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ESE PhD Thesis Defense: “Multiferroic Micro Electromechanical Systems for Magnetic Sensing and Wireless Power Transfer in Biomedical Applications”

April 16 at 9:00 AM - 11:00 AM

Multiferroic micro-electromechanical systems (MEMS) enable small, room temperature, low power magnetic sensing and wireless power transfer (WPT) in biomedical applications. Current biomagnetic sensing relies on sensitive magnetometers like superconducting quantum interference devices (SQUIDs), but their reliance on cryogenic temperatures is undesirable.


This thesis presents the theory, design, microfabrication, and characterization of multiferroic MEMS magnetic sensors and WPT devices. Iron cobalt/silver (Fe50Co50/Ag) magnetostrictive material is coupled to piezoelectric aluminum nitride (AlN) to form a multiferroic sensor. Low frequency biomagnetic signals are upconverted around the length-extensional beam’s 7-16 MHz mechanical resonance to provide Q enhancement to the sensitivity. The up conversion exploits a nonlinear phenomenon of magnetostrictive materials with applied mechanical strain. For two devices studied, modulated sensitivities of 58.4 mA/T and 37.7 mA/T were observed along with resolutions of 5.03 nT/√Hz and 2.72 nT/√Hz over a bandwidth larger than the biomagnetic frequency spectrum (0.1Hz to 1kHz). The sensors’ sensitivity was limited by Duffing nonlinearity and the relatively low piezoelectric coefficients of AlN.


To improve sensitivity, magnetoelectric sensors were fabricated using (Fe0.5Co0.5)0.92Hf0.08 coupled to 28% aluminum scandium nitride (Al0.72Sc0.28N). Increasing sensitivity improved the resolution from 5.03 nT/√Hz to 2.16 nT/√Hz. To delay the onset of thermal Duffing nonlinearity, various anchoring tether lengths were explored in Fe0.5Co0.5/Ag – AlN magnetoelectric sensors to provide better heat conduction away from the structure. Also, silicon dioxide (SiO2) was added to compensate the temperature coefficient of frequency (TCF). Larger achievable strain was verified before the onset of Duffing nonlinearity, providing increased modulation of the Fe0.5Co0.5/Ag and a resolution of 1.11 nT/√Hz, an 86% improvement when compared to a long tether device with the same layer stack (8.02 nT/√Hz) and a 78% improvement over the initial (Fe50Co50/Ag) – AlN long tether devices with no SiO2 thermal compensation.


WPT measurements were taken using (Fe50Co50/Ag) – AlN magnetoelectric devices. By sending a magnetic field at the device resonance frequency, optimal WPT can be achieved. Devices were packaged with a magnetic bias circuit and the output power was measured. For a device at 7.44MHz, an output power of 126.8 nW and a power density of 1196.2 uW/mm3 is projected when measuring with both electrodes.

Michael D’Agati

PhD Candidate

Michael D’Agati is a current PhD candidate in Electrical Engineering at the University of Pennsylvania under Dr. Troy Olsson. Currently, Michael’s research focuses on the investigation of multiferroic MEMS magnetic sensors and wireless power transfer devices for biomedical applications. He received his Bachelor of Engineering (B.E.) degree in Electrical Engineering from Stony Brook University in 2018 and his Master of Science (M.S.) degree in Electrical Engineering from the University of Pennsylvania in 2020. In 2016 he won the prestigious Goldwater Scholarship for his work on all-carbon, non-toxic supercapacitor electrodes, utilizing carbon nanotubes and graphene for implantable energy storage applications. In 2020, the National Science Foundation awarded him the Graduate Research Fellowship Award for his research on multiferroic sensors and wireless power transfer systems. Google Scholar Link: https://scholar.google.com/citations?user=yHKinioAAAAJ&hl=en&oi=ao


April 16
9:00 AM - 11:00 AM
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Electrical and Systems Engineering
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Fisher Bennett Hall, Room 401
3340 Walnut Street
Philadelphia, PA 19104 United States
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