Transducer In Pulse-echo Mode Research Articles

Ultrasonic Imaging of Concrete/ RCC Structures using Immersion Technique

There has been a rapid increase in the construction of under-water concrete structures all over the world and the maintenance and rehabilitation of these concrete structures pose a major concern for estimating the quality and the useful remaining life of these structures. To cater to such needs, the detection of defects, porosities and rebar locations inside the Concrete/Reinforced Cement Concrete (RCC) structures have been carried out using the in-house developed single-channel ultrasonic imaging system at Electronics Division, BARC, India. Commercially, the inspection of under-water concrete structures is being carried out by utilizing Ultrasonic Pulse Velocity (UPV) method in Transmit-Receive (T-R) mode to indirectly estimate the density and strength of the concrete structure under test. UPV method requires a skill to interpret the data provided by the UPV instrument. The in-house developed single-channel system can perform imaging of Concrete/ RCC structures both in Pulse Echo (PE) as well as in T-R mode and can function in UPV mode. The imaging system performs data acquisition and temporal averaging of the RF bipolar data to achieve high Signal-to-Noise Ratio (SNR) ( > 20 dB). In this paper, different types of concrete blocks with simulated defects and RCC blocks with steel rebars have been utilized for the inspection using the single-channel imaging system in water-immersion mode. The B-Scan images have been acquired for the concrete and RCC sample test blocks, using 54 KHz water immersion transducer in PE mode. The acquired B-Scan images have revealed the internal details of the Concrete and RCC sample test blocks, resembling the defects generated in the test blocks. The A-Scan waveform was also acquired on the 1 metre thick concrete block in contact PE mode, which shows the capability of the single channel ultrasonic imaging system for the inspection of such thick concrete blocks.

Embedded system for ultrasonic imaging of under-water concrete structures

Many of the modern concrete structures such as sea-links and bridges are built in water. They require structural health monitoring (SHM) and audit to ascertain the quality and estimation of remaining useful life. To meet these requirements, a single-channel ultrasonic imaging system has been designed and developed to detect defects, porosities and rebar locations inside the Concrete/ Reinforced Cement Concrete (RCC) structures. This real-time and reconfigurable embedded system whas evaluated by carrying out under-water imaging of Concrete and RCC test blocks. Conventionally, Ultrasonic Pulse Velocity (UPV) method is being utilized over three decades in Transmit-Receive (T-R) mode to estimate the density and strength of the concrete structure under test. UPV method requires a skill to interpret the data provided by the UPV instrument. The novelty of the single-channel system discussed in this paper is that it is capable of inspecting Concrete/ RCC structures both in Pulse Echo (PE) as well as in T-R mode. An application software has been developed using C# in a visual environment for image acquisition and the control of Data Acquisition (DAQ) hardware has been interfaced to the computer via USB. The imaging system performs data acquisition and coherent averaging of the RF bipolar data to achieve Signal-to-Noise Ratio (SNR) higher than 20 dB. The performance of the system was evaluated by acquiring B-Scan images of the water submerged concrete test blocks having Side Drilled Hole (SDH) and RCC blocks with one as well as two steel rebars, using 54 kHz water immersion transducer in PE mode. The acquired B-Scan images have revealed the internal details of the sample test blocks, resembling the defects generated in the test blocks. High voltage tone burst bipolar pulser with maximum output of (± 350 V) has been specifically designed for this system to inspect highly attenuative porous and non-homogeneous Concrete/ RCC materials for the detection of SDH and reinforced steel bars in the concrete test blocks, using B-Scan imaging technique.

Water content monitoring in water-petroleum emulsions using a 5 MHz Ultrasonic transducer in pulse-echo mode

Water content monitoring in water-petroleum emulsions using a 5 MHz Ultrasonic transducer in pulse-echo mode

Multi-mode ultrasonic waves focusing in a variable focus technique for simultaneous sound-velocity and thickness measurement

A double-focus technique, using a spherically focused immersion transducer, has been developed for simultaneous sound-velocity and thickness measurement. This is an effective method that does not require pre-experiments or predictive parameters. In previous studies, the single-mode wave model, usually used, cannot explain the additional reflection peaks on the V(z,t) curve, which denote two-dimensional amplitudes as a function of the movement along distance z and the time t. In this research, a multi-mode wave model, interpreting the results of depth scanning of thin solid plates, using a spherically focused ultrasound transducer in pulse-echo mode, is presented. The existence of additional reflection peaks in the solid plate due to mode conversion, which are usually neglected, are described in the new model. A comprehensive interpretation of the measurements is proposed, instead of ignoring the transverse waves and mode conversion. The distribution of energy among multiple reflected focuses and the vertical displacements of the transducer are numerically analysed. The experiments on a 0.5 mm thick stainless steel and a 0.5 mm thick aluminium alloy have been carried out to verify the model. This study contributes to the identification of longitudinal-wave focuses, especially in cases of simultaneous measurement on multi-layered materials.

Impact of sol-gel transition on the ultrasonic properties of complex model foods: Application to agar/gelatin gels and emulsion filled gels

Quantitative ultrasound (US) techniques have an attractive potential for the non-invasive and real-time characterization of the structural and mechanical properties of food. The objective of the present study is to unravel the determinants of the variations of US properties during sol-gel transition of emulsion filled gels of agar and gelatin, due to the relative contributions (i) of their individual components and (ii) of their combined interactions. Nine model foods were designed, accounting gradually for the complexity of an emulsion filled gel composed of water, sucrose, agar, gelatin and sunflower oil. A quantitative US device was designed to monitor the sol-gel transition of the model foods. US velocity, reflectivity and attenuation were measured at 50 °C (sol-state) and 20 °C (gel-state) with a 1 MHz transducer in pulse-echo mode. US data were then compared to visco-elastic shear moduli and density measurements. Bulk elastic modulus was shown to prevail over density for explaining the variations of US velocity and reflectivity during sol-gel transition, while high gelatin concentration and interactions between agar and gelatin had an impact on US attenuation. In addition to the fact demonstrated here that US reflectivity is easier to measure compared to velocity and attenuation, the literature reports that this parameter also highly depends on the mechanical coupling of interfaces. Therefore, this study is a baseline for future investigations on the potential of US reflectivity for the characterization of physical interactions between food and more complex surfaces, so that to mimic tongue-food interaction during oral processing.

Real-time 3D ultrasound based motion tracking for the treatment of mobile organs with MR-guided high-intensity focused ultrasound

Introduction: Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) treatments of mobile organs require locking the HIFU beam on the targeted tissue to maximise heating efficiency. We propose to use a standalone 3 D ultrasound (US)-based motion correction technique using the HIFU transducer in pulse-echo mode. Validation of the method was performed in vitro and in vivo in the liver of pig under MR-thermometry.Methods: 3 D-motion estimation was implemented using ultrasonic speckle-tracking between consecutive acquisitions. Displacement was estimated along four sub-apertures of the HIFU transducer by computing the normalised cross-correlation of backscattered signals followed by a triangulation algorithm. The HIFU beam was steered accordingly and energy was delivered under real-time MR-thermometry (using the proton resonance frequency shift method with online motion compensation and correction of associated susceptibility artefacts). An MR-navigator echo was used to assess the quality of the US-based motion correction.Results: Displacement estimations from US measurements were in good agreement with 1 D MR-navigator echo readings. In vitro, the maximum temperature increase was improved by 37% as compared to experiments performed without motion correction and temperature distribution remained much more focussed. Similar results were reported in vivo, with an increase of 35% on the maximum temperature using this US-based HIFU target locking.Conclusion: This standalone 3D US-based motion correction technique is robust and allows maintaining the HIFU focal spot in the presence of motion without adding any burden or complexity to MR thermal imaging. In vitro and in vivo results showed about 35% improvement in heating efficiency when focus position was locked on the target using the proposed technique.

Remote sparse distributed sensors to image bondline defects between a composite panel and a stiffener

Adhesive bonding is widely used to fix skins to reinforcing elements, like stiffeners, in aerospace composite structures. A well-cured bond offers uniform stresses, good joint strength, and improved fatigue and impact resistance, and is therefore crucial to the performance of the entire structure. In the previous work by the authors, ultrasonic feature guided wave (FGW) has been discussed as a screening tool for quick inspection of the bondline between a CFRP panel and stiffener. However, it was found that material damping and weak reflections by defects along the feature makes the use of a single transducer in pulse echo mode quite inefficient. In this study, a structural health monitoring (SHM) technique is proposed to inspect the bondline, based on the radiation of plate modes into the CFRP panel when an incident FGW interacts with a defect in that bondline. A sparse array of sensors organized on the CFRP panel away from the stiffener was used to capture the waves radiating into the panel. A synthetic focusing method was applied to process the recorded signals for imaging the damaged area in the bond. Adhesive defects with varying dimensions were successfully identified in 3D FE simulations, with supporting experimental results to validate this method.

Relation between the Ultrasonic Attenuation and the Porosity of a RTM Composite Plate

We propose a comparative study of X-ray tomography and ultrasonic reflection methods, for determining the porosity of a composite plate realized in LOMC with an industrial process. We measure the attenuation of ultrasound propagating in the thickness by using 10MHz plane transducer in pulse-echo mode. Comparing these results to the 2D porosity tomographic map allows establishing a relation between attenuation and porosity. A C-scan picture of the plate given by the echoes reflected by the rear surface also provides a local information on the attenuation. Furthermore, we propose a method for the mapping of the reflecting sources as the included bubbles and the interfaces resin/fibers.

Damage Detection of Filament Wound Composite Cylinder Using Ultrasonic Waves

This paper experimentally investigates the damage detection of filament-wound (FW) thick-wall composite cylinder using ultrasonic waves. The multi-layered cylinder has a 20 mm-thick steel liner with an inner radius of 421 mm, an 11 mm-thick layer of unidirectional carbon fiber reinforced composite that is wound on the steel liner, and a 2.15 mm-thick layer of coating over the composites. Damages are pre-manufactured in different wall depths of the cylinder. The main damages to be detected include the defects in the composite layer, the interface debonding between the composite layer and the steel liner, and the change of thickness of the steel liner due to corrosion. To interrogate above mentioned damages, the longitudinal waves are excited using an ultrasonic transducer in pulse-echo mode along the radial direction of the cylinder. The continuous wavelet transform (CWT) is used to analyze the reflected-ultrasonic signals in order to obtain the Time-of-Flight (ToF) and the amplitude ratio of different interfaces. Based on the ToF and amplitude ratios, the location and size of the damages are identified and the thickness of the steel liner is determined. Experimental results show that the ultrasonic pulse-echo technique combined with the CWT is feasible in damage detection of multi-layered filament-wound composite cylinder especially when a coating layer exists.

A conical air-coupled capacitance transducer for surface imaging

This paper describes the construction and operation of an air-coupled capacitance transducer with a conical backplate. This was designed to produce a focal region over an extended distance along the transducer axis. Measurements were performed to examine both the frequency response of the transducer in pulse-echo mode, and the lateral resolution for imaging purposes. The radiated field was measured and compared to theory, and the extent of the focal region determined. Images of surface topography are presented, to illustrate the range of application of the transducer.

Prediction of surface echo from a non-planar surfac

A model has been derived to predict the echo issuing from an irregular liquid-solid interface and received by a focused transducer in pulse-echo mode. The transient radiation of the transducer is described by the Rayleigh integral. The Kirchhoff's approximation for reflection is applied to model the beam-surface interaction and the emission-reception reciprocity principle is applied. Acquisitions have been made on surfaces showing grooves extending perpendicularly to the incident plane. Computed and experimental results are in a good agreement.