Nondiffracting bulk-acoustic X waves in crystals

The concept of nondiffracting waves is generalized to encompass bulk-acoust ic waves within crystalline media. We introduce acoustic Bessel beams and g eneralized X waves for anisotropic elastic materials. Detailed numerical pr edictions for propagation-invariant bulk-acoustic beams of various orders, and also X pulses, are presented for experimental verification. The materia l parameters used have been chosen appropriately for quartz, the most impor tant material for acoustic device applications.