| Popis: |
An ‘acoustic fiber’, analogous to optical fiber, is presented as a means of long-distance data and energy transfer. Low-loss axial guided waves are produced along a cable-like waveguide, which is composed of a solid core and a cladding layer, where the cladding’s acoustic speeds of sound, both longitudinal and transverse, exceed those of the core. A similar condition exists in glass fiber optic cables consisting of a core surrounded by a cladding of lower index of refraction. This results in total internal reflection of light at the core-cladding interface and effective confinement of light to the core. A specific acoustic waveguide construction is analyzed, composed of an aluminum cladding with longitudinal wave speed of 6.198 km/s and shear wave of 3.122 km/s and copper core with longitudinal speed of 4.505 km/s, and shear speed of 2.164 km/s. Finite element simulations show that a guided wave mode that is confined largely to the core exists and is capable of propagating long distances with very little loss to the surroundings. A 6 mm diameter aluminum-cladded copper core (2 mm diameter) fiber was found to have a propagation loss of 0.023 dB/m when operating at 2 MHz predict (neglecting material attenuation). When including material attenuation, the same waveguide produced a propagation loss of 0.24 dB/m. Similarly, a 12 mm cladding with 4.8 mm core at 1 MHz had losses of 0.10 dB/m, and a 22 mm diameter cladding with 9 mm core at 500 kHz had losses of 0.062 dB/m. Relationships were found between frequency, total diameter and core diameter yielding the highest efficiencies. The minimum total dimension of an aluminum-clad-copper acoustic fiber was found to have an inverse relationship with frequency. The optimum ratio of core to total diameter was about 0.45 but between values of 0.35 and 0.5, attenuation was relatively constant (insensitive to frequency). Outside of that range, attenuation climbed rapidly. Due to this property, attenuation in properly designed fibers should always be dominated by, and roughly equivalent to, the material attenuation rather than attenuation due to leakage. |
