## 3 Wireless Communication and Power Transmission
### Antenna Design  
This section presents the antenna of implantable devices. The antenna serves as the physical foundation for both wireless data transmission and power transmission, being capable of receiving and transmitting signals. Implantable antennas are thus required to possess characteristics such as compact size, low power consumption, and robust anti-interference capabilities. Simultaneously, biocompatibility must be taken into consideration. Implantable antennas should prevent short circuits and the generation of harmful radiation to surrounding tissues to safeguard the health of patients. Consequently, medical antennas are confined to a specified frequency range [109]. Commonly employed implantable antenna structures encompass helical/meandering antennas, planar inverted F antennas (PIFA), and conformal antennas. In recent years, the key innovation aspects have predominantly centered around multi-band applications, reconfigurable features, novel materials, and manufacturing processes, among others. Spiral antenna: The helical antenna offers the advantage of a small volume. The polarization field it generates is circular, and it exhibits the characteristic of omnidirectional radiation. With relatively low requirements for directivity, it is well-suited for implantable devices. In 2019, Tutku Karacolak put forward an implantable antenna for continuous glucose monitoring, which operates in the Medical Implant Communication Service (MICS) (402-405 MHz) and Industrial, Scientific, and Medical (ISM) (2.4-2.48 GHz) frequency bands. The antenna was optimized for the dual frequency bands. The dual-frequency design enables the implant to switch between sleep and wake-up modes, thereby conserving energy and prolonging the service life of the implant [110] (for detailed data, refer to Table 4). Simultaneously, with the advent of 3D printing technology, it has become possible to fabricate novel antennas with intricate shapes. In 2020, [PERSON] proposed a new type of 3D printed double-cone nested antenna. This antenna is composed of two conical spiral arms that are intertwined and oriented in opposite directions to implement an orthogonal circular polarization scheme. The nested conical spiral is manufactured through 3D laser printing and copper plating processes. The outer spiral arm is designed to resonate at 2.4 GHz, while the inner arm is intended for operation at 5.4 GHz. The entire antenna structure is arranged in an array, and its lattice can be dynamically altered between linear or triangular topological structures to reconfigure the radiation pattern [111]. Meanwhile, some researchers are dedicated to the optimization of antenna structures. Among them, [PERSON] developed a circularly polarized miniaturized implantable antenna specifically designed for wireless cardiac pacemakers [112]. The circular polarization characteristic endows this antenna with unique advantages, enabling it to maintain reliable \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Transmission Power** & \begin{tabular}{c} **Energy Transmission** \\ **Distance** \\ \end{tabular} & **Size** \\ \hline \begin{tabular}{c} Inductive coupled \\ stimulator [105] \\ \end{tabular} & \(>\)2.7 μW & 14 cm & 5 mm \(\times\) 7.5 mm \\ \begin{tabular}{c} At a distance of 2 cm, \\ the received voltage \\ resonance energy \\ transmission system [106] \\ \end{tabular} & 1–3 cm & \begin{tabular}{c} The diameter of \\ the receiving coil \\ is 1.9 cm \\ current of 10 mA. \\ \end{tabular} \\ \begin{tabular}{c} Ultrasonic piezoelectric \\ transducer [107] \\ \end{tabular} & 16 mW & 10 cm & 40 mm \(\times\) 8 mm \\ \
\begin{tabular}{c} Triboelectric \\ nanogenerator [108] \\ \end{tabular} &
\begin{tabular}{c} Maximum 0.7 V \\ (150\% stretching) \\ \end{tabular} & N/A & 6 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Different types of wireless charging data. communication with external devices in different orientations and effectively reducing the influence of human multipath reflections.