Ultra-Miniaturized Triband Antenna with Reduced SAR for Skin and Deep Tissue Implants

Abstract

In this study, an ultra-miniaturized implantable antenna is developed for biotelemetry applications. It has triple-band characteristics in the industrial, scientific, and medical (ISM) bands of 902928 MHz for data telemetry and 24002483.5 MHz for power-saving applications and midfield band (18241980 MHz) for wireless power transfer simultaneously. The size of the proposed antenna is 0.068 λg × 0.048 λg × 0.0036 λg and it is the smallest size of any triple-band implantable antenna ever devised without using shortening vias. Such a compact size is achieved by meandering the shape of the radiating patch and adding open-ended ground slots. Unlike most miniaturized implantable antennas reported in the available literature, no shortening pin is used and this makes the fabrication of the antenna very easy. The bandwidths measured in minced pork muscles are 14% and 24% in the lower and upper ISM bands, respectively, and 12% in the midfield band. The maximum values of the realized gain of the proposed antenna obtained in the heterogeneous skin phantom at 915, 1900, and 2450 MHz are -27.2, -22.2, and -19.9 dBi, respectively. In addition, the specific absorption rates (SARs) in the heterogeneous skin and muscle tissues at the three resonance frequencies are calculated and show compliance with the IEEE standards for ensuring human safety. Finally, the range of the biotelemetry link is evaluated by calculating the wireless communication link budget at data rates of 7 kbps, 100 kbps, and 10 Mbps at the resonance frequencies.