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Ultrasonic wave propagation in epoxy materials is modeled to understand NDE procedures and also to provide reliable input to more complex models of guided wave propagation in layered structures. The models are extended to simulate wave propagation in materials with mechanical properties varying in the spatial dimension and it is achieved by using electric circuit transmission line analogs to the viscoelastic mechanical system.

Newly designed magnetorestrictive transducers are applied for the excitation and detection of guided waves in metal pipes of small diameter (mm). The optimized transducer system based on a simulation of the overall signal pathway could be used to study the wave propagation in pipes filled with water or supercritical C[O.sub.2].

Ultrasonic measurements of attenuation versus frequency were made on model systems comprising olive oil, sucrose and tripalmitin for representing the constituents of chocolate. Results suggest that the addition of sucrose crystals at high concentration leads to modification in the effect of ultrasonic scattering from tripalmitin crystals in olive oil.

The article gives a proposal of a novel architecture for a data acquisition system, which intends to support the next generation of ultrasonic imaging instruments operating at or above 100 MHz.

An analysis of the error generation mechanisms that affect the accuracy of measurements of ultrasonic wave attenuation coefficient and phase velocity as functions of frequency is presented. Errors can originate from digital processing of acoustic signals however an appropriate sampling frequency, effective anti-aliasing filters, and the use of floating point computations of adequate precision for time-to-time frequency transformation render such errors negligible.

An analysis of a new type of feedthrough recursive surface acoustic wave (SAW) device is presented. The way in which a combination of acoustic and electronic pathways can ensure good control and tracking of both the desired selectivity and the central frequency are shown.

Ultrasonic compression wave absorption is examined. The aim is to monitor seeded crystallization of copper (II) sulphate pentahydrate from aqueous solution

Research describing truncation errors in ultrasonic wave scattering models is presented. An heuristic is developed to determine covergence criteria for summation of the infinite series of partial waves.

The principal dimensions of adhesive bonding of metal assemblies were investigated using artificial neural networks and ultrasonic Lamb waves. Specifically, the dimensions of two forms of adhered joints, namely, Lap and T-form, between metal plates were examined. Experimental results showed that the procedure yields reliable estimates of the necessary dimensions in bondlines not included in network training. Moreover, the interconnected weights of simplified networks provide evidence of the characteristics in Lamb wave signals that underlie the effectiveness of the approach.

Proportionality between the ultrasonic wave attenuation coefficient in epoxies and other polymers and frequency is a commonly observed but little understood phenomenon. How it is ultimately explained will depend on the breadth of the frequency range over which it is significant. This paper presents results of experiments to measure loss in a single epoxy material over 5 decades of frequency using 4 complementary techniques dynamic mechanical analysis, microwave excited low-frequency resonances, a novel guidedwave technique based on a metal-epoxy-metal sandwich, and a conventional pulse mode ultrasonic spectrometer. The results are confined to bulk shear waves in the epoxy. They confirm the linear relationship between attenuation and frequency, and it is shown that the broadband behavior of the attenuation and shear wave phase velocity is consistent with the Kramers-Kronig relationships. [ABSTRACT FROM AUTHOR]

Ultrasonic imaging of bioflims in water is difficult due to the very low contrast in acoustic impedance between the biofilm and water. In this paper, biofilms ex- posed to moist air are scanned through the substrate in order to obtain echoes from the bioflim/air interface. A 50 MHz scanning system was used to scan 1 mm X 1 mm areas of biofilms in a 10 μm grid pattern. Two fast Fourier transform (FFT) based methods for enhancement of the film thickness measurement resolution are compared. Using these techniques, the surface topography of biofilms with thickness less than the acoustic wavelength can be imaged. [ABSTRACT FROM AUTHOR]

The impulse response for the acoustic radiation coupling between two disks has been found in a closed analytic form for the case of a transmitter larger in diameter than a coaxially aligned receiver. In order to verify experimentally the derived expression piezoelectric transducers were used as transmitters and receivers. An analysis of piezoelectric transduction is presented in order to account for transduction effects in the experimental system. Discrete time models of the transmitter and receiver processes valid for times less than one reverberation period are formed based on Redwood's equivalent circuits adapted by z-transform techniques. Recurrence relationships are derived and used in the manner of digital filters to calculate the transducer output due to any type of input. In the case of the transmitter, the force acting on the front face is calculated for any applied electrical waveform, whereas the receiver model calculates the voltage generated across the device due to any force function acting on the receiver face. The transducer models are used in conjunction with the disk to disk impulse response to calculate the voltage generated across the receiver due to any electrical waveform applied to the transmitter. Responses measured experimentally in water are presented and compared with predicted waveforms; receiver amplifier insertion characteristics are included in the model and a correction is made to take into account ultrasonic absorption by water. Good agreement is shown between the predicted and measured waveforms. [ABSTRACT FROM AUTHOR]

Calculation of the transient response of piezoelectric elements by analytical means is only possible for a small range of exciting functions for which simple Laplace transforms exist. Calculation tends to be tedious due to the large number of terms which must be evaluated. A method is presented by which the Laplace transformed three-port model of a piezoelectric element is approximated by a discrete time system by application of the z-transform. A recurrent time domain solution is developed and this is applied in the manner of a digital filter to a variety of exciting functions. The method has the advantage that the response to any real input can be evaluated and it is thus of considerable use in the testing of piezoelectric elements or the measurement of their physical properties in transient tests. Experimental results are presented which show that the technique is reliable and accurate. [ABSTRACT FROM AUTHOR]

Ultrasonic transducer arrays are extensively used for the nondestructive evaluation of materials for aerospace and other applications. However, their use with composites requires some technique development because of reflections at the layer boundaries and the effects of attenuation. When used in full matrix capture mode, algorithms such as the total focusing method (TFM) must be applied to obtain the image. In composite materials, improvement to the algorithm is required to include the effects of material anisotropy (affecting wave speed) and optimum aperture limits to optimize the signal-to-noise ratio and location detection for a defect in the material. This paper presents simulations of the ultrasonic array signals in multilayer anisotropic materials with and without a simulated defect. A kernel model for plane wave propagation in the material is combined with an angular spectrum decomposition (for finite transducer elements) and transducer frequency response, to model the full array signals. Inclusion of the defect is through its far-field scattering response. The model facilitates the study of imaging algorithm development by identification of the effects of anisotropy, signal-to-noise ratio, and aperture limit. An analytical method for the calculation of the effective group velocity in the composite at low frequency is demonstrated, permitting rapid calculation of time delay laws in practice.

Proportionality between the ultrasonic wave attenuation coefficient in epoxies and other polymers and frequency is a commonly observed but little understood phenomenon. How it is ultimately explained will depend on the breadth of the frequency range over which it is significant. This paper presents results of experiments to measure loss in a single epoxy material over 5 decades of frequency using 4 complementary techniques--dynamic mechanical analysis, microwave excited low-frequency resonances, a novel guidedwave technique based on a metal-epoxy-metal sandwich, and a conventional pulse mode ultrasonic spectrometer. The results are confined to bulk shear waves in the epoxy. They confirm the linear relationship between attenuation and frequency, and it is shown that the broadband behavior of the attenuation and shear wave phase velocity is consistent with the Kramers- Kronig relationships.