A Miniaturized Meander Line Implantable Antenna at 1.4 GHz WMTS Band for Brain Implants and Biotelemetry Applications

This paper presents a compact implantable antenna based on a meander Line geometry, specifically tailored for brain implants that monitor Intracranial pressure and support biotelemetry within the WMTS band of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1395-1400 \text{MHz}$</tex>. The antenna occupies only <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$17.61 ~\text{mm}^{3}$</tex>, with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6.8 ~\text{mm} \times 6.8 ~\text{mm}$</tex> surface area and a thickness of 0.381 mm. It is built using Rogers RT/Duroid 5880 (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon_{r}=2.2, \tan \delta=0.0009$</tex>) as both the substrate and superstrate. The design incorporates a meandered line as the radiating element along with a shorting pin to improve impedance matching, reduce size, and extend bandwidth. Testing with both a standardized brain phantom and a seven-layer brain phantom confirmed a maximum gain of -13.77 dBi and an impedance bandwidth of 395 MHz. Specific Absorption Rate (SAR) evaluations yielded <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$253.856 ~\mathrm{W} / \text{kg}$</tex> for 1 g and 48.62 W/kg for 10 g in the seven-layer phantom, while a realistic human head model produced SAR values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$112.6 ~\mathrm{W} / \text{kg}(1 ~\mathrm{g})$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$38.65 ~\mathrm{W} / \text{kg}(10 ~\mathrm{g})$</tex>. All SAR measurements meet IEEE safety standards, ensuring the safety of brain tissue. Additionally, a link budget analysis over a 10 -meter distance was conducted to verify the stability, reliability, and coverage of the biotelemetry link.