A highly miniaturized circularly polarized self-duplexing implantable antenna with enhanced performance for wireless capsule endoscopy applications.

Abstract

Multiband implantable antennas are crucial components of biomedical implantable devices (BIDs), enabling the establishment of wireless communication links with external base stations. These types of antennas perform various functions such as data transmission, wireless power transfer, and control signaling. However, this scenario requires an external multiplexer in the BIDs to separate various frequency bands, imposing size constraints on the BIDs. This work proposes a self-duplexing circularly polarized implantable (SDCPI) antenna for wireless capsule endoscopy (WCE) application having two separate ports, with port 1 providing a wideband response covering MICS (402 MHz), ISM (433 MHz) band, and port 2 covering ISM (915 MHz) band. The proposed SDCPI antenna achieved a very compact volume of π × (5.1)² × 0.127 = 10.3 mm³ by semi-circular slots on the radiating patch and shorting pins. The proposed capsule integrated implantable antenna was thoroughly analyzed through simulations in various parts of the digestive tract (stomach, small intestine, and colon) and was later fabricated and tested. The measurements were carried out in minced pork, and the results obtained showed close resemblance to the simulated results. The proposed SDCPI antenna offers a -10 dB impedance bandwidth and CP bandwidth of 151 and 273 MHz, and 10% and 15% at 402 and 915 MHz, respectively. Furthermore, it exhibits measured gain of -36 and - 25 dBi at 402 and 915 MHz, respectively. To evaluate the human safety of the proposed SDCPI antenna, specific absorption rate (SAR) at 402 and 915 MHz was estimated in the stomach, small intestine, and colon, and was found to be within the limits allowed by the IEEE standards. Additionally, the wireless communication link establishment capabilities of the proposed SDCPI antenna were gauged through link margin analysis. This analysis confirmed that at 402 MHz, the presented SDCPI antenna can establish reliable communication up to 25, 9.7, and 4.5 m when placed in the small intestine for bit rates of 1, 12, and 78 Mbps, respectively. Likewise, at 915 MHz, the suggested SDCPI antenna offers seamless communication up to 28, 14.7, and 5.3 m when placed in the small intestine for bit rates of 1, 12, and 78 Mbps, respectively. These results verify that, to the best of the authors' knowledge, the proposed highly miniaturized SDCPI antenna is the first self-duplexing CP implantable antenna for WCE applications offering simultaneous transmission and reception without requiring an external multiplexer.