a process whereby the olfactory response of a gas chromatograph , equipped with a focused surface acoustic wave interferometer integrating detector is converted to a visual image for the purpose of performing pattern recognition . as volatile analytes exit a gas chromatography column a surface acoustic wave interferometer is used to monitor the condensation and re - evaporation of these analytes by periodically measuring the resonant frequency of the interferometer . a time varying output parameter is then converted to a polar display . this form of electronic nose provides a recognizable visual image of specific vapor mixtures containing possibly hundreds of different chemical species . because the method provides a means of adapting and learning to recognize new vapors using these images , it is a useful method for testing chemical compositions as well as the vapors associated with bacteria and human disease .