Mimicking the olfactory system by a thickness-shear-mode acoustic sensor array

Mimicking the mammalian olfactory system by an array of twelve thickness-shear-mode (TSM) acoustic wave sensors with different adsorptive materials to form an artificial odour-sensing system has been investigated. The adsorptive materials chosen include polyethylene glycol-20M, hexadecyltriphenyl phosphonium iodide, N-(2hydroxylbenzyl) dodecylamine, tween 65, dinonyl phthalate, polyethylene glycol 400-monostearate, epoxy resin, tri-n-octylphosphinoxid, di-iso-octyl phthalate, polyethylene glycol-6000, thionalid and dimethylpropaneldiol succinate. The frequency shift data obtained from the sensor array responding to the odours originated from different groups of organic compounds such as ketones (acetone, butanone, acetophenone, cyclohexanone, and acetylacetone), esters (methyl acetate, ethyl acetate, n-propyl acetate, and n-butyl acetate), and aldehydes (formaldehyde, benzaldehyde, glyoxal and furfural) are transformed to relative values to compensate the effect of the variation of the actual coating frequency shift, Delta f. The relative frequency shift data matrices are subjected to modified principal component analysis (MPCA) treatment with or without data preprocesssing. The odours of different organic molecule samples are easily recognized from the two-dimensional displays of the first two principal components. The discrimination of aromas originated from different essential oils from France (Adoucissant TM663, Atlantic TM3387, and Spat Tacus TM5970) and different fruits such as apples, bananas, oranges, and pears is also possible.