Acoustic chemometrics—from noise to information

Acoustic chemometrics is presented as an interdisciplinary approach, covering diverse fields including applied engineering, electronics, signal analysis 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-dependent `acoustic signalsʹ (by relevant technical means), which—followed by some form of pertinent signal analysis—are subjected to chemometric data analysis. 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 applied acoustic chemometrics—non-invasive monitoring of pneumatic gas/particle transportation processes. Many of our acoustic chemometrics forays so far have specifically been oriented towards `listening onlyʹ, exclusively relying on passive sensors: we are deliberately only interested in utilising whatever complex acoustic signals may be discerned from `noisyʹ processes/products—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 acoustic input impulse or signal with which to excite, or probe, the system under investigation (`active listeningʹ, `active sensorsʹ, transducer technology). While many of our first generation applications thus for the most part have had the character of strictly empirical calibrations in which the detailed physical/chemical signal–response relation need not per force be known, we have also started parallel work of a more basic research nature, aimed at elucidating the fundamental mechanisms behind the satisfactory first achievements of acoustic chemometrics.