Implantable ferrite antenna for biomedical applications

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University of Alabama Libraries

We have developed an implantable microstrip patch antenna with dimensions of 10×10×1.28 mm, operating around the Industrial, Scientific and Medical (ISM) band (2.4 – 2.5 GHz). The antenna is characterized in skin-mimicking gels and compared with simulation results. The experimental measurements are in good agreement with simulations, having a -16 dB reflection coefficient and -18 dBi realized gain at resonance, with a 185 MHz -10 dB bandwidth. The simulated effects of ferrite film loading on antenna performance are investigated, with comparisons made for 5 and 10 µm thick films, as well as for 10 µm thick films with varying magnetic loss (tan δµ = 0.05, 0.1 and 0.3). Our simulations reveal that the addition of 10 µm thick magnetic layers has effectively lowered the resonant frequency by 70 MHz, while improving return loss and -10 dB bandwidth by 3 dB and 40 MHz, respectively, over the uncoated antenna. Ferrite film coating also improved realized gain within the ISM band, with largest gain increases at resonance found for films having lower magnetic loss. Additionally, the gain (G) variance at ISM band limits, ΔGf(2.5GHz)-f(2.4GHz), decreased from 1.97 to 0.44 dBi for the antenna with 10 µm films over the non-ferrite antenna. The measured dip-coated NiCo ferrite films effectively reduces the antenna resonance by 110 MHz, with a 4.2 dB reflection coefficient improvement as compared to an antenna without ferrite. The measured ferrite antenna also reveals a 6 dBi and 35 MHz improvement in realized gain and -10 dB bandwidth, respectively, at resonance. Additionally, the ferrite-coated antenna shows improved directivity, with wave propagation attenuated at the direction facing the body internal. These results indicate that implantable antenna miniaturization and reliable wireless communication in the operating frequency band can be realized with ferrite loading.

Electronic Thesis or Dissertation
Electrical engineering, Biomedical engineering, Electromagnetics