An Ultra-Miniaturized Self-Quadruplexing Antenna for Next-Generation Wireless Implantable Devices

Abstract

This work introduces a small self-quadruplexing antenna created for use in implantable medical devices (IMDs), capable of simultaneously and independently supporting transmission and reception across four different frequency bands without the need for any external multiplexer or switching circuitry. The proposed antenna operates at 868 MHz, 915 MHz [industrial, scientific and medical (ISM)], 1400 MHz [wireless medical telemetry service (WMTS) band] and 2450 MHz (ISM band) when Ports 1, 2, 3, and 4 are excited, respectively. The antenna is replicated inside a rectangular gadget that is situated inside a human phantom head model. It consists of four independently excited circular quadrants sharing a common ground plane, with compactness achieved through the use of shorting pins, strategically shaped slots and high dielectric substrate to reduce structure size. The total antenna volume is only 24.69 mm3. Mutual coupling between any two ports is maintained below -23 dB. The antenna provides peak gains of -22.8, -25.3, 25.4, and -20.2 dBi at 868, 915, 1400, and 2450 MHz, respectively. To comprehend the antenna’s electromagnetic activity, Characteristic Mode Analysis (CMA) is used. To confirm that the antenna is suitable for implantation in the body, a specific absorption rate (SAR) analysis and a link budget analysis are carried out. The maximum 1 g SAR values are found to be within safe limits, while link margin analysis confirms the potential for reliable wireless communication in biomedical telemetry applications. By integrating multiple functions into a single structure, this self-quadruplexing design offers a novel and efficient alternative to conventional multiplexed systems in IMDs.