Piezo-Optical Transducer for High Sensitive Strain Gauges

A piezo-optical transducer of a new design for high-sensitive strain gauges is presented. The transducer photoelastic element (PE) has a cruciform shape that allows increasing the sensitivity to deformation using an inexpensive and technological fused quartz. This material has no plastic deformation and its elastic properties do not change with time. Thus, there is no hysteresis and parameters degradation with time in comparison with strain-resistive sensors. The high compression damage threshold provides a high overload resistance, and therefore a wide dynamic range of deformation measurement. In the mounted state, the PE is under the preliminary compressive stresses along two orthogonal directions, which ensures: 1) a reliable glueless force-closure between the PE and the load element; 2) its operation both in compression and in tension; and 3) practically excludes the temperature dependence of the device output signal. The transducer output signal generating was studied with the help of accurate numerical simulation. The simulated transducer gauge factor was 7389. The experimentally measured gauge factor was 7340, which agrees to the simulated one and validates the simulations, and is more than three orders of magnitude higher than values 2–6 for the strain-resistive gauges. The minimum detectable absolute and relative strain values were $3.5\times 10^{-12}$ m and $2.7\times 10^{-10}$ at a PE diameter 12 mm. Dynamic range was at least 6 $\times \,\,10^{4}$ . The transfer function slopes were $441~\mu \text{A}$ /N and $36.6~\mu \text{A}$ /nm. The transducer main characteristics are superior to those of the most sensitive strain-resistive load cell used only to calibrate the deadweight machines.