Acoustic chemometrics - from noise to information

Acoustic chemometrics is presented as an interdisciplinary approach, coveri ng diverse fields including applied engineering, electronics, signal analys is and chemometrics. The objectives for acoustic chemometrics are manifold, but quantitative analysis (chemical/physical) and process monitoring plays a major role as does physical characterisation of products, machinery-and process states. Potential applications in many industry sectors abound. In one particular sense, acoustic chemometrics is simple: obtaining problem-de pendent 'acoustic signals' (by relevant technical means), which-followed by some form of pertinent signal analysis-are subjected to chemometric data a nalysis. In this context it is often the power of multivariate calibration that comes to the fore. Here we give one major exemplar of the use of appli ed acoustic chemometrics-non-invasive monitoring of pneumatic gas/particle transportation processes. Many of our acoustic chemometrics forays so far h ave specifically been oriented towards 'Listening only', exclusively relyin g on passive sensors: we are deliberately only interested in utilising what ever complex acoustic signals may be discerned from 'noisy' processes/produ cts-because we find this approach the most challenging e.g., in contrast to ultrasound approaches, in which one also is in control of an appropriate a coustic input impulse or signal with which to excite, or probe, the system under investigation ('active Listening', 'active sensors', transducer techn ology). While many of our first generation applications thus for the most p art have had the character of strictly empirical calibrations in which the detailed physical/chemical signal-response relation need not per force be k nown, we have also started parallel work of a more basic research nature, a imed at elucidating the fundamental mechanisms behind the satisfactory firs t achievements of acoustic chemometrics. (C) 1998 Elsevier Science B.V. AU rights reserved.