IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 69, NO. 4, APRIL 2021 1885 Miniaturized Dual-Band Circularly Polarized Implantable Antenna for Capsule Endoscopic System Shahzeb Hayat , Syed Ahson Ali Shah , Member, IEEE, and Hyoungsuk Yoo , Senior Member, IEEE Abstract— This study proposes a miniaturized dual-band antenna with a circular-polarization characteristic for a wireless-capsule endoscopic system operating in the industrial, scientific, and medical bands: 915 and 2450 MHz. The proposed capsule device is intended for deep-tissue implantation with the standard dimensions of 26 × 11 mm 2 . The key features of the proposed antenna are its CP characteristic at both bands, satisfactory gain values, and a smallest volume (6.5 × 6.5 × 0.05 = 2.11 mm 3 ) with a via-less ground plane compared with the state-of-the-art device. The CP wave performance and the miniaturization of the antenna are achieved via the introduction of slots accompanied by meandered line segments in a radiating patch and open-end slots in a ground plane. Furthermore, the proposed antenna offers a reasonable axial ratio (AR) of <3 dB at the desired frequency bands. The circularly polarized radiator attains the AR bandwidths (BWs) of 33.0% and 8.67% and the measured -10 dB impedance BWs of 13.63% and 6.28% at 915 and 2450 MHz, respectively. The measurements of the reflection coefficient and radiation pattern are performed using a fabricated prototype of the proposed antenna system in a saline solution and minced pork. Finally, the safety considerations and link budget calculations are evaluated to analyze the performance of the proposed capsule device. Due to the AR BW, impedance BW, and ease of fabrication, the proposed antenna system is a suitable candidate for use in endoscopic applications. Index Terms— Antenna, capsule device, circular polarization, industrial, scientific, and medical (ISM) band, link budget, wireless capsule endoscopy. I. I NTRODUCTION I NGESTIBLE and implantable medical devices (MDs) allow the measurement of physiological signals at a certain distance [1]. These devices are embedded in the human body to perform diagnostic and therapeutic functions. During Manuscript received July 18, 2019; revised July 29, 2020; accepted August 21, 2020. Date of publication October 8, 2020; date of current version April 7, 2021. This work was supported by the Ministry of Education, Science, and Technology, National Research Foundation of Korea through the Basic Science Research Program under Grant 2019R1A2C2004774. (Corresponding author: Hyoungsuk Yoo.) Shahzeb Hayat and Syed Ahson Ali Shah are with the Department of Electronic Engineering, Hanyang University, Seoul 04763, South Korea (e-mail: hsyoo@hanyang.ac.kr). Hyoungsuk Yoo is with the Department of Biomedical Engineering and the Department of Electronic Engineering, Hanyang University, Seoul 04763, South Korea (e-mail: hsyoo@hanyang.ac.kr). Color versions of one or more of the figures in this article are available online at https://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2020.3026881 swallowing, the ingestible MDs pass through the gastroin- testinal (GI) tract and provide physiological data as well as real-time biological images of the entire GI tract to the external controller via a radio frequency link. Typically, the wireless- capsule endoscopic (WCE) system is an ingestible MD with the standard dimensions of 26 mm × 11 mm, which con- tains a transceiver, a small camera, light-emitting diodes, an optical dome, an antenna, and batteries [2]. Many factors, including the resonance frequency, capsule dimensions, image resolution, transmission distance, battery capacity, and image frame rate, should be considered within the overall frame- work of the device. Current WCEs typically use one-way wireless telemetry and have a low image resolution (256 × 256 pixels), with a frame rate of 2 frames/s [3]. However, doctors prefer high-resolution images for accurate diagnosis and treatment. Thus, a circular polarized (CP) antenna with sufficient bandwidth (BW) and gain is needed to accommodate the frequency shifting in a realistic environment and maintain stable operation in human tissue. Therefore, the design of an ingestible and implantable antenna for biomedical applications has attracted considerable research attention [4]–[9]. Most implantable antennas are linearly polarized and are vulnerable to multipath interference and polarization mismatch caused by the random capsule direction and position in the GI tract [10]–[16]. To reduce the multipath distortion and improve the bit error rate, CP antennas have been investigated intensively in previous studies. A conformal wideband CP antenna was designed for capsule endoscopic applications [2]. However, the configuration of a helical [3] and conformal implantable antenna [2] increases the profile of the prototype. In [17], a miniaturized CP antenna was designed via the capacitive-loading technique to achieve an axial BW of 1.6% at 2.45 GHz. A patch antenna with multiple slots operating at 2.45 GHz was reported, which achieved the axial ratio (AR) and impedance BWs of 8.13% and 6.2%, respectively [18]. A conformal wideband CP antenna with several slots in the radiating patch and a shorting pin in the structure to achieve the CP behavior of antenna was presented [19]. Recently, a dual-band implantable antenna having linear polarization at 1.4 GHz and CP at 2.45 GHz was designed using orthogonal strips and a shorting pin [20]. A single-band CP implantable antenna was designed in [21]. The antenna miniaturization and CP behavior were achieved via the incorporation of L-shaped 0018-926X © 2020 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: Kwangju Institute of Science and Technology. Downloaded on January 01,2024 at 12:27:57 UTC from IEEE Xplore. Restrictions apply.