Resonantly loaded apertures for high‐resolution near‐field surface imaging

Abstract

General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. AbstractA novel type of microwave probes based on the loaded aperture geometry has been proposed and experimentally evaluated for dielectrics characterization and high-resolution near field imaging.Experimental results demonstrate the possibility of very accurate microwave spectroscopic characterization of thin lossy dielectric samples and biological materials containing water. High resolution images of the subwavelength lossy dielectric strips and wet and dry leaves have been obtained with amplitude contrast around 10-20dB and spatial resolution better than one tenth of a wavelength in the near field zone. A microwave imaging scenario for the early-stage skin cancer identification based on the artificial dielectric model has also been explored. This model study shows that the typical resolution of an artificial malignant tumour with a characteristic size of one tenth of a wavelength can be discriminated with at least 6dB amplitude and 50 degrees phase contrast from the artificial healthy skin and with more than 3dB contrast from a benign lesion of the same size. It has also been demonstrated that the proposed device can efficiently deliver microwave energy to very small, subwavelength, focal areas which is highly sought in the microwave hyperthermia applications.

Ultra-Resonance Microwave Defectoscopy of Metal Surfaces

“…Microwave reflectometry is a very useful tool in defect finding in many industrial and engineering applications [1]. It is used in different scenarios in non-destructive testing and imaging, for example, detection of faults in constructions [2] and composite materials [3], non-destructive testing of building structural integrity [4], biomaterials imaging [5], etc.…”

Super-Resolution Defect Characterization Using Microwave Near-Field Resonance Reflectometry and Cross-correlation Image Processing

“…At the same time, due to the extended length dimension (~λ/4) of the insert as compared to its width, very high raw image resolution is only possible in the direction orthogonal to the LA length [17]. Additionally, ghost dual-peak image features appear as a result of dipole-mode near field coupling which can be considered as a disadvantage for image interpretation [16]- [18].…”

High-Resolution Microwave Near-Field Surface Imaging Using Resonance Probes

“…Recently there has been a significant amount of work aimed at the design of EM field collimating and near field probing devices based on metal-dielectric structures such as dielectric cones [35] and partially metallized dielectric prisms [20], near field antennas [21], resonantly loaded apertures [36] and metamaterial lenses [37], [38]. Dielectric conical probes enable relatively high spatial resolution, ~λ/5, [35] with moderate imaging contrast (>3dB).…”

“…In this paper, we study two resonant microwave probe types that enable fine spatial resolution while retaining very high imaging contrast: (a) loaded subwavelength slot aperture [29], [36] and (b) helix antenna [39]. Resonantly loaded apertures (LA) allow significant enhancement of the electric and magnetic near fields as well as deep subwavelength field collimation in the near field zone [29], [36]. Due to this property very high imaging resolution is feasible along with a possibility of low power operation.…”

“…The imaging performance of these probes is evaluated using planar dielectric samples and printed circuit boards comprised of conductive elements printed on the FR4 dielectric substrate. These imaging scenarios are relevant in a wide range of applications including dielectric [36] and passive antenna arrays characterization. Special attention is given to the accurate characterization of the target geometry variation in printed arrays based on a simple cross-correlation technique.…”