Multi-element Transducer Array Research Articles

Magneto-thermal-acoustic imaging of magnetic nanoparticles with tissue structure imaging function

Magneto-thermal-acoustic imaging with magnetic nanoparticles (MNPs) is a novel medical imaging modality based on the thermoacoustic (TA) effect of MNPs. We proposed a new dual-modality imaging strategy that combines the TA and echo signals. Based on the synthetic aperture method, we used TA signals to image cancer tissues labeled with MNPs and applied echo signals to achieve tissue structure imaging. In the simulation, we constructed a breast cancer model and assumed that cancer tissue was labeled with MNPs. Under a limited field of view, the TA and echo signals were collected using a multi-element transducer array. By fusing the imaging results of the TA and echo signals, we obtained a boundary distribution map of the breast cancer model, and accurately located the tumor tissue. In this experiment, we built a multi-channel acquisition system. Pork tissue labeled with MNPs was used as the breast cancer phantom. We collected a total of 120 TA and echo signals at 1 mm intervals using a multi-element transducer array and faithfully imaged the boundary distribution map of the phantom. Compared with the traditional linear back projection method based on focused transducers, we demonstrated that the proposed method not only improves the lateral resolution of the image, but also makes accurate cancer identification easier. This provides a promising medical imaging technology for clinical applications.

Calibration of Multibeam Echo Sounder Transducer Array Based on Focused Beamforming

The detection accuracy of the multibeam echo sounder (MBES) can be damaged severely and inevitably due to the mismachining tolerance of the transducer array. Therefore, it is necessary to demonstrate the performance of the multi-element transducer array to guarantee the accuracy of the processing algorithms. In this paper, a kind of multi-element MBES receiving transducer array self-calibrating method is proposed to manage the serious defocusing problem of the conventional methods. We analyze the error source and their effect on the MBES detection. The near-field beamforming and the least residual error criterion methods are employed to calibrate the average element spacing. The integrated self-calibrating method is managed to calibrate the transducer array, considering the coupling between the circuits and the element with a channel uniformity problem. An experiment is carried in a small-size tank to evaluate the method proposed. The outfield experimental data are compensated by the average element spacing and the beam response error estimated in the tank experiment. The simulations and the field data processing results indicate that the novel method proposed can effectively demonstrate the performance of the receiving transducer array and guarantee the coverage of the MBES system.

Toward real-time assessment of material properties using elastic guided waves

Elastic guided waves are one of the most promising quantitative ultrasound techniques for the assessment of elastic properties in plate-like structures. Measurements of guided waves, associated with suitable waveguide modeling, can yield accurate estimates of waveguide properties like thickness and stiffnesses. Such a model-based approach requires solving a multi-parametric inverse problem to match experimental data with guided modes. Sensitivity studies suggest that isolated areas of the dispersion curves have predominant influence on specific model parameters. In particular, guided waves in a free plate exhibit a resonant behavior at frequencies where their group velocity vanishes while their phase velocity remains finite (so-called zero-group velocity Lamb modes). In this study, we investigate the feasibility of exploiting targeted data in the vicinity of these particular points, along with data associated with the cut-off frequencies. To this end, guided waves measurements are performed on a series of materials (anisotropic plates and tri-layer structures) using a linear multi-element transducer array and dedicated signal processing. A genetic algorithm-based inverse problem is then solved to recover the waveguide properties. Preliminary results indicate that, owing to the measurements versatility in terms of acquisition speed, this approach has the potential for inferring reliable structural and material properties in real-time.

Architecture of a real‐time delay calculator for digital beamforming in ultrasound system

In ultrasound systems synthetic transmit aperture and phased array imaging are widely used for obtaining the high quality images. These imaging systems require dynamic focusing of the multi-element transducer array at large number of scan points during transmission and reception. The array can be focused at any point by applying proper delay values to the signals, received or transmitted by each element of the array. Dynamic focusing requires on-line computation of the delay values, for large number of scan points, corresponding to all the elements of the array. This paper describes a delay calculation algorithm and corresponding hardware architecture for dynamically focusing the convex transducer array at large number of scan points. The hardware architecture for the 64-element convex transducer array, which scans 128 scan lines having 1024 scan points on each scan line, consumes 61k gates. It shows around 57–86% improvement in terms of hardware consumption with respect to those of other available architectures. To reduce the overall complexity and latency of the delay calculator, a 28- bit radicand square root calculator architecture which requires less initial memory than that of the linear approximation and less hardware resources than that of the quadratic approximation is also presented.

Simple Test Of Transducer Arrays By Imaging Of Ultrasound Emission Into Air

Abstract: A simple test method, feasible for remote or online testing of multi-element ultrasound transducer arrays, is presented. The test requires only a conventional ultrasonic B-mode image visualizing the transducer under investigation emitting into air. In preparation of the test a gray value profile is computed from the image data. Defective trans-ducer elements cause deviations in the profile, which are analyzed by means of a statistical procedure. The perform-ance of the test was investigated using an ultrasonic imaging system (SonixTOUCH, Ultrasonix Medical Corporation, Richmond, Canada) in research mode and masking single elements or element groups to simulate damaged piezoelec-tric elements. The test method allows to detect 2 adjacent defective elements out of a total of 128 transducer elements. Keywords: ultrasound diagnostic, multi-element trans-ducer arrays, quality assessment, statistic evaluation Introduction The quality and reliability of a diagnosis drawn on the basis of a ultrasonic investigation depends to a great ex-tend on the technical quality of the imaging system. Over the last years a number of test methods has been estab-lished which are able to detect different failure types at specific points in the signal chain and at different levels [1]. The ultrasound probe - a high sensitive, mechatronic device - is considered to be the most failure-prone part of the system [2]. Consequently a simple, user independent and reliable test of the transducer elements is a prerequi-site for a broader acceptance of technical quality assur-ance (TQA) in the user community. The analysis of B-mode images acquired when the ultrasound waves are emitted into air could provide such a test modality.

Wideband focused transducer array for optoacoustic tomography

The calculation procedure of the parameters of a multielement transducer array for the optoacoustic tomography of biological objects with high spatial resolution values is proposed. A multielement transducer with given spatial resolution values in three dimensions has been developed based on the proposed procedure for the early detection of breast cancer. The transducer array consists of a set of 8 linear PVDF piezoelectric films located on a plane and a focusing cylindrical acoustic lens. A map of the transducer’s focal area and point spread function have been measured using the constructed transducer array. Spatial resolutions of the transducer array obtained experimentally are in agreement with their calculated values.

Planar phased-array transducers associated with specific electronic command for acousto-optic deflectors

Diffraction efficiency with planar phased-array transducers for wide-band acousto-optic deflectors has been studied in theory and experiment. Multi-element transducer arrays provide beam steering of the acoustic wave. Improvements of performances obtained by the use of an appropriate RF command are evaluated. The reliability of the theoretical model based on phased-array antenna theory is shown at 1.55 µm wavelength through experimental results with a planar phased-array transducer tellurium dioxide (TeO2) light deflector.

Electro-dynamic phased array lens for controlling acoustic wave propagation

An electro-dynamic phased array acoustic lens having an array of cells, each of which may be separately controlled to alter characteristics of an incident acoustic wave. Because each cell of the acoustic lens controls the delay and amplitude of the acoustic wave passing through that cell, such an acoustic lens may be used in combination with a single-element transducer to control the characteristics of acoustic waves with a similar degree of control, or more, as that provided by a phased multi-element transducer array. The acoustic lens may also be used in combination with a multi-element transducer, such that all elements of the transducer may be fired at the same phase and amplitude. In other words, an ultrasonic wave that passes through a given cell of the acoustic lens is phase offset as determined by that cell. The acoustic lens may be used in an ultrasonic ablation system to control the ultrasonic waves used to ablate the tissue.

A new approach to calculate the field radiated from arbitrarily structured transducer arrays

A efficient time-domain algorithm, based on the spatial pulse response approach, is proposed for the determination of the acoustic fields radiated by means of acoustical sources. The computations are performed by the discrete representation array modelling (DREAM) procedure, specially adapted to study the planar and arbitrarily structured multielement transducer arrays. DREAM, based on the discrete representation computational concept, acts as the generator of the array velocity potential impulse response, and thus, does not require any analytical solutions prior to the computations. The computations are valid for all field regions and may be performed for any excitation form. Apart from the classic case of rigid baffle conditions, the free and soft planar baffle also can be considered. The use of the time-domain solution for causal Green's function for lossy media enables the wideband absorption effects to be modeled. The accuracy of computations depends on temporal and spatial discretization and can be obtained as required. The quantitative rules, which determine the required discretizations to be predicted, are proposed. The computational examples show that DREAM allows the different and various transducers to be modeled. Its possibilities are illustrated by computations for the multielement transducers, including the beam-steered, amplitude-weighted sonar array, the focusing annular transducer, and the diverging and converging cylindrical array.

Sonar beamforming based upon monaural localization techniques

Sonar beamforming is usually accomplished using multielement transducer arrays. A novel alternative beamforming system is proposed, which uses a single fixed active element placed within an irregular reflecting surface. The proposed system is based upon one suggested mechanism of monaural localization. Interference resulting from reflections off the surface modifies the spectra of incoming acoustic signals. The signal source is located by correlating the output signal spectrum with the known spectral responses of the receiving system for all angles. Computer simulations and tests using an experimental active system indicate that the proposed technique could be a useful alternative in certain sonar applications.

Medical ultrasonic imaging—Principles and instrumentation

Ultrasonic B‐scan instruments are used extensively for imaging the internal structures of the abdomen, the fetus, the heart, and the peripheral vascular system. Such diverse anatomical applications have resulted in a diverse set of specialty instruments. These instruments may be divided into two general categories: (a) those based on mechanical motion of the transducer and (b) those based on linear array technology. In the former, one dimension of the two‐dimensional image is obtained by moving (usually rotating) a circularly symmetric acoustic beam. In the latter, a nonsymmetric beam is moved not by physical motion of the transducer, but by appropriate phasing of a multielement transducer array. Each technique has its own set of advantages and disadvantages. This paper presents some of the basic physical principles of ultrasonic propagation and how they impact the design of these imaging devices. Particular attention will be given to contrasting the physical principles of the two categories and the limitations imposed. Representative images illustrating the important imaging characteristic will be presented.

A hand-held electronically switched array for rapid ultrasonic scanning

This paper describes the design and construction of a simple multi-element transducer array capable of converting an A-scan unit to a real-time, hand-held section scanner. Elements are connected in groups of four to give a finer stepping interval than is possible with discrete transducers. Application of the array as an inexpensive alternative to conventional B-scanners is discussed, in addition to its more obvious application as a non-invasive method of imaging the moving heart.

Coupled-wave analysis of light diffraction by a multi-element acoustic transducer array

The diffraction efficiency of Bragg devices consisting of multi-element transducer arrays has been analyzed using the coupled-wave theory. An analytical solution of the diffraction efficiency has been obtained for the case where all transducer elements have equal length and center-to-center spacing and each element is driven with equal amplitude and constant phase difference from one element to the next. Numerical calculations have been made for planar-type and staircase-type arrays for the purpose of achieving a practical deflector design. The present calculations yield absolute values of the diffraction efficiency and are more accurate in the high-efficiency region than Gordon’s formula, which was derived from small-signal analysis.

An Experimental Study of Acoustic Interactions between Transducer Elements in a Model Array

A model array of 100 ADP crystal transducers designed to vibrate in a fundamental longitudinal mode was fabricated for the purpose of studying acoustic interactions in the NRL Acoustic Research Tank. To promote these interactions, the transducers were designed to have radiating faces of fractional wavelength size. Measurements were made on the full array as well as on smaller arrays. The objective of the study was to learn more about the parameters that affect the velocities or displacements of individual elements and thus the nearfield pressure patterns of multielement transducer arrays. Data obtained and presented in the form of curves, charts, and patterns indicate how the phase and amplitude of the displacements of transducer radiating faces is affected by parameters such as negative admittances, electrical drive conditions, and transducer element variations, location, and separation.