In the area of implanted medical devices, antenna-enabled biotelemetry is gaining attention for its potential to overcome the limitations of inductive biotelemetry. Such issues include low data rate, restricted communication range, and sensitivity to inter-coil misalignment. At Greece’s National Technical University of Athens, two researchers have developed a two-step design methodology for implantable planar inverted-F antennas (PIFAs). Asimina Kiourti and Konstantina S. Nikita proposed miniature, scalp-implantable PIFAs at 402, 433, 868, and 915 MHz. Their antennas exhibit identical volume of π x 62 x 1.8 mm3 and 10-dB bandwidths of 27, 28, 38, and 40 MHz.
In their efforts to provide insight into implantable PIFA design and the selection of biotelemetry frequency, the researchers studied the design and radiation performance of miniature antennas for integration in head-implanted medical devices operating in both the medical-implant-communication-service (MICS; 402.0 to 405.0 MHz) and industrial-scientific-medical (ISM; 433.1 to 434.8, 868.0 to 868.6, and 902.8 to 928.0 MHz) bands. They then created a parametric model of a skin-implantable antenna and both fabricated and tested a prototype. To speed the design process, the researchers suggest a two-step methodology: approximate antenna design inside a simplified model geometry and then perform Quasi-Newton optimization inside a canonical model of the intended implantation site. The antennas are further analyzed inside an anatomical model of a human head.
The results reveal that the exhibited radiation performance (radiation pattern, gain, specific absorption rate, and quality of communication with exterior equipment) greatly depends on design parameters and operating frequency. The researchers tackle the choice of canonical versus anatomical tissue models for design purposes while addressing patient safety and link budget at various frequencies. For the different stages of antenna design and analysis, both finite-element (FE) and finite-difference-time-domain (FDTD) numerical solvers were used. See “Miniature Scalp-Implantable Antennas for Telemetry in the MICS and ISM Bands: Design, Safety Considerations and Link Budget Analysis,” IEEE Transactions On Antennas And Propagation, Aug. 2012, p. 3568.