Ultrasonic Burst Research Articles

Monitoring of trabecular bone induced microdamage using a nonlinear wave‐coupling technique

Bone tissue contains microcracks which may affect its mechanical properties as well as the whole trabecular structure. The relationship between crack density and bone strength is nevertheless poorly understood. Efficient nonlinear (NL) ultrasound methods have been widely developed for nondestructive testing and geophysical applications to detect microdamage. Moreover it has been reported that elastic nonlinearities increase with induced damage. We propose to monitor trabecular bone microdamage using a NL wave coupling technique. Ultrasonic short bursts times of flight (TOF) are modulated as result of NL interaction with a low‐frequency (LF) wave in the medium. TOF modulation (TOFM), or propagation velocity variations, are directly related to NL elasticity variations. This technique allows measuring the instantaneous TOFM as a function of the LF pressure. It is thus possible to analyze separately elasticity variations in tension and in compression, and to distinguish the tension to compression phase from the compression to tension phase (hysteresis). In several trabecular bone samples, different TOFM amplitudes in tension and in compression are observed, probably due to microdamage. For increasing damage levels progressively induced by quasi‐static compression testing, linear and nonlinear ultrasound parameters are compared to biomechanical parameters.

Genetic manipulation engineers the elasticity of arabidopsis thaliana

Arabidopsis thaliana is a model species widely used in plant science studies. It grows fast and exhibits wood formation in its stem and root resembling softwood produced by angiosperm trees. The Arabidopsis model allows rapid testing of methods for wood composition modification possibly adaptable for tree breeding. We estimated ultrasonically the modulus of elasticity in Arabidopsis stems and roots in both radial and in-plane direction for two commonly used ecotypes (Columbia and Landsberg erecta). Plants were grown in greenhouse conditions and six inflorescence stems per ecotype were measured in vivo applying 4 MHz out-of-plane and 2 MHz in-plane ultrasonic tone bursts. The effects of AtCAD1 gene expression silencing in Col ecotype were tested using the same method. We recorded a (10%, p=0.1) decrease in the elastic modulus of the lignin-decreased Atcad 1 samples (10-20% decrease in lignin content), and a significant (29%, p=0.02) difference between the sound velocities in the two ecotypes. In-plane elasticity results are also presented. The results are the first ultrasonically measured modulus values for this commonly used plant model species, creating a quantitative mechanical measure for the effects of wood composition modification.

Optical measurements of the self-demodulated displacement and its interpretation in terms of radiation pressure

Using a sensitive optical interferometer, the low frequency displacement nonlinearly generated by an ultrasonic tone burst propagating in a liquid is studied. Close to the source, the low frequency displacement contains a quasi-static component, which is affected by diffraction effects farther from the transducer. The experimental setup provides quantitative results, which allow the determination of the nonlinearity parameter of the liquid with a good accuracy. Such measurements are carried out in water and ethanol. Finally, the pressure associated with the low frequency displacement is discussed. Introducing the temporal mean value of the displacement, as already done in lossless solids, the noncumulative part of this second order pressure is associated with the static part of the low frequency displacement. This interpretation leads to extend the definition of the Rayleigh radiation pressure usually introduced for a continuous plane wave radiated in a confined fluid.

Eight-channel ultrasonic device for non-invasive quality evaluation in packed milk

An eight-channel ultrasonic detecting device for microbiological quality evaluation of packed liquid foods is presented in this paper. This device makes possible a non-invasive detection of the microbial growth in liquid foods with no need to open the carton-based packages where they are contained. Thermal and humidity stabilization are required inside the measuring chamber. The changes in the liquid media produced by the microorganism growth induce variations in the ultrasonic propagation parameters giving a non-invasive evidence of the developing contamination. For that purpose, the amplitude and time of flight of an ultrasonic 800kHz tone burst travelling through an UHT milk pack are analysed. Inoculated and sterile packs were tested to evaluate the performance of this new non-invasive ultrasonic microbiological quality sensor.

Intense acoustic bursts as a signal-enhancement mechanism in ultrasound-modulated optical tomography

Biophotonic imaging with ultrasound-modulated optical tomography (UOT) promises ultrasonically resolved imaging in biological tissues. A key challenge in this imaging technique is a low signal-to-noise ratio (SNR). We show significant UOT signal enhancement by using intense time-gated acoustic bursts. A CCD camera captured the speckle pattern from a laser-illuminated tissue phantom. Differences in speckle contrast were observed when ultrasonic bursts were applied, compared with when no ultrasound was applied. When CCD triggering was synchronized with burst initiation, acoustic-radiation-force-induced displacements were detected. To avoid mechanical contrast in UOT images, the CCD camera acquisition was delayed several milliseconds until transient effects of acoustic radiation force attenuated to a satisfactory level. The SNR of our system was sufficiently high to provide an image pixel per acoustic burst without signal averaging. Because of the substantially improved SNR, the use of intense acoustic bursts is a promising signal enhancement strategy for UOT.

Single Ping-multiple measurements: sonar bearing angle estimation using spatiotemporal frequency filters

Presented is a mixed-signal full-custom VLSI chip designed to receive sonar return signals from an ultrasonic microphone array, and extract input bearing angles of the incoming signals. Processing utilizes simple low-power analog spatiotemporal bandpass filters to extract wavefront velocity across the array, which translates to input bearing angle. Processing uses phase information of array signals, not onset or offset of ultrasonic burst. With such synchronous processing, multiple angle readings from different returns of the same ultrasonic transmit burst are possible. Compatible microphone arrays are compact in size-test array has a total baseline of 26.5 mm. In a test with ultrasonic beacon 65 cm from a microphone array, angular precision of 1/spl deg/ was demonstrated in most instances in the range -60/spl deg/ to 60/spl deg/. Applications include sonar localization of remote objects, sonar imaging, and improved interference rejection between objects within the field of view of the sensor microphones. The chip was fabricated on a standard 3M2P CMOS process with a 0.5-/spl mu/m feature size.

Performance considerations of ultrasonic distance measurement with well defined properties

Conventional ultrasonic distance measurement systems based on narrow bandwidth ultrasonic bursts and amplitude detection are often used because of their low costs and easy implementation. However, the achievable results strongly depend on the actual environments where the system is implemented: in case of well defined objects that are always located near the measurement direction of the system, in general good results are obtained. If arbitrary objects are expected that are moreover located in arbitrary positions in front of the sensor, strongly object dependent areas where objects are detected with decreasing accuracy towards their borders must be taken into account. In previous works we developed an ultrasonic measurement system that provides accurate distance measurement values within a well defined detection area that is independent of the reflection properties of the objects. This measurement system is based on the One Bit Correlation method that is described in the following. To minimise its implementation efforts, it is necessary to examine the influence of the system parameters as e.g. the correlation length to the results that are expected in case of different signal to noise ratios of the received signal. In the following, these examinations are shown and the obtained results are discussed that allow getting a well conditioned system that makes best use of given system resources.

On the acoustic vaporization of micrometer-sized droplets

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 micros tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 microm, independent of droplet diameter which ranged from 5 to 27 microm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet's imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.

Historical Perspectives

When pharmacologic closure of patent ductus arteriosus (PDA) in the preterm infant using indomethacin was introduced in 1976, there was a paucity of knowledge about the factors controlling the caliber of the ductus arteriosus both before and after birth. Additionally, mortality and morbidity of prematurity (associated with what was then usually referred to as hyaline membrane disease) was remarkably high in the early 1970s. As early as the 1950s, some neonatologists recognized PDA as a complication of what later became designated as “respiratory distress syndrome” (RDS), although it was not until the advent of intermittent mandatory ventilation (IMV) and continuous positive airway pressure (CPAP) that the concept gained prominence. Patency of the ductus appeared to be a major complication, especially in the smallest of preterm babies (at that time, < 1,350 g]) and usually carried a terminal prognosis. The advent of IMV and CPAP kept these small babies alive for a sufficient period of time for the patent ductus to become recognized progressively as a distinct clinical entity and an important early complication of preterm birth. Observant neonatologists noted that babies who had RDS often improved up to a point, beyond which they worsened. The usual story was that the baby experienced ventilatory failure, was treated with mechanical ventilation, and began to improve, with lower inspired oxygen requirements. After a few days, when discussions ensued about taking the baby off the ventilator, the infant’s improvement would cease. The radiographic picture changed from a clearing of the initial ground glass appearance coupled with a relatively small heart to an enlarging heart and the pulmonary edema of congestive heart failure due to a left-to-right shunt across the PDA. Beginning in the mid-1960s, aggressive surgeons advocated operative closure of the PDA in these small preterm infants, but multiple centers consistently reported unacceptably high …

Air-coupled ultrasonic transmissionmeasurement through paper during wetting

In the first part of this work ultrasonic thickness resonanceswere measured with offset paper samples, 80-240 g m-2 ingrammage. The resonance frequency was found to be linearlydependent on the grammage of the samples. In the second part ofthis investigation 240 g m-2 offset paper samples werewetted with a mist pulse of either water or isopropanol. Thispulse, 61±4 ms in duration, was generated by ahigh-power ultrasonic actuator. The change in resonancefrequency, initially 660±5 kHz, was monitored during thewetting of the paper sample. An ultrasonic burst, frequency swept from 500 to 900, 600 to 1000 and 1300 to 1700 kHz, wastransmitted through the sample at a 10 Hz repetition rate. Thismade it possible to follow the wetting of the sample at severalfrequencies by the same measurement. It was also possible tofollow the temporal development of the apparent absorptioncoefficient of the sample. The shape of the transmission curvessuggests that two different processes, capillary wetting and diffusion wetting, can be distinguished.

Ultraschall-Burst-Phasen- Thermografie

Phased Ultrasonic Burst Thermography. Phased ultrasonic burst thermography is a new nondestructive technique originating from ultrasound lock-in thermography. It provides thermal wave imaging of defects by ultrasonic stimulation. Relatively short ultrasound bursts yield faster measurements and better reproducibility in relation to the well established lock-in method. The advantages of phase images remain valid: the recognition of defect depth and the suppression of temperature gradients. Application of phased ultrasonic burst thermography to typical defects of aircraft components and ceramic turbine blade coatings provide specific information on their nature.

Characterizing aluminum sintering using in-situ NDE

Considerable attention has been given to the use of nondestructive evaluation techniques to reduce the costs associated with the manufacture of powder-metallurgy components. One such technology that is being developed at the U.S Department of Energy’s Ames Laboratory is an in-situ noncontact technique to characterize sintering. The method consists of a high-temperature electromagnetic acoustic transducer to measure the amplitude and velocity of an ultrasonic tone burst traveling through a sample during sintering. Results from the in-situ noncontact nondestructive evaluation measurements indicate that real-time in-situ monitoring of sintering is attainable.

Backscattering enhancements due to reflection of meridional leaky Rayleigh waves at the blunt truncation of a tilted solid cylinder in water: Observations and theory

Leaky surface waves once launched on an elastic object in water will undergo partial reflection at the truncations of the object. Under certain conditions, such reflections can radiate locally flat acoustic wavefronts with a reversal of the acoustic wave vector, and thus a large backscattered signal is produced. A stainless-steel circular rod with flat ends was ensonified through an angular region appropriate for launching meridional Rayleigh waves, and the resulting backscattering enhancement is consistent with the hypothesized end-reflection process. The observed backscattering peak is in general agreement with predictions from a convolution formulation [P. L. Marston, J. Acoust. Soc. Am. 102, 358–369 (1997)]. The tilt of the cylinder was varied to explore the peak’s width, and the results are consistent with an extension of the theory for the dephasing of the Rayleigh wave given here. The amplitude measurements used ultrasonic tone bursts having ka of 50 and 83, and the enhancement is predicted to be significant over a wide range of ka.

Vaporization of micrometer size droplets in simulated in vivo environments

Droplets were generated for a range of albumin (bovine) concentrations. Resulting emulsions were examined for size distribution, number density and yield. Albumin concentrations as low as 1 mg per ml were capable to form stablized droplets. Changes in number density and mean size were observed. Reducing the amount of albumin by a factor of 16 resulted in an increase of the number density by a factor of 40 while the mean droplet size decreased by a factor of 2.5. The measured droplet yield was approximately 30%. Droplets were vaporized using short ultrasonic tone bursts for frequencies ranging from 1.5 to 8 MHz. Two 1-cm Zerdine 81 layers of acoustic attenuation of 0.5 dB/MHz/cm were overlaid on the flow tube used. Droplets were phase transitioned in saline and in blood. Pressure thresholds for vaporization were acquired for conditions with and without Zerdine as well as saline or blood as bulk fluid. It has been seen that the threshold in saline increased by approximately 25% by introducing the Zerdine layers (1.5 MHz) and 60% for the Zerdine-blood combination. [Work supported in part by PHS Grant No. R01 HL54201 from the National Heart, Lung and Blood Institute.]

Surface waves above thin porous layers and periodic structures

Airborne surface waves above thin air-saturated porous layers and periodic structures have been studied in the low-ultrasonic frequency domain. These waves were observed performing two different kinds of experiments. Because surface waves are related to a pole in the reflection coefficient, we adapted a setup based on near-field acoustical holography to the frequency range of interest. In this way, it was possible to measure the reflection coefficient of the porous layer as a function of the angle of incidence. The existence of a surface wave was observed for different layer thickness. Second, the velocity of the inhomogeneous waves has been determined directly by time-of-flight measurements of ultrasonic bursts, by phase velocity measurements with a sine signal, and from interference patterns of standing waves. The results are compared to predictions using several models. The reflection coefficient above the reticulated polyurethane foams was predicted by an equivalent fluid model, the frame being motionless at the frequencies considered here. For the calculations of the velocity above rectangular- and triangular-groove gratings, we adapted models developed for electromagnetic waves above these structures to acoustics.

Continuous Monitoring of Binary Gas Mixture Concentration With Application to Turbine Blade Cooling Experiments

Turbine blade cooling experiments often use mixtures of air and a heavy gas CO2,SF6 to simulate coolant/mainstream density ratios. If the mixing of the mainstream with the coolant ejected from the blade is of interest, then it may be necessary to determine the spatial distribution of the heavy gas concentration in the flowfield. Commercial analyzers are too slow and have other disadvantages when used for this purpose. To meet this special need, a device has been developed to monitor the heavy gas concentration continuously in a small sample stream by determining the speed of sound in the sample. Together with the temperature of the sample, the information is sufficient to determine the concentration. The device measures the time of propagation for an ultrasonic burst transverse to the stream. The temperature of the gas contained in the device is controlled and measured. Calibration with several gas mixtures (air and CO2,SF6, He) has shown an uncertainty Cmeas−Ctrue of 2 percent over the full concentration range of 0–100 percent for CO2 and SF6. The device is operable in the pressure range from −50 to 100 kPa gage and in the temperature range from 0°C to 40°C. The instrument is rugged and will survive in noisy, turbulent environments. [S0889-504X(00)01202-2]

Characterization of ultrasound-contrast agents by short-burst excitation

A two-frequency method has been adapted to the use of short ultrasonic bursts for the determination of bubble size. The advantage of a burst method is threefold. The overall energy transfer into the volume of interest is smaller as compared to cw. Second, it allows simple methods for improving spatial resolution. Finally, only one transducer will eventually be required in a pulse-echo mode. The experimental setup is designed to fully compensate for transducer characteristics and sample artifacts such as attenuation through window material and contrast agent solution. This leads to a constant sound pressure exposure for contrast agent in the focal volume. The data acquisition employs the frequency tracking procedure where spectra for narrow-band excition are analyzed for fundamental, second harmonic, and sidebands. A technique of nonconstant imaging frequency is used to avoid ambiguities due to coincidences between higher harmonics of the fundamental and multiples of the sideband frequencies. Measurements with shell-encapsulated microbubbles showed the behavior demonstrated by previous cw methods. Higher harmonics as well as sidebands were present due to the nonlinear dynamics of the contrast agents. [This work was supported in part by USPHS Grant Nos. RO1 DK42290 and 1RO1 HL54201.]

Method and apparatus for myocardial wall measurement

A closed-loop single-crystal ultrasonic sonomicrometer capable of identifying the myocardial muscle/blood interface and continuously tracking this interface throughout the cardiac cycle using a unique piezoelectric transducer. During steady-state, a reference volume SVm is adjusted so that it remains within the myocardium while half of an interface volume SVi is in the myocardium and one-half is in the ventricular chamber. Every 100 ns, a 0.5 μs duration ultrasonic burst of 10 MHz pulses is transmitted from the piezoelectric transducer. Myocardial layers and red blood cells in the ventricular chamber reflect the ultrasonic energy back to the piezoelectric transducer. The echoes are then amplified and applied to a Doppler decoder, which then mixes them with a local oscillator signal having a 2 kHz offset relative to the transmitted signal. When the offset signal is mixed with returning ultrasonic echoes, the resulting Doppler signals are shifted in the frequency domain by 2 kHz. The received Doppler signal is then processed by an amplitude-locked-loop circuit which maintains the steady state throughout the cardiac cycle. Initially, the Doppler decoded signal is sampled at two distinct time intervals corresponding to sample volumes SVm and SVi. The outputs from these two sample volumes are then bandpass filtered to remove frequencies contributed by red blood cells. The true RMS values from both sample volumes then are compared and an error signal is generated. The integrated error signal is adjusted for correct depth placement and applied to a voltage-controlled delay circuit. The amplitude-locked-loop circuit continuously adjusts the position of the two sampled volumes SVm and SVi, so that they always remain within, and thereby effectively track, the muscle/blood interface. As a result, the apparatus can measure absolute myocardial wall thickness.

Filtration technique enhanced by electro-acoustic methods

Results from an experimental study of electric and/or ultrasonic field assisted filtration are presented. Both electric and ultrasonic fields can reduce fouling of the filtration medium and have significant influence on filtration capacity. The extent of filtration improvement is affected mostly by particle size, surface charge, acoustic frequency, and field strengths. Theoretical examinations of the use of electric field and/or ultrasonic field to enhance filtration efficiency were laid out. Some aspects regarding orthokinetic interaction in acoustic agglomeration were considered. Energy consumptions of the filtrations of different suspensions used in experiments were also determined. For pyrite suspension the best results with ultrasound were obtained when filtration was done as follows: 15-s negative pressure filtration, 15-s negative pressure filtration with 22-kHz ultrasonic burst (0.5 s) and 20-s drying with negative pressure. In this case the moisture content of cake was 7% while in the reference cake it was 14%. The cake capacity was fourfold greater than in the reference case. The best results for phosphoric acid were obtained when combined use was made of the ultrasound and the electric field. In this case the filtration capacity increased fifteenfold while the use of ultrasound on its own increased the filtration capacity tenfold.

An ultrasonic system for measurement of absolute myocardial thickness using a single transducer

We have developed an ultrasonic instrument that can measure absolute regional myocardial wall motion throughout the cardiac cycle using a single epicardial piezoelectric transducer. The methods in place currently that utilize ultrasound to measure myocardial wall thickness are the transit-time sonomicrometer (TTS) and, more recently, the Doppler echo displacement method. Both methods have inherent disadvantages. To address the need for an instrument that can measure absolute dimensions of myocardial wall at any depth, an ultrasonic single-crystal sonomicrometer (SCS) system was developed. This system can identify and track the boundary of the endocardial muscle-blood interface. With this instrument, it is possible to obtain, from a single epicardial transducer, measurement of myocardial wall motion that is calibrated in absolute dimensional units. The operating principles of the proposed myocardial dimension measurement system are as follows. A short duration ultrasonic burst having a frequency of 10 MHz is transmitted from the piezoelectric transducer. Reflected echoes are sampled at two distinct time intervals to generate reference and interface sample volumes. During steady state, the two sample volumes are adjusted so that the reference volume remains entirely within the myocardium, whereas half of the interface sampled volume is located within the myocardium. After amplification and filtering, the true root mean square values of both signals are compared and an error signal is generated. A closed-loop circuit uses the integrated error signal to continuously adjust the position of the two sample volumes. We have compared our system in vitro against a known signal and in vivo against the two-crystal TTS system during control, suppression (ischemia), and enhancement (isoproterenol) of myocardial function. Results were obtained in vitro for accuracy (> 99%), signal linearity (r = 0.99), and frequency response to heart rates > 450 beats/min, and in vivo data were acquired for end-systolic dimension (r = 0.99), end-diastolic dimension (r = 0.99), and percent wall thickness (r = 0.99). Both in vitro and in vivo tests indicate that the SCS functions identically to the two-crystal TTS. Use of the SCS allows measurement of absolute wall thickness and hence myocardial function, for both acute and chronically instrumented animal studies, with minimal or no trauma to myocardium.