Development of ultrasound piezoelectric ceramics transducer technology

 1.Medical ultrasound imaging technology is the four medical imaging technologies of modern medical imaging technology, and has been widely used in the cardiology, obstetrics, ophthalmology, liver, kidney, gallbladder and vascular system. Compared with other imaging technologies, ultrasound imaging technology has the unique advantages of good real-time performance, no damage and low cost,ultrasonic wired ceramic disc is widely used in the practical clinical practice. Ultrasound imaging technology is a technique for imaging processing by using ultrasonic waves emitted from ultrasonic transducers to enter the human tissue and reflect echoes at different tissue boundaries of the human body. The ultrasonic transducer is both an ultrasonic transmitter and an echo receiver. It is the most critical acoustic component in medical ultrasound imaging systems and is a guarantee for obtaining high quality images. The birth of various new imaging functions and methods is also inseparable from the innovation of transducer technology. This paper discusses the development and prospects of ultrasound imaging transducer technology.

2. piezoelectric composite transducer

    At present, piezoelectric ceramics are the most commonly used materials in ultrasonic imaging transducers, which have high electromechanical conversion efficiency.Easy to be matched with circuits, stable performance, easy processing and low cost, it is widely used. At the same time, electric ceramic materials also have large acoustic impedance, which is not easy to match the acoustic impedance of human soft tissue and water; mechanical quality,high factor, narrow bandwidth,high brittleness, low tensile strength, it is difficult to shape large-area components, and ultra-thin high frequency conversion.The device is not easy to process and other defects. In the 1970s, American R.ENewnham and LE.Cross and others began to treat eggs.In the study of composite materials, composite materials are based on a certain connection between piezoelectric ceramics and polymer materials.The volume ratio and the spatial geometric distribution of the space are combined. The most widely studied piezoelectric composites are 1-3 type piezoelectric composites, which have high sensitivity, low acoustic impedance, low mechanical quality factor and easy processing . Composite ultrasonic transducers can achieve multi frequency imaging, harmonic imaging and other non-linear imaging, and their performance is significantly better than that of piezoelectric ceramic materials. At present, some broadband conversions made of piezoelectric composite materials have been used. The energy device is applied to clinical multi-frequency imaging and harmonic imaging. However, due to the influence of the use of polymer materials in the composite transducer, the effective area of the piezo ceramic, the acoustic impedance and the complicated manufacturing process, the one-dimensional multi-array transducer is still fabricated to use piezoelectric ceramics.

3.piezoelectric single crystal transducer

Japan's Nomura began researching on piezoelectric crystal materials. In the mid-1990s, piezoelectric crystal materials have attracted wide attention from researchers due to their excellent piezoelectric properties. Currently, piezoelectric crystal transducers are followed by composite transducers. Its piezoelectric coefficient and electromechanical coupling coefficient are much higher than the commonly used PzT piezoelectric ceramic materials. The transducer array designed with piezoelectric crystal material has much higher sensitivity and bandwidth than piezoelectric ceramic transducers. In 1999, Toshiba Corporation of Japan developed a 3.5MHz PZNTgl/9 ultrasonic transducer, which achieved high resolution and strong penetrating power and was used in clinical practice. In 2003, the University of Southern California in the United States developed a high frequency single-element piezoelectric single crystal transducer made of sulphonate material (LiNbO3), which obtained a good penetration depth and image signal-to-noise ratio. However, since the single crystal growth process is much more complicated than the ceramic preparation process, piezoelectric monocrystalline films at a comparable for piezoelectric ceramics cannot be produced at present, and only a small number of piezoelectric single crystal transducers are used in the clinical applications.

4. wideband transducer

    Early markings on the ultrasound probe such as 2.5, 3.5, 5, 7, 10MHz and other operating frequencies generally refer to the heart frequency, which has a bandwidth of about 1 MHz, can be called a single-center frequency narrow-band transducer and is still large. which has a large loss of high frequency signal to the deep tissue echo, affecting the sharpness and sensitivity of the ultrasound image degree in the mid-1980s, based on the attenuation of ultrasound in biological tissues and their ultrasound maps.The influence of the image is the development of a broadband transducer, such as the center frequency of 3.5MHz effective bandwidth can reach about 3MHz transducer, which uses high frequency piezoelectric knock sensor to improve resolution when detecting superficial tissue, and The low frequency forms an echo signal with less attenuation, resulting in a sharper image display of the deep tissue structure.In the 1990s, variable frequency broadband transducers and ultra-wideband transducers were used in the clinical diagnostics.If the same transducer can be converted to generate ultrasonic waves with center frequency of 2.5, 3.5, and 6 MHz, the bandwidth of the band can reach more than 5MHz. Ultra-wideband transducers have been able to generate ultrasound from 1.8 to 12 MHz. Current The harmonic imaging technology widely used in bed is also developed on the basis of broadband transducers. Like technology. Since the wideband transducer is capable of receiving multiple harmonics generated by sound waves in the tissue, its package contains a large amount of human body information,which can improve the axial resolution of the image, and can improve the spirit of the ultrasound imaging system.