Load Cell Based on Binocular Test Body and SAW Strain Sensor With a Radio Frequency Reflectometry Read-Out System

The load cell is an indispensable component of many engineering machinery and industrial automation for measuring and sensing force and torque. In this paper, we propose to investigate a force sensor design combining Surface Acoustic Wave (SAW) strain sensor with binocular load cell structure. For this purpose, we use a binocular test body instrumented with both resistive strain gauge as a reference and SAW strain sensor. The system enables the generation of extremely localized and accurate positive and negative strains. Static and dynamic measurements are performed using calibrated weights and a shock hammer respectively. For SAW sensor, a one-port resonator with frequency operation in the range of 410MHz was fabricated and mounted on the test body. For electronic conditioning, we use a low-cost RF electronic conditioning based on radar architecture using the integrated circuit AD8302. The system enables the measurement of S-11 reflection coefficient (module and phase) with sensitivity and noise spectral density of (29 mV/dB, 250 nV/root Hz) and (10 mV/degrees, 83 nV/root Hz) respectively. The SAW sensor mounted on body proof was successfully tested in static and dynamic mode using this electronic architecture. The results show good linearity, sensitivity values of 0.023 mV/ppm and 0.09 mV/ppm were obtained for amplitude and phase measurements respectively. The dynamic response was performed using a shock hammer and a comparison with conventional strain gauge shows a good agreement.