Multi-Channel Implantable Cubic Rectenna MIMO System With CP Diversity in Orthogonal Space for Enhanced Wireless Power Transfer in Biotelemetry

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 (
$R_{x}$
). 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 (
$T_{x}$
), 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
$T_{x}$
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 (
$P_{\mathrm {RF}}$
) of 0 dBm, where a single cubic rectenna element (CRE) provides dc power (
$P_{\mathrm {DC}}$
) 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
$P_{\mathrm {DC}}$
to
$0.5\mathbf {/}1.39$
and
$0.51\mathbf {/}1.64$
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
$T_{x}$
and FPCR are excited with 1 W power.