Graduation Year


Document Type




Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department


Major Professor

Manh-Huong Phan, Ph.D.

Committee Member

Hariharan Srikanth, Ph.D.

Committee Member

Sarath Witanachchi, Ph.D.

Committee Member

Sanjukta Bhanja, Ph.D.


Co-based microwires, magneto-LC resonance sensor, real-time monitoring


The scientific studies associated with material engineering and device miniaturization are the core concepts for future technology innovation. The exploring and tailoring of material properties of amorphous magnetic microwires, recently, have revealed remarkable high sensitive magnetic field sensitivity down to the picoTesla regime at room temperature. This superior magnetometer is highly promising for active sensing and real-time monitoring building block for modern industrial devices and healthcare applications.

The low-field, high sensitivity regime of the GMI response over a wide frequency range (1 MHz - 1 GHz) in the Co-rich melt-extracted microwires was optimized through novel Joule annealing methods (single- and multi-step current annealing techniques). Optimization of current value through multi-step current annealing (MSA) from 20 mA to 100 mA for 10 minutes is the key to improving the GMI ratio, and its field sensitivity up to 760% and 925%/Oe at f ≈ 20 MHz. The respective GMI ratio and field sensitivity are 1.75 times and 17.92 times higher than those of the as-prepared counterpart. The employment of the MSA technique successfully enhances the surface domain structures of the Co-rich microwires. This alternative tailoring method is suitable for improving the GMI sensitivity for a small field detection. The high sensitive response of the GMI to a weak magnetic field is highly promising for biomedical sensing applications.

Real-time monitoring of position, motion, and rotation of a non-stationary object is crucial for product packaging, conveying, tracking, and safety compliance in industrial applications. The effectiveness of current sensing technology is limited by sensing distance and messy environments. A new class of high-frequency GMI-based sensor was designed and fabricated using the optimal Co-rich microwire. The impedance spectrum from the optimal sensing element showed a high GMI ratio and high field sensitivity response at low magnetic fields. The GMI sensor based longitudinal effect was found to be more sensitive than the commercially available Gaussmeters. The practical utility of the high sensitivity of the miniaturized sensor at weak magnetic fields for far-off distance monitoring of position, speed and gear rotating was demonstrated. This GMI-based sensor is highly promising for real-time position detection, oscillatory motion monitoring, and predictive failure of a rotating gear for industrial applications.

Monitoring the rate of respiration and its pattern is crucial to assessing an individual’s health or progression of an illness, creating a pressing need for fast, reliable and cost-effective monitors. A new sensor based on a magnetic coil, which is made of Co-rich melt-extracted microwire for the detection of small magnetic fields was fabricated. The 3 mm diameter coil is wound from a Co-rich magnetic microwire. Unlike some typical solenoids, the MMC is sensitive to small magnetic fields due to a significant change in impedance attributed to the high-frequency giant magneto-impedance (GMI) effect. An application of the MMC sensor for the detection of a position-varying source of a small magnetic field (~0.01 – 10 Oe) in real-time bio-mechanical movement monitoring in human was demonstrated. This newly developed MMC magneto-LC resonance technology is highly promising for active respiratory motion monitoring, eye movement detection and other biomedical field sensing applications.