Devices incorporating phonon filters

DETAILED DESCRIPTION Much to our surprise, we discovered that phonons can be transmitted efficiently through a plurality of interfaces without debilitating conversion of the phonons to heat.
In one experiment we demonstrated that high frequency (200-300 GHz), extremely short wavelength (300-200 Angstroms) phonons could be made to propagate through a 50-period acoustic superlattice of alternating layers of GaAs and AlGaAs, a structure which includes 101 interfaces in the superlattice alone.
By making the layers of materials having different acoustic impedances (Z) and by making each layer of thickness t=.
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o /4, we were also able to build a phonon filter which selectively reflected phonons of wavelength .
lambda.
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o.
As a consequence, the reflected phonons represent a quasi-monochromatic source which could be used for imaging, spectrographic or other applications.
Alternatively, the superlattice layers may be made of different acoustic impedances but of thickness t=.
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o /2, in which case phonons of wavelength .
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o are selectively transmitted through the superlattice and represent a quasi-monochromatic source.
An interesting application of the reflection mode embodiment is an acoustic spectrometer in which the phonons from a phonon source are reflected from an acoustic superlattice to a plurality of detectors arranged in tandem.
The detectors receive phonons of different wavelengths .
lambda.
depending on the angle of incidence of the phonon wave with the normal to the superlattice.
Accordingly, which detectors exhibit output signals determines the spectral content of the phonon source.
In another embodiment of the spectrometer, a single detector is employed, but the phonon source is scanned to determine its spectral content.