QEPAS Sensor Based on the Tracking of the Photoacoustic Induced Frequency Shift of a Tuning Fork Maintained in Self-Sustained Oscillation by Electrical Excitation

The quartz tuning fork (QTF) is a piezoelectric transducer with a high quality factor that was successfully employed in sensitive applications such as atomic force microscopy or Quartz-Enhanced Photo-Acoustic Spectroscopy (QEPAS). The variability of the environment (temperature, humidity) can lead to a drift of the QTF resonance. In most applications, regular QTF calibration is absolutely essential. Because the requirements vary greatly depending on the field of application, different characterization methods can be found in the literature. We present a review of these methods and compare them in terms of accuracy. Then, we further detail one technique, called Beat Frequency analysis, based on the transient response followed by heterodyning. This method proved to be fast and accurate. Further, we demonstrate the resonance tracking of the QTF while changing the temperature and the humidity. Finally, we integrate this characterization method in our Resonance Tracking (RT) QEPAS sensor and show the significant reduction of the signal drift compared to a conventional QEPAS sensor.

Download Full-text

Application of Micro Quartz Tuning Fork in Trace Gas Sensing by Use of Quartz-Enhanced Photoacoustic Spectroscopy

Sensors ◽

10.3390/s19235240 ◽

2019 ◽

Vol 19 (23) ◽

pp. 5240 ◽

Cited By ~ 2

Author(s):

Haoyang Lin ◽

Zhao Huang ◽

Ruifeng Kan ◽

Huadan Zheng ◽

Yihua Liu ◽

...

Keyword(s):

Photoacoustic Spectroscopy ◽

Tuning Fork ◽

Gas Sensing ◽

Modulation Depth ◽

Quartz Tuning Fork ◽

Acoustic Resonance ◽

Photoacoustic Signal ◽

Integration Time ◽

Sampling Volume ◽

Qepas Sensor

A novel quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a micro quartz tuning fork (QTF) is reported. As a photoacoustic transducer, a novel micro QTF was 3.7 times smaller than the usually used standard QTF, resulting in a gas sampling volume of ~0.1 mm3. As a proof of concept, water vapor in the air was detected by using 1.39 μm distributed feedback (DFB) laser. A detailed analysis of the performance of a QEPAS sensor based on the micro QTF was performed by detecting atmosphere H2O. The laser focus position and the laser modulation depth were optimized to improve the QEPAS excitation efficiency. A pair of acoustic micro resonators (AmRs) was assembled with the micro QTF in an on-beam configuration to enhance the photoacoustic signal. The AmRs geometry was optimized to amplify the acoustic resonance. With a 1 s integration time, a normalized noise equivalent absorption coefficient (NNEA) of 1.97 × 10−8 W·cm−1·Hz−1/2 was achieved when detecting H2O at less than 1 atm.

Download Full-text

Analysis of the Frequency Shift versus Force Gradient of a Dynamic AFM Quartz Tuning Fork Subject to Lennard-Jones Potential Force

Sensors ◽

10.3390/s19081948 ◽

2019 ◽

Vol 19 (8) ◽

pp. 1948

Author(s):

Chia-Ou Chang ◽

Wen-Tien Chang-Chien ◽

Jia-Po Song ◽

Chuang Zhou ◽

Bo-Shiun Huang

Keyword(s):

Frequency Shift ◽

Tuning Fork ◽

Equations Of Motion ◽

Quartz Tuning Fork ◽

Spring Constant ◽

Potential Force ◽

Jones Potential ◽

Lennard Jones ◽

The Relationship ◽

Sample Distance

A self-sensing and self-actuating quartz tuning fork (QTF) can be used to obtain its frequency shift as function of the tip-sample distance. Once the function of the frequency shift versus force gradient is acquired, the combination of these two functions results in the relationship between the force gradient and the tip-sample distance. Integrating the force gradient once and twice elucidates the values of the interaction force and the interatomic potential, respectively. However, getting the frequency shift as a function of the force gradient requires a physical model which can describe the equations of motion properly. Most papers have adopted the single harmonic oscillator model, but encountered the problem of determining the spring constant. Their methods of finding the spring constant are very controversial in the research community and full of discrepancies. By circumventing the determination of the spring constant, we propose a method which models the prongs and proof mass as elastic bodies. Through the use of Hamilton’s principle, we can obtain the equations of motion of the QTF, which is subject to Lennard-Jones potential force. Solving these equations of motion analytically, we get the relationship between the frequency shift and force gradient.

Download Full-text

HCl ppb-level detection based on QEPAS sensor using a low resonance frequency quartz tuning fork

Sensors and Actuators B Chemical ◽

10.1016/j.snb.2016.04.114 ◽

2016 ◽

Vol 233 ◽

pp. 388-393 ◽

Cited By ~ 35

Author(s):

Yufei Ma ◽

Ying He ◽

Xin Yu ◽

Cheng Chen ◽

Rui Sun ◽

...

Keyword(s):

Resonance Frequency ◽

Tuning Fork ◽

Quartz Tuning Fork ◽

Qepas Sensor

Download Full-text

The Coefficient of the Voltage Induced Frequency Shift Measurement on a Quartz Tuning Fork

Sensors ◽

10.3390/s141121941 ◽

2014 ◽

Vol 14 (11) ◽

pp. 21941-21949

Author(s):

Yubin Hou ◽

Qingyou Lu

Keyword(s):

Frequency Shift ◽

Tuning Fork ◽

Quartz Tuning Fork ◽

Shift Measurement

Download Full-text

Near-Infrared Quartz-Enhanced Photoacoustic Sensor for H2S Detection in Biogas

Applied Sciences ◽

10.3390/app9245347 ◽

2019 ◽

Vol 9 (24) ◽

pp. 5347

Author(s):

Fagang Zhao ◽

Yutong Gao ◽

Lin Yang ◽

Yuqing Yan ◽

Jiashi Li ◽

...

Keyword(s):

Laser Power ◽

Near Infrared ◽

Tuning Fork ◽

Signal Amplitude ◽

Quartz Tuning Fork ◽

Detection Sensitivity ◽

Integration Time ◽

Optical Source ◽

H2s Detection ◽

Qepas Sensor

A quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for H2S detection operating in near-infrared spectral range is reported. The optical source is an erbium-doped fiber amplified laser with watt-level optical power. The QEPAS spectrophone is composed of a quartz tuning fork with a resonance frequency of 7.2 kHz, a quality factor of 8500, and a distance between prongs of 800 µm, and two tubes with a radius of 1.3 mm and a length of 23 mm acting as an organ pipe resonator. With this spectrophone geometry, the photothermal noise contribution of the spectrophone was removed and the theoretical thermal noise level was achieved. The position of both tubes with respect to custom quartz tuning fork has been investigated as a function of signal amplitude, Q-factor, and noise of the QEPAS sensor when a high-power laser was used. Benefit from the linearity of the QEPAS signal to the excitation laser power, a detection sensitivity of 330 ppb for H2S detection was achieved at atmospheric pressure and room temperature, when the laser power was 1.6 W and the signal integration time was set to 300 ms, corresponding to a normalized noise equivalent absorption of 3.15 × 10−9 W cm−1/(Hz)1/2. The QEPAS sensor was then validated by measuring H2S in a biogas sample.

Download Full-text