TRANSMISSION OF SOUND THROUGH THIN PLATES

The transmission of high frequency sound through plates of brass and nickel has been studied for angles of incidence ranging from 0 to 70 degrees, using effective plate thicknesses varying from one-twentieth of a wave-length to one wave-length. In addition to strong transmissions in the region below the normal critical angle, very sharp and intense transmission maxima are observed at angles of incidence greatly in excess of the critical angle. These transmission maxima fall within three clearly denned angular regions: (i) angles between zero and the critical angle for longitudinal waves; (ii) angles between the critical angle for longitudinal waves and the critical angle for transverse waves; and (iii) angles above the critical angle for transverse waves. In Regions (i) and (ii) the observed data are in satisfactory agreement with a recent theory advanced by Reissner, and good values of the elastic constants are obtained. By an extension of Lamb's theory for flexural vibrations in bars the results in Region (iii) can be interpreted.