Integrated Methane Sensor Prototype Based on H-QEPAS Technique with a 3D-Printed Gas Chamber

Abstract

In the paper, a heterodyne quartz-enhanced photoacoustic spectroscopy (H-QEPAS)-based integrated methane (CH₄) sensor prototype is reported. The CH₄ absorption line located at 1650.96 nm was selected as the target spectral line. The design features an integrated, 3D-printed gas chamber for reduced size and weight. To realize the coordinated operation of each hardware component, a control program was designed based on LabVIEW platform, enabling the adjustment of various hardware parameters. The piezoelectric signal generated by the quartz tuning fork (QTF) was amplified via a trans-impedance amplifier (TIA), acquired by a data acquisition card (DAQ), and then transmitted to a virtual lock-in amplifier (LIA) on the PC terminal for processing. The dimensions of the integrated CH₄ sensor prototype are 33 cm in length, 27 cm in width, and 15 cm in height. The final test results demonstrate that the sensor prototype exhibits an excellent concentration linear response, with a detection limit of 26.72 ppm and a short detection time of approximately 4 s.

1. Introduction

Monitoring methane (CH₄) is essential due to its significant environmental impact and widespread industrial relevance. On one hand, it identifies early explosion risks of CH₄ in scenarios such as coal mines and gas infrastructure [1,2,3,4]. On the other hand, it aids environmental protection by locating emission sources to curb CH₄ emissions [5,6,7,8]. It not only reduces energy waste resulting from natural gas leakage but also facilitates the evaluation of CH₄ recyclability through concentration detection [9,10,11,12]. Therefore, there is an urgent need for alternative methodological frameworks to achieve rapid detection of CH₄.

The method for gas detection has witnessed substantial advancements, with a diverse array of approaches having been developed [13,14,15,16,17,18,19]. Laser absorption spectroscopy has provided robust support for gas detection, attributed to its superior detection stability, remarkable adaptability to hazardous measurement environments, and inherent capability of enabling remote online monitoring [20,21,22]. As a technique belonging to the category of laser absorption spectroscopy, photoacoustic spectroscopy (PAS) [23,24,25,26,27] determines the concentration of a target gas by measuring the intensity of the acoustic waves it generates upon light absorption. Photoacoustic gas sensors have been successfully deployed in a variety of real-world monitoring scenarios, demonstrating their practicality beyond laboratory environments. Commercial systems based on photoacoustic spectroscopy are widely used for applications such as CH₄ leak detection in natural gas infrastructure, industrial safety monitoring of combustible gases, greenhouse gas emission assessment, and environmental compliance monitoring. These systems highlight the strong demand for sensitive, selective, and reliable gas sensors capable of operating under field conditions. Common acoustic wave transducers in PAS include microphone and quartz tuning fork (QTF) [28,29,30,31]. By using QTF, quartz-enhanced photoacoustic spectroscopy (QEPAS) [32,33,34] was proposed in 2002. It skillfully leverages the inherent merits of QTF, such as its compact configuration, narrow bandwidth, robust anti-interference performance, and cost-effectiveness [35,36,37,38,39]. When the laser wavelength matches the gas absorption line, the gas absorbs laser energy and undergoes a transition to the excited energy level. Owing to the intrinsic instability of the higher energy level, the gas subsequently falls back to the ground state, converting the absorbed energy into thermal energy [40,41,42]. Modulating the laser at a specific frequency can induce periodic expansion of the gas, thereby generating acoustic waves [43,44,45]. The acoustic waves drive the QTF into vibration, which subsequently generates piezoelectric signals. Systematic processing of these signals enables the effective derivation of key data pertaining to gas concentrations [46,47]. To date, the highly sensitive QEPAS technology has been widely adopted in various critical fields, making significant contributions to the advancement of science and technology across multiple domains.

Conventional quartz-enhanced photoacoustic spectroscopy (QEPAS) is an extremely sensitive technique, but it also suffers from several inherent limitations. First, the quartz tuning fork (QTF) must be driven close to its mechanical resonance, typically in the tens of kilohertz range. This requires high-frequency, low-noise electronics and a lock-in amplifier operating at the QTF resonance, which increases system complexity and cost. Second, the QTF resonance frequency is essentially fixed, so the modulation frequency has only a narrow tolerance. Any drift in the QTF resonance or in the modulation conditions can lead to a noticeable loss in signal amplitude and stability. Third, the useful photoacoustic signal is a very small current at high frequency, so it has to be amplified with large gain. By contrast, heterodyne quartz-enhanced photoacoustic spectroscopy (H-QEPAS) [48,49] is well suited for implementing transient or beat-frequency based retrieval schemes, while preserving all intrinsic benefits of QEPAS such as high sensitivity, compactness and wavelength independence. Experimental comparisons have shown that, for a similar detection limit, H-QEPAS can operate with shorter averaging times than conventional QEPAS, enabling faster gas-concentration measurements. Specifically, only a shortened excitation time is requisite to furnish the energy for transient response generation, thereby achieving a substantial enhancement in the sensor’s response speed. To further broaden the application scope of sensors and adapt to complex environments, sensors require further integration and portability [50,51,52,53]. Compared to traditionally machined components, 3D-printed gas chamber offers significantly reduced weight and volume [54,55,56]. They can be tightly integrated with optical components, enhancing the mechanical stability of the system.

In this paper, an integrated sensor prototype for CH₄ detection was proposed with a 3D-printed gas chamber. The designed sensing system comprises two layers: the lower layer contains the power supply module; the upper layer includes optical components. A LabVIEW programming framework to create a human–machine interface that supports dynamic configuration of experimental setting. Rather than aiming for the ultimate detection limit, the proposed system is specifically tailored to meet the application’s need for moderate detection sensitivity, compact design, and compatibility with cost-effective near-infrared diode laser sources. These features collectively indicate that the present H-QEPAS prototype provides a practical platform for the development of portable CH₄ monitoring instruments, particularly for on-site measurements in industrial or technological gas environments, where compactness, reliability, and ease of integration are of primary importance.

2. Experimental Setup

2.1. Selection of Absorption Line of CH₄

Diode lasers emitting in the near-infrared wavelength range offer advantages such as compact size, low cost, and fiber-coupled output capability. Therefore, selecting absorption lines within the near-infrared region enables the use of diode lasers as excitation sources for gas sensing applications. A simulation of CH₄ absorption lines in the spectral range from 1635 nm to 1665 nm was performed, as shown in Figure 1. The simulation was based on the HITRAN 2020 database under standard conditions, including a temperature of 300 K, atmospheric pressure, and an optical path length of 1 cm. As can be clearly observed, the absorption feature near 1650 nm exhibits a relatively strong CH₄ absorption strength while showing minimal spectral interference from common atmospheric constituents such as H₂O and CO₂. Since the selectivity of QEPAS-based sensors is primarily determined by the targeted molecular absorption line, non-spectral interference background gases do not contribute to the photoacoustic signal. Consequently, the absorption line located at 1650.96 nm was selected for subsequent CH₄ detection experiments, providing good intrinsic selectivity and reduced cross-sensitivity under typical ambient conditions.

2.2. The Principle of H-QEPAS

The principle of H-QEPAS as depicted in Figure 2. In the H-QEPAS scheme, a diode laser is wavelength-modulated at a frequency f_m that is slightly detuned from the resonance frequency f₀ of the quartz tuning fork (QTF), so that f_m = f₀ ± Δf, At the same time, the laser wavelength is rapidly scanned across a selected gas absorption line. This modulation transfers a periodic intensity variation to the laser beam whenever it passes through an absorbing gas. When the modulated laser beam propagates through the target gas, periodic absorption of the optical power produces cyclical local heating and cooling. This thermo-elastic process generates acoustic waves. The acoustic waves are focused on the QTF placed near the laser beam. The pressure fluctuations periodically drive the prongs of the QTF. Because the QTF is a High-Q mechanical resonator, each acoustic pulse excites it and the QTF subsequently undergoes free vibrations, ringing down at its own resonance frequency f₀. The QTF is made of piezoelectric quartz. Its mechanical free vibrations induce an alternating electrical charge on the electrodes. This charge is converted into a transient current output that faithfully reflects the temporal evolution of the QTF ring-down after each excitation event. The transient QTF current is fed to a lock-in amplifier and demodulated at the first harmonic of the modulation frequency, this extracts the component of the QTF response that is phase-coherent with the laser modulation, strongly suppressing broadband noise. The result is the 1f H-QEPAS signal, which contains both amplitude and phase information. By simultaneously exploiting the transient ring-down of the QTF and the heterodyne condition f_m = f₀ ± Δf, H-QEPAS achieves sensitive gas-concentration measurements while also providing access to the QTF’s dynamical parameters Q and f₀.

2.3. The Output Performance of the Diode Laser

To ensure a single mode laser output, a continuous wave distributed feedback (CW-DFB) diode laser is employed as the excitation source. The performance curve of the laser’s output wavelength variation with current at different temperatures was tested and the results are shown in Figure 3. As indicated by the dashed line in Figure 3a, the output wavelength can satisfy the selected absorption spectral line when the temperature is set to 15 °C and the current is set to 64.9 mA. As shown in Figure 3b, the output power at different temperatures is largely consistent, with the power at 64.9 mA being approximately 10 mW.

2.4. 3D-Printing Gas Chamber

3D-printing stands out for its strengths in high integration, elevated production efficiency, and cost-effectiveness. To address the limitations in size and stability of conventional H-QEPAS sensors produced through machining processes, 3D-printing was leveraged to fabricate a gas chamber, utilizing commercial acrylate-based UV-curable photopolymer resin as the base material. It is noted that freshly printed photopolymer materials may release residual volatile compounds after fabrication. To minimize potential interference, the printed gas cell was thoroughly post-processed, including solvent cleaning and prolonged air exposure prior to experimental measurements. In addition, all measurements were performed under continuous gas flow conditions, which further reduces the accumulation of any residual outgassing species. The design configuration of the gas chamber is depicted in Figure 4, with measurements of 42 mm in length, 27 mm in width, and 8 mm in height. This unit integrates a QTF, a set of acoustic micro-resonators (AmRs), and a fiber-coupled GRIN (Gradient Refractive Index) lens incorporated specifically for laser transmission and collimation purposes. The 3D-printed gas chamber is sealed using quartz glass windows. The QTF is centrally mounted inside the gas cell, with the laser beam aligned to pass through the gap between the QTF prongs. A pair of AmRs is positioned symmetrically along the laser propagation axis to enhance the photoacoustic signal through acoustic confinement. When accounting for all its components, the total mass of this 3D-printed gas chamber amounts to 6 g.

The design of the 3D-printed gas chamber was optimized to enhance the H-QEPAS signal by improving acoustic confinement and coupling efficiency. The AmRs were designed with dimensions corresponding to approximately one quarter of the acoustic wavelength associated with the QTF resonance frequency, enabling effective buildup of acoustic pressure at the position of the QTF prongs. Specifically, each AmR had a length of 5 mm, an inner diameter of 0.5 mm, and an outer diameter of 1.27 mm, which provide efficient acoustic coupling between the photoacoustic source region and the QTF and thereby maximize the detected signal. The laser beam was carefully aligned to traverse the inter-prong gap of the QTF with an optimized beam-prong separation. This configuration maximizes photoacoustic driving efficiency by strengthening the acoustic coupling to the QTF, while maintaining sufficient clearance to prevent any mechanical interaction with the prongs. Moreover, the compact, highly integrated geometry of the 3D-printed chamber reduces acoustic attenuation and improves mechanical robustness, thereby increasing the detected signal amplitude and improving measurement repeatability. Collectively, these design choices lead to a higher signal-to-noise ratio and enhanced overall system performance.

2.5. Design of LabVIEW-Based Control Program

The laser controller provides stable current and temperature for the diode laser. It communicates with the PC via a USB serial port. The current and temperature can be sequentially set to the laser controller via a LabVIEW program. The modulation signals for the laser originate from a signal generator circuit equipped with two signal channels capable of generating distinct waveforms. Within the H-QEPAS system, the modulation signal comprises a sine wave and a sawtooth wave. The sine wave modulates the laser’s output wavelength, while the sawtooth wave induces a periodic variation in the piezoelectric signal. It is worth noting that the sine wave serves as a reference signal in the subsequent demodulation process. The control program for the signal generator is also based on LabVIEW platform. The program allows adjustment of signal type, amplitude, frequency, and offset.

The lock-in amplifier is a core component in spectral detection, capable of extracting weak signals with frequencies identical to the reference signal. Its fundamental principle is phase-sensitive detection. Assume the measured signal is

$$x(t)=A_I\sin (wt+\phi )+N(t)$$

(1)

Here, A_I sin(wt + φ) is a useful signal, N(t) is noise. The reference signal consists of two components with a phase difference of 90°:

$$\left\{\begin{array}{l}{R}_1=A_R\sin (wt+\delta )\\ R_2=A_R\cos (wt+\delta )\end{array}\right.$$

(2)

Signal x(t) is multiplied by the reference signal, and then through the product-to-sum formulas, Equations (3) and (4) are obtained, respectively:

$$S_1=x(t)R_1={\displaystyle \frac{1}{2}}{A}_I{A}_R\cos (\phi -\delta )-{\displaystyle \frac{1}{2}}{A}_I{A}_R\cos (2wt+\phi +\delta )+A_{R}N(t)\sin (wt+\delta )$$

(3)

$$S_2=x(t)R_2={\displaystyle \frac{1}{2}}{A}_I{A}_R\sin (\phi -\delta )+{\displaystyle \frac{1}{2}}{A}_I{A}_R\sin (2wt+\phi +\delta )+A_{R}N(t)\cos (wt+\delta )$$

(4)

The terms in Equations (3) and (4) denote the DC component, the second harmonic components, and the product of noise and the reference signal. Given that the reference signal is periodic and uncorrelated with noise, this product term vanishes. Subsequent to low-pass filtering, the resulting equation is as follows:

$$\left\{\begin{array}{l}X={\displaystyle \frac{1}{2}}{A}_I{A}_R\cos (\phi -\delta )\\ Y={\displaystyle \frac{1}{2}}{A}_I{A}_R\sin (\phi -\delta )\end{array}\right.$$

(5)

The signal’s magnitude and phase information can be obtained as shown in Equation (6):

$$\left\{\begin{array}{l}{A}_I={\displaystyle \frac{2\sqrt{X^2+Y^2}}{A_R}}\\ \phi -\delta =\arctan {\displaystyle \frac{Y}{X}}\end{array}\right.$$

(6)

The lock-in amplifier program developed in LabVIEW for the host computer is shown in Figure 5. Since the piezoelectric signal is converted into a discrete signal after acquisition, the process is modified to a digital signal processing procedure.

The aforementioned program block diagrams are integrated via sub-VIs and then enter the circular queue in sequence. When the corresponding key event occurs, the sub-VI is dequeued, and the key value is input into the corresponding instrument through the USB serial port. The front panel of the corresponding button is shown in Figure 6, and the right half of the figure displays the concentration at different times.

2.6. The Architecture of Integrated CH₄ Sensor Prototype

The workflow of the integrated CH₄ sensor prototype is illustrated in Figure 7a. A 1.65 μm laser beam emitted from the diode laser is delivered via an optical fiber to a GRIN lens for collimation and subsequently coupled into the gas chamber. The laser propagates sequentially through the AmRs and the QTF where photoacoustic signals are generated. These photoacoustic signals induce free vibration of the QTF, thereby yielding piezoelectric signals. Owing to the ultra-weak nature of the piezoelectric signals, they are input into a trans-impedance amplifier (TIA) for amplification. The amplified piezoelectric signals are converted into digital signals by a data acquisition card (DAQ, USB6503; Henkai Electronic Technology Co., Ltd., Zhengzhou, China), enabling subsequent processing by a lock-in amplifier in LabVIEW. In this system, both the signal generator (JDS6600; Minghe Electronic Technology Co., Ltd., Hangzhou, China) and the laser controller (DFB2000; Ningbo Haierxin Optoelectronic Technology Co., Ltd., Ningbo, China) are coordinately controlled via the LabVIEW program. The signal generator can produce two types of modulation signals including sine wave and ramp wave, which are transmitted to the laser controller after superposed by an adder. CH₄ gases with different concentrations are prepared by adjusting the flow rate ratio of 20,000 ppm CH₄ and pure nitrogen (N₂). The schematic diagram of the internal structure of the device is presented in Figure 7b. The internal structure of the device is divided into upper and lower layers: the lower layer integrates the power supply module and the signal generator; the upper layer arranges the laser controller, adder, TIA, and 3D-printed gas chamber; the DAQ runs through both upper and lower layers and is mounted laterally to achieve full-system signal acquisition. All controlled modules establish communication connections with the PC terminal via USB serial ports. The modules corresponding to each number in the figure are specified in the figure caption. The physical photograph of the device is shown in Figure 7c, with dimensions of 33 cm in length, 27 cm in width, and 15 cm in height. The front of the system is equipped with an air inlet and outlet to facilitate the gas to be detected. A transparent window is installed on the top of the system, allowing real-time observation of the laser controller’s operating status.

3. Results and Discussions

The frequency characteristics of the QTF are crucial parameters in H-QEPAS, exerting a significant influence on the detection performance of the sensing system. The signal response of the QTF within a frequency interval of ±30 Hz centered at 32.76 kHz is illustrated by red dots in Figure 8, incorporating a total of 400 signal points. All signal points underwent square normalization processing, followed by the acquisition of a Lorentzian fitting curve. Based on the fitting curve, the resonant frequency (f₀) of the QTF employed in the experiment was determined to be 32,762.81 Hz, with a bandwidth (w) of 2.73 Hz. Employing the formula Q = f₀/w, the quality factor of the QTF was calculated as 12,001.03.

Given that the amplitude of harmonic signals exhibits a positive correlation with the signal-to-noise ratio (SNR), adjustments to the modulation depth exert a direct influence on the harmonic signal amplitude. To investigate the effect of modulation depth on detection sensitivity, modulation depth spanning from 0 mA to 100 mA was established to acquire the harmonic amplitude variation curve, as illustrated in Figure 9. Experimental results demonstrate that the harmonic amplitude presents a typical nonlinear relationship with modulation depth, and its variation trend is consistent with theoretical expectations. Quantitative analysis reveals that the system possesses a unique optimal modulation depth of 44.86 mA, at which the second harmonic amplitude achieves a maximum value. Accordingly, 44.86 mA was adopted as the standard modulation parameter for subsequent experimental procedures.

A concentration detection experiment was conducted. By adjusting the flow rate ratio, CH₄ gas with concentrations ranging from 1000 ppm to 20,000 ppm was prepared in the experiment. The detection signals output by the prototype were exported from the test program, and the results are shown in Figure 10a. The linear response characteristic of CH₄ concentration was evaluated through the signal peaks, and the corresponding fitting curve is presented in Figure 10b. This behavior is consistent with the basic principles of photoacoustic spectroscopy (PAS) and the H-QEPAS mechanism used in this study. The photoacoustic signal arises when the target gas absorbs modulated laser radiation and relaxes non-radiatively, leading to periodic heating and the generation of an acoustic pressure wave. According to the Lambert–Beer law, optical absorption is linearly related to concentration only when the laser energy is not completely absorbed. When the concentration increases to the point where the laser beam is almost completely absorbed, further increases in concentration do not lead to a proportional increase in absorbed energy, thus limiting the potential for the photoacoustic signal to rise. Experimental results demonstrate that the prototype detection system exhibits excellent linear response performance to CH₄ at different concentrations, with a goodness of fit R² reaching 0.998 and a linear fitting function of y = 4.8663 × 10⁻⁵x + 0.00991. The concentration inversion algorithm in the program can be implemented based on this fitting function. To investigate the detection limit of the prototype, the noise standard deviation of the signal tail was measured, yielding a result of 1.29 mV. Based on this noise data, the detection limit of the prototype was calculated as 26.72 ppm.

H-QEPAS can capture the entire heterodyne signal waveform in a very short period of time and simultaneously measure f₀ for the QTF. Signals from H-QEPAS systems were measured at a CH₄ concentration level of 2%. The results are shown in Figure 11, the heterodyne signal frequency could be calculated as Δf = 1/Δt = 3.17 Hz, and then the f₀ of QTF can be retrieved according to the formula: f₀ = f_m + Δf = 32,762.81 Hz.

It should be emphasized that the 3D-printed gas chamber employed in this study is used exclusively as a laboratory prototype to facilitate rapid structural iteration and system integration during the early development stage. The use of 3D printing does not constitute a methodological claim for industrial or commercial gas analyzers. In practical field or industrial applications, gas chambers are typically fabricated from materials such as stainless steel or fluoropolymers to minimize outgassing, adsorption effects, and long-term drift.

Environmental factors such as humidity and ambient temperature are known to influence QEPAS-based sensors. In the present H-QEPAS system, humidity mainly affects the signal through vibrational-translational (V-T) relaxation processes. The presence of water vapor can enhance the relaxation efficiency of CH₄ molecules, leading to an increased photoacoustic signal amplitude, while excessive humidity may introduce additional background absorption. Since the selected CH₄ absorption line at 1650.96 nm exhibits weak interference from H₂O, the influence of humidity is expected to be dominated by relaxation effects rather than spectral overlap. Ambient temperature variations can influence gas absorption parameters, acoustic propagation, and the resonance characteristics of the QTF. However, within typical laboratory temperature fluctuations, these effects are relatively small. Moreover, the H-QEPAS scheme allows real-time retrieval of the QTF resonance frequency, which effectively mitigates the impact of temperature-induced frequency drift. Therefore, the proposed sensor is expected to maintain stable performance under moderate environmental variations. A more systematic investigation of humidity and temperature effects will be carried out in future work.

As summarized in

Table 1. Quantitative comparison between traditional QEPAS and H-QEPAS systems.

Method	Wavelength	MDL (ppm) (@Integration Time)	Response Time	Reference
QEPAS	2.64 μm	85.00 (@2 s)	50 s	[57]
QEPAS	3.58 μm	55.57 (@1 s)	30 s	[58]
H-QEPAS	1.65 μm	28.35 (@114 s)	4 s	[59]
H-QEPAS	1.65 μm	26.72 (@100 s)	4 s	this work

, the proposed H-QEPAS sensor operating at 1.65 μm achieves a favorable trade-off between fast temporal response and high detection sensitivity for CH₄. While maintaining a 4 s response time, this work attains a minimum detection limit (MDL) of 26.72 ppm with an integration time of 100 s, which outperforms the previously reported 1.65 μm H-QEPAS result of 28.35 ppm obtained at 114 s integration time. The simultaneous reduction in MDL and integration time indicates an improved overall measurement efficiency, reflecting enhanced signal generation and heterodyne demodulation performance in the proposed scheme. In contrast, conventional QEPAS implementations exhibit substantially slower dynamics response despite delivering markedly higher MDLs under short integration conditions. Therefore, the present H-QEPAS approach provides a clear advantage for applications demanding rapid, real-time tracking of CH₄ concentration variations, such as leak detection and transient monitoring, while preserving competitive sensitivity.

To provide a concise, performance-oriented comparison of portable CH₄ sensing technologies, we benchmark four representative approaches—H-QEPAS, non-dispersive infrared (NDIR), tunable diode laser absorption spectroscopy (TDLAS), and cavity-enhanced absorption spectroscopy (CEAS)—using the reported detection limits as the primary figures of merit. The proposed integrated H-QEPAS sensor achieves a 26.72 ppm MDL, indicating superior volumetric sensitivity among the compared portable in situ techniques while maintaining strong potential for miniaturization and system integration. In contrast, portable NDIR sensor (300 ppm MDL [60]) quantify CH₄ via broadband mid-IR absorption in a short gas cell with optical filtering; despite their low cost and simplicity, performance is typically constrained by limited effective path length and detector drift, rendering sub-100 ppm operation difficult without larger multi-pass cells and rigorous environmental compensation. Handheld open-path TDLAS sensor report a MDL of 43.14 ppm·m (path-integrated [61]), offering clear advantages for standoff leak screening; however, the ppm·m metric is inherently dependent on plume thickness and measurement geometry, leading to substantial variability in the equivalent volumetric concentration sensitivity under field conditions. CEAS sensor extend the effective optical path length using a high-reflectivity cavity and retrieve CH₄ from broadband spectra, but practical performance (MDL 460 ppm [62]) can be limited by coupling stability and cavity contamination. Overall, the integrated H-QEPAS approach combines the lowest reported detection limit (26.72 ppm) with reduced optical alignment burden, underscoring its promise for portable leak inspection, confined-space safety monitoring, and scalable deployment in distributed sensing nodes. Looking forward, continued miniaturization—through tighter optical–acoustic co-packaging, low-power drive and demodulation electronics, and robust flow-through materials—should further reduce size, weight, and power consumption, enabling truly handheld form factors and facilitating large-scale deployment in battery-powered.

4. Conclusions

This paper reported a high-performance integrated CH₄-QEPAS sensor prototype. A hardware control and concentration inversion program were developed based on the LabVIEW platform, enabling real-time data display on a PC terminal. The system achieves accurate detection of CH₄ gas concentration by heterodyne modulating a DFB diode laser with a central wavelength of 1650.96 nm. In the experiment, the gas chamber fabricated via 3D-printing integrates core components including a GRIN lens, a QTF, and AmRs. Experimental results demonstrate that the amplitude of the harmonic signal exhibits a significant positive correlation with the gas concentration, with R² up to 0.998, verifying the excellent performance of the system in weak signal extraction. Under this condition, the detection limit of CH₄ concentration is calculated to be approximately 26.72 ppm. It should be noted that the experiments presented in this work were conducted under controlled laboratory conditions using CH₄ diluted in nitrogen, which does not fully represent ambient air environments with variable humidity and complex gas compositions. Therefore, the current results are not intended to directly demonstrate sensor performance for atmospheric CH₄ monitoring. Instead, the proposed H-QEPAS system is particularly relevant for applications involving technological or process gases, where CH₄ is monitored in inert carrier gases such as nitrogen or argon. Typical scenarios include chemical production lines, material processing, and industrial gas quality control, where low humidity and well-defined gas matrices are commonly encountered. In such environments, the compactness, stability, and near-infrared operation of the developed sensor provide clear advantages. These results establish a foundation for future investigations under more complex gas matrices, including humid air, where the influence of water vapor and background gases on sensor performance can be systematically evaluated.