JP2005079599A - High loss factor composite absorption material and microwave absorber thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase loss factor of a composite absorber that is used for a micro absorber. <P>SOLUTION: In a conventional method of increasing loss factor of a composite absorber by dispersing conductive particles such as carbon or the like in a dielectric, conductive particles of low resistivity in which volume resistivity is lower than approx. 2 (Ω-cm) are dispersed. Therefore, loss factor reached its maximum at millimeter-wavelength or extremely high frequencies. According to the present invention, conductive particles of high resistivity in which volume resistivity is higher than approx. 2 (Ω-cm) so as to make the loss factor of composite absorber reach its maximum in a microwave frequency band. This enables increasing substantially the loss factor of the composite absorber in microwave frequencies. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to a microwave absorber and a material thereof, and in particular, a synthetic absorber in which conductive particles having appropriate conductivity are dispersed in a non-conductive dielectric material serving as a base, and a microwave using the same. It relates to an absorber.

      The electromagnetic loss of the synthetic absorbent is generally frequency-dependent, and many of them exhibit Debye-type dispersion characteristics. Conventional synthetic absorbers that have been used as microwave absorbers have dispersed conductive particles such as carbon, graphite, and metal having a conductivity greater than about 50 (S / m) in the base material of a chemical substance. Incidentally, the conductivity of 50 (S / m) corresponds to a volume resistivity of 2 (Ω-cm).

      Thus, the loss rate (tan delta) indicating the degree of electromagnetic wave absorption of the synthetic absorbent in which conductive particles having high conductivity (low resistivity) are dispersed becomes maximum at millimeter waves and higher frequencies. When the frequency becomes lower than that in the microwave band, the loss rate decreases rapidly. As a result, a synthetic absorbent material having a large loss rate could not be obtained in the microwave region (wavelength region).

      The problem to be solved by the present invention is to bring the frequency at which the loss rate of the synthetic absorbent material is maximum to a microwave frequency band having a wavelength of about a centimeter from a very high frequency higher than the conventional millimeter wave. It is. Thereby, an attempt is made to increase the loss rate in the microwave frequency band.

      For that purpose, instead of using the conventional high conductivity particles dispersed in the synthetic absorbent material, low conductivity particles such as semiconductor particles having a conductivity of about 50 (S / m) or less and special carbon are used. Is to use. The reason will be described below with reference to the drawings.

      The horizontal axis in FIG. 1 is the relative frequency obtained by dividing the frequency of the electromagnetic wave by the frequency (peak frequency) at which the imaginary part of the relative dielectric constant of the synthetic absorbent is maximized, and the vertical axis is the loss rate (tan delta) of the synthetic absorbent. This shows that the loss rate of the synthetic absorbent becomes substantially maximum at the peak frequency. FIG. 2 shows how the peak frequency changes with respect to the numerical value obtained by dividing the conductivity of the conductive particles dispersed on the horizontal axis by the relative dielectric constant of the matrix. In other words, the relative permittivity of the matrix that is usually easily obtained is about 10 at most, so if it is 10 and the conductivity of the conductive particles is, for example, 60 (S / m), the peak of the composite absorbent material The frequency is a millimeter wave frequency of 30 GHz. Therefore, in this case, from FIG. 1, the loss rate of 3 GHz in the microwave band of 1/10 of the peak frequency is a small value of about 0.156 times (= 0.025 / 0.16) of the maximum loss rate at 30 GHz. I understand that.

  Therefore, from FIGS. 1 and 2, in order to set the frequency (approximately peak frequency) at which the loss rate is maximum to a microwave frequency band of 30 GHz or less, at least the conductivity of the conductive particles is 50 (S / m) or less. The volume resistivity of the conductive particles may be 2 (Ω-cm) or more.

  When a microwave absorber or absorbent sheet is constructed using the synthetic material having a high loss rate according to the present invention, electromagnetic waves can be sufficiently absorbed even if it is thinner than the conventional one, so that a thinner and lighter microwave absorber is manufactured. The economic effect is very large.

A graph of the loss rate of a synthetic absorbent against relative frequency The graph of the peak frequency with respect to the electrical conductivity of the electroconductive particle divided | segmented by the dielectric constant of the base material.

Claims (3)

      In a synthetic absorbent material in which a non-conductive dielectric as a base and non-magnetic and conductive particles are dispersed therein, the volume resistivity of the conductive particles is 2 (Ω-cm) or more and 2 mega ( A synthetic absorbent that is equal to or less than Ω-cm).       The synthetic absorbent material satisfying claim 1, wherein the conductive particles are a semiconductor, carbon, or a conductive polymer.         A microwave absorber or a microwave absorbing sheet using the synthetic absorbent material according to claim 1 or 2.

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