Index of content:
Volume 106, Issue 3, September 1999
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
106(1999); http://dx.doi.org/10.1121/1.427166View Description Hide Description
The principle and the basic experimental results of the acoustic phase conjugation by nonlinear piezoelectricity are described. Acoustic phase conjugate waves at frequency ω are generated as a result of the interaction between incident acoustic waves at ω and pump electric fields at 2ω. An original explanation based on the modulation of soundvelocity by the electric field together with the concept of time grating is given. Coupling equations for the PZTceramics as a nonlinear material are derived. Experimental results of the soundvelocity modulation and the phase conjugate generation in nonlinear piezoelectricPZTceramics are shown. Amplitude reflectivity of the phase conjugation was 23% for the acoustic incidence at 10 MHz.
Acoustic phase conjugation by nonlinear piezoelectricity. II. Visualization and application to imaging systems106(1999); http://dx.doi.org/10.1121/1.427167View Description Hide Description
Phase conjugate waves of ultrasound were generated in PZTceramics through nonlinear piezoelectric interaction between an incident ultrasonic field at ω and an electric field at 2ω. The amplitude reflectivity of the phase conjugator was 23% at 10 MHz. The behavior of the incident waves and the phase conjugate waves were visualized by stroboscopic schlieren technique. Time-reversal property and the automatic correction of wavefront distortion in the phase conjugate process were confirmed. A scanning ultrasonic imaging system with a PZT phase conjugator has been built. This system was used to visualize test samples composed of solid plates and phase disturbers. Images by phase conjugate reflection yielded clear figures of the solid plates in spite of the existence of phase disturbers made of agarose gel with rough surfaces, whereas conventional images showed serious distortion.
Lamb wave characterization of the effects of long-term thermal-mechanical aging on composite stiffness106(1999); http://dx.doi.org/10.1121/1.427168View Description Hide Description
Lamb waves offer a promising method of evaluating damage in composite materials. The Lamb wavevelocity is directly related to the material parameters, so an effective tool exists to monitor damage in composites by measuring the velocity of these waves. The Lamb Wave Imager™ (LWI) uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. In this study, the time-of-flight as well as the elastic stiffnesses and for composite samples which have undergone combined thermal and mechanical aging are obtained. The samples examined include a baseline specimen with 0 cycles, specimens which have been aged 2350 and 3530 cycles at high strain levels, and one specimen aged 3530 cycles at low strain levels.
Mode-locking of acoustic resonators and its application to vibration cancellation in acoustic heat engines106(1999); http://dx.doi.org/10.1121/1.427169View Description Hide Description
Vibration induced in engine hardware by a working fluid can be very significant in high-power, high-amplitude acoustic heat engines, and is a serious impediment to their practical use. This vibration can cause fatigue and destruction of engine components as well as fuel lines, cooling lines, and sensor wires. The forces involved make anchoring such an engine to an “immovable” object impractical. Rigidly attaching two such engines together, and acoustically coupling them with a duct of such a length and diameter that the two engines mode-lock in antiphase (thus canceling the longitudinal vibration) appears to be an inexpensive, viable solution. This paper describes in detail experiments demonstrating the feasibility of this idea, and the underlying theory.