Direction Of Sound Propagation Research Articles

Sound propagation and damping in the vicinity of thesmectic−A–hexatic−Bphase transition of 4-propionyl-4′−n-heptanoyloxyazobenzene

Sound velocity and damping were measured in 4-propionyl-${4}^{\ensuremath{'}}\ensuremath{-}n$-heptanoyloxyazobenzene above its $\mathrm{Sm}\ensuremath{-}A\char21{}\mathrm{Hex}\ensuremath{-}B$ phase transition. The measurements were taken at 1 MHz (velocity) and at 3, 9, 15, and 21 MHz (damping) as a function of the angle \ensuremath{\theta} between the sound propagation direction and the normal to the smectic layers. The velocity presents a marked anomaly for $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{},$ whereas a much smaller anomaly is observed for $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{},$ indicating that the phase transition occurs essentially within the smectic layers. Analysis of these measurements allows the de Gennes elastic constants $A,$ $B,$ and $C$ to be determined. Like the velocity, the damping presents significant pretransitional effects for $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{},$ reminiscent of those generally observed in the vicinity of second-order or weakly first-order phase transitions. The damping also increases for $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ when $\stackrel{\ensuremath{\rightarrow}}{T}{T}_{A\ensuremath{-}\mathrm{Hex}},$ but the behavior observed does not resemble the usual critical behavior. It is shown that this pseudocritical behavior stems essentially from a contribution of the anharmonic effects. The anisotropy of the critical effects on velocity and damping can be explained by the theory elaborated by Andereck and Swift for the $\mathrm{Sm}\ensuremath{-}A\char21{}\mathrm{Sm}\ensuremath{-}C$ transition and transposed to the $\mathrm{Sm}\ensuremath{-}A\char21{}\mathrm{Hex}\ensuremath{-}B$ transition. Analysis of the velocity measurements indicates that the specific-heat exponent is of the order of 0.6. This value, which is far from that associated with the three-dimensional $\mathrm{XY}$ universality class -0.007 to which this transition should in principle belong, confirms the results obtained by calorimetry. The critical relaxation time is characterized by the dynamic exponent $z\ensuremath{\nu}\ensuremath{\simeq}1,$ which corresponds to conventional critical slowing down.

An investigation of penetration depth control using parallel opposed ultrasound arrays and a scanning reflector.

A theoretical study of penetration depth control in superficial hyperthermia utilizing parallel opposed linear ultrasound arrays and a double-faced (V-shaped) scanning reflector is presented. This is a dual array system (DAS), where one array operates at a low frequency and the other at a high frequency (1 and 5 MHz, respectively in this study). The arrays are positioned facing each other and both are aimed at a double-faced scanning reflector which distributes the energy over the scanned surface. Each reflecting surface is angled at 45 degrees with respect to the sound propagation direction so that both beams are deflected in the same direction toward the treatment volume. The system was designed to be compatible for combined operation with a medical linear accelerator for the delivery of simultaneous thermoradiotherapy. It is demonstrated that by varying the excitation magnitude of one array relative to the other, it is possible to control the magnitude of absorbed energy as a function of depth, and thus improved control of the heating pattern in all three spatial dimensions is obtained. This improvement is demonstrated with bio-heat transfer simulations which show how penetration depth control translates into control of temperature distributions. The simulations also show that the DAS is able to produce more uniform temperature distributions in highly perfused tissue.

Experimental demonstration of a Fermi surface at one-half filling of the lowest Landau level.

We report the first direct observation of the cyclotron motion of new quasiparticles in a 2D electron system near 1/2 filling factor. Just as electrons in a metal geometrically resonate with a sound wave when a magnetic field is applied perpendicular to the sound propagation direction, near 1/2 filling factor we observe resonance of a surface sound wave with cyclotron orbits of charge carriers. The presence of a Fermi surface and geometric resonance of a sound wave with Chern-Simons gauge transformed fermions were explicitly predicted in a recent theory of the half filled Landau level.

Ultrasonic studies of thermally assisted flux flow and intrinsic pinning in high- Tc phase Bi-Pb-Sr-Ca-Cu-O ceramics

The temperature dependence of the ultrasonic attenuation coefficient α ( T, H) and sound velocity V s( T, H) were measured under magnetic fields for high- T c phase Bi-Pb-Sr-Ca-Cu-O ceramic samples aligned with the c-axis. In the case H · k , where k is the direction of sound propagation, a broad peak was observed in the α( T, 10T)-α( T, 0 T) versus T curve at T ∼ 65 K accompanied with a broad step in the V s( T, 10 T) - V s( T, 0 T) versus T curve. On the other hand, the peak and the step were also observed in the case of H | k , were the temperature position shifted down to T∼50 K, and the width was narrower than in H · k . The behavior was explained in terms of thermally assisted flux flow in which flux lines are pinned by intrinsic pinning centers.

Brillouin scattering study of the anisotropic acoustic anomaly in ferroelectric and ferroelastic phase transitions

A brief review is given for the Brillouin scattering studies of the dependence of the acoustic anomaly on the direction of sound propagation in structural phase transitions in ferroelectric and ferroelastic crystals. Near the ferroelectric phase transition temperature, the polarization fluctuation shows a characteristic anisotropic anomaly due to electrostatic and elastic long range forces. This anisotropy is observed directly or indirectly as the anisotropic acoustic anomaly by the Brillouin scattering. Near the ferroelastic phase transition, the acoustic mode softens only along a characteristic direction in the crystallographic system. Brillouin scattering has an advantage to observe directly the dependence of the sound wave frequency on the propagation direction.

Quantization of the acoustoelectric current in a two-dimensional electron system in a strong magnetic field.

An expression for the off-diagonal component of the acoustoelectric tensor is obtained from the momentum-conservation law. The acoustoelectric current along the direction of sound propagation exhibits plateaus as a function of gate voltage if the circuit in the perpendicular direction is open. The product jB has the same plateaus as a function of magnetic field. The values of jB at the plateaus are equidistant and are separated by deep minima. The ratio of the plateau values of the current to the open-circuit voltage is equal to ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{y}}$. This effect can be used for measuring the intensity of a surface acoustic wave propagated through the heterojunction.

Errors in the automatic measurement of spatial acoustic intensity in the direction of sound energy propagation with a rotating probe

For the automatic measurement of spatial acoustic intensity the authors have devised a rotating probe comprising two microphones, which are arranged in parallel with the axis of the probe's holder and shifted by a minute distance from each other in the direction of the microphone axis. If measurements are carried out, once before any rotation of the probe, and twice at two different predetermined angles of its rotation around the holder axis, then it is possible to determine easily the three components of an acoustic intensity vector in the corresponding three co-ordinate axis directions. Theoretical and experimental investigations are presented of the possible error in automatic measurement of spatial acoustic intensity in the direction of sound energy propagation with such a probe. On the basis of the theory of measurement with a rotating probe and the fundamental error theory of the acoustic intensity method, it is possible to calculate the theoretical error in the direction of sound energy propagation. The results of calculations of this error agree well with those of measurements, and it is shown that the measurement error in the direction of sound energy propagation depends upon the frequency of the sound wave as well as on the incidence angle on the probe. These results have made it possible to determine the measurement error limit in the direction of sound energy propagation.

Quantitative flaw characterization with scanning laser acoustic microscopy : Generazio, E.R.; Roth, D.J. Materials Analysis by Ultrasonics — Metals, Ceramics, Composites. Edited by A Vary. pp. 331–348. Noyes Data Corporation, New Jersey, United States (1987)

Surface roughness and diffraction are two factors that have been observed to affect the accuracy of flaw characterization with scanning laser acoustic microscopy. Inaccuracies can arise when the surface of the test sample is acoustically rough. It is shown that, in this case, Snell's law is no longer valid for determining the direction of sound propagation within the sample. The relationship between the direction of sound propagation within the sample, the apparent flaw depth, and the sample's surface roughness is investigated. Diffraction effects can mask the acoustic images of minute flaws and make it difficult to establish their size, depth, and other characteristics. It is shown that for Fraunhofer diffraction conditions the acoustic image of a subsurface defect corresponds to a two-dimensional Fourier transform. Transforms based on simulated flaws are used to infer the size and shape of the actual flaw.

Quantitative flaw characterization with scanning laser acoustic microscopy : Generazio, R.E.; Roth, D.J. Analytical Ultrasonics in Materials Research and Testing. Proceedings of a conference, NASA Lewis Research Center, Ohio (United States), 13–14 Nov. 1984. pp. 341–358. NASA Conference Publication 2383 (1986)

Surface roughness and diffraction are two factors that have been observed to affect the accuracy of flaw characterization with scanning laser acoustic microscopy. In accuracies can arise when the surface of the test sample is acoustically rough. It is shown that, in this case, Snell's law is no longer valid for determining the direction of sound propagation within the sample. The relationship between the direction of sound propagation within the sample, the apparent flaw depth, and the sample's surface roughness is investigated. Diffraction effects can mask the acoustic images of minute flaws and make it difficult to establish their size, depth, and other characteristics. It is shown that for Fraunhofer diffraction conditions the acoustic image of a subsurface defect corresponds to a two-dimensional Fourier transform. Transforms based on simulated flaws are used to infer the size and shape of the actual flaw.

Anisotropic attenuation of zero sound in superfluid3He-A

The anisotropic attenuation of zero sound in superfluid3He-A at 29.3 bar pressure has been measured at 24.4, 34.2, 44.2, 54.0, 63.9, 73.7, 83.5, and 93.4 MHz. The clapping mode resonance has been observed at all frequencies, and the reentrant normal flapping resonance has been measured for the first time. Analysis of these results leads to anf-wave pairing parameter,x 3 −1 −0.1±0.05, and a determination of strong coupling corrections to the energy gap far fromT c. This is expressed by an enhancement of the zero-temperature energy gap by a factor 1.3±0.1 above that of weak coupling, 2.03k B T c . The clapping mode data is consistent with a nontrivial, strong coupling correction to the mode frequency, reducing it by 6%. The3He was confined to a slab 250 µm in thickness and the superfluid texture was oriented by a magnetic field. This allowed attenuations up to 100 cm−1 to be resolved and the attenuation from pair-breaking processes alone to be determined for the first time. The sound attenuation was measured for angles between the sound propagation direction and the1vector of 0, π/4, and π/2. The sensitivity of the numerically evaluated attenuation to quasiparticle collision time,f-wave parameter, and uniformity of the orbital texture is explored.

Effects of fiber motion on the acoustic behavior of an anisotropic, flexible fibrous material

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the direction of sound propagation was parallel or normal to the fiber arrangement. Normal-incidence sound-absorption measurements were taken for both fiber orientations over the frequency range 140–1500 Hz and with bulk densities ranging from 4.6–66.7 kg/m3. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a resonance, which modified the absorption that was primarily attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of resonances in the data were not present. From comparing these two sets of data and from considering the material structure, the resonance in the data for fibers normal to the direction of sound propagation was attributed to fiber motion. An analytical model for the acoustical behavior of the material displayed the same fiber-motion characteristics shown in the measurements.

Ultrasonic absorption in the magnetic superconducting system Er1−x\HoxRh4B4

Ultrasonic attenuation measurements as a function of temperature at constant magnetic fields and as a function of magnetic field at constant temperatures in Er1−xHoxRh4B4 show interesting behavior at low temperatures. The enhanced attenuation observed in the superconducting state and the sharp change in attenuation at magnetic phase transition for the superconductors in this system are attributed to spin-phonon interaction. The peculiar dependence of attenuation on orientation of magnetic field with respect to sound wave propagation direction evidences indirectly the coexistence of magnetic order and superconductivity. A two-level model of phonon-phonon interaction is proposed to elucidate the occurrence of relaxation type attenuation maxima observed in the temperature-dependent attenuation curves of all the samples. Furthermore, the attenuation behavior at low temperatures in high magnetic fields may also manifest the occurrence of a new magnetoelastic coupling effect.

Coupling of zero sound to the real squashing mode in rotating 3He-B.

Rotation of superfluid $^{3}\mathit{B}$ in an magnetic field enhances the coupling of the nonzero ${\mathrm{m}}_{\mathrm{J}}$ substrates of the real squashing collective mode to the zero sound, and the fivefold line splitting becomes observable even when H is parallel to \ensuremath{\Omega} and to the direction of sound propagation. Equilibrium vortex lattices and vortex-free states can be distinguished by their characteristic absorption spectra. The dependence of the sound attenuation on the angular velocity in magnetic fields up to 32 mT is reported; the data are qualitatively compared with theory.

Real‐time visualization of acoustic wave fronts by using a two‐dimensional microphone array

This article describes a real‐time visualization system for sound fields. The system includes a two‐dimensional microphone array (8×8), which eliminates the need for mechanically scanning the microphone and enables real‐time processing. Three methods are tested for drawing interpolated images of sound fields from the sparse sampling points. A frequency‐detection circuit is introduced to show the direction of sound propagation stroboscopically. Superposition of visualized sound wave fronts on the video picture of the field helps one to understand the sound fields present.

Abnormal behavior of sound velocity and damping in the vicinity of the smectic-A-smectic-C transition in terephthal-bis-p-p'-butylaniline (TBBA).

Sound velocity and damping measurements, taken at various angles $\ensuremath{\theta}$ between the normal to the smectic layers and the sound propagation direction, are reported for TBBA near its $\mathrm{Sm}A\ensuremath{-}\mathrm{S}\mathrm{m}C$ transition. Both velocity and damping present marked pretransitional anisotropic effects above ${T}_{\mathrm{Ac}}$. The anisotropy of the transition also manifests itself on the positions of the damping peaks of which that for $\ensuremath{\theta}={0}^{\ensuremath{\circ}}$ moves towards low temperatures as the frequency increases, whereas no displacement is observed for 0=45\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{}. The results are compared with the predictions of the current theories.

Ultrasound attenuation peaks due to order parameter collective modes in impure superconductors with strong electron-hole asymmetry

First we develop the general theory of order parameter collective modes and their sound attenuation in dirty superconductors with even-parity pairing. For the BCS state the theory yields a peak in the attenuation of longitudinal ultrasound whose height is proportional to ωo[ηJ(s)]2 and whose positiont p ≡1 -T p /T c and width are proportional to ωo/Γ = 2sql(s=v s /v F ). Here, η is the particle-hole asymmetry parameter,J(s) a given function, ωo the sound frequency, and Γ=1/2τ −1 the normal state scattering rate. For η ∼T c /T o ∼ 0.1,s=2/3, and ωo/Γ ∼ql « 1, the peak agrees qualitatively with the peaks found earlier for the polar and axial states. However, at low temperatures the attenuation goes like T4 instead ofT 3. We conclude that the observed longitudinal ultrasound peaks in the heavy-fermion superconductors UBe13 and UPt3 can be explained equally well by any anisotropic state having nodes in the gap, in particular, by a conventional state whose gap has the full symmetry of the Fermi surface. The nature of the state is reflected mainly in the dependence of the peak on the direction of sound propagation.

Experimental estimation of the viscous component of ultrasound attenuation in suspensions of bovine skeletal muscle myofibrils

It has been suggested that viscous losses, caused by the motion of myofibrils relative to their environmental fluid, could be the major cause of ultrasound attenuation in muscle. This Paper presents theoretical and experimental estimates of the viscous component of attenuation in suspensions of myofibrils. Experimental estimates were made by monitoring the effects of varying the viscosity and density of the suspending fluid and ranged from 0.55 to 0.72 cm 2 g −1 protein at 7 MHz, when expressed as mass attenuation coefficients. This represented 16–22% of the total attenuation measured in suspensions. Corresponding theoretical calculations were lower: 0.44 and 0.21 cm 2 g −1 protein, respectively, for suspensions with the myofibrils aligned along and across the direction of sound propagation. It was concluded that most of the attenuation was caused by other absorption processes.

Errors of the sound propagation direction measured by an automatic measurement technique of acoustic intensity.

This technique uses a new type of intensity probe which consists of two microphones arranged side by side and which are slid back and forth by a small distance in the direction of the microphone axes. This probe is turned twice on its holder axis by steps of a fixed angle for measuring the three components of an acoustic intensity vector. It is the purpose of this paper to investigate, theoretically and experimentally, the error of the sound propagation direction measured by this automatic measurement technique. This error can be calculated from the measurement theory of the probe and the theory of fundamental errors in the acoustic intensity method. The calculated results agree fairly well with the measured ones. These results show that the error in measurement of sound propagation direction is influenced by the incident angle and frequency of the sound incident to the probe. The limit of the error due to these effects was clarified.

Interaction of two parallel cylinders located in tandem along the direction of sound wave propagation

up to the limit state for a quasistatic change in the pressures Pz and P2If Pl = Pz* = 0 or P2 = P2* = 0, then it follows from (3.2) that the elastic strains of the disc under consideration up to the limit state assure the conditions P2 < P2* and Pz < Pz*, respectively. To determine the domain of quasistatic change in the pressures Pz and P2 in which the strains of a circular disc with optimal inhomogeneity are elastic, numerical integration of the fundamental equations must be used.

Effects of fiber motion on the acoustical behavior of an anisotropic, flexible fibrous material

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the direction of sound propagation was parallel or normal to the fiber arrangement. Normal incidence sound absorption measurements were taken for both fiber orientations over the frequency range 140 to 1500 Hz and with bulk densities ranging from 4.6 to 67 kg/cu m. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a strong resonance, which increased absorption above that attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of strong resonances in the data were not present. The resonance in the data for fibers normal to the direction of sound propagation is attributed to fiber motion. An analytical model was developed for the acoustic behavior of the material displaying the same fiber motion characteristics shown in the measurements.