Acoustic Particle-Size Analyzer for Planetary Exploration

An acoustic method of determining the size of loose particles has been developed at the breadboard level. This is intended as a precursor to a planetary flight instrument that can conduct grain-size analyses using a highly miniaturized sensor head requiring no complex sample processing or handling. When a particulate material (sand, dust) in actively being crushed, it emits a sound or acoustic signature that is diagnostic of the particle size distribution of the material, as well as the hardness of the grains. This principle hβas been applied in the breadboard development which has confirmed the ability of the technique to discriminate between samples based on their size distribution. A brief anecdotal comparison serves to illustrate the principle underlying the proposed instrument. It has probably been most people's experience that sugar spilled on a tabletop creates a distinctive crunching sound if a cup is pressed down onto it. But if flour is spilled on the tabletop, the same cup will generate only a muffled "squeaky" sound. The human ear can readily distinguish the sound of crushing sugar, salt, and flour without having to see what the cup is sitting on. In other words, this simple tabletop "experiment" can do first order grain-size discrimination by registering diagnostic acoustic signatures for each material. We are proposing to take the next, considerably more sophisticated step by replacing the human ear with highly sensitive acoustic transducers that can explore both audible and non-audible frequencies.