A Wearable Dual-Mode Repeater Antenna for Implant Communications

Abstract

A novel wearable cavity-backed slot repeater antenna is presented to improve the link between implant antennas and the outside world. This proposed repeater antenna consists of two slots on opposite sides of a shallow rectangular cavity. These slots are activated in an alternating way, selecting the mode of operation: in-body or off-body. Through the antenna’s in-body mode, signals transmitted by the implant antenna are received and conveyed to the off-body gateway via its off-body mode. Both modes are designed to operate in the 2.4 GHz industrial, scientific, and medical (ISM) Band. The antenna is fed by a single diagonal stripline, and the two slots encounter the stripline at the same location with impedance matching obtained through offset feeding. The antenna has an overall size of 33.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 37$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 3.14$ </tex-math></inline-formula> mm and has been shown to perform well near numerical and physical phantoms, communicating with deep tissue implants with an outstanding maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|{S_{21}}|$ </tex-math></inline-formula> value of −37.4 dB measured at 6 cm depth.