An Ultra-Miniaturized High Efficiency Implanted Spiral Antenna for Leadless Cardiac Pacemakers

This article presents an ultra-miniaturized implant antenna with a volume of 22.22 mm$^{3}$ in the Medical Implant Communication Service (MICS) frequency band 402-405 MHz to be integrated with a leadless cardiac pacemaker. The proposed antenna has a planar spiral geometry with a defective ground plane exhibiting a radiation efficiency of 3.3% in the lossy medium with more than 20 dB of improved forward transmission, while the coupling can be further enhanced by adjusting the thickness of the antenna insulation and the antenna size according to the application area. The implanted antenna demonstrates a measured bandwidth of 28 MHz, covering beyond the MICS band needs. The proposed circuit model of the antenna describes the different behaviors of the implanted antenna over a wide bandwidth. The antenna interaction within human tissues and the improved behavior of the electrically small antenna are explained in terms of radiation resistance, inductance, and capacitance that are obtained from the circuit model. The results are demonstrated using electromagnetic computations and are validated by the measurement using liquid phantom and animal experiments.