Transducer Arrangement Research Articles

Transducer-matched multipulse excitation for signal-to-noise ratio improvement in diode laser-based photoacoustic systems.

.We analyze transducer-matched multipulse excitation as a method for improving of the signal-to-noise ratio (SNR) for diode laser-based photoacoustic systems. We discuss the principle of the technique, its advantages, and potential drawbacks and perform measurements to analyze the obtainable SNR increase. We show in experiment and computationally that a lower boundary estimate of 1.2 to 1.8 fold SNR improvement can be provided using transducer-matched pulse bursts, depending on the transducer and particular arrangement. Finally, we analyze implications that the transducer resonance effects may have on the recently introduced advanced photoacoustic techniques. The findings are of immediate interest to modalities utilizing dense pulse sequences and systems possessing limited pulse energy. In particular, transducer-matched multipulse excitation may be beneficial for diode-based photoacoustic systems operated with transducers in the range of 1 to 5 MHz since the required hardware is readily available.

Transverse Damage Localization and Quantitative Size Estimation for Composite Laminates Based on Lamb Waves

The damage detection method for composite laminates introduced in this research uses piezoelectric (lead zirconate titanate, PZT) transducers to excite/sense the Lamb wave signals. The complicated wave signals scattered by damage are accurately processed using a continuous wavelet transformation (CWT) based on the Gabor wavelet. The transducers are arranged on a composite laminate in the form of a network of square detection cells and triangular subcells. The damage location is estimated using the concept of centroid in two-stage detection method. The first stage detection is carried out by exciting a transducer at the center of each detection cell to locate the damaged cell and subcell. The damage localization is improved by exciting an additional transducer at the corner of the damaged subcell during the second stage detection. The damage size is then quantitatively estimated using cubic spline curve (CSC) and elliptical parametric (EP) methods based on the damage edge points. The damage location is estimated in two detection stages for high-accuracy because the damage edge points are calculated with reference to the estimated location of the damage. The arrangement of transducers and signal processing technique remain the same at all the stages of damage detection. Results from previous detection stages contribute to the improvement of damage detection in the subsequent stages. The size of detection cell plays a crucial role in designing the detection stages, and the proposed method can accurately quantify both location and size of the damage in composite laminate.

Increased Excitability Induced in the Primary Motor Cortex by Transcranial Ultrasound Stimulation.

Background: Transcranial Ultrasound Stimulation (tUS) is an emerging technique that uses ultrasonic waves to noninvasively modulate brain activity. As with other forms of non-invasive brain stimulation (NIBS), tUS may be useful for altering cortical excitability and neuroplasticity for a variety of research and clinical applications. The effects of tUS on cortical excitability are still unclear, and further complications arise from the wide parameter space offered by various types of devices, transducer arrangements, and stimulation protocols. Diagnostic ultrasound imaging devices are safe, commonly available systems that may be useful for tUS. However, the feasibility of modifying brain activity with diagnostic tUS is currently unknown.Objective: We aimed to examine the effects of a commercial diagnostic tUS device using an imaging protocol on cortical excitability. We hypothesized that imaging tUS applied to motor cortex could induce changes in cortical excitability as measured using a transcranial magnetic stimulation (TMS) motor evoked potential (MEP) paradigm.Methods: Forty-three subjects were assigned to receive either verum (n = 21) or sham (n = 22) diagnostic tUS in a single-blind design. Baseline motor cortex excitability was measured using MEPs elicited by TMS. Diagnostic tUS was subsequently administered to the same cortical area for 2 min, immediately followed by repeated post-stimulation MEPs recorded up to 16 min post-stimulation.Results: Verum tUS increased excitability in the motor cortex (from baseline) by 33.7% immediately following tUS (p = 0.009), and 32.4% (p = 0.047) 6 min later, with excitability no longer significantly different from baseline by 11 min post-stimulation. By contrast, subjects receiving sham tUS showed no significant changes in MEP amplitude.Conclusion: These findings demonstrate that tUS delivered via a commercially available diagnostic imaging ultrasound system transiently increases excitability in the motor cortex as measured by MEPs. Diagnostic tUS devices are currently used for internal imaging in many health care settings, and the present results suggest that these same devices may also offer a promising tool for noninvasively modulating activity in the central nervous system. Further studies exploring the use of diagnostic imaging devices for neuromodulation are warranted.

Development of Single‐Fiber Piezocomposite Transducers for 3‐D Ultrasound Computer Tomography

Ultrasound Computer Tomography (USCT) medical imaging is a promising approach for early detection of breast cancer. At Karlsruhe Institute of Technology (KIT) a 3‐D USCT system is developed. The region‐of‐interest (ROI) of 10 × 10 × 10 cm3 volume is surrounded by a aperture of 2014 semi‐spherical positioned ultrasound transducers. Results from a first patient study reveals the requirement of a significantly increased ROI to cover bodily variations. Design considerations and simulations show a demand for circular transducers with a diameter of ca. 500 µm, increasing the opening angle of the transducers to ca. 60°. Piezofiber composite technology is predestinated to simply provide circular transducers of the required dimensions. Moreover, piezocomposites based on single PZT (lead zirconate titanate Pb[ZrxTi1‐x]O3) fibers enable a cost‐effective and series‐production alternative to currently used dice‐and‐fill composites. A transducer design is presented which utilizes individually arranged single piezoceramic fibers with 460 μm in diameter within piezocomposite discs. As a result, fibers are independently addressable as single transducer elements allowing for the desired transducer arrangement. The electrical performance of each piezoceramic fiber is determined proofing a strong dependence both of the coupling coefficient and the resonance frequency from the transducer thickness. In further processing, the piezocomposite discs are connected to printed circuits, integrated into a cylindrical housing, and backfilled with polyurethane. Ultrasound characteristics such as sound pressure and opening angle are evaluated quantitatively. The results show that the transducer opening angles lie in the expected range, that the desired center frequency is achieved and that the bandwidth could be preserved compared to former dice‐and‐fill transducers.

Excitation and propagation of torsional T(0,1) mode for guided wave testing of pipeline integrity

Guided wave testing is one of non-destructive testing techniques for pipeline inspection using low-frequency ultrasonic waves. Guided wave testing uses a set of equally placed piezoelectric transducers around a pipe, and the number of transducers in the array is a key factor for suppressing higher order flexural modes. This paper presents an effective approach for the excitation and propagation of torsional T(0,1) wave mode for detecting defects in a steel pipe by using finite element numerical simulations and experimental studies. From the numerical and experimental results, the optimised design for transducer arrangement is investigated. The relationship between defect type, dimension and transducer arrangement is also investigated. To validate the finite element modelling, the numerical results are then compared to the experimental data. Finally, the sensitivity of reflected signal from defects to two types of transducer array design is evaluated, and circumferential displacement along the pipe is investigated by using polar plots at different axial positions.

Active control of sound through full-sized open windows

There is a pressing need to address urban sustainability challenges of increasing ambient temperatures and noise levels in densely-populated, high-rise cities. Solutions that utilise active noise control on open windows to reduce indoor noise levels seem promising, as natural ventilation is still maintained. Active noise control utilizes acoustic transducers arranged around the open window to generate a secondary incidence noise that destructively interferes with the real noise. The two most common techniques of transducer arrangement, distributed and boundary layouts, are investigated for the typical single-glazed sliding window. Finite element method is used to establish the control performance of the active noise control system and the passive attenuation provided by the sliding window. Based on the investigated fundamental limits of active control, the distributed layout has consistently yielded better performance than the boundary layout. The distributed-layout method can also reduce noise more effectively than a fully-glazed window. Moreover, sources distributed only in the partial opening of a simulated sliding window can attenuate noise as effectively as the fully-glazed window. The distributed-layout method is tested on a full-sized window, where the active control system has up to 16 channels and evenly distributed across the window opening. In the test with tonal sounds, the feasibility of the active control system is demonstrated. The experimental results have validated the simulation findings for normal incidence plane waves.

Far-field directivity of parametric loudspeaker arrays set on curved surfaces

• Parametric loudspeaker arrays exploit nonlinear wave propagation to generate focused sound. • The convolution model predicts the far-field directivity of planar parametric loudspeaker arrays. • The convolution model is extended to parametric loudspeaker arrays set on curved surfaces. • The extended model is applied to spherical omnidirectional parametric loudspeakers. • The performance of different distributions of transducers for omnidirectional loudspeakers is analyzed. Parametric loudspeaker arrays comprise arrangements of piezoelectric ultrasonic transducers that emit highly directive audible sound, thanks to the nonlinear parametric array phenomenon. Most parametric loudspeakers consist of planar arrays of transducers though, lately, devices have been developed which involve their distribution on curved surfaces. In this work, we present an extension of the recently proposed convolution model for planar arrays to predict the far field directivity of curved parametric loudspeakers. An expression is first given to compute the audible secondary pressure field generated by a single ultrasonic transducer placed at any point on a general curved surface, and pointing in its normal direction. Assuming weak non-linearity, the total audible pressure produced by all transducers on the surface is then recovered from the superposition principle. As an application, we predict the far-field pressure generated by an omnidirectional parametric loudspeaker consisting of hundreds of ultrasonic transducers set on a sphere. A critical aspect for the performance of the omnidirectional source is that of finding a proper distribution for them on the spherical surface. Two options are analyzed: getting an optimal solution for a Fekete-like problem, and resorting to an equal-area partitioning scheme, which is more feasible for a practical construction of the source. Numerical simulations are carried out for both alternatives.

Three Dimensional Characterization of Defects by Ultrasonic Time-of-Flight Diffraction (ToFD) Technique

Ultrasonic time-of-flight diffraction (ToFD) technique has high accuracy in locating and sizing discontinuities. The primary reason for this accuracy is the use of time instead of amplitude for measurement of the depth and size of discontinuities. Despite the many advantages of ToFD, it suffers from a number of shortcomings, the most notable one being its two-dimensional character. The goal of this paper is to develop an algorithm, as a prerequisite, to extend ToFD measurements to a three-dimensional space. For this purpose, a combination of multiple transmitting and receiving probes is proposed instead of just one pair commonly used in ToFD measurements. The approach for locating and sizing defects in a 3D space follows the methods used in radar and acoustic positioning systems. Non-iterative techniques are used for positioning a single source (defect) based on signals collected by several transducers. The estimation formula, in the form of a closed-form solution, is derived by linear least-squares minimization. In addition to existing conventional passive algorithms, a new active algorithm is also proposed for the general arrangement of transducers. This algorithm is tested on a steel specimen having an artificially implanted discontinuity and the three-dimensional location of the defect is estimated.

A Review on Nondestructive Techniques and Characteristics of Composite Materials for the Aerospace System

In the aerospace industry contactless measurement has been a very versatile and adaptable in recent years, mainly because of its diverse applications. Usually ultrasonic measurement requires acoustic contact media which may disserve the sample and varies for different materials. In the operational hand, acoustic contact media like water is also not preferred for on-aircraft inspection. The air coupled inspection technique among other nondestructive testing techniques is often not enticing due to acoustic mismatch and wave propagation. Though, acoustical mismatch of the transducers can be reduced by application of a matching layer and also by using different corresponding transducers. Air-coupled transducers are the captivating alternatives for the inspection. This paper comprises different air coupled inspection techniques i.e. through transmission and guided wave generation as well as its working modes. Various transducer arrangements, the advantages of air-coupled ultrasonic guided wave inspection over other NDT techniques and their specifications are discussed revolving around the materials. Composite materials have superior properties like tensile strength, better heat resistance which cannot be materialized in single. The utilization of composite materials like CFRP, GFRP, other polymers and ceramic composites seeks the improvement in lift to weight ratio. An overall review deals with air coupled techniques and scrutiny of different materials concerning this technique, which includes characteristics of various composite materials used in aerospace industry.

In vivo fascicle length measurements via B-mode ultrasound imaging with single vs dual transducer arrangements

Ultrasonography is a useful technique to study muscle contractions in vivo, however larger muscles like vastus lateralis may be difficult to visualise with smaller, commonly used transducers. Fascicle length is often estimated using linear trigonometry to extrapolate fascicle length to regions where the fascicle is not visible. However, this approach has not been compared to measurements made with a larger field of view for dynamic muscle contractions. Here we compared two different single-transducer extrapolation methods to measure VL muscle fascicle length to a direct measurement made using two synchronised, in-series transducers. The first method used pennation angle and muscle thickness to extrapolate fascicle length outside the image (extrapolate method). The second method determined fascicle length based on the extrapolated intercept between a fascicle and the aponeurosis (intercept method). Nine participants performed maximal effort, isometric, knee extension contractions on a dynamometer at 10° increments from 50 to 100° of knee flexion. Fascicle length and torque were simultaneously recorded for offline analysis. The dual transducer method showed similar patterns of fascicle length change (overall mean coefficient of multiple correlation was 0.76 and 0.71 compared to extrapolate and intercept methods respectively), but reached different absolute lengths during the contractions. This had the effect of producing force–length curves of the same shape, but each curve was shifted in terms of absolute length. We concluded that dual transducers are beneficial for studies that examine absolute fascicle lengths, whereas either of the single transducer methods may produce similar results for normalised length changes, and repeated measures experimental designs.

Directed self-assembly of three-dimensional user-specified patterns of particles using ultrasound

Particles dispersed in a fluid medium are organized into three-dimensional (3D) user-specified patterns using ultrasound directed self-assembly. The technique employs standing ultrasound wave fields created by ultrasound transducers that line the boundary of a fluid reservoir. The acoustic radiation force associated with the standing ultrasound wave field drives the particles into organized patterns, assuming that the particles are much smaller than the wavelength, and do not interact with each other. A direct solution method is theoretically derived to compute the ultrasound transducer operating parameters required to assemble a user-specified pattern of particles in any 3D simple, closed reservoir geometry with any arrangement of ultrasound transducers. This method relates the ultrasound wave field and its associated radiation force to the ultrasound transducer operating parameters by solving a constrained optimization problem that reduces to eigendecomposition. Experimental validation of the method is accomplished by assembling 3D patterns of carbon nanoparticles in a cubic water reservoir lined with four ultrasound transducers. Additionally, the versatility of the method is demonstrated by simulating ultrasound directed self-assembly of complex 3D patterns of particles in cubic and noncubic reservoir geometries lined with many ultrasound transducers. This method enables employing ultrasound directed self-assembly in a variety of engineering applications, including biomedical and materials fabrication processes.

Ultrasound directed self-assembly of three-dimensional user-specified patterns of particles in a fluid medium

We use ultrasound directed self-assembly to organize particles dispersed in a fluid medium into a three-dimensional (3D) user-specified pattern. The technique employs ultrasound transducers that line the boundary of a fluid reservoir to create a standing ultrasound wave field. The acoustic radiation force associated with the wave field drives particles dispersed in the fluid medium into organized patterns, assuming that the particles are much smaller than the wavelength and do not interact with each other. We have theoretically derived a direct solution method to calculate the ultrasound transducer operating parameters that are required to assemble a user-specified 3D pattern of particles in a fluid reservoir of arbitrary geometry. We formulate the direct solution method as a constrained optimization problem that reduces to eigendecomposition. We experimentally validate the solution method by assembling 3D patterns of carbon nanoparticles in a water reservoir and observe good quantitative agreement between theory and experiment. Additionally, we demonstrate the versatility of the solution method by simulating ultrasound directed self-assembly of complex 3D patterns of particles. The method works for any 3D simple, closed fluid reservoir geometry in combination with any arrangement of ultrasound transducers and enables employing ultrasound directed self-assembly in a myriad of engineering applications, including biomedical and materials fabrication processes.

Stereophonic reproduction based on multi-beam-forming with curved-type parametric array loudspeaker

A parametric array loudspeaker (PAL) has a flat surface arrangement of ultrasonic transducers and achieves a sharper directivity by utilizing an ultrasound wave. It can form a narrow audible space called an “audio spot” that can provide a target sound to a particular listener. In addition, the PAL can achieve a stereophonic reproduction by designing the audio spots for the positions of ears on the basis of delay-and-sum beamforming. However, designing wider audio spots for several listeners is difficult for the conventional PAL because it has overly sharp directivity. To solve this problem, we propose a new stereophonic reproduction with a curved-type PAL that can expand the audio spots. The curved-type PAL consists of ultrasonic transducers arranged on a concave surface. It can form a wider directivity compared with the conventional flat-type PAL. The proposed method steers the acoustic beam by designing the focal point to the positions of ears, and the radius of the curved-type PAL varies the width of the acoustic-beams. In this study, we carried out an objective evaluation experiment to confirm the effectiveness of the proposed method. As a result, we confirmed that the proposed method can design two wider acoustic beams for the stereophonic reproduction.

Implementation of a MIMO system for Wireless Power Transfer Using Acoustic Approach

<span>This paper presents a development of Acoustic energy transfer (AET) system through the air medium by implementing a Multiple Input-Multiple Output (MIMO) arrangement of transducers to transmit energy. AET system allows power to be transmitted without wire connection. The MIMO system is proposed in this paper to increase the efficiency of the transmitting power by multiplying the received power. The simulation and experimental works are carried out using a Class E power converter and the obtained results are analyzed accordingly. Based on the experimental results, the 18.57mW output power is obtained at 40kHz operating frequency when triple transducer is used. It contributes to 30.96% efficiency to the power transfer system.</span>

Qualitative assessment of concrete by ultrasound tomography

Ultrasonic tomography is a non-destructive method that enables the mapping of an internal section of a structure from multiple projections for the identification of discontinuities and/or damages. This study addresses the application of the ultrasonic tomography method for the qualitative assessment of concrete. Several experimental tests with variations in concrete composition, presence of voids, arrangement and frequency of transducers were conducted on concrete prisms. The results show the ultrasonic tomography was more efficient than conventional ultrasonic tests. Analyses of several transducers arrangements revealed a large number of measurements not necessarily returns better images. The great potential of the ultrasonic tomography technique for the evaluation of homogeneity and detection of discontinuities and damages of concrete structures has been confirmed.

Ultrasound directed self-assembly of user-specified patterns of nanoparticles dispersed in a fluid medium

We employ an ultrasound wave field generated by one or more ultrasound transducers to organize large quantities of nanoparticles dispersed in a fluid medium into two-dimensional user-specified patterns. To accomplish this, we theoretically derive a direct method of calculating the ultrasound transducer parameters required to assemble a user-specified pattern of nanoparticles. The computation relates the ultrasound wave field and the force acting on the nanoparticles to the ultrasound transducer parameters by solving a constrained optimization problem. We experimentally demonstrate this method for carbon nanoparticles in a water reservoir and observe good agreement between experiment and theory. This method works for any simply-closed fluid reservoir geometry and any arrangement of ultrasound transducers, and it enables using ultrasound directed self-assembly as a scalable fabrication technique that may enable a myriad of engineering applications, including fabricating engineered materials with patterns of nanoscale inclusions.

Ultrasound directed self-assembly of user-specified patterns of nanoparticles dispersed in a fluid medium

We employ an ultrasound wave field generated by one or more ultrasound transducers to organize large quantities of nanoparticles dispersed in a fluid medium into two-dimensional user-specified patterns. To accomplish this, we theoretically derive a direct method of calculating the ultrasound transducer parameters required to assemble a user-specified pattern of nanoparticles. The computation relates the ultrasound wave field and the force acting on the nanoparticles to the ultrasound transducer parameters by solving a constrained optimization problem. We experimentally demonstrate this method for carbon nanoparticles in a water reservoir and observe good agreement between experiment and theory. This method works for any simply closed fluid reservoir geometry and any arrangement of ultrasound transducers, and it enables using ultrasound directed self-assembly as a scalable fabrication technique that may facilitate a myriad of engineering applications, including fabricating engineered materials with patterns of nanoscale inclusions.

Development of an ultrasonic airflow measurement device for ducted air.

In this study, an in-duct ultrasonic airflow measurement device has been designed, developed and tested. The airflow measurement results for a small range of airflow velocities and temperatures show that the accuracy was better than 3.5% root mean square (RMS) when it was tested within a round or square duct compared to the in-line Venturi tube airflow meter used for reference. This proof of concept device has provided evidence that with further development it could be a low-cost alternative to pressure differential devices such as the orifice plate airflow meter for monitoring energy efficiency performance and reliability of ventilation systems. The design uses a number of techniques and design choices to provide solutions to lower the implementation cost of the device compared to traditional airflow meters. The design choices that were found to work well are the single sided transducer arrangement for a “V” shaped reflective path and the use of square wave transmitter pulses ending with the necessary 180° phase changed pulse train to suppress transducer ringing. The device is also designed so that it does not have to rely on high-speed analogue to digital converters (ADC) and intensive digital signal processing, so could be implemented using voltage comparators and low-cost microcontrollers.

Objective assessment and design improvement of a staring, sparse transducer array by the spatial crosstalk matrix for 3D photoacoustic tomography.

Accurate reconstruction of 3D photoacoustic (PA) images requires detection of photoacoustic signals from many angles. Several groups have adopted staring ultrasound arrays, but assessment of array performance has been limited. We previously reported on a method to calibrate a 3D PA tomography (PAT) staring array system and analyze system performance using singular value decomposition (SVD). The developed SVD metric, however, was impractical for large system matrices, which are typical of 3D PAT problems. The present study consisted of two main objectives. The first objective aimed to introduce the crosstalk matrix concept to the field of PAT for system design. Figures-of-merit utilized in this study were root mean square error, peak signal-to-noise ratio, mean absolute error, and a three dimensional structural similarity index, which were derived between the normalized spatial crosstalk matrix and the identity matrix. The applicability of this approach for 3D PAT was validated by observing the response of the figures-of-merit in relation to well-understood PAT sampling characteristics (i.e. spatial and temporal sampling rate). The second objective aimed to utilize the figures-of-merit to characterize and improve the performance of a near-spherical staring array design. Transducer arrangement, array radius, and array angular coverage were the design parameters examined. We observed that the performance of a 129-element staring transducer array for 3D PAT could be improved by selection of optimal values of the design parameters. The results suggested that this formulation could be used to objectively characterize 3D PAT system performance and would enable the development of efficient strategies for system design optimization.

Analysis and Validation of a Planar High-Frequency Contactless Absolute Inductive Position Sensor

This paper presents a low cost precise and reliable inductive absolute position measurement system. It is suitable for rough industrial environments, offers a high inherent resolution (0.1%-0.01% of measurement range), can measure target position over a wide measurement range, and can potentially measure multiple target locations simultaneously. The basic position resolution is improved by adding two additional finer pitched receive channels. The sensor works on principles similar to contactless resolvers. It consists of a rectangular antenna printed circuit board and a passive LC resonant circuit. A mathematical model and the equivalent circuit of this kind of sensor are explained in detail. Such sensors suffer from transmitter to receiver coil capacitive crosstalk, which results in a phase sensitive offset. This crosstalk will be analyzed by measurements. Moreover, the mechanical transducer arrangement, the measurement setup, and the measured results will be presented.