Ultrasonic transducers

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Ultrasonic transducers

Introduction

Ultrasonic transducers

    Ultrasonic waves are useful for detecting and evaluating objects in any kind of medium: gas, liquid or solid, except for a vacuum. Ultrasonic waves have been a practical and powerful tool for several decades, particularly for medical diagnostics in hospitals and nondestructive testing in industry, because electromagnetic waves attenuate rapidly in the human body and metal objects. The safety of ultrasonic waves is, in general, high in comparison with X-rays, and practical measurements and imaging can be carried out with less expensive devices than other methods. The low propagation speed of ultrasonic waves is also a useful feature for measurement and imaging, since the time of flight can be easily used to estimate the distance between the object and the ultrasonic transducer, which can be used to create two-dimensional or even three-dimensional pictures. 

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    The propagation speed of ultrasonic waves ranges from 300 m/s to 10 000 m/s, which is much lower than electromagnetic waves, by the order of 10^ 4 to 10^6 . The speed of sound, for example, in air, in water and in iron is 340 m/s, 1500 m/s and 6000 m/s, respectively. This means that the frequency of an ultrasonic signal is lower than that of an electromagnetic one by the order of 10^4 to 10^6 for the same spatial resolution, and an ultrasonic waveform can be directly converted to digital code without frequency shifting. Consequently, sophisticated signal-processing techniques can be applied to enhance the sensitivity and resolution of ultrasonic systems. The phased-array technique and dynamic control of the focal point are commonly used in medical ultrasonic instruments.

Biomedical Sensors and Instruments

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Table Of Contents

Part I Materials and design of ultrasonic transducers

1 Piezoelectricity and basic configurations for piezoelectric ultrasonic transducers

1.1 Introduction 3

1.2 The piezoelectric effect 4

1.3 Piezoelectric materials 13

1.4 Piezoelectric transducers 20

1.5 Summary, future trends and sources of further information

2 Electromagnetic acoustic transducers2.1 Introduction 36

2.2 Physical principles 36

2.3 Lorentz-force-type transducers 41

2.4 Magnetostriction-type transducers 60

2.5 Conclusion

3 Piezoelectric ceramics for transducers

3.1 The history of piezo electrics 70

3.2 Piezoelectric materials: present status

4 Thin-film PZT-based transducers

4.1 Introduction 117

4.2 PZT deposition using the hydrothermal process 118

4.3 Applications using the bending and longitudinal vibration of the d 31 effect

4.4 Thickness-mode vibration, d 33 140

4.5 Epitaxial film 150

4.6 Conclusions

5 High-Curie-temperature piezoelectric single crystals of the Pb(In 1/2 Nb 1/2 )O 3 –Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 ternary system

5.1 Introduction 154

5.2 PIMNT ceramics 157

5.3 PIMNT single crystals grown by the flux method 163

5.4 PIMNT single crystals grown by the Bridgman method 165

5. 5 Recent research into PIMNT single crystals and their applications 175

5.6 Future prospects and tasks 177

5.7 Conclusions

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