Vibrations with frequencies in the range of 2.0 X
10^5 cycles per second. Ultrasonic vibrations may
be generated by applying alternating electric
current to quartz, tourmaline, or Rochelle salt,
or by the effect of oscillating magnetism on a rod
of magnetic material immersed in a liquid.
Ultrasonics are used to seal documents within
polyester foils by fusing. (195 )