MAGNETOELECTRIC AND OPTO-MECHANICAL MAGNETIC SENSING
Open Access
- Author:
- Freeman, Eugene
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 27, 2017
- Committee Members:
- Srinivas A Tadigadapa, Dissertation Advisor/Co-Advisor
Srinivas A Tadigadapa, Committee Chair/Co-Chair
Jerzy Ruzyllo, Committee Member
Susan E Trolier-Mckinstry, Committee Member
Steven Schiff, Outside Member - Keywords:
- Magnetoelectric
Whispering Galley Mode
Passively Powered
Wireless
Quartz
Micromachined
Magnetometer
Chip-scale
Optomechanical
Glassblowing - Abstract:
- Magnetic sensors are of ever increasing relevance to modern society. Magnetic sensors have found practical applications in smartphones, aerospace, automotive, industrial and biomagnetic sensing. Most applications are navigational owing the earth’s relatively stable magnetic field, although rotational and speed sensors are found in automotive and industrial settings. Availability of low-cost and reliable magnetometer technologies have contributed their ubiquitous nature. However, the most sensitive magnetic fields emitted from the brain can only be detected by superconducting quantum interference devices (SQUIDs), which require cryogenic cooling to maintain a superconducting state and require magnetic shielding. An inexpensive room temperature magnetometer technology capable of magnetoencephalography (MEG) and other biomagnetic signals is an active area of research. This dissertation provides three significant contributions to this problem. First, a detailed and comprehensive set of methods are explored and demonstrated in an effort to optimize the magnetoelectric magnetometer, a promising magnetometer technology that may replace SQUIDs in some applications. Second, a novel chip-scale whispering gallery mode magnetometer is proposed, modeled using a finite element simulator and experimentally demonstrated with a 6 × 10−8 T/√Hz limit of detection (LOD) and the potential for much lower LOD is demonstrated. Third, a novel passively-powered micromachined quartz magnetoflexoelastic magnetometer is experimentally demonstrated and the effect of separation distance from a coupling antenna is quantified and modeled using a modified Butterworth-van Dyke model. This device has the potential to be a wireless implantable sensor that is much closer to the biomagnetic signal source. Via optimization of the mechanical coupling, flux concentration, alignment of Metglas magnetic domains, and a (1-x)[Pb(Mg 1/3 Nb 2/3 )O 3 ]-x[PbTiO 3 ] (PMN-PT) d 33 macro fiber composite to improve piezoelectric response; resulting in a magnetic field sensitivity of 50 pT at 20 Hz for a d33 Metglas/PMN-PT laminate. Mechanical coupling is improved by reducing the thickness and porosity of the epoxy. The Metglas residual stress reduction and easy axis alignment is accomplished by a 30 minute 400 ◦C anneal under a 160 mT magnetic field in an oxygen free environment. Resulting in the highest reported magnetostriction coefficient of 79.3 µm/m·mT. Finally, different piezoelectric materials and configurations such as single crystal PMN-PT and macro fiber composite PMN-PT are explored. A novel magnetometer consisting of chip-scale whispering gallery mode resonators with high-Q factors (>10 7 ) are realized using MEMs fabrication techniques. A permanent magnet is elastically coupled to a whispering gallery mode borosilicate microbubble. Magnetic forces from applied external magnetic fields induce deformation in the microbubble which can be sensitively monitored through changes in the optical resonance characteristics. The force is calculated and the the resultant deformation is simulated in the microbubble. The effect of different permanent magnet orientations and microbubble shell thickness is experimentally investigated and modeled. A sensitivity of 1.9 GHz/mT on a microbubble with 1.1 µm shell thickness is experimentally demonstrated along with a limit of detection of 6 × 10−8 T/√Hz at 30 Hz, which was limited by a noisy laser system. Finally, this dissertation demonstrates the passively-powered wireless operation of a magnetoflexoelastic magnetometer. The wireless coupling is achieved using coupled near-field resonant loop antennas, which excite the high Q-factor (∼6000) micromachined quartz resonator. Magnetostrictive curves are acquired both wired and wirelessly at distances up to 45 mm to confirm the phenomenon is magnetoflexoelastic in nature. A 49.1 Hz/Oe sensitivity was achieved in wireless operation and the ultimate detectable limit was 7 µT at 0.5 Hz. Highly sensitive, wirelessly powered, and maintenance-free sensors are of great interest to the biomedical, geological, hazardous environment, and traffic control communities.