Spatial phase‐inversion technique for parametric source with suppressed carrier.

Abstract

Two planar projectors with the identical rectangular apertures are placed side by side. Both the projectors are radiating bifrequency ultrasound beams of finite amplitude in the air. The frequencies are 40 and 42 kHz but the initial phases are different. Especially, two extreme cases are considered: one is conventional in‐phase driving, and the other is phase inversion driving. Sound pressure profiles were measured along and across the sound beam axis for the primary waves and the difference frequency wave of 2 kHz. The second and third harmonic components of the difference frequency were measured as well. Obviously, the pressure levels of the primary waves were suppressed considerably near the beam axis due to phase cancellation when the driving signals were out‐of‐phase by 180 degrees. The beam pattern of the difference frequency was, however, almost the same as the case where the signals were in phase. Interestingly, the pressure levels of the harmonics were reduced more than ten decibels. The validity of experimental results has been supported by good agreement with the theoretical predictions based on the Khokhlov‐Zabolotskaya‐Kuznetsov model equation. [Work supported by JSPS.]