Transducer Location Research Articles

SCOUT: Skull-Corrected Optimization for Ultrasound Transducers

Transcranial focused ultrasound has been studied for non-invasive and localized treatment of many brain diseases. The biggest challenge for focusing ultrasound onto the brain is the skull, which attenuates ultrasound and changes its propagation direction, leading to pressure drop, focus shift, and defocusing. We presented an optimization algorithm which automatically found the optimal location for placing a single-element focused transducer. At this optimal location, the focus shift was in an acceptable range and the ultrasound was tightly focused. The algorithm simulated the beam profiles of placing the transducer at different locations and compared the results. Locations with a normalized peak-negative pressure (PNP) above threshold were first found. Then, the optimal location was identified as the location with the smallest focal volume. The optimal location found in this study had a normalized PNP of 0.966 and a focal volume of 6.8% smaller than without the skull. A Zeta navigation system was used to automatically place the transducer and track the error caused by movement. These results demonstrated that the algorithm could find the optimal transducer location to avoid large focus shift and defocusing. With the Zeta navigation system, our algorithm can help to make transcranial focused ultrasound treatment safer and more successful.

Measuring nearshore waves at break point in 4D with Stereo-GoPro photogrammetry: A field comparison with multi-beam LiDAR and pressure sensors

Measuring nearshore waves remains technically challenging despite wave properties are being used in a variety of applications. With the promise of high-resolution and remotely-sensed measurements of water surfaces in four dimensions (spatially and temporally), stereo-photogrammetry applied to video imagery has grown as a viable solution over the last ten years. However, past deployments have essentially used costly cameras and optics, requiring fixed deployment platforms and hindering the applicability of the method in the field.Focusing on close-range measurements of nearshore waves at break point, this paper presents a detailed evaluation of a field-oriented and cost-effective stereo-video system composed of two GoProTM(Hero 7) cameras capable of collecting 12-megapixel imagery at 24 frames per second. The so-called ‘Stereo-GoPro’ system was deployed in the surf zone during energetic conditions at a macrotidal field site using a custom-assembled mobile tower. Deployed concurrently with stereo-video, a 16-beam LiDAR (Light Detection and Ranging) and two pressure sensors provided independent data to assess stereo-GoPro performance. All three methods were compared with respect to the evolution of the free-surface elevation over 25 min of recording at high tide and the wave parameters derived from spectral analysis. We show that stereo-GoPro allows producing digital elevation models (DEMs) of the water surface over large areas (250 m2) at high spatial resolution (0.2 m grid size), which was unsurpassed by the LiDAR. From instrument inter-comparisons at the location of the pressure transducers, free-surface elevation root-mean square errors of 0.11 m and 0.18 m were obtained respectively for LiDAR and stereo-GoPro. This translated into a maximum relative error of 3.9% and 12.5% on spectral wave parameters for LiDAR and stereo-GoPro, respectively. Optical distortion in imagery, which could not be completely corrected with calibration, was the main source of error. Whilst stereo-video processing workflow remains complex, cost-effective stereo-photogrammetry already opens new opportunities for deriving wave parameters in coastal regions, as well as for various other practical applications. Further tests should try to address specifically challenges associated to variable ambient conditions and acquisition configurations, affecting measurement performance, to guarantee a larger uptake of the technique.

Low-cost instrumentation for high frequency ultrasonic guided wave laboratory research in free rock bolts

Guided wave ultrasound offers the ability to inspect slender structures from a single transducer location. However, the propagation of guided waves is more complex than the propagation of bulk waves used in conventional ultrasonic testing, and the experimental equipment required is more sophisticated. Typical equipment is expensive and may limit research and industrial application. This paper investigates what can be achieved by using low-cost instrumentation for laboratory measurements. The application is the measurement of guided waves in rock bolts (cylindrical rods) at relatively high frequencies (5 MHz). The dispersive wave propagation requires the use of narrowband excitation signals. The use of a bench-top waveform generator and oscilloscope is compared to the use of a compact and low-cost USB oscilloscope, which includes an arbitrary waveform generator. The introduction of a pre-amplifier mitigated the poorer noise performance of the USB oscilloscope, and comparable results were obtained from the two setups. It is demonstrated that waves propagated 9 m in a free rock bolt, with 10 dB/m attenuation, could be detected and analyzed with a measurement setup costing approximately USD 1110.

Damage detection method for square steel tube based on CS-NME algorithm via ultrasonic guided waves

The utilization of ultrasonic guided wave (UGW) technology has garnered considerable attention in non-destructive testing field, particularly for steel components. However, for square steel tubes with noncircular cross sections, this method encounters severer frequency dispersion, which hampers the accuracy of damage identification. To address this issue, the approach utilizing the normal mode expansion (NME) method combined with cuckoo search (CS) algorithm to develop a layout strategy for ultrasonic transducer position and length is proposed, which enables single mode excitation of UGW while reducing the interference from redundant clutter signals, thereby enhancing the accuracy of damage detection. The efficacy of the proposed approach is evaluated via numerical simulations and laboratory experiments. The results show that this method can significantly reduce the interference of other modes by optimizing the location and length of ultrasonic transducers, and successfully detect the hole and crack damage on the square steel tube.

Reconstruction of missing wind data based on limited wind pressure measurements and machine learning

In structural health monitoring (SHM), wind field monitoring sometimes suffers from data loss owing to monitoring device failure, which inevitably creates barriers to subsequent data analysis and data mining. To this end, a novel strategy for reconstructing missing wind field data based on machine learning (ML) utilizing limited wind pressure measurements is proposed in this paper. Several ML algorithms, including decision tree, random forest, gradient boosting regression tree, support vector regression, Gaussian process regression, and backpropagation neural network, are employed to characterize potential relationships between wind pressure information (including time series and statistical parameters of wind pressures) and wind field information (e.g., wind direction and wind speed). Moreover, the effect of input information (including the type of input variables as well as the number and location of pressure transducers providing input data) on reconstruction performance and efficiency is investigated. Field measured records from an SHM system in a 600-m-high supertall building during typhoons are utilized to validate the feasibility and robustness of the proposed strategy. The results show that the presented strategy can effectively reconstruct missing wind field information in the SHM of the skyscraper during typhoons. Compared with the time series of wind pressures, selecting statistical parameters of wind pressures as input variables can effectively improve the performance and efficiency of reconstruction models. Choosing appropriate input information (e.g., using multiple input variables, adopting data from a larger number of pressure transducers, and utilizing data from pressure transducers closer to an anemometer) is beneficial for enhancing the performance of reconstruction models.

Model-based navigation of transcranial focused ultrasound neuromodulation in humans: Application to targeting the amygdala and thalamus

BackgroundTranscranial focused ultrasound (tFUS) neuromodulation has shown promise in animals but is challenging to translate to humans because of the thicker skull that heavily scatters ultrasound waves. ObjectiveWe develop and disseminate a model-based navigation (MBN) tool for acoustic dose delivery in the presence of skull aberrations that is easy to use by non-specialists. MethodsWe pre-compute acoustic beams for thousands of virtual transducer locations on the scalp of the subject under study. We use the hybrid angular spectrum solver mSOUND, which runs in ∼4 s per solve per CPU yielding pre-computation times under 1 h for scalp meshes with up to 4000 faces and a parallelization factor of 5. We combine this pre-computed set of beam solutions with optical tracking, thus allowing real-time display of the tFUS beam as the operator freely navigates the transducer around the subject’ scalp. We assess the impact of MBN versus line-of-sight targeting (LOST) positioning in simulations of 13 subjects. ResultsOur navigation tool has a display refresh rate of ∼10 Hz. In our simulations, MBN increased the acoustic dose in the thalamus and amygdala by 8–67 % compared to LOST and avoided complete target misses that affected 10–20 % of LOST cases. MBN also yielded a lower variability of the deposited dose across subjects than LOST. ConclusionsMBN may yield greater and more consistent (less variable) ultrasound dose deposition than transducer placement with line-of-sight targeting, and thus could become a helpful tool to improve the efficacy of tFUS neuromodulation.

Influence of reference transducer location on hearing protector attenuation metrics for impulse noise

The ANSI/ASA S12.42-2010 standard can be used to estimate the attenuation for impulsive noises between 130 and 170 decibels peak sound pressure level (dB pSPL). The ANSI/ASA S12.42 method uses a complex transfer function between the signal received in the ear of an acoustic test fixture (ATF) and a reference transducer. The reference transducer is at the same radial distance from the impulse source and at less than 30 degrees from the ATF angle. The reference transducer is specified as a pencil-type pressure (> 40.6 cm long). The maximum angle and the minimum pencil probe dimensions could be incompatible near the source, or may introduce artifacts or hazards. In this study, several hearing protectors were evaluated with two rifles (A-Bolt .300 Winchester Magnum and Colt AR-15 5.56 caliber), two ATFs (GRAS 45CB), and five transducers (four ¼” microphones and one surface mount microphone). The ATFs were on opposite sides of the gun at distances for field levels between 180- and 140-dB pSPL. For each location and rifle, S12.42 metrics were calculated for all 20 combinations of ATF ear and reference transducer. Results indicated that S12.42 metrics were minimally affected by the locations of the reference transducers.

The numerical analysis in heat transfer, fluid flow, and irreversibility of a pin-fin heatsink under the ultrasonic vibration with different transducer power assignment scenarios

The hydrothermal performance and entropy generation rate in a pin–fin heatsink were numerically investigated under different vibration transducer power distribution scenarios between 11 transducers located at 3 walls of the heatsink. Two cases were investigated; Case#A and Case#B which are different in 3 transducer locations on one wall of the heatsink. The highest convection coefficient (h) in Case#A was obtained for a variable power scenario, which escalated pressure drop (ΔP) by 91.94%. However, the highest h in Case#B was obtained for the constant power scenario. In addition, h, average temperature of CPU, and thermal resistance factor in Case#A are 5.84% higher than, 0.41% lower than, and 5.34% lower than those in Case#B. The PEC factor for Case#A is higher than unity (1.31) only under the constant power scenario, while the PEC of Case#B is higher than unity under different studied scenarios. Frictional irreversibility (Ṡfr) for Case#A was obtained as 1.45–74.56% higher than that for Case#B due to the swirl flow generated by the high-power transducers and creating the huge velocity gradients in Case#A. Nevertheless, the high flow mixing in Case#A leads to reducing the temperature gradients against Case#B, thereby thermal irreversibility (Ṡth) in Case#A is almost 7.05–19.69% lower than that of Case#B.

Model-based measurements in the monitoring tasks of high-power plants

The tasks of the measuring information obtaining about the state of the blading section and structural elements of gas turbine engines, as typical representatives of high-power plants, in the process of their experimental research and testing are considered. Such measurements are usually characterized by extreme environmental conditions, complex shapes and multidimensional movements of the monitored surfaces, strict constraints on the number and location of primary transducers, etc. As a result, the required measurement information is obtained under the influence of a large number of interfering factors, which are not always available for direct measurements and consideration in the experimental data processing. The approach based on the modeling the immeasurable components counting the current parameters of the power plant mode and environmental conditions is considered as an alternative to the direct measurements. The use of online models allows (in addition to increasing the reliability of measurements) to evaluate the unique characteristics of the monitored object (e.g., changes in shape) and, in some cases, to predict its critical state. The examples of the practical implementation of the approach in specific measurement systems designed for bench testing of gas turbine engines are also given in the article.

Scope of applicability of the technique for constructing magnetic induction lines for flaw defectometry of extended objects

A technique for approximate solution of the inverse geometric problem of magnetostatics for a plate made of a soft magnetic ferromagnet in a magnetic field is presented. The technique is presented both for the case of the location of magnetic transducers directly above the surface defect of loss of continuity of the metal, and for the case in which the magnetic transducers are located above the defect-free surface of the plate. It is assumed that the plate is accessible from one side only. The sizes of defects in which the proposed technique works reliably are determined. It is shown that the proposed technique can be used in mobile devices to carry out flaw detection of drill pipes using the MFL (Magnetic flux leakage) method directly at drilling sites.

Sleeved waveguide ultrasonic sensor for monitoring concrete health

This article reports the development of a novel embedded waveguide ultrasonic sensor for detecting the onset of damage in reinforced concrete structures. A sleeved waveguide is proposed to confine guided ultrasonic waves in one-dimension, with leakage to the surrounding media only through specially created openings, thus reducing attenuation losses and enhancing the capability to inspect large structures from a single transducer location. The test frequency and mode are identified through modelling, and the interaction of leaky guided ultrasonic waves with delamination within the concrete volume is studied. Numerical simulations validated by experiments are used to study the changes in wave features such as mode velocity, wavelength and wave reflection in the delamination region, helping to estimate its location. Further simulation studies are carried out to demonstrate the possibility of using multiple waveguide sensors and sleeve openings to provide a full view of the concrete volume. The results are encouraging for practical long-range and large-scale monitoring of concrete volumes using the proposed sleeved waveguide ultrasonic sensors.

Distant RF field sensing with a passive Rydberg-atomic transducer

We combine a rubidium vapor cell with a corner-cube prism reflector to form a passive RF transducer, allowing the detection of microwave signals at a location distant from the active components required for atomic sensing. This compact transducer has no electrical components and is optically linked to an active base station by a pair of free-space laser beams that establish an electromagnetically induced transparency scenario. Microwave signals at the transducer location are imprinted onto an optical signal which is detected at the base station. Our sensing architecture with a remote standalone transducer unit adds important flexibility to Rydberg-atom based sensing technologies, which are currently subject to significant attention. We demonstrate a ∼30 m link with no particular effort and foresee significant future prospects of achieving a much larger separation between the transducer and the base station.

Using genetic algorithms to optimize the location of transducers for an active noise barrier

The effectiveness of an active noise barrier is heavily dependent on the positioning of secondary sources and error sensors. Typically, these components are located at the edge of the barrier; however, research suggests that alternative distributions may improve the performance of the active barrier. This paper utilizes a genetic optimizer to determine optimal transducer locations based on specific criteria. Two approaches are employed: the Two-step approach which, first identifies optimal control source positions and then seeks the best error microphone locations, and the Multi-parameter approach, which optimizes all active noise control parameters simultaneously. The acoustic fields of primary and secondary sources are analyzed for various numbers of control sources progressively increasing from 2 to 10 units. Results indicate that the Multi-parameter approach achieves higher outcomes and requires less computational effort. This approach is more desirable than the Two-step approach. The best configuration for the active noise barrier is determined to be control sources and error microphones placed at a height below the barrier’s edge and are distributed with an interval between a half and a full wavelength. The number of error sensors should be close to the number of secondary sources and both transducers should be placed at the farthest distance from the barrier surface, but oppositely. Furthermore, the study shows that when the primary noise source is close to the barrier adjacent transducers should not be spaced uniformly.

The Effect of Piezoelectric Transducer Location on Heat Transfer Enhancement of an Ultrasonic-Assisted Liquid-Cooled CPU Radiator

The Effect of Piezoelectric Transducer Location on Heat Transfer Enhancement of an Ultrasonic-Assisted Liquid-Cooled CPU Radiator

Design and characterization of a multi-frequency semi-pilot ultrasonic reactor: Application to the extraction and oxidation of flaxseed-gum

The aim of this study was to design and study a new multi-frequency ultrasonic semi-pilot tank by evaluating the operational parameters with respect to calorimetric efficiency and sonochemical activity. The device was then applied to the extraction of flax-gum from the seeds and its oxidation by TEMPO method. The ultrasonic tank was used in single and multi-frequency modes (20 kHz, 40 kHz and 100 kHz). It has been shown that in single mode, the geometry and location of the ultrasonic transducers had a direct impact on the energy transfer efficiency and that the immersed radial probes gave transfer rates in the range of 66.9–82.8%. The production rate of molecular iodine was found to be better at a frequency of 100 kHz whatever the output powers used. The extraction of polysaccharides from flax seeds is proportional to the power density and can be done under mild conditions to preserve the integrity of macromolecules. Ultrasound assisted oxidation is efficient and we have highlighted that this could be done at low acoustic powers thank to the 100 kHz frequency. Thus, the results show that ultrasonic vessels are relevant for the scaling up of pretreatment of biomass and chemical processes.

Development of Single-Channel Dual-Element Custom-Made Ultrasound Scanner with Miniature Optical Position Tracker for Freehand Imaging.

Handheld ultrasound has great potential in resource-limited areas, and can improve healthcare for rural populations. Single-channel ultrasound has been widely used in many clinical ultrasound applications, and optical tracking is considered accurate and reliable. In this study, we developed a 10 MHz lead magnesium niobate-lead titanate (PMN-PT) dual-element ultrasound transducer combined with a miniature optical position tracker, and then measured the rectus femoris of the thigh, upper arm, and cheek muscles. Compared to single-element transducers, dual-element transducers improve the contrast of near-field signals, effectively reduce noise, and are suitable for measuring curved surfaces. The purpose of position tracking is to calculate the location of the ultrasound transducer during the measurement process. By utilizing positioning information, 2D ultrasound imaging can be achieved while maintaining structural integrity. The dual-element ultrasound scanner presented in this study can enable continuous scanning over a large area without a scanning width limitation. The custom-made dual-element ultrasound scanner has the advantage of being a portable, reliable, and low-cost ultrasound device, and is helpful in popularizing medical care for remote villages.

A Multidirectional Cyclic Direct Simple Shear Device for Characterizing Dynamic Soil Behavior

AbstractA newly constructed multidirectional cyclic direct simple shear (mcDSS) device with unique capabilities is introduced. This mcDSS apparatus, called the Illinois mcDSS (or I-mcDSS) device, for the first time brings together the following capabilities: (1) servo-hydraulic control that can apply stress- or strain-based monotonic, cyclic (e.g., sinusoidal, saw tooth, and square), and high-frequency broadband loads at realistic earthquake loading rates, improving over previous devices with pneumatic control; (2) unidirectional and bidirectional loading; (3) bender elements to measure (S-wave) velocity; (4) a cell for applying consolidation stresses different from at-rest values as well as back-pressure saturation; and (5) a multidirectional load cell on top of the specimen to minimize the effect of compliance and component friction on load measurements. The I-mcDSS device tests cylindrical specimens confined using either a wire-reinforced membrane or stacked rings. Experiments conducted on a uniformly graded Ottawa sand are presented to illustrate each key I-mcDSS feature. Test repeatability is demonstrated for monotonic and bidirectional cyclic tests. Drained or constant volume, K0-consolidated, strain-controlled monotonic, unidirectional cyclic, and bidirectional (circular, figure-8, and broadband) cyclic tests on dry specimens yielded shear stress–shear strain relations, peak effective-stress friction angles (ϕ′peak-DSS), and volumetric strains, or excess pore water pressures, consistent with the literature. However, depending on load cell and displacement transducer locations, device compliance was observed to affect shear stress–shear strain response at shear strains less than 1 %. When compared with triaxial compression (TC) peak effective-stress friction angles (ϕ′peak-TC), ϕ′peak-DSS was about 5° smaller than ϕ′peak-TC if the horizontal plane is considered the failure plane, whereas ϕ′peak-DSS ≈ ϕ′peak-TC if the horizontal plane is considered the plane of maximum shear stress. Lastly, measured S-wave velocities at varying confinements are consistent with published correlations.

Investigation of the Vibration Transmission Characteristics of the Aero-Engine Casing System by Rotating Force Exciter

This work aims to study the dynamic characteristics of an entire aero-engine casing by experiments using a new type of rotating exciter. New vibration sensor layout rules are proposed according to experimental results and vibration transmission characteristics. The vibration response of the aero-engine casing is carried out, and the vibration response of different casing measuring points is also studied. The finite element model of the engine casing’s structure is established to obtain the natural frequency of the whole aero-engine casing, which agrees well with the experimental measurement. We find that the vibration acceleration transmission value of the radial measuring point of bearing No. 1, but not the fan sensor, is more suitable for detecting the running state of the fan rotor. In addition, the sensor in the intermediate casing can detect the vibration of the high-pressure rotor. Bolt loosening of the flange has little effect on the vibration transmission characteristics of the casing. This work aims to provide experimental data of whole aero-engine vibration characteristics with a new rotating exciter for the vibration test, which can help optimize the location of the vibration transducer for the engine and the assembly technology design for the whole engine structure.

Dynamics of cavity structures and wall-pressure fluctuations associated with shedding mechanism in unsteady sheet/cloud cavitating flows

The physics and mechanism of sheet/cloud cavitation in a convergent–divergent channel are investigated using synchronized dynamic surface pressure measurement and high-speed imaging in a water tunnel to probe the cavity shedding mechanism. Experiments are conducted at a fixed Reynolds number ofRe = 7.8 × 105for different values of the cavitation numberσbetween 1.20 and 0.65, ranging from intermittent inception cavitation, sheet cavitation to quasi-periodic cloud cavitation. Two distinct cloud cavitation regimes, i.e. the re-entrant jet and shockwave shedding mechanism, are observed, accompanied by complex flow phenomenon and dynamics, and are examined in detail. An increase in pressure fluctuation intensity at the numbers 3 and 4 transducer locations are captured during the transition from re-entrant jet to shockwave shedding mechanism. The spectral content analysis shows that, in cloud cavitation, several frequency peaks are identified with the dominant frequency caused by the large-scale cavity shedding process and the secondary frequency related to re-entrant jet/shockwave dynamics. Statistical analysis based on defined grey level profiles reveals that, in cloud cavitation, the double-peak behaviours of the probability density functions with negative skewness values are found to be owing to the interactions of the re-entrant jet/shockwave with cavities in the region of 0.25 ~ 0.65 mean cavity length (Lc). In addition, multi-scale proper orthogonal decomposition analysis with an emphasis on the flow structures in the region of 0.25 ~ 0.65Lcreveals that, under the shockwave shedding mechanism, both the re-entrant jet and shockwave are captured and their interactions are responsible for the dynamics and statistics of cloud shedding process.

The use of circumferential guided waves to monitor axial cracks in pipes

Guided wave testing is in routine use to detect corrosion, particularly in the oil and gas sector, but the detection of axial cracking is difficult using the axially propagating waves commonly used for corrosion detection. This paper presents a novel guided wave monitoring technique for the detection of axial cracking in piping. Circumferential SH0 waves, travelling around the circumference were used in a monitoring configuration to detect axial defects in a 6 inch schedule 80 steel pipe. Finite Element (FE) analysis showed that both the defect reflection and the decline in the transmitted SH0 wave can be used for defect detection. Baseline subtraction was utilised to produce residual signals that can be better analysed for small defect reflections. The Root-Mean-Square (RMS) of the residual signal after baseline subtraction was found to be the most satisfactory means of monitoring defect progression. An amplification effect was identified where the residual signal is compounded by continued interaction with the defect on each revolution of the incident wave. The FE predictions were validated by an experiment in which an Electrical Discharge Machining (EDM) notch was grown in four stages. Temperature compensation using Location Specific Temperature Compensation (LSTC) was applied to the experimental data, allowing residuals to be compared for a ∼10 °C temperature swing over a monitoring period of over 2 months. It was determined that a 10 mm long (∼23% of wavelength), 5 mm deep (∼45% of the wall thickness) defect at an axial offset from the line of the transducers of 1.5 wavelengths (65 mm) would be readily detectable with a very high Probability of Detection (POD) and virtually no chance of a false call. Therefore, this novel guided wave monitoring system for axial crack detection is likely to be attractive for applications in a range of industries for its sensitivity to axial cracking combined with large coverage from a single transducer location.