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Optical torsional sensor for Robotic Applications

Spinning optical resonator sensor for torsional vibrational applications measurements

Project Lead

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Assoc. Prof. Dr. Eng. Amir R. Ali 

Project Members

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Andrew Gatherer, B.Sc. (2016)

Brief description for the project:

Spinning spherical resonators in the torsional vibrational applications could cause a shift in its whispering gallery mode (WGM). The centripetal force acting on the spinning micro sphere resonator will leads to these WGM shifts. An analysis and experiment were carried out in this project to investigate and demonstrate this effect using different polymeric resonators. In this experiment, centripetal force exerted by the DC-Motor on the sphere induces an elastic deformation of the resonator. This in turn induces a shift in the whispering gallery modes of the sphere resonator. Materials used for the sphere are polydimethylsiloxane (PDMS 60:1 where 60 parts base silicon elastomer to 1 part polymer curing agent by volume) with shear modulus (G=1 kPa), (PDMS 10:1) with shear modulus (G=300 kPa), polymethylmethacrylate (PMMA, G=2.6*10^9 GPa) and silica (G=3*10^10 GPa). The sphere size was kept constant with 1mm in diameter for all above materials. The optical modes of the sphere exit using a tapered single mode optical fiber that is coupled to a distributed feedback laser. The transmission spectrum through the fiber is monitored to detect WGM shifts. The results showed the resonators with smaller shear modulus G experience larger WGM shift due to the larger mechanical deformation induced by the applied external centripetal force. Also, the results show that angular velocity sensors used in the torsional vibrational applications could be designed using this principle.

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Challenges of the project:

The results of this study were to examine the centripetal deformation of polymer microspheres for tensional vaibrational applications. The results show that polymeric resonators may experience WGM shift when exposed to an external angular velocity. The analytical results agree reasonable well with the numerical results. By increasing the angular velocity of the metallic disk increases the change in the wavelength, which has been shown in this paper. Also, this simulation corroborates the fact that the type of material used has farm more of an effect on the change in wavelength of the light than the eccentricity, but that the eccentricity has substantial effect. Also the results show that angular velocity sensors could be designed using this principle.