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Measurements of the frequency dependence of ultrasonic attenuation can be used as the basis for the estimation of particle size distributions (PSDs) in solid-in-liquid suspensions. The method requires matching the attenuation simulated by a candidate PSD in combination with a wave propagation model to the measured function in a fitting procedure. Uncertainty in the type of candidate PSD, whether based on fractional volume or fractional number of the dispersed particles, can cause errors in the overall estimation process, particularly for the median particle size. These uncertainties are investigated in the first part of this paper. The second part deals with uncertainties associated with the values for the physical properties of the suspended particles, seven of which are required in the simulation stage. It is shown that the particle sizing exercise is relatively insensitive to all of the physical properties except density, for which values are necessary to an accuracy commensurable with that required for the two principal parameters associated with the PSD?median size and standard deviation. The discussion is limited to small (less than 1-?m) silica particles dispersed in water. The results will have more general application. [ABSTRACT FROM PUBLISHER]

Estimates of particle size distributions (PSDs) in solid-in-liquid suspensions can be obtained from measurements of ultrasonic wave attenuation. The technique is based on adaptively fitting theoretical wave propagation models to the measured data across a frequency range. These models break down at high solid concentrations and it is believed that this failure is due to the effective viscosity of the mixture in the vicinity of the particles being different from that of the continuous phase. This paper discusses PSD estimation when a number of different viscosity formulations are incorporated into the wave propagation model. The viscosity model due to Happel provides the best estimate of PSD in suspensions of medium concentration. [ABSTRACT FROM AUTHOR]

This paper reports a study of the backscattered ultrasonic signal from a solid layer containing spherical cavities, to determine the conditions in which an effective medium model is a valid description of the response. The work is motivated by the need to model the response of porous composite materials for ultrasonic non-destructive evaluation (NDE) techniques. The numerical simulation predicts the response of a layer containing cavities at a single set of random locations, and compares it to the predicted response from a homogeneous layer with ensemble-averaged material properties (effective medium model). The study investigates the conditions in which the coherent (ensemble-averaged) response is obtained even from a single configuration of scatterers. Simulations are carried out for a range of cavity sizes and volume fractions. The deviation of the response from effective medium behavior is modeled, along with the trends as a function of cavity radius, volume fraction, and frequency, in order to establish an acceptability criterion for application of an effective medium model. [ABSTRACT FROM AUTHOR]

This paper reports a study of the backscattering behavior of a solid layer containing randomly spaced spherical cavities in the long wavelength limit. The motivation for the work arises from a need to model the responses of porous composite materials in ultrasonic NDE procedures. A comparison is made between models based on a summation over discrete scatterers, which show interesting emergent properties, and an integral formulation based on an ensemble average, and with a simple slab effective medium approximation. The similarities and differences between these three models are demonstrated. A simple quantitative criterion is established which sets the maximum frequency at which ensemble average or equivalent homogeneous medium models can represent echo signal generation in a porous layer for given interpore spacing, or equivalently, given pore size and concentration. [ABSTRACT FROM AUTHOR]

Classical long wavelength approximate solutions to the scattering of acoustic waves by a spherical liquid particle suspended in a liquid (an emulsion) show small but significant differences from full solutions at very low kca (typically kca < 0.01) and above at kca > 0.1, where kc is the compressional wavenumber and a the particle radius. These differences may be significant in the context of dispersed particle size estimates based on compression wave attenuation measurements. This paper gives an explanation of how these differences arise from approximations based on the significance of terms in the modulus of the complex zero-order partial wave coefficient, A0. It is proposed that a more accurate approximation results from considering the terms in the real and imaginary parts of the coefficient, separately. [ABSTRACT FROM AUTHOR]

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]

This paper concerned with modeling ultrasonic wave propagation in epoxy materials to better understand NDE procedures and to provide reliable input to more complex models of guided wave propagation in layered structures. Different physical models are considered in the context of how well they simulate the (known) linear relationship between bulk wave attenuation coefficients and frequency. The identified models are then extended to simulate wave propagation in materials with mechanical properties, which vary gradually in the spatial dimension. This is achieved using electric circuit transmission line analogs to the viscoelastic mechanical system. Verifying experimental results are included. [ABSTRACT FROM AUTHOR]

This paper is concerned with the design of magnetostrictive transducers for the excitation and detection of guided waves in metal pipes of small diameter (mm) and their application to the study of wave propagation in pipes filled with water or supercritical CO2. Optimized system design is based on a simulation of the overall signal pathway which includes the electric circuit conditions at the transducers, mode excitability, and the wavenumber filtering effect of the spatial distribution of the exciting alternating magnetic field. A prototype system was built, and experimental observations on small diameter pipes indicated good agreement with expected results from simulations. The reassigned spectrogram has been used to compare expectation on the basis of guided wave dispersion curves for fluid-filled pipes with experimental data. [ABSTRACT FROM AUTHOR]

Ultrasonic measurements of attenuation versus frequency were made on model systems comprising olive oil, sucrose, and tripalmitin to represent the constituents of chocolate. Corresponding measurements also were made on chocolate flowing in a pipeline at a pilot plant where the temperature, pressure, and temper of the chocolate were precisely controlled and monitored. Experimental results combined with simulation studies indicate that the effect of ultrasonic scattering from tripalmitin crystals in olive oil is modified by the addition of sucrose crystals at a high concentration. It is proposed that the presence of seed crystals in chocolate (temper) cannot be detected ultrasonically in the practical measurement range 1–12 MHz due to a similar process. [ABSTRACT FROM AUTHOR]

Random interleaved sampling has become a widespread operating mode for digital storage oscilloscopes. Different repetitions of (notionally) the same waveform are recorded at random time shifts and are interleaved in memory, resulting in an increase of the equivalent sampling frequency. This procedure requires substantial time, particularly if further averaging is required. In this paper, an approach that ensures accurate time shifts is presented for repeated waveform measurements. Operating two independent oscillators with related frequencies forms the accurate shifts. One of these is used to excite a waveform of interest repeatedly, and the other clocks the analog-to-digital converter (ADC). This architecture was implemented using a commercial ‘off-the-shelf’ field programmable gate array. Examples of experimental waveforms, which are sampled at 2160 MHz using an ADC that is clocked at 80 MHz, are presented. They are compared with the simulated and independently measured waveforms where appropriate. [ABSTRACT FROM AUTHOR]

A cross-disciplinary experimental study related to both ultrasonic instrumentation and analytical chemistry is reported. The hydrolysis process was conducted by time-resolved titration in a fully automated manner. Acquired ultrasonic records were processed in order to estimate the propagation delay of the ultrasonic pulse in the evolving medium. The limited hardware resolution of two different ultrasonic instruments employed was improved by calculating the center of gravity of the recorded pulses. Application of signal averaging to the acquisition of raw records in the custom-built instrument eliminated spurious records almost completely. The estimated ultrasonic delays were corrected for temperature changes that were measured independently. This procedure transformed the ultrasonic titration curves into two almost straight lines that intersected at the equivalence point. The results obtained showed that it was possible to detect changes as small as 200 ppm by using the ultrasonic instrument in situ at significantly lower setting times compared to a conventional pH-meter. [ABSTRACT FROM AUTHOR]

This paper proposes a novel architecture for a data acquisition system intended to support the next generation of ultrasonic imaging instruments operating at or above 100 MHz. Existing systems have relatively poor signal-to-noise ratios and are limited in terms of their maximum data sampling rate, both of which are improved by a combination of embedded averaging and embedded interleaved sampling. "On-the-fly" pipelined operation minimizes control overheads for signal averaging. A two-clock sampling timing system provides for effective sampling rates that are a factor of 20 or more above the basic sampling rate of the analog-to-digital converter (ADC). The system uses commercial field-programmable gate array devices operated at clock frequencies commensurable with the ADC clock. Implementation is via the Xilinx Xtreme digital signal processing development kit, available at low cost. Sample rates of up to 2160 MHz have been achieved in combination with up to 16384 coherent averages using the above-mentioned off-the-shelf hardware. [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]

This paper focuses on the analysis of frame jitter and the impact of data acquisition architecture on the associated disturbances to the acquired record. Frame jitter leads to the same random shift of all samples in an acquired record. It results in errors in the estimates of time intervals, and makes consecutive records slightly incoherent - compromising data averaging procedures. Two complementary algorithms are developed for the quantification of frame jitter, and their performance has been simulated and verified by experiment. They allow the estimation of the standard deviation of the frame jitter using a low-resolution instrument even in noisy environments. An expression for the minimum value of the standard deviation of the frame jitter has been obtained and verified experimentally for typical architectures of data acquisition systems. It is shown that this value could be reduced by specific improvements in the design of data acquisition system architectures. [ABSTRACT FROM AUTHOR]

This paper presents 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. In the first stage of the analysis we show that electronic system noise, expressed in the frequency domain, maps into errors in the attenuation and the phase velocity spectra in a highly nonlinear way; the condition for minimum error is when the total measured attenuation is around 1 Neper. The maximum measurable total attenuation has a practical limit of around 6 Nepers and the minimum measurable value is around 0.1 Neper. In the second part of the paper we consider electronic noise as the primary source of measurement error; errors in attenuation result from additive noise whereas errors in phase velocity result from both additive noise and system timing jitter. Quantization noise can be neglected if the amplitude of the additive noise is comparable with the quantization step, and coherent averaging is employed. Experimental results are presented which confirm the relationship between electronic noise and measurement errors. The analytical technique is applicable to the design of ultrasonic spectrometers, formal assessment of the accuracy of ultrasonic measurements, and the optimization of signal processing procedures to achieve a specified accuracy. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of a new type of feedthrough recursive surface acoustic wave (SAW) device. The device combines a conventional SAW structure with positive feedback in a way that allows use of selective properties of the SAW structure, control of the central frequency and bandwidth, achieving significantly higher quality factors for given dimensions of the structure, and reduction of the sidelobe level. Several possible implementations are discussed from a simple one that uses external circuitry to the most advanced that includes digital supervisory control. Equations are presented that relate the central frequency, bandwidth, and sidelobe level to the parameters of the SAW structure and feedback loop. The simulation results were found to be in good agreement with experimental data. These data show the control of the central frequency within 1%, a 10-fold increase in the quality factor compared to the original SAW structure, and a reduction of the sidelobe level by 20 dB irrespective of the influence of second order effects and random manufacturing fluctuations. [ABSTRACT FROM AUTHOR]

Ultrasonic compression wave absorption is investigated as a means to monitor the seeded crystallization of copper (II) sulphate pentahydrate from aqueous solution. Simple models are applied to predict crystal yield, crystal size distribution, and the changing nature of the continuous phase. The Allegra-Hawley scattering formulation is used to simulate ultrasonic absorption as crystallization proceeds. Experiments confirm that simulated attenuation is in agreement with measured results. [ABSTRACT FROM AUTHOR]

Provides information on a study which described the application of ultrasonic Lamb waves and artificial neural networks in quantitative classification of adhesive bondline dimensions. Discussion on Lamb waves and neural networks; Verification of the Lamb wave propagation; Results of the experiments; Conclusions.

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]

Absorption of ultrasound in adhesive materials is significant in forming ultrasonic signals obtained in nondestructive evaluation (NDE) procedures, and may also have diagnostic value in the evaluation of adhesive materials themselves. This paper investigates the effects of filler particles in adhesive polymers on ultrasonic compression wave absorption and phase velocity dispersion as functions of frequency. Wave propagation is affected by relaxations in the continuous polymer phase as well as by scattering at filler particles. The complex compression wave number for the composite material is derived on the basis of conventional theories of scattering in randomly distributed fields of particles, together with a formulation of the particle diffraction problem based on a combination of the cases for solid particles in solid continua and solid particles in liquid continua first proposed by Ying and Truell, and Allegra and Hawley, respectively. Experiments are described which demonstrate the effects of relaxations and scattering on absorption and phase velocity as functions of frequency in an epoxy material containing a mineral filler. Good agreement is obtained between theory and experiment. © 1998 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

An acoustic near plane-wave absorption spectrometer has been developed for use in small samples of liquid (30 ml) over bandwidths of up to 60 MHz, using a two transducer short-pulse transmission technique. The instrument is controlled by computer, and on-line digital signal processing is used to correct for transducer insertion, radiation coupling, and the transient responses of transmitter and receiver electronics. The raw data acquisition time is short and the instrument in its present form could be used to estimate absorption at 100-ms intervals. The instrument can be used on both stationary chemical systems and systems undergoing chemical reaction. Experimental results are presented that show excellent agreement with absorption measurements by traditional (slower) techniques. [ABSTRACT FROM AUTHOR]