| Medical ultrasonic engineering is widely used in clinic medicine.Beam-forming is a key technology in ultrasound imaging system and determines the imaging quality of related ultrasound equipment.In order to improve the quality of ultrasound imaging,a t beam-forming technique based on non-diffracting wave has been studied.Non-diffracting waves can propagate over a long distance without divergence.As one type of non-diffracting wave,Bessel wave has good localization of sound field energy distribution.Another type of non-diffracting wave called X-wave can be obtained through weighted superposition of Bessel beams with different orders and different frequencies.Unlike the continuous waves of Bessel wave,X-wave is a pulse wave and has more clinical application value.In order to study the characteristics of non-diffracting waves,the non-diffracting waves including Bessel waves and X-waves is simulated based on the Rayleigh-Sommerfeld integral formula in the study.The specific works are as follows:1.The characteristics,development history and applications of non-diffracting waves is introduced,the theory of wave diffraction and integral diffraction is discussed.And based on the study,the Rayleigh-Sommerfeld integral formula is determined as the calculation formula to simulate non-diffracting waves field.2.By simulating the sound fields of Bessel waves and X-waves through the uses of MATLAB,it is found that this type of non-diffracting waves like can be implemented by transducers in limited sizes.The simulation results suggest that although the transducers,which generate Bessel waves and X-waves,are required to be continuous in theory,they can be approximated by discrete transducers with several rings of concentric circles.Through the simulation,it is known that the non-diffracting waves can be generated by physical devices.Considering the good non-diffraction of Bessel waves and X-waves,this study potentially has more practical value in the field of medical imaging. |
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