JP2020090870A - Radio wave absorption heating element, backing material for supporting the heating element, and method for manufacturing heating element provided with them - Google Patents

Abstract

To provide a radio wave absorption heating element which can favorably generate heat even when submerged in water, and also can reduce labor and cost in manufacturing and construction.SOLUTION: A radio wave absorption heating element 43 absorbs a radio wave of a predetermined frequency emitted from the lower side to the upper side so as to generate heat. This radio wave absorption heating element 43 is made of a material having a uniform relative dielectric constant and relative magnetic permeability and has a water absorption property, with a cross-sectional area that spreads in the horizontal direction (direction orthogonal to the radio wave irradiation direction) increased from the lower side to the upper side (in the direction away from the side to be irradiated with the radio wave).SELECTED DRAWING: Figure 2

Description

The present invention relates to a radio wave absorption heating element, a base material that supports the heating element, and a method for manufacturing a heating member including the same.

Patent Document 1 discloses a conventional heating block. This heat generating block is laid in a passageway of each house in a snowfall area and used for snow melting. This heat generating block is arranged above a radio wave transmission body that leaks radio waves of a predetermined frequency. The heat generating block absorbs the radio waves and generates heat when irradiated with the radio waves of a predetermined frequency leaked from the radio wave transmitter. This heating block has a predetermined thickness when viewed from above in a square shape when viewed from above when installed in a passage or the like. In the installed state, the heat generating block is formed by laminating a base material, a radio wave absorbing heat generating body, and a reflecting material that reflects radio waves in this order from the bottom to the top. The base material is made of sand mortar. The radio wave absorption heating element is formed in a flat plate shape with mortar using slag that absorbs radio waves as an aggregate. In addition, a waterproofing agent is added to the radio wave absorption heating element to improve water repellency of mortar and the like and reduce water intrusion. For this reason, even if the heat generating block is exposed to water, the moisture absorption of the radio wave absorbing heat generating element is suppressed, the change in the relative permittivity and the relative permeability is small, and the deterioration of the heat generating performance can be suppressed.

JP, 2017-206811, A

However, since the radio wave absorption heating element of Patent Document 1 is in the form of a flat plate, the thickness of the radio wave absorption heating element and the distance from the radio wave transmission element greatly affect the radio wave absorption performance, that is, the heat generation performance. Therefore, in order to obtain good heat generation performance, it is necessary to increase the manufacturing accuracy of the electromagnetic wave absorption heating element and the construction accuracy of the heat generating block, which increases labor and cost.

The present invention has been made in view of the above-mentioned conventional circumstances, and can generate good heat even when exposed to water, and can reduce the labor and cost in manufacturing and construction. It is an issue to be solved to provide a heat generating member.

A radio wave absorption heating element according to a first aspect of the present invention is a radio wave absorption heating element that absorbs radio waves of a predetermined frequency irradiated in a fixed direction to generate heat.
At least one of a relative permittivity and a relative permeability in a cross section having a water absorbing property and extending in a direction orthogonal to a radio wave irradiation direction is increased in a direction away from a side irradiated with the radio wave. ..

In this radio wave absorption heating element, at least one of the relative permittivity and the relative magnetic permeability in the cross section extending in the direction orthogonal to the radio wave irradiation direction increases in the direction away from the side irradiated with the radio wave, so that in the radio wave irradiation direction. Even if the construction position is displaced or if water is contained and contains water, radio waves of a predetermined frequency can be absorbed somewhere in the thickness direction of the radio wave absorption heating element to generate heat. For this reason, this radio wave absorption heating element can satisfactorily generate heat without strict control of manufacturing accuracy and construction accuracy.

A radio wave absorption heating element according to a second aspect of the present invention is a radio wave absorption heating element that absorbs a radio wave of a predetermined frequency emitted in a certain direction to generate heat.
It is made of a material with a uniform relative permittivity and relative permeability, has water absorbency, and the cross-sectional area that expands in the direction orthogonal to the radio wave irradiation direction increases in the direction away from the side that is irradiated with the radio wave. It is characterized by

This radio wave absorption heating element is made of a material having a uniform relative permittivity and relative magnetic permeability, and the cross-sectional area expanding in the direction orthogonal to the radio wave irradiation direction increases in the direction away from the side irradiated with the radio wave. Therefore, the equivalent relative permittivity and the equivalent relative permeability increase from the bottom to the top. Therefore, this radio wave absorption heating element can absorb a radio wave having a predetermined frequency and generate heat somewhere in the radio wave irradiation direction. In addition, this radio wave absorption heating element can absorb radio waves of a predetermined frequency somewhere in the radio wave irradiation direction and generate heat even if the construction position in the radio wave irradiation direction is displaced or if water is contained and contains water. .. For this reason, this radio wave absorption heating element can satisfactorily generate heat without strict control of manufacturing accuracy and construction accuracy.

The term "uniform" as used herein is not limited to being completely uniform, and may vary within a range that does not hinder the heat generation performance.

Therefore, the radio wave absorption heating elements of the first invention and the second invention can generate good heat even when exposed to water, and can reduce the labor and cost in manufacturing and construction.

The base material of the third invention is made of resin and is arranged in contact with the back surface of the radio wave absorption heating element of the first invention or the second invention on the side irradiated with the radio wave, and supports the radio wave absorption heating element. It is characterized by

Since this base material is made of resin, it is difficult to contain water. Therefore, this base material can suppress changes in relative permittivity or relative permeability when exposed to water.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a heat-generating member, wherein the recess of the third aspect of the present invention has a recess in which a space in a horizontal cross section increases from the bottom to the top. The first step of placing,
A second step of pouring a radio wave absorbing heat generating material into the recess after the first step;
It is characterized by having.

According to this method of manufacturing a heat generating member, a heat generating member that efficiently absorbs radio waves of a predetermined frequency to generate heat can be easily manufactured at a construction site.

It is a perspective view showing a snow melting system of Example 1. FIG. 3 is a cross-sectional perspective view showing a cross-section of the heat generating member and the radio wave transmission body of the first embodiment. It is a schematic diagram showing a direction of an electric field of a radio wave leaked from a radio wave transmitter. (A) is a perspective view showing dimensions of a wedge-shaped radio wave absorption heating element, and (B) is a cross-sectional view showing a cross section in the XY plane of (A). It is a schematic diagram at the time of the approximate calculation of the characteristic of the wedge-shaped radio wave absorption heating element. It is a conceptual diagram which shows the structure of a multilayer type electromagnetic wave absorber. 7 is a graph showing return loss of a wedge-shaped radio wave absorption heating element and a flat plate radio wave absorption heating element. It is a schematic diagram showing an arch type measuring device. It is a schematic diagram showing the incidence direction of the electric wave to a sample. 7 is a graph showing the relationship between the number of peaks of a wedge-shaped radio wave absorption heating element and the return loss. 7 is a graph showing the relationship between the number of peaks of a wedge-shaped radio wave absorption heating element and the amount of scattering. It is a graph which shows the frequency and the relationship of return loss when sand:slag ratio is changed. It is a perspective view which shows the state which embeds a radio wave transmission body in the 2nd groove part. It is a perspective view which shows the state which has arrange|positioned the base material in the 1st groove part. It is a perspective view showing the state where pouring slag mortar which has fluidity was poured into each crevice of a substrate. It is a perspective view which shows the state which arrange|positioned the radio wave reflection material on slag mortar. FIG. 3 is a perspective view showing a state in which a sand mortar having fluidity serving as a protective material is poured from above the radio wave reflection material. FIG. 3 is a perspective view showing a flat plate-shaped electric wave absorption heating element in which the relative permittivity or relative permeability increases from the lower layer to the upper layer. FIG. 3 is a perspective view showing a quadrangular pyramid-shaped radio wave absorption heating element. It is a perspective view showing a radio wave transmission object in which a plurality of slots extend in a direction parallel to a direction in which the radio wave transmission object extends.

A preferred embodiment of the present invention will be described.

In the radio wave absorption heating element of the second invention, the end portion on the side irradiated with the radio wave extends linearly in a direction orthogonal to the radio wave irradiation direction, and from the side irradiated with the radio wave from both sides of the end portion. The distance between the side surfaces extending in the away direction may be a wedge shape that increases in the direction away from the side on which the radio waves are emitted. In this case, when the radio wave absorption heating element is arranged so as to intersect the direction of the electric field E of the radio wave having a predetermined frequency for irradiating the end portion of the radio wave absorption heating element which extends linearly in the direction orthogonal to the radio wave irradiation direction, It can absorb radio waves well and generate heat. Note that, as shown in FIG. 3, the direction of the electric field E of the radio wave is orthogonal to the direction in which the slot 21 formed in the radio wave transmission body 20 described later extends.

The radio wave absorption heating element of the second invention may have a quadrangular pyramid shape whose apex is located on the side irradiated with the radio wave. In this case, the radio wave absorption heating element can satisfactorily absorb the radio wave and generate heat regardless of the direction of the electric field E of the radio wave having the predetermined frequency to be applied. Therefore, the radio wave absorption heating element can be constructed without considering the direction of the electric field E.

When the radio wave absorption heating element of the first invention and the second invention is irradiated with a radio wave of a predetermined frequency, the surface of the side opposite to the side irradiated with the radio wave may rise in temperature. If this radio wave absorption heating element is used in a snow melting system, snow can be melted well.

The substrate of the third invention can be molded into a foam. In this case, since this base material is a foam, it has a high heat insulating property and can suppress heat escaping downward. Further, this base material can be made to have a low dielectric constant by using a foam. The base material may be formed by foaming a material having a low relative dielectric constant.

The base material of the third invention may have a relative dielectric constant of 1.0 to 1.5. In this case, since the radio wave is less absorbed and reflected by the base material, the radio wave easily reaches the radio wave absorption heating element, and the radio wave absorber can satisfactorily generate heat. The relative permittivity of the base material is preferably 1.0 to 1.3, more preferably 1.0 to 1.1. The closer the relative permittivity of the base material is to 1.0, the less absorption and reflection of radio waves, and the better the radio wave absorber can generate heat.

Next, a first embodiment embodying a method of manufacturing a radio wave absorption heating element, a base material, and a heating member including these of the present invention will be described with reference to the drawings.

<Example 1>
The radio wave absorption heat generating body 43, the base material 41, and the heat generating member 40 including these of the first embodiment are used in a snow melting system, as shown in FIGS. 1 and 2. The snow melting system includes a radio wave transmitter 10, a radio wave transmitter 20, and a heating block 30. The heat generating block 30 has a heat generating member 40, and is laid in a passageway or the like of each house in a snowfall area.

The radio wave transmitter 10 transmits a radio wave having a predetermined frequency (2.45 GHz). The radio wave transmitter 20 is a stainless steel rectangular steel pipe whose one end is connected to the radio wave transmitter 10 and which extends in one direction. The cross-sectional shape of the radio wave transmitter 20 orthogonal to the extending direction is a horizontally long rectangular shape. In this cross-sectional shape, the outer dimension of the short side is 50.0 mm, the inner dimension of the short side is 46.8 mm, the outer dimension of the long side is 100 mm, and the inner dimension of the long side is 96.8 mm.

The radio wave transmitter 20 has a plurality of slots 21 formed on its upper surface in a construction state in which the radio wave transmitter 20 is disposed below the heat generating block 30. The slot 21 is a slit-shaped hole. The slot 21 extends in a direction orthogonal to the direction in which the radio wave transmitter 20 extends. The slot 21 has a width of 3 mm and a length of 30 mm. The slots 21 are formed at 10 mm intervals. The radio wave transmitter 20 leaks radio waves upward from each slot 21. The direction of the electric field E of the radio wave leaking from the radio wave transmitter 20 is orthogonal to the direction in which the slot 21 extends, as shown in FIG. That is, the direction of the electric field E of the radio wave leaking from the radio wave transmitter 20 is parallel to the direction in which the radio wave transmitter 20 extends. A heat generating block 30 described later is laid in a passage or the like with the central portion of the lower surface of the heat generating block 30 (the lower surface of the base material 41) contacting the upper surface of the radio wave transmitter 20.

As shown in FIG. 2, the heat generating block 30 has a heat generating member 40, a radio wave reflection material 50, and a protective material 60. The heat generating member 40 includes a radio wave absorption heating element 43 and a base material 41. The heating block 30 has a square shape (300 mm on a side) in a plan view (hereinafter referred to as “plan view”) viewed from above in a construction state laid in a passage or the like.

The base material 41 is made of expanded polystyrene (expanded polyethylene). That is, the base material 41 is a resin foam. This base material 41 can have a relative dielectric constant of 1 to 1.5 by adjusting the expansion ratio. Table 1 shows the relative permittivity and relative permeability of the base material 41 made of styrofoam having a foaming ratio of 50 times.

The outer shape of the base material 41 is a rectangular parallelepiped. The base material 41 has a square shape in plan view (each side is 300 mm) and has a vertical thickness of 130 mm. In the base material 41, nine recesses 41A extending in one direction over two parallel sides are formed in parallel in parallel with each other in a plan view. Each of the recesses 41</b>A faces upward and opens in a construction state in which the heat generating block 30 (base material 41) is laid in a passage or the like. In the installed state, each recess 41A has an inverted isosceles triangular cross-sectional shape orthogonal to the direction in which the recess 41A extends. The depth of the lowermost end of each recess 41A is 70 mm. These recesses 41A are in a state in which a wedge-shaped radio wave absorption heating element 43 described later is fitted. Further, the base material 41 has a thickness of 60 mm below the lower end of each recess 41A in the installed state.

The base material 41 is laid in a passage or the like such that each recess 41A extends in a direction orthogonal to the direction in which the radio wave transmitter 20 extends. That is, each recess 41A is constructed so as to extend in a direction parallel to the direction in which the plurality of slots 21 formed in the radio wave transmitter 20 extend. Further, the base material 41 is constructed in a state where the central portion of the lower surface is in contact with the upper surface of the radio wave transmitter 20. In this way, the base material 41 constructed so that the lower surface of the radio wave transmission body 20 contacts the upper surface of the radio wave transmission body 20 is disposed below the radio wave absorption heat generation body 43 while being in contact with the lower surface of the radio wave absorption heat generation body 43. The absorption heating element 43 is supported.

The radio wave absorption heating element 43 is formed of mortar using slag as an aggregate (hereinafter referred to as “slag mortar 43C”). Slag is an electric furnace oxidation slag that has the property of absorbing radio waves and converting them into heat. The slag mortar 43C is formed by kneading slag, cement, and water so that the relative dielectric constant and the relative magnetic permeability are uniform. Table 2 shows the formulation (mass ratio) of slag, cement and water of slag mortar 43C.
This slag mortar 43C has water absorption in a hardened state.

Here, the cement is usually Portland cement, but may be other Portland cement, mixed cement, ecocement, or special cement. The Portland cement includes ordinary Portland cement, early strength Portland cement, super early strength Portland cement, moderate heat Portland cement, low heat Portland cement, sulfate resistant Portland cement, and low alkali type of each of these. The mixed cement includes blast furnace cement, silica cement and fly ash cement. The eco-cement includes ordinary eco-cement and quick-setting eco-cement. Further, the special cement includes white Portland cement, alumina cement, ultra-rapid cement, grout cement, and oil well cement.

In one heating block 30, the radio wave absorption heating element 43 is formed by nine convex portions 43A extending in parallel in one direction. Each convex portion 43A projects downward when the heating block 30 (radiowave absorption heating element 43) is laid in a passage or the like. In the installed state, each of the convex portions 43A has a top portion 43B at the lower end extending linearly in the horizontal direction. Further, in this state, each of the convex portions 43A has an inverted isosceles triangular cross-sectional shape orthogonal to the top portion 43B. That is, in the installed state, each of the convex portions 43A has a lower end (end portion on the side where radio waves are radiated) linearly extending in the horizontal direction (direction orthogonal to the radio wave irradiation direction), and diagonally upward from both sides of the lower end. The flat side surface extending in the direction (away from the side where the radio wave is irradiated) has a wedge shape that continuously increases from the lower side to the upper side (direction away from the side where the radio wave is irradiated). Each convex portion 43A has a vertical dimension of 70 mm in the installed state, and a vertical dimension of the top portion 43B is 300 mm.

In the installed state, each convex portion 43A is in a state of being fitted into each concave portion 41A formed in the base material 41. That is, each convex portion 43A extends parallel to the direction orthogonal to the direction in which the radio wave transmitter 20 extends (the direction in which the slot 21 extends) in the installed state. Moreover, since the radio wave absorption heating element 43 is supported by the base material 41 whose lower surface is in contact with the upper surface of the radio wave transmission element 20, the top 43B of the lower end of the radio wave absorption heating element 43 is separated from the upper surface of the radio wave transmission element 20 by 60 mm. It is arranged so as to extend to the open position. Further, each wedge-shaped convex portion 43A has a vertical dimension of 70 mm, which is larger than a half wavelength of a radio wave having a frequency of 2.45 GHz.

The radio wave absorption heating element 43 adjusts the equivalent relative permittivity and the equivalent relative permeability such that the radio wave having a frequency of 2.45 GHz is most easily absorbed in the vicinity of the upper surface (the surface opposite to the side where the radio wave is irradiated). By doing so, the electric wave of the frequency of 2.45 GHz leaking from the electric wave transmitter 20 is absorbed near the upper end to generate heat, and the temperature of the upper surface rises.

The radio wave reflection material 50 is arranged on the upper surface of the radio wave absorption heating element 43 in a construction state in which the heat generation block 30 is laid in a passage or the like. The radio wave reflection material 50 is a metal wire mesh in which a part of the welded wire mesh is damaged to improve the radio wave reflection performance (see FIG. 16). The radio wave reflection material 50 is arranged so that the defective portion 51 extends in a direction orthogonal to the direction in which the radio wave transmission body 20 extends in a construction state laid in a passage or the like.

The protective material 60 is sand mortar poured from above the radio wave reflection material 50 onto the upper surface of the radio wave absorption heating element 43. Table 3 shows the formulation (mass ratio) of the sand mortar. The protective material 60 fixes the radio wave reflection material 50 at a predetermined position with respect to the heat generating member 40, and forms the upper surface of the heat generating block 30. The protective material 60 has a thickness of 8 mm. The protective material 60 is applied with at least the upper surface exposed.

<Characteristics of wedge type electromagnetic wave absorption heating element 43>
Next, characteristics of the wedge-shaped radio wave absorption heating element 43 (hereinafter, referred to as "wedge type radio wave absorption heating element 43") will be described.

FIG. 4A shows the dimensions of one convex portion 43A of the wedge-type radio wave absorption heating element 43. A length of one convex portion 43A of the wedge-type radio wave absorption heating element 43 in the Z-axis direction is a, a length of the bottom surface in the X-axis direction is b, a length in the Y-axis direction is c, and a position z is on the Z-axis. Let b _{z be} the length in the X-axis direction. The convex portion 43A of the wedge-type radio wave absorption heating element 43 is divided into sufficiently thin layers as shown in FIG. By averaging the relative permittivity and relative permeability of each of the divided layers and treating them as a flat plate having uniform electric characteristics, the characteristics of the wedge-type radio wave absorption heating element 43 can be calculated by approximate calculation. At this time, the averaged relative permittivity is called equivalent relative permittivity, and the averaged relative permittivity is called equivalent relative permeability. The white arrow pointing downward in FIG. 5 indicates the direction of the radio wave to be emitted. A cross section in the XY plane at the position z on the Z axis is shown in FIG. The occupied area S _u of the radio wave absorbing and heat-generating material and the occupied area S _{a of} air in this cross section are expressed by equations (1) and (2), respectively.

When the average of the relative permittivities is calculated by this area ratio, it is expressed as in formula (3), and when the average of the relative magnetic permeability is calculated, it is expressed as in formula (4).

FIG. 6 shows the structure of the multilayer type electromagnetic wave absorber. The normalized input impedance of the first layer and the normalized input impedance of the second layer are represented by equations (5) and (6).

here,

When formulas (5) to (7) are expanded to the N layer, they are represented by formulas (8) and (9).

The reflection coefficient S and the return loss RL(dB) can be expressed by the equations (10) and (11) by using Z _N calculated by the equations (5) to (9) and the characteristic impedance Z _{0 of} air. ..

FIG. 7 shows the return loss of the wedge-type radio wave absorption heating element 43 calculated using the above equation. Compared with the return loss of the conventional flat plate type electromagnetic wave absorption heating element, the return loss of the target (reference) can be satisfied in a wide frequency band. From this, it is considered that the target return loss can be satisfied even if the relative permittivity and relative permeability change due to manufacturing errors or water content.

Next, the result of measuring the return loss using the sample 83 will be described.
<Sample 83>
The bottom of the test piece 83 is 300×300 mm. The height is 70 mm, which is larger than the half wavelength of a radio wave having a frequency of 2.45 GHz. The number of convex portions 83A (hereinafter referred to as the number of peaks) that fits in the bottom area is an odd number so that the top portion 83B of the convex portion 83A is located at the center where the radio wave is irradiated.

Table 4 shows the formulation (volume ratio) of the slag mortar 43C, and Table 5 shows the production conditions. The number of peaks of the specimen 83 to be used is 9 in consideration of manufacturing cost, and the ratio of mountain sand to be used as fine aggregate and slag (hereinafter referred to as sand:slag ratio)=0:10. Specimens 83 having a mountain count of 1, 3, 5, 7, 9 are prepared by compounding. In order to clarify the relationship between the change in the sand:slag ratio and the return loss, 9 peaks are manufactured even with the sand:slag ratio=2:8, 4:6.

Table 6 shows the mass ratio of the components of the slag obtained by the qualitative analysis of the inorganic elements by fluorescent X-rays in terms of oxides. The particle size of the slag used is 0.3 to 0.6 mm, and the cement is usually Portland cement.

Specimen 83 was cured in air for 1 day and cured in water for 5 days, and thereafter dried in a thermo-hygrostat at 100 degrees for 72 hours or more.

<Measurement method>
FIG. 8 shows the arch-type measuring device 90, and FIG. 9 shows the direction of incidence of radio waves on the specimen 83. In this measurement, the return loss is measured by the S-parameter measurement method using the arch measuring device 90. The radio wave is emitted from the port 1 of the network analyzer 95, and is irradiated onto the sample 83 by the transmitting antenna (double rigid horn antenna) 91 via the coaxial cable. The irradiated radio waves are either reflected and absorbed by the specimen 83 or transmitted through the specimen 83. The transmitted radio wave is reflected by the metal sample installation base 92, received by the receiving antenna 93 together with the radio wave reflected on the surface of the sample 83, and received by the port 1 via the coaxial cable.

At this time, assuming that the incident wave at port 1 is α ₁ and the reflected wave is β ₁ , the reflection coefficient is expressed by equation (12).

Since the reflection coefficient represented by the equation (12) is a vector quantity, if the real part is a, the imaginary part is b, and the imaginary unit is j, it can be represented by the equation (13). When this is converted into a reflection coefficient of a scalar quantity, the equation (14) is obtained. The return loss RL (dB) is calculated from the equation (15) using the scalar reflection coefficient of the equation (14).

The radio wave scattered in the X-axis direction shown in FIG. 9 is measured by the arch-type measuring device 90 shown in FIG. Radio waves are emitted from the port 1 of the network analyzer 95, and the sample 83 is irradiated from the transmitting antenna 91 via the coaxial cable. The strength of the transmitted radio wave is about 10 dBm. The radio wave reflected obliquely on the surface of the specimen 83 is received by the port 2 of the spectrum analyzer 96 via the receiving antenna 93 (double rigid horn antenna). The receiving antenna 93 is installed at positions of 15, 30, 45, 60, and 75 degrees to the left and right around the transmitting antenna 91. The total amount of reflection at all positions is evaluated as the amount of scattering of the wedge-type radio wave absorption heating element 43.

FIG. 10 shows the relationship between the number of peaks and the return loss at a frequency of 2.45 GHz, and FIG. 11 shows the relationship between the number of peaks and the amount of scattering. The maximum return loss is 28.6 dB when the number of peaks is 9. It is considered that the number of peaks 9 has sufficient heat generation performance because heat is sufficiently generated if there is a return loss of 15 dB or more. However, the wedge-type radio wave absorption heating element 43 may have a shape in which radio waves obliquely enter the slope of the convex portion 43A depending on the shape thereof. In that case, the irradiated radio waves are obliquely reflected and scattered on the surface of the specimen 83, so that it is feared that the proportion of scattering becomes higher than that of the flat plate-shaped absorber, and only the return loss is large. Therefore, it cannot be said that the absorption performance is high. Looking at the amount of scattering in FIG. 11, when the number of peaks is 1, the maximum is −23.2 dBm, and then it is rapidly reduced, and when the number of peaks is 3 or more, it becomes constant around −26.5 dBm to −26 dBm. Further, the amount of scattering when a radio wave is applied to a pyramid type electromagnetic wave absorber made of urethane and a flat plate type electromagnetic wave absorbing heat generating body which are generally impregnated with carbon used in an anechoic chamber is −25.9 dBm and −25.4 dBm, respectively. Met. If the number of peaks is 3 or more, it is less than any of them, and the amount of scattering is sufficiently small.

From the above, it is considered that the number of peaks 9 having the highest return loss and the scattering amount of −26.6 dBm, which is sufficiently small, is the shape of the wedge-type radio wave absorption heating element 43 having the highest radio wave absorption performance. Further, from FIG. 11, it is considered that the amount of scattering is sufficiently small even with the number of peaks other than 1, and the electromagnetic wave absorption performance is sufficient.

FIG. 12 shows the relationship between the frequency and the return loss when the sand:slag ratio is changed. At a frequency of 2.45 GHz, the return loss reaches a maximum of 23.7 dB at a sand:slag ratio of 0:10, then decreases as the slag ratio decreases, and reaches a minimum of 14 at a sand:slag ratio of 4:6. It takes 0.5 dB.

The higher the slag ratio is, the maximum return loss is reached in the low frequency band. The frequency is about 4.6 GHz at sand:slag ratio = 4:6, about 4.3 GHz at 2:8, and about 3 at 0:10. 1.9 GHz. After that, at about 5 GHz or higher, a return loss of 20 dB or more is stably obtained at any sand:slag ratio of 0:10 to 4:6.

It can be understood from the equations (5) to (11) that the frequency having the maximum return loss shifts to a lower frequency as the relative permittivity and relative permeability of the radio wave absorber increase. Since the slag has a sufficiently large relative permittivity and the like as compared with the sand and sand, the larger the ratio of the slag, the greater the relative permittivity and the like, and the radio waves in the low frequency band can be absorbed.

Within the measurement range, the frequency with the maximum return loss is higher than 2.45 GHz. Therefore, change to a slag with a higher relative permittivity, increase the relative permittivity of the slag by firing, replace a part of the slag with carbon, etc. with a higher relative permittivity, etc. It is considered that the wedge-type radio wave absorption heating element 43 having higher radio wave absorption performance at the frequency of 2.45 GHz can be manufactured by changing the frequency of the return loss of 2.45 GHz to a frequency lower than 2.45 GHz.

According to the wedge type radio wave absorption heating element 43, there is no large change in the return loss even when a manufacturing error occurs based on the equations (1) to (11), and the relative dielectric constant rises from FIG. 12 even when water is included. Therefore, it is considered that the return loss does not decrease because the frequency with the maximum return loss shifts to a low frequency. Therefore, from the measurement results, it is considered that the wedge-type radio wave absorption heating element 43 in which the return loss is unlikely to decrease due to manufacturing errors and changes in the relative dielectric constant due to water content can be designed.

<Construction method of snow melting system>
The snow melting system may be completed by a construction method in which a plurality of the heat generating blocks 30 described above are prepared and the heat generating blocks 30 are lined up and laid above the radio wave transmitters 20 embedded in the site of each house. The snow melting system including the radio wave transmitter 20, and the heat generating member 40 can be completed by the construction method described below. In addition, here, a case will be described in which a snow melting system having a width of 300 mm is installed linearly.

First, as shown in FIG. 13, a groove 100 in which the radio wave transmitter 20 and the heat generating member 40 can be embedded is linearly formed in the site of each house where the snow melting system is installed. The groove 100 is formed by a first groove portion 101 and a second groove portion 102 extending to the center of the bottom surface of the first groove portion 101. The first groove portion 101 has a width of 300 mm and is formed so that the upper surface of the protective material 60 formed on the upper side of the heat generating member 40 is exposed. The second groove portion 102 has the same width as the outer dimension (100 mm) of the long side of the radio wave transmitter 20, and is formed with the same depth as the outer dimension (50.0 mm) of the short side of the radio wave transmitter 20. The first groove portion 101 and the second groove portion 102 are formed by hardening with concrete.

Next, as shown in FIG. 13, the radio wave transmitter 20 is embedded in the second groove portion 102 such that the surface of the radio wave transmitter 20 on which the plurality of slots 21 are formed faces upward. The radio wave transmitter 20 has one end connected to the radio wave transmitter 10.

Next, as shown in FIG. 14, in plan view, a plurality of base materials 41 made of expanded polystyrene, each side of which is in the positive direction of 300 mm, are formed over the entire first groove portion 101 so that each recess 41A opens upward. Align and place. At this time, the base material is formed such that each recess 41A extends in a direction parallel to the direction in which the plurality of slots 21 of the radio wave transmitter 20 extend (a direction orthogonal to the direction in which the radio wave transmitter 20 extends). 41 is arranged (1st process).

In the plan view, one side is 300 mm in plan view, and the other side orthogonal to this side may be longer than 300 mm. In this case, by arranging the long sides of the base material in parallel with the direction in which the first groove portion 101 extends, the number of base materials aligned in the entire first groove portion 101 can be reduced.

Next, as shown in FIG. 15, slag mortar 43C having fluidity before curing is poured into each recess 41A of the base material 41 (second step). At this time, the slag mortar 43C is poured to a position slightly higher than the upper end of the recess 41A of the base material 41. The wedge type radio wave absorption heating element 43 is formed by hardening the poured slag mortar 43C.

Next, as shown in FIG. 16, a defective wire net that is the radio wave reflection material 50 is arranged on the slag mortar 43C. At this time, the radio wave reflection material is arranged so that the defective portion 51 of the defective wire mesh extends in the direction parallel to the direction in which the plurality of slots 21 of the radio wave transmitter 20 extend (the direction orthogonal to the direction in which the radio wave transmitter 20 extends). Place 50.

Next, as shown in FIG. 17, a sand mortar 60A having fluidity that serves as the protective material 60 is poured from above the radio wave reflecting material 50.

After that, the slag mortar 43C that is the radio wave absorption heating element 43 and the sand mortar 60A that is the protective material 60 are left until they harden, and the construction of the snow melting system is completed.

As described above, the wedge-type radio wave absorption heating element 43 of Example 1 is formed of the slag mortar 43C having a uniform relative dielectric constant and relative magnetic permeability. Further, the wedge-type radio wave absorption heating element 43 has water absorption. This wedge-type radio wave absorption heating element 43 has a lower end portion so that a cross-sectional area expanding in the horizontal direction (direction orthogonal to the radio wave irradiation direction) increases from the lower side to the upper side (direction away from the side irradiated with the radio wave). (The end on the side where the radio waves are radiated) extends linearly in the horizontal direction (the direction orthogonal to the direction in which the radio waves are radiated), and diagonally upward from both sides of this lower end (the direction away from the side where the radio waves are radiated). The distance between the side surfaces extending in the direction of the distance increases from the lower side to the upper side (away from the side where the radio waves are radiated). More specifically, the wedge-type radio wave absorption heating element 43 has a top portion 43B at the lower end extending in a straight line in the horizontal direction, and a cross-sectional shape orthogonal to the top portion 43B is an inverted isosceles triangle. Further, the wedge-type radio wave absorption heating element 43 is supported by the base material 41 whose lower surface is in contact with the upper surface of the radio wave transmission body 20 in the installed state.

In the wedge-type radio wave absorption heating element 43 thus formed, the equivalent relative permittivity and the equivalent relative permeability increase from the lower side to the upper side. In addition, the wedge-type electromagnetic wave absorption heating element 43 intersects the direction of the electric field E of the electric wave of frequency 2.45 GHz which irradiates the top portion 43B at the lower end linearly extending in the horizontal direction of the wedge-type electromagnetic wave absorption heating element 43 from below. Since 43 is arranged, radio waves can be absorbed well and heat can be generated. Further, the wedge-type radio wave absorption heating element 43 can absorb a radio wave having a frequency of 2.45 GHz to generate heat somewhere in the vertical direction (radio wave irradiation direction). In other words, the wedge-type electromagnetic wave absorption heating element 43 is capable of generating a radio wave having a frequency of 2.45 GHz in the vertical direction of the wedge-type electromagnetic wave absorption heating element 43 even if the construction position is vertically displaced or if water is included to absorb water. It can be absorbed and generate heat somewhere in the radio wave irradiation direction). Therefore, the wedge-type radio wave absorption heating element 43 can generate heat well without strict control of manufacturing accuracy and construction accuracy.

Therefore, the wedge-type radio wave absorption heating element 43 of the first embodiment can satisfactorily generate heat even when exposed to water, and can reduce the labor and cost in manufacturing and construction.

Further, since the wedge-type radio wave absorption heating element 43 is supported at the optimum position by the base material 41, the radio wave leaking from the radio wave transmission element 20 is absorbed near the upper end to generate heat, and the temperature of the upper surface rises. .. Therefore, the snow melting system including the heat generating member 40 including the wedge-type radio wave absorption heating element 43 can melt the snow satisfactorily.

The base material 41 of Example 1 is made of expanded polystyrene and has a relative dielectric constant of 1.0489. Further, the base material 41 is arranged below in contact with the lower surface (the back surface on the side where radio waves are radiated) of the wedge type radio wave absorption heating element 43 in the installed state, and supports the wedge type radio wave absorption heating element 43. ..

In this way, the base material 41 allows the wedge-type radio wave absorption heating element 43 to be easily installed at an appropriate height. Further, since the base material 41 is made of expanded polystyrene, it is difficult to contain water. Therefore, the base material 41 can suppress changes in the relative permittivity or relative permeability when exposed to water. Therefore, the wedge-type radio wave absorption heating element 43 and the base material 41 are integrated to generate a radio wave having a frequency of 2.45 GHz. When designed to absorb, the wedge-type radio wave absorption heating element 43 can surely absorb the radio wave having the frequency of 2.45 GHz and generate heat. Further, since the base material 41 is made of expanded polystyrene, the relative dielectric constant is low. Therefore, the base material 41 can reduce the influence of the wedge-type radio wave absorption heating element 43 on the radio wave absorption amount as compared with the sand mortar, so that the wedge-type radio wave absorption heating element 43 emits the radio wave of the frequency of 2.45 GHz. It can efficiently absorb and generate heat. Further, since the base material 41 has less influence on the amount of radio wave leakage of the radio wave transmitter 20, the design of the radio wave transmitter 20 is facilitated. Further, since the base material 41 is made of styrofoam, it has high heat insulation and can suppress heat escaping downward.

In addition, in the method for manufacturing the heat generating member 40 of the first embodiment, the styrofoam is made in the direction parallel to the direction in which the plurality of slots 21 of the radio wave transmission body 20 extend (the direction orthogonal to the direction in which the radio wave transmission body 20 extends). The first step of arranging the base material 41 so that the respective concave parts 41A formed in the base material 41 extend and the respective concave parts 41A open upward, and the respective concave parts of the base material 41 after the first step. A second step of pouring the slag mortar 43C having fluidity before curing into 41A is provided. According to the method of manufacturing the heat generating member 40, the heat generating member 40 that efficiently absorbs a radio wave having a frequency of 2.45 GHz and generates heat can be easily manufactured at a construction site.

The present invention is not limited to the first embodiment described by the above description and the drawings, and for example, the following embodiments are also included in the technical scope of the present invention.
(1) In Example 1, the wedge-type radio wave absorption heating element 43 was used. However, as shown in FIG. 18, a plurality of layers having water absorbing properties are laminated to form a flat plate-shaped radio wave absorption heating element 143. May be. The radio wave absorption heating element 143 changes the mixing ratio of slag, cement, and water in each layer to increase the relative permittivity or relative permeability from the lower layer to the upper layer (direction away from the side irradiated with radio waves). is doing. Also in this case, even if the construction position is shifted in the vertical direction, or if water is contained and contains water, radio waves of a predetermined frequency can be absorbed somewhere in the thickness direction of the radio wave absorption heating element 143 to generate heat. .. Therefore, the radio wave absorption heating element 143 can generate heat well without strict control of manufacturing accuracy and construction accuracy. In FIG. 18, the same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

(2) In Example 1, the wedge-type radio wave absorption heating element 43 was used. However, as shown in FIG. 19, each projecting portion 243A projecting downward is formed in a plurality of quadrangular pyramid shapes in the installed state. May be. That is, each convex portion 243A is formed in a quadrangular pyramid shape whose apex is located on the side where radio waves are radiated. The radio wave absorption heating element 243 can satisfactorily absorb the radio wave and generate heat regardless of the direction of the electric field E of the radio wave of a predetermined frequency emitted from below. Therefore, the radio wave absorption heating element 243 can be arranged without considering the direction of the electric field E of the radio wave. In FIG. 19, the same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

(3) In the first embodiment, the plurality of slots 21 of the radio wave transmitter 20 extend in the direction orthogonal to the direction in which the radio wave transmitter 20 extends. However, as shown in FIG. 20, the radio wave transmitter 120 extends. The plurality of slots 121 of the radio wave transmitter 120 may extend in a direction parallel to the direction in which the slots 121 extend. More specifically, it may be formed alternately on both sides of the position shifted to both ends from the central portion of the long side in the cross-sectional shape orthogonal to the extending direction of the radio wave transmitter 120. The direction of the electric field E of the radio wave leaked from the radio wave transmitter 120 is orthogonal to the direction in which the radio wave transmitter 120 extends. Therefore, by disposing the wedge-type radio wave absorption heating element 43 on the radio wave transmission element 120 so that the top portion 43B extends in parallel to the direction in which the radio wave transmission element 120 extends, the heat generated by the wedge type radio wave absorption heating element 43 is generated. The range can be widened in the direction orthogonal to the direction in which the radio wave transmitter 120 extends.

(4) In Example 1, nine wedges 43A were formed in the positive direction wedge-type radio wave absorption heating element 43 having a side length of 300 mm in plan view, but the number is not limited to nine and two or more. You may form the convex part of this.
(5) In Example 1, the cross-sectional shape of the convex portion 43A of the wedge-type radio wave absorption heating element 43 is an inverted isosceles triangle, but the radio wave absorption heating element lower end may not be sharp. Although the side surface is flat, it may be formed as a curved surface that is recessed inward.
(6) Each of the convex portions of the electromagnetic wave absorption heating element may be formed by cutting the top of the quadrangular pyramid to flatten the tip. For example, the tip end of the quadrangular pyramid cut may be flattened along a plane orthogonal to the radio wave irradiation direction.
(7) In Example 1, the base material 41 made of expanded polystyrene was provided, but the base material may be formed of another material as long as it has a relative dielectric constant of 1 to 1.5. For example, the base material may be formed of foamed resin such as foamed polypropylene or urethane foam.
(8) In the first embodiment, the base material 41 is disposed in contact with the back surface of the wedge-type radio wave absorption heating element 43 on the side irradiated with radio waves, and supports the wedge-type radio wave absorption heating element 43. Type electric wave absorption heating element 43, the relative electric permittivity, the relative magnetic permeability, the equivalent relative permittivity, the equivalent electric relative magnetic permeability is not limited to the electric wave absorption heating element which changes, and these have a constant electric wave absorption heating element or a different form. The base material may support the radio wave absorption heating element.
(9) Although the base material 41 is provided in the first embodiment, the base material 41 may not be provided.

10... Radio wave transmitter 20, 120... Radio wave transmitter 21, 121... Slot 30... Heat generating block 40... Heat generating member 41... Base material 43, 143, 243... Radio wave absorbing heat generating body

Claims (9)

A radio wave absorption heating element that absorbs radio waves of a predetermined frequency irradiated in a certain direction to generate heat,
At least one of a relative permittivity and a relative permeability in a cross section having a water absorbing property and extending in a direction orthogonal to a radio wave irradiation direction is increased in a direction away from a side irradiated with the radio wave. Electric wave absorption heating element. A radio wave absorption heating element that absorbs radio waves of a predetermined frequency irradiated in a certain direction to generate heat,
It is made of a material with a uniform relative permittivity and relative permeability, has water absorbency, and the cross-sectional area that expands in the direction orthogonal to the radio wave irradiation direction increases in the direction away from the side that is irradiated with the radio wave. A radio wave absorption heating element characterized by being. The end on the side irradiated with the radio wave extends linearly in a direction orthogonal to the radio wave irradiation direction, and the distance between the side surfaces extending from both sides of the end in the direction away from the side irradiated with the radio wave is the radio wave. The radio wave absorption heating element according to claim 2, wherein the radio wave absorption heating element has a wedge shape that increases in a direction away from a side irradiated with. The radio wave absorption heating element according to claim 2, wherein the apex is in the shape of a quadrangular pyramid located on the side irradiated with the radio wave. The radio wave absorption heating element according to any one of claims 1 to 4, wherein when a radio wave having a predetermined frequency is irradiated, the temperature of the surface opposite to the side irradiated with the radio wave rises. .. It is made of resin and is arranged in contact with the back surface of the radio wave absorption heating element according to any one of claims 1 to 5 on the side irradiated with the radio waves, and supports the radio wave absorption heating element. Base material to be. The base material according to claim 6, which is molded into a foam. The base material according to claim 6, which has a relative dielectric constant of 1.0 to 1.5. A first step of arranging the base material according to claim 6 in which a concave portion in which a space in a cross section that expands in the horizontal direction increases from the lower side to the upper side is formed so that the concave portion faces upward.
A second step of pouring a radio wave absorbing heat generating material into the recess after the first step;
A method of manufacturing a heat generating member, comprising: