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Acoustic Detection Module for QEPAS![]()
ADM01 Acoustic Detection Module for QEPAS Zoomed-In View Through Window Quartz Microresonator Tubes See QEPAS Tab for More Details Related Items ![]() Please Wait ![]() Click to Enlarge Schematic Showing Module Interior Features
The Acoustic Detection Module is a photoacoustic cell designed to be easily built into a complete quartz-enhanced photoacoustic spectroscopy (QEPAS) system. The ADM01 module has an inlet and outlet allowing a gas sample to be pumped into the airtight chamber, which contains microresonator tubes and a custom quartz tuning fork (QTF). When an external laser source passes through the wedged windows, the tubes enhance the acoustic signal generated by the relaxation of the excited gas particles. This acoustic signal is transduced by the custom QTF and then amplified by the integrated high-gain preamplifier, enabling excellent signal-to-noise ratio. For more information on this technique, see the QEPAS tab. Gas Interface The Ø1/2" wedged windows for 200 nm - 11 µm are interchangeable to support additional wavelengths, and the microresonator tubes can be changed for measuring a different gas matrix than N2. Please contact us for assistance and details. Mounting Alignment
![]() Click to Enlarge QEPAS Diagram Photoacoustic spectroscopy is a technique based on the photoacoustic effect that is able to accurately detect trace gas concentrations for a wide variety of applications. Similar to laser absorption spectroscopy, a laser beam is sent through a gastight chamber to excite the target gas molecules. However, instead of detecting the absorption lines with an optical detector, the pressure wave generated by the relaxation of those molecules is detected by a transducer. In the case of quartz-enhanced photoacoustic spectroscopy (QEPAS), the transducer is a sharply resonant QTF. The high-Q acoustic resonance enables the detection of weak excitation within small volumes, bypassing the acoustic resonance restrictions of conventional methods. When the laser source is modulated with a sine wave, the induced pressure (sound) wave will have double the frequency as that of the light modulation; therefore, the laser source modulation must be at half of the resonance frequency of the quartz tuning fork (QTF). The resulting amplitude from the QTF is directly proportional to the concentration of trace gas in the sample. The QTF also has good environmental noise immunity due to its being an acoustic quadrupole, since the primary vibrational modes require the prongs to move away from each other to be piezoelectrically active. Sound from external sources has a longer wavelength than the prong separation and will cause the prongs to move in the same direction, resulting in no piezoelectric response. For more information on the science of QEPAS, please see the citation below. ADM01 Acoustic Detection Module P. Patimisco, A. Sampaolo, L. Dong, F. K. Tittel, and V. Spagnolo, "Recent advances in quartz enhanced photoacoustic sensing," Appl. Phys. Rev. 5, 011106 (2018).
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