Microscale magnetic devices have garnered significant attention due to their non-volatility, which is the result of energy stored in the spinning of electrons. The key to operating magnetic devices is to control the magnetization, and among all the mechanisms, the strain-mediated multiferroics approach is particularly energy efficient. This approach uses a piezoelectric-magnetoelastic heterostructure, where an input voltage is applied on a piezoelectric thin film to actuate an acoustic response. This film is coupled with magnetostrictive elements, so the induced strain reorients the magnetization vector. This reorientation is currently widely used for storing information like in memory applications. In this dissertation, it will be explored for other applications such as controlling magnetic beads for cell manipulation and producing an electromagnetic signal as an acoustically actuated antenna.Chapter 1 introduces the concept of multiferroics and the theoretical foundations required for analysis and design. Techniques will be presented for both simulation and fabrication aspects. Several published papers on relevant topics will be reviewed. These works indicate that the multiferroics approach has great potential for achieving energy efficiency and miniaturization.
Chapter 2 focuses on the magnetic device's use in a cell manipulation application. A design for a magnetically activated cell sorting device is proposed, and the analytical and experimental work involved is described in detail. A multiphysics finite element model was built in order to estimate the time-dependent magnetic forces and the movement trajectory of the cells. This model was used to design the device after verifying its accuracy against experimental values. Three different designs are investigated: (1) a single magnet for cell manipulation, (2) a single magnet for individual cell manipulation, and (3) an array of magnets for individual cell manipulation. The final array design is able to individually control each magnet to individually capture or release a single cell as required for time-dependent post processing.
Chapter 3 focuses on the use of multiferroics in an acoustically actuated antenna application. A design is proposed and all analytical and experimental work involved is described in detail. The device is based on magnetoelectric coupling and operates at acoustic resonance in a standing shear bulk wave mode. The methodology for combining the device's micromagnetic, solid mechanics, and electromagnetic behavior is discussed. Multiphysics models are built in order to estimate the mechanical and magnetization response in both transmission and reception modes for the proposed design. The radiation of the magnetic material, the piezoelectric substrate, and the parasitic effects of the wires are investigated. The fabricated device successfully demonstrates mechanical resonance and magnetoelectric coupling. The results show the device's potential for miniaturization and its promise for future compact antenna design.
Finally, Chapter 4 summarizes the contents and the main results of the dissertation.