Multi-Channel Implantable Cubic Rectenna MIMO System With CP Diversity in Orthogonal Space for Enhanced Wireless Power Transfer in Biotelemetry
Vikrant Kaim, Neeta Singh, Binod Kumar Kanaujia, Ladislau Matekovits, Karu P. Esselle, Karumudi Rambabu
Abstract
For wireless power transfer (WPT), an implantable cubic rectenna multi-input-multi-output (MIMO) system (CRMS), operating in dual industrial, scientific, and medical (ISM) frequency bands of 2.45 and 5.8 GHz, is presented as a receiver ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{x}$ </tex-math></inline-formula> ). CRMS is evolved to the proposed biocompatible full-package cubic rectenna (FPCR) by including the power and data management circuit modules. The dual frequency bands differentiated by orthogonal circular polarization (CP) in a spatial quadrature would serve as propagation channels for power, data, and control signals. Four dual-branch rectifiers are designed using both distributed and lumped elements on the backside of individual antenna elements. To demonstrate the feasibility of the proposed work as an integrated system for WPT, the structures are fabricated individually, where the transmitter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{x}$ </tex-math></inline-formula> ), which is an external antenna, and rectifiers are tested in free space and FPCR in a custom-made canonical phantom. After validation of individual measurements, power delivery from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{x}$ </tex-math></inline-formula> to the FPCR is conducted experimentally to measure the integrated system’s radiofrequency (RF)-dc total conversion efficiency (TCE). The FPCR is designed to receive low RF power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {RF}}$ </tex-math></inline-formula> ) of 0 dBm, where a single cubic rectenna element (CRE) provides dc power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {DC}}$ </tex-math></inline-formula> ) of 0.26 and 0.33 mW at 2.45 and 5.8 GHz, respectively. Thereafter, the interconnection of CREs in a series/parallel configuration improved <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {DC}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5\mathbf {/}1.39$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.51\mathbf {/}1.64$ </tex-math></inline-formula> mW, respectively. Additionally, human safety is considered by evaluating a maximum permissible exposure (MPE) limit and specific absorption rate (SAR) distribution in a canonical tissue model when both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{x}$ </tex-math></inline-formula> and FPCR are excited with 1 W power.