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Ultrasonic Sensors
Published in Bogdan M. Wilamowski, J. David Irwin, Control and Mechatronics, 2018
Ultrasonic sensors work with acoustic frequencies above 20 kHz, which is at the upper limit of audible human hearing. Ultrasonic sensing in robotics is popular due to the ability to directly achieve range sensing cheaply, simply, unobtrusively, and with low power consumption. Ultrasonic sensing is sometimes called SONAR derived from SOund NAvigation and Ranging. The basic principle of ranging is the measurement of the time-of-flight, tof, between transmission and reception of ultrasonic acoustic emissions. From the speed of sound, c, and tof, the range is c tof/2. The speed of sound varies with atmospheric conditions of temperature, humidity, and pressure as discussed below. The time-of-flight (TOF) can be measured from transmitting a pulse and processing the echo or using a continuous swept frequency transmission and examining the frequency of the echo. The former pulse echo technique is more common due to its processing and hardware simplicity. The frequency, f, of transmission can range from 25 to 500 kHz with corresponding wavelengths of (λ = c/f) approximately 14 mm down to 1 mm, respectively. Finer discrimination of targets is obtained using smaller wavelengths with the disadvantage of reduced maximum range due to the greater absorption losses during propagation in air as described below. Range measurement in the 25–60 kHz band is limited to around 10 m due geometric beam spreading and absorption losses in air.
Use of Ultrasonics in the Nondestructive Testing and Evaluation of Metals
Published in Dale Ensminger, Leonard J. Bond, Ultrasonics, 2011
Dale Ensminger, Leonard J. Bond
A very important class of solder joints includes those on a conductor pad on a printed circuit board (flat packs) wherein only one side of the joint is accessible. The second method includes an active and a passive transducer combination, which contacts only one element of the joint. Evaluation is based on the response of the joint to an acoustic stimulus of constant force magnitude and contact pressure. The response of the joint depends upon its acoustic impedance or stiffness [153]. A good joint shows high stiffness and damps the vibrations of the active transducer throughout the active band of frequencies. Several frequency ranges have been used, including 150 to 650 kHz, 200 to 950 kHz, and 500 kHz to 1.5 MHz. Any defect in the solder joint affects its impedance, which is reflected in the response of the joint to the acoustic stimulus. Even voids, inclusions, and other perhaps nonserious defects cause effects in the spectra that are identifiable. The most serious defects are large cracks in the heel, dewetted joints, and joints that are barely tacked at some position. Figure 8.31 presents tracings of the spectra obtained from (a) a good solder joint, (b) a solder joint that is barely tacked at the heel and toe, and (c) a solder joint that contains a 15% crack at the heel but otherwise is solid.
Speckle Metrology for Microsystem Inspection
Published in Wolfgang Osten, Optical Inspection of Microsystems, 2019
Dynamic loading was the first application case in the series of verification tests of the MSI. The resonant structure is attached to a thin piezoelectric plate. A Wavetek model 23 generates harmonic oscillations serving as an input to a Brüel & Kjæer type 2713 voltage amplifier that drives the PZT. Typical natural frequencies are in the range of 1–500 kHz. The pictures in Figure 15.28 make it obvious that the sensor has a variety of modes, for example, a pronounced torsional vibration at 5.1 kHz imaged at M = 0.6. Smaller beams are in resonance at higher frequencies, but they are difficult to see at low magnification. Therefore, the same region was analyzed with better resolution using the long-distance microscope at M = 2.
Optimal design of transducers based on the Halbach arrays permanent magnet structure
Published in Nondestructive Testing and Evaluation, 2023
Cheng He, Ce Li, Yishun Yan, Ran Wei, Shujuan Wang
As for meshing, the mesh in the patch, magnetic flux conductor, and permanent magnet regions is refined to ensure the accuracy of the calculated static magnetic field in these areas. The mesh in other regions is automatically generated by the software. The ultrasonic guided wave frequency range studied in this paper is 20 kHz to 500 kHz, with a minimum wavelength of approximately 6 mm for the T(0,1) wave. In finite element simulations, to ensure the accuracy of the results, the maximum size of the mesh should not exceed 1/8 of the wavelength. Therefore, the maximum mesh size in the patch, magnetic flux conductor, and permanent magnet regions is set to 0.75 mm, while in other regions, it is set to 1.5 mm. Finally, the static electromagnetic field solver in the software is selected to solve the model.
Detection and localization of corrosion using identical-group- velocity Lamb wave modes
Published in Nondestructive Testing and Evaluation, 2023
Liping Huang, Jiawei Ding, Jing Lin, Zhi Luo
For comparison, the behaviours of S0 mode in the normal plate and the corrosion plate were analysed in Figure 10, which was usually used in traditional Lamb wave tomography [35–37]. The group delays of S0 mode at 500 kHz (fd = 2 MHz-mm) with the wavelength of 8.14 mm in the two plates were checked, since it provides best sensitivity to corrosion according to literature [35]. The group delay in the normal plate is 200.8 μs, and that in the corroded plate is the 201.7 μs, only producing a time lag of 0.9 μs. Compared to S0 mode, the combination of A1 mode and S1 mode provides a larger time lag, which makes CI a better index for detecting corrosions. Besides, since CI is obtained from two individual modes in the same signal from one pair of transmitter and receiver in one measurement, the baseline signal is unnecessary, and temperature changes and zero-drift in measurement would not affect the results. In a word, benefited from all those, CI can be a candidate index in baseline-free corrosion detection.
Optimization of laser parameters for improved corrosion resistance of nitinol
Published in Materials and Manufacturing Processes, 2020
K. E. Ch. Vidyasagar, Abhishek Rana, Dinesh Kalyanasundaram
The nitinol coupons were processed using a nanosecond pulsed fiber laser-based machining system. The system uses a fiber laser source (model number: SP-050-A-RMZ-B-Y; SPI Lasers Limited, UK) operating at a wavelength at 1064 nm with a pulse frequency ranging between 25 and 500 kHz and pulse width of 250 ns. The maximum average laser power (Lp) at the exit of the galvoscanner is ∼50 W. Two types of laser processing, namely, micropits and straight-line grooves, were evaluated during preliminary experiments. A significant difference in the value of rate of corrosion or corrosion rate (CR), corrosion voltage (Ec), and current (Ic) was observed on the straight-line groove type of laser processing on nitinol coupons in comparison with pristine and micropit-type of laser processing (ref. to Figure S1(a) of the supplementary section). Hence, further optimization experiments were performed on straight-line type of laser processing of nitinol coupons. The focus spot size of laser beam was 30 ± 4 μm.