The ultrasonic characteristics of couplant oils for propagation of transverse waves were determined by diffracted SH waves. Although paraffin and silicone oils with nearly straight chains showed negligible transmissibility, regardless of viscosity, saturated naphthenic hydrocarbon oils (NHO) with bridged rings showed superior transmissibility, depending on viscosity. The good transmissibility arises from the appearance of a quasielastic shear response under ultrasonic vibration, based on the interlocking of sterically hindered molecules.
The characteristics of the sound field of under-expanded cold jet impingement flows were studied by measuring the noise emanating from two convergent and one convergent-divergent nozzle when the jet impinges on a flat plate kept perpendicular to the direction of the jet. The measurements were conducted upstream of the nozzle over an extensive envelope of jet operating conditions such as chamber stagnation pressure, mass flow rate through the nozzle, and diameter of the nozzle.
Five kinds of leaves and agar sheets (as an imitation of leaves) suspended in water were characterized nondestructively using ultrasonic transmission analysis of longitudinal ultrasonic waves. The wave patterns of morning glory, persimmon, hydrangea, fragrant olive and tea were found to be simple compared with those of artificial solids. As the thickness of tea leaves increases, the phase velocity increases and attenuation coefficient, frequency and phase decrease. In contrast, the phase velocity of agar sheets decreases with increasing thickness and content of agar. This shows that acoustic properties of leaves cannot be interpreted by their agar component alone.
The propagation characteristics of SH waves passing through titanium containing absorbed hydrogen were investigated as a function of hydrogen content. With increase in hydrogen content, the propagation time decreases, the logarithmic damping ratio of the receiving waves increases and the phase becomes delayed at frequencies below 5.7MHz, indicating lattice hardening due to hydrogen solution, dynamic vibration of octahedral interstitial hydrogen atoms and an increment of the y hydride phase with the larger lattice.
We have studied the behaviour of guided waves on an elastic plate of linearly decreasing thickness as they reach their frequency-thickness product cut-off. We show that most of them are reflected, and that some of them are converted into waves which propagate further in the decreasing thickness direction.
The transmission frequency spectrum at normal incidence of a water-loaded glass plate has been studied searching for modes of a predominantly leaky nature. Near the cut-off frequency of the mode A2, an antisymmetric mode A3'of a predominantly leaky nature was observed in the frequency spectrum of the leaky field. The mode A3' is completely separated from the neighbouring modes A2 and A3 by displacing the time-window of the recording oscilloscope into the free-emission regime. It is demonstrated that plate modes of a different nature contribute to the specular acoustic field and to the leaky field.
Measurements of the source level and directivity pattern of an underwater paraboloidal sound source based on electrical discharge are presented. The energy density of the pressure pulse is determined for both the spherical wave and the wave reflected by the paraboloid, together with their source levels. The directivity pattern of the paraboloidal source is obtained, calculating the total energy of its acoustic signature. Spectral analysis performed in octave bands from 1kHz to 500kHz shows that the directivity increases with frequency as for a circular piston of equal aperture.
A method to determine the transversal wave velocity in submerged plates is presented. It is based on an analysis of the transmission coefficient of the plate between its first and second critical angles, where the only bulk waves present in the plate are shear waves. According to the resonance theory of plate modes, the parametric representation of the transmission coefficient of a plate in the complex plane (an Argand diagram) is a circle. It turns out that the experimental Argand diagram can be given the same orientation as the theoretical diagram by introducing a time-delay between the transmitted and the reference signal during the normalisation process. Between the first and second critical angles, this time-delay depends on the transversal wave velocity only. We propose to determine the time-delay required for a correct orientation of the Argand diagram and to calculate from it the transversal wave velocity.
We describe a new approach to imaging an object profile using the scattered wavefield. The object is illuminated by broadband radiation and the scattered field is received by a circular array of sensors encircling the object. The notable findings are: Firstly, since the measured scattered field is proportional to the object Fourier transform, errors due to finite Fourier transformation may be avoided, resulting in a better reconstruction. Secondly, a circular array allows us to use the object Fourier transform over a much larger pass disc than a linear array would allow. As a result, we obtain a sharper reconstruction for the same number of receivers and illuminations. Thirdly, with broadband radiation a reduction in the number of illuminations can been achieved. For example, it is demonstrated that with just four illuminations we can cover more than 80% of the pass disc. Thus, a trade-off can be made between the bandwidth and the number of illuminations.
The dispersion curves of a fluid plate obtained by solving the dispersion equation in the complex frequency plane or in the complex angular plane show a fundamental difference for low frequency-thickness products. The aim of this paper is to compare the behaviour of both solutions in this case and to give an approximate analytic solution of the dispersion equation in the complex angular plane, which is in good agreement with the exact one.
The instantaneous elastodynamic Poynting vector and its time-averaged complex cognate can be used to visualize not only the instantaneous energy flux associated with elastodynamic waves but also their traveling and standing wave components. A novel geometric interpretation is made for the instantaneous Poynting vector in an elastodynamic medium to aid in that visualization. It is noted that the geometry of the instantaneous Poynting vector's time evolution can, with suitable symmetries in the geometry of the medium, and thus of the stress tensor, be related to the time-averaged complex Poynting vector.
Ultrasonic velocity has been measured in binary mixtures of acetyl acetone (HAA) and di-isobutyl ketone (DIBK) with a number of non-polar solvents, at 303.16K and 2MHz. The data have been used for evaluation of isentropic compressibility, inter-molecular free length and specific acoustic impedance, with the aim of identifying a suitable nuclear extractant from studies of molecular interaction in the systems.
In this work the possibility of realizing a novel accelerometer by using a ring-shaped piezoceramic, loaded by a seismic mass in its inner space. has been investigated. Measurements were carried out by using two different electrode configurations in order to reveal both symmetrical and antisymmetrical modes. The experimental results show that this structure allows an increase of the sensitivity, by increasing the seismic mass, without sacrificing the useful bandwidth. as happens in traditional accelerometers. Moreover, for the symmetrical modes, this sensor exhibits planar isotropy, i.e., it shows the same response for any mechanical excitation in the plane.
Automatic identification of groups of dolphins has become desirable for comparison of behaviour involving a population of wild dolphins. Software methods have been developed to detect and process their tonal whistles to allow feature extraction to be carried out before automatic identification. The preliminary results of applying these techniques to 101 whistle contours were successfully characterised including 8 from two simultaneously whistling animals where the contours crossed each other in frequency. A further 15 whistles that were not successfully characterised could not be characterised visually either.
A new auto-regressive based (AR) adaptive notch filtering algorithm is formulated for howling cancellations. The algorithm, being both time and order recursive, consists of a lattice structure followed by an all-pole filter. The roots of predictor polynomials, associated with each stage of the lattice filter, are constrained to be on the unit circle and in complex conjugate pairs. The all-pole filter has all its poles equal to the zeros of the last stage predictor polynomial multiplied by a positive number less than unity. Simulation and real time results attest to the practical usefulness of the proposed algorithm.
It is likely that any assessment of the environmental sustainability of a new road scheme will contain a consideration of the noise impact on those living and working within the vicinity of the proposed scheme. In particular, there will be an assessment of how noise levels are likely to change with increasing traffic flow. This work seeks to determine how accurate such assessments will be, in general. The correlation has been studied between the noise level within the small urban environment and the volume of traffic flow. Data from ten sites were used where there were both continuously monitored traffic flow data and noise data from a survey. A calculation of the increase in noise level per extra vehicle movement per hour gave a value of 0.0023 plus or minus 0.0005 dB(A)(L10) at 1500 vehicle per hour. The calculation of Road Traffic Noise (CRTN) method would have yielded a slightly higher value overall of the range of vehicle movements considered. (A)
A novel method for the computational determination of proper modes in 2D composite membranes is presented, together with some results in a simple case. In this method the evolution of each eigenset is tracked as the structure is modified from an initial simpler form to its final configuration.
By including the effect of fluid loading for the thin spherical shell in a proper manner, so- called shell theories can predict the water borne pseudo-Stoneley waves described extensively in the literature. Shell theories give reasonably good results for the motion of a bounded elastic shell by using the assumption that various parts of the shell move together in some reasonable manner. Without proper fluid loading, however, shell theories do not predict the pseudo-Stoneley resonances observed in nature and predicted by exact theory. With proper fluid loading, as well as rotary inertia and translational and rotary kinetic energy terms, a shell theory can exactly predict these water borne resonances. These resonances are predicted by the shell theory and compared with results from exact elastodynamical calculations.
Describes an application of the dynamic focusing technique for underwater 3D acoustic imaging. In particular, the integration of dynamic focalization with an FFT implementation of phase-shift beamforming has been developed in order to avoid an increase in computational complexity. The resulting system, which uses narrow-band signals, permits the formation of 3D images at a high frame rate and without the limitations imposed by the depth of field on fixed-focused beamforming. Some simulations made it possible to test the proposed system, and the related results are reported
Relations for the theoretical estimation of isentropic compressibility K s and speed of sound U in binary non-electrolyte liquid mixtures based on the Prigogine-Flory-Patterson (PFP) theory have been obtained. K s and U have been theoretically calculated using the PFP theory for eleven binary mixtures: n-hexane+n-heptane, n-hexane+n-dodecane, di-n-propyl ether (DPE)+n-heptane, benzene+n-heptane, benzene+ tetrachloromethane (CTC) and cyclohexane+CTC at 298.15 K; ethyl acetate (EA)+n-hexane, EA+cyclohexane, EA+benzene and EA+CTC at 303.15 K and benzene+cyclohexane at 293.15, 298.15, 303.15 and 323.15 K
