提出了一类新的声束,其径向轴对声场分布像大写字母“M”,故称之曰M形波束.分别给出了无限大孔径和有限孔径两种情形下M形声束的数学描述;计算了M形声束沿声轴以及在各截面上的声场分布.作为算例,给出了半径为2.5 cm,中心频率为1 MHz,厄密系数B2=4的一假想的换能器辐射声场分布.计算结果表明,这一换能器辐射的声场,在离开声源大约10 cm范围之内,具有M形声束形状;在大约这一距离以后的10 cm范围声束形状相对均匀.也讨论了这种M形波束在超声热疗和成像等领域的潜在应用.“,”In this paper,new families of sound beams are presented,which produce the sound fields with an axial-symmetric amplitude distribution like the capital letter“M”and are termed the M-shape waves. A simple mathematical description is derived for two situations:infinite aperture and finite aperture. The beam distributions in the field of the M-shape sound source are computed on the acoustic axis and at various cross sections. A numerical example is given for a hypothetical transducer with 2.5 cm radius,1 MHz center frequency and the Hermite coefficient B2=4,this trans-ducer will radiate M-shape beam within the regions of about 10 cm from the source and the field pattern is relatively uniform at the ranges of about 10 cm behind this distance. Possible applications of M-shape beam in some areas such as hyperthermia and advanced imaging techniques,are also discussed.