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Small-Force Measurement by Photo-Elastic Transducer

Transducer is a device that converts one form of energy to another. It is also the collective term used for both sensors which can be used to sense a wide range of different energy forms such as movement, electrical signals, radiant energy, thermal or magnetic energy etc., and actuators which can be used to switch voltages or currents. Transducer is often employed at the boundaries of automation, measurement, and control systems.

In this paper, the author focused on the characterization and validation of a force transducer which converted force into frequency by photo-elastic effect in a solid-state laser. And the basic information about mass standard used in mass metrology and low-force measurements was introduced, which showed that in mass metrology, the most sensitive transducers had a limited range of linearity and could only be used to measure small differences among artifacts of nearly equal mass.

The author conducted a prospective study by using a monolithic Nd:YAG laser from a cylindrical crystal with flat end faces. He presented the general layout of the experiment and some indications of the configuration of the photo-elastic sensor of force via figures. And the calibration with micro-masses and sensitivity of the photo-elastic force sensor were described. Besides, the beat frequency was also expressed.

The investigation result indicated that the sensitivity of this kind of force sensor can reach high values by reducing the dimensions of the monolithic laser. And compared to theory, the result also showed that sensitivity of about 110 MHz·N‒1 , in the case of a (2 × 2) mm laser rod sensor, can be obtained. Also, the response of the photo-elastic force sensor was quasi-linear in the measurement range.

In a conclusion, the reported results were in a good mutual agreement but showed notable discrepancies with theoretical predictions, especially for high sensitivities obtained when the dimensions of the laser sensor are small.

Article by Naceur-Eddine Khelifa, from Laboratoire Commun de Métrologie, Paris, France.

Full access: http://mrw.so/hdPf1    
Image by jvwolf91, from Flickr-cc.



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