A novel technique to design a wideband implantable antenna has been proposed by using magneto-dielectric material. The antenna is a half cutting of a coplanar waveguide fed antenna with symmetric geometry printed on a flexible substrate with 24 µm thickness. A piece of magneto-dielectric sheet with 0.25 mm thickness is attached on the bottom layer of the antenna to tune the antenna bandwidth. The antenna is simulated in a one-layer body phantom. Simulation shows that the antenna has a wide bandwidth covering 902-928 MHz Industrial, Scientific, and Medical (ISM) band when the body phantom is filled with muscle. There are frequency bandwidth shifts when the body phantom is filled with different tissues of skin, small intestine, and stomach, respectively. The antenna has wide bandwidth covering ISM band in these tissues. Measurement has been done in meat mince. The measured bandwidth of proposed antenna is 810-1062 MHz. The proposed antenna has a compact size of 4 mm × 12 mm × 0.274 mm suitable to be applied in capsule endoscope, wireless pacemaker, etc. 1. INTRODUCTION Implantable biomedical devices using wireless communication have attracted much research interest in medical area due to virtues of live signal transmission and less pain to patient. These devices include wireless capsule endoscope, wireless cardiac pacemaker, glucose monitoring system, neural recording system, etc. [1-5]. Implantable antenna is an important component of an implantable wireless biomedical device to transfer data between inner body and outside body. Implantable antennas are required with miniaturized volume to reduce the physical uncomfortableness caused by the implantation inside body. The size of an ordinary antenna is inversely proportional to its working frequency. The popularly used frequency bands of implantable devices include Industrial, Scientific, and Medical (ISM, 433.05-434.79 MHz, 902-928 MHz, and 2.4-2.4835 GHz) bands, Medical Implant Communication Services (MICS, 402-405 MHz), Ultra-Wideband (UWB, 3.1-10.6 GHz)). It is easy to design a small antenna at UWB and ISM 2.4 GHz bands. However, the human body would absorb more energy with increase of frequency when electromagnetic waves propagate inside human body. Bands of ISM 2.4 and UWB with higher frequency are difficult to transfer high quality signals. Lower bands of ISM 433 MHz and MICS with narrow frequency bands of 1.74 MHz and 3 MHz, respectively, are difficult to obtain high data rate. Therefore, ISM 902-928 MHz band is a promising band to transfer high data rate signal for implantable devises [1, 3]. Many research works have been done on compact implantable antenna design [1, 2, 4-12]. Conventional miniaturization techniques are adopted including etching slots on patch [2, 4, 5], using multiple layer stacked structure [6, 7], and meandering strip/line in folded or helical shape [1, 4, 5, 8-12]. Dielectric, magnetic, and magneto-dielectric (MD) materials with high permittivity or permeability are also used as substrates to obtain antenna size reduction [13, 14].
