| 摘要 |
<p>A method of establishing an ultrasonic standing wave in a fluid medium is described in which the standing wave is produced by an acoustic energy output along a path extending through the fluid medium, the frequency of said energy output being changed cyclically while maintaining an essentially constant mean frequency. The cyclic frequency change sweeps said energy output frequency between upper and lower limits that represent a difference of at least one half-wavelength at the mean acoustic frequency over the length of said path, so that a fully resonant standing wave appears in each cycle, regardless of transient ambient variations. For stability, the cycle time of the sweep is maintained substantially greater than the travel time of the acoustic energy output over the length of the path.</p> |
