Vibrationdata.com Tutorials - The tutorials and course materials require a username and password which can be obtained with an annual subscription fee.
Ultrasonics - Dedicated to the art and science of ultrasonic nondestructive testing and allied fields.
Super High Resolution Ultrasonic Measurement System - 5-micro-meter resolution measurement by non contact system in the air; RS-232 interface; Thickness, Deviation, Distance, Level of any kind of material.
How Stuff Works: How Ultrasound Works - Illustrated narrative takes you inside the ultrasound machine and shows you how this technique is used to look inside you.