Array Of Transducer Elements Research Articles

A spiral wave front beacon for underwater navigation: Transducer prototypes and testing

Transducers for acoustic beacons which can produce outgoing signals with wave fronts whose horizontal cross sections are circular or spiral are studied experimentally. A remote hydrophone is used to determine its aspect relative to the transducers by comparing the phase of the circular signal to the phase of the spiral signal. The transducers for a "physical-spiral" beacon are made by forming a strip of 1-3 piezocomposite transducer material around either a circular or spiral backing. A "phased-spiral" beacon is made from an array of transducer elements which can be driven either in phase or staggered out of phase so as to produce signals with either a circular or spiral wave front. Measurements are made to study outgoing signals and their usefulness in determining aspect angle. Vertical beam width is also examined and phase corrections applied when the hydrophone is out of the horizontal plane of the beacon. While numerical simulations indicate that the discontinuity in the physical-spiral beacon introduces errors into the measured phase, damping observed at the ends of the piezocomposite material is a more significant source of error. This damping is also reflected in laser Doppler vibrometer measurements of the transducer's surface velocity.

Novel concept of therapeutic array transducer element using coresonance between oscillations of hemispherical piezoceramic shell and water sphere

For therapeutic array transducers, it is required to reduce the electrical impedance of their elements so that the transducer can produce high ultrasonic power at a relatively low drive voltage. For this purpose, a new concept of concave hemispherical piezoceramic transducer element using its breathing mode has been investigated. The vibrational behavior of such a transducer is theoretically, numerically, and experimentally analyzed. Both resonance frequencies of the breathing-mode oscillation of a piezoceramic spherical shell and the volume oscillation of a water sphere are not only inversely proportional to their diameters, but also very close to each other at the same diameter. Numerical simulation of the transducer element showed high acoustical coupling achieved by the coresonance between the piezoceramic and the water sphere half enclosed by the shell. To confirm the effect by the coresonance, simulation replacing water by virtual materials, having the same acoustic impedance as water but different longitudinal velocities, was performed. The electrical impedance curves of the concave shell were very sensitive to the longitudinal velocities of the virtual materials, whereas those of the convex shell remained unchanged, which strongly support the hypothesis. Experimental results with a prototype transducer element will also be discussed.

TRANSMIT BEAMFORMING IN 3-DIMENSIONAL ULTRASOUND

An ultrasound system comprises a probe including a two-dimensional (2D) array of transducer elements that form an aperture having a plurality of receive elements that are configured to receive ultrasound signals. The transducer elements form at least one transmit sub-aperture that is configured to be interconnected with a fixed group of the transducer elements within the aperture. Transmitters generate electrical transmit signals, and at least one transmit sub-aperture processor (tx SAP) maps the transducer elements within the fixed group of the transducer elements to the transmitters in a transmit configuration based on a beam steering direction.

ULTRASOUND IMAGING WITH SYNTHETIC RECEIVE APERTURE AND WIDE APERTURE, FOCUSED TRANSMIT BEAM

A method and an instrument for ultrasound imaging using an array of transducer elements which is connected to the instrument with a limited number of wires, where focusing of the transmit beam improves image signal to noise ratio above state of the art methods. This allows the use of higher ultrasound frequencies providing improved image resolution.

Modified synthetic transmit aperture algorithm for ultrasound imaging

The modified synthetic transmit aperture (STA) algorithm is described. The primary goal of this work was to assess the possibility to improve the image quality achievable using synthetic aperture (SA) approach and to evaluate the performance and the clinical applicability of the modified algorithm using phantoms. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point in the image and for all possible combinations of the transmit–receive pairs. The weights are calculated using the angular directivity functions of the transmit–receive elements, which are approximated by a far-field radiation pattern of a narrow strip transducer element vibrating with uniform pressure amplitude over its width. In this way, the algorithm takes into account the finite aperture of each individual element in the imaging transducer array. The performance of the approach developed was tested using FIELD II simulated synthetic aperture data of the point reflectors, which allowed the visualization (penetration) depth and lateral resolution to be estimated. Also, both simulated and measured data of cyst phantom were used for qualitative assessment of the imaging contrast improvement. The experimental data were obtained using 128 elements, 4 MHz, linear transducer array of the Ultrasonix research platform. The comparison of the results obtained using the modified and conventional (unweighted) STA algorithms revealed that the modified STA exhibited an increase in the penetration depth accompanied by a minor, yet discernible upon the closer examination, degradation in lateral resolution, mainly in the proximity of the transducer aperture. Overall, however, a considerable (12 dB) improvement in the image quality, particularly in the immediate vicinity of the transducer’s surface was demonstrated. The modified STA method holds promise to be of clinical importance, especially in the applications where the quality of the “near-field” image, that is the image in the immediate vicinity of the scanhead is of critical importance such as for instance in skin- and breast-examinations.

Breathing-Mode Ceramic Element for Therapeutic Array Transducer

A new concept of piezoceramic array transducer element using breathing mode has been proposed for therapeutic application. Finite element numerical simulation showed that a concave hemispherical piezoceramic shell with a diameter slightly larger than the wavelength in water is effective for obtaining good acoustic matching with water. A hemispherical piezoceramic element with an inner diameter of 4.0 mm and a thickness of 0.2–0.4 mm produced more than several times higher acoustic power output than a conventional thickness-mode element at the same drive voltage in the simulation. Its good acoustic matching with water is considered to be accomplished by the combined resonance with the spherical bulk of water half covered by the shell, because the resonance was very sensitive to the change in sound speed of the virtual material replacing water with the same acoustic impedance in simulation.

Research on Fabrication Techniques and Performance Analysis for 3×3 Cymbal Transducer Array

The single array element of cymbal transducer has a low transmitting power, poor directivity and narrow bandwidth, which however can be improved, even overcome by array forming. First of all, 9 cymbal transducer array elements were designed and made on the basis of the research results obtained in the early stage, and were assembled into a 3x3 array by using a set of stable and reliable array forming techniques developed from the research. The array was shaped by casting with organic silica-gel and then getting cured. The array was tested in air for resonance frequency and equivalent circuit parameters demonstrating the stability of array forming techniques. The array and a single array element were also tested in anechoic water-tank for transmitting, receiving and directivity performances, and the result indicates that, the array forming by elements can strengthen the transmitting power and improve the directivity effect, but may reduce the free-field receiving sensitivity. The research has a great significance to the development of a new super multi-element cymbal array.

Curved 2-D Array Ultrasound Transducer And Method For Volumetric Imaging

An ultrasound imaging system includes an imaging probe having an array of transducer elements that is flat and relatively elongated in the azimuth direction and is curved outwardly in the elevation direction. As a result, when the transducer elements are scanned in a step-wise manner, the acoustic pattern of the probe diverges in the elevation direction. The probe therefore provides a large field of view in the near field despite using relatively few transducer elements. The probe also includes sub-array beamformers to delay signals transmitted and received from the transducer elements in respective sub-arrays. The received signals are coupled to an imaging system which includes a signal path that processes the received signals into signals corresponding to a volumetric image. A display coupled to the signal path can then show a volumetric image of anatomical features in a volumetric region adjacent the array of transducer elements.

3Pb5-1 Therapeutic array transducer element using coresonance between hemispherical piezoceramic shell and water sphere(Poster Session)

3Pb5-1 Therapeutic array transducer element using coresonance between hemispherical piezoceramic shell and water sphere(Poster Session)

3D conformal MRI-controlled transurethral ultrasound prostate therapy: validation of numerical simulations and demonstration in tissue-mimicking gel phantoms

MRI-controlled transurethral ultrasound therapy uses a linear array of transducer elements and active temperature feedback to create volumes of thermal coagulation shaped to predefined prostate geometries in 3D. The specific aims of this work were to demonstrate the accuracy and repeatability of producing large volumes of thermal coagulation (>10 cc) that conform to 3D human prostate shapes in a tissue-mimicking gel phantom, and to evaluate quantitatively the accuracy with which numerical simulations predict these 3D heating volumes under carefully controlled conditions. Eleven conformal 3D experiments were performed in a tissue-mimicking phantom within a 1.5T MR imager to obtain non-invasive temperature measurements during heating. Temperature feedback was used to control the rotation rate and ultrasound power of transurethral devices with up to five 3.5 × 5 mm active transducer elements. Heating patterns shaped to human prostate geometries were generated using devices operating at 4.7 or 8.0 MHz with surface acoustic intensities of up to 10 W cm−2. Simulations were informed by transducer surface velocity measurements acquired with a scanning laser vibrometer enabling improved calculations of the acoustic pressure distribution in a gel phantom. Temperature dynamics were determined according to a FDTD solution to Pennes’ BHTE. The 3D heating patterns produced in vitro were shaped very accurately to the prostate target volumes, within the spatial resolution of the MRI thermometry images. The volume of the treatment difference falling outside ±1 mm of the target boundary was, on average, 0.21 cc or 1.5% of the prostate volume. The numerical simulations predicted the extent and shape of the coagulation boundary produced in gel to within (mean ± stdev [min, max]): 0.5 ± 0.4 [−1.0, 2.1] and −0.05 ± 0.4 [−1.2, 1.4] mm for the treatments at 4.7 and 8.0 MHz, respectively. The temperatures across all MRI thermometry images were predicted within −0.3 ± 1.6 °C and 0.1 ± 0.6 °C, inside and outside the prostate respectively, and the treatment time to within 6.8 min. The simulations also showed excellent agreement in regions of sharp temperature gradients near the transurethral and endorectal cooling devices. Conformal 3D volumes of thermal coagulation can be precisely matched to prostate shapes with transurethral ultrasound devices and active MRI temperature feedback. The accuracy of numerical simulations for MRI-controlled transurethral ultrasound prostate therapy was validated experimentally, reinforcing their utility as an effective treatment planning tool.

Beamforming Design to Suppress Response from Strong Reflectors

A novel algorithm of beamforming design is proposed on the basis of the constrained least squares method for suppressing the unwanted response from strong reflectors while preserving the response from soft tissues. The constrained least-squares method is suitable for multi-objective optimization such as that required for beamforming design. In the proposed algorithm, not only the apodization weight but also the phase shift of the transmit and receive signals of each array transducer element are optimized. Imaging of hypoechoic cysts located next to strong reflectors was numerically simulated. It was demonstrated that the artifacts due to the strong reflectors can be significantly reduced by the proposed beamforming design.

Ultrasound probe distributed beamformer

An ultrasound beamforming probe includes an array of transducer elements and a processing board that carries a signal processor. Receive signal connections, for a receive aperture formed from multiple transducer elements, are coupled to the first signal processor. A location memory is connected to the signal processor and holds a spatial location for the receive aperture. The signal processor retrieves the spatial location, determines a beamforming phase shift derived from the spatial location for each transducer element in the receive aperture, and applies the respective phase shift to each receive signal.

3D ultrasonic imaging apparatus and method

A probe for electronic volume data acquisition using ultrasound incorporates a plurality of transducer elements arranged in a two dimensional array having an azimuth direction and an elevation direction. The transducer elements have a first element size in the azimuth dimension and a second element size in the elevation dimension. At least one of the first and second element sizes is at least twice a characteristic wavelength of a waveform used to drive the array of transducer elements, where the characteristic wavelength is defined as the wavelength corresponding to a center frequency of the waveform. Image data is generated in a scanning process using a CAC-BF technique in an azimuth dimension and/or an elevation dimension, to form an ultrasound image line, image plane, or image data cube.

Lamb wave generation with an air-coupled piezoelectric concave array using square-wave burst excitation

In this paper, an improved pulse generator is proposed to emit a low-voltage square-wave burst. This generator will be used to excite a concave piezoelectric transducer array. Unlike classical single-pulse excitation circuits, this generator is also able to generate a square-wave burst signal. The Lamb waves generated in an aluminium plate with the square-wave burst generator are compared with those obtained using a classical single-pulse generator. Also, the signal conditioning system for all the transducer array elements has been implemented and tested.

Effect of kerf filler on the electromechanical coupling coefficient of an ultrasonic transducer array element

Electromechanical coupling coefficient directly reflects the electromechanical energy conversion capability of a piezoelectric device. We show theoretically that the kerf filler in the ultrasonic array transducer can degrade this coupling coefficient. A closed form expression has been derived that can quantitatively describe the electromechanical coupling coefficient of an ultrasonic transducer array element with arbitrary aspect ratio and having polymer kerf filler in between transducer elements.

Finite element modeling and experimental characterization of crosstalk in 1-D CMUT arrays

Crosstalk is the coupling of energy between the elements of an ultrasonic transducer array. This coupling degrades the performance of transducers in applications such as medical imaging and therapeutics. In this paper, we present an experimental demonstration of guided interface waves in capacitive micromachined ultrasonic transducers (CMUTs). We compare the experimental results to finite element calculations using a commercial package (LS-DYNA) for a 1-D CMUT array operating in the conventional and collapsed modes. An element in the middle of the array was excited with a unipolar voltage pulse, and the displacements were measured using a laser interferometer along the center line of the array elements immersed in soybean oil. We repeated the measurements for an identical CMUT array covered with a 4.5-microm polydimethylsiloxane (PDMS) layer. The main crosstalk mechanism is the dispersive guided modes propagating in the fluid-solid interface. Although the transmitter element had a center frequency of 5.8 MHz with a 130% fractional bandwidth in the conventional operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 2.1 MHz, and had a cut-off frequency of 4 MHz. In the collapsed operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 4.0 MHz, and had a cut-off frequency of 10 MHz. Crosstalk level was lower in the collapsed operation (-39 dB) than in the conventional operation (-24.4 dB). The coverage of the PDMS did not significantly affect the crosstalk level, but reduced the phase velocity for both operation modes. Lamb wave modes, A0 and S0, were also observed with crosstalk levels of -40 dB and -65 dB, respectively. We observed excellent agreement between the finite element and the experimental results.

Electromechanical coupling coefficient of an ultrasonic array element

One of the most important parameters for characterizing piezoelectric materials is the so-called electromechanical coupling coefficient, k, which describes the electromechanical coupling strength. Although this parameter should be an intrinsic material parameter, it appears to depend on the aspect ratio of the resonator. There are three different values defined for three extreme geometries, k33, k33′, and kt, and they differ by more than 50%. Unfortunately, these three values cannot describe resonators of general geometries and also create conceptual confusion. Here, we provide a unified formula that will accurately describe the coupling coefficient of rectangular slender bar transducer array element with any aspect ratio.

Ultrasound transducers for imaging and therapy

Ultrasound applicators able to both image a treatment site and administer ultrasound therapy include an array of transducer elements that can be focused. In several embodiments, an electronically phased array is used for controlling the focal point of an ultrasound beam. The ultrasound beam produced thereby can also be electronically steered. To reduce the quality factor or Q of the array when the array is used for imaging, an electronic switch is selectively closed, placing a resistance in parallel with each of the array elements. A flexible array is employed in several embodiments and is selectively bent or flexed to vary its radius of curvature and thus control the focal point and/or a direction of focus of the array. In another embodiment, each of the transducer elements comprising the array are individually mechanically pivotable to steer the ultrasonic beam produced by the transducer elements.

Transcranial ultrasound focus reconstruction with phase and amplitude correction

Therapeutic and diagnostic ultrasound procedures performed noninvasively through the skull require a reliable method for maintaining acoustic focus integrity after transmission through layered bone structures. This study used a multiple-element, phased-array transducer to reconstruct ultrasound foci through the human skull by amplitude and phase correction. It was previously demonstrated that adaptive phase correction using a multiple-element, focused transducer array yields a significant correction to an acoustic field that has been distorted by the heterogeneities of the skull bone. The introduction of amplitude correction, in a regime in which acoustic pressures from individual transducer array elements are adjusted to be normalized at the focus, has demonstrated a 6% (-0.27 dB) average decrease in acoustic sidelobe acoustic intensity relative to the focal intensity and a 2% (-0.09 dB) average decrease in the full-width-at-half-maximum (FWHM) of the acoustic intensity profile at the focus. These improvements come at the expense of significant ultrasound intensity loss--as much as 30% lower (-1.55 dB)--at the focus because the amplitude correction method requires that, at constant power, a larger proportion of energy is absorbed or reflected by regions of the skull that transmit less energy. In contrast, a second correction method that distributes pressure amplitudes such that the sections of the skull which transmit more ultrasound energy are exposed with higher ultrasound intensities has demonstrated an average sidelobe intensity decrease of 3% (-0.13 dB) with no change in the FWHM at the focus. On average, there was a 2% (0.09 dB) increase in the acoustic intensity at the focus for this inverse amplitude correction method. These results indicate that amplitude correction according to the transmission properties of various segments of the skull have a clear effect on ultrasound energy throughput into a target site within the brain parenchyma.

Flexible geometry for real-time ultrasound volume imaging

An ultrasonic imaging method and apparatus are described for electronically scanning a volumetric region using a two dimensional array of transducer elements coupled to a beamformer. Elements of the array are actuated to transmit ultrasonic energy into the volumetric region. Echo signals are received by elements of the array in response to the transmitted ultrasonic energy. Beams are formed which sample the volumetric region that allows choices of size, location and geometry shapes such as in one of a circular and elliptical beam pattern.