For the piezoelectric crystal, not only a mechanical source distribution at the surface, but an electrical source distribution also can excite the elastic wave fields.

对于压电晶体，不仅表面力源，而且表面电源分布也能激发弹性波场。

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Sound waves travel outward like balloons expanding around their source. The sound's power is distributed on the surface of the wave which increases with the square of the distance from its source.

声波的扩散就好比气球的膨胀，声波从声源向四周扩散，声音的能量也随着声波四散开来。

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