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The permittivity and loss angle of disc-shaped polymer specimens were measured by using three Split-Post Dielectric Resonators (9.5 GHz, 25 GHz & 34 GHz), a plano-concave open resonator (36 GHz), a bi-concave open resonator (20 GHz to 50 GHz), a helical cavity (10 GHz), and two free- space Gaussian-beam transmission systems (22 – 33 GHz & 60 – 90 GHz). The measured materials were PMMA, polycarbonate, THV 500GZ fluoropolymer, and two grades of PTFE. The work supports the need for materials for manufacture of components for 5G applications.

The design and calibration of a Near-Field Scanning Microwave Microscope (NSMM) for measurement of permittivity and loss on the small scale are described. The instrument described uses a wire probe that is electromagnetically coupled to a resonant cavity. Using an electrostatic model based on image charges (Gao and Xiang 1998) permittivity and loss may be determined. The paper describes progress in two specific areas: (i) The implementation of an optical beam-deflection method for obtaining contact mode between the probe tip and specimens. (ii) Improvements to the calibration process to improve the traceability and accuracy of the measurement of loss by using the Laplacian ‘complex frequency’ in the image-charge model. This is demonstrated by measurements on polar liquids.

Bio-sensing by electromagnetic waves from GHz towards THz frequencies, although not yet established as a common method for biomedical applications, offers challenging opportunities, which are complementary to the established optical methods, often based on plasmonic waves and resonances. The longer wavelength - in comparison to visible and IR provides a disadvantage in terms of the smallest possible interaction volume, which can be partially overcome by evanescent field methods. However, the high absorption of micro- and millimetre waves by liquid water, which is the most abundant component of biological substances, provides a unique observation window, which is substantially different and therefore complementary to the other parts of the electromagnetic spectrum.

This paper examines the measurement of the specific absorption rate (SAR) of radio frequency energy during magnetic resonance imaging using an optical electric field sensor (OEFS). The sensor was used to measure SAR in a simple phantom during a 3-Tesla MRI scan and the results compared to computer simulations and also those obtained through temperature measurements. Good agreement is demonstrated. The optical electric field sensor has much higher sensitivity for SAR measurement than thermometers and the measurements are much quicker. The application of this technology allows the spatial distributions of SAR within phantoms during MRI to be measured.

A dielectric probe for performing near-field imaging in the millimeter-wave band is presented. The probe consists of a rectangular slab of low-loss dielectric material which is metalized on two sides and sharpened to a point of approximately 20 µm. This structure forms a parallel-plate waveguide which offers broadband operation and strong field enhancement and localization at the tip with a spatial resolutions of λ/250. A method of exciting the probe using a metal rectangular cavity resonator is also described.

This paper describes an NPL project for providing traceability for SAR measurement in mobile phone dosimetry. Electric field implantable probe calibration facilities have been developed for this purpose. Computer simulation has been used to assist in analysing the uncertainty budgets for these calibrations. A new international intercomparison has been proposed for measurement of this parameter.