The term acoustics can mean sound or the science of sound. It is in the latter sense that it is used here. Acoustics thus covers all aspects of sound waves, from low-frequency sound waves to ultrasound waves and beyond to what are simply called acoustic waves. As a means of sensing and actuation, acoustic waves have developed in a number of directions. The most obvious is the use of sound waves in the audible range for the sensing of sound (microphones, hydrophones, dynamic pressure sensors) and for actuation using loudspeakers. Another direction that has contributed greatly to the development of sensors and actuators is the extensive work in sonar - the generation and detection of acoustic energy (including infrasound and ultrasound) in water, initially for military purposes and later for the study of oceans and life in the oceans, and even down to fishing aids. Out of this work has evolved the newer area of ultrasonics, which has found applications in the testing of materials, material processing, ranging, and medicine. The development of surface acoustic wave (SAW) devices has extended the range of ultrasonics well into the gigahertz region and for applications that may not seem directly connected to acoustics, such as oscillators in electronic equipment. SAW devices are important not only in sensing, especially in mass and pressure sensing, but also in a variety of chemical sensors.

Chapter Contents:

• 7.1 Introduction
• 7.2 Units and Definitions
• 7.3 Elastic Waves and Their Properties
• 7.3.1 Longitudinal Waves
• 7.3.2 Shear Waves
• 7.3.3 Surface Waves
• 7.3.4 Lamb Waves
• 7.4 Microphones
• 7.4.1 The Carbon Microphone
• 7.4.2 The Magnetic Microphone
• 7.4.3 The Ribbon Microphone
• 7.4.4 Capacitive Microphones
• 7.5 The Piezoelectric Effect
• 7.5.1 Electrostriction
• 7.5.2 Piezoelectric Sensors
• 7.6 Acoustic Actuators
• 7.6.1 Loudspeakers
• 7.6.2 Headphones and Buzzers
• 7.6.2.1 The Magnetic Buzzer
• 7.6.2.2 The Piezoelectric Headphone and Piezoelectric Buzzer
• 7.7 Ultrasonic Sensors and Actuators: Transducers
• 7.7.1 Pulse-Echo Operation
• 7.7.2 Magnetostrictive Transducers
• 7.8 Piezoelectric Actuators
• 7.9 Piezoelectric Resonators and SAW Devices
• 7.10 Problems

Inspec keywords: hydrophones; surface acoustic wave devices; pressure sensors; loudspeakers; chemical sensors; microphones; actuators; ultrasonic transducers

Other keywords: microphones; sound waves; SAW devices; surface acoustic wave devices; loudspeakers; hydrophones; acoustic energy detection; dynamic pressure sensors; ultrasound waves; acoustic waves; chemical sensors; acoustic sensors; actuators

Subjects: Chemical sensors; Acoustic wave devices; Sensing devices and transducers; Transduction; devices for the generation and reproduction of sound; Chemical sensors; Sensing and detecting devices; Pressure measurement; Audio equipment and systems; Acoustical measurements and instrumentation; Pressure and vacuum measurement; Sonic and ultrasonic transducers and sensors