Echo Height Research Articles

Mean grain size determination in marbles by ultrasonic first backwall echo height measurements

In ultrasonic grain size determination several techniques are in use. In this paper, the Ultrasonic Relative Attenuation (URA) method has been used to estimate the mean grain size of marble samples. Also, mean grain size versus first backwall echo height graphs have been plotted to see the direct relation between these two parameters. The results show less than 10% difference compared with values obtained in an optic microscope. In a comparison, mean grain size values of marbles determined by ultrasonic velocity methods are given.

Buckland Park all‐sky interferometric meteor radar

A VHF all‐sky interferometric meteor radar system has been developed and installed at Buckland Park, South Australia. The radar is portable, allows a wide range of operating parameters, and can also be operated as a boundary layer radar. The analysis techniques have been developed using extensive simulations in an attempt to improve on standard techniques used by previous investigators. The results suggest that although pulse repetition frequencies (PRFs) around 2 kHz allow meteor velocity and deceleration estimation, PRFs around 500 Hz maximize count rate and improve the quality of meteor echo height estimates for this radar. Typical results are presented, indicating the radar obtains annual count rate variation of between 9000 and 14,000 height resolvable underdense meteors per day.

Meteor head echo altitude distributions and the height cutoff effect studied with the EISCAT HPLA UHF and VHF radars

Abstract. Meteor head echo altitude distributions have been derived from data collected with the EISCAT VHF (224MHz) and UHF (930MHz) high-power, large-aperture (HPLA) radars. At the high-altitude end, the distributions cut off abruptly in a manner reminiscent of the trail echo height ceiling effect observed with classical meteor radars. The target dimensions are shown to be much smaller than both the VHF and the UHF probing wavelengths, but the cutoff heights for the two systems are still clearly different, the VHF cutoff being located several km above the UHF one. A single-collision meteor-atmosphere interaction model is used to demonstrate that meteors in the (1.3–7.2)µg mass range will ionise such that critical electron density at 224MHz is first reached at or around the VHF cutoff altitude and critical density at 930MHz will be reached at the UHF cutoff altitude. The observed seasonal variation in the cutoff altitudes is shown to be a function of the seasonal variation of atmospheric density with altitude. Assuming that the electron density required for detection is in the order of the critical density, the abrupt altitude cutoffs can be explained as a consequence of the micrometeoroid joint size-speed distribution dropping off so fast at the large-mass, high-velocity end that above a certain altitude the number of detectable events becomes vanishingly small. Conversely, meteors at the low-mass end of the distribution will be gradually retarded such that the ionisation they generate never reaches critical density. These particles will remain unobservable.Key words. Radio science (instruments and techniques) – Interplatery physics (interplanetary dust) – General or miscellaneous (new fields)

Study on In-Pipe Corrosion Diagnosis System -Estimation of Corrosion on Screw Parts Using a Surface SH Probe-

Correlating to changes in society’s expectations, there is an increasing demand for the diagnosis of building equipment. Examination and diagnosis of air-conditioning pipes is an important safeguard against unexpected trouble such as pipe leakage. It is particularly important to inspect the screwed parts of pipes because their thickness is thinner than other parts due to the thread. In the past, radiography and endoscopy have been used for the inspection of screwed parts, but radiographic testing must be performed by a licensed technician, and endoscopy requires halting of plant operations. In this paper, we introduce a method for detecting and estimating the size and position of corrosion using ultrasonic testing, surface SH waves. We describe the algorithms used to estimate the corrosion size using the edge echo height, and the corrosion position using a simple numerical echo height model. And finally, we show the results of using the algorithms in experiments on pipes with artificial corrosion.

Comparison of Echo Heights between Fatigue Crack and EDM Notch

Comparison of Echo Heights between Fatigue Crack and EDM Notch

CUTLASS HF radar observations of high-velocity E-region echoes

Abstract. A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms–1 , while the other group had significantly larger velocities, of the order of 700 ms–1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms–1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms–1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm–1 ) and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere)

Ultraschallprüfung an Schweißnähten

A model for the evaluation of critical results from ultrasonic weld inspection is presented. Interfering indications from geometry, especially from the root can be calculated by the model within a few minutes. The model can consider different reflector types like arbitrarely oriented and positioned rectangles, ellipses, flat bottom holes, side drilled holes and notches. With respect to reference reflectors, an echo height estimation can be carried out. The model can also be used by NDT- personnel for training purposes.

825 表面波による鋼材の低サイクル疲労き裂進展評価

The crack growth behavior on steel compact specimens was investigated by the echo characteristic of surface wave emitted toward the end of notch under low cycle fatigue. The echo height reflected from the edge of crack and the round-trip propagation time from the surface wave probe to the edge of crack were measured for evaluating the crack growth behavior. The crack was generated from the edge of notch when the round-trip propagation time suddenly increased or the ratio of the echo height suddenly decreased. After that, The crack grew with repeating progress and stagnation alternately, and the compact specimen broke. Judging from the results of fracture surface observed by the scanning electron microscope, The fracture surface is a stripe pattern, and the distance between the lines corresponded to the part of the stagnation.

Echo Height Measurements with the WSR-88D: Use of Data from One Versus Two Radars

Abstract The new Doppler radars of the National Weather Service (i.e., the WSR-88D radars) are operated continuously in a volume scanning mode (called Volume Coverage Pattern, VCP) with the elevation tilt angles fixed for several VCPs. Because of the fixed VCPs, the radar data can be used to determine the heights of precipitation echo features only to limits of accuracy that depend upon the elevation angles used in the VCP, the radar beamwidth, and the range of echoes. Data from adjacent WSR-88D radars, if used simultaneously, could reduce significantly the height uncertainties inherent in single radar measurements. This is illustrated for idealized situations and also for an event involving a long-lived, tornadic thunderstorm. The use of coordinated scan strategies and combined data analysis procedures for adjacent WSR-88D radars during significant thunderstorm events should be considered for operational applications.

NMR spin-echo measurements of reversible and irreversible motion of a driven vortex lattice

We report measurements of flux-line motion that is driven by a periodic rocking of the external magnetic field through a small angle in the type-II superconductor NbTi alloy filaments. The effect of the motion is to reduce the height of the ${}^{93}\mathrm{Nb}$ NMR spin-echo signal. By investigating a broad range of parameters that characterize the rocking motion and the NMR pulse sequence, the scaling behavior discussed earlier [W. G. Clark, F. Lefloch, and W. H. Wong, Phys. Rev. B 52, 7488 (1995)] is found to persist into a regime where irreversible flux-line motion causes an additional reduction of the echo height. The earlier model is extended phenomenologically to include irreversible displacements of the axis about which each vortex rocks. A second scaling relation for this mechanism that is seen experimentally is contained in the extended model. The results suggest that the irreversible part of the motion is driven by the rf pulse that forms the spin echo.

The Vertical Structure of TOGA COARE Convection. Part I: Radar Echo Distributions

Radar data collected by the 5-cm MIT radar, which was deployed aboard the R/V Vickers during the intensive observing period of the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment, are partitioned into convective and stratiform Cartesian grid columns. The vertical structure of convective echo is examined through the use of two variables: echo top height and the height of the 30-dBZ reflectivity contour. The first of these variables has traditionally been used to describe the vertical structure characteristics of convection, and the second has recently been linked to internal microphysical properties and lightning. Histograms of the relative frequency of convective-only echo top heights and 30-dBZ contour heights were constructed for the three cruises of the Vickers, with each cruise experiencing different phases of the intraseasonal oscillation (ISO). Cruise 1, which was dominated by the convectively ‘‘inactive’’ phase of the ISO was characterized by the highest frequency of shallow convection (based on echo top heights), whereas cruise 2, which was dominated by a particularly well-defined passage of the convective phase of the ISO, exhibited the tallest echo top heights. Cruise 3 convection was influenced by moderate westerly surface winds characteristic of postwesterly wind burst conditions, and convection was of intermediate height. When viewed as a function of ‘‘internal’’ vertical structure (i.e., 30-dB Z contour height), the frequency distributions vary less from cruise to cruise, with cruises 1 and 2 having nearly identical distributions of convective 30-dBZ contour heights. Furthermore, when the contribution to convective rainfall is examined as a function of 30-dBZ contour height, it is seen that relatively more rain fell from vertically ‘‘intense’’ convection (i.e., convection with tall 30-dBZ contours) during cruises 1 and 3 than during cruise 2. Instantaneous correlations between rainfall rate and radar echo height were highly scattered about a mean value of about 0.55, whereas rainfall rate and 30-dBZ contour height correlations peaked at about 0.8 and exhibited much less scatter.

Crack Growth Evaluation on Lap Adhesive Joints Using Surface Wave.

The crack growth behavior on the lap joints with various adhesive thicknesses was investigated by the echo characteristics of surface wave emitted toward the adhesive layer under shearing forces. The echo height reflected from the edge of adhesive layer and the round-trip propagation time from the surface wave probe to the adhesive layer were measured for evaluating the crack growth behavior. The crack was generated along the adhesive interface when the ratio of the round-trip propagation time suddenly increased. After that, the crack rapidly grew. In the case where the distance between the surface wave probe and the adhesive layer was 10 mm, the crack of the adhesive layer was able to detect when the ratio of the round-trip propagation time became about 1% and the ratio of echo height reflected from the edge of adhesive layer became about 60%. Moreover, the shearing stress of crack generation was about 52% of the shearing strength.

VIMHEX 1972 revisited: The life cycles of two tropical convective mesosystems over land

The evolutions of two slow-moving convective mesosystems observed in Venezuela during VIMHEX-II were studied using time changes in radar echo characteristics. The duration of the echo, maximum echo area, maximum echo height and mean echo velocity were about 6 hours, 5000km2, 16km, and 95°/5.2m s−1 for mesosystem A and about 11 hours, 12000km2, 14km, and 90°/3.2m s−1, for mesosystem B, respectively. The rainfall distributions associated with the mesosystems are described and correlated with the radar echo characteristics. The synoptic conditions are discussed, as well as the modification of the environment produced by the mesosystems. The relative wind profiles suggest that mesosystem A behaved more like a typical tropical squall line, with inflow at almost all levels at the front of the mesosystem, while mesosystem B behaved like a typical mid-latitude squall line, with inflow at lower levels and outflow at upper levels at the front of the mesosystem.

Evaluation of Function of Spot-Welded Joint Using Ultrasonic Inspection : Nondestructive Evaluation on Tension Shearing Strength with Neural Network

The spot-welded joint is widely used as a structural part. In the quality control of the joint, one of the most important issues is to quantitatively estimate connective strength such as tension shearing load from the information detected by nondestructive testing as accurately as possible. In this paper, a system based on an ultrasonic inspection device and a neural network is proposed to evaluate the tension shearing load of each spot-welded joint. The network is configured by learning the pattern sets dealing with the interaction between the scanning graphs of the welded region using ultrasonic testing and tension shearing load of the joints. The input of the network is the echo height at each scanning position of the welded region. The output from the system was examined by comparing it with the experimental results, and the validity of the system was thereby confirmed.

Gaussian-approximation formalism for evaluating decay of NMR spin echoes.

We present a formalism for evaluating the amplitude of the NMR spin echo and stimulated echo as a function of pulse spacings, for situations in which the nuclear spins experience an effective longitudinal magnetic field {ital h}{sub {ital z}}({ital t}) resulting from an arbitrary number of independent sources, each characterized by its own arbitrary time correlation function. The distribution of accumulated phase angles for the ensemble of nuclear spins at the time of the echo is approximated as a Gaussian. The development of the formalism is motivated by the need to understand the transverse relaxation of {sup 89}Y in YBa{sub 2}Cu{sub 3}O{sub 7}, in which the {sup 89}Y experiences {sup 63,65}Cu dipolar fields which fluctuate due to {sup 63,65}Cu {ital T}{sub 1} processes. The formalism is applied successfully to this example, and to the case of nuclei diffusing in a spatially varying magnetic field. Then we examine a situation in which the approximation fails{emdash}the classic problem of chemical exchange in dimethylformamide, where the methyl protons experience a chemical shift which fluctuates between two discrete values. In this case the Gaussian approximation yields a monotonic decay of the echo amplitude with increasing pulse spacing, while the exact solution yields distinct {open_quote}{open_quote}beats{close_quote}{close_quote}more » in the echo height, which we confirm experimentally. In light of this final example the limits of validity of the approximation are discussed. {copyright} {ital 1996 The American Physical Society.}« less

VHF echoes from the midlatitude mesosphere and the thermal structure observed by lidar

Observations with a 46.5‐MHz radar system at Aberystwyth, Wales (52°N, 4°W) over the period February 1990 to May 1994 have shown a pronounced seasonal variation in the height range of mesospheric echoes. These were observed over the range 64–84 km in all seasons, but those at still greater heights were confined to summer months. Coordinated radar and lidar observations at the same site during 1993 have shown that these intense echoes in summer, analogous to polar mesosphere summer echoes (PMSE), are associated with low mesopause temperatures; the weaker echoes observed in winter seem to be associated with regions of superadiabatic lapse rates; and echoes are observed both above and below the maxima in temperature inversions commonly observed below the mesopause. The types of instability implied in these associations of echo height and temperature structure are considered.

Anisotropic spin diffusion and multiple spin echoes in3He-4He solutions

We propose a θ1-t1-θ2 pulse-NMR experiment to detect the spin-diffusion anisotropy, Δ=D∥-D⊥, in degenerate spin-polarized3He-4He mixtures, where D⊥ and d∥are the transverse and longitudinal spin diffusion coefficients. In such an experiment the nonlinearity of the dynamics produces multiple spin echoes (MSE). At the 3He concentration x3 ≈ 4% the spinrotation parameter vanishes (μM →0), so that the nonlinearity of the equations of motion is entirely due to the anisotropy. In this situation, detection of MSE amounts to observation of ΔD. For slight anisotropy, i.e. ΔD/D∥ ≲0.25, we use a perturbation scheme similiar to that developed by Einzel et al. (in that case, for small μ M and small demagnetizing field) to calculate the second and third echo heights. For larger anisotropy we numerically calculate the echo heights. We find that for ΔD/D∥ = 0.5 the heights are ≈ 2 % of the first echo, and should be detectable. The (θ1, θ2) tip-angle dependence of the ΔD echoes is different from that of the μM and demagnetization echoes, and furthermore, they occur at right angles to these echoes (in spin space). Thus, even when small spin-rotation and demagnetization effects are present, the θ1-t1-θ2 experiment provides a sensitive means of detecting the anisotropy.

Multiple spin echoes due to anisotropic spin diffusion in3He−4He solutions

In a polarized Fermi fluid longitudinal and transverse spin diffusion constants will differ from one another below a temperatureT a. Although Leggett-Rice effects are absent in degenerate spin-polarized3He−4He solutions at the3He concentrationx 3=3.8%, analysis of the equations of motion reveals that multiple spin echoes will still occur in θ1-t 1-θ2 NMR experiments due to the anisotropy in the spin-diffusion coefficients, ΔD=D ‖-D ⊥≠0. The absence of Leggett-Rice effects provides a unique opportunity to observe the nonlinear dynamics introduced by the anisotropy. It is shown that for temperatures below but nearT a, the second and third echo heights can be as much as 10% of the first echo.

A statistical study of polar mesosphere summer echoes observed by EISCAT

A comprehensive survey of data on ‘Polar Mesosphere Summer Echoes’, observed by the EISCAT VHF radar during 1988–1993, confirms that (1) these echoes are a summer phenomenon, with a season lasting from June to August; (2) PMSE occur most frequently around noon and midnight, and thus follow a semidiurnal pattern; (3) PMSE occur at a mean height of 85±2 km; (4) there is often a good correlation between the vertical Doppler velocity and the rate of change of echo height, which suggests that the echoing structures move bodily, perhaps in response to gravity waves. Previous results on the lack of correlation between the occurrence of PMSE and noctilucent clouds are reinforced.

Simplified NDE of a closed vertical crack using ultrasonics

Ultrasonic testing using a normally incident longitudinal wave is used for sizing a closed crack. The crack exists vertically on the back-wall of the inspected plate. In order to evaluate the closed crack, the relationship between the first back-wall echo height and the crack depth for an open crack as the basis for evaluating the closed crack is determined experimentally and is introduced to the analysis of echo height for the closed crack. The unknown parameters in the evaluation of the closed crack, such as crack depth and the stress closing the crack, are determined by comparing the first back-wall echo height obtained through both analysis and experiment on the closed crack.