DEVELOPMENT OF IMPLANTABLE ANTENNAS FOR BIOMEDICAL DEVICES

Abstract

In this thesis, several designed implantable antennas are simulated, fabricated, and tested successfully. To achieve ISM band characteristics with highly compact size, the meandered shaped antenna is expostulated. By considering the weightage of dual band antenna, the proposed design is simulated with serpentine structure of size 12 mm3 . The two ISM bands (lower and upper) with resonating frequencies 0.93 GHz and 2.43 GHz are attained with help of sorting pin and slots on patch surface. In the ISM bands, the impedance bandwidth of 7.7 % and 5.5 % are achieved in lower and higher frequency bands respectively. The acceptable SAR values of 1007.7 and 856.3 are secured in ISM bands at frequencies at 0.93 GHz and 2.43 GHz respectively. To avoid back radiation through ground surface, the ground slots are completely avoided. It has been deeply observed that the designed antenna does not possess ultra-wide band (broad band) status. To increase the impedance bandwidth, magnetodielectric substrates are used. The initial design of serpentine teeth shaped antenna is considered with extremely compact volume of 4.572 mm3 and resonated at frequency of 2.44 GHz (ISM band). This design of antenna is embedded on roger RT duroid material and got impedance bandwidth 190 MHz only from frequency 2.34 GHz to 2.53 GHz. To further enhance the impedance bandwidth, the magnetodielectric substrates such as MDS1, MDS2, MDS3 having different value of relative permeability and relative permittivity are simulated and got impedance bandwidth of 450 MHz, 350 MHz, and 350 MHz at resonating frequencies 1.78 MHz, 2.01 GHz, and 2.13 GHz respectively. This proposed antenna with MDS materials has shown acceptable value of SAR 979.1, 977.8, and 971.6 respectively. This work is carried out with no use of sorting pin and no ground slots. It has shown excellent performance in terms of size and impedance bandwidth. The circular polarization feature of implantable antenna has a lot of demand. Such antennas are not affected by multipath losses and ensure patients not to sit in rigid posture during data transmission. To achieve CP characteristics, the antenna is designed with increased current path length of serpentine structure. The increased path length of patch surface method is adopted to reduce the resonating frequency and size too. The proposed antenna is carried out with volume 12.29 mm3 at resonating frequency of 2.41 GHz. This antenna is circularly polarized with axial ratio bandwidth of 80 MHz from 2.45 GHz to 2.53 GHz. In this xx work, an acceptable value of SAR 901, and gain of -23.45 dB are obtained. The better results are attained with no use of sorting pin, no patch staking techniques, and no metamaterials. A simple square shaped meander design with triangular slots is proposed. The proposed antenna is tested in skin mimicking gel successfully and got results in agreement. In this thesis, multiple antennas are designed with different techniques like spiral, meander, serpentine structure, sorting pin (via through ground) with materials like Rogers RT duroid, and MDS. All designed antennas are fabricated with superstrate layer which avoids direct contact of conducting part of antenna with human tissues. For validation of simulated results, the skin mimicking gel is prepared under specific conditions.