Simultaneous multiple synchronous detection in photoacoustic measurements

Abstract.Photoacoustic detection of multiple compounds can be done in at least a few ways. One of the simplest methods is performing sequential measurements at selected wavelengths at which the compounds under detection would absorb. The main disadvantage of the method is relatively long time of the measurements – proportional to the number of wavelengths at which the measurements are performed. Time of the measurements can be significantly shortened e.g. by means of a simultaneous detection at a few light wavelengths, intensity of each modulated with a different frequency. Typical approach to implementation of such a setup requires use of a corresponding number of synchronous detectors. The paper presents a solution based on a single A/D converter and programmable logic circuit that implements high precision, simultaneous, synchronous detection of a few signals of different frequencies. The discussed equipment is capable of simultaneous recording of shape of all these signals independently. Strongly reduced hardware concept results in low cost and small size of the device.