Carbon monoxide impurities in hydrogen detected with resonant photoacoustic cell using a mid-IR laser source.

We report on a photoacoustic sensor system based on a differential photoacoustic cell to detect the concentration of CO impurities in hydrogen. A DFB-QCL laser with a central wavelength of 4.61 µm was employed as an exciting source with an optical power of 21 mW. Different concentrations of CO gas mixed with pure hydrogen were injected into the photoacoustic cell to test the linear response of the photoacoustic signal to the CO concentration. The stability of the long-term operation was verified by Allan-Werle deviation analysis. The minimum detection limit (MDL, SNR=1) results 8 ppb at 1 s and reaches a sub-ppb level at 100 s of integration time. Dynamic response of the system is linear and has been tested up to the concentration of 6 ppm. Saturation conditions are expected to be reached for CO concentration larger than 100 ppm.

End-to-end methane gas detection algorithm based on transformer and multi-layer perceptron.

In this paper, an end-to-end methane gas detection algorithm based on transformer and multi-layer perceptron (MLP) for tunable diode laser absorption spectroscopy (TDLAS) is presented. It consists of a Transformer-based U-shaped Neural Network (TUNN) filtering algorithm and a concentration prediction network (CPN) based on MLP. This algorithm employs an end-to-end architectural design to extract information from noisy transmission spectra of methane and derive the CH4 concentrations from denoised spectra, without intermediate steps. The results demonstrate the superiority of the proposed TUNN filtering algorithm over other typically employed digital filters. For concentration prediction, the determination coefficient (R2) reached 99.7%. Even at low concentrations, R2 remained notably high, reaching up to 89%. The proposed algorithm results in a more efficient, convenient, and accurate spectral data processing for TDLAS-based gas sensors.

Photoacoustic Heterodyne CO Sensor for Rapid Detection of CO Impurities in Hydrogen.

Hydrogen (H2) fuel cells have been developed as an environmentally benign, low-carbon, and efficient energy option in the current period of promoting low-carbon activities, which offer a compelling means to reduce carbon emissions. However, the presence of carbon monoxide (CO) impurities in H2 may potentially damage the fuel cell's anode. As a result, monitoring of the CO levels in fuel cells has become a significant area of research. In this paper, a novel photoacoustic sensor is developed based on photoacoustic heterodyne technology. The sensor combines a 4.61 µm mid-infrared quantum cascade laser with a low-noise differential photoacoustic cell. This combination enables fast, real-time online detection of CO impurity concentrations in H2. Notably, the sensor requires no wavelength locking to monitor CO online in real-time and produces a single effective signal with a period of only 15 ms. Furthermore, the sensor's performance was thoroughly evaluated in terms of detection sensitivity, linearity, and long-term stability. The minimum detection limit of 11 ppb was obtained at an optimal time constant of 1 s.

Noninvasive Skin Respiration (CO2) Measurement Based on Quartz-Enhanced Photoacoustic Spectroscopy.

A noninvasive method for disease diagnosis that does not require complex specialized laboratory facilities and chemical reagents is particularly attractive in the current medical environment. Here, we develop a noninvasive skin respiration sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) that can monitor the skin elimination rate of carbon dioxide (CO2). A 3.8 mW distributed feedback laser emitting at 2.0 µm is used as an excitation source, and a three-dimensional (3D)-printed acoustic detection module is designed to apply to the skin as a sensor head. The performance of the noninvasive skin respiration sensor is assessed in terms of detection sensitivity, linearity, long-term stability, and water effect. A minimum detection limit of 35 ppb is achieved at the optimal integration time of 670 s. The skin respiration measurements from eight healthy volunteers are recorded, and the real-time results are analyzed.

A review of high-intensity focused ultrasound as a novel and non-invasive interventional radiology technique.

High-intensity focused ultrasound (HIFU) is a non-invasive interventional radiology technology, which has been generally accepted in clinical practice for the treatment of benign and malignant tumors. HIFU can cause targeted tissue coagulative necrosis and protein denaturation by thermal or non-thermal effects, guided by diagnostic ultrasound or magnetic resonance imaging, without destruction of the normal adjacent tissue, under sedation or general anesthesia. HIFU has become an important alternative to standard treatments of solid tumors, including surgery, radiation, and medications. The aim of this review is to describe the development, principle, devices, and clinical applications of HIFU.

Detection of Hydrogen Sulfide in Sewer Using an Erbium-Doped Fiber Amplified Diode Laser and a Gold-Plated Photoacoustic Cell.

A photoacoustic detection module based on a gold-plated photoacoustic cell was reported in this manuscript to measure hydrogen sulfide (H2S) gas in sewers. A 1582 nm distributed feedback (DFB) diode laser was employed as the excitation light source of the photoacoustic sensor. Operating pressure within the photoacoustic cell and laser modulation depth were optimized at room temperature, and the long-term stability of the photoacoustic sensor system was analyzed by an Allan-Werle deviation analysis. Experimental results showed that under atmospheric pressure and room temperature conditions, the photoacoustic detection module exhibits a sensitivity of 11.39 µV/ppm of H2S and can reach a minimum detection limit (1σ) of 140 ppb of H2S with an integration time of 1 s. The sensor was tested for in-field measurements by sampling gas in the sewer near the Shanxi University canteen: levels of H2S of 81.5 ppm were measured, below the 100 ppm limit reported by the Chinese sewer bidding document.

Photoacoustic heterodyne breath sensor for real-time measurement of human exhaled carbon monoxide.

A breath sensor for real-time measurement of human exhaled carbon monoxide is reported. This breath sensor is based on a novel photoacoustic heterodyne gas sensing technique, which combines the conventional photoacoustic spectroscopy with the beat-frequency detection algorithm, thus offering a fast response time and a convenient optical alignment, as well as eliminating the needs for frequency calibration and wavelength locking. The principle of photoacoustic heterodyne gas sensing was explained in detail. The performance of the photoacoustic heterodyne breath sensor was evaluated in terms of minimum detection limit, response time, and linearity. The exhaled carbon monoxide levels of eight volunteers were measured and the results demonstrate the reliability and feasibility of this breath sensor.