Determination of melon seed physical parameters and calibration of discrete element simulation parameters.

To improve the accuracy of the Hami melon discrete element model, the parameters of the Hami melon seed discrete element model were calibrated by combining practical experiments and simulation tests. The basic physical parameters of Hami melon seeds were obtained through physical experiments, including triaxial size, 100-grain mass, moisture content, density, Poisson's ratio, Young's modulus, shear modulus, angle of repose, suspension speed and various contact parameters. Taking the repose angle of seed simulation as an index, the parameters of each simulation model were significantly screened by the Plackett-Burman test.

A mini-resonant photoacoustic sensor based on a sphere-cylinder coupled acoustic resonator for high-sensitivity trace gas sensing.

This paper reports a mini-resonant photoacoustic sensor for high-sensitivity trace gas sensing. The sensor primarily contains a sphere-cylinder coupled acoustic resonator, a cylindrical buffer chamber, and a fiber-optic acoustic sensor. The acoustic field distributions of this mini-resonant photoacoustic sensor and the conventional T-type resonant photoacoustic sensor have been carefully evaluated, showing that the first-order resonance frequency of the present mini-resonant photoacoustic sensor is reduced by nearly a half compared to that of the T-type resonant photoacoustic sensor.

Highly sensitive trace gas detection based on a miniaturized 3D-printed Y-type resonant photoacoustic cell.

We report, what we believe to be, a novel miniaturized 3D-printed Y-type resonant photoacoustic cell (YRPAC) consisting of a frustum of cone-type buffer chamber and a cylindrical resonant chamber. The volume of the designed YRPAC is about 7.0 cm, which is only about a half of the T-resonant photoacoustic cell (TRPAC).

Ultra-High-Sensitivity, Miniaturized Fabry-Perot Interferometric Fiber-Optic Microphone for Weak Acoustic Signals Detection.

An ultra-high-sensitivity, miniaturized Fabry-Perot interferometric (FPI) fiber-optic microphone (FOM) has been developed, utilizing a silicon cantilever as an acoustic transducer. The volumes of the cavity and the FOM are determined to be 60 microliters and 102 cubic millimeters, respectively. The FOM has acoustic pressure sensitivities of 1506 nm/Pa at 2500 Hz and 26,773 nm/Pa at 3233 Hz.

High-sensitivity miniature dual-resonance photoacoustic sensor based on silicon cantilever beam for trace gas sensing.

We report a miniature dual-resonance photoacoustic (PA) sensor, mainly consisting of a small resonant T-type PA cell and an integrated sensor probe based on a silicon cantilever beam. The resonance frequency of the miniature T-type PA cell is matched with the first-order natural frequency of the cantilever beam to achieve double resonance of the acoustic signal. The volume of the designed T-type PA cell is only about 2.

High-Sensitivity Multitrace Gas Simultaneous Detection Based on an All-Optical Miniaturized Photoacoustic Sensor.

We propose an all-optical miniaturized multigas simultaneous detection photoacoustic (PA) sensor, which is primarily composed of a copper tube, a silica cantilever, and four single-mode fibers. Three single-mode fibers are used as excitation fibers to transmit lasers of different wavelengths, and the remaining one is used as a probe fiber. The volumes of the PA cell (PAC) and the sensor are 36 μL and 71 cubic millimeters, respectively.

All-optical high-sensitivity resonant photoacoustic sensor for remote CH gas detection.

This paper presents an all-optical high-sensitivity resonant photoacoustic (PA) sensor to realize remote, long-distance and space-limited trace gas detection. The sensor is an integration of a T-type resonant PA cell and a particular cantilever-based fiber-optic acoustic sensor. The finite element simulations about the cantilever vibration mode and the PA field distributions are carried out based on COMSOL.

Ppb-level detection of methane based on an optimized T-type photoacoustic cell and a NIR diode laser.

This paper presents an optimized T-type resonant photoacoustic (PA) cell for methane (CH) gas detection. The noise transmission coefficients and PA field distributions of the T-type resonant PA cell have been evaluated using the finite element method and thermoviscous acoustic theory. The optimized T-type resonant PA cell, together with a near-infrared (NIR) distributed feedback (DFB) laser source, a high-speed spectrometer and a fiber-optic acoustic sensor constitutes a PAS system for CH detection.

Label-Free Near-Infrared Plasmonic Sensing Technique for DNA Detection at Ultralow Concentrations.

Biomolecular detection at a low concentration is usually the most important criterion for biological measurement and early stage disease diagnosis. In this paper, a highly sensitive nanoplasmonic biosensing approach is demonstrated by achieving near-infrared plasmonic excitation on a continuous gold-coated nanotriangular array. Near-infrared incident light at a small incident angle excites surface plasmon resonance with much higher spectral sensitivity compared with traditional configuration, due to its greater interactive volume and the stronger electric field intensity.

Multiplexable high-temperature stable and low-loss intrinsic Fabry-Perot in-fiber sensors through nanograting engineering.

This paper presents a method of using femtosecond laser inscribed nanograting as low-loss- and high-temperature-stable in-fiber reflectors. By introducing a pair of nanograting inside the core of a single-mode optical fiber, an intrinsic Fabry-Perot interferometer can be created for high-temperature sensing applications. The morphology of the nanograting inscribed in fiber cores was engineered by tuning the fabrication conditions to achieve a high fringe visibility of 0.

Simultaneous measurement of acoustic pressure and temperature using a Fabry-Perot interferometric fiber-optic cantilever sensor.

A Fabry-Perot (F-P) interferometric fiber-optic cantilever sensor is presented for simultaneous measurement of acoustic pressure and temperature, which are demodulated by a single high-speed spectrometer. The acoustic pressure wave pushes the cantilever to produce periodic deflection, while the temperature deforms the sensor and causes the F-P cavity length to change slowly. The absolute length of the F-P cavity of the fiber-optic cantilever sensor is calculated rapidly by using a spectral demodulation method.

Fiber-optic photoacoustic gas sensor with temperature self-compensation.

A high-precision fiber-optic photoacoustic (PA) gas sensor with temperature self-compensation is reported. The target gas diffuses into a micro-chamber and absorbs the laser energy to generate a PA signal, which is detected by a Fabry-Perot interferometric cantilever. The temperature affects not only the acoustic sensitivity of the cantilever, but also the PA conversion efficiency.

High-sensitivity photoacoustic gas detector by employing multi-pass cell and fiber-optic microphone.

A high-sensitivity photoacoustic (PA) spectroscopy (PAS) system is proposed for dual enhancement from both PA signal excitation and detection by employing a miniaturized Herriott cell and a fiber-optic microphone (FOM). The length of the optical absorption path of the PA cell is optimized to ∼374 mm with 17 reflections. The volume of the PA cell is only 622 µL.

Highly Sensitive Photoacoustic Microcavity Gas Sensor for Leak Detection.

A highly sensitive photoacoustic (PA) microcavity gas sensor for leak detection is proposed. The miniature and low-cost gas sensor mainly consisted of a micro-electro-mechanical system (MEMS) microphone and a stainless-steel capillary with two small holes opened on the side wall. Different from traditional PA sensors, the designed low-power sensor had no gas valves and pumps.

An auto-correction laser photoacoustic spectrometer based on 2f/1f wavelength modulation spectroscopy.

An auto-correction laser photoacoustic (PA) spectrometer based on 2f/1f wavelength modulation spectroscopy (WMS) has been proposed and demonstrated for trace gas detection to eliminate concentration measurement errors due to light power variations. A 1.53 μm distributed feedback (DFB) laser is used as a light source to excite the 2f PA signal that is generated by gas absorption.

Integration of T-type half-open photoacoustic cell and fiber-optic acoustic sensor for trace gas detection.

We present a novel T-type half-open resonant photoacoustic (PA) cell for trace gas detection. The T-type PA cell has just one buffer volume, and a fiber-optic acoustic sensor is placed at one end of the resonator. Compared with the conventional H-type PA cell, the first-order resonant frequency of the T-type PA cell is reduced by half and the PA signal is enhanced with the same resonator.

Fiber-optic photoacoustic sensor for remote monitoring of gas micro-leakage.

We present a fiber-optic photoacoustic (PA) sensor for remote monitoring of gas micro-leakage. The gas sensing head is a miniature ferrule-top PA cavity with a cantilever beam. Gas diffuses into the cavity from the gap around the cantilever beam, and a small hole opens on the side wall.

Lock-in white-light-interferometry-based all-optical photoacoustic spectrometer.

An all-optical photoacoustic spectroscopy based on lock-in white-light interferometry is proposed for trace gas detection. The cavity length of the fiber-optic Fabry-Perot cantilever microphone is demodulated by a high-speed white-light interferometer, whose spectral sampling is synchronously triggered by a phased locked signal. To improve the signal-to-noise ratio, the demodulated digital photoacoustic signal is further processed by a specially designed virtual lock-in amplifier.

Fast demodulated white-light interferometry-based fiber-optic Fabry-Perot cantilever microphone.

We demonstrate a highly sensitive and stable fiber-optic Fabry-Perot cantilever microphone based on fast demodulated white-light interferometry. The cavity length of the low-finesse Fabry-Perot interferometry is absolutely measured by realizing a high-speed demodulation method utilizing a full spectrum, with the advantages of both high resolution and large dynamic range. An acoustic test demonstrates high sensitivities and linear responsivities at frequencies below 2 kHz.

A Q-switched Ho:YAG laser assisted nanosecond time-resolved T-jump transient mid-IR absorbance spectroscopy with high sensitivity.

Knowledge of dynamical structure of protein is an important clue to understand its biological function in vivo. Temperature-jump (T-jump) time-resolved transient mid-IR absorbance spectroscopy is a powerful tool in elucidating the protein dynamical structures and the folding/unfolding kinetics of proteins in solution. A home-built setup of T-jump time-resolved transient mid-IR absorbance spectroscopy with high sensitivity is developed, which is composed of a Q-switched Cr, Tm, Ho:YAG laser with an output wavelength at 2.

Treatment of facial port-wine stains with a new intense pulsed light source in Chinese patients.

Background: Intense pulsed light (IPL) systems have been used for the treatment of port-wine stains (PWS) for more than 10 years. Some of them have been reported in the treatment of laser-resistant PWS.

Objective: To conduct a prospective trial to assess the efficiency and complications of a new IPL source in the treatment of PWS in Chinese patients.

[Tunable fiber laser based photoacoustic spectroscopy for acetylene detection].

An acetylene detection system has been constructed with a tunable erbium-doped fiber laser (TEDFL) based photoacoustic spectrometer. Combining wavelength modulation and second harmonic signal detection technique, the system is able to effectively eliminate the background noise generated by absorption of the cell windows and the wall of the acoustic resonator. The system was applied to low concentration acetylene flowing measurement, through optimizing the systemic optics, acoustics and electron detection technique condition.

Tunable fiber laser and fiber amplifier based photoacoustic spectrometer for trace gas detection.

A new wavelength modulated photoacoustic spectrometer based on a near-infrared tunable erbium doped fiber laser (TEDFL) and an erbium doped fiber amplifier (EDFA) is first developed for trace gas detection. This sensor has been applied to the detection of ammonia using a first longitudinal resonant photoacoustic cell with double absorption optical path (L=20cm) and lock-in harmonic detection technique. The minimum detectable limit of 3 parts-per-billion volume (signal-to-noise ratio=1) and response time of approximately 1min is achieved at room temperature and atmospheric pressure with 100ms time constant and 500mW optical power at the 1531.