Microwave sensing techniques for materials characterisation

Mohammed, Ali Musa (2022). Microwave sensing techniques for materials characterisation. University of Birmingham. Ph.D.

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Abstract

Microwave cavity resonators are of major interest for characterisation of dielectric materials in many applications such as petroleum and chemical, biomedical and pharmaceutical, food and agriculture industries. In this thesis new and improved techniques for implementing microwave measurement techniques for dielectric characterisation of both liquid and solid materials have been developed. This has been actualised through several original contributions: a new high-Q and sensitive re-entrant cavity resonator structure; novel techniques of materials measurements for liquids enabled by a coaxial cavity resonator using a simplified analytical formula; a new concept of sample placement and measurements of substrate materials of varying thickness using resonant method; higher order mode re-entrant cavity resonator for dielectric property measurements at millimetre-wave frequencies; insight into capabilities of 3D printing in making effective and low-cost sensing device at both microwave and millimetre-wave frequencies; simplified evaluation method of materials effective conductivity by resonant technique; and the development of new unified analytical model for the extraction of dielectric properties of materials under test. The performance of these improved and new sensors, novel measurement techniques and the new derived analytical models of extracting the materials properties were verified through a large number of measurements on various materials. Dielectric characterisation of crude oils and their derivatives at 2 GHz using re-entrant cavity and concentration measurements of both binary and ternary mixtures at discrete resonance frequencies of 2 GHz and 6 GHz were reported. Measurements of low and medium dielectric loss liquids over a broadband using the coaxial cavity resonator at four different resonant modes from 2 GHz to 8 GHz were presented. Furthermore, measurement of liquid materials using a 60 GHz cavity resonator, dielectric constant measurement of substrates materials using modified re-entrant cavity at 2 GHz and estimation of the effective conductivity of the metals, metal coated polymers and alloys made using different fabrication technology were carried out to validate the devices and measurement techniques. Experimental results are in good agreement with both simulation and reported data in the literature.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):