Electronically switchable dual-band capsule antenna for wireless endoscopic applications

This paper presents a highly compact linearly polarized planar dual annular ring antenna designed for wireless capsule endoscopy. The focus of this work on the small intestine is motivated by clinical practice in capsule endoscopy. Most capsule endoscopy systems are specifically designed to examine the small intestines, which are difficult to access with conventional wired endoscopes and are the primary region of interest for many gastrointestinal pathologists. The antenna is derived from a conventional annular ring structure and supports dual-band operation, covering both Wi-Fi frequencies at 2.45 GHz and 5.8 GHz. With a radius of only 4.7 mm, the planar geometry occupies minimal space inside the capsule, leaving more room for essential electronics and the battery. The antenna achieves bandwidths of 20.8% at the lower band and 6.7% at the upper band. A key feature of the design is the capability for electronic switching of the higher band, which enables efficient power management. This allows continuous transmission of critical data, such as control signals, over the lower band, while high-volume data, such as images and video, can be transmitted on demand over the upper band through microcontroller-controlled switching. This mechanism ensures battery conservation as well as reduced time average SAR levels for higher safety. In-vitro testing of the prototypes was conducted, and the measured gains of -17.3 dBi and  -18 dBi at the lower and upper bands have been achieved. Furthermore, the antenna exhibits specific absorption rate (SAR) values of 21.5 W/kg and 24.7 W/kg for the two operating bands. To ensure safe operation in compliance with IEEE and ECC standards, maximum transmit powers of 93 mW and 81 mW can be utilized, respectively, while maintaining reliable link quality and extended communication coverage. The link margin remains at 21.1 dB and 12.3 dB at 2.45 GHz and 5.8 GHz, respectively, ensuring an excellent link reliability at a distance of 4 m.