Abstract:This paper is a review of analog front-end circuitry used in photoacoustic equipment with microphone or piezoelectric detection. A block structure of the front end as well as detailed circuit diagrams of preamplifiers dedicated for piezoelectric sensors and measurement condenser and electret microphones are described. The presented circuits are optimized toward low-noise operation. Practical remarks regarding the design of the remaining analog blocks are also given. The analysis shows that it is possible to de… Show more
“…Quartz enhanced photoacoustic spectroscopy (QEPAS) is a very sensitive spectroscopic technique in which detection of gas absorption induced with a laser is performed with a quartz tuning fork (QTF) [1][2][3][4]. Preamplifiers for piezoelectric sensors are implemented as voltage amplifiers or charge transimpedance amplifiers [5]. Until recently all QTF amplifiers dedicated for QEPAS were based on a transimpedance configuration, ut quartz has quite a high voltage constant (118 V•m/N) and a low charge constant (4.6 pC/N), which results in good properties of the amplifiers based on the voltage configuration.…”
The signal-to-noise ratio (SNR) is a major factor that limits the detection sensitivity of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors. The higher the electrical signal level compared to the noise amplitude is the lower the concentration of gases that can be detected. For this reason the preamplifier circuits used in QEPAS should be optimized for low-frequency narrow-band applications. Moreover, special care should be taken when choosing a particular operational amplifier in either a transimpedance or voltage (differential) configuration. It turns out that depending on the preamp topology different operational amplifier parameters should be carefully considered when a high SNR of the whole QEPAS system is required. In this article we analyzed the influence of the crucial parameters of low-noise operational preamplifiers used in QEPAS applications and show the resulting limitations of transimpedance and voltage configurations.
“…Quartz enhanced photoacoustic spectroscopy (QEPAS) is a very sensitive spectroscopic technique in which detection of gas absorption induced with a laser is performed with a quartz tuning fork (QTF) [1][2][3][4]. Preamplifiers for piezoelectric sensors are implemented as voltage amplifiers or charge transimpedance amplifiers [5]. Until recently all QTF amplifiers dedicated for QEPAS were based on a transimpedance configuration, ut quartz has quite a high voltage constant (118 V•m/N) and a low charge constant (4.6 pC/N), which results in good properties of the amplifiers based on the voltage configuration.…”
The signal-to-noise ratio (SNR) is a major factor that limits the detection sensitivity of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors. The higher the electrical signal level compared to the noise amplitude is the lower the concentration of gases that can be detected. For this reason the preamplifier circuits used in QEPAS should be optimized for low-frequency narrow-band applications. Moreover, special care should be taken when choosing a particular operational amplifier in either a transimpedance or voltage (differential) configuration. It turns out that depending on the preamp topology different operational amplifier parameters should be carefully considered when a high SNR of the whole QEPAS system is required. In this article we analyzed the influence of the crucial parameters of low-noise operational preamplifiers used in QEPAS applications and show the resulting limitations of transimpedance and voltage configurations.
“…(2) A capacitive load (e.g., the input capacitance of an impedance converter) acts as a voltage divider. Observations (1) and (2) impose a design with a very high input impedance so that the signal amplitude and signals with low frequency are not lost [ 21 ]. (3) C s acts as a high source impedance at the low frequencies the device targets.…”
Lung sounds acquired by stethoscopes are extensively used in diagnosing and differentiating respiratory diseases. Although an extensive know-how has been built to interpret these sounds and identify diseases associated with certain patterns, its effective use is limited to individual experience of practitioners. This user-dependency manifests itself as a factor impeding the digital transformation of this valuable diagnostic tool, which can improve patient outcomes by continuous long-term respiratory monitoring under real-life conditions. Particularly patients suffering from respiratory diseases with progressive nature, such as chronic obstructive pulmonary diseases, are expected to benefit from long-term monitoring. Recently, the COVID-19 pandemic has also shown the lack of respiratory monitoring systems which are ready to deploy in operational conditions while requiring minimal patient education. To address particularly the latter subject, in this article, we present a sound acquisition module which can be integrated into a dedicated garment; thus, minimizing the role of the patient for positioning the stethoscope and applying the appropriate pressure. We have implemented a diaphragm-less acousto-electric transducer by stacking a silicone rubber and a piezoelectric film to capture thoracic sounds with minimum attenuation. Furthermore, we benchmarked our device with an electronic stethoscope widely used in clinical practice to quantify its performance.
Nowadays, various collaborations are creating immense machines to try to track and understand the origin of high-energy cosmic particles (e.g., IceCube, ANTARES, Baikal-GVD, P-ONE). The detection mechanism of these sophisticated experiments relies mainly on an optical signal generated by the passage of charged particles on a dielectric medium (Čerenkov radiation). Unfortunately, the dim light produced by passing particles cannot travel too far until it fades away, creating the necessity to instrument large areas with short spacing between sensors. The range limitation of the optical technique has created a fertile ground for experimenting on the detection of acoustic signals generated by radiation—thermoacoustics. Despite the increased use of the thermoacoustic technique, the instrumentation to capture the faint acoustic signals is still scarce. Therefore, this work has the objective to contribute with information on the critical stages of an affordable submersible thermoacoustic sensor: namely the piezoelectric transducer and the amplifying electronics. We tested the sensor in a
non-anechoic tank using an infrared (
) Q-switched Nd:YAG laser as a pulsed energy source to create the characteristic signals of the thermoacoustic phenomena. In accordance with the thermoacoustic model, a polarity inversion of the pressure signal was observed when transiting from temperatures below the point of maximum density of water to temperatures above it. Also, the amplitude of the acoustic signal displayed a linear relationship with pulse energies up to
(
). Despite the use of cost-effective parts and simple construction methods, the proposed sensor design is a viable instrument for experimental thermoacoustic investigations on high-energy particles.
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