A Performance-Enhanced Antenna for Microwave Biomedical Applications by Using Metasurfaces

Abstract

In this paper, we introduce a novel antenna employing specifically-designed metasurfaces to improve the radiating performance in close proximity to the human body, as required in microwave biomedical applications. We firstly present design guidelines to realize a thin metasurface acting as an impedance matching layer between the radiating element and the biological tissue, based on the transmission line equivalent model. Additionally, for the first time to the best of our knowledge, we combine an artificial magnetic conductor as the backing element of the antenna, to improve the gain and reduce the undesired back radiation. To validate the proposed approach, we conceived a numerical test-case consisting of a bow-tie antenna operating close to a biological phantom at 2.56 GHz. Numerical simulations demonstrated the performance enhancement in terms of higher field penetration within tissues and better radiating behavior when the bow-tie antenna is working in presence of both the metasurfaces. Furthermore, measurements carried out over fabricated prototypes confirmed the numerical results, validating the overall design procedure. The herein presented methodology can be helpful in several applications when the radiating elements operate in close proximity to biological tissues, as in medical imaging, on-body communication, mobile phones and consumer devices.

Radar near-field sensing using metasurface for biomedical applications

“…2b , the wave impedance in near-field free-space, Z E ( r = λ /2) = Z F , is obtained as 342 Ω at the proposed distance which is close to the free-space wave impedance in the far-field region, 377 Ω. In addition, as expressed in (6), Z L = Z S is defined as the impedance of a general lossy dielectric medium which can be used as the biological load impedance for the skin model 13 .…”

“…Over the last decade, several prototypes have been developed that demonstrate the potential of using AI-powered radar systems for non-invasive glucose sensing 2 , wearable sweat monitoring 3 , 4 , multi-person vital sign tracking 5 – 7 , gait monitoring 8 , fall detection 9 , human eye activity monitoring 10 , and imaging 11 . Compact radars are also often used in wearable technology, such as smartwatches, for routine human health monitoring 12 , 13 . Radar system development for industrial and biomedical microwave applications has recently accelerated due to an increase in interest in millimetre (mm)-wave communication for near-field sensing using low-profile and low-cost antennas providing sufficient energy penetration into the body 14 .…”

“…Additionally, the majority of studies on near-field focusing consider the antenna’s radiation in free space. The human body creates a different environment in the antenna’s radiation region, which leads to detuning and impedance mismatching, which degrades the antenna performance and lowers the penetration power density into the body, making the prior methods unsuitable for biomedical applications when the human body is in contact with the radiating elements 13 . To address this issue, some efforts in literature have been reported.…”

Electromagnetic metamaterials for biomedical applications: short review and trends

“…effective permittivity values that improve the antennatissue EM radiation coupling [37]. Moreover, AMCs are typically used as antenna grounds to enhance gain and directivity, allowing miniaturization without affecting the antenna's efficiency [38].…”

Miniaturized circularly polarized metasurface antenna based on characteristic mode analysis

“…In recent years, metasurface antennas have had outstanding performance in improving antenna gain and broadening bandwidth. They are widely used in handheld devices, convenient devices, and wireless satellite communication 1,2 . However, the metasurface antenna also has the problem of oversized size which is not suitable for the application in compact space antenna arrays.…”