# A Small Implantable Compact Antenna for Wireless Telemetry Applied to Wireless Body Area Networks
## 1 Introduction  
In recent years, with the continuous advancement of medical technology, Implantable Medical Devices (IMDs) have seen significant development. As the most critical component of these devices, the implantable antenna directly impacts the efficiency and stability of wireless communication for IMDs [1]. A reliable wireless network is also an essential condition for the normal operation of IMDs. In recent years, research on Wireless Body Area Networks (WBANs) has focused on implantable devices, which, as an integral part of the fifth-generation mobile communication system, have been widely applied in the medical,sports, and military fields [2]. The operating environment for implantable antennas is within human tissue, which acts as a high-dielectric material [3]. Each tissue layer has a different dielectric constant. This inhomogeneity in dielectric constants can lead to unstable propagation of electromagnetic waves within the body, causing frequency detuning when the antenna is implanted in different tissues. Therefore, expanding the antenna's bandwidth can mitigate the impact of this phenomenon on antenna performance [4]. In reference [5], two intersecting rectangular slots were etched on the ground plane to expand the antenna's impedance bandwidth, but the overall size of the antenna was relatively large. In reference [6], slots were introduced on the radiating patch plane, and two shorting pins were inserted between the patch and the ground plane to achieve a wider impedance bandwidth, further increasing the complexity of the antenna structure. To facilitate the implantation of the antenna within human tissue and reduce the discomfort of the implantable device, compact antennas are the inevitable trend. In reference [7], parallel rectangular slots on the radiating patch and an open rectangular slot on the ground plane were introduced to achieve antenna compactification. However, a covering layer was not used to isolate the antenna from human tissue. In reference [8], the antenna was miniaturized by introducing three zigzag rectangular slots on the edges of the radiating patch, adding a circular slot in the middle of the patch, and introducing an open slot on the ground plane. However, the dielectric substrate and covering layer materials used were not biocompatible. In reference [9], a bent rectangular slot was introduced on the patch to reduce the antenna size, but biocompatible materials were not used to isolate the antenna from human tissue. In reference [10], multiple symmetric L-shaped rectangular slots on the patch and open-type rectangular slots on the ground plane were used to achieve antenna compactification. For the design of implantable antennas, biocompatibility is also a very important feature. In reference [11], to achieve biocompatibility, the antenna was encapsulated with PDMS material to avoid direct contact between the antenna and human tissue. However, PDMS material has poor durability and is prone to deformation and aging in complex environments. In reference [12], biocompatible alumina ceramic material was used to encapsulate the antenna, enhancing its biocompatibility. However, alumina ceramic material has high processing costs, complex processing techniques, and is brittle, making it prone to breakage. To improve the use of antennas in wireless body area networks, antennas should be bendable so that they can better adapt to human body tissues [13; 14], thereby reducing signal attenuation and improving the communication stability of the antenna in complex human environments. The flexibility and adaptability of such antennas gives them a significant advantage in implantable systems. Microstrip patch antennas also have the advantages of small size [15], flexibility, and ease of fabrication, making them more suitable for use as implantable antennas for human tissue applications. Based on the above analysis, when designing the antenna, considerations must be given to the antenna size, bandwidth, and biocompatibility.