order to transmit or block electromagnetic waves in the electromagnetic shield disclosed in Patent Document 1, it is necessary to artificially control the elastic structure. As a result, when using the electromagnetic shield disclosed in Patent Document 1 to prevent information leakage due to interception of electromagnetic waves, the control may become complicated.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an electromagnetic shield that can modulate electromagnetic waves without requiring artificial control.

[0007] The electromagnetic shield of the present disclosure comprises a plurality of substrates each having one or more conductors, and adjacent substrates are supported such that the distance between the conductors changes due to natural disturbances present around the substrates.

[0008] According to the present disclosure, electromagnetic waves can be modulated without the need for artificial control.

[0009] 11 is a perspective view of an electromagnetic shield according to embodiment 1. FIG. 12 is an enlarged view of a main part of FIG. 1. FIG. 13 is a conceptual diagram of a change in frequency characteristics of a complex transmission coefficient, showing a change in the absolute value of the complex transmission coefficient. FIG. 14 is a conceptual diagram of a change in frequency characteristics of a complex transmission coefficient, showing a change in the argument of the complex transmission coefficient. FIG. 15 is a perspective view of an electromagnetic shield according to embodiment 2. FIG. 16 is an enlarged view of a main part of FIG. 5. FIG. 17 is a perspective view of an electromagnetic shield according to embodiment 3. FIG. 18 is an enlarged view of a main part of FIG. 7. FIG. 19 is a perspective view of an electromagnetic shield according to embodiment 4. FIG. 19 is an enlarged view of a main part of FIG. 9. FIG. 11 is a perspective view of an electromagnetic shield according to embodiment 5. FIG. 12 is an enlarged view of a main part of FIG.

[0010] In order to explain the present disclosure in more detail, embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0011] First Embodiment An electromagnetic shield 10 according to a first embodiment will be described with reference to FIGS.

[0012] First, the configuration of the electromagnetic shield 10 will be described with reference to Figures 1 and 2. Figure 1 is a perspective view of the electromagnetic shield 10 according to the first embodiment. Figure 2 is an enlarged view of a main part of Figure 1.

[0013] The three-dimensional Cartesian coordinate system of the electromagnetic shield 10 shown in Fig. 1 is defined by three axes, an x-axis, a y-axis, and a z-axis, which are orthogonal to each other in space. Fig. 1 shows an example in which the vertical direction of the electromagnetic shield 10 is the x-axis, the horizontal direction (or width direction) of the electromagnetic shield 10 is the y-axis, and the height direction (or thickness direction) of the electromagnetic shield 10 is the z-axis. The arrows on the x-axis, y-axis, and z-axis indicate the positive directions of their respective axes.

[0014] 1 is provided, for example, to separate the inside and outside of a building. The electromagnetic shield 10 has a flat inner surface 10a facing the inside of the building and a flat outer surface 10b facing the outside of the building. The inner surface 10a and the outer surface 10b are arranged parallel to each other. In addition to buildings, the electromagnetic shield 20 can also be provided on moving objects such as vehicles, trains, and airplanes.

[0015] Here, inside the building, there is installed equipment that emits electromagnetic waves containing information to be prevented from leaking. Such equipment may be, for example, a wireless device that emits electromagnetic waves for wireless communication, or an electronic device that emits electromagnetic noise. On the other hand, outside the building, there may be installed a receiving device that can receive the electromagnetic waves containing the information and eavesdrop on that information.

[0016] As shown in Fig. 1, the electromagnetic shield 10 has a plurality of substrates 11 therein. All of the substrates 11 are disposed between an inner surface 10a and an outer surface 10b of the electromagnetic shield 10. The electromagnetic shield 10 is configured by forming one stage parallel to the xy plane from a plurality of substrates 11 arranged along the x-axis direction and a plurality of substrates 11 arranged along the y-axis direction, and stacking the plurality of stages along the z-axis direction. In Fig. 1, one stage parallel to the xy plane is formed from three substrates 11 arranged along the x-axis direction and three substrates 11 arranged along the y-axis direction, and stacking the three stages along the z-axis direction.

[0017] All of the substrates 11 have the same shape and are periodically arranged. The substrates 11 are, for example, rectangular. One substrate 11 has one or more conductors 12. All of the conductors 12 have the same shape and are periodically arranged on one substrate 11. The conductors 12 are, for example, rectangular.

[0018] 1 shows an example in which one substrate 11 has four conductors 12. Although the substrate 11 and the conductors 12 are rectangular, the shapes of the substrate 11 and the conductors 12 are not limited to this. Furthermore, the shapes of the substrate 11 and the conductors 12 do not have to be the same. For example, the substrate 11 and the conductors 12 may be round, diamond-shaped, triangular, or the like.

[0019] 1 and 2 , in the electromagnetic shield 10, adjacent substrates 11 in the x-axis direction, y-axis direction, and z-axis direction are supported so that the distance between their conductors 12 changes due to disturbances that naturally exist around the electromagnetic shield 10 (around the substrates 11). Specifically, adjacent substrates 11 in the x-axis direction, y-axis direction, and z-axis direction are connected to each other by elastic bodies. Figures 1 and 2 show an example in which the elastic bodies are springs 13. One end of the spring 13 is connected to one of the two adjacent substrates 11, and the other end of the spring 13 is connected to the other substrate 11.

[0020] Note that the disturbances that naturally exist around the electromagnetic shield 10 include, for example, vibrations, wind, and sound. The elastic body may be rubber.

[0021] Here, adjacent substrates 11 in the x-axis direction are spaced apart by a distance D1 when the springs 13 are not stretched or contracted. Adjacent substrates 11 in the y-axis direction are spaced apart by a distance D2 when the springs 13 are not stretched or contracted. Adjacent substrates 11 in the z-axis direction are spaced apart by a distance D3 when the springs 13 are not stretched or contracted. Distances D1, D2, and D3 are the distances between the conductors 12.

[0022] Therefore, because the electromagnetic shield 10 has the above-mentioned configuration, adjacent substrates 11 are connected to each other by springs 13, and therefore the substrates 11 also vibrate in response to vibrations occurring in the electromagnetic shield 10 and in the building in which the electromagnetic shield 10 is installed.

[0023] Vibrations in a building occur due to natural phenomena such as wind and sound, or due to artificial phenomena such as the movement of people and moving objects outside the building. Vibrations in the electromagnetic shield 10 also occur when wind pressure and sound pressure are applied directly to the electromagnetic shield 10. These natural and artificial phenomena occur naturally and are not artificially controlled with the purpose of generating vibrations in the electromagnetic shield 10.

[0024] Furthermore, because these vibrations are generated by the complex contribution of various vibration factors, the magnitude, frequency, and direction of the vibrations change irregularly depending on the time of day and the installation position of the electromagnetic shield 10. In other words, the multiple substrates 11 included in the electromagnetic shield 10 vibrate randomly depending on the time of day and the installation position without requiring a power source.

[0025] In this way, the vibrations of the substrate 11 occur randomly in time and position, and the distances D1, D2, and D3 between adjacent substrates 11 also change randomly. In this case, the local complex transmission coefficient in a specific region of the electromagnetic shield 10 depends on the distances D1, D2, and D3 in that specific region. Here, the complex transmission coefficient indicates the amount of change in the amplitude and phase of the electromagnetic wave when it passes through the electromagnetic shield 10.

[0026] Next, the above points will be explained with reference to FIGS.

[0027] Fig. 3 is a conceptual diagram of the change in frequency characteristic of the complex transmission coefficient, showing the change in the absolute value of the complex transmission coefficient (in other words, the transmission amplitude of the electromagnetic wave). Fig. 4 is a conceptual diagram of the change in frequency characteristic of the complex transmission coefficient, showing the change in the argument of the complex transmission coefficient (in other words, the transmission phase of the electromagnetic wave). Note that the frequency characteristics I, II, and III shown in Fig. 3 and Fig. 4 are three predetermined combinations randomly selected from combinations of two or more values ​​of the distances D1, D2, and D3.

[0028] 3, when the distances D1, D2, and D3 change, the absolute value of the complex transmission coefficient changes according to the magnitude of the frequency. For example, when the frequency of the electromagnetic wave passing through the electromagnetic shield 10 is f1, the transmission amplitude of the electromagnetic shield 10 differs for each of the frequency characteristics I, II, and III.

[0029] 4, when the distances D1, D2, and D3 change, the argument of the complex transmission coefficient changes according to the magnitude of the frequency. For example, when the frequency of the electromagnetic wave transmitted through the electromagnetic shield 10 is f1, the transmission phase of the electromagnetic shield 10 differs for each of the frequency characteristics I, II, and III.

[0030] For this reason, electromagnetic waves incident on the electromagnetic shield 10 undergo changes in transmission amplitude and transmission phase depending on the time and position of transmission before leaking outside the building. In other words, electromagnetic waves incident on the electromagnetic shield 10 are modulated depending on the time and position of transmission before leaking outside the building.

[0031] Therefore, when electromagnetic waves used in wireless communication and electromagnetic waves (electromagnetic noise) emitted from electronic devices are incident on the electromagnetic shield 10, each electromagnetic wave is randomly modulated in terms of time and position by the electromagnetic shield 10. As a result, the information contained in the electromagnetic waves becomes information different from the original information before the electromagnetic waves were modulated, and is leaked outside the building.

[0032] Therefore, the electromagnetic shield 10 can modulate the electromagnetic waves that pass through it using disturbances such as vibrations, wind, and sound that naturally exist around the electromagnetic shield 10. As a result, the electromagnetic shield 10 can prevent information contained in the original electromagnetic waves from being eavesdropped on, even if someone outside the building who intercepts the electromagnetic waves improves the reception sensitivity.

[0033] The substrates 11 and conductors 12 do not have to be arranged periodically. Furthermore, the characteristics of the springs 13 do not have to be uniform. In this case, the randomness of modulation of the electromagnetic waves that pass through the electromagnetic shield 10 can be further increased.

[0034] As described above, the electromagnetic shield 10 according to the first embodiment includes a plurality of substrates 11 each having one or more conductors 12, and adjacent substrates 11 are supported so that the distance between the conductors 12 changes due to natural disturbances present around the substrates. Therefore, the electromagnetic shield 10 can modulate electromagnetic waves without requiring artificial control.

[0035] Second Embodiment An electromagnetic shield 20 according to a second embodiment will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a perspective view of the electromagnetic shield 20 according to the second embodiment. Fig. 6 is an enlarged view of a main part of Fig. 5.

[0036] 1 according to a first embodiment, an electromagnetic shield 10 is provided with an elastic body between adjacent substrates 11, thereby modulating electromagnetic waves with disturbances such as vibrations, wind, and sound pressure. In contrast, an electromagnetic shield 20 according to a second embodiment, shown in FIG. 5, is configured such that a plurality of substrates 24 are assembled in a propeller shape, thereby modulating electromagnetic waves with disturbances such as wind.

[0037] As shown in Fig. 5, the electromagnetic shield 20 has a flat inner surface 20a facing the inside of the building and a flat outer surface 20b facing the outside of the building. The inner surface 20a and the outer surface 20b are arranged parallel to each other. The electromagnetic shield 20 also includes a plurality of fixing members 21 and a plurality of propellers 22 therein. All of the fixing members 21 and all of the propellers 22 are arranged between the inner surface 20a and the outer surface 20b. The xy plane, the inner surface 20a, and the outer surface 20b constitute reference planes.

[0038] The fixed member 21 is fixed to, for example, the outer surface 20b side. This fixed member 21 is axially shaped and is disposed so as to extend in the y-axis direction. One or more propellers 22 are rotatably supported by each fixed member 21. Figure 5 shows an example in which three fixed members 21 are provided and three propellers 22 are rotatably supported by each fixed member 21.

[0039] 5 and 6, the propeller 22 is composed of, for example, a rotating shaft 23, a substrate 24, and a conductor 25. The arrow shown in FIG.

[0040] The rotating shaft 23 is disposed so as to be perpendicular to the longitudinal direction of the fixed member 21. Furthermore, the rotating shaft 23 is disposed so as to extend in the Z-axis direction. The base end of the rotating shaft 23 is supported by the fixed member 21 so as to be rotatable around its axis as the center of rotation. Meanwhile, the tip of the rotating shaft 23 is a free end. Furthermore, the rotating shaft 23 has a plurality of branch shafts 23a. Each branch shaft 23a is provided radially from the tip of the rotating shaft 23.

[0041] A substrate 24 is provided at the tip of each branch shaft 23a. The substrate 24 forms the blades of the propeller 22. The substrate 24 is disposed so that its front and back surfaces are inclined with respect to the xy plane. All of the substrates 24 have the same shape. The substrate 24 is, for example, rectangular.

[0042] One substrate 24 has a plurality of conductors 25. All of the conductors 25 have the same shape and are periodically arranged on one substrate 24. The conductors 25 are, for example, rectangular. Furthermore, by being provided on the substrate 24, the conductors 25 are arranged so that their surfaces are inclined with respect to the xy plane.

[0043] That is, the substrates 24 are supported at regular intervals around the axis of the rotation shaft 23 so that the conductors 25 are inclined with respect to the xy plane, which serves as the reference plane. Therefore, the substrates 24 are rotatable so that the distance between the conductors 25 of the substrates 24 and the conductors 25 of the other substrates 24 supported by the rotation shaft 23 changes due to disturbances that naturally exist around the electromagnetic shield 20 (around the substrates 24). Note that examples of disturbances that naturally exist around the electromagnetic shield 20 include wind.

[0044] 5 shows an example in which one propeller 22 includes four substrates 24, each having eight conductors 25. In the electromagnetic shield 20, the number of propellers 22, the number of substrates 24 per propeller 22, and the number of conductors 25 per substrate 24 can be adjusted as needed.

[0045] Therefore, by configuring the electromagnetic shield 20 as described above, when wind strikes the substrate 24 on which the blades of the propeller 22 are formed, the propeller 22 rotates.

[0046] The wind blowing against the electromagnetic shield 20 occurs due to natural phenomena such as wind and rain, or due to artificial phenomena such as the movement of people and moving objects outside the building. Furthermore, when the electromagnetic shield 20 is provided on a moving object, the electromagnetic shield 20 is also subjected to wind generated by the movement of the moving object. These natural and artificial phenomena occur naturally and are not artificially controlled for the purpose of blowing wind against the electromagnetic shield 20.

[0047] Furthermore, the direction and speed of the wind are determined by a complex combination of factors, such as weather conditions and the location of surrounding objects. When the electromagnetic shield 20 is installed on a moving object, the moving speed and direction of the moving object also contribute. Therefore, the direction and speed of the wind blowing against the electromagnetic shield 20 change irregularly depending on the time of day and the installation location of the electromagnetic shield 20. In other words, the propellers 22 of the electromagnetic shield 20 rotate at random speeds depending on the time of day and the installation location, without requiring a power source.

[0048] In this way, the rotation of the propeller 22 occurs randomly in time and position, causing the distance, facing angle, and overlapping area to change randomly between the conductor 25 of the substrate 24 of one propeller 22 and the conductor 25 of the substrate 24 of another propeller 22 adjacent to that propeller 22. In this case, the local complex transmission coefficient in a specific region of the electromagnetic shield 20 depends on the distance, facing angle, and overlapping area in that specific region.

[0049] For this reason, electromagnetic waves incident on the electromagnetic shield 20 undergo changes in transmission amplitude and transmission phase depending on the time and position of transmission before leaking outside the building. In other words, electromagnetic waves incident on the electromagnetic shield 10 are modulated depending on the time and position of transmission before leaking outside the building.

[0050] Therefore, when electromagnetic waves used in wireless communication and electromagnetic waves (electromagnetic noise) emitted from electronic devices are incident on the electromagnetic shield 20, each electromagnetic wave is randomly modulated in terms of time and position by the electromagnetic shield 20. As a result, the information contained in the electromagnetic waves becomes information different from the original information before the electromagnetic waves were modulated, and is leaked outside the building.

[0051] Therefore, the electromagnetic shield 20 can modulate the electromagnetic waves that pass through it using disturbances such as wind that naturally exist around the electromagnetic shield 20. As a result, the electromagnetic shield 20 can prevent information contained in the original electromagnetic waves from being eavesdropped on, even if someone outside the building who intercepts the electromagnetic waves improves the reception sensitivity.

[0052] The propellers 22 and the conductors 25 do not have to be arranged periodically. Furthermore, the number of substrates 24 installed per propeller 22, the number of conductors 25 installed per substrate 24, the inclination angles of the front and back surfaces of the substrates 24 with respect to the xy plane, the shapes of the substrates 24, and the shapes of the conductors 25 do not have to be the same. In this case, the randomness of modulation of the electromagnetic waves passing through the electromagnetic shield 10 can be further increased.

[0053] As described above, the electromagnetic shield 20 according to the second embodiment includes a substrate 24 having one or more conductors 25, and a plurality of rotation shafts 23 that support the substrate 24 around an axis with the conductors 25 tilted relative to a reference plane, and the substrate 24 rotates in response to disturbances naturally present around the substrate 24 such that the distance between the conductors 25 of the substrate 24 and the conductors 25 of the substrates 24 supported by the other rotation shafts 23 changes. Therefore, the electromagnetic shield 20 can modulate electromagnetic waves without requiring artificial control.

[0054] Third Embodiment An electromagnetic shield 30 according to a third embodiment will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a perspective view of the electromagnetic shield 30 according to the third embodiment. Fig. 8 is an enlarged view of a main part of Fig. 7.

[0055] The electromagnetic shields 10 and 20 according to the first and second embodiments shown in Figures 1 and 3 are configured to modulate electromagnetic waves by external disturbances such as vibrations, wind, and sound. In contrast, the electromagnetic shield 30 according to the third embodiment shown in Figure 7 modulates electromagnetic waves by electromagnetic fields that are other physical phenomena.

[0056] 7 , the electromagnetic shield 30 has a flat inner surface 30a facing the inside of the building and a flat outer surface 30b facing the outside of the building. The inner surface 30a and the outer surface 30b are arranged parallel to each other. The electromagnetic shield 30 also includes a plurality of substrates 31, a plurality of conductors 32, a plurality of varactors 33, and a plurality of support members 34 therein. The plurality of substrates 31, the plurality of conductors 32, the plurality of varactors 33, and the plurality of support members 34 are arranged between the inner surface 30a and the outer surface 30b.

[0057] The substrates 31 are stacked in the z-axis direction. In this case, the z-axis direction is the stacking direction. The substrates 31 adjacent to each other in the z-axis direction are connected to each other via support members 34. The support members 34 connect the four corners of the back surface of one adjacent substrate 31 to the four corners of the front surface of the other adjacent substrate 31. Therefore, the multiple substrates 31 are stacked at regular intervals by the support members 34. Note that the substrates 31 do not have to be stacked at regular intervals. Also, only one substrate 31 may be used.

[0058] 7 and 8, one substrate 31 has a plurality of conductors 32. All of the conductors 32 have the same shape and are periodically arranged on one substrate 31. Specifically, one substrate 31 has one or more pairs of conductors 32.

[0059] The varactor 33 connects the pair of conductors 32. The varactor 33 is provided on the surface of the substrate 31. The varactor 33 constitutes a connecting member. The varactor 33 has a characteristic that its capacitance value changes depending on the value of the applied voltage. Furthermore, the capacitance of the varactor 33, which is a physical property, changes due to disturbances that naturally exist around the electromagnetic shield 30 (around the substrate 31). In this case, the disturbances that naturally exist around the electromagnetic shield 30 are, for example, electromagnetic fields.

[0060] 7 shows an example in which two substrates 31 are stacked, and each substrate 31 is provided with 12 pairs of conductors 32 connected by one varactor 33. In the electromagnetic shield 30, the number of stacked substrates 31, the number of pairs of conductors 32 provided on one substrate 31, and the number of varactors 33 provided between the pairs of conductors 32 can be adjusted as appropriate.

[0061] Therefore, by configuring the electromagnetic shield 30 as described above, an electric field and a voltage V1 associated with this electric field are generated between a pair of conductors 32 connected by a varactor 33 due to the electromagnetic field that naturally exists around the electromagnetic shield 30.

[0062] The electromagnetic field that naturally exists around the electromagnetic shield 30 is generated by electromagnetic waves for wireless communication emitted by wireless devices, electromagnetic waves (electromagnetic noise) emitted by electronic devices, electromagnetic waves from various other devices, and electromagnetic waves caused by electrostatic discharge when human bodies or objects come close to each other. The phenomenon of generating such electromagnetic fields occurs naturally and is not artificially controlled for the purpose of generating an electric field and the voltage V1 associated with this electric field in the electromagnetic shield 30.

[0063] Furthermore, the frequency spectrum, polarization, and direction of arrival of those electromagnetic waves are determined by a complex combination of various conditions, such as the positional relationship between the electromagnetic wave radiation source and the electromagnetic shield 30, and the arrangement of objects on the propagation path of the electromagnetic waves from the radiation source (equipment) to the electromagnetic shield 30. For this reason, the frequency spectrum, polarization, and direction of arrival of those electromagnetic waves change irregularly depending on the time of day and the installation position of the electromagnetic shield 30. In other words, the voltage V1 generated in the electromagnetic shield 30 changes randomly depending on the time of day and the installation position without requiring a power source.

[0064] In this way, the voltage V1 generated in the electromagnetic shield 30 changes randomly over time and position, which also randomly changes the capacitance of the varactor 33. At this time, the local complex transmission coefficient in a specific region of the electromagnetic shield 30 depends on the voltage V1 in that specific region.

[0065] Therefore, the electromagnetic waves incident on the electromagnetic shield 30 leak outside the building after undergoing changes in transmission amplitude and transmission phase depending on the time and position of transmission. In other words, the electromagnetic waves incident on the electromagnetic shield 30 are modulated depending on the time and position of transmission before leaking outside the building.

[0066] Therefore, when electromagnetic waves used in wireless communication and electromagnetic waves (electromagnetic noise) emitted from electronic devices are incident on the electromagnetic shield 30, each electromagnetic wave is randomly modulated in terms of time and position by the electromagnetic shield 30. As a result, the information contained in the electromagnetic waves becomes information different from the original information before the electromagnetic waves were modulated, and is leaked outside the building.

[0067] Therefore, the electromagnetic shield 30 can modulate the electromagnetic waves that pass through it using disturbances such as electromagnetic waves that are naturally present around the electromagnetic shield 30. As a result, the electromagnetic shield 30 can prevent information contained in the original electromagnetic waves from being eavesdropped on, even if someone outside the building who intercepts the electromagnetic waves improves the reception sensitivity.

[0068] The conductors 32 do not have to be arranged periodically. Furthermore, the shapes of the substrates 31, the conductors 32, the varactors 33, and the characteristics of the varactors 33 do not have to be identical. In this case, the randomness of modulation of the electromagnetic waves passing through the electromagnetic shield 30 can be further increased.

[0069] As described above, the electromagnetic shield 30 according to the third embodiment includes one or more substrates 31 each having one or more pairs of conductors 32, and a varactor 33 that connects the pair of conductors 32 and whose physical properties change in response to disturbances naturally present around the substrates. Therefore, the electromagnetic shield 30 can modulate electromagnetic waves without requiring artificial control.

[0070] Fourth Embodiment An electromagnetic shield 40 according to a fourth embodiment will be described with reference to Figs. 9 and 10. Fig. 9 is a perspective view of the electromagnetic shield 40 according to the fourth embodiment. Fig. 10 is an enlarged view of a main portion of Fig. 9. Note that components having the same functions as those described in the third embodiment above are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0071] The electromagnetic shield 30 according to the third embodiment shown in Fig. 7 modulates electromagnetic waves by an electromagnetic field, which is a physical phenomenon. In contrast, the electromagnetic shield 40 according to the fourth embodiment shown in Fig. 9 modulates electromagnetic waves by an electromagnetic field and other physical phenomena such as light, vibration, and heat. That is, the electromagnetic shield 40 according to the fourth embodiment modulates electromagnetic waves by two different types of physical phenomena.

[0072] 9 , the electromagnetic shield 40 has a flat inner surface 40a facing the inside of the building and a flat outer surface 40b facing the outside of the building. The inner surface 40a and the outer surface 40b are arranged parallel to each other. The electromagnetic shield 40 also includes a plurality of substrates 31, a plurality of conductors 32, a plurality of varactors 33, and a plurality of energy harvesting elements 41 therein. The plurality of substrates 31, the plurality of conductors 32, the plurality of varactors 33, and the plurality of energy harvesting elements 41 are arranged between the inner surface 40a and the outer surface 40b. The electromagnetic shield 40 has the same configuration as the electromagnetic shield 30, but also includes the energy harvesting elements 41 as connecting members.

[0073] 9 and 10 , the pair of conductors 32 are connected by a varactor 33 and an energy harvesting element 41. This energy harvesting element 41 is provided on the surface of the substrate 31. The energy harvesting element 41 has the property that the amount of power it generates changes depending on the energy of light, vibration, heat, and the like. That is, the amount of power generated, which is a physical property of the energy harvesting element 41, changes depending on the disturbances that naturally exist around the electromagnetic shield 40 (around the substrate 31). In this case, the disturbances that naturally exist around the electromagnetic shield 40 are, for example, any one of light, vibration, and heat.

[0074] 9 shows an example in which two substrates 31 are stacked, and each substrate 31 is provided with 12 pairs of conductors 32 connected by one varactor 33 and one energy harvesting element 41. Note that in the electromagnetic shield 40, the number of stacked substrates 31, the number of pairs of conductors 32 provided on one substrate 31, the number of varactors 33 provided between pairs of conductors 32, and the number of energy harvesting elements 41 provided can be adjusted as appropriate.

[0075] The following description of the operation of the electromagnetic shield 40 will be given for the case where the energy harvesting element 41 generates power by receiving light. The operation is the same even when the energy harvesting element 41 generates power by receiving vibration, heat, or the like.

[0076] Therefore, with the electromagnetic shield 40 having the above-described configuration, an electric field and a voltage V1 associated with this electric field are generated between the pair of conductors 32 connected by the varactor 33 due to the electromagnetic field that naturally exists around the electromagnetic shield 40. Furthermore, with the electromagnetic shield 40 having the above-described configuration, the energy harvesting element 41 generates electricity between the pair of conductors 32 connected by the energy harvesting element 41 due to light that naturally exists around the electromagnetic shield 40, and a voltage V2 associated with this power generation is generated.

[0077] The light naturally present around the electromagnetic shield 40 is natural phenomena such as sunlight, and artificial phenomena such as light emitted from a television monitor. These natural and artificial phenomena occur naturally and are not artificially controlled for the purpose of irradiating the electromagnetic shield 40 with light.

[0078] Furthermore, the intensity of light naturally present around the electromagnetic shield 40 and the voltage V2 generated in the energy harvesting element 41 in response to that light intensity are determined by a complex combination of various conditions, such as the positional relationship between the light radiation source (light source) and the electromagnetic shield 40, and the placement of objects on the propagation path of the light from the radiation source to the electromagnetic shield 40. For this reason, the light intensity and voltage V2 change irregularly depending on the time of day and the installation position of the electromagnetic shield 40. In other words, the voltage V2 generated in the electromagnetic shield 40 changes randomly depending on the time of day and the installation position without requiring a power source.

[0079] In this way, the amount of power generated by the energy harvesting element 41 changes randomly over time and position, and the voltage V2 generated between the pair of conductors 32 also changes randomly. In this case, the local complex transmission coefficient in a specific region of the electromagnetic shield 40 depends on the voltage V2 in that specific region.

[0080] Therefore, the electromagnetic waves incident on the electromagnetic shield 40 leak outside the building after undergoing changes in transmission amplitude and transmission phase depending on the time and position of transmission. In other words, the electromagnetic waves incident on the electromagnetic shield 40 are modulated depending on the time and position of transmission before leaking outside the building.

[0081] Therefore, when electromagnetic waves used in wireless communication and electromagnetic waves (electromagnetic noise) emitted from electronic devices are incident on the electromagnetic shield 40, each electromagnetic wave is randomly modulated in terms of time and position by the electromagnetic shield 40. As a result, the information contained in the electromagnetic waves becomes information different from the original information before the electromagnetic waves were modulated, and is leaked outside the building.

[0082] Therefore, the electromagnetic shield 40 can modulate the electromagnetic waves that pass through it using disturbances such as light, vibration, and heat that are naturally present around the electromagnetic shield 40. As a result, the electromagnetic shield 40 can prevent information contained in the original electromagnetic waves from being eavesdropped on, even if someone outside the building tries to intercept the electromagnetic waves by improving the reception sensitivity.

[0083] The pair of conductors 32 connected by the varactors 33 and the energy harvesting elements 41 do not have to be arranged periodically. Furthermore, the shapes and characteristics of the energy harvesting elements 41 and the varactors 33 do not have to be identical. In this case, the randomness of the modulation of the electromagnetic waves passing through the electromagnetic shield 40 can be further increased.

[0084] As described above, the electromagnetic shield 40 according to the fourth embodiment includes one or more substrates 31 each having one or more pairs of conductors 32, and an energy harvesting element 41 that connects the pair of conductors 32 and whose physical properties change in response to disturbances naturally present around the substrates. Therefore, the electromagnetic shield 40 can modulate electromagnetic waves without requiring artificial control.

[0085] Fifth Embodiment An electromagnetic shield 50 according to a fifth embodiment will be described with reference to Figs. 11 and 12. Fig. 11 is a perspective view of the electromagnetic shield 50 according to the fifth embodiment. Fig. 12 is an enlarged view of a main portion of Fig. 11. Note that components having the same functions as those described in the third embodiment above are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0086] The electromagnetic shield 30 according to the third embodiment shown in Fig. 7 modulates electromagnetic waves using an electromagnetic field, which is a physical phenomenon, whereas the electromagnetic shield 50 according to the fifth embodiment shown in Fig. 11 modulates electromagnetic waves using light, temperature, sound, and other physical phenomena.

[0087] 11 , the electromagnetic shield 50 has a flat inner surface 50a facing the inside of the building and a flat outer surface 50b facing the outside of the building. The inner surface 50a and the outer surface 50b are arranged parallel to each other. The electromagnetic shield 50 also includes a plurality of substrates 31, a plurality of conductors 32, and a plurality of sensors 51 therein. The plurality of substrates 31, the plurality of conductors 32, and the plurality of sensors 51 are arranged between the inner surface 40a and the outer surface 40b. The electromagnetic shield 50 includes the sensors 51 as connecting members instead of the varactors 33 of the electromagnetic shield 30.

[0088] 11 and 12 , the pair of conductors 32 are connected by a sensor 51. This sensor 51 is provided on the surface of the substrate 31. The sensor 51 detects light intensity, temperature, sound pressure, etc., and has the characteristic that its electrical impedance Z changes in response to these detections. That is, the impedance Z, which is a physical property of the sensor 51, changes depending on disturbances that naturally exist around the electromagnetic shield 50 (around the substrate 31). For example, if the sensor 51 is an optical sensor, the disturbance is light. If the sensor 51 is a temperature sensor, the disturbance is temperature. If the sensor 51 is a sound sensor, the disturbance is sound.

[0089] 11 shows an example in which two substrates 31 are stacked, and each substrate 31 is provided with 12 pairs of conductors 32 connected by one sensor 51. Note that in the electromagnetic shield 50, the number of stacked substrates 31, the number of pairs of conductors 32 provided on one substrate 31, and the number of sensors 51 installed between the pairs of conductors 32 can be adjusted as appropriate.

[0090] The operation of the electromagnetic shield 50 will be described below in the case where the sensor 51 is an optical sensor. Even if the sensor 51 is a temperature sensor or a sound sensor, the operation is the same.

[0091] Therefore, by configuring the electromagnetic shield 50 as described above, the sensor 51 connecting the pair of conductors 32 detects light that is naturally present around the electromagnetic shield 50, and an impedance Z is generated inside the sensor 51.

[0092] The light naturally present around the electromagnetic shield 50 includes natural phenomena such as sunlight and artificial phenomena such as light emitted from a television monitor. These natural and artificial phenomena occur naturally and are not artificially controlled for the purpose of irradiating the electromagnetic shield 50 with light.

[0093] Furthermore, the intensity of light naturally present around the electromagnetic shield 50 and the impedance Z generated in the sensor 51 according to that light intensity are determined by a complex combination of various conditions, such as the positional relationship between the light radiation source (light source) and the electromagnetic shield 50, and the placement of objects on the propagation path of the light from the radiation source to the electromagnetic shield 50. For this reason, the light intensity and impedance Z change irregularly depending on the time of day and the installation position of the electromagnetic shield 50. In other words, the impedance Z generated in the electromagnetic shield 50 changes randomly depending on the time of day and the installation position.

[0094] In this way, the intensity of light detected by the sensor 51 changes randomly over time and position, and the impedance Z of the sensor 51 also changes randomly. At this time, the local complex transmission coefficient in a specific region of the electromagnetic shield 50 depends on the impedance Z in that specific region.

[0095] For this reason, electromagnetic waves incident on the electromagnetic shield 50 undergo changes in transmission amplitude and transmission phase depending on the time and position of transmission before leaking outside the building. In other words, electromagnetic waves incident on the electromagnetic shield 50 are modulated depending on the time and position of transmission before leaking outside the building.

[0096] Therefore, when electromagnetic waves used in wireless communication and electromagnetic waves (electromagnetic noise) emitted from electronic devices are incident on the electromagnetic shield 50, each electromagnetic wave is randomly modulated in terms of time and position by the electromagnetic shield 50. As a result, the information contained in the electromagnetic waves becomes information different from the original information before the electromagnetic waves were modulated, and is leaked outside the building.

[0097] Therefore, the electromagnetic shield 50 can modulate the electromagnetic waves that pass through it using disturbances such as light, temperature, and sound that naturally exist around the electromagnetic shield 50. As a result, the electromagnetic shield 50 can prevent information contained in the original electromagnetic waves from being eavesdropped on, even if someone outside the building tries to intercept the electromagnetic waves by improving the reception sensitivity.

[0098] The pairs of conductors 32 connected by the sensors 51 do not have to be arranged periodically. Furthermore, the shapes and characteristics of the sensors 51 do not have to be identical. In this case, the randomness of modulation of the electromagnetic waves passing through the electromagnetic shield 50 can be further increased.

[0099] As described above, the electromagnetic shield 50 according to the fifth embodiment includes one or more substrates 31 each having one or more pairs of conductors 32, and a sensor 51 that connects the pair of conductors 32 and whose physical properties change in response to disturbances that naturally exist around the substrates. Therefore, the electromagnetic shield 50 can modulate electromagnetic waves without requiring artificial control.

[0100] It should be noted that within the scope of the present disclosure, the embodiments may be freely combined, or any component in each embodiment may be modified, or any component in each embodiment may be omitted.

[0101] The electromagnetic shield according to the present disclosure can prevent leakage of information contained in electromagnetic waves by modulating the electromagnetic waves using disturbances that naturally exist around the substrate, and is suitable for use as an electromagnetic shield, etc.

[0102] 10, 20, 30, 40, 50 electromagnetic shield, 10a, 20a, 30a, 40a, 50a inner surface, 10b, 20b, 30b, 40b, 50b outer surface, 11 substrate, 12 conductor, 13 spring, 21 fixing member, 22 propeller, 23 rotating shaft, 23a branch shaft, 24 substrate, 25 conductor, 31 substrate, 32 conductor, 33 varactor, 34 support member, 41 energy harvesting element, 51 sensor, D1 to D3 distance, V1, V2 voltage, Z impedance.

Claims

1. An electromagnetic shield comprising a plurality of substrates each having one or more conductors, the substrates being supported such that the distance between the conductors of adjacent substrates changes in response to disturbances naturally occurring around the substrates.

2. The electromagnetic shield according to claim 1, characterized in that adjacent substrates are supported via an elastic body.

3. The electromagnetic shield according to claim 1 or 2, characterized in that the elastic body is a spring.

4. The electromagnetic shield according to claim 1 or 2, characterized in that the elastic body is rubber.

5. The electromagnetic shield according to any one of claims 1 to 4, characterized in that the disturbance is at least one of vibration, wind, and sound.

6. An electromagnetic shield comprising: a substrate having one or more conductors; and a number of rotating shafts supporting the substrate about an axis with the conductors tilted relative to a reference plane, wherein the substrate rotates such that a distance between the conductors of the substrate and the conductors of substrates supported by other rotating shafts changes in response to disturbances naturally present around the substrate.

7. The electromagnetic shield according to claim 6, characterized in that the disturbance is wind.

8. An electromagnetic shield comprising: one or more substrates having one or more pairs of conductors; and a connecting member that connects the pairs of conductors and whose physical properties change in response to disturbances naturally present around the substrates.

9. The electromagnetic shield according to claim 8, wherein the coupling member is a varactor, and the capacitance of the varactor changes due to disturbances naturally present around the substrate.

10. The electromagnetic shield according to claim 9, wherein the disturbance is an electromagnetic field.

11. The electromagnetic shield according to claim 8, characterized in that the connecting member is an energy harvesting element, and the amount of power generated by the energy harvesting element changes depending on disturbances naturally present around the substrate.

12. The electromagnetic shield according to claim 11, wherein the disturbance is any one of light, vibration, and heat.

13. The electromagnetic shield according to claim 8, wherein the connecting member is a sensor, and the impedance of the sensor changes due to disturbances naturally present around the board.

14. The electromagnetic shield according to claim 13, wherein the disturbance is any one of light, temperature, and sound.

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