Directive Low-Band UWB Antenna for In-body Medical Communications
A new antenna structure is presented in this paper. The antenna is operating at the Ultra-Wideband (UWB) band, 3.75—4.25 GHz, defined originally in Body Area Networks (BAN) part of IEEE 802.15.6 standard. The antenna size is 89 mm × 60 × 21 mm. The antenna is a directive with a measured gain of 8 dBi at 4 GHz center frequency. Since the proposed antenna is designed to meet the aspects of a receiving antenna for wireless capsule endoscopy localization, the antenna behavior in close proximity to a human body, in particular the small intestine area, is performed. For this end, initial on-body simulations were carried out by means of a tissue-layer model emulating the dielectric properties of the human body tissues at 4 GHz center frequency. This was followed by voxel model investigations. The human body impact on the antenna characteristics was analyzed firstly, followed by the examination of the power flow propagation inside the tissues. These analyses are consistent to evaluate the antenna ability to communicate with a capsule placed at the small intestine. Later, the antenna free-space propagation was assessed and validated by measurements. These results are followed by a measured on-body investigation conducted on male and female persons. Simulation results were obtained by CST Microwave Studio. Results were confirmed by measurements, conducted in an anechoic chamber at University of Oulu, Finland. The results were measured in frequency domain and later post-processed to a time domain. Consequently, measured results converge to the simulation ones. It is concluded that, the antenna could be used for Wireless Capsule Endoscopy communications with UWB signaling complying with IEEE 802.15.6 standard.