Experimental verification of the Kramers-Kronig relationship for acoustic waves

A spectral technique for effectively and accurately measuring acoustic attenuation over a wide frequency range is reported. The spectral technique for phase measurement developed by W. Sachse and Y.H. Pao (1978) was used to determine the acoustic dispersion. For acoustic waves, a very simple and useful Kramers-Kronig relationship was previously derived by M. O'Donnell, E.T. Jaynes, and J.G. Miller (1981). The attenuation was calculated, using this relationship, from the measured dispersion and then compared with the attenuation that was measured independently. Dispersion was deduced from the measured attenuation and compared with the measured dispersion. The results of two highly attenuative specimens are presented. The agreement between the calculated attenuation and measured attenuation is excellent. The deduced dispersion also agrees well with the measured one. This agreement verifies the simple Kramers-Kronig relationship used. It further shows the accuracy of the spectral techniques for attenuation and dispersion measurements over a wide frequency range.     

Universal space-time properties of X waves

Exact results concerning spatiotemporal universal features of three-dimensional propagation-invariant solutions of the wave equation (X waves) are derived. In particular, relations connecting the pulse transverse extension to the longitudinal coordinate and the propagation velocity to the spatial field distribution are obtained for the whole class of X waves.     

Ultrasonic nondiffracting transducer for medical imaging

The nondiffracting J(0) Bessel beam is evaluated, and its application to medical imaging is suggested. Computer simulations and experimental results for a ten-ring annular Bessel shaded transducer are described. Both continuous-wave (CW) and pulse-wave (PW) excitations are shown and compared to conventional Gaussian beams. The nondiffracting beam has about 1.27-nm radius main lobe with a 20-cm depth of field compared to the Gaussian transducer of the same size with a 1.27-mm radius main lobe at a focus of 12 cm and 2x4-cm depth of field. The side lobes of the nondiffracting beam are the same as the J(0) Bessel function. The effects of heterogeneity due to tissue on the nondiffracting beam and on the focused Gaussian beam are also reported.     

Generation of long-range nondiffracting narrow light beams

A type of nondiffracting narrow light beam that propagates across a long range with a narrow beamwidth is presented. This beam is formed by a distorted concave spherical wave front that can be generated by a Galilean transmitting telescope with an eyepiece that has a spherical aberration. We observed an unusual image with a striped pattern in the laser beam's atmospheric backscatter that provided an opportunity to examine this effect. We demonstrate the mechanism of the generation and the characteristics of the long-range nondiffracting beam. The results show that a nondiffracting core beam with a width of the order of millimeters with a propagation distance of the order of a kilometer is generated by a 10-cm-diameter laser beam.     

对JJG 229检定规程检定方法差错的实验验证

依据JJG 229——2010《工业铂、铜热电阻》检定规程规定的条件和方法,采用两支标称电阻值(Rtp)为25Ω的标准铂电阻温度计作标准,多支Pt100型工业铂热电阻作被检样品,两个不同准确度的测量仪器,完成两种检定方法比较试验。试验时标准器分别用自测Rtp值和上级证书值,用比较法完成对工业铂热电阻的检定。从结果可以看出:用自测标准Rtp值检定,增加的结果偏差是用上级证书值的5倍以上,表明标准器由从本级标准装置赋值开展检定是不科学的,其效果可能南辕北辙。     

Range-finding by triangulation with nondiffracting beams

Nondiffracting beams are useful for alignment applications because the size of the beam does not change as the beam propagates. In this research we report a technique that allows for distance measurements with nondiffracting beams. With our approach a diffractive optical element is designed that generates two off-axis, tilted, nondiffracting Bessel function beams. These beams intersect at a desired distance from the input plane, producing interference. We generate these Bessel function arrays with a programmable spatial light modulator allowing external control over the intersection distance.     

Experimental revealing of polarization waves

Stationary and traveling waves of the states of optical polarization are considered in the framework of Jones vector formalism. The feasibility of revealing these waves in holographic and interference arrangements is substantiated and demonstrated.     

Temporal focusing by use of composite X waves

It is shown that highly focused pulses can be shaped by exciting a finite aperture with a spread-out pulse train of X waves. The basis of the proposed scheme is that the peaks of X waves, characterized by different apex angles, travel at different velocities. This property allows one to vary the temporal starting points of the initial excitations of a sequence of X waves so that all their peaks meet at a chosen focusing point. It is demonstrated that this simple criterion can be effective in producing a highly focused, composite X-wave pulse that exhibits a slower decay behavior than the individual X-wave components used in synthesizing it.     

Experimental verification of the simplified line-spring model

The recently developed simplified line-spring model is employed to obtain estimates of the crack opening displacement (COD) in surface cracked plates in tension and circumferentially cracked pipes in pure bending. The predictions of the model for the plate are compared to experimental data obtained from a series of tests on surface cracked X70 line pipe steel plates, on the other hand the results from the model for the pipe are compared to previously presented experimental and theoretical results. The simplified model seems to offer estimates of the COD which are in reasonably good agreement with both experimental data and existing theoretical results.

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Résumé On utilise le modèle simplifié dit line-spring — qui consiste à simuler les forces de rétention de propagation d'une fissure de surface dans le ligament restant, en dispensant des efforts et des moments sur une fissure traversante de même longueur — en vue d'estimer le déplacement d'ouverture d'une fissure dans des tôles fissurées en surface et soumises à traction, et dans des tubes fissurés circonférentiellement et soumis à flexion pure.Les prédictions du modèle dans le cas d'une tôle sont comparées aux données expérimentales recueillies dans une série d'essais sur des tôles fissurées en surface d'acier pour pipe-line X70. Par ailleurs, les prédictions du modèle dans le cas du tube sont comparées à des résultats théoriques et expérimentaux obtenus précédemment.Le modèle simplifié utilisé parait offrir des estimations du COD en assez bon accord avec les résultats expérimentaux d'une part, et l'application des théories existantes d'autre part.

     

Experimental verification of scaling laws for punch-impact-loaded structures

Scaling laws are developed for the punch-impact response of structures, including elastic-plastic effects and ductile failure. The scaling laws are validated by a set of half- and full-size punch experiments performed on mild- and stainless-steel plates. Full- and half-scale agreement is generally within ten percent, with deflections somewhat larger and energy absorbed somewhat smaller for the full-scale prototype when compared with the respective values for the one-half-scale model. An approximate energy analysis is included which provides estimates of plate central deflections up to the point of through-punching.     

Experimental verification of stress compensation in the SBTC-cut

The authors have demonstrated experimental verification of the stress compensation feature for the fast thickness shear mode of vibration of stress-compensated for B-mode and temperature-compensated for C-mode (SBTC)-cut quartz resonators. For the resonator design used in the cylindrical probe structure, the motional resistance for the B-mode of vibration was approximately 12% of that of the C-mode. The relatively large motional resistance for the C-mode of vibration of the SBTC-cut was found to be largely due to the lower piezoelectric coupling for the thickness excitation of this mode. In addition the proximity of the third overtone of the A-mode to the fifth overtone of the C-mode also contributed to the increase in the motional resistance. The authors have obtained experimental data on the temperature dependence of the planar stress coefficient and pressure dependence of the frequency-temperature characteristic for both the thickness-shear modes of the SBTC-cut. It is noted that such a doubly rotated cut can have applications in the design of either stable frequency sources or sensors for pressure and temperature measurements.     

Generation of nondiffracting beams through an opaque disk

A new method of generating nondiffracting beams is presented. It consists of focusing a Gaussian beam in the vicinity of an opaque disk. A beam is generated whose central peak is surrounded by a wide number of bright rings (approximately 250). After collimation, the beam propagates without changing the rings' radii, similar to a diffraction-free beam. The central peak can conserve its dimension over more than 5 m. The diameter of the central peak is adjusted by choosing the focal length of the collimating lens. Experimental results are well predicted by our theoretical developments that simulate exactly the paraxial diffraction.     

周期性基础地震波衰减性能及其试验验证EI北大核心CSCD

为了验证周期性结构对波的阻隔作用,基于Bloch-Floquet理论,推导周期性结构的频散关系,得到周期性结构的频率带隙。建立一维层状周期性基础数值模型,分别以环境振动和地震波作为输入波,通过数值模拟和振动台试验对有无周期性基础的三层钢框架模型进行了频域分析和时程分析。结果表明:当输入波的频率处于周期性基础频率带隙内时,可以有效地减小上部结构的动力响应;当输入波的主频处于周期性基础频率带隙外时,无法减小上部结构的动力响应。因此,通过调节周期性基础频率带隙宽度使其覆盖地震波的主要频段,可以有效阻隔地震波的传播,减小工程结构的地震响应。     

预制空心板桥梁格模型的荷载试验验证

以某预应力空心板桥为例,采用梁格法建立有限元模型,用荷载试验实测数据对其挠度计算值及其挠度横向分布进行对比验证。可为空心板桥建模精细化提供参考。     

Experimental verification of models for determining dispersion from attenuation

A modified broadband, through-transmission technique is used to compare the accuracy of three models: a nearly local model, a time-causal model, and a discrete minimum phase model, in determining the dispersion from the measured attenuation. By directly measuring the dispersion without first measuring the absolute phase velocity at different frequencies, the new technique eliminates the needs for measuring the speed of sound in the water and the trigger delays in data sampling, and minimizes the uncertainty in determining the phase spectra. Three specimens are used in the study: a block of Plexiglas that has a linear attenuation, a layer of a special rubber compound with an attenuation proportional to f(1.38) and a phantom made of castor oil that has an attenuation proportional to f(1.67). For linear attenuation all three models accurately predict the dispersion. For nonlinear attenuation, the time causal model is shown to be the most accurate model in predicting the dispersion. The nearly local model slightly overpredicts the dispersion in the case of the rubber compound and significantly overpredicts the dispersion in the case of the castor oil. The dispersion determined by the discrete minimum phase model seems to converge to the dispersion determined by the time causal model when the limit of integration is high enough.