Magnetic-Based Polydimethylsiloxane Microspheres for Magnetic Field Measurement

Magnetic-based polydimethylsiloxane microspheres (MPMs) are fabricated and its applications for measurement of magnetic field are investigated. The MPMs are prepared by first incorporating the uniformly sized Mn
₃
O
₄
nanocrystals into polydimethylsiloxane (PDMS) matrix and then using a self-assembling method to obtain a chain of microspheres on the fiber taper. The MPMs are regarded as optical resonators, demonstrating whispering gallery modes (WGMs) with a high
$Q$
factor in the 1310-nm band. Experimental results show that the resonance wavelengths of the WGM spectra depend on the strength of the magnetic field since the change in the applied filed causes the mechanical deformation of the MPMs, leading to a shift in the resonant wavelength of the resonator. Using as magnetic field sensors, the performances of the MPMs in terms of sensitivities and measurement ranges have been optimized. Thus, the sensitivity of 101.9 pm/mT and the measurement range up to 8 mT are achieved with an MPM (
$\sim 270~\mu \text{m}$
in diameter). Besides, the performance of the MPM after two-week storage is analyzed, showing the excellent long-term stability.