Self-Quadruplexing Antenna for Scalp-Implantable Devices

This article presents a compact self-quadruplexing antenna for scalp-implantable devices. The proposed self-quadruplexing antenna operates at 168 MHz [industrial, scientific, and medical (ISM) band], 433 MHz (ISM band), 915 MHz (ISM band), and 1400 MHz [wireless medical telemetry service (WMTS) band] when Ports 1, 2, 3, and 4 are activated, respectively. The proposed antenna is simulated inside a rectangular device in the head of a human phantom. The suggested antenna comprises four individually excited semicircular meandered resonators with a common ground plane. The compactness of the design is achieved using a high dielectric substrate and using semicircular meandered resonators. The meandered resonators enlarge the current path, resulting in significant miniaturization. As a result, the proposed antenna consumes a small volume of
$12\,\, \times 14.5 \times 0.13 = 22.62$
mm3. The coupling among all ports is also minimized using an ultrathin substrate. Consequently, the mutual coupling between any two ports is less than −21.8 dB. It provides a peak gain of −36.24, −34.78, −31.39, and −30.10 dBi at 168, 433, 915, and 1400 MHz, respectively. The link budget and specific absorption rate (SAR) analyses are performed to see the possible applications in the head implant, which show promising results. The 10-g SAR values of 0.017, 0.016, 0.014, and 0.013 W/kg are realized at 168, 433, 915, and 1400 MHz, respectively. Based on a link margin (LM) ≥10 dB, the proposed self-quadruplexing antenna can communicate up to 20, 17.5, 12, and 9 m at 168, 433, 915 and 1400 MHz, respectively (at
$B_{r} = 120$
Mbps). Furthermore, the simultaneous transmit and receive (STAR) ability of this antenna is validated using software-defined radios (SDRs). To the best of the authors’ knowledge, this is the first-ever self-quadruplexing implantable antenna designed so far.