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SUMMARYThe dielectric constant of liquid crystals at microwave and millimeter-wave frequencies is measured directly with an inductively coupled ring resonator of a microstrip line configuration, which is widely used for the development of many adaptive devices such as variable delay lines. By comparing the electromagnetic simulation value and the measured value of the resonant frequency of the ring resonator on a liquid crystal as a dielectric substrate, we can determine the relative permittivity ε // g for the major axis of the liquid crystal molecules parallel to the RF electric field and the relative permittivity ε ⊥ g from the major axis normal to the field, as well as the dielectric birefringence ∆ε′. Although it is dependent on the microstrip line configuration and viscosity of the liquid crystal, the orientation of the liquid crystal molecules cannot be controlled completely. Therefore, ε // g becomes smaller than the permittivity of the liquid crystal material. This paper studies the cause. The physical meaning of the effective orientation coefficient η a is elucidated from photographs indicating imperfections of the liquid crystal molecular orientation and from calculations of the electrostatic energy immediately below the conductor and elsewhere. In a microstrip line device using liquid crystal, the effective value of ε // g to be used in circuit design should be the value obtained by multiplying η a by the permittivity of the material itself.

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The effects of machined circular holes on the mechanical properties and failure characteristics of a unidirectional CFRP were investigated. Our approach was to change the location and the number of holes: (i) a two-set hole was machined with different modes: (A) parallel, (B) 45°and (C) a direction perpendicular to the loading direction; and (ii) multiple holes from n = 0 to 5 were made in the sample parallel to the loading direction. The higher tensile and higher fatigue strengths were obtained for the CFRP sample produced by mode A, compared to modes B and C. This was attributed to the different extend of the maximum stress and stress distribution, caused by the geometrical effects on the sample. The ultimate tensile strength (σUTS) of the sample was well predicted by the geometrical criterion. If the number of holes was increased from n = 0 to n = 2, the tensile strength decreased dramatically. However, the tensile strength did not strongly decrease further for samples with multiple holes from n = 2 to 5. The tensile strength is correlated with the maximum stress adjacent to the hole(s). Those stress values were verified by a 2D digital image correlation and a finite element analysis. Material failure of the CFRP during tensile loading was revealed by nondestructive testing using a piezoelectric ceramic, and debonding of the fibers occurred even at a low applied stress of approximately 35% σUTS.

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