Echo Configuration Research Articles

Temperature Hotspot Detection on Printed Circuit Boards (PCBs) Using Ultrasonic Guided Waves-A Machine Learning Approach.

This paper addresses the challenging issue of achieving high spatial resolution in temperature monitoring of printed circuit boards (PCBs) without compromising the operation of electronic components. Traditional methods involving numerous dedicated sensors such as thermocouples are often intrusive and can impact electronic functionality. To overcome this, this study explores the application of ultrasonic guided waves, specifically utilising a limited number of cost-effective and unobtrusive Piezoelectric Wafer Active Sensors (PWAS). Employing COMSOL multiphysics, wave propagation is simulated through a simplified PCB while systematically varying the temperature of both components and the board itself. Machine learning algorithms are used to identify hotspots at component positions using a minimal number of sensors. An accuracy of 97.6% is achieved with four sensors, decreasing to 88.1% when utilizing a single sensor in a pulse-echo configuration. The proposed methodology not only provides sufficient spatial resolution to identify hotspots but also offers a non-invasive and efficient solution. Such advancements are important for the future electrification of the aerospace and automotive industries in particular, as they contribute to condition-monitoring technologies that are essential for ensuring the reliability and safety of electronic systems.

Ultrasonic Monitoring of Part’s Height and Layer Thickness in Powder Bed Fusion

This paper presents a preliminary study on an in-situ ultrasonic measurement technique applied to monitoring part’s height and defect occurrence during the Laser Powder Bed Fusion process. Firstly the ultrasonic wave speed is determined for LPBF manufactured 100Cr6 samples with a pulse echo configuration and a 10Mhz ultrasonic wave. A measured propagation speed value, of 5660 ±100m/s in every direction confirms the isotropy of the obtained LPBF samples. Secondly, the ultrasonic pulse echo technique is used to monitor the part’s height evolution during the process based on the measured propagation velocity. This new method provides in-situ measurements showing that the actual remelted layer thickness value oscillates in the range of ± 30% of the theoretical layer thickness.

Damage Detection Method Based on Continuous Wavelet Transformation of Lamb Wave Signals

A damage estimation method based on continuous wavelet transformation (CWT) of the normalized Lamb wave signals is proposed here. Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged in the form of square detection cells on a plate-like structure. Excitation sequences based on pitch–catch and pulse–echo configurations are tested for the same arrangement of the transducers. The possibilities of the existence of damage for each actuator–senor pair are formed by using the normalized coefficient of CWT. The size of the possible damage region is directly controlled through envelopes defined by the coefficients of CWT, and no additional parameter is required to define its size. The aggregate damage image is constructed by the fusion of damage possibilities from all actuator–sensor pairs using damage indices based on conjunctive and compromised fusion schemes. The results indicate that the proposed method can estimate the location and severity of multiple damage with signals directly from the damaged plate, without the need of baseline signals from the undamaged plate, and the time-compensated signals provide better damage imaging than the raw signals. The most accurate and computationally inexpensive combination is the pulse–echo configuration with damage index based on conjunctive image fusion scheme. The method is computationally inexpensive and can be applied for multiple damage estimations in large structures to reduce the evaluation cost and inspection time during on-line structural health monitoring.

Transverse-to-transverse diffuse ultrasonic double scattering

Previously, a transverse-to-transverse single scattering model (T-T SSR) was developed for a pulse echo configuration, which may have limitations for strongly scattering materials. In this work, a transverse-to-transverse double scattering model (T-T DSR) is presented to model the transverse ultrasonic backscatter more accurately. First, the Wigner distribution of the transducer beam pattern is extended to a transverse wave. Next, the multiple scattering framework is followed to derive the transverse and longitudinal components of the second-order scattering. Then, a quasi-Monte Carlo (QMC) method is used with Graphics Processing Unit (GPU) acceleration to calculate numerical results of the final expression which contains a five-dimensional integral. The correlation length, the focal length of the transducer, and incident angle are used to investigate differences between the T-T DSR model and the T-T SSR model. Finally, a backscatter experiment is performed on two stainless steel specimens with different grain sizes to determine the respective correlation lengths. The results show that the T-T DSR model has better performance over the T-T SSR model for evaluating the grain size of these relatively strongly-scattering specimens.

An ultrasonic guided wave approach for the inspection of overhead transmission line cables

Inspection of overhead transmission line cables is performed using various non-destructive testing techniques, such as visual, temperature, and eddy current-based inspection; yet each of these techniques have their respective shortcomings and safety concerns. The use of ultrasonic guided waves as a non-destructive testing technique is well established for simple geometries such as plates, pipes, and rods. However, its application for multi-wire cables is still in development. In this study, ultrasonic guided waves excited by a shear mode transducer collar are utilised as a defect detection technique for untensioned aluminium conductor steel reinforced cable specimens. The identification and analysis of wave propagation for a broad range of frequencies is performed using a laser scanning vibrometer, and the effect of defect size on wave propagation is studied. Signal processing algorithms, such as wavelet denoising and time scaling, are then deployed for inspection quality enhancement and analysis under noisy conditions. Results yield an extended range of defect detection coverage in pulse echo configuration; with successful detection of defects that correspond to a 4.5% reduction in the cable’s cross sectional area; and up to 24% improvement of signal-to-noise ratio.

Modelling of Acoustic Impedance Transfer Function for Liquids Subjected to a Centrifugation Process

During the sedimentation process, the acoustic impedance transfer function of the liquids through which the pulse propagates has variable acoustic impedance. This acoustic impedance that characterizes a liquid during centrifugation is determined by the pulse–echo configuration results in conjunction with the subsequent experimental results. The system transfer function obtained in this fashion has been shown to agree with a direct measurement of the same function in a reference set-up. Based on laboratory experiments and the derived model, determination of separation efficiency with a high accuracy range of measurements is produced. The value of having a model of this type for a complete system is that one can then examine in detail how changes in the transfer function of the medium affect the system performance; estimates of the effects of system changes can also be made without performing costly experimental validation studies.

Estimation of wall parameters based on range profiles

Compensation of wall effects is of main concern in SAR through-wall sensing. Wall parameters are essential for the compensation, which are normally not known a priori. A model of SAR working in side-looking strip mode for through-wall imaging is established, with the path of signal due to refraction taken into consideration. Through analyzing the echo configuration in time domain, a new procedure for estimating wall parameters using high range resolution profiles is provided. By extracting time delay of target counterpart, the thickness and permittivity of wall are figured out exactly by employing numerical equation method and intersecting of searching curves. With the estimated parameters, focused image of targets in a room is acquired after wall effects are compensated in imaging processing with back projection algorithm. Simulation results verify the validity of the theoretical analysis and imaging algorithm.

Quantitative evaluation of orientation-specific damage using elastic waves and probability-based diagnostic imaging

Different from the damage with relatively smooth boundaries or edges such as a through-thickness hole or delamination which scatters elastic waves omnidirectionally, orientation-specific damage of sizable length in a particular dimension (e.g., a crack or a notch) often exerts strong directivity to elastic wave propagation. As a consequence the damage-scattered waves may not be captured efficiently by sensors at certain locations, posing a challenging issue to elastic-wave-based damage identification. In this study, the influence of damage orientation on Lamb wave propagation was quantitatively scrutinised. Based on the established correlation between damage parameters (location, orientation, shape and size) and extracted signal features, a probability-based diagnostic imaging approach was developed, in conjunction with use of an active sensor network in conformity to a pulse–echo configuration. Relying on enhancive signal features including both the temporal information and signal intensity, this imaging approach is capable of indicating the orientation of individual damage edges clearly and further shape/size of the damage. The effectiveness of the approach was demonstrated by predicting orientation-specific damage cases including a triangular through-thickness hole (through finite element simulation), a through-thickness crack and an L-shape crack (through experiment) in aluminium plates. With the assistance of a two-level synthetic image fusion scheme, all damage cases were visually and quantitatively highlighted in the probability images.

Estimation of wall parameters by exploiting correlation of echoes in time domain

Compensation of the effects of wall on through-the-wall synthetic aperture radar (SAR) imaging is a main concern. Wall parameters are essential for the compensation, which are normally not known a priori. After analysis of echo configuration characteristics in time domain, a new procedure for estimating wall parameters is proposed, which is based on the idea of exploiting the correlation between the measured returns reflected from the wall and the corresponding estimates calculated from a SAR return model of the wall together with electromagnetic theory. The new approach deals with echo data without imaging or localisation processing, and has a less resolution requirement.

The use of ultrasonic guided waves and wavelets analysis in pipe inspection

One of the main applications of guided waves is for pipe inspection, since its one-dimensional geometry allows inspecting long distances in a short time. As with most configurations (frequency, thickness) ultrasonic waves with many modes of propagation are generated, recent research focuses mostly on the generation and reception of specific modes, mainly by means of sophisticated arrays of transducers. In this paper this problem is addressed with a different approach, by processing ultrasonic signals with a low signal/noise ratio acquired with a single transducer in an pulse–echo configuration. In order to improve the evaluation of results, frequency bandpass filters and wavelet analysis were tested. Results showed that even when very noisy signals are utilized, signal processing improve the signal/noise (S/N) ratio up to 12 dB approximately and enhance the analysis of the results, thus demonstrating its usefulness.

On the theory of ultranarrow pure-electronic zero-phonon lines

A pure-electronic zero-phonon line, which represents an optical analog of the Mossbauer γ-resonance line, is a cornerstone of three remarkable areas of spectroscopy and optics of impurity solids, namely, ultrahigh-resolution spectroscopy, persistent hole-burning spectroscopy, and spectroscopy of single impurity molecules. In recent experiments made by the photon echo technique, a zero-phonon line width as small as 78 Hz was achieved (with the Q-factor, i.e., the ratio of the transition frequency to the line width being 2×1014:78≈ 1012), which is several tenfold lower than the frequency shift of the vibronic spectrum caused by the momentum of the absorbed or emitted photon of optical range. We estimate the position, intensity, and width of zero-phonon lines under conditions when these characteristics, as well as properties of the phonon wing, are determined not only by Stokes losses but also by the photon recoil effect. It is shown that the latter effect, within the approximation used, does not lead to strong and easily detectable phenomena. They, however, take place, and their study is becoming more topical with improving accuracy and sophistication of the experimental technique (in the photon echo configurations, etc.).

Mode conversion and the path of acoustic energy in a partially water-filled aluminum tube

Mode conversion is observed in a water-loaded thin-walled Al tube with a horizontal central axis. A 1 MHz pulse is applied to the tube by a transducer coupled to the tube's external wall in a pulse–echo configuration. The tube is filled to 36 different levels, and a waveform is acquired at each level. Analysis shows that the acoustic energy must propagate both in the tube wall as an A 0-mode Lamb wave and as a bulk wave in the water. Mode conversion between these two waves is shown to take place both in the air–water interface and as energy leakage in the water-loaded portion of the tube. A unique echo train is observed at each fill level, suggesting that a liquid level sensor can be developed based on this mode conversion.

Two cases of severe weather in Catalonia (Spain). A diagnostic study

A diagnostic study of two cases of severe thunderstorms in Catalonia (the north-eastern region of Spain) is presented. The first occurred on 24 August 1993. A squall line, with bow echo configuration in the radar images, crossed Catalonia from west to east. Strong winds, large hail up to 7 cm in diameter, and heavy rain producing floods were observed. The meteorological situation was characterized by an upper-level trough approaching Spain from the north-west. This upper trough developed a low, which displaced the warm, dry air located over the Iberian Peninsula towards the east and north-east. The warm, dry air overran the cold, humid Mediterranean air producing a strong inversion (LID) capped by an elevated mixed layer over the western Mediterranean and also over the Ebro valley. Hand-drawn analyses permitted the identification of a secondary trough; a combination of this trough and a jet streak located over Spain was responsible for the mesoscale lifting mechanism that was able to break the LID and maintain the deep convection. The second case occurred on 31 August 1994. A tornado developed over south Catalonia and large hail, up to 5 cm in diameter, also fell. The meteorological situation was also characterised by an upper-level trough advancing from the west towards Spain. Accurate hand-drawn analyses identified a small thermal low over Catalonia leading to strong convergence at low levels. Over the same area, two jet streaks overlapped their left exit and right entrance zones, producing an enhancement of the ascending motion forced by the low-level convergence. However, the typical environment for supercell development was not present over Catalonia. The tornado was probably produced by a non-supercell thunderstorm. Copyright © 1999 Royal Meteorological Society

Radar and Other Observations of Two Vaulted Storms in Northeastern Colorado

Abstract Detailed radar echo structures and histories of two storms are presented. Both advanced into cloudless skies and had prominent, bounded weak echo regions. The storms had comparable size and intensity, and their environments provided similar amounts of shear and potential instability. One was an organized, multicellular storm, and had detailed photographic coverage from an aircraft. The combination of visual and radar data suggests the possibility of seeding of turrets in the “flanking line” by ice particles falling from the anvil. The other storm was a supercell. It had a rather steady echo configuration with a radar echo vault for about 40 min, and produced an exceptionally heavy hailswath, with hail up to 10 cm deep. However, the heavy hailfall at the ground started before vault formation and ended well before vault dissipation. The hailfall relates best to the onset of the strong updraft that (presumably) produced the vault, but does not relate to the mere fact of the existence of the bounded ...

Contrast echocardiographic features of pulmonary hypertension and regurgitation.

Linear contrast echo configuration on the pulmonary valve M-mode echogram was assessed in 28 patients with pulmonary hypertension, in 10 with pulmonary regurgitation, and in 10 normal subjects. Contrast echo parallel lines filling the total systolic phase of the pulmonary valve were recorded in normal subjects. Contrast echo lines stopping in early systole around the pulmonary valve mid-systolic notch were seen in all the patients with pulmonary hypertension in relation to changes with the pulmonary flow. Contrast echo lines reversing the early diastole and crossing the pulmonary valve echogram during diastole were detected in all the patients with pulmonary regurgitation, consistent with the reversed flow across the valve. The use of contrast echocardiography to diagnose both pulmonary hypertension and regurgitation may provide further useful information, particularly when the orientation and time of appearance of the contrast echo lines are related to the systolic and/or diastolic phases of the pulmonary valve M-mode echogram.

Echo delay and overlap with emitted orientation sounds and doppler-shift compensation in the bat,Rhinolophus ferrumequinum

The compensation of Doppler-shifts by the bat,Rhinolophus ferrumequinum, functions only when certain temporal relations between the echo and the emitted orientation sound are given. Three echo configurations were used: With increasing delay or decreasing duration of the Doppler-shifted echo the compensation amplitude for a sinusoidally modulated +3 kHz Dopplershift (modulation rate 0.08 Hz) decreases for all stimulus configurations (Figs. 1, 2, 3). The range of the Doppler-shift compensation system is therefore limited by the delay due to acoustic travel time to about 4 m distance between bat and target. In this range the overlap duration of the echo with the emitted orientation sound is always sufficiently long, when compared with data on the orientation pulse length during target approach from Schnitzler (1968) (Fig. 5).

VHF power spectra of the radar aurora

Power spectra of VHF radar auroral echoes were obtained near Anchorage, Alaska, during October 15–23, 1970. These spectra were obtained concurrently with standard range-time-intensity (RTI) film strips of the echoing region using the same radar system. In this paper, these spectra and the RTI film strips are examined and are compared with previously defined radar auroral classifications. The results indicate that there are at least two, and possibly three, separate types of spectra that correspond to identifiable echo configurations on the RTI film strips. Identification of the two-stream instability as an irregularity-producing mechanism for one of these spectral types is possible but not definitive. Another type of spectrum is similar to the type II spectra seen in the equatorial electrojet. The third spectral type bears no similarity to any results obtained at the equator.

Spread-Fobservations by the Alouette Topside Sounder Satellite

Ionograms recorded by the Alouette topside sounder satellite exhibit a variety of spread-F echo configurations. The observed echoes are found to be consistent with three qualitative radio-propagation models involving aspect-sensitive scattering by thin magnetic-field-aligned irregularities, ducting along broad irregularities, and refraction within large-scale reductions of electron density. A large number of Alouette ionograms were examined for the three types of spread F to determine their frequency of occurrence. Spread F appeared on 54 per cent of the topside ionograms; the three types exhibit markedly different patterns of occurrence in geomagnetic latitude and local time.

OPERATIONAL USE OF WEATHER RADAR COMPOSITES IN FLORIDA

A weather radar facsimilv network providing rapid collection and compositing of radarscope photographs has been established in Florida by the Weather Bureau in support, of Project Mercury. Equipmclnt and operational procedures are discussed in some detail and scwral synoptic examples of radar cornpositing from PPI photographs are presented. These examples include echo configurations associated with an casterly wave and two well-organized squall lincs that moved across thc Florida Pc~llillsula. Itatdar composites for these situations are compared with coded radar observations and Radar Sulnnlary Charts and tllc advantages and possible future utilization of radar composites are cited.

WEATHER NOTE: A RADAR ECHO CONFIGURATION ASSOCIATED WITH A SERIES OF WATERSPOUTS

The appearance of the echo on the WSR-57 PPI scope during the occurrence of a series of waterspouts near Daytona Beach, Fla., is described. The main features were a hole in the center of the echo and a very steep reflectivity gradient in a V-shaped notch on one edge of the echo. Photos and an eyewitness account are included.