A Tissue-Independent Implantable Antenna For Frequency-stable Biotelemetry in the ISM Band

This paper presents the design and simulation of a 2.45 GHz (ISM band) microstrip patch antenna, utilizing a 0.254 mm Rogers 6010LM substrate (ε<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> = 10.2) and an equally thick Teflon superstrate (ε<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> = 2.1), for tissue-independent implantable biotelemetry. A 3-layer tissue model comprising 4 mm skin, 5 mm fat, and 21 mm muscle is initially simulated in CST Microwave Studio™. The antenna without superstrate, implanted 2 mm below the skin-air interface, initially resonates at 2.457 GHz. Incorporating the optimized superstrate tunes the resonance to 2.447 GHz and significantly enhances the antenna’s efficiency (from 0.68% to 2.76%), impedance matching (|S<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf>| from −20 dB to −38 dB), and realized gain (from −15.6 dBi to −9.7 dBi). Subsequently, the cross-tissue evaluation of the skin-optimized, superstrate-loaded antenna at 2 mm depth below each interface demonstrates resonance at 2.492 GHz (fat) and 2.438 GHz (muscle). The antenna’s frequency stability, defined by its overlapping −10 dB in-tissue bandwidth, yields ISM bandwidth overlaps of 64.3% in skin, 74.2% in muscle, and 16.7% in fat. SAR analysis confirms compliance with the IEEE standards, validating its robust tissue-independent operation and suitability for reliable subcutaneous and intramuscular biotelemetry applications.