Optical Probing of Acoustic Emission Waves

Absolute Sensitivity of Air, Light and Direct-Coupled Wideband Acoustic Emission Transducers

“…In the limit kT»hv, the RMS time displacement fluctuation of a surface area on a solid, isotropic, half-space is approximately (2) where fj.f is bandwidth, k is Boltzmann's constant, T is temperature in Kelvin, f is the frequency of the vibration and Z is the complex mechanical impedance defined as Z=F/v, (3) where F is the applied force and v is the resultant surface velocity. Using Eq.…”

“…For noncontacting transducer types we determine the sensitivity using published expressions and experimental results [3,13,14,15].…”

“…For the knife-edge and optical heterodyne sensors calculations we use the expressions of Whitman and Korpel [15], and Palmer and Green [3]. The knife-edge technique, while quite sensitive for high-frequency harmonic (CW) signals, is inherently narrowband because maximum sensitivity is achieved when the probe beam diameter is equal to onehalf the acoustic wavelength.…”

“…Studies have also been made comparing the merits of various optical sensors [2] and evaluating their applicability to acoustic emission (AE) [3]. In this paper, the calculated and measured sensitivities of such transducers are compared with the sensitivity of transducers capable of detecting low amplitude AE events in steels [4,5].…”

Sensitive Laser Interferometer for Acoustic Emission and Ultrasonic NDE

“…With transparent materials, the interferometer can measure internal wave propagation as well. Commonly, the surface displacements are measured at one or more spots [1,2] on the surface -the probe beam can be focused to spots whose diameters range from 0.02 to less than .002mm depending on the f/no of the beam. These temporal records of surface displacement or internal strain correspond to bandwidths limited solely by the electronic amplifier.…”