Visualisation des ondes sonores et ultra-sonores par la méthode des striations

The method of striations can be used to observe directly sound waves of frequency 4000 c/s. By making the waves traverse certain products, e.g. glass wool, or by reflecting them from their surfaces, one can judge from photographs the relative importance of their transmission and reflection factors. One can even judge the efficacy of certain surfaces (ceilings of different relief forms like caissons and girders) from the point of view of their reflecting, absorbing and diffusing powers. The use of ultrasonic waves on models at appropriate scale permits the calculation of the role of the nature of the walls in an enclosure. Finally, reflexion of ultrasonics in air from a plane surface, observed either stroboscopically or under continuous illumination, can be used to investigate the formation of stationary waves parallel to the surface and to determine phase velocities greater than normal; so an excellent picture of the propagation of electromagnetic waves in a tube can be obtained.