Millimeter wave complex dielectric permittivity and complex magnetic permeability measurements of absorbing materials (Gaussian optics)

This dissertation presents new methods for characterization of materials in the millimeter wave range. Historically, this has been the most difficult part of the electromagnetic spectrum for accurate measurements of material properties. New instrumentation has now been developed for operation in this frequency band. The new techniques developed in the course of this work allowed precise measurement of dielectric properties as well as the separation of magnetic properties from dielectric in the millimeter wave range.; A new quasi-optical spectrometer with a waveguide reference channel has been designed and built for the precision measurement of the real part of dielectric permittivity of medium and highly absorbing materials over an extended W-band frequency range (70–118 GHz). A new method of phase measurement with this unique unbalanced quasi-optical waveguide bridge spectrometer has been developed. The phase of the electromagnetic wave transmitted through the specimen can be measured accurately, leading to the determination of the real part of the complex dielectric permittivity of moderate and highly absorbing dielectric materials with high precision. A simple quasi-optical transmission configuration of the spectrometer, a single free space channel provides the transmittance data with a high resolution from which the spectra of the imaginary part of dielectric permittivity of materials are evaluated accurately. A backward wave oscillator (BWO) is used as the source of tunable coherent radiation for the spectrometer. The high output power of the BWO and the high sensitivity of the receiver system, which employs a specially constructed liquid helium cooled InSb detector, enable adequate sensitivity in transmission for highly absorbing materials. Systematic study of dielectric and magnetic properties of various materials has been performed with the quasi-optical free space method in the millimeter wave range from 34GHz to 117GHz for the first time. Specific results for the materials are presented, discussed and compared with those obtained by using different techniques.; The study of the magnetic properties of magnetic materials has been performed with the new spectrometer constructed with the electromagnet providing a constant magnetic field (of up to 10kOe) transverse to the direction of propagation of the millimeter wave radiation. This work presents the general principles and the first application of the transverse magneto-optical effect for the direct measurement of complex magnetic permeability in the millimeter wave range. This technique was applied to the measurement of the millimeter wave complex permeability of a standard soft microwave ferrite, hard oriented and non-oriented ferrites. Experiments demonstrate the high sensitivity of the millimeter wave magneto-optical method and its capability to provide accurate magnetic permeability data in the millimeter wave range. A new experimental procedure is described which leads to the determination of the millimeter wave permeability and permittivity of ferrites. The results of measurement of the real and the imaginary parts of millimeter-wave complex permeability are presented and discussed. The frequency dependence of the millimeter wave specific Faraday-rotation power have been measured in the magnetized Sr-hexaferrite and experimental results are discussed.