Читать книгу Ferroic Materials for Smart Systems - Jiyan Dai - Страница 12

An example of smart system using piezoelectric material is the distance radar system in a car or a sonar system in submarines as shown in Figure 1.6, where the key sensing element is based on piezoelectric material to realize the conversion between electrical energy and acoustic energy for sending and receiving sound waves. Other application examples of piezoelectric devices include active damping system, micro‐scanning system in scanning probe imaging instrument (such as AFM), force sensor, accelerometer, energy harvesting, etc.

Figure 1.6 Piezoelectric materials‐based sonar system for car (a) and submarine (b).

Medical ultrasound imaging system with piezoelectric material as the transducer to convert electrical and acoustic energies is another very good example of device application where the piezoelectric material plays the roles of sensing and actuating functions. Figure 1.7 shows photos of ultrasound transducers developed in our group. Knowledge in ultrasound transducer fabrication, characterization, and applications will be intensively introduced in Chapter 6.

Figure 1.7 (a) Transducers and (b) B‐mode image of a wire phantom acquired with PolyU‐made array ultrasound transducer.

A very new application example is piezoelectric‐based fingerprint ID system in mobile phone. The currently used finger identification system is based on capacitance measurement to obtain two‐dimensional (2D) information of fingerprint, but it faces the problem of difficulty to identify the fingerprint when the finger is dirty or wet. Ultrasound fingerprint identification system based on piezoelectric ultrasonic transducer and imaging system can obtain a three‐dimensional image of fingerprint with a certain depth. This can overcome the problems of the current fingerprint identification system in most mobile phones. InvenSense, Inc. is one of the main suppliers of this solution, and Figure 1.8 is an illustration of the ultrasonic fingerprint system.

Figure 1.8 Illustration of concept of a ultrasonic transducer‐based fingerprint ID system based on complementary metal‐oxide‐semiconductor micro‐electro‐mechanical systems (CMOS‐MEMS) technology.