In an ultrasound transducer, the piezoelectric layer is the most crucial component as the active element to achieve the energy conversion between mechanical energy and electrical energy. However, fabricating ultrasonic transducers with both broad bandwidth and high sensitivity remains technically challenging. Moreover, it is generally known that sensitivity is another essential technical parameter for ultrasonic transducers. In this case, ultrasonic transducers with broad bandwidth are always preferred. However, the high operating frequency will result in a large acoustic attenuation, further decreasing the detecting range of transducers thus, the operating frequency of diagnostic-imaging transducers is below 10 MHz and is usually fixed at 3–5 MHz to ensure a reasonable detecting range. Generally, a shorter pulse length will incur a better axial imaging resolution in diagnostic-imaging transducers, wherein a shorter pulse length can be achieved by increasing the operating frequency or enhancing the bandwidth of transducers. Especially for ultrasound-based diagnostic imaging with the advantages of being efficient, nonradiative and operating in real-time, ultrasonic transducers are usually applied for visualizing internal body structures. In recent years, high-performance ultrasonic transducers have been widely used in many industrial and scientific areas, including energy conversion, non-destructive determination, information acquisition, medical diagnosis, etc. The obtained results suggested that the ACP is an effective and convenient technology to improve transducer performances, especially for the bandwidth. Moreover, the optimization mechanism of transducer performance by the ACP method was discussed. This bandwidth is higher than that of all reported transducers with similar center frequency. Particularly, a superhigh bandwidth of 142.8% was achieved in the transducer of ACP 1–3 PMN-PT single crystal combined with suitable matching and backing layers. The results indicate that the ACP method can significantly enhance the bandwidth and slightly increase the insertion loss of transducers. The effect of the ACP method on the bandwidth and insertion loss (sensitivity) was explored. Herein, transducers ( f c = 3 MHz) made of DCP and ACP 1–3 piezocomposites (prepared by PZT-5H ceramics and PMN-PT single crystals) were fabricated. Recent studies showed that the alternating current poling (ACP) method could develop the properties of piezocomposites, which had great potential to improve transducer performance. Ultrasonic transducers are the basic core component of diagnostic imaging devices, wherein the piezoelectric materials are the active element of transducers.
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