# Articles

IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology has been selected for inclusion in the Web of Science

#### Feature Article

James C. Lin

###### Review on Advanced Short-Range Multimode Continuous-Wave Radar Architectures for Healthcare Applications

José-María Muñoz-Ferreras, Zhengyu Peng, Roberto Gómez-GarcíaChangzhi Li

[download url="https://ieeexplore.ieee.org/document/9715153/"]

##### Development and Characterization of Skin Phantoms at Microwave Frequencies

Jasmine Boparai, Milica Popović.

Realistic tissue-mimicking phantoms are required for experimental evaluation and validation of microwave reflectometry prototype systems for skin cancer detection before performing any tests on human subjects.

These phantoms must accurately emulate the dielectric properties for both healthy and malignant skin tissues. In this work, we develop and experimentally investigate multiple skin phantoms with tumor inclusions in the frequency range of 0.5–26.5 GHz. These heterogeneous phantoms are realized by varying the tumor size and placement relative to the skin. The tumors with irregular borders are also investigated. For analyzing the effect of underlying skin on dielectric properties, two skin thicknesses are considered: 8 mm and 2.5 mm. The proposed heterogeneous phantoms are developed using inexpensive materials: oil, gelatin, deionized water and formaldehyde. The dielectric properties of fabricated phantoms are characterized with Keysight performance probe connected with a FieldFox handheld vector network analyzer. Our results demonstrate that the dielectric properties of the developed phantoms closely agree with those of the excised malignant human tissues reported in the literature over the entire frequency range of 0.5–26.5 GHz and can be hence reliably used for experimental validation in studies towards microwave-based diagnostics of skin lesions.

[download url="https://ieeexplore.ieee.org/document/9666044/"]

##### Towards Brain MRI Adaptable to Head Size: Bowing RF Coil Phased Arrays

William Mathieu, Milica Popović, Reza Farivar.

Purpose: Bowing phased arrays allow for the idea of hybrid rigid-flexible RF coils, in which parts of a larger phased array are broken up into rigid sub-arrays, connected by flexible coil elements, permitting coils to expend or shrink to match different human head sizes.

Methods: two arrays were constructed, a conventional rigid array used as a control and an array composed of flexible bowing elements. Bowing elements comprise of a flexible half and a rigid half. The arrays were then supported on translating boards connected so that a flexible gap between the boards corresponds to the bowing elements. The gap between the rigid coil elements was varied by discrete values to assess its performance under different bowing conditions. Results: signal-to-noise-ratio (SNR) and noise performance was compared between the two arrays. It is seen that a bowing array outperforms its rigid counterpart in terms of average SNR, max SNR, and signal coverage. We conclude that bowing array elements present a viable solution to the proposed hybrid rigid-flexible coil arrays.

[download url="https://ieeexplore.ieee.org/document/9716146/"]

##### Simultaneous Monitoring of Multiple People’s Vital Sign Leveraging a Single Phased-MIMO Radar

Zhaoyi Xu, Cong Shi, Tianfang Zhang, Shuping Li, Yichao Yuan, Chung-Tse Michael Wu, Yingying Chen, Athina Petropulu.

Vital sign monitoring plays a critical role in tracking the physiological state of people and enabling various health-related applications (e.g., recommending a change of lifestyle, examining the risk of diseases).

Traditional approaches rely on hospitalization or body-attached instruments, which are costly and intrusive. However, in recent years there is an emergence of contact-less vital sign monitoring techniques that rely on radio frequency signals. Early studies with continuous wave radars/WiFi devices have shown good success in detecting the vital signs of a single individual, while simultaneous monitoring of the vital signs of multiple, closely spaced subjects remains a challenge. In this paper, using an off-the-shelf Texas Instrument automotive FMCW radar, we design and implement a time-division multiplexing (TDM) phased-MIMO radar sensing system that allows high-precision vital sign monitoring of multiple subjects. The proposed sensing system can steer the beam towards the desired directions with a micro-second delay. The steerable beam enables capturing the vital signs of multiple individuals at the same radial distance to the radar. The proposed system enables the formation of a virtual array with aperture longer than that of the physical array. A Capon beamformer is used at the receiver side to combine the data collected from different transmit and receive antenna pairs corresponding to the virtual array. As all those pairs provide independent information about the targets, their combination significantly boosts the receiver signal-to-noise ratio. Based on the designed TDM phased-MIMO radar, we develop a system to automatically localize multiple human subjects and estimate their vital signs. Extensive evaluations show that under two-subject scenarios, our system can achieve more than 98.06% accuracy for breathing rate (BR) and more than 82.89% accuracy for heartbeat rate (HR) estimation, at a subject-to-radar distance of $\text{1.6}\;m$ when the targets are facing the radar. The minimal subject-to-subject angle separation is $30^\circ$ at a subject-to-radar distance of $\text{1.6}\;m$, corresponding to a close distance of $\text{0.3}\;m$ between two subjects, which outperforms the state-of-the-art.
[download url="https://ieeexplore.ieee.org/document/9772616/"]