Application of one-bit time reversal technique to mechanical strain monitoring in plates

This paper presents the application of the one-bit time reversal technique to a longitudinal strain sensor. The setup consists of a pair of piezoelectric transducers bonded in the extremities of a strip of aluminum plate. When the plate is subjected to traction, time reversal focalization is performed, the mismatch between the impulse response at initial and strained levels causes loss in the focusing quality. The strain can be evaluated by measuring either the time of flight shift or the amplitude decrease in the focused signal. One-bit time reversal can simplify the electronic device to perform the proposed technique. In this work, the results using one-bit and normal time reversal implementation were compared. Experiments were performed using three different 2-2 piezocomposite transducers pairs at 500, 1000 and 2250 kHz. The longitudinal strain was applied up to 150 μ-strain using a strain gauge as a reference. The time reversal energy efficiency was used as a spectrum figure of merit and obeys the sensitivity behavior. The one-bit time reversal variation provided good focused signal for all experiments and no significant loss in focus quality. Moreover, every configuration showed a higher sensitivity than its normal time reversal version, at least 10% depending on the transducer. The one-bit technique reveals an important enhancement for the method; it holds the natural advantage of being simpler and the benefit of higher sensitivity.