| 摘要 |
<p>The bifocal ultrasonic transmitter lens for pulse-echo operation consists of an outer ring-type resonator (1) in the centre of which is a concentric circular resonator (2). A combination lens assembly (3) is positioned in front of the two resonators. The lens has two spherical surfaces of different curvature (6, 7) so that their focal lengths are also different. The diameter of the central face is equal to or less than the diameter of the central resonator. The separate resonators may be driven with the same or different frequencies. For phase correction, delay may be introduced in the feeder or a mechanical phase-shifting device may be fitted to the lens itself. This takes the form of a step (4) at the outer edge of the central lens.</p> |
