This paper presents the comparison study of wavenumber-based defect detection performance in full field laser scanning techniques. Two types of wave excitation are used for damage detection; guided waves and standing waves. A piezoelectric actuator is mounted on surface of the thin plate to generate guided and standing waves with a single excitation frequency. Subsequent responses on each grid point are measured using a Laser doppler vibrometer (LDV) with a mirror tilting device. Full field wave image is then generated from the measured wave signals. After the laser scanning, wavenumber based processing is applied to the measurements to generate two types of full wave field images and to detect structural damage. Three wavenumber based signal processing are applied to the wave filed images to estimate damage size and depth, including the Local wavenumber mapping, Acoustic Wavenumber Spectroscopy, 2D wavelet based wavenumber spectroscopy. For the comparison of these two techniques, several experiments are performed on thin walled structures with several different types of damage, including corrosion in an aluminum plate and debonding on composite plates. This paper outlines pros and cons of these two excitation techniques in terms of several parameters, including damage sensitivity, processing time and their applicability.
Three different ultrasonic nonlinearity parameter measurement methods are available: the capacitive detection method to measure absolute values of nonlinearity parameters; the laser interferometry detection as a non-contact method; the contact piezoelectric transducer based relative measurement method. Among all these three methods, the contact piezoelectric transducer detection method has been used as the most practical approach due to its operational simplicity for materials damage assessments. One of the main drawbacks of this technique, however, has been the low sensitivity of the receiving transducers, especially for the second harmonic signals, causing a high uncertainty in measurements. In this work, it is demonstrated with a copper  single crystal that a couple of high Q-value band-pass filters and a low-noise preamplifier introduced in the system not only improve the measurement accuracy but also make it possible to determine absolute values of nonlinearity parameters without using the complex capacitive detection method.