基于VMD-HT的N₂O气体TDLAS二次谐波信号解调方法的研究

Study on the Demodulation Method of N₂O Gas TDLAS Second Harmonic Signal Based on VMD-HT

摘要: 针对可调谐半导体激光吸收光谱(TDLAS)技术中二次谐波信号的调谐与提取问题，提出了一种基于变分模态分解(VMD)与希尔伯特变换(HT)相结合的二次谐波解调方法。相较于传统锁相放大器(LIA)方法，该方法在无需外部参考信号，便可有效提取TDLAS信号中的二次谐波分量。主要通过对TDLAS信号进行带通滤波，以抑制非目标频段的干扰；随后采用变分模态分解(VMD)将滤波后的信号分解为若干内涵模态分量(IMF)；进一步计算各IMF的包络信号，并通过希尔伯特变换提取其瞬时特性；最终，从具有目标频率特征的包络分量中提取二次谐波，实现对气体浓度信号的高效无参考解调。仿真结果对比表明，该方法在二次谐波信号提取的准确性和特征保留方面表现优越。

Abstract: Addressing the tuning and extraction of the second harmonic signal in tunable diode laser absorption spectroscopy (TDLAS) technology, a second harmonic demodulation method based on the combination of variational mode decomposition (VMD) and Hilbert transform (HT) is proposed. Compared with the traditional lock-in amplifier (LIA) method, this approach can effectively extract the second harmonic component in TDLAS signals without the need for an external reference signal. The method primarily performs bandpass filtering on the TDLAS signals to suppress interference from non-target frequency bands; then employs VMD to decompose the filtered signal into several intrinsic mode functions (IMFs); further calculates the envelope of each IMF and extracts their instantaneous characteristics via the Hilbert transform; finally, extracts the second harmonic from the envelope component with the target frequency feature, achieving efficient and reference-free demodulation of gas concentration signals. Simulation results demonstrate that this method outperforms in accuracy and feature preservation for second harmonic signal extraction.