A four-off-beam acoustic micro-resonator (AmR) structure is proposed to improve the photoacoustic signal intensity in quartz-enhanced photoacoustic spectroscopy (QEPAS) for trace gas sensing. Two vertical-array-based double-off-beam AmR structures are arranged on each side of the quartz tuning fork (QTF) horizontally to construct a four-off-beam AmR structure using a rectangular prism. This QEPAS scheme based on the four-off-beam AmR is evaluated in the water-vapor detection of air at normal atmospheric pressure and room temperature (27C). Comparing with the bare QTF scheme, the new QEPAS configuration enhances the photoacoustic spectroscopy signal by a factor of 25.84 times, achieving a minimum detection limit of 278 ppbv with a normalized noise equivalent absorption coefficient of 1.27x10 $^-9$ W/Hz $1/2$ in water vapour detection at a wavelength of 1368.597 nm.

In this paper, a multicomponent gas detection system based on photoacoustic spectroscopy (PAS) is proposed with a combination of frequency division multiplexing (FDM) and time division multiplexing (TDM), combining a resonance photoacoustic cell and broadband microphone. A PAS gas cell with a wide frequency response bandwidth was used to achieve the FDM by selecting a specific modulation frequency of each component gas. The sawtooth wave driver current of each laser was output at a constant time interval for achieving the TDM. Compared with the laser channel control using a photoswitch, the driver current control was a simpler and more convenient means to implement TDM. The four gas components of methane ( C H 4 ), water ( H 2 O ) vapor, carbon dioxide ( C O 2 ), and acetylene ( C 2 H 2 ) were selected as sample gases for testing the feasibility of the method. The experimental results showed that the gas detection limits of C H 4 , H 2 O vapor, C O 2 , and C 2 H 2 were 75.435, 2.502, 341.960, and 4.284 ppm, respectively. In addition, the linear fittings of gas concentration were 0.99386, 0.99772, 0.98995, and 0.98955, respectively.

In this paper, a dual-spectroscopy gas sensing system based on ring cavity laser and quartz tuning fork (QTF) is designed. 15 m erbium-doped fiber with 1500 ppm doping concentration is used as gain medium, piezoelectric transducer (PZT) and acousto-optic modulator (AOM) are used as detection method. The first fiber collimator (FC) emits laser beam, laser is received by the second FC after passing through an off-beam acoustic micro-resonator (AmR) for quartz-enhanced photoacoustic spectroscopy (QEPAS) signal excitation and enhancement. The received laser is transmitted through the optical fiber and then incident on the QTF prongs by the third FC, which excites and quartz-enhan-ced photothermal spectroscopy (QEPTS) signal. Combined with the ring intra-cavity fiber laser and wavelength scanning and intensity modulation technology, dual-spectroscopy gas detection is realized. Compared with the single detection of QEPAS or QEPTS signals, the detection limit is enhanced. Under the conditions of 400mW pump power and 2500 ppmv acetylene (C ₂ H ₂ ) gas concentration, the signal to noise ratio (SNR) of QEPAS, QEPTS and dual-spectroscopy signals are 838.07, 1117.47 and 2096.26, respectively, and the minimum detection limits (MDL) of 2.98 ppmv, 2.24 ppmv, 1.19 ppmv are achieved, respectively.

The utilization of unmanned sailboats as a burgeoning instrument for ocean exploration and monitoring is steadily rising. In this study, a dual sail configuration is put forth to augment the sailboats’ proficiency in its wind-catching ability and adapt to the harsh environment of the sea. This proposition is based on a thorough investigation of sail aerodynamics. The symmetric rigid wing sails NACA 0020 and NACA 0016 are selected for use as the mainsail and trailing wing sail, respectively, after considering the operational environment of unmanned sailboats. The wing sail structure is modeled using SolidWorks, and computational fluid dynamics (CFD) simulations are conducted using ANSYS Fluent 2022R1 software to evaluate the aerodynamic performance of the sails. Key aerodynamic parameters, including lift, drag, lift coefficient, drag coefficient, and thrust coefficient, are obtained under different angles of attack. Furthermore, the effects of mainsail aspect ratios, mainsail taper ratios, and the positional relationship between the mainsail and trailing sail on performance are analyzed to determine the optimal structure. The thrust provided by the sail to the boat is mainly generated by the decomposition of lift, and the lift coefficient is used to measure the efficiency of an object in generating lift in the air. The proposed sail structure demonstrates a 37.1% improvement in the peak lift coefficient compared to traditional flexible sails and exhibits strong propulsion capability, indicating its potential for widespread application in the marine field.

In this paper, we propose a scheme to eliminate the laser power losses that occur in photoacoustic spectroscopy (PAS) multi-point gas sensing that uses a reference gas channel, and we then design a new two-optical-path PAS gas cell that is constructed using both sensing and reference gas cells. The second harmonic PAS signals are extracted from the sensing and reference gas cells using a lock-in amplifier, and the ratio of these signals is used to calculate the gas concentration in an approach that can effectively eliminate the influence of laser power losses on the system's detection performance. Acetylene (C ₂ H ₂ )gas is detected at 1532.83 nm in multi-point PAS experiments and the effectiveness of the proposed loss elimination scheme is verified. Using three new two-optical-path PAS gas detection devices, the linear responses of the proposed sensor to the acetylene concentration are determined, with yielded R-square values of 0.99834, 0.99788, and 0.99603 being obtained.

The development of energy-efficient propulsion systems for autonomous sailboats requires innovative sail designs that balance aerodynamic performance and maritime operational reliability. This study presents a novel rigid wing sail system comprising a NACA 0020 main sail with an embedded NACA 0018 tail sail, specifically designed for uncrewed ocean navigation. Through systematic CFD analysis using ANSYS Fluent 2022R1, three configurations were compared: (1) the proposed hybrid wing–tail system, (2) a single main wing sail, and (3) traditional flap sails. The investigation focused on two key design parameters—tail sail area (25–40% of main sail area) and deflection angle (0–15°)—that were evaluated across angles of attack from 0° to 30° under typical marine wind conditions. The results reveal three critical findings: First, the hybrid system achieves a 29.5% higher peak lift coefficient than a single wing sail and an 11.6% improvement over slotted-flap sails. Second, increasing the tail sail area to 35% of the main sail optimizes both the lift coefficient (C_{L max} = 1.16) and the lift-to-drag ratio (L/D = 7.5 at 9° angles of attack). Third, as the tail deflection angle increases, the maximum lift–drag ratio shifts forward, and at small angles of attack, the maximum lift–drag ratio increases by 40%. The hybrid wing–tail sail design proposed in this study significantly enhances the aerodynamic performance of uncrewed sailing boats, providing new insights for the sustainable development of marine renewable energy technologies and autonomous vessels.