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. 2025 Feb 5;25(3):946.
doi: 10.3390/s25030946.

A Highly Sensitive Light-Induced Thermoelastic Spectroscopy Sensor Using a Charge Amplifier to Improve the Signal-to-Noise Ratio

Hanxu Ma  1   2 , Shunda Qiao  1   2 , Ying He  1   2 , Yufei Ma  1   2
Affiliations

A Highly Sensitive Light-Induced Thermoelastic Spectroscopy Sensor Using a Charge Amplifier to Improve the Signal-to-Noise Ratio

Hanxu Ma et al. Sensors (Basel). .

Abstract

A highly sensitive light-induced thermoelastic spectroscopy (LITES) sensor employing a charge amplifier (CA) is reported for the first time in this invited paper. CA has the merits of high input impedance and strong anti-interference ability. The usually used transimpedance amplifier (TA) and voltage amplifier (VA) were also studied under the same conditions for comparison. A standard commercial quartz tuning fork (QTF) with a resonant frequency of approximately 32.76 kHz was used as the photothermal signal transducer. Methane (CH4) was used as the target gas in these sensors for performance verification. Compared to the TA-LITES sensor and VA-LITES sensor, the reported CA-LITES sensor shows improvements of 1.83 times and 5.28 times in the minimum detection limit (MDL), respectively. When compared to the LITES sensor without an amplifier (WA-LITES), the MDL has a 19.96-fold improvement. After further optimizing the gain of the CA, the MDL of the CA-LITES sensor was calculated as 2.42 ppm, which further improved the performance of the MDL by 30.3 times compared to the WA-LITES. Additionally, long-term stability is analyzed using Allan deviation analysis. When the average time of the sensor system is increased to 50 s, the MDL of the CA-LITES sensor system can be improved to 0.58 ppm.

Keywords: charge amplifier; light-induced thermoelastic spectroscopy (LITES); methane (CH4) detection; minimum detection limit (MDL); quartz tuning fork (QTF).

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
The principle of LITES technique.
Figure 2
Figure 2
The diagram of three different amplifiers (a) TA. (b) VA. (c) CA.
Figure 3
Figure 3
The scheme of composite experimental circuit board for three amplifiers.
Figure 4
Figure 4
The simulated absorption spectra of different gasses at 6020–6080 cm−1.
Figure 5
Figure 5
The characteristics of the DFB diode laser. (a) Wavelength output characteristics. (b) Power output characteristics.
Figure 6
Figure 6
Experimental schematic of the LITES sensor.
Figure 7
Figure 7
Frequency response characteristics of the used QTF.
Figure 8
Figure 8
The relationship between the modulation depth and 2f signal for the LITES sensor.
Figure 9
Figure 9
The 2f peak signals of WA-LITES, TA-LITES, VA-LITES, and CA-LITES sensors.
Figure 10
Figure 10
The noise level at pure N2 environment. (a) WA-LITES sensor. (b) TA-LITES sensor. (c) VA-LITES sensor. (d) CA-LITES sensor.
Figure 11
Figure 11
Concentration response for CA-LITES sensor. (a) 2f signal shapes. (b) 2f signal peak as a function of CH4 concentration.
Figure 12
Figure 12
The noise of CA-LITES sensor at pure N2 environment after optimizing the gain.
Figure 13
Figure 13
Allan deviation analysis of the CA-LITES sensor.
See this image and copyright information in PMC

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