Non-contact ultrasonic techniques

Delamination Visualization in CFRP Laminated Concrete Structures Using Pulsed Laser-Based Ultrasonic Propagation Images

“…To filter out the forward wave, the wavenumber filtering concept is applied in this study. First, the wave propagation image is transformed from the time/space domain to the frequency/wavenumber domain by 3D Fourier transform [2]. The time signals are primarily filtered by a bandpass filter to increase the SNR.…”

“…The holography based imaging technique, one of the full-field ultrasonic wave imaging techniques, requires a highly diffusive target surface. Also, holographic images can be obtained clearly in dark environments and hence this method is not suitable for the general purpose of SHM/NDT, although it has non-contact inspection capability [2]. Dynamic responses can be collected by laser Doppler vibrometry (LDV) which measures the vibrational velocity of target structures.…”

Air-coupled ultrasonic through-transmission thickness measurements of steel plates

“…The transmitting and receiving of the ultrasonic waves have also been done using a variety of transduction methods, e.g. electrostatic transducers [17,34], piezoelectric transducers [15,35], electromagnetic transducers (EMAT) [36,14], and pulsed laser [14]. EMAT and laser based methods are strictly speaking not air-coupled ultrasound, as no sound waves are transmitted through the air into the solid.…”

Theory and applications of high frequency broadband ultrasound via a thin layer in contact with a solid

“…To realize ultrasonic testing without the use of water, several techniques, e.g., the air-coupled capacitance transducer (Schindel, et al, 1995), (Alvarez-Arenas, et al, 2012), (Gan, et al, 2003), , (Robertson, et al, 2002) and (Oralkan, et al, 2003), the electromagnetic acoustic transducer (Houck, et al, 1967), (Ludwig, et al, 1993), (Ogi, et al, 1995) and (Ogi, et al, 2001), laser ultrasound (White, 1963), (Rose, 1984), (Liu, et al, 2002), (Green, 2004) and (Arias and Achenbach, 2004), and microphone array (Chu, et al, 2014), (Rigelsford and Tennant, 2006) and (Brandes and Benson, 2007), have been proposed. Several megahertz broadband ultrasound can be transmitted and received by the aircoupled capacitance transducer (Alvarez-Arenas, et al, 2012) and the electromagnetic acoustic transducer (Ogi, et al, 1995), and this type of transducers are applicable for inspection of high temperature objects (Gan, et al, 2003).…”