Jacques Y. Guigné

Acoustic beam levitation

A system is described that uses acoustic energy to position an object, which simplifies the application of forces in defined directions to the object and which enables the application of large forces to the object. The system includes transducers (21-24, FIG. 1) that direct separate acoustic beams (31-34) at the object (12), with the system constructed so the beams do not create standing wave patterns. A plurality of beams whose phases at the object are not closely controlled, are directed at different surface areas of the object so the beams do not substantially overlap at the object and create possible canceling effects. A very large force is applied to the bottom (124 FIG. 8) of an object lying in a gravity environment, by directing a plurality of beams (141-145) at the same area at the bottom of the object, and with the beams being controlled so they are substantially in phase at the object area. This plurality of beams can also replace one or all of the transducers (21-24, FIG. 1) to provide much stronger forces to position and manipulate the object. The wavelength (B, FIG. 2) of the acoustic energy in each beam is preferably much less than one-tenth the diameter (C) of the object in order to obtain efficient momentum transfer of energy to the object.

Near‐field acoustic intensity mapping using a closed surface

A procedure for constructing near‐field acoustic intensity maps is presented in this paper. The normally coincident measurement locations for the X, Y, and Z components about each grid point are repositioned in order to construct an imaginary box centered on the grid point. The position and orientation of these measurements define the surfaces of the box, and are used to estimate the intensity vector at box center. This process is repeated at each grid point in the plane of interest. The technique allows a statistical assessment to be made of the intensity map’s reliability without making assumptions about the nature of the acoustic field.

Stationarity of acoustic intensity measurements on steel plates

The problem of identifying reproducible frequency bands useful for the nondestructive evaluation of steel plates using the dynamic acoustical intensity scanning concept (DAIS) is addressed. Reproducible frequency bands are essential so that subsequent changes in sound intensity patterns can confidently be attributed to structural changes rather than to random fluctuations. A number of evaluation methods are tried. Stationary frequency bands are identified by all methods in the range of 100–4000 Hz. The most sensitive and practical evaluation method is deemed to be the comparison of intensity versus time data collected separate from the plate scans. This method is accurate, convenient, and can be automated to exclude all unwanted frequency bands during testing. The remanent intensity factor technique, while useful in identifying stationarity, is less sensitive and more difficult to implement.

Dynamic mechanical and acoustic characterization of a PVC‐based commercial damping elastomer.

Experiments carried out on a PVC‐based commercial damping elastomer, Isodamp C‐1002, are used to illustrate a forced vibration, nonresonant method for the determination of complex modulus in the frequency range 10 Hz–10 kHz, using tensile and compressive excitation. For tensile excitation, a simple model was successful in interpreting the data up to the resonance frequency of the sample. Compressive excitation, on the other hand, required a model that incorporated the inertial mass acting on the force transducer; however, interference from sample resonance was excluded. Sources of error in both cases could be traced to the phase angle, which is sensitive to resonance phenomena, and low signal to noise ratio. Transmission loss and echo reduction measurements were carried out on immersed 1‐×1‐ft samples in the frequency range 4–100 kHz using a narrow beam parametric array source to minimize edge diffraction and tank reverberation effects.