A Triple Band Flexible Antenna based on Asymmetric Spiral Split Rings Coupled to External Loop

In this paper a small flexible antenna is designed and proposed for implantable applications in the 401-406 MHz Medical Device Radio Communication Service (MedRadio), 433-434.8 MHz, and 2.4-2.5 GHz Industrial Scientific Medical (ISM) bands. The proposed antenna has a unique structure exploiting spiral split rings to achieve both miniaturization and excellent impedance matching (S11< -10 dB) within the 401-406 and 433-434.8 MHz bands. For resonance in the 2.4-2.5 GHz ISM band, the spiral split rings are coupled with an external feeding loop ring. This comprehensive band coverage enables the antenna to facilitate data transfer, wireless power charging, and saving. The proposed antenna has obtained a gain value of -22.44, -22.07, and -25.66 dBi at 403 MHz, 433 MHz, and 2.45 GHz respectively in a simplified body model of 400×50×50 mm3. Additionally, this antenna design has demonstrated robust performance in different simplified body models. Furthermore, the antenna’s simple structure makes it a strong candidate for applications in the field of biomedical implants.