Novel Compact Antennas for Biomedical Implants and Wireless Applications

GOSALIA, KEYOOR. Novel Compact Antennas for Biomedical Implants and Wireless Applications. (Under the direction of Dr. Gianluca Lazzi.) Novel design methodologies and implementation techniques for antennas with an extremely small form factor (kr ¿ 1; k is the wavenumber and r is the radius of enclosing spherical volume) are presented. These size reduction techniques are applied to design antennas for two emerging fields: Short (or long) range wireless connectivity and human body implants (prosthetic devices). The first test bed describes compact microstrip patch antennas employing polarization diversity for optimizing the available channel bandwidth in conventional wireless communications. Extremely small antennas (for implantation in an eye ball) operating at microwave frequencies for a visual prosthesis are designed and implemented for the second test bed. The visual prosthesis under consideration is an implantable prosthetic device which attempts to restore partial vision in the blind (patients suffering from retinal degeneration) by artificial stimulation of the retinal cells. Mutually exclusive power and data transfer via a wireless link with the implanted device is proposed where inductive coil coupling transfers power at low frequencies while data communication is performed using extraocular and intraocular antennas at microwave frequencies. The microwave data telemetry link is characterized computationally (using Finite Difference Time Domain-FDTD) and experimentally with appropriately sized external and implanted antennas. It is observed that the head and eye tissues act as a form of dielectric lens and improve the coupling performance between the two antennas (with intraocular antenna embedded in the eye ball) as compared to coupling in free space. The data telemetry link is characterized with novel small microstrip patch and planar wire dipole as intraocular antennas. An electromagnetic and thermal analysis of the operation of such a visual prosthesis is performed. Electromagnetic power deposition in the head is evaluated in terms of Specific Absorption Rate (SAR). Temperature rise in the tissues is characterized by computationally discretizing and implementing the bio-heat equation in three dimensions in an anatomically accurate head model. Novel Compact Antennas for Biomedical Implants and Wireless Applications