Finite element simulation and development of a LED-based photoacoustic spectroscopy system for quality assessment of some food liquids

The photoacoustic method is a sensing technique resulting from combination of optical and ultrasonic methods. The photoacoustic effect is the product of local heating with absorption of light energy, instantaneous expansion of matter and generation of pressure and sound propagation in the matter. In this study, in order to develop a photoacoustic spectroscopy system with LED light sources, in the first step, the photoacoustic interaction with a cuvette filled with liquid was simulated using Comsol Multiphysics 5.5. In the second step, a photo-acoustic spectroscopy system with light sources at eight wavelengths from 395-940 nm was designed and constructed. Finally, in order to evaluate the photoacoustic system, three samples i.e. milk, water and olive oil were subjected to photoacoustic spectroscopy and the measurement results were compared with the simulation results for the same samples. The results showed that the intensity of the acoustic response of the samples at different wavelengths varied significantly with the light absorption coefficient, so that the maximum amplitude of the acoustic signal was obtained for milk, water and olive oil at the wavelengths of 450, 395 and 450 nm with values of 0.34, 0.22 and 0.74 Pa, respectively. This was in agreement with the simulation results in terms of relative differences. Moreover, the adulteration of adding water to milk at volume ratios of 5, 10, 15 and 20% was evaluated with the system and analyzed with principal component analysis (PCA) which showed a satisfactory discrimination of adulterated samples from pure milk. The system developed in this study can be used to assess the quality of food liquids.