An ultra-miniaturized dual-band circularly polarized implantable antenna for neuromuscular prosthetic interfaces

This research article presents an ultra-miniaturized dual-band circularly polarized implantable antenna, operating in the 915 MHz and 2,450 MHz Industrial, Scientific, and Medical (ISM) bands. The antenna has an electrical dimension of 0.0122λ _o  × 0.0122λ _o  × 0.00099λ _o , making it suitable for space-constrained neuromuscular implantable medical devices.

Dual-band operation and antenna miniaturization are accomplished through the integration of π, trapezoidal, and I-shaped slots. Circular polarization (CP) is generated by employing asymmetric L-shaped hook slots and a mirrored Y-slot. This design eliminates the need for vias, ground-plane alterations, and intricate feeding techniques.

The proposed design achieves right-hand circular polarization (RHCP) at 915 MHz and left-hand circular polarization (LHCP) at 2,450 MHz. Prototype measurements conducted in a muscle-mimicking solution indicate reflection coefficient bandwidths of 10.33 % and 5.8 %, axial ratio bandwidths of 8.5 % and 4.9 %, and gains of -21.3 dBi and -20.9 dBi at the lower and upper ISM bands, respectively. Specific absorption rate (SAR) analysis yields peak values of 224.6 and 208.2 W/kg (1 g average) and 43.44 and 33.6 W/kg (10 g average) at 915 and 2,450 MHz, confirming compliance with implantable antenna safety standards. Link margins exceeding 20 dB are obtained at transmission distances of 3.34 m and 11.09 m for the respective ISM bands.

The proposed implantable antenna features an ultra-miniaturized size and supports dual-band operation with CP property. Experimental validation confirms that the proposed dual-band CP implantable antenna is well suited for neuromuscular prosthetic interface applications.