There is a strong need to characterize the dielectric properties of polymers and ceramics at frequencies above 1 MHz for telecommunications and medical applications.  In addition, accurate permittivity and dielectric loss data at high frequency will elucidate new information about electric polarization mechanisms in solids, liquids, and composites.   We have explored dielectric measurement methods spanning the frequency range between 1 MHz and 100 GHz.  There are two general types of measurement techniques, resonant and transmission.  Resonant measurements at discrete frequencies have high accuracy for low loss dielectrics with dissipation factors below 1%.  We have established several resonant methods: a dielectric post technique in the 1-10 GHz range, a split-cavity method between 15-20 GHz and a Fabry-Perot method between 20-70 GHz. Transmission/reflection methods are generally broadband and are applicable for dissipation factors above 1%.   A reflection method for the 1 MHz to 2 GHz frequency range is applied to liquids and polymers.  Waveguide techniques have been applied to X-band (8-12 GHz), K-band (18-26 GHz) and W-band (75-110 GHz).  Free space transmission methods are currently being developed for frequencies up to 3 THz.<br/>The dielectric properties of a wide range of polymer (LDPE, HDPE, PTFE, acrylates, and liquid crystal polymer) and oxide (silica, alumina and barium strontium titanate) were investigated. Acrylate based polymers had relaxation frequencies in the MHz-GHz range at room temperature, which were attributed to side group polarization.  Low permittivity crystalline oxides, such as silica and alumina, do not have significant dielectric relaxation up to frequencies of 100 GHz; however, high permittivity barium strontium titanates show a significant increase in dielectric loss with frequency.  The intrinsic and extrinsic contributions to loss above 1 MHz will be discussed for polymer, ceramic, crystalline and amorphous materials along with implications on how the magnitudes of dielectric permittivity and loss influence material selection for transmission lines, antenna substrates and reflecting surfaces that are used in the microwave and mm-wave frequency ranges.

Dielectric characterization in the MHz-THz frequency range

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ACS Fall 2022

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