Miniaturized Magnetostrictive Antennas for Wireless Sensing Applications

Abstract

Magnetostrictive (MES) antennas have been widely used for wireless sensing applications. Miniaturization of MES antennas can open new applications in in-vivo wireless sensing with higher spatial resolution and solve challenges involved in the miniaturization of conventional electromagnetic antennas. In this thesis two different methods have been explored for easy and fast fabrication of miniaturized MES antennas down to sub-mm sizes from the amorphous magnetostricive film Metglas 2826 MB and their advantages and disadvantages have been studied. Laser micromachining is shown to be a more versatile method compared to fabrication using Diesaw to fabricate antennas of different shapes easily. The frequency response of the fabricated antennas is first studied in air and characterized using Finite Element Analysis and analytical modelling to characterize the quality factor and magnetomechanical coupling efficiency. The antennas are then tested in water to understand the effects of viscous damping on antenna response and check the feasibility of sensing in liquid or wet environment. After characterization, a highly sensitive pH sensitive MES antenna of size 6 mm x 1 mm x 28 um with a sensitivity of 15 kHz/pH is fabricated using a pH sensitive copolymer of Acrylic Acid and Isooctyl Acrylate and characterized using solutions of different pH. The challenges involved in further miniaturization of the sensors and future work is also discussed.