Magnetoacoustic Spectroscopy

LumaSense leverages Magnetoacoustics to measure oxygen. Because Oxygen does not absorb infrared light, it cannot be measured by Photoacoustic Spectroscopy (PAS). However, if an alternating magnetic field is applied to a gas sample which contains Oxygen, the gas will expand and contract causing a pressure wave proportional to the concentration of Oxygen present. In the Magnetoacoustic detector (MA), the frequency at which the magnetic field oscillates is different to the pulsation frequencies of the incident infrared light in the PAS-chamber, so the resulting Oxygen signal can be detected by the same microphone. Theoretically, this gives an absolute measurement of Oxygen concentration. However, in order to obtain the same high degree of accuracy as with PAS, it is necessary to compare this signal to a reference signal. 

This reference signal is used to cancel out measurement errors caused by the magnetic field itself. In the MA, the inlet gas and Oxygen reference gas are united in the same field, but the corresponding signals are detected by separate microphones. The pressure wave caused by Oxygen present in the inlet gas sample is detected by the same microphone that detects the PAS signal; the signal arising from the reference gas is detected by a second microphone. Because the amount of Oxygen in the reference sample is known (20,95%), the reference signal can be compared to the signal from the inlet gas sample to determine the absolute concentration of Oxygen present. The short rise time of this magnetoacoustic technique allows real-time Oxygen monitoring.