Numerical simulations of partial elements excitation for hemispherical high-intensity focused ultrasound phased transducer

The hemispherical phased transducer maximizes the coverage of the skull and the ultrasonic energy per unit area of the skull is minimized,thereby reducing the risk of skull burns,but the transducer has a small focal area adjustment range,increasing the focal length of treatment is an urgent question for this type of transducer.In this paper,a three-dimensional high-intensity focused ultrasound(HIFU)transcranial propagation model is established based on the human head structure.The finite difference time domain(FDTD)is combined with the Westervelt acoustic wave nonlinear propagation equation and Penne's biological heat conduction equation for numerical simulation of the sound pressure field and temperature field.Forming a treatable focal area in a small-opening hemispherical transducer with a small amount of numerical simulation calculation focusing at a set position to determine the minimum partial excitation area ratio of focusing.And then,applying these preliminary results to a large-opening diameter hemispherical transducer and the temperature field formed by it or full excitation is studied.The results show that the focus area with the excitation area ratio of less than 22%moves forward to the transducer side when the excitation sound is formed.When the excitation area ratio is greater than or equal to 23%,it focuses at the set position.In the case of partial incentives,using 23%of the partial array,the adjustable range of the treatable focal area formed in the three-dimensional space is larger than that of the full excitation.

Inspection of pipeline girth welds with ultrasonic phased array technique

A novel automatic ultrasonic system used for the inspection of pipeline girth welds is developed, in which a linear phased array transducer using electronic scan is adopted. Optimal array parameters are determined based on a mathematical model of acoustic field for linear phased army derived from Huygens＇ principle. The testing method and the system structure are introduced. The experimental results show that the phased array transducer system has the same detectability as that of conventional ultrasonic transducer system, but the system architecture can be simplified greatly, and the testing flexibility and the testing speed can be improved greatly.

Simulation study of the superharmonic field generated from a phase array transducer

Ultrasound imaging is the most widely used noninvasive medical imaging modality. Its latest elite concept is Superharmonic Imaging which is the most talked-about future of medical diagnostic ultrasound. In this paper, the computational and analytical study for superharmonic field generation from phased array transducer of 16 × 16 elements is presented. For this, the model preferred, includes the calculation for diffraction effect in frequency domain and nonlinear effect in time domain. The attenuation is included along with the diffraction in frequency domain as well. The comparative analysis of superharmonic field is also carried out with simulated fundamental and second harmonic fields by the same model. Similarly, the comparison with the results from the literature is also reported.