# Sensitivity Analysis of an Implanted Antenna within Surrounding Biological Environment
## 1 Introduction  
Implantable Medical Devices (IMDs) have been popularly studied recently. As the modern health care system evolves, IMDs are used frequently in order to continuously monitor personal health conditions. IMDs has the potential to be light and small and able to serve various applications. However, the huge difficulty for the utilization of IMDs is their charging since no wire could be connected to an in-body IMD. Highly integrated radio-frequency (RF) circuits and developments of wireless inductive links have a significant impact on IMDs [1; 2; 3]. Miniaturized antennas provide wireless communication capability to transmit signals through organs or tissues towards a receiver outside the body and/or receive commands to adjust the implant settings. They also allow continuous monitoring and therapeutic treatment without constraints to the patient's mobility. Medical implants have the advantages of being light and small. These antennas can obtain real-time information in biomedical telemetry and transmit physiological data to the external antenna. For different purposes, they are used for body-centric communication [4], glucose monitoring [5], and other body parts of telemetry [6; 7; 8]. Since the charging process is always noninvasive, obtaining an optimal electromagnetic link is challenging, necessitating, among others, designation of several design parameters like operational frequency, implanted device shape, and maximum power deposited on the tissues while implant size needs to be minimal to avoid tissue damage and increase patient safety. For biomedical uses, several frequency bands are authorized: Medical Device Radiocommunication (MedRadio) Service band (401-406 MHz), and the Industrial, Scientific, and Medical (ISM) bands (433.1-434.8 MHz, 868-868.6 MHz, 902.8-928 MHz and 2.4-2.5 GHz). Also, a Radio Frequency (RF) medical energy transmission system normally consists of two parts: an antenna for receiving energy from external power source and a rectifying circuit for converting AC power to DC power [9; 10; 11; 12]. As one of the three common methods for wireless power transfer in large scale, microwave radiation has its own advantages by operating in the farfield range: smaller and more robust to physical positioning or disorientations than two other transmission methods, and perfectly fit the requirements for an IMD. Therefore, many researches have been published with their own designs or analyses in thisdomain: [PERSON] et al. have designed an antenna embedded into muscle phantom at 2.4 GHz [13]; [PERSON] et al. have also proposed and tested their design which is implanted into head model at 400 MHz [14]; the research team of [PERSON] has studied another miniaturized antenna that is simulated in a skin box as well [15]. In [16], a miniaturized circular antenna was designed to support both energy and information transmission. The antenna is embedded into a three-layer cylindrical model of arm and its performance is evaluated. It has dual resonant frequency which covers MedRadio (401-406 MHz) and ISM bands (902-928 MHz). The wireless transmission link was analyzed and allowed to determine the amount of power that could be received from an external antenna at maximum authorized input power. However, it was observed that the performance of the implanted antenna and the characteristics of the transmission link are highly dependent on many parameters defining the electromagnetic problem. Geometrical parameters considered in the study like implantation depth, orientation of the antenna, and distance between exciting source and embedded antenna strongly affect the overall efficiency of the system. Also, physical parameters relevant to materials used for the miniaturized system or relevant to the environment (biological tissues) impact the global efficiency. Indeed, 3D computational models can be applied for solving the global electromagnetic problem involving implanted antenna and the environment.