# Approach-Based Analysis on Wireless Power Transmission for Bio-Implantable Devices
## 3 Analysis of Various WPT Approaches
### WPT Systems Based on Antenna Modifications  
Some of the WPT systems (listed in Table 4) were developed by using different or modified antennas for the betterment of their performance. In this section, this is discussed briefly. A rectenna implantable in the arm, assisted by a rectifier and a new antenna called planar inverted F-antenna (PIFA) was designed for power transmission and data telemetric services wirelessly in radio communication for medical devices (401-406 MHz), in industry, science and medicine, with (902.8928 MHz) frequency bands [39]. The rectifier circuit is included with the help of a ground plane of the taken antenna in this system. The antenna size taken is 16 \(\times\) 14 \(\times\) 1.27 mm\({}^{3}\) and the techniques for slot loading given to the selected radiator provide a dual band operation and also good minimization in the antenna size. This body of work addressed the stability level of PIFA at resonance, its radiation measures and responses in terms of security in detail. In addition, a matching layer attached to the arm was introduced to enhance the power connection and transfer efficiency at small input powers. Hence, in this body of work, the overall system called rectenna was constructed and thoroughly checked for coverage distance and efficiency. Another modified antenna model proposed in [40] has an antenna which is multi-band in its shape and applicable for implantable and ingestible devices. It has three bands of frequency. The first one is the implanted medical communication service (MICS) and \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref.** & **Approach** & **Operating Frequency** & **Performance** & **Remarkable Observation** \\ \hline \multirow{3}{*}{[39]} & System with dual & \multirow{3}{*}{915 MHz} & Boost up of directivity of & (i) & Covering distance of WPT \\  & band PIFA & & antenna and & is 50 cm; \\  & & & radiation efficiency & (ii) & Improves PTE 4.4 times the \\  & & & & System without PIFA \\ \hline \multirow{3}{*}{[40]} & Non-leaky WPT and & \multirow{3}{*}{402–405 MHz (MICS)} & Apprx. 4 mW power & Power leakage control attained \\  & T-shaped ground & slotted antenna & & attained & using Near Field Plate \\ \hline \multirow{3}{*}{[41]} & A triple-loop & \multirow{3}{*}{13.6 MHz} & 13.5\% PTE at 20 mm & A 3-coil inductive link also \\  & -echnique-based WPT & & distance coverage & established to improve PTE \\ \hline \multirow{3}{*}{[42]} & Design with Reactive & \multirow{3}{*}{2.45 GHz (ISM)} & \multirow{3}{*}{1.8\% PTE} & 1.92 W/Kg SAR and Antenna \\  & near field of antenna & & & misalignment issue \\  & & & & also addressed \\ \hline \multirow{3}{*}{[43]} & Intermodulation & Rectenna 2T of 2.448 and & Minimizes the interference & (i) & Strengthen the power \\  & technique for & 2.452 GHz; & in NRIC link; Implantation & & link efficiency; \\  & antenna alignment & 4-MHz intermodulation & depth is 2 mm. & (ii) & Less harm to human tissue \\ \hline \multirow{3}{*}{[44]} & \multirow{3}{*}{Inductive Coupling (for BMID)} & \multirow{3}{*}{400 MHz} & \multirow{3}{*}{\(-\)30.12 dB wireless power} & (i) & 3D bowtie receiver antenna \\  & & & & for implant lodged in CSF \\  & & & & fluid connected \\  & & & & with an external \\  & & & & loop-type antenna; \\  & & & & avoiding restore of a \\  & & & & discharged battery \\  & & & & through surgery \\ \hline \multirow{3}{*}{[45]} & New Antenna sensor & \multirow{3}{*}{2450 MHz} & \multirow{3}{*}{Smaller size;} & (i) & Antenna sensor: peak gain \\  & (for wireless & & & of \(-\)9.7 dB; \\  & endoscopy system) & & High gain and sensitivity; & (ii) & Stomach disease can also \\  & & & & be detected \\ \hline \multirow{3}{*}{[46]} & Antenna with split & \multirow{3}{*}{272 MHz to 1504 MHz;} & \multirow{3}{*}{Peak gain:} & (i) & Antenna size reduced to \\  & & & & 91.44 mm\({}^{3}\); \\ \cline{1-1}  & resonant rings & & \(-\)32@MICS and & (ii) & WPT with metasurface \\ \cline{1-1}  & & & \(-\)34@ISM & & extends battery life \\ \cline{1-1}  & & & & for implants. \\ \hline \hline \end{tabular}
\end{table}