A Serpentine PIFA Antenna for Implantable RFID Tag M. Shahidul Islam, K. P. Esselle, S. Sabrin and K. M. Morshed Department of Engineering Faculty of Science and Engineering Macquarie University, Sydney, NSW 2109, Australia Email: shahidul.islam@mq.edu.au Ladislau Matekovits Departimento di Elettronica e Telecomunicazioni Politecnico di Torino, 10129 Torino, Italy Email: ladislau.matekovits@polito.it Abstract— A serpentine planar inverted-F antenna (PIFA) is designed for Medical Implant Communications Services (MICS) band (401-406MHz) and presented in this paper. Resonance frequency of implantable antenna is generally detuned towards lower frequency due to the proximity effect of high permittivity human tissue. In addition, biocompatible coating material on the antenna also leads frequency shifting of the antenna. To overcome this frequency detuning problem, the proposed serpentine PIFA is sealed in a high dielectric constant (Silicon,  r =11.9) material. The proposed PIFA antenna is predicted to be functional in MICS band under IEEE standard safety regulation. Gain of the antenna is -33dBi. Keywords— Serpentine PIFA antenna, implantable RFID tag, Wireless Bio-telemetry, MICS band. I. INTRODUCTION Planar inverted-F antenna (PIFA) is a low profile, compact antenna. However, its narrow operating bandwidth which in turn dictates low transmission data rate represents a noticeable shortcoming. To overcome this aspect, various schemes have been proposed and applied to design PIFA antennas with enhanced bandwidth. In our proposed PIFA, improvement of the antenna bandwidth is obtained by connecting the RFID tag’s ground plane with the antenna ground plane so that the PIFA overall ground plane becomes larger. Considering the specific application, once implanted in human/animal body, the antennas suffer from frequency detuning due to the effects of human/animal tissue surrounding the antenna (skin, fat etc.). Dielectric constant and conductivity of human/animal tissue may change for various reasons, for example ageing, diseases. This also leads shifting of the antenna resonance frequency. Research on the use of PIFA antennas for implantable medical devices (IMD) have received a considerable attention, as it is demonstrated by the large number of publications. Design and performances of a fabricated prototype of an UHF implantable antenna for an RFID tag is presented in [1]. Two Implantable PIFA antennas are explored in [2] for Medical Implant Communications Services (MICS) band (401-406MHz). Mutual coupling effects of PIFAs are described in [3] for a MIMO terminal with the array of antennas. In [4], a frequency tuning technique is illustrated for a PIFA to operate for multiple frequency bands. A compact and proximity-fed PIFA is presented in [5] for wireless medical applications. A low profile and small size PIFA antenna for UHF RFID tag is presented in [6]. In our recent work [1], an I-PIFA is designed and implemented for 900MHz Australian ISM band and effects of fresh rat tissue samples (collected from local hospital) on the antenna is studied. In this paper, we present an implantable PIFA antenna for an RFID tag to be implanted in human body. The manuscript is organized as follows: Section II presents the geometry and design of the proposed antenna. Section III presents the predicted results in human body tissue environment followed by the conclusion in Section IV. II. ANTENNA GEOMETRY AND DEGIGN Geometry and design of the proposed PIFA antenna is shown in Fig. 1. Parametric study of the antenna is performed by numerical analysis using CST Microwave Studio software. The overall dimensions of the final design are 27.5mm×16mm×5.44mm. The total thickness (5.44mm) of Rogers RO3210 substrate is constructed by placing four substrates together. Three of them are Rogers RO3210 (each 1.28mm thick) and other one is FR4 substrate (1.6mm thick). Fig. 1. Antenna geometry and leading dimensions The radiating patch on the top is printed on a 1.28mm thick substrate (Rogers RO3210, dielectric constant, ε r = 10.2). ISAP2015 Copyright (C) 2015 IEICE 882