Applications of quartz tuning forks in spectroscopic gas sensing

TLDR

Quartz‑enhanced photoacoustic spectroscopy (QEPAS) employs a quartz tuning fork as a resonant acoustic transducer, offering immunity to environmental acoustic noise, a simple detection module, and the ability to analyze sub‑milliliter gas samples, as summarized by recent studies. The paper outlines future developments of the QEPAS technique. The authors analyze noise sources and tuning‑fork properties under varying gas pressure, temperature, and composition, conduct a long‑term stability study of an ammonia sensor, and describe the architecture of an autonomous QEPAS‑sensor controller. They report a sensitivity of 5.4 × 10⁻⁹ cm⁻¹ W⁻¹/² Hz, comparable to recent results, and demonstrate very low sensor drift that permits data averaging over more than three hours of continuous measurements.

Abstract

A recently introduced approach to photoacoustic detection of trace gases utilizing a quartz tuning fork (TF) as a resonant acoustic transducer is described in detail. Advantages of the technique called quartz-enhanced photoacoustic spectroscopy (QEPAS) compared to conventional resonant photoacoustic spectroscopy include QEPAS sensor immunity to environmental acoustic noise, a simple absorption detection module design, and its capability to analyze gas samples ∼1mm3 in volume. Noise sources and the TF properties as a function of the sampled gas pressure, temperature and chemical composition are analyzed. Previously published results for QEPAS based chemical gas sensing are summarized. The achieved sensitivity of 5.4×10−9cm−1W∕√Hz is compared to recent published results of photoacoustic gas sensing by other research groups. An experimental study of the long-term stability of a QEPAS-based ammonia sensor is presented. The results of this study indicate that the sensor exhibits very low drift, which allows data averaging over >3h of continuous concentration measurements. Architecture and practical implementation of autonomous QEPAS-sensor controller electronics is described. Future developments of QEPAS technique are outlined.