Study Of The Nonlinear Acoustic Field Generated From A Phased Array Focusing Transducer

High intensity focused ultrasound (HIFU) has attracted much attention as a new non-invasive cancer therapy technique. It focuses the ultrasonic energy into the target tissues inside the body, and the temperature of the target tissues rapidly increases in a short time, leading to the tumor cells coagulation necrosis with minimal impact on the normal tissues outside the focusing area. The phased array technology has some advantages of electronic beam focusing and multi-focuses, it is required to control the exciting vector and the phase of the elements based on the depth and size of the lesion area.In this paper a new method is proposed by combining the inverse matrix algorithm with Gaussian superposition technique to calculate the nonlinear sound field of the phased array. A1-D phased array is used as the numerical model, the difference between the linear sound field results of the Gaussian superposition technique and the Fresnel integral is less than0.5%, which verifies the feasibility of the approach. And then, the1-D、2-D、3-D phased array models are structured in the numerical simulation of the nonlinear sound field, the primary sound field and the harmonic sound field of the single-focus mode and the double-focus mode are calculated. The second harmonic wave’s characteristics and its’influence on the primary wave with the nonlinear effects are analyzed. Finally, the effect of the spacing between the elements to the grating lobes of the phased array is analyzed by changing the spacing. The results of this paper will promote the application of the phased array in HIFU.