Abstract
A study of the front-end electronics for quartz tuning forks (QTFs) employed as optoacoustic transducers in quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing is reported. Voltage amplifier-based electronics is proposed as an alternative to the transimpedance amplifier commonly employed in QEPAS experiments. The possibility to use differential input/output configurations with respect to a single-ended configuration has also been investigated. Four different architectures have been realized and tested: a single-ended transimpedance amplifier, a differential output transimpedance amplifier, a differential input voltage amplifier and a fully differential voltage amplifier. All of these amplifiers were implemented in a QEPAS sensor operating in the mid-IR spectral range. Water vapor in ambient air has been selected as the target gas species for the amplifiers testing and validation. The signal-to-noise ratio (SNR) measured for the different configurations has been used to compare the performances of the proposed architectures. We demonstrated that the fully differential voltage amplifier allows for a nearly doubled SNR with respect to the typically used single-ended transimpedance amplifier.
Highlights
Optical sensors are well established for real-time, in situ and non-invasive trace gas detection [1].They are widely exploited in different fields, such as breath analysis [2], environmental monitoring [3], industrial control [4] and explosive detection [5]
The use of an instrumentational implementation of a fully differential input, in which the quartz tuning forks (QTFs) is placed between the inverting and amplifier (AD623) [28] in the voltage input amplifier (Figure 2a) allows for the implementation of a non-inverting inputs of the amplifier and none of these inputs are tied to the local signal ground of fully differential input, in which the QTF is placed between the inverting and non-inverting inputs the signal amplifier
Four different architectures were tested for the front-end amplifier electronics of a QTF employed as an optoacoustic transducer in a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor
Summary
Optical sensors are well established for real-time, in situ and non-invasive trace gas detection [1]. The front-end electronics must be designed in order to collect the QTF signal as well as to keep the noise as low as possible With this aim, several architectures can be studied for enhancing the SNR. The quartz charge constant, i.e., the electric charges developed per applied stress, is 4.6 pC/N, while the voltage constant, which represents the electric field produced in the quartz per applied stress, results 118 V·m/N [19,20,21,22] These parameters characterize the piezoelectric properties of quartz and suggest that the QTF could have a low charge sensitivity but a high voltage sensitivity, and that the front-end electronics to be used is a voltage amplifier. QEPAS signal (corresponding to the maximum of the water absorption features) and the standard deviation of the normalized QEPAS signal acquired far from the absorption features
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