Method for measuring the resonant frequency of photoacoustic detector in the real-time mode

A sub-ppbv-level Acetone and Ethanol Quantum Cascade Laser Based Photoacoustic Sensor – Characterization and Multi-Component Spectra Recording in Synthetic Breath

“…Again, both additive and multiplicative characteristics of single and sum spectra could be verified among these measurements with synthetic breath which reinforces the assumption of constant relaxation efficiency. In terms of spectral reconstruction, i.e., both a quantification and separation of a measured sum spectrum into its individual components, the CO 2 content can be determined via the measured resonance frequency obtained by the ARMS (refer to [54] ). As the present humidity content is continuously monitored by a pTH -sensor (BME 680, Robert Bosch GmbH, Germany) within the measuring cell and the resonance shift coefficients of water and CO 2 were specified above, the present CO 2 content [ can be recalculated via where is the resonance frequency of the background signal (5049 Hz), the measured water concentration, the change in resonance frequency through water addition (5.4 Hz/%v- H 2 O) and the frequency coefficient regarding CO 2 (15.0 Hz/%v-CO 2 ), respectively.…”

“…Additionally, we applied an acoustic resonance monitoring system (ARMS) to the PAC as explained in [54] . This ARMS is based on a speaker sweep approach yielding resonance frequency and the -factor determination.…”

Wavelet-Based Machine Learning Algorithms for Photoacoustic Gas Sensing

“…The PAD was filled with a gas mixture to reach atmospheric pressure, following which it was sealed. The PAD structure is very close to the cell described in detail in [31]. The detector is also equipped with two electret microphones, one in the center of the acoustic channel.…”

“…This approach enables the measurement of the PAD's lowest resonant frequency in nearly real time (approximately 0.1 s) with an error margin of around ±0.1 Hz. More detailed information on the measurement technique can be found in [31]. Since the resonant frequency of the PAD is directly related to the speed of sound in the gas mixture it contains, the resonant frequency is significantly influenced by the temperature and composition of the mixture.…”

“…The ADC controller receives the electrical signals from the PAD, which allows one to set the required pulse repetition rate for OPO radiation. The alignment of the resonant frequency of the detector with the pulse repetition rate of the radiation source enables a substantial enhancement of the PAD signal [31].…”