Design of Compact Microstrip Antenna for Biomedical Applications

Abstract

Implantable Medical Devices (IMDs) have recently become a popular research area because of their potential to improve one’s quality of life. IMDs are the devices that are implanted into human tissues for diagnostic, monitoring, and therapy purposes. Biotelemetry for IMDs enables bidirectional data transfer and control signal reception without the need for cables attached to bedside monitors. Because of the rising number of age-related symptoms and the need for telemedicine in old age centers, IMD sector is expected to grow. Among all the components used in these devices, an antenna is a fundamental element for wireless data transmission outside the human body. The current study examines implantable biomedical antennas in depth. One of the biggest challenges in IMDs is that the human body changes the antenna’s general properties and absorbs majority of its radiation. Moreover, at lower frequencies it is difficult to lower the proportions of the antenna to meet the size requirements of an implantable device. The antenna material should be biocompatible in order to protect the surrounding body tissues from allergic reactions and the proposed antenna design must also exhibit more expanded SAR distribution to meet the IEEE safety standards. Therefore, this thesis focuses on design approaches, constraints, simulation techniques and manufacturing and testing of implantable antennas. Compact and biocompatible antennas have been fabricated which can yield the performance parameters good enough to meet the safety standards and size requirements. In-silico, in-vitro and ex-vivo techniques are used for testing and validation of antenna prototypes. For in-vitro testing, skin mimicking solution has been prepared for testing of proposed antenna prototype at particular frequency bands, whereas chicken sample is utilized for ex-vivo testing. Four antennas are designed, fabricated and tested for implanting inside human body at ISM (2.4-2.48 GHz) and MICS (402-405 MHz) bands. To make the antenna compact enough, high dielectric substrate material, slotting technique and shorting pin technique is used. To enhance the biocompatibility of antennas, high dielectric substrates are used for covering the antenna as superstrate layers which also improve some of the antenna parameters especially gain and helps further to reduce the size. All of the proposed antennas in this thesis are novel, miniaturized, within safety limits for human body, can operate successfully within appropriate medical band ranges and have better performance than other antennas available in recently reported literature. This ensures that the fabricated antenna is ready to use with immediate effect and can prove to be helpful in implantable devices for biotelemetry applications.