Near-Reflectionless Wireless Transmission Into the Body With Cascaded Metasurfaces

The ability to transmit wireless signals into the body is important for medical communication, sensing, and powering technologies. However, the efficiency of signal transmission is limited by the large reflection encountered at the interface between air and biological tissue. Here, we demonstrate an approach to overcome this reflection using cascaded metasurfaces (MSs) with deeply subwavelength thickness to transform the wave impedance at the air–tissue interface. We develop a procedure to systematically synthesize these MSs using a multilayer tissue model that can account for different body compositions. Using this procedure, we design a three-layer MS operating at 2.45 GHz with $\lambda /24.5$ thickness. Full-wave simulations in a computational human body model show that the MS provides transmission equivalent to replacing the background with a tissue-matched medium, while experimental measurements demonstrate 12.1 dB enhancement of transmission into a multilayer tissue phantom.