ABSTRACT
Ultrasonic measurement is a promising, nondestructive sensing method of characterizing materials by transmitting mechanical waves at frequencies above 20 kHz through a material, and investigating the characteristics of the transmitted or re–ected ultrasound waves. Offering advantages including nondestructiveness, rapidity, relatively low cost, and potential for automatic application, ultrasonic techniques provide a very useful and versatile method for investigating the physical properties of materials. Ultrasonic waves may be re–ected and transmitted when they pass from one
7.1 Introduction .................................................................................................. 177 7.2 Principles ...................................................................................................... 178
7.2.1 Propagation of Ultrasound ................................................................ 178 7.2.2 Acoustic Impedance ......................................................................... 180 7.2.3 Re–ection and Transmission ............................................................. 180
7.3 Device and Apparatus ................................................................................... 181 7.3.1 Ultrasonic Transducer ....................................................................... 181 7.3.2 Ultrasound Testing Technique .......................................................... 189
7.3.2.1 Pulse-Echo Method ............................................................ 189 7.3.2.2 Through-Transmission Method .......................................... 190 7.3.2.3 Doppler Method ................................................................. 192 7.3.2.4 Ultrasound Data Displays .................................................. 192 7.3.2.5 Noncontact Ultrasonic Measurement................................. 194
7.4 Applications .................................................................................................. 196 7.4.1 Determination of Fruit Firmness by Nondestructive Ultrasonic
Measurement ..................................................................................... 197 7.4.2 Nondestructive Measurement of Cheese Texture Using
Ultrasound ........................................................................................ 199 7.4.2.1 Through-Transmission Measurement ................................ 201 7.4.2.2 Pulse-Echo Measurement .................................................. 201 7.4.2.3 Noncontact Measurement ..................................................203
