Acoustic Field Simulation Of64-element Phased Array

As a noninvasive tumor therapy technology, High Intensity Focused Ultrasound (HIFU) technology has been developing fast in recent years. Wherein the focused ultrasound transducer technology is one of the key technologies in clinical HIFU therapy system. Currently, HIFU clinical treatment more widely used is a single-element transducer array, Single transducer array element can only form a single focal region, achieving scanning therapeutic need to mechanical adjust the relative distance between the transducer and patients. Multi-element phased array transducers can change the focal position and form multiple focus by phase control. But phased transducer control circuits and production process are complex and high cost, and the focusing effect by the transducer parameters greater impact, so the safety and effectiveness of clinical treatment can not be protected, has yet to be widely applied in clinical. In HIFU tumor therapy, phased transducer structure and parameters directly affect the formation of sound field distribution, comparatively studing of the impact of these parameters on the formation of focal region by numerical simulation method is necessary.ObjectiveBy studying the effects of transducer phased structure parameters of the sound field distribution and the phased transducer single focus, variation of the sound field to provide an effective theoretical data and related basis of HIFU clinical treatment.MethodsIn this study, we simulate the pressure with the Westervelt for the nonlinear propagation of ultrasound, combined with finite-difference time-domain FDTD numerical simulation at different time and space. Here, simulate the effect of different frequencies of sound field when the64element phased array of equal distance ring is self-focus. Second, using time reversal method to control the phase of each array element to focus on the target position and comparising the sound field of the equal and unequal distance ring transducers, taking the ratio of intensity of side lobes and main lobe as a safety threshold. Finally, we simulate the sound field of the focal plane as the array element is8.5mm. the distance of adjacent ring is7mm. Detailed analysis of the contents and results are as follows.Results1. In the water when the frequency is0.5-0.8MHz. the greater the frequency, the greater the focus pressure and sidelobe, the closer to the focal position of the transducer.2. When setting the focus on the sound axis, the focus pressure performed by the unequal distance ring transducers is less than the equal distance ring transducers.and when the focal length is greater than the geometric focal length,the ratio of intensity of side lobes and main lobe ratio of the unequal distance ring transducers is0.46, exceeding the safety threshold of0.25.3. When the trasducer’s diameter is8mm, the distance of adjacent ring is7mm, the ratio of side lobes and main lobe is less than the transducer which distance of adjacent ring is7mm. When the trasducer’s distance of adjacent ring is7mm,diameter is8.5mm, the ratio of side lobes and main lobe is less than the transducer which diameter is8mm and the focus pressure is greater than it.4. Simulating the sound pressure field of the equal distance transducer which diameter is8.5mm,distance distance of adjacent ring is7mm(1) The phased array focused on the target focus along axis and off-axis.And when focal length of the setting focus along axis is more than80mm, the pressure of the focus deceased, side lobes increased.(2) With the setting focal length increasing, the ratio of side lobes and main lobe decreased firstly and then increased, the pressure of focus increased firstly and then decreased. The farther the sound axis deviation, the shorter the range of the focal length of the side lobes≤0.25of the main lobe is and the lower the focus of the sound pressure is.(3) When the length of two foci is form7mm to4mm, the intensity of side lobes increases and then decreases. When the length of two foci is form3mm to2.5mm, two foci gradually mixes together.(4) When focusing on five foci, it can form region on the target focus.and there will be the focal region formed between the side lobes.Conclusion 1. The focus pressure, side lobe amplitude and the size of the focal region will be affected by frequency.2. The performance of equal distribution phased array element transducer is better than the unequal distribution transucer.3. Equal distribution transducer array can focus in certain range.When the target focus is far away from the position of the transducer self-focused, the ratio of side lobes and the main lobe is greater, the pressure of focus is lower.4. The distance between two foci has an effect to the side lobes of the two foci. When the length of two foci is less than3mm, two foci gradually mixes together. However, the shape may not be a regular ellipsoid.