High-resolution magnetic field biosensor based on optical resonators

Abstract

In this paper, we study the effect of using magnetorheological polydimethylsiloxane (MR-PDMS) spheres as micro optical resonators. Recently, optical sensors based on whispering gallery mode (WGM) have drawn much attention due to the high optical quality factors they can exhibit with several applications in a variety of fields. The modes of such resonators are highly affected by changes in morphology of the cavity (for instance: shape, size or refractive index) caused by a change in the physical input we are aiming to measure. In the presence of a magnetic field, the embedded particles become polarized, exerting forces upon one another because of dipolar interactions. In our case, these forces lead to changes in the morphology of the resonator through mechanical deformation of the size, which in turn causes WGM shifts. Experiments were conducted on earthworms for the similarity of the nerve impulses flowing which mimic those of human body specifically the brain and ultra-small magnetic fields can then be detected. Moreover, the coupling of a MR cantilever beam to the optical resonator leads to additional induced forces for the same magnetic field input and thus increasing the resolution by 3 orders of magnitude. Results indicate that the proposed sensor can be used for magnetic field detection with high quality factor and resolution.