Elastic Resonance Research Articles

Parametric attenuation and amplification of acoustic signals in the media with hysteretic quadratic nonlinearity

It is demonstrated that in a mesoscopic material with quadratic hysteretic nonlinearity a weak acoustic signal is initially attenuated in the field of a strong pump wave propagating in the same direction as the signal and is initially amplified in the field of a strong pump wave propagating in the opposite direction. The attenuation of a signal in the field of a strong standing pump wave is predicted. Consequently the subharmonic route to chaos observed in elastic nonlinear resonators does not seem to be favorable in resonance bars composed of mesoscopic materials (such as rocks, soil, concrete or damaged atomic materials). Theoretical predictions are in agreement with the available experimental data.

A comparative study of the scattering cross sections from incident plane wave acoustic waves on submerged evacuated and water-filled elastic shells

Employing the acoustic background for the case of elastic solids and elastic shells has facilitated the study of elastic resonances excited by incident acoustic signals. Once an adequate acoustic background became available it became possible to properly isolate and characterize such resonances. The recent development of an acoustic background for water-filled elastic shells allows for the characterization of water-filled shells. We present a comparative study for the elastic shell case for the evacuated and water-filled cases and thereby seek to elucidate new resonance mechanisms for the fluid-filled case.

Effect of Fe and Zr ion implantation and high-current electron irradiation treatment on chemical and mechanical properties of Ti–V–Al Alloy

Using Rutherford backscattering spectroscopy, nuclear elastic resonance analysis, atomic force microscopy, transmission electron microscopy, and wear resistance and microhardness tests, the alloy Ti41–V41–Al18 was investigated after Fe ion (60 kV) and Zr (40 kV) ion implantation and subsequent high-current electron beam (HCEB) irradiation at an energy flow density of 6 J/cm2, called duplex treatment. Profiles show that the maximum concentration of Fe ions was 16.5 at. % at 85 nm from sample surface and that of Zr ions was 0.85 at. % at 56 nm. The maximum of the Fe concentration profile was found to shift to the large sample depth toward after increasing the implantation dose. The surface alloy layer is composed of a number of structures: grains of dislocation substructure (2×1010 cm−2), grains with plates, and grains with packed martensite. The disorientation of regions is observed. After HCEB treatment, the disorientation of microregions increases (Δα=7.5°) and particles of Ti2Fe are formed. After double implantation, the dry friction wear and the friction coefficient decreased. After the duplex treatment, the thickness of the hardened layer and the wear resistance increased.

Effectiveness of Ti, TiN, Ta, TaN, and W2N as barriers for the integration of low-k dielectric hydrogen silsesquioxane

The interactions between low-k (dielectric constant) material hydrogen silsesquioxane (HSQ) and barrier layers, Ti, Ta, physical-vapor deposited (PVD), and chemical-vapor deposited (CVD) TiN, PVD TaN, and CVD W2N, have been investigated by using sheet-resistance measurement, x-ray diffraction, transmission electron microscopy, Rutherford backscattering spectrometry, elastic resonance scattering, and forward recoil spectrometry. The conventionally used dielectric PETEOS [plasma-enhanced chemical vapor deposition tetraethylorthosilicate (TEOS)] was also studied as a control. The results show that none of these barriers except Ti can react with HSQ and PETEOS at elevated temperatures. However, significant outdiffusion of hydrogen due to the degradation of the HSQ films upon annealing exists for all barrier/HSQ structures, and exhibits a strong barrier dependence. Metal barriers Ti and Ta, and CVD TiN can retard the H outdiffusion, whereas PVD TaN and PVD TiN induce the H outdiffusion from the HSQ films. The microstructural and structural considerations and a proposed “nitride effect” mechanism can give some reasonable interpretations to these observations. Upon annealing, the structural and/or compositional changes of these barrier films give rise to corresponding sheet resistance variations. The phase transformation of the Ta film on HSQ is completely inhibited because of the possible role of diffusing H atoms, as compared to the phase transformation occurring in the Ta film on PETEOS.

Diffraction topography using white X-ray beams with low effective divergence

The divergence of the incident X–ray beam as seen from a point in the specimen, the effective divergence α, is of the order of a microradian at a third generation synchrotron radiation source. This entails two effects on white– beam X–ray diffraction topography. 1. The specimen–detector distance can be varied at will in the metre range without appreciable blurring of the image. Thus the discontinuous change in distortion associated with magnetic domains, or implanted layers in a piezoelectric material, can often be directly measured. It was also possible to observe focusing effect due to continuous spatial variations of lattice plane orientation. This effect was visualized in the cases of the images of single dislocations, from elastic resonance patterns, and on wafer–bonded samples. 2. The small value of α can also be described as yielding appreciable lateral coherence of the beam. Propagation of the diffracted beam, i.e. Fresnel diffraction, can turn variations of the phase of the diffracted beam into changes in intensity, hence contrast. In the case of a periodic spatial variation of the phase due to periodic poling, the Talbot effect in the diffracted beam provides the possibility of measuring the difference in phase of a structure factor in inversion–related domains, i.e. for Friedel pairs.

Two-dimensional X pendulum vibration isolation table

We have extended to two dimensions a previously developed vibration isolation table using crossed wire suspensions (X mechanisms). A load table is suspended using a combination of normal and upside-down X mechanisms so that it moves freely with a very long period in both horizontal directions but is moderately stiff in all other degrees of freedom. Periods of 5 s are easily achievable. The transfer function of the prototype reported here contains a number of elastic mode resonance peaks, but it is shown by analysis how to reduce or eliminate nearly all of these.

Two-dimensional low-frequency vibration attenuator using X pendulums

We have designed and constructed an improved two-dimensional X pendulum vibration–isolation table. It achieved a lower resonant frequency (7 s) than previous prototypes, and the effects of many parasitic elastic resonances have been reduced by careful balancing, leading to much improved vibration isolation around a few hertz.

Defect-mediated elastic resonances in He-atom scattering from single-crystal surfaces

Experimental evidence for a new atom-surface resonant mechanism involving surface defects is presented. After an initial selective adsorption trapping into surface bound states of a NaCl ~001! surface, He atoms are subsequently scattered from surface defects back into the continuum. The inverse process also occurs: He atoms scatter from a defect and some of the amplitude enters the bound state eventually followed by selective desorption from the bound state via diffraction. For the 90°-scattering geometry used, the resonances show up as sharp peaks in the angular distributions of the quasielastic intensity between the diffraction peaks and are symmetric about the specular peak. A general description of the process is given which shows that it is a universal feature of any scattering system which can exhibit selective adsorption type resonances. @S0163-1829~98!00639-0#

Vibration of a cavitating elastic wing in a periodically perturbed flow: Excitation of subharmonics

Vibration of an elastic cavitating wing in periodically perturbed flows is analyzed. Because cavity thickness and length are perturbed, too, an excitation with a fixed frequency leads to a parametric vibration of the wing, and this vibration spectra’s amplitudes have nonlinear dependencies on amplitudes of the perturbations. Numerical analysis was carried out for two-dimensional flow of an ideal fluid. Wing vibration was described by the equation for a beam in bending motions. As a result, two frequency bands of an essential vibration increase are found. A high-frequency band is mainly associated with an elastic resonance of the wing, and a cavity can do certain damping there. A low-frequency band is associated with cavity volume oscillations. The governing parameter for the low-frequency vibration is the Strouhal number (Sh) based on the cavity length. The most significant vibration in the low-frequency band corresponds to approximately constant values of Sh and has the most extensive subharmonics.

Study of the proton-rich nucleus 8B in the resonance scattering of radioactive 7Be by hydrogen

The excitation function is measured for 7Be+p elastic resonance scattering at an angle of 180° in the center-of-mass frame. The measurements are made by a new method which combines the advantages of inverse kinematics and thick targets. New information is obtained about the structure of the levels in the 8B nucleus.

Matrix theory of elastic resonance scattering

A fundamental matrix theory is developed for the exact isolation (in both magnitude and phase) of resonance amplitudes contained in the elastic field scattered by a penetrable target. Similarities and differences between this matrix theory and the classical resonance scattering theory [L. Flax, L. R. Dragonette, and H. Uberall, J. Acoust. Soc. Am. 63, 723–731 (1978)] are discussed. The matrix theory is then applied to cylindrical and spherical fluid-filled cavities, and analytical expressions for the resonance amplitudes are derived. In the vicinity of resonance frequencies, the resonance amplitude expressions have forms similar to the Breit–Wigner formula. In order to check the validity of the matrix theory, numerical calculations are performed for a cylindrical water-filled cavity in an aluminum medium. Resonance spectra of the cavity are presented for some partial waves and their characteristics are also discussed.

Experimental measurements and theoretical modeling of acoustic scattering by a cube

Acoustic backscattering can be used to assess quantitatively the size and concentration of suspended sediments above the seabed. This technique depends on a knowledge of the backscattering form function for the scattering particles, which for simplicity are normally assumed to be spheres. In order to investigate the scattering from other shapes a series of measurements have been made of the acoustic backscattering behavior of both nonmetallic (glass) and metallic (steel) cubes over a wide frequency range. A laboratory system using a parametric array was used to make measurements between 20 and 200 kHz on cubes of side 20 mm, corresponding to ka values up to 10. Results are presented for a range of incidence angles involving incidence on a face, an edge, and a corner. At higher frequencies elastic resonances are observed, while at lower frequencies the average form function shows characteristics similar to those due to creeping waves on a sphere. The results are compared with theoretical predictions obtained with a boundary element model and a combined finite element/boundary element model. The agreement is observed to be very good. [Work partially supported by the MAST program of the EC, contract MAS3-CT95-0017 (TRIDISMA).]

Leaky waves and the elastic wave resonance reflection on a crystal-thin solid layer interface. II. Leaky waves given rise to by exceptional bulk waves

A study is made of the elastic wave resonance reflection in a crystal-thin solid layer structure near the velocity of a leaky wave which originates from an exceptional bulk wave. The latter is a homogeneous mode with group velocity parallel to the boundary of a medium which satisfies the condition of the mechanically free surface. On the surface coated with a thin layer, the exceptional bulk wave can transform into the leaky wave and then there arises a narrow interval of incident angles where the coefficients of mode conversion suffer abrupt and strong variations in phase and magnitude. A criterion of occurence of the leaky wave is found. Approximate expressions describing the behavior of the coefficients of mode conversion within the resonance interval of incident angles are derived and analyzed.

Donors in a strong magnetic field and elastic magnetic-impurity resonance in diamondlike semiconductors

The possibility of resonance during elastic intravalley scattering in n-type semiconductors is investigated in connection with the crossing (due to anisotropy of the effective mass) of the energy levels of excited states of a shallow donor as functions of the magnetic field. The hybridization of states of different frequencies in the vicinity of a crossing is attributed to the emergence of a nonzero dipole moment of the excited impurity atom and, accordingly, a long-range potential, which creates carrier-transport anomalies. The lower part of the donor spectrum is calculated as a function of the magnetic field in Si with B∥〈001〉 and in Ge with B∥〈111〉 or B∥〈110〉. A crossing occurs in Ge in the field range 9.9 T<B<16.7 T and in Si in the field range 10.5 T<B<37.7 T. The characteristic longitudinal relaxation time and the transverse conductivity, which are determined by scattering at excited donors in the presence of the hybridization of states, are calculated.

HADRONIC FORM FACTORS AND PERTURBATIVE QCD

▪ Abstract The electromagnetic form factors of hadrons at large momentum transfer have been the subject of intense theoretical and experimental scrutiny over the past two decades, yet there is still not a universally accepted framework for their description. This review is a synopsis of their current status. The basic theoretical approaches to form factors at large momentum transfer are developed, emphasizing the valence quark and Feynman (soft) pictures. The discussion includes the relation of these descriptions to the parton model, as well as the roles of factorization, evolution, Sudakov resummation and QCD sum rules. This is followed by a discussion of the experimental status of pion and nucleon elastic form factors and resonance production amplitudes in the light of recent data; the successes and shortcomings of various theoretical proposals are highlighted.

Acoustic scattering by nonmetallic and metallic cubes in the elastic resonance regime: Experimental measurements and combined finite element/boundary element modeling

The acoustic backscattering behavior of both nonmetallic (glass) and metallic (steel) cubes has been investigated over a wide frequency range where elastic resonances are important in determining the acoustic response of the cubes. A laboratory system incorporating a parametric array was used to make measurements between 20 and 200 kHz using cubes of side (l) 20 mm, and a combined finite element/boundary element code was used to numerically model scattering by the cubes. The frequency range covered corresponds to ka values up to 10, where a=l(3/4π)1/3 is a characteristic dimension of the cube. Results are presented for three scattering geometries involving incidence on to a face, an edge, and a corner. The backscattered form function differs greatly for the different geometries and is seen to depart significantly from that of a rigid cube when ka&amp;gt;5 due to the elastic resonances of the cube. The resonance contributions are clearly seen when the rigid background is subtracted from the elastic predictions.

Evidence for a deep bound-state level in the 4HeNaCl(001) potential

Through a systematic high-resolution study of the elastic bound state resonances observed in the inelastic background of the angular distributions of 4He scattering from the NaCl(001) surface, carried out at 90 K, we obtained clear and conclusive evidence that a deep level in the 4HeNaCl(001) interaction potential exists at −7.07 meV. Important deviations from the free-atom dispersion are observed, as expected for deep bound-state levels. We discuss the physical reasons why deep-level resonances, which are observed in inelastic scattering, may not be detectable in elastic scattering experiments. This finding appears to be crucial with respect to the theory of atom-surface potentials since former quantum-mechanical and close-coupling calculations excluded the existence of a deep level in 4HeNaCl(001) in agreement with elastic scattering studies but at odds with phenomenological predictions.

Analysis of elastic cavitating wing vibration

A two-dimensional unsteady potential flow outside an elastic partially cavitating wing is analyzed numerically by using the Birnbaum equation on the hydrofoil chord and the Lagrange–Cauchy integral on the cavity. The angle of attack has a small periodic perturbation, and cavity thickness and length also take perturbations. Wing vibration is considered to be vibration of a variable thickness beam with two clamp bolts near the beam center. A monofrequency flow perturbation induces monofrequency flexural vibration of a noncavitating wing, but the vibration of a cavitating wing has multifrequency. Computation of NACA-16009 hydrofoil vibration was made for various free-stream speeds, module of elasticity, fluid, and wing densities, and as a result, three frequency bands of a vibration increase are determined. The low-frequency band is connected with a cavity volume oscillation. There is a considerable influence of cavity length on vibration. The high-frequency band is connected with elastic resonances of the wing. A solitary resonance was found in the middle band. This resonance has a nonlinear dependence on the loss coefficient and does not have a dependence on cavity dimensions and wing elasticity. This resonance appearance is connected with an interaction of lift and media inertia forces.

Defect-Mediated Diffraction Resonances in Surface Scattering

A new elastic surface resonance has been observed in angular distributions of He atoms scattered from a single crystal surface NaCl(001). The process has been identified as a coherent selective adsorption into one of the surface bound states followed by incoherent scattering from defects into the continuum. The reverse process has also been identified. These resonances open up possibilities for other highly defined two-dimensional elastic and inelastic surface scattering experiments. [S0031-9007(97)02364-8]

Surface and near surface structure and composition of high-dose implanted and electron beam annealed single crystal copper

Cu(111),(100) single crystals implanted with Ti up to 8 × 10 17 cm −2 followed by high-current electron beam annealing (HCEB) have been investigated by means of transmission electron microscopy (TEM), Rutherford back-scattering (RBS), nuclear reaction elastic resonance (NRER) and scanning electron microscopy (SEM). Ti, O, C concentration profile behaviour in Cu single crystals has been studied. Cu layer structure after Ti implantation became multi-component. It was found that this layer included a surface amorphous carbon film, a layer consisting of TiC, a layer consisting of (110)CuTi/(111)TiC and a subsequent Cu single crystal possessing subgrains of 170–180 nm. A small-angle disorientation up to 5 ° between the subgrains was observed. As a result of HCEB irradiation, a portion of carbon film evaporated, and Ti carbide dispersed to 2–4 nm. The Cu structure essentially changed. The Cu layer contacting the carbide became a nano-dimensional substructure with an average crystallite size of 50–70 nm. At a depth of 0.1 μm the Cu structure is represented as a disoriented striped substructure: the discrete disorientation between the stripes was about 6–7 °. Net dislocation substructure was observed inside the stripes, the dislocation scalar density of which was < γ> = 5.2 × 10 10 cm −2.