The Storage Echo in Piezoelectric Powders
A model is proposed to account for the long-lived “storage” echo observed in piezoelectric powders. We suggest that the two RF writing pulses burn holes in the frequency distribution of the powder grains such that the powder remembers the spectral density of the writing sequence. When the powder is subsequently excited with a weak reading pulse, the linear ringing response of the previously uniform population, now modified by the hole burning, produces the storage echo. At weak writing powers, the information is only written into grains preferentially oriented relative to the RF field, producing a storage echo which is sensitive to tapping and which has a cos2 θ angular dependence. At higher writing powers, the echo should become more isotropic and persist even after sieving the powder.
KeywordsAngular Dependence Rotation Model Resonant Excitation Hole Burning Uniform Population
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