The invention relates to a dual-frequency hollow focused ultrasonic
detector. The
detector comprises a cylindrical shell, an acoustic focusing lens arranged in the shell, an annular sound absorption material layer, an annular back lining material layer, annular ultrasonic transducers and a
signal line, wherein the annular sound absorption material layer and the annular back lining material layer are arranged in the shell in an overlapped mode, the annular ultrasonic transducers are arranged on the back lining material layer and face the acoustic focusing lens, and the
signal line is electrically connected with the ultrasonic transducers. A line outlet for leading out the
signal line is formed in the sidewall of the shell. The acoustic focusing lens comprises a semispherical first lens part and a similar-conical second lens part, an incident
laser is coaxial with the
detector, the resolution is enhanced, the detection sensitivity is improved, and the imaging effect is good; by means of the first lens part and the second lens part adopting two different acoustic-impedance acoustic materials, photo-acoustic signal collimation is achieved, acoustic focusing is achieved, and the acoustic resolution is enhanced. The ultrasonic transducers with two different dominant frequencies are adopted, the wide-band performance of the dual-frequency hollow focused ultrasonic detector is improved, and more
pathologic messages of a detected portion in the transverse direction and the longitudinal direction can be obtained.