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

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

Development of a mechanical strain sensor based on time reversal of ultrasonic guided waves

The development of a strain sensor based on the time reversal focusing technique is presented. The sensor is composed by a strip of aluminum plate with two ultrasonic piezocomposite transducers bonded at the ends of the plate. The time reversal technique acts as a dispersion compensator of the guided waves propagating in the plate, allowing time recompression of the waves. When the plate is subjected to a longitudinal traction, a time reversal focusing is performed between the transducers in order to detect the change in the focus due to strain. The strain can be evaluated by measuring the change of the amplitude and shift in the time of flight, and comparing them with a reference signal obtained at zero strain state. In order to improve the systems sensitivity, 2-2 piezocomposite transducers designed to operate between 0.2 to 3.0 MHz are used. Experiments are conducted by applying strain up to 150 μ-strain. The results show an increase in sensitivity when compared with the results of the conventional mono-element transducer greater than 200%. Results presented here can be used in the project of stress monitoring transducers and structural health systems