Ultracompact Gas Sensors Incorporating Quartz-Enhanced Photoacoustic Spectroscopy
This invention integrates a quartz oscillator into a photoacoustic device to allow for the detection of resonant acoustic waves, permitting sensitive detection of gases using an extremely small unit. Technology Photoacoustic spectroscopy (PAS) is an established domain of experimental physics based on the detection of sound waves generated in a medium upon absorption of modulated laser radiation. This invention is a new method using a high-finesse quartz oscillator (such as a frequency fork used in quartz watches) to detect resonant acoustic waves. It purports to perform sensitive photoacoustic spectroscopy of gases using an extremely small unit. This spectroscopic method is called Resonant Piezoelectric Detection (RPD).
Advantages Initial experiments show that RPD can reach or exceed a parts-per-million (ppm) detection limit. Unlike the PAS cavity, RPD sample cell can have an arbitrary shape because absorption is detected in the immediate vicinity of the TF. In addition, the proposed RPD technique uses low cost, mass-produced elements. The cost of a detector unit that includes a TF and a preamplifier based on a single-chip operational amplifier is estimated at less than $5; making the potential for this product unparalleled.
Potential Applications Rice’s resonant piezoelectric detection (RPD) can be used for chemical analysis of gas species, especially where sample volume is limited. Traditional PAS uses an acoustic cavity filled with a necessarily sizable volume of lossy medium such as air, which does not enable the signal to accumulate over ~200 cycles to satisfy the resonant conditions. In RPD, resonant signal enhancement is achieved by the low-loss quartz crystal instead of the absorbing medium. Thus, using a path length of ~0.5 mm, a weak gas absorption can be detected with RPD where it is practically impossible with traditional PAS or direct absorption spectroscopy.
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