Design Of Phased Array Transducers Research Articles

Sound fields radiated from a linear phased array based on analytical solutions of transient elastic waves

Beam characteristics of a linear phased array transducer are critical to its engineering applications as well as to its design. This paper proposes a method for the theoretical calculation of ultrasound field radiated by a linear phased array coupled to an elastic solid by a longitudinal wave couplant. In this case, the ultrasound field can be determined by superposition of the exact and analytical solutions of transient elastic waves induced by a number of discrete line sources normally acting on an elastic half-space. Based on the theoretical calculation, this work investigated the influences of several important parameters in a linear array transducer, such as wave length, array size, ratio of element width to inter-element spacing, to the ultrasound field characteristics. Interesting phenomena and useful results are obtained, which provide fast and accurate guidance for linear phased array transducer design. It also satisfies diverse and specific demands for actual engineering testing using arrayed transducers.

Evaluation of a novel therapeutic focused ultrasound transducer based on Fermat’s spiral

The purpose of this study was to evaluate a novel phased array transducer design rule for therapeutic focused ultrasound applications. This design rule uses the discretized Fermat’s spiral to determine the positioning of the transducer elements for a given number of elements and f-number. Using this principle, three variations of Fermat’s spiral were generated, aimed at (1) grating lobe minimization, (2) side lobe minimization, and (3) an optimized element packing efficiency. For each spiral, sparse layouts using identical circular elements and fully populated layouts based on additional Voronoi tessellation were evaluated numerically. Evaluation criteria included the element size distribution, beam steering capabilities, focal plane pressure distribution, prefocal pressure distribution, and practical considerations. Finally, one Voronoi-tessellated design with a focal length and aperture diameter of 16 cm and a natural frequency of 1.3 MHz was evaluated experimentally through hydrophone measurements. The numerical evaluation showed that while sparse arrays possess superior beam steering capabilities for a given number of elements, the focal point quality and prefocal pressure distribution is substantially more favorable when using the Voronoi-tessellated designs. Beam steering was shown to be feasible with the tessellated designs for lateral deflections up to 10 mm and axial deflections up to 20 mm. The experimental evaluation showed that such a transducer is capable of inducing 40.00 MPa rarefactional and 237.50 MPa compressional peak pressure levels at 800 W instantaneous acoustic output power under free-field conditions, making the system potentially relevant for thermal ablation therapy, histotripsy applications, and shockwave-enhanced heating.

High intensity focused ultrasound with large aperture transducers: A MRI based focal point correction for tissue heterogeneity

The risk of undesired tissue damage to thoracic cage, heart, and lung during MR guided HIFU ablations of breast cancer can be greatly reduced if a phased array transducer design with a lateral beam direction is used in combination with a large aperture. The disadvantage is an increased sensitivity to focus aberrations due to tissue heterogeneity. Here, the authors propose to restore the focal coherence by using a matched aperture phase correction, which is based on a noninvasively obtained tissue model. The method combines high resolution MRI with ultrasound wave measurements of different tissue types to determine a phase correction, which compensates focal point aberrations caused by tissue heterogeneity. 3D segmentation of tissue is used to quantify the relative proportion of each tissue type along a line running from the center of each element of the phased array to the target focal point. For tissue types with a celerity difference of 3%, the proposed method allows to quantify the phase aberration with an accuracy of 6° ± 20° and a correlation factor R(2) = 0.95. Using the refocusing method for a complex heterogeneous phantom resulted in 95% of the maximal pressure, whereas only 70% of the maximal pressure is obtained in absence of any phase correction. Since the proposed refocusing algorithm is compatible with a standard interventional preplanning and requires only a minimal amount of processing, it presents a promising approach to compensate for aberration in heterogeneous tissues such as the human breast.

Analysis of phased array transmitters and beamformers.

As phased array ultrasonic transducers become more wide spread in underwater acoustic measurement applications, a better understanding of their basic performance characteristic is of benefit. The beam patterns of a phased array can be approximated by a steady state analysis. This approach indicates the directional response of an array in response to a sinusoidal excitation. However, a steady state examination does not properly describe transient behavior of the transmit waveform and also the received signal that is subsequently beamformed. We further investigate the transient performance of the beamformer using a closed-form solution to the acoustic wave equation for a multielement ultrasonic phased array transducer. The model produces transducer beam patterns and transient beamformer output for a series of reflective targets in the far-field of the transducer. The results show a close agreement with laboratory measurements and provide a tool for further investigation of phased array transducer design and performance.

Phased array transducer design and method for manufacture thereof

A phased array transducer and method for the manufacture thereof having a design that allows the array to focus in a near field of interest and a far field of interest. The array includes a plurality of even and odd numbered transducer elements where the even and odd numbered elements have an active region of particular widths. The width of the active region of the odd numbered elements is different than the width of the active region of the even numbered elements so that the odd numbered elements can be used to image in one field of interest while the even numbered elements can be used to image in another field of interest.

Broadband phased array transducer design with frequency controlled two dimension capability and methods for manufacture thereof

There is provided a transducer array with a plurality of piezoelectric elements having a minimum and maximum thickness. In one embodiment, the maximum thickness is less than or equal to 140 percent of the minimum thickness. In an alternate embodiment, the maximum thickness is greater than 140 percent of the minimum thickness and the transducer array is capable of simulating the excitation of a wider aperture two-dimensional transducer array. One or more matching layers may be used to further increase bandwidth performance. In addition, a two crystal transducer element as well as a composite transducer structure may be formed using the principles of this invention.

A silicon electrostatic ultrasonic transducer

An electric ultrasonic transducer is developed by using a silicon IC process. Design considerations are first presented to obtain high sensitivity and the desired frequency responses in air. The measured transmitter sensitivity is 19.1 dB (0 dB=1 mubar/V) at a point 50 cm away from the devices, when the devices are operated at 150 kHz. The receiving sensitivity is 0.47 mV/Pa in the 10-130-kHz range, with bias voltages as low as 30 V. An electronic sector scanning operation is also achieved by time-sequentially driving seven elements arranged in a linear array on the same chip. The results should be helpful in the design of phased-array transducers integrated with electronic scanning circuits.