We report the successful realization of quartz-enhanced photo-acoustic (QEPAS) sensors employing quartz tuning forks (QTFs) with novel geometrical parameters. We investigated the influence of QTF sizes on the main resonator parameters, in order to identify the best design parameters optimizing the QTF figures of merit for optoacoustic gas sensing. To evaluate the QTF acousto-electric energy conversion efficiency, we operated the QEPAS sensors in the near- IR and selected water vapor as the target gas. QTFs are forced to resonate at both the fundamental and the first overtone vibrational mode frequencies. Our results shows that two QTF designs exhibit an higher quality factor (and consequently an higher QEPAS signal) when operating on the first overtone mode with respect to the fundamental one.
The paper presents results of investigation into properties of digital filters implemented in compliance with ANSI S1.11
Standard: Octave-Band and Fractional-Octave Band Analog and Digital Filters. The discussed solutions are digital one-third-octave IIR filters with Direct Form I topology. Performed simulations showed that the filters exhibit strong
problems with stability, especially in the case of low center frequency filters. Another problem clearly visible in all
investigated structures was poor attenuation at the frequencies above the passband. Although the filters were
implemented according to the ANSI standard, none of them met all of the requirements of the standard.