Near field radio link design in fat phantom for Wireless Capsule Endoscopy application

Abstract

Medical devices such as Wireless Capsule Endoscopy (WCE) that need wireless imaging and monitoring, operating at 402 MHz, is considered to be in the near field region due to the distance being shorter than the wavelength. In this paper, the radio link calculation method in the near field region is investigated. Normal Mode Helical Antenna (NMHA) is used as the transmitter antenna which is placed inside of a fat phantom of 11.6 F/m and the receiver antenna at distance 0.1 to 1.0 m apart. For link budget establishment, parameters such as power density, W and receiver antenna effective area, Ae are investigated through electromagnetic simulation. The distance dependency of W is examined and the result of W 1/(distance)2 is obtained. The relation of Ae of the receiver antenna is found to be the size of the cross-section area of the antenna. A radio link equation is formed by employing W, Ae and other propagation loss factors of a medium and is then compared with the power received, PR and S21 obtained from simulation. The agreement between calculated and simulated results shows that this equation can be used in the near field region.