A microwave test system to measure the complex permittivity of solid and powder materials as a function of temperature has been developed. The system is based on a TM multi-mode cylindrical cavity with a slotting structure, which provides purer test modes compared to a traditional cavity. To ensure the safety, effectiveness, and longevity, heating and testing are carried out separately and the sample can move between two functional areas through an Alundum tube. Induction heating and a pneumatic platform are employed to, respectively, shorten the heating and cooling time of the sample. The single trigger function of the vector network analyzer is added to test software to suppress the drift of the resonance peak during testing. Complex permittivity is calculated by the rigorous field theoretical solution considering multilayer media loading. The variation of the cavity equivalent radius caused by the sample insertion holes is discussed in detail, and its influence to the test result is analyzed. The calibration method for the complex permittivity of the Alundum tube and quartz vial (for loading powder sample), which vary with the temperature, is given. The feasibility of the system has been verified by measuring different samples in a wide range of relative permittivity and loss tangent, and variable-temperature test results of fused quartz and SiO powder up to 1500 °C are compared with published data. The results indicate that the presented system is reliable and accurate. The stability of the system is verified by repeated and long-term tests, and error analysis is presented to estimate the error incurred due to the uncertainties in different error sources.
In this paper, a digital metamaterial of arbitrary base based on liquid crystal (LC) is proposed. The digital metamaterial can be multiplexed for different desirable functions by properly biasing the LC for different code patterns. Simulation results of two common functions, beam steering with a steering elevation angle 27 • and RCS reduction of at least 10 dB from 51 to 56 GHz, have been presented to prove the concept. The feasibility has been further confirmed by preliminary measurement.INDEX TERMS Coding metamaterial, digital metamaterial, liquid crystal (LC), coding particle, beam steering, RCS reduction.
The sintering and microwave dielectric properties of a ceramic material based on the mixing of Mg 3 B 2 O 6 and Zn 3 B 2 O 6 have been widely studied using first-principles calculations and experimental solid-state reactions. Characterization methods include the Network Analyzer, X-ray, Raman diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and differential-thermal and thermo-mechanical analyzer. The increasing amount of Mg 2+ results in the appearance of Mg 2 B 2 O 5 and ZnO, and the mutual substitution (Mg 2+ and Zn 2+ ) phenomenon has emerged in Zn 3 B 2 O 6 and Mg 2 B 2 O 5 . The mechanisms have been explained with the help of DFT calculations. The bond parameters and electron distributions of the ZnO 4 tetrahedron and MgO 6 octahedron have been modified due to substitution. The sintering, substitution, and phase formation properties have been analyzed quantitatively through the energy parameters. The best dielectric properties were obtained for x = 0.20 sintered at 950°C, ε r = 6.47, Q × f = 89 600 GHz (15.2 GHz), τ f = −48.6 ppm/°C, relative density = 96.7%. The mixing of Zn 3 B 2 O 6 and Mg 3 B 2 O 6 ceramics is a feasible method to obtain a ceramic with low sintering temperature and excellent dielectric properties.
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