Wearable and portable radio frequency devices for medical microwave imaging

Abstract

In the past decades, microwave imaging techniques have attracted significant attention as an emerging, low-cost and early-stage technique for various human disease diagnoses including intracranial heart rate detection, breast and brain cancer imaging and fluid accumulation in human torso monitoring. Furthermore, microwave imaging is becoming an alternative technique for long-term breast cancer detection and real-time therapy monitoring compared to traditional medical imaging technologies such as X-ray and magnetic resonance imaging (MRI). However, it requires a low-cost and custom-made microwave hardware system. To track this issue, an ultra-wideband (UWB) antenna design together with radar techniques and additive manufacturing methods are explored in this thesis.

This thesis focuses on the development of radio frequency (RF) sensing devices for both wearable and portable medical microwave imaging applications. The contribution of this thesis addresses areas such as inkjet-printed flexible antennas, mechanically driven reconfigurable artificial magnetic conductors (AMCs), soft body-coupled antennas and arrays, and a robotic-based data acquisition (DAQ) system for microwave breast imaging.

In this thesis, UWB antennas are chosen, as a wideband spectrum can balance the trade-off between the imaging resolution and the penetration depth in the human body.

First, the inkjet printing technique is explored and then utilised to fabricate a modified monopole UWB antenna on flexible substrates. Second, a new concept of reconfigurable AMCs using mechanical movements alone is developed to enhance the antenna performance. Third, a new stretchable spacer using a soft mixture of Ecoflex- 30 and barium titantanate (BT-BaTiO3) ceramic powder is studied and fabricated to reduce the reflection at the boundary of air and skin. By assembling the above designed inkjet-printed antenna and stretchable dielectric spacers, the resulting antennas are then further miniaturised, which allows a greater number of sensing antennas to be placed directly on the limited body surface, hence improving the microwave imaging performance. Fourth, a number of the assembled antennas are used to construct two soft antenna arrays targeting wearable imaging using delay-and-sum (DAS) beamforming. Simulations are carried out using MRI-delivered realistic breast phantoms. The reconstructed 2D imaging results demonstrate that the proposed antenna array is capable of detecting and imaging a single sphere tumour with a radius of 5 mm located in the glandular region.

Finally, the experimental performance of a designed portable imaging system using the above designed soft antenna array and a modified Vivaldi antenna is evaluated for microwave breast imaging using the developed low-cost robotic-based DAQ platform. Experimental results confirm the capability of the developed devices for performing microwave tumour detection using a 3D-printed breast phantom.

All the thesis contributions enable a wearable and portable RF system to support long-term healthcare applications.