Compact High-Data-Rate Implantable Antennas for Leadless Cardiac Pacemakers

Abstract

In recent years, biomedical telemetry has revolutionised healthcare by enabling real time remote monitoring of physiological parameters, reducing the need for frequent hospital visits and in-person check-ups. At the heart of this advancement are Im plantable Medical Devices (IMDs), which facilitate wireless monitoring for a range of critical applications, including endoscopy, blood pressure tracking, cardiac defibrilla tors, pacemakers, and blood glucose monitoring. Among these innovations, leadless pacemakers have gained significant attention due to their minimally invasive design and improved patient comfort. However, their effectiveness depends largely on a well-optimised implantable antenna, which is essential for ensuring reliable wireless communication. This thesis focuses on addressing key challenges including miniaturisation, res onant frequency detuning, and multipath fading within the human body’s lossy electromagnetic environment. Three novel implantable antenna designs are presented in this work. The first contribution presents an implantable antenna with a rectangular patch design, incorporating a U-shaped slot, an inductive shorting pin, and multiple edge slots. It achieves a volume of 9.44 mm³, offering a 3.39 GHz bandwidth and a fractional bandwidth of 138%. The antenna supports a broad frequency range from 0.76 to 4.15 GHz, covering key medical bands, including the Industrial, Scientific, and Medical (ISM) bands at 0.869, 0.915, and 2.45 GHz; the Wireless Medical Telemetry Service (WMTS) band at 1.4 GHz; and the midfield communication band around 1.6 GHz. Simulation results within a homogeneous phantom (HP) of heart tis sue indicate gain values of −32.4 dBi at 0.915 GHz, −27.94 dBi at 1.4 GHz, and −19.8 dBi at 2.45 GHz. The second contribution presents an ultra-compact im plantable antenna featuring a central C-shaped slot. It has a volume of 8.33 mm³, a fractional bandwidth of 152.7%, and operates within a frequency range of 0.67 to 5 GHz, covering essential medical bands. These include the ISM bands at 0.915 GHz and 2.45 GHz, the WMTS band at 1.4 GHz, and the midfield band at 1.6 GHz. Simulation results indicate gain values of −31.3 dBi at 0.915 GHz, −25.8 dBi at 1.4 GHz, and −21.9 dBi at 2.45 GHz. The third contribution introduces a 2×1 ultra-wideband multiple-input, multiple-output (UWB-MIMO) antenna de signed with two loop radiators and a shared slotted ground plane. The antenna achieves a compact volume of 16.4 mm³, a wide fractional bandwidth of 165.12%, and operates from 710 MHz to 7438 MHz with a high isolation level of −21 dB. The individual MIMO antenna elements exhibit peak gain values of −34.7 dBi at 0.915 GHz, −28.4 dBi at 1.4 GHz, −23.3 dBi at 2.45 GHz, and −20.1 dBi at 5.8 GHz. Furthermore, at a signal-to-noise ratio (SNR) of 20 dB, the antenna achieves a channel capacity of 15.04 bps/Hz, highlighting its suitability for high-data-rate telemetry in next-generation leadless pacemakers. Specific Absorption Rate (SAR) analysis confirms that all three implantable antennas comply with regulatory safety standards, ensuring patient safety.