Ultrasonic Band Gaps in Aggregates of Sintered Aluminum Beads

An experimental examination of the transmission power spectrum of a block of sintered aluminum beads is discussed. Periodic structures such as these have complicated dispersion curves that contain stop bands and pass bands. Thus the power transmission spectrum for the agglomeration of sintered beads is strikingly different than that for a solid aluminum block. The positions of the observed band gaps are shown to agree with theoretical predictions. The width of the bands is directly related to the sintering level and the corresponding coupling between beads. Unlike previous one‐dimensional work, the medium considered here is three dimensional. Also, the rare modes that may lie in the band gaps or those near the edges of the bands are expected to localize. Therefore, this sintered bead structure is a promising candidate for the discovery of localizing ultrasound. [Work supported by NSF.]