A Multi-Input-Multi-Output Sensing Radar with Nonlinear Tag for In-Body Implant Localization

This work presents a multiple-input multiple-output (MIMO) sensing radar with a nonlinear tag for measuring the position of the implant in deep tissue. To be able to localize the deep-tissue implant, two difficulties, the self-interference from multiple scattering of tissue layers and strong reflections from the air-skin interface, must be effectively solved. The sensing radar consists of two RF signal generators, power amplifiers, low-noise amplifiers, duplexers, and circularly-polarized antennas, and the nonlinear tag is composed of a flexible antenna and a mixing diode. The Chinese Remainder Theorem (CRT) is used to solve the distance ambiguity problem, and an optimization algorithm is developed to estimate the actual depth of the tag from the measured phases. The experimental results show that the maximal detection range can be reached to 5 cm with a mean error of 0.1 mm. The vertical distance of the tag has a mean error smaller than 7.6 mm.