Listening in

Abstract

Professor Yongxin Guo from the National University of Singapore talks to us about his research on biomedical antennas. In a collaboration with the University of Electronic Science and Technology of China, Professor Guo presents an optimised bandwidth biomedical antenna. The fabricated circularly polarised antenna was constructed on a single-layer planar substrate With the advancement of wireless technologies, researchers have been able successfully to implant antennas inside the human body, which has allowed the wireless monitoring of vital signs. Transdermal or percutaneous wires running out of the body from an implanted device can be cumbersome and lead to infection, making them unsuitable for long term uses and applications. The use of biomedical antennas allows low impact, long-term monitoring. Data can be transmitted wirelessly from a variety of different implantable medical devices such as pacemakers, insulin pumps and cochlear implants. Recently, various research groups have also tried to wirelessly power implanted devices using far-field antennas, which would enable devices to remain inside the body for long periods of time. Antenna research for biomedical applications focuses heavily on topics such as antenna miniaturisation. The antennas, in general, are designed to operate in a desired frequency band, say 2.4–2.5 GHz. Those produced for implantable applications have several design considerations. For long-term implants the tissue thicknesses of the patient will change over time, resulting in an overall resonance frequency shift of the antenna. If a narrowband antenna is used, the frequency will be detuned and the new frequency will have to be found by trial and error. A redesign of the external transceiver would also be required. Broadband antennas are better adapted for these situations, as minor shifts in frequency will still remain inside the usable operational bandwidth. A large bandwidth corresponds to high data rate signal. This is useful for certain applications like capsule endoscopy, where video signals are transmitted outside of the body, broadband antennas can provide high data rates for their large operational bandwidth. Through the analysis of antennas in human body models, known as voxels, their performances can be stabilised and safety issues caused by the radiation can be accounted for. Broadband antennas, like the one proposed in this paper, are highly useful for reliable telemetry in implantable medical devices. A broad bandwidth enables information to be transmitted quickly and with higher reliability. Transmitting over multiple channels using a broadband antenna provides greater flexibility for a telemetry signal. In this paper the team used a cross-shaped structure to generate two orthogonal modes for circularly polarised radiation. By embedding the cross-shaped slot in the ground plane and optimising its dimensions, the impedance and axial ratio bandwidth have been enhanced to cover the 2.4–2.48 GHz ISM band. There are several slot geometries that can be embedded in the ground plane for axial ratio bandwidth enhancement, but cross-shaped slots achieve good circularly polarised radiation with simple structure. For biomedical antennas, one of the design practices is to keep the antenna design simple. With the advancements in material sciences, novel materials are being developed that mimic human tissues. Advances in semiconductor technology and electronic components have led to the miniaturisation of the biomedical devices such as microchip implants. The next decade might witness further miniaturisation of electromagnetic interfaces suitable for integration with the micro-scaled biomedical devices. With such devices, the hope is that researchers will be able to address the diseases that have been untreatable, and will enhance their capability to help with current health issues with much higher precision. A Gustav voxel model was used to access the effects of the human body on the antennas performance