A pulsed ultrasound transducer system for two component flow

Photoacoustics (PA) is a promising technology for medical imaging due to its superior contrast and resolution. This technique can be implemented either in time domain by powerful nanosecond laser pulses or in frequency domain (FD) by low power intensity-modulated continuous wave (CW) chirped laser irradiation (“the photoacoustic radar”). In our previous work [1,2] FD-PA imaging with linear frequency-swept optical modulation was implemented and the application of various signal processing methods to obtain depth-selective imaging was demonstrated. Later on we compared the FD and the pulsed techniques with respect to the maximum detectable depth using a dual-mode PA system [3]. Comparable depths were found with the FD technique exhibiting significantly superior signal-to-noise ratio (SNR). Very recently [4] we demonstrated that by combining the additional imaging channel that CW method possess due to its phase information with the cross-correlation amplitude results, the contrast and resolution of the image can be improved. In this study the contrast of images produced with both techniques is compared for various depths of a scattering medium. Experiments were implemented using two ultrasonic transducers with different center frequencies of 3.5 and 0.5 MHz. The samples consisted of two black rubber squares of areas 2x2 mm 2 and 4x4 mm 2 located at the same depth. These specifications were devised to enhance the comparison to the limits of the system, in other words, as we are trying to determine how small and how deep we can detect an absorber in a highly scattering medium, by comparing the contrast of the two rival methods. The wavelength of both pulsed and CW lasers utilized was 1064 nm and laser energies were controlled under the safety standard limits [5]. Since the CW method provides the capability to control the waveform shape and its bandwidth (BW), it is essential to examine the optimal BW of the frequency-modulated chirps to maximize the signal-to-noise ratio (SNR). It is demonstrated theoretically and experimentally that the optimal frequency BW does not depend exclusively on the transfer function of the ultrasonic transducer and its -6 dB BW, but also on the acoustic and optical properties of the tissue and lesion. To be specific, other than the transducer’s BW, acoustic attenuation of the medium and optical absorption and speed of sound in the lesion are key factors. Some results are demonstrated in figures 1 and 2 by utilizing the high frequency transducer. Figure 1.a shows the cross-correlation amplitude in the PA radar method generated in the middle of a black rubber square of 4x4 mm 2 in 19 mm depth of a 0.47% intralipid solution. Figure 1.b shows the transient response of the same sample to a pulsed laser. Comparison of these signal traces, demonstrates the higher SNR achieved by the CW method. Figures 2.a and b are the complete images produced at a specific depth corresponding to the surface of the black rubber samples. These images are constructed by complete scanning of a 15x15 mm 2 area using the CW and pulsed methods. It demonstrates that at the ultimate depth for the high frequency transducer, the pulsed laser achieved better detectivity. Nevertheless by employing the additional phase channel it is demonstrated that the contrast and resolution of the CW method is superior for shallower absorbers in the case of high frequency transducer. Next experiment exhibits the results of imaging a sample (absorption coefficient: 2 cm

Introduction It is perhaps not surprising that using extremely high power and short pulse duration pump sources leads to dramatic nonlinear processes in optical fibres; in contrast, the generation of a supercontinuum from a continuous pump wave of relatively meagre power is at first sight, astounding. Yet supercontinua spanning over 1000 nm have been generated with pump powers of a few tens of watts – orders of magnitude lower than pulse pumped systems. The key to continuous wave (CW) supercontinuum generation is the utilisation of modulation instability (MI). This is inherent to any anomalously dispersive, nonlinear medium, and has been observed in a wide range of systems. This instability can enable the creation of the extremes of peak power and pulse duration necessary for dramatic nonlinear processes to occur, even from very low power CW pump lasers. But although MI from CW pump lasers was observed in the 1980s by Itoh et al. (1989), other factors required for efficient continuum generation were missing, causing another decade to pass before such results were obtained. A full review of experimental results will be presented later, but for reference, some examples of continuous wave supercontinua are shown in Fig. 8.1, which illustrate the high spectral power and the spectral smoothness and flatness which are characteristic of CW continuum generation. Although significantly different from the physical mechanisms involved in ultra-short – femtosecond based – supercontinuum generation, the basic physical processes underpinning CW continuum generation are the same as for longer pump pulses (greater than a few picoseconds) and the observations and conclusions developed in the 1980s surrounding these type of sources apply to the CW regime.

Frequency-modulated ultrasound signals like chirp-signals show variations in phase at the different transmission angles. Analyzing the phase of ultrasound chirp-echoes enables to accurately determine distance and polar angle to the point of reflection. Though single piezoceramic ultrasound transducers have a small bandwidth, an ultrasound transducer made of a combination of piezoceramic elements with different resonance frequencies as presented in this work enables transmission of broadband chirp- signals and shows the required rotational symmetry. Frequency-modulated chirp-signals transmitted by ultrasound sensors with broad bandwidth show different variations in phase at different directions of the radiated sound pattern. With the phase information of the echo signal it is possible to determine the angle of the point of reflection with respect to the main transmission direction of the ultrasound transducer, representing the polar angle in a spherical coordinate system with the main transmission direction being the z axis. Processing the frequency-modulated chirp-signal by use of a correlation algorithm delivers high accuracy of the distance measurement. Using only one ultrasound transducer transmitting a broadband signal and assuming rotational symmetry, we get the distance and one of the two angles needed to exactly determine the 3D coordinates of the reflection point, instead of getting only the distance like in other known systems. Off the shelf ultrasound transducers for air applications are based on different technologies, like electrostatic transducers, PVDF (Polyvinylidene fluoride) transducers, piezoceramic and piezocomposite transducers. Although typical constructions of electrostatic transducers are not well suited for industrial environment, many air ultrasound applications are based on this transducer type producing high sound pressure amplitudes by simultaneous small power consumption. Though electrostatic transducers have also an advantageous broad bandwidth, they are not appropriate to be used for polar angle measurements, because they still cannot be produced with a good rotational symmetry. The only air ultrasound transducers that show appropriate rotational symmetry are piezoceramic transducers. Piezoceramic transducers have a narrow bandwidth and are driven most effectively at their geometry-dependent resonance frequencies.

This current work offers the experimental method which is capable of measuring the air-methane gas using L-wave by an ultrasound sensor in a constant volume chamber (CVC). For experimental method, a constant volume chamber is integrated with of a high-sensitive ultrasound sensor, a conventional ultrasound sensor, a non-resistance cable, a temperature sensor, a pressure sensor and two mounted zigs. The main conditions, for the experiment defined in this work, are composed of 2 bar of initial pressure, 296 K of temperature, air-CH4 mixture of gas fuel, 25 V of input voltage, 3 Hz of pulse rate and 0.2-2 of measurement distance (m) for two different ultrasonic sensors. The resonant frequency is set 67.6, 70.6, 73.6 and 76.6 kHz by adjusting wavelength inside the circuit system. It is shown that sensitivity in ethylene vinyl acetate matching layer (EVAM) type is remarkably increased comparing with the chemical wood matching layer (CWM) type. Moreover, in comparison to the conventional CWM type, the amplitude height of EVAM type shows 1.19 V at 1st, 1.05 V at 2nd, 0.63 V of 3rd, 0.40 V at 4th and 0.27 V at 5th in CVC. With regards to the average percentage, the EVAM type is shown up to 116, 250, 270,263 and 350 % for 1st, 2nd, 3rd, 4th and 5th comparing with the conventional. Consequently, the voltage characteristics improved by EVAM type layer is demonstrated that energy transfer is higher than CWM type in CVC and efficiently led to increasing the ultrasonic sensitivity in an air-methane mixture.

Ultrasonic transducers working in the air with the continuous wave within the 50–500 kHz frequency range

This research put forward an exogenous liquid level measurement method based on continuous sound wave amplitude. The distribution of round piston transducers in the sound field of a metal solid was analyzed by building 15 Multi-Gaussian Beam superposition models; the calculation method for echo sound pressure was worked out according to the reflection and refraction properties of ultrasonic wave. The continuous wave with three amplitudes was used as the driving source of ultrasonic sensor, and two single-crystal sensors with the same diameter were used as the transmitting terminal and receiving terminal of ultrasonic waves to carry out experiments for four groups of containers of different wall thickness and to compare the characteristics of echo energy of driving sources with three amplitudes above and below the liquid levels with different wall thickness. Two groups of sensors of different diameters were used to measure the liquid levels of experimental models, and the measuring errors of the two groups of sensors were analyzed and compared. The experimental result shows that the measuring error of the model is less than 5 mm, so it is applicable to the level measurement of liquids or liquid mixtures in many sectors.

The performance of a new ultrasound transducer, which can measure velocity profiles non-invasively through high-grade stainless steel pipes, was evaluated for the first time with secondary wastewater sludges. This work is a follow-up study on the feasibility work initially done by the same authors. In-line process control based on accurate rheological characterisation for treated wastewater sludge could lead to significant savings in chemicals and will optimise dewatering processes producing drier sludges. In this work, a wastewater sludge at three concentrations was tested in order to investigate the capabilities of the in-line ultrasound technique for different viscosities and fluid properties. The rheological parameters obtained using the new ultrasound sensor and ultrasonic velocity profiling with combined pressure difference (UVP + PD) technique were compared with results obtained using conventional tube viscometry. Comparison with tube viscometer results showed that yield stresses could be overestimated by 120% if data are not available in the low shear-rate ranges. This non-invasive transducer proved to be sensitive enough to obtain flow curves over a large shear-rate range, improving the prediction of the yield stress and requiring about 50% less energy than the invasive system.Keywords: ultrasonic velocity profiling, UVP + PD methodology, sludge rheology, non-Newtonian, tube viscometry, non-invasive, sludge dewatering

Improved water resource management framework for water sustainability and security

The visually impaired are at a considerable disadvantage because they often lack the information for avoiding obstacles and hazards in their path. They have very little information on self-velocity, objects, direction - which is essential for travel. Previously developed navigation systems use costly equipment which is often not affordable by the common blind community. The navigation systems available are heavy and very complicated to operate. This research has been aimed at design and development of a smart and intelligent cane which helps in navigation for the visually impaired people. The navigator system designed will detect an object or obstacle using ultrasonic sensors and gives audio instructions for guidance. The signals from the ultrasound sensor are processed by a microcontroller in order to identify sudden changes in the ground gradient and/or an obstacle in front. The algorithm developed gives a suitable audio instruction depending on the duration of ultrasound travel which in turn is made available by an mp3 module associated with the system. This work presents a new prototype of navigation system on a cane which can be used as a travel aid for blind people. The product developed is light in weight, hence, does not cause fatigue to the user. This project is developed by keeping in view the affordability and reliability. An obstacle as close as 4cm can be detected by this module. A resolution of 15cm of obstacle distance has been designed and achieved. This system can also detect potholes on the path.

Monitoring of an ascending air bubble in a viscous fluid/fiber matrix medium using a phased array transducer

There are two basic types of sample/hold circuits- inverting and noninverting-and two important parameters for these circuits-aperture time and acquisition time. Peak detectors are special forms of sample/hold modules in which the peak value of an input signal, once reached, is automatically held. The last networks discussed in this article are comparators, in which one or more summing resistors are connected to the inverting output of the operational amplifier.

An invention is disclosed for locating a region of interest in the calcaneus. A pair of ultrasound transducers are positioned on the medial and lateral sides of the heel, respectively. The positioning is based on a size of a portion of the body of a subject upon whom the ultrasound assessment of the calcaneus is to be made. In a presently preferred embodiment, the length of the foot from the back to the head of the first metatarsal is used in conjunction with a proportionality constant and an angle, to position the pair of transducers. The positioning so obtained facilitates (i) reproducible measurements and (ii) comparisons of the results obtained in one person with another, because relatively analogous portions of the highly heterogeneous calcanei are assessed in both. In an alternative embodiment, a single transducer is positioned similarly on the heel, operating in pulse-echo mode.

A high intensity and high frequency ultrasound radiation ultrasonic transducer was fabricated by the hydrothermal deposition technique of lead zirconate titanate polycrystalline thick film. This ultrasonic transducer had a 45 micron meters thick hydrothermal PZT layer on a 50 micron meters thick titanium substrate, and an active area was 5 mm times 5 mm. The piezoelectric constant d33 of this PZT thick film was 44 pm/V and the acoustic impedance was about 8 Mrayl. This prototype ultrasonic transducer radiated a sound pressures of over 100 kPa at over 20 MHz in degassed water using a thickness vibration mode of the PZT film. The radiated sound pressures was measured using a commercial hydrophone that was proofed of the receiving sensitivity at 1 MHz to 60 MHz. The hydrophone was held 40 mm in front of a surface of the prototype transducer. This measuring point was a central ultrasonic beam axis from the prototype transducer. An applied voltage to the prototype ultrasonic transducer was 40 V at ten cycles burst waveform of sine wave when measuring the radiated sound pressure. Additionally, when a driving signal was 20 MHz continuous sine waves, cavitations and an acoustic streaming was generated along a line of the central ultrasonic beam axis. The observation of generated cavitations when the continuous high intensity ultrasonic radiation from the transducer was conducted with the KI oxidation method. The cavitations was measured by measuring the oxidation reaction from the generating of cavitations in a KI solution. A volume of the KI solution for the measurement of cavitations was 50 ml

Uncontrolled overtopping during flood events can endanger embankment dams. Erosion of the downstream slope and scouring of its base caused by the high velocity and energy of the overflow can indeed lead to breach formation until complete failure. In this context and faced with the important number of overtopped embankment dams to be rehabilitated, since the early eighties, researchers have investigated surface protection solutions for downstream slope. Overlays against erosion such as seeded goetextile or cable-tied cellular concrete blocks, are not sufficient. In fact, they can resist only short events with low discharge and velocity. Solution to overcome more severe overflow lies in overlays which dissipate flow energy along the downstream embankment slope. Conventional steps resulting from Roller Compacted Concrete (RCC) techniques fulfill efficiently this challenge. However, flows over steep stepped chutes are quite complex, characterizing by great aeration, high turbulence and confused wavy free surface. Then, most of hydraulic studies of such flows are performed on physical model. Yet, understanding and definition of flow behaviour and accurate approach to estimate energy dissipation are still lacking. General guidelines of hydraulics of aerated flows over stepped macro-roughness chutes and for optimal design of protection overlay remain confusing. To contribute to reduce these uncertainties, experimental study of flow over stepped chutes equipped with macro-roughness elements is performed in a laboratory gated flume for mild ( 1:7H : 1V ) and weak ( 3H : 1V ) chutes. Thus, they are representative of the range of embankment dams and spillways slopes. Three types of stepped macro-roughness overlays are assessed, namely rectangular conventional steps, steps equipped with endsills fixed on their nose over all the flume width and steps equipped with rectangular spaced blocks. Endsills overlays were characterized with different longitudinal distributions whereas blocks overlays consisted in different transverse patterns. Tests were conducted for the three nappe, transition and skimming flow regimes. Results can be extrapolated to 1/5 to 1/15 scaled prototypes using the Froude similarity with negligible scale effects. Flow depth, local air concentration and longitudinal velocities are measured with a double fiber-optical probe. Pressures at macro-roughness faces are taken with piezo-resistive sensors. Sequent depths of the hydraulic jump forced in the stilling basin at the flume base are measured with ultrasound sensors. Thus, this experimental phase of the thesis has allowed: to define flow parameters (regimes, depths, velocity and air concentration distributions, hydrodynamic forces) for tested overlays, to highlight that air-water flow depth is divided into: a rough boundary layer influenced by shear stress and by drag form (macro-turbulence) caused by macro-roughness, a homogeneous aerated layer which represents the main portion of flow involved in energy dissipation mechanism, a free surface layer which must be considered in the side walls design, to stress that energy dissipation is mainly a question of drag losses, to validate indirect method of hydraulic jump for energy dissipation estimation, to estimate relative energy loss for several stepped macro-roughness overlays. Tests finally show that an optimal alternative to dissipate the overflow energy during an overtopping event consists in spaced blocks, with transverse space larger than the width of block and fixed alternately on conventional steps. However, experimental results remain related and limited to their tested domains. Then, in order to provide more general governing equations of aerated flows over macro-roughness stepped chutes, a numerical modeling of two phase flows over conventional stepped flume was performed in collaboration with the Laboratory of Applied Hydrodynamics and Hydraulic Constructions at University of Liege. A quasi-2D numerical model based on the finite volume method was developed. It consists in applying the classical depth-averaged simplified Navier-Stokes equations (viscosity and Coriolis terms neglected) to a 1D incompressible air-water mixture flow over mild and steep slopes with a stepped topography. Self-aeration process is modeled by a transport equation of depth-averaged air concentration whereas turbulent structures are indirectly implemented through the Boussinesq coefficient. This first 1D-approach of semi-theoretical description of aerated flow over steps is tested for a 30o gated stepped flume and a 52° crested spillway laboratory model. This numerical model leads to realistic results regarding mixture depth, mean flow velocity, air concentration and wave amplitudes of the flow free surface. Finally, on the basis of existing protections of embankment dams and previous studies, the present experimental and numerical results contribute to extend the knowledge of high velocity aerated flows over macro-roughness and to provide elements of guidelines to optimize stepped macro-roughness overlays for embankment dams safety.

Self-heating phenomenon of piezoelectric elements excited by a tone-burst electric field