Zal N. Sanjana

Method and apparatus for selective transmission and reflection of sound through a solid

A device is disclosed which allows an object to be tuned to an incoming sound wave magnitude and wavelength, such that the sound wave will alternatively be passed therethrough without detectable reflection or be completely reflected. The apparatus is intended to be mounted within a hollow object and adjust the perceived distance between the exterior walls of that object to mimic a single thick wall. A signal processing means is supplied which detects the sound wave magnitude and wavelength impinging on the wall facing the sound wave source. The wavelength is passed to the signal processing means, which transmits a complimentary signal to the second wall of the hollow object. The complimentary signal allows the hollow object to resonate as a whole as if it were a solid of a thickness much different from its actual thickness, allowing the sound wave to pass undisturbed therethrough or be reflected therefrom.

Quasi-residual strain and moduli measurements in materials using embedded acoustic waveguides

Following the processing and manufacture of resin and composite parts and during their lifetime, the distribution of internal residual strain and any variations in moduli are generally unknown. Real-time information on these parameters would be valuable for improving material performance and reliability. It is believed that measurements related to material residual stresses or strain and moduli can be obtained by measuring the longitudinal wave velocities within acoustic waveguides (AWG) embedded within a material. The concept is that the wave velocities within embedded AWG are related to the material bulk modulus, density and Poissons Ratio which are all in some degree related to the material state of cure, and finally the internal residual stresses. Based on this concept it is shown that the AWG of different diameters embedded within the same resin part of uniform internal stress distribution, the AWG wave velocities should vary in relation to the square root of the AWG diameter. Experimental results using AWG of 5, 10, 16, 20, 40 and 62 mil diameter Nichrome embedded within Shell 815 clear resin with optically measured uniform strain, demonstrate a direct relationship between AWG velocities and the square root of the AWG diameter. Consequently, it is reasoned that for a part with several embedded AWG, each of the same diameter, then differences in the AWG velocities would yield information on differences in the residual strain and moduli within the part.

Attenuation of Ultrasound by Hollow Ceramic Spheres Embedded Within a Curing Resin

The basic technology of using embedded acoustic waveguides (AWG) for cure and NDE monitoring of resins and composite materials has evolved[1–11] over the last forty years. A recent paper[11] describes new applications of AWG in which acoustic wave transmissions between two embedded waveguides allows cure monitoring of large areas of a composite panel and also, in principle, the sensing of voids occurring during curing (simulated by burying hollow ceramic spheres within a composite panel). A surprising result was the system sensitivity, as the presence of only 0.16% by volume of hollow ceramic spheres could be detected. This result prompted the more detailed study reported here of ultrasound attenuation by voids (hollow ceramic spheres) embedded within a curing resin.