3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg" display="inline" id="d1e413"> <mml:mo>×</mml:mo> </mml:math> 3 interferometers for acoustic detection: Experimental analysis and comparison

This paper presents the development, application and comparison of interferometers using 3 × 3 configuration for acoustic assessment. The comparison is performed considering Michelson interferometer (MI) and Sagnac interferometer (SI) under frequency sweep from 250 Hz and 16 000 Hz. The results indicated higher signal-to-noise ratio (around 65 dB and 75 dB, for MI and SI, respectively) and sensitivity of the SI approach (4.68 ± 0.91 deg/Pa) when compared with MI (1.22 ± 0.74 deg/Pa). Then, the pulse detection tests are made in different configurations for the interferometers to verify the acoustic response of a well-known aluminum plate sample. Considering the MI, the tested configurations are both arms in the same side of the sample, arms at opposite sides of the sample and only one arm in contact with the sample. Similarly, for the SI, the configurations with the interferometer in contact and without contact with the sample are compared. In this test, both interferometers are able of detecting the resonance frequency (around 9400 Hz), where the MI configuration with one arm at each side of the sample is the one with the highest signal variation (392.10 ± 134.56 deg) among the tested configurations in MI. In addition, the SI in contact with the sample presented the highest signal variation (59.83 ± 21.10 deg) among the ones tested. Therefore, both approaches resulted in highly sensitive sensors able of detecting acoustic signals in a wide frequency range, which enable a myriad of applications in environmental sensing, acoustic emission detection for materials characterization and structural health monitoring • Development of interferometers using 3 × 3 configuration for acoustic assessment. • Comparison between Michelson and Sagnac interferometers under wide frequency sweep. • Pulse detection tests to verify the acoustic response of metals.