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

Abstract

In recent years, biomedical telemetry has revolutionised healthcare by enabling realtime remote monitoring of physiological parameters, reducing the need for frequent
hospital visits and in-person check-ups. At the heart of this advancement are Implantable Medical Devices (IMDs), which facilitate wireless monitoring for a range of
critical applications, including endoscopy, blood pressure tracking, cardiac defibrillators, 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, resonant 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 tissue 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 implantable 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 designed 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.