Micromachined piezoelectric ultrasonic transducer with ultra-wide frequency bandwidth

An ultrasonic transducer with a wide frequency bandwidth is always preferred for diagnostic ultrasound imaging, because a wide frequency bandwidth can reduce the duration of an ultrasonic pulse and enhance the axial imaging resolution. However, the frequency bandwidth of both conventional ultrasonic transducer and normal piezoelectric micromachined ultrasonic transducer (pMUT) is quite limited. To overcome this limitation, the mode-merging pMUT is presented in this letter. By using the rectangular membrane with large length/width aspect ratio, several resonant modes are excited within a narrow frequency range. When this pMUT works in a largely damped medium, excited modes are merged together and result in an ultra-wide bandwidth. A -6 dB bandwidth of 95% is measured in water for the proposed pMUT without matching layer, which is much broader than that of conventional pMUTs. Benefited from such ultra-wide frequency bandwidth, the pulse duration of 1 μs is achieved at a central frequency of 1.24 MHz. If this ultra-wide bandwidth pMUT is utilized to replace the conventional transducer for diagnostic ultrasound imaging, the axial resolution can be significantly enhanced without compromising imaging depth.