# Approach-Based Analysis on Wireless Power Transmission for Bio-Implantable Devices
## 3 Analysis of Various WPT Approaches
### WPT Systems Based on Antenna Modifications
The well-built coupling of transmitting and receiving antennas in the reactive near field ensures more PTE. Normally, wireless power transmission often faces the problems of antenna orientation and the misalignment in the antenna's polarization, which degrade the WPT efficiency and safety aspects for human tissue. Article [43] proposed an antenna alignment method that uses intermodulation to safely correct the misalignment of WPT antennas where a 2-tone (2T) waveform response is used to improve rectification and create intermodulation. Intermodulation energy is returned through a magnetically resonant coupling element. Because of the monotonous relationship between the performance of intermodulation and the level of misalignment of the antenna, the internal (inside the body) antenna could be aligned with the external (outside the body) antenna. This approach provides less damage to the tissue and no intrusion between the excitation of the 2T response and the magnetically coupled inductive connection. This approach has been experimentally validated. The inductive method of charged brain implantable medical devices (BIMD), instead of a battery powered BIMD, can provide good powering and keep away from the resection restore of a discharged battery. This has been studied and experimented on by [PERSON] and [PERSON] [44]. A 3D bowtie antenna lodged in cerebrospinal fluid (CSF) connected with an outer loop-type antenna reduces the high intrinsic reactive portion of the input impedance. A cerebrospinal fluid (CSF) spoof was made to experimentally check the energy transfer efficiency between external and internal antennas. A measurement of the 0.9 mm\({}^{3}\) fabricated implantable internal antenna prototype on the CSF spoof (phantom) provided results in a \(-\)30.12 dB wireless power connection, which exceeds current survey work in terms of the efficiency and size of the link for implantable 3-dimensional antennas. Along with these, let us examine another wireless system, [PERSON] et al. proposed in [45] a wireless capsule endoscopy system, which is specified with more gain and a highly sensitive small antenna sensor. In this system, the antenna is miniaturized by applying a two-layer radiation patch without reducing the radiation gain. The antenna sensor provides the merit of a peak gain utmost \(-\)9.7 dBi with a volume of (2.6 \(\times\) 3 \(\times\) 0.381) mm\({}^{3}\) in the (2.4-2.4835 GHz) ISM frequency band. Additionally, stomach ailments can be found by the resonant frequency of the antenna's sensor. Overall, the small capacity, increased gain, and high sensitivity from the proposed antenna form an excellent role for endoscopy wireless systems. Finally, let us examine another WPT system [46] that is designed by amalgamating a meta-surface with magnetic negative characteristics (MNG) to enhance efficiency as the MNG of meta-material has strong magnetic resonant behavior. The implantable antenna used in this system has split resonance rings to reduce its size. Here, meta-surface is placed 6 mm from the receiver antenna, which is 5 mm from surface of the skin and so the meta-surface will be 1 mm away from the surface of the skin in its converse direction. With  
Figure 5: A 3-loop and 3-coil linked inductive WPT transmission. this set-up, this antenna exhibits ultra-wide band properties that can offset from 272 MHz to 1504 MHz, with 138.7% relative bandwidth. In addition, the antenna is extremely dense at 91.44 mm\({}^{3}\) (12 mm \(\times\) 12 mm \(\times\) 0.635 mm) when compared to other designs. By integrating the split resonant ring, the proposed antenna was stimulated to have wideband characteristics in the required band. In addition, with the consideration of biosecurity for practical use, an efficient WPT system was integrated into the meta-surface to enable the charging of the embedded device and extend its life.