Ultrasonic imaging technology has advanced rapidly, the escalating demand for imaging quality has driven the continuous development of ultrasonic transducers featuring high-performance. Among them, the crucial factors constraining the further enhancement of imaging quality are the frequency of the device and the intensity of the echo signal. Piezoelectric composites have become a hotspot for ultrasonic transducers and imaging applications due to their excellent properties. However, due to the limitations of the accuracy of the cutting process, the development of piezoelectric/polymer composites is often undermined by undesirable pseudo-vibrations, especially in high-frequency applications, which will significantly reduce energy conversion efficiency. In this study, a novel design method of 1–3 piezoelectric composites with gradient nanoparticle doped polymer is proposed to eliminate the undesired lateral vibrations. Based on the optimized composites, a high-performance composite ultrasonic transducer with a center frequency of 8.51 MHz is prepared. Compared with the traditional composite transducer, the optimized transducer improves the echo voltage amplitude significantly, reaching nearly 3 times. The above advantages are further verified in high-quality ultrasound and photoacoustic imaging. The optimization method has valuable guidance for the design of high-frequency composite transducers, which have great potential in ultrasonic and photoacoustic imaging applications.

With the increasing popularity of fintech, i.e., financial technology, the e-commerce market has grown rapidly in the past decade, such that mobile devices enjoy unprecedented popularity and are playing an ever-increasing role in e-commerce. This is especially true of mobile payments, which are attracting increasing attention. However, the occurrence of many traditional financial mishaps has exposed the challenges inherent in online authentication technology that is based on traditional modes of realizing the healthy and stable development of mobile payment. In addition, this technology ensures user account security and privacy. In this paper, we propose a Secure Mutual Authentication Protocol (SMAP) based on the Universal 2nd Factor (U2F) protocol for mobile payment. To guarantee reliable service, we use an asymmetric cryptosystem for achieving mutual authentication between the server and client, which can resist fake servers and forged terminals. Compared to the modes currently used, the proposed protocol strengthens the security of user account information as well as individual privacy throughout the mobile-payment transaction process. Practical application has proven the security and convenience of the proposed protocol.