中文摘要：

脉冲压缩方法通过采用编码信号激励与脉冲压缩接收来提高超声检测的时间分辨率和信噪比。然而，受换能器带宽的限制，编码信号的时间带宽积往往有限，影响脉冲压缩效果。开展了基于超声阵列的多频脉冲压缩方法研究，超声阵列是由具有不同中心频率和带宽的多个阵元组成，从而使得整个阵列具有比单个换能器更宽的带宽。提出了压缩后叠加取包络的脉冲压缩方法，并研究了这种方法在提高时间分辨率和主副瓣比上的技术方案，对多频脉冲压缩的超声阵列进行了设计与优化，发现多频脉冲压缩方法能很大程度地提高时间分辨率，并能有效地抑制各阵元信号叠加产生的周期副瓣。理论和实验结果表明，这种压缩后叠加取包络的方法得到的时间分辨率在性能上受阵元带内不平整度的影响很小，能使阵元压缩包络中的主副瓣比得到明显改善。

英文摘要：

By using the coding signal excitation and pulse compression receiver, pulse compression technique man- ages to increase the time resolution and signal-to-noise ratio in ultrasonic detection. However, the relative small time bandwidth product limited by the transducer bandwidth, leads to a poor compression result. The multi-frequency pulse compression method based on ultrasonic array is studied. The array consists of the elements with different center frequencies and bandwidths, respectively, thus it has a larger bandwidth than a single-element transducer. A compression-superimposition-envelope method is proposed, with the research of technical solution to improve time reso- lution and mainlobe-to-sidelobe ratio. The reasonable design and optimization of ultrasonic array are given, to achieve the nmlti-frequency pulse compression result of great enhancement on time resolution, and good suppression on the periodic sidelobe resulting from the superposition. Theories and experiments show that the time resolution performance enhancement brought by the compression-superimposition-envelope method is robust to the roughness within the element bandwidth, as well as the improvement on the mainlobe-to-sidelobe ratio.