Simultaneous Ultrasonic Measurement of Thickness and Speed of Sound in Elastic Plates Using Coded Excitation Signals

Abstract

Layer thickness and the speed of sound are important parameters for nondestructive testing applications. If one of the parameters is known, the other one can be determined by simple time-of-flight (TOF) measurement of ultrasound. However, often these parameters are both unknown. In this contribution, we examine and adapt ultrasonic imaging techniques using coded excitation signals to simultaneously measure the thickness and the speed of sound of homogeneous elastic plates of unknown material. Good axial resolution is required to measure thin samples. We present a new approach for transmission signal conditioning to improve axial resolution. This conditioning consists of enhancing spectral components that are damped by the transducer prior to transmit. Due to the long duration of coded excitation signals, pulse compression techniques are required for TOF measurements. Common pulse compression filters are discussed, and appropriate filtering of the compression waveform is designed to keep the sidelobe level (SLL) acceptably low. An experimental assessment of the presented measurement techniques reveals that the signal conditioning substantially increases the axial resolution. However, a tapered Wiener filter should be used for the best tradeoff between SLL and axial resolution. We used the proposed method to measure different plates of steel, aluminum, and polymethylmethacrylate of various thicknesses, and the results show very good agreement with the reference values, which we obtained with a micrometer screw and by standard TOF measurement, respectively. The relative error for the plate thickness is smaller than 2.2% and that for the speed of sound is smaller than 3%. It is remarkable that plate thickness could be measured down to 60% of the wavelength.

Research on Golay-coded excitation in real-time imaging of high frequency ultrasound biomicroscopy

“…The reason may be that the signal transmission and measurement are affected by the bandwidth and noise of the transducer. In future investigations, the instantaneous frequency characteristics of the encoded impulse response should be matched to that of the transducer in order to reduce the power loss in the transducer and to increase the signal-to-noise ratio 25 .…”

“…Therefore, other phase coding modes could be introduced in future research, such as M-sequence 27 and chirp code 28 . At the same time, new pulse compression www.nature.com/scientificreports/ methods such as mismatched filter 29 , Wiener filter 25 , and others can be introduced in further research to reduce the influence of side lobes on the compressed echo signals and to improve the signal-to-noise ratio and image quality.…”

Classification of Sonar Targets in Air: A Neural Network Approach

“…Accordingly, peak positions correspond to targets’ propagation delays. This approach is also known as pulse compression in the area of sonar and radar systems (see also [34,35,36], and [37]). The emitted chirp signal had been recorded before at 1 m distance and was averaged ten times to improve its signal to noise ratio—in contrast to the measured target echoes, for which no averaging was performed (single echoes).…”

“…For each target’s echo, its ROI (ROInormalt in Figure 5) is centered around the largest corresponding peak in its pulse-compressed echo. Peak detection in pulse-compressed echo signals is a common method for identification of possible targets in sonar as well as radar systems (see also [34,35,36] and [37]) and is therefore assumed to be a valid step before target classification in our case. ROIs for non-target samples (ROInt in Figure 5) are randomly put outside target ROIs, but inside possible ranges for target echoes.…”

Top Coating Anti-Erosion Performance Analysis in Wind Turbine Blades Depending on Relative Acoustic Impedance. Part 2: Material Characterization and Rain Erosion Testing Evaluation

“…The viscoelastic characterization of the LEP materials at the appropriate working frequency range is limited for dynamic tests based on the vibration of rods or beams [21,22] and only possible using ultrasonic waves [23][24][25]. Moreover, the use of the ultrasound technique in thin film applications has additional issues as coupled thickness layer determination [26][27][28][29][30]. Alternatively, it is well known for viscoelastic materials, that the frequency (strain rate) and temperature dependencies of polymer properties are both related.…”