Cylindrical Transducer Array Research Articles

Cylindrical Transducer Array for Intravascular Shear Wave Elasticity Imaging: Preliminary Development.

We present an intravascular ultrasound (IVUS) transducer array designed to enable shear wave elasticity imaging (SWEI) of arteries for the detection and characterization of atherosclerotic soft plaques. Using a custom dicing fixture, we have fabricated single-element and axially-segmented array transducer prototypes from 4.6-Fr to 7.6-Fr piezoceramic tubes, respectively. Focused excitation of the array prototype at 4 MHz yielded a focal gain of 5× in intensity, for an estimated 60 mW/cm2 [Formula: see text] and 1.6-MPa negative peak pressure at 4.5-mm range in water. The single-element transducer generated a peak radial displacement of [Formula: see text] in a uniform elasticity phantom, with axial shear waves detectable by an external linear array probe up to 5 mm away from the excitation plane. In a vessel phantom with a soft inclusion, the array prototype generated peak displacements of 2.2 and [Formula: see text] in the soft inclusion and vessel wall regions, respectively. A SWEI image of the vessel phantom was reconstructed, with measured shear wave speed (SWS) of 1.66 ± 0.91 m/s and 0.97 ± 0.59 m/s for the soft inclusion and vessel wall regions, respectively. The array prototype was also used to obtain a SWEI image of an ex vivo porcine artery, with a mean SWS of 3.97 ± 1.12 m/s. These results suggest that a cylindrical intravascular ultrasound (IVUS) transducer array could be made capable of SWEI for atherosclerotic plaque detection in coronary arteries.

An equivalent circuit based electro-vibro-acoustic model of a cylindrical transducer array.

Cylindrical transducer arrays are used in many applications such as SONAR, depth sounding, ultrasound imaging, etc. This study developed the equivalent circuit (EC)-based-model of a cylindrical array with theoretical acoustic coupling. The electro-mechanical-acoustic coupling impedance matrix was first constructed to determine the response of the array. The electrical and mechanical impedances of the individual transducers were obtained by the EC model. The acoustic radiation impedances were obtained by the theoretical model. The cylindrical array is modeled by coupling the EC model and acoustic radiation impedances. The acoustic transfer matrix was then constructed using the theoretical method to determine both the far-field and near-field acoustic responses. The characteristics of the transducer array were represented with the electrical admittance, velocity response as a function of the voltage, transmit voltage response, beam pattern, and normalized pressure curve. To verify the proposed model, the analysis results were successfully compared to those of the fully coupled finite element model. Due to its high accuracy and computational efficiency, the proposed EC-based-model is expected to be useful for the conceptual design stage, which requires frequent design changes.

Cylindrical Transducer for Intravascular ARFI Imaging: Design and Feasibility

Intravascular acoustic radiation force impulse (IV-ARFI) imaging has the potential to identify vulnerable atherosclerotic plaques and improve clinical treatment decisions and outcomes for patients with coronary heart disease. Our long-term goal is to develop a thin, flexible catheter probe that does not require mechanical rotation to achieve high-resolution IV-ARFI imaging. In this work, we propose a novel cylindrical transducer array design for IV-ARFI imaging and investigate the feasibility of this approach. We present the construction of a 2.2-mm-long, 4.6-Fr cylindrical prototype transducer to demonstrate generating large ARFI displacements from a small toroidal beam, and we also present simulations of the proposed IV-ARFI cylindrical array design using Field II and a cylindrical finite-element model of vascular tissues and soft plaques. The prototype transducer was found to generate peak radial displacements of over [Formula: see text] in soft gelatin phantoms, and simulations demonstrate the ability of the array design to obtain ARFI images and distinguish soft plaque targets from surrounding, stiffer vessel wall tissue. These results suggest that high-resolution IV-ARFI imaging is possible using a cylindrical transducer array.

Evaluation of target angular position algorithms for multi-beam fishery sonars.

Two methods for measuring the angular position of a reference target when observed with a horizontally transmitting, multi-beam fishery sonar are described. The theory behind realizations of both a Split-Beam (SB) algorithm and an Interpolated Neighbouring Beam (INB) algorithm is described for a cylindrical transducer array. The algorithms were implemented on both simulated and real data collected during field calibrations. The estimated precision was ±0.2 to ±0.25°, for both algorithms when the target was within the central part of the beam. The precision was reduced for targets with large inclination angles, or in the beam-overlap region of the SB's two half-transducer arrays. The SB algorithm provides an accurate target location within the entire main lobe of the acoustic beam. For the INB method, the accuracy is only good within a small sector close to the acoustic axis, or within ±1.5°-±2.5° depending on the sonar operating frequency. Repeated calibration trials have shown that the SB algorithm can be used to track the reference-target position in real-time with adequate accuracy for use on fishery acoustic surveys.

Variation of Mutual Radiation Impedance with Calculation Area in a Cylindrical Array

Variation of Mutual Radiation Impedance with Calculation Area in a Cylindrical Array J. S. Kim Multimedia Engineering, Tongmyong University, Busan 608-711 M. J. Kim and K. L. Ha Department of Physics, Pukyong National University, Busan 608-737 Heeseon Seo and Cheeyoung Joh 6th R&D Institute, Agency for Defense Development, Jinhae 645-600 (Received 23 April 2008) For e ciency in the analysis of the acoustic elements arrayed on a cylindrical ba e, the total mutual radiation impedance variation with the calculation range and ka was investigated. The total mutual radiation resistance and reactance were calculated for the range of ka from 8 to 50 and for the range of area ratios from 2 % to 100 %. Using this result, we will determine an appropriate calculation range for the required accuracy. This study will provide essential data for the design of a cylindrical transducer array. PACS numbers: 43.58.Bh, 43.30.Jx, 43.30.Yj

Single-crystal lead magnesium niobate-lead titanate (PMN/PT) as a broadband high power transduction material

Two experimental underwater acoustic projectors, a tonpilz array, and a cylindrical line array, were built with single crystal, lead magnesium niobate/lead titanate, a piezoelectric transduction material possessing a large electromechanical coupling factor (k33 = 0.9). The mechanical quality factor, Q(m), and the effective coupling factor, k(eff), determine the frequency band over which high power can be transmitted; k(eff) cannot be greater than the piezoelectric material value, and so a high material coupling factor is a requisite for broadband operation. Stansfield's bandwidth criteria are used to calculate the optimum Q(m) value, Q(opt) approximately 1.2 (1-k(eff)2 1/2/k(eff). The results for the tonpilz projector exhibited k(eff) = 0.730, Q(m) = 1.17 (very near optimal), and a fractional bandwidth of 0.93. For the cylindrical transducer array, k(eff) = 0.867, Q(m) = 0.91 (larger than the optimum value, 0.7), and the bandwidth was 1.16. Although the measured bandwidths were less than optimal, they were accurately predicted by the theory, despite the highly simplified nature of the Van Dyke equivalent circuit, on which the theory is based.

The design, fabrication, and acoustic calibration of a 1-3 piezoelectric polymer composite-based cylindrical array module for towed applications

A cylindrical transducer array module containing eight double-layered 1–3 piezocomposite elements was acoustically calibrated in the frequency range 10–100 kHz. Each wedge-shaped element, covering approximately one octant (45) of the cylindrical radiating aperture, was housed in a molded syntactic foam hub component with its outer surface conforming to a cylindrical aperture 12.7 mm in diameter. The construction approach described would allow one to connect several modules of similar (or varying) diameter along the axial direction for towed-array applications requiring directional transmit and receive performance. The double-layer element design provides two independent electrical control points for optimizing the spatial and spectral response in both transmit and receive modes. The cylindrical module fabrication approach, associated tooling, and measured acoustic results for a single module under various drive conditions will be presented to illustrate the utility of this new transducer technology. [Work sponsored by the U.S. Navy.]

Some practical considerations in the design of sandwich transducers and their arrays

This paper describes the evolution of a 10.5 kHz sandwich element, developed to suit a cylindrical transducer array. It is essentially a guide to the practical problems encountered in designing sandwich elements, and the equations used are very much simplified. The approach is somewhat empirical, the eventual design being reached after differing prototype elements had been constructed; however, even with a more exact analysis it is unlikely that the need for prototype elements can be dispensed with.

Computation of the Nearfield/Farfield Radiation from a Cylindrical Transducer Array

A computer model has been created to study the pressure field of a large, low-frequency cylindrical sonar array. The pressure at a field point was taken to be the superposition of the complex pressures of the individual transducer elements. The pressure field of an element was taken to be the farfield approximation of the element's free field weighted by an angle-dependent function that approximates the effect of the baffle. Array field points were not calculated in the nearfield of the elements. Both horizontal and vertical beam patterns were computed for ranges from the nearfield to the farfield of the array. By combining the data from many beam patterns, a contour plot of SPL as a function of range and bearing was constructed. By correcting the field for spherical spreading loss, another contour plot was generated that displays the nearfield/farfield transition region. The results indicate that single probe calibration might be made to useful accuracy at ranges much less than the classic farfield range.

Nearfield Cavitation for a Cylindrical Array

Computer calculations were done for the near- and farfields of a cylindrical transducer array of 192 elements. Calculations were done for four different beam depression angles; for each beam depression angle, 12 different phasing sets were used; the sets corresponded to various percentages (0% to 180%) of the phases required to phase the array to a plane at that depression angle. The nearfield pressure maps that were computed show that as the plane wave phasing percentage increased, the peak pressures on the array increased slowly, while the peak pressures in the nearfield off of the array increased rapidly, particularly when the percentage of plane-wave phasing was greater than 100%, which resulted in severe nearfield focusing. An approximate method is presented for predicting the levels of the harmonics generated in the water by the occurrence of cavitation off of the array. When the theoretical acoustic pressure exceeds the ambient static pressure, the acoustic signal is represented as a clipped sine wave, which in turn is represented as a Fourier sine series whose coefficients represent the levels of the fundamental and harmonics.

Study of the Beam Patterns of a Cylindrical Transducer Array Located within an Elliptic Shell

A two-dimensional mathematical model consisting of a cylindrical radiator within an elliptic shell has been investigated. In this study, a velocity distribution was specified on the cylinder to simulate staves of a cylindrical transducer array. A portion of the staves were phased to a plane in order to transmit a directive beam. Farfield beam patterns were computed as the active array was steered by rotation within the elliptic shell. It was found that the peak intensity and side-lobe levels of the beam patterns varied with beam steering. The lobe structure was not symmetric about the main lobe for off-axis steering angles, and a region of relatively high side lobes appeared on one side of the main lobe. However, the main lobe was always in the beam-steering direction, and the beamwidth was not altered.