Analysis of the axial transmission technique for the assessment of skeletal status

Ultrasonic wave propagation in human cortical bone has been investigated in vitro using the so-called axial transmission technique. This technique, which relies on velocity measurement of the first arriving signal, has been used in earlier investigations to study bone status during fracture healing or osteoporosis. Two quasi-point-source elements, one transmitter and one receiver (central frequency 0.5 MHz), were used to generate a wide ultrasonic beam, part of which strikes the sample surface at the longitudinal critical angle, and to receive the signals reflected from the sample surface. The analysis of the field reflected from a fluid-solid interface for an incident spherical wave predicts the existence of a lateral wave propagating along the sample surface at a velocity close to the longitudinal velocity, in addition to the ordinary reflected wave and vibration modes. The transducer-sample and the transmitter-receiver distances were chosen such that the lateral wave is the first arriving signal. Validation of the measuring technique was performed on test materials and was followed by experiments on human cortical bones. Experimental results (arrival time and velocity) strongly suggest that the first detected signal corresponds to the lateral wave predicted by theory.     

A Simple Model for Nonlinear Confocal Ultrasonic Beams

A confocally and coaxially arranged pair of focused transmitter and receiver represents one of the best geometries for medical ultrasonic imaging and non-invasive detection. We develop a simple theoretical model for describing the nonlinear propagation of a confocal ultrasonic beam in biological tissues. On the basis of the parabolic approximation and quasi-linear approximation, the nonlinear Khokhlov-Zabolotskaya-Kuznetsov （KZK） equation is solved by using the angular spectrum approach. Gaussian superposition technique is applied to simplify the solution, and an analytical solution for the second harmonics in the confocal ultrasonic beam is presented. Measurements are performed to examine the validity of the theoretical model. This model provides a preliminary model for acoustic nonlinear microscopy.     

A large ultrasonic bounded acoustic pulse transducer for acoustic transmission goniometry: modeling and calibration

A large, flat ultrasonic transmitter and a small receiver are developed for studies of material properties in acoustic transmission goniometry. While the character of the wave field produced by the transmitter can be considered as a plane wave as observed by the receiver, diffraction effects are noticeable near critical angles and result in the appearance of weak but detectable arrivals. Transmitted ultrasonic waveforms are acquired in one elastic silicate glass and two visco-elastic acrylic glass sample plates as a function of the angle of incidence. Phase velocities are determined from modeling of the shape of curves of the observed arrival times versus angle of incidence. The waveform observations are modeled using a phase propagation technique that incorporates full wave behavior including attenuation. Subtle diffraction effects are captured in addition to the main bounded pulse propagation. The full propagation modeling allows for various arrivals to be unambiguously interpreted. The results of the plane wave solution are close to the full wave propagation modeling without any corrections to the observed wave field. This is an advantage as it places confidence that later analyses can use simpler plane wave solutions without the need for additional diffraction corrections. A further advantage is that the uniform bounded acoustic pulse allows for the detection of weak arrivals such as a low energy edge diffraction observed in our experiments.     

Ultrasonic monitoring of malolactic fermentation in red wines

The progress of malolactic fermentation in red wines has been monitored by using ultrasonic techniques. The evolution of ultrasonic velocity of a tone burst 1 MHz longitudinal wave was measured, analyzed and compared to those parameters of oenological interest obtained simultaneously by analytical methods. Semi-industrial tanks were used during measurements pretending to be in real industrial conditions. Results showed that the ultrasonic velocity mainly changes as a result of the conversion by lactic acid bacteria of malic acid into lactic acid and CO₂. Overall, the present study has demonstrated the potential of the ultrasonic technique in monitoring the malolactic fermentation process.     

The influence of magnetic field swept rate on the ultrasonic propagation velocity of magnetorheological fluids

Structure of magnetorheological (MR) fluids depends on the strength of the magnetic field applied and on the mode of its application. The ultrasonic wave propagation velocity changes under the effect of an external magnetic field as a result of formation of clusters arranged along the direction of the field in the MR fluids. Therefore, we propose a qualitative analysis of these clustering structures by measuring properties of ultrasonic propagation. Since the MR fluids are opaque, the non-contact inspection using this ultrasonic technique can be very useful. In this study, we measured ultrasonic propagation velocity in MR fluid influenced by an external magnetic field for different swept rate precisely. With increasing magnetic field intensity, the changes of the ultrasonic wave velocity are more pronounced. Sedimentation effect takes place in certain time for different swept rate due to magnetic particle size and it follows linear relationship in log scale. Significant differences of the ultrasonic wave velocity are established between the case when the field is swept at a constant rate and the case when it is stepped up.     

Theory of transit time ultrasonic flowmeters

A theory of transit time ultrasonic flowmeters for clean fluids is developed from the equations of fluid mechanics applied simultaneously to the fluid and the sound vibrations. These equations are linearized (weak sound) and use is made of the electroacoustic reciprocity theorem to give a relation between the voltages and currents at the transducer terminals and the fluid velocity. The technique of “reciprocal operation” of a transit time ultrasonic flowmeter is described and the way this technique eliminates zero drift is explained. The theory can be applied to meters with broad sound beams (which provide a better average over velocity profiles) or meters in which the wavelength of sound is not necessarily small compared with the duct diameter. Small modificaition of the sound field (due to flow) is assumed and the resulting phase (or amplitude) shift of the received signal is expressed as an integral throughout the fluid of the dot product of the fluid velocity and a weight vector defined in terms of the sound fields in the stationary fluid. Simple flowmeter designs which approach the ideal of complete immunity to velocity distribution are described.     

Three-dimensional hybrid model for predicting air-coupled generation of guided waves in composite material plates

For contact-less, non-destructive testing (NDT) purposes using air-coupled ultrasonic transducers, it is often required to numerically simulate the propagation of ultrasonic waves in solid media, and their coupling through air with specific transducers. At that point, one could simulate the propagation in the air and then in the solid component, using a Finite Element (FE) model. However, when three-dimensional (3D) modeling becomes necessary, such a solution reveals to be extremely demanding in terms of number of degrees of freedom and computational time. In this paper, to avoid such difficulties, the propagation in air from an ultrasonic transmitter to a tested solid plate is modeled in 3D using a closed-form solution. The knowledge of the transducer characteristics (diameter, frequency bandwidth, efficiency in Pa/V) allows the spatial distribution and actual pressure (in Pa) of the acoustic field produced in the air to be predicted, for a given input voltage. This pressure field is applied in turn as a boundary condition in a 3D FE model, to predict the plate response (displacement and stress guided beams) for a given distance between the transmitter and the plate, and for a given angle of orientation of the transmitter with respect to the plate. The FE model is so restricted to modeling of the solid structure only, thus reducing very significantly the number of degrees of freedom and computational time. The material constituting the plate is considered to be an anisotropic and viscoelastic medium. To validate the whole modeling process, an air-coupled ultrasonic transducer is used and oriented at a specific angle chosen for generating one specific Lamb mode guided along a composite plate sample, and a laser probe measures the normal velocity at different locations on the surface of the plate. In the field of NDT, it is generally suitable to excite a pure Lamb mode in order to ease the interpretation of received signals that would represent waves scattered by defects. After a validation step, the numerical model is then used to investigate the effect of the material anisotropy on the purity of the incident guided mode.     

Thermographic measurement of the effect of humidity in mortar porosity

The objective of this analysis is to examine the influence of the moisture in the porosity measurement by means of thermal non-destructive test and ultrasound techniques. It is possible to determine the concrete durability by the calculation of its porosity. Porosity is determined in an indirect way, measuring mortar diffusivity by means of active thermography. Using ultrasound techniques, the porosity is related with the ultrasonic propagation of velocity. The diffusivity has been calculated using the W.J. Parker equation. In the ultrasound technique, using the pulse transmission method, ultrasonic propagation velocity was measured as a function of the water content. The conclusions express the correlation between both methods.     

State-of-the-art advantages and drawbacks on the application of vibrational spectroscopy to monitor alcoholic fermentation (beer and wine)

Wine production is directly linked with the monitoring of the fermentation and critical fermentation parameters such as total sugars and ethanol concentration, and the production of CO₂. Commonly used sensors applied in the wine industry to monitor wine fermentation are those based in single sensors such as temperature probes and manual density measurements (e.g., specific gravity). These sensors are used several times per day and have been the only source of data available from which the stage of the fermentation and the evolution rate could be monitored. Therefore, an ideal method for fermentation process control and monitoring should enable a direct rapid, precise, and accurate determination of several target compounds, with minimal or no sample preparation and reagent consumption. This article reviews the state of the art in the applications of both near and mid infrared spectroscopy to monitor beer and wine fermentation.     

Ultrasonic velocity in water-ethanol-sucrose mixtures during alcoholic fermentation

During alcoholic fermentation, sucrose and water are transformed into ethanol and carbon dioxide by the action of yeast enzymes. The measurement of the velocity of an ultrasonic pulse travelling through a fermentation tank can be used to characterize the state of the process. In this work, an experimental study of the density and ultrasonic velocity in the ternary mixture (water-ethanol-saccharose) is presented. Experimental results were compared to ideal density and to commonly used expressions of the sound velocity in liquid mixtures (Urick, Natta-Baccaredda and Nomoto). A semiempirical approach was proposed to improve the efficiency of theoretical models when dealing with mixtures of associated liquids.     

Acoustic wave in a suspension of magnetic nanoparticle with sodium oleate coating

The ultrasonic propagation in the water-based magnetic fluid with doubled layered surfactant shell was studied. The measurements were carried out both in the presence as well as in the absence of the external magnetic field. The thickness of the surfactant shell was evaluated by comparing the mean size of magnetic grain extracted from magnetization curve with the mean hydrodynamic diameter obtained from differential centrifugal sedimentation method. The thickness of surfactant shell was used to estimate volume fraction of the particle aggregates consisted of magnetite grain and surfactant layer. From the ultrasonic velocity measurements in the absence of the applied magnetic field, the adiabatic compressibility of the particle aggregates was determined. In the external magnetic field, the magnetic fluid studied in this article becomes acoustically anisotropic, i.e., velocity and attenuation of the ultrasonic wave depend on the angle between the wave vector and the direction of the magnetic field. The results of the ultrasonic measurements in the external magnetic field were compared with the hydrodynamic theory of Ovchinnikov and Sokolov (velocity) and with the internal chain dynamics model of Shliomis, Mond and Morozov (attenuation).     

Water content and its effect on ultrasound propagation in concrete--the possibility of NDE

It is known that water content or moisture affects the strength of concrete. The purpose of this study is to examine the possibility of the NDE of concrete from a knowledge of the relationship between water content and ultrasonic propagation in concrete. The results of measurements made on the ultrasound velocity and the frequency component on ultrasonic propagation as a function of the water content in concrete are reported. Test pieces of concrete made from common materials were made for the fundamental studies. The test piece dimensions were 10 cm in diameter and 20 cm in length. Test pieces were immersed in water for about 50 days to saturate them. To measure the effect of different water contents, test pieces were put in a drying chamber to change the amount of water between measurements. This procedure was repeated until the concrete was completely dried and the weight no longer changed. Water contents were defined as weight percentage to full dried state. Thus water content could be changed from 8% to 0%. Using the pulse transmission method, ultrasonic propagation in the frequency range 20 to 100 kHz was measured as a function of water content. The sound velocity varied gradually from 3000 m/s to 4500 m/s according to the water content. The frequency of maximum transmission also depended on the water content in this frequency range. It is considered that the ultrasonic NDE of concrete strength is feasible.     

An ultrasonic transducer array for velocity measurement in underwater vehicles

A correlation velocity log (CVL) is an ultrasonic navigation aid for marine applications, in which velocity is estimated using an acoustic transmitter and a receiver array. CVLs offer advantages over Doppler velocity logs (DVLs) in many autonomous underwater vehicle (AUV) applications, since they can achieve high accuracy at low velocities even during hover manoeuvres. DVLs require narrow beam widths, whilst ideal CVL transmitters have wide beam widths. This gives CVLs the potential to use lower frequencies thus permitting operation in deeper water, reducing power requirements for the same depth, or allowing the use of smaller transducers. Moving patterns in the wavefronts across a 2D receiver array are detected by calculating correlation coefficients between bottom reflections from consecutive transmitted pulses, across all combinations of receiver pairings. The position of the peak correlation value, on a surface representing receiver-pairing separations, is proportional to the vessel's displacement between pulses. A CVL aimed primarily for AUVs has been developed. Its acoustical and signal processing design has been optimised through sea trials and computer modelling of the sound field. This computer model is also used to predict how the distribution of the correlation coefficients varies with distance from the peak position. Current work seeks to increase the resolution of the peak estimate using surface fitting methods. Numerical simulations suggest that peak estimation methods significantly improve system precision when compared with simply identifying the position of the maximum correlation coefficient in the dataset. The peak position may be estimated by fitting a quadratic model to the measured data using least squares or maximum likelihood estimation. Alternatively, radial basis functions and Gaussian processes successfully predict the peak position despite variation between individual correlation datasets. This paper summarises the CVL's main acoustical features and signal processing techniques and includes results of sea trials using the device.     

Leaky Rayleigh wave investigation on mortar samples

Aggressive mineralized ground water may harm the concrete cover of tunnels and other underground constructions. Within a current research project mortar samples are used to study the effects of sulfate interaction in accelerated laboratory experiments. A nondestructive test method based on ultrasonic surface waves was developed to investigate the topmost layer of mortar samples. A pitch and catch arrangement is introduced for the generation and reception of leaky Rayleigh waves in an immersion technique allowing the measurement of their propagation velocity. The technique has been successfully verified for the reference materials aluminium, copper, and stainless steel. First measurements performed on mortar specimens demonstrate the applicability of this new diagnostic tool.     

特殊几何构件超声衍射时差法技术有限元模拟

衍射时差法(Time of flight diffraction,TOFD)技术是一种能够探测和精确测量缺陷尺寸的新型超声无损检测方法,针对该检测方法具有缺陷检出率高、缺陷定位定量精度高等优点。本文采用商业有限元软件ABAQUS,对汽包筒体与球形封头不等厚对接和超高压水晶釜两种特殊几何构件进行了超声TOFD技术的二维数值模拟研究,分析了超声波在这两种构件中的传播特性和规律。经分析从构件表面不同位置接收到的波型,当构件中存在损伤时,通过接收损伤所引起的衍射波,可判断构件中是否存在缺陷。模拟结果表明能够将超声TOFD技术应用于这两种特殊结构的压力容器构件,可扩大超声TOFD技术的应用范围。     

First experiments on ultrasonic crop density measurement

An on-line crop density measurement delivers interesting information about the local crop condition. Once this measurement is established in a non-destructive way, crop density monitoring could be performed during the growing season and results would immediately be used for a site-specific application of nitrogen.In this work, some primary results are shown from an ultrasonic crop density measurement. A commercial sensor, normally used for level measurements, is equipped with an extra output, providing a signal corresponding with the ultrasonic wave transmitted through a band of crop. Because of the properties of the measured signal, a non-linear transformation of the measured signal is necessary. With the result of this static compensation, a good estimation can be found of the energy in the received wave, closely related with the volumetric density of the crop.Once the appropriate signal is found, an experimental set-up is constructed for dynamic crop density measurements. A small wagon is placed on two parallel rails with a stroke of crop in between. On both sides of this wagon, two ultrasonic transducers are placed. One as transmitter of the ultrasonic wave, the other one as receiver at the other side of the crop. With this arrangement, a first calibration curve is made, delivering an exponential relationship between the transmitted energy and volumetric crop density.     

Fiber optic liquid leak detection technique with an ultrasonic actuator and a fiber Bragg grating

We present a technique for liquid leak detection in which ultrasonic and optical waves are introduced into a fiber simultaneously. The system is based on an ultrasonic technique using an ultrasonic actuator and a fiber Bragg grating receiver. A fiber-guided ultrasonic wave is utilized to stress the fiber Bragg grating, which is remote from the ultrasonic transmitter. When the traveling ultrasonic wave encounters a liquid, part of the wave will leak out from the fiber, which results in an ultrasonic strain decrease in the fiber Bragg grating. The ultrasonic wave and its attenuation are detected by the light variation of a narrowband laser source reflected and transmitted from the fiber Bragg grating, and the amplitude variation of the ultrasound can eventually be correlated with the fiber area coupled with the liquid.     

Ultrasonic pelvimetry. A method for preliminary estimation of the pelvic outlet

Vaginal sound, with transmitter crystals of 2 MHz, is used when measuring the interspinous diameter. The echo from the pelvic wall, the effect on the measured spinal diameter by altering the position of the ultrasonic transmitter, and the influence of air or faeces between the ultrasound transmitter and the pelvic wall, have been analysed in a series of model trials on a dummy submerged in water. Thereafter clinical trials were performed on 102 women, pregnant in their 9th month. The results obtained when measuring the interspinous diameter on the ultrasonic tomogram were compared with the results obtained when measuring the same distance on a frontal x-ray picture taken using the orthographic technique according to Borell-Frenström. The method is suitable for selecting those cases with suspect constriction of the pelvic outlet for an x-ray examination by the Borell-Fernström technique.     

Beam and phase effects in angle-beam-through-transmission method of ultrasonic velocity measurement

The accuracy of a plane wave approximation for phase velocity measurements in isotropic and anisotropic material using the angle-beam-through-transmission method has been investigated numerically and experimentally. In this method the velocity is measured in different propagation directions as a function of incidence angle. The effect of two factors on the measurement accuracy have been discussed: intrinsic phase shift of the transmitted signal through a fluid-solid interface and beam diffraction due to the finite beam size of receiver and transmitter. It is shown that the interface-induced phase shift can introduce an error in time delay measurements of the shear wave after the first critical angle and that this time delay error can be accurately corrected for. Numerical results obtained by a time-domain beam model show that except at the critical angles, the finite width of the transmitter and receiver only affects the amplitudes of the transmitted signals and has almost no effect on the measured zero-cross time delay; therefore the plane wave approximation for obtaining phase velocity from the measured time delay data by this method and the plane wave interface-induced phase correction are fully applicable.