A step towards the electrophotonic nose: integrating 1D photonic crystals with organic light‐emitting diodes and photodetectors

An innovative integrated sensing platform for the detection of various chemical analytes via translating the photonic stop‐band shift of a one‐dimensional photonic crystal (PC) into an electrical current change is proposed. The miniaturized sensing platform features an organic light‐emitting diode (OLED) as a light source and an organic photodetector (OPD) as a light sensor and allows for the detection of ethanol vapor concentrations down to ≈ 10 parts per million (ppm) in nitrogen, which corresponds to a stop‐band shift of ≈ 27 pm. The resolution of the proposed platform exceeds the capabilities of most commercial spectrometers and by far the human eye, while, at the same time, such a sensor is less expensive and less power consuming than a spectrometer. The presented setup is generic and can detect optical changes in the transmission of PCs, which can be induced by both vapor adsorption or by a liquid analyte, as demonstrated with a microfluidic setup.     

Frequency-multiplexed gas sensing using chirped laser molecular spectroscopy

A method for frequency-multiplexed multi-sample gas sensing is presented. It enables measuring multiple samples placed simultaneously in the setup, without any optical or mechanical switching. Samples are measured using heterodyne detection and signal from each sensing path is encoded at different carrier frequency. Subsequently, a signal from particular sample is retrieved through heterodyne beatnote demodulation at unique frequency. This technique is particularly suitable for real-time calibration of the sensor through a sequential (or simultaneous) detection of three signals: from unknown sample, reference sample and baseline. Basic setup is demonstrated and proof-of-concept experiments are presented. Very good agreement with spectra measured using standard tunable diode absorption spectroscopy is obtained.     

Deposition and microstructure characterization of atmospheric plasma-sprayed ZnO coatings for NO2 detection

This work studied the possibility of using a sensor based on plasma-sprayed zinc oxide (ZnO) sensitive layer for NO₂ detection. The atmospheric plasma spray process was employed to deposit ZnO gas sensing layer and the obtained coating structure was characterized by scanning electron microscopy and X-ray diffraction analysis. The influences of gas concentration, working temperature, water vapor in testing air on NO₂ sensing performance of the ZnO sensors were studied. ZnO sensors showed a good sensor response and selectivity to NO₂ at an optimal working temperature.     

Molecular relaxation effects in hydrogen chloride photoacoustic detection

A photoacoustic (PA) sensor has been developed to monitor hydrogen chloride at sub-ppm level in the 1740-nm region. The system was designed to control the process in the novel low-water-peak optical fiber manufacturing process. Relaxation effects in hydrogen chloride PA detection in oxygen–helium and nitrogen–helium gas mixtures are presented, showing that the generation of the PA signal is strongly affected by the ratio of these substances. In addition, the role of water vapor in the PA signal is investigated.     

Synthesis of MFI zeolite films on optical fibers for detection of chemical vapors

We report the development of a novel zeolite-incorporated optical fiber sensor and demonstrate its capability for in situ detection of chemical vapors. The sensor comprises a polycrystalline silicalite thin film grown upon the cleaved end face of a standard single-mode optical fiber. The sensor device operates by measuring the optical reflectivity of the zeolite crystals, which changes reversibly in response to the amount of chemical vapor adsorbed in its crystalline microporous structure. The sensor has been successfully demonstrated for measuring the concentration of isopropanol vapor in mixtures with nitrogen gas.     

Ultrasonic sensing of a plasmoid

An atmospheric plasmoid that is obtained in a discharge above the water surface has been known since 2000 and studied in several laboratories. The main parameters, in particular, the gas temperature, must be measured for interpretation of this phenomenon. The temperature measurements are complicated, since the plasmoid ascends in air and can be detected by sensors at a relatively short time interval. A method for the ultrasonic sensing of a plasmoid is developed. A scheme of the setup for the ultrasonic sensing is presented and a procedure is described. The speed of sound in a gas is one-to-one related to the gas temperature. The plasmoid temperature is calculated using the speed of ultrasound on the assumption that the plasmoid is formed from water vapor. In accordance with the experimental results, the plasmoid temperature decreases from 2800 to 600–700 K over a lifetime of 500 ms. A decrease in the temperature results from heat emission and mixing with surrounding air.     

Advances in high throughput screening of gas sensing materials

The workflow of a high throughput screening setup for the rapid identification of new and improved gas sensor materials is presented. The polyol method was applied to prepare nanoparticulate metal oxides as base materials. These materials have been modified by surface and volume doping. Using multielectrode substrates and high throughput impedance spectroscopy (HT-IS) a wide range of materials could be screened on a short time scale. Selected examples reflect the state of the art for applying HT-IS in search of new selective gas sensing materials.     

A quartz-enhanced photoacoustic spectroscopy sensor for measurement of water vapor concentration in the air

A compact and highly linear quartz-enhanced photoacoustic spectroscopy(QEPAS)sensor for the measurement of water vapor concentration in the air is demonstrated.A cost-effective quartz tuning fork(QTF)is used as the sharp transducer to convert light energy into an electrical signal based on the piezoelectric effect,thereby removing the need for a photodetector.The short optical path featured by the proposed sensing system leads to a decreased size.Furthermore,a pair of microresonators is applied in the absorbance detection module(ADM)for QTF signal enhancement.Compared with the system without microresonators,the detected QTF signal is increased to approximately 7-fold.Using this optimized QEPAS sensor with the proper modulation frequency and depth,we measure the water vapor concentration in the air at atmospheric pressure and room temperature.The experimental result shows that the sensor has a high sensitivity of 1.058parts-per-million.     

全光型石英增强光声光谱

设计并演示了一种全光型石英增强光声光谱技术, 该技术在传统的石英增强光声光谱系统中增加了另一束探测光束, 把与气体浓度成正比的石英晶振振臂的振动幅值转化为探测光束的强度变化, 实现了探测气体处无电子元件的全光学系统. 如此的设计使该系统具有较强的抗电磁干扰能力和非常小的传感头体积, 能够用于探测空间受限或探测环境恶劣的情况下, 并实现远距离探测. 在这种配置下, 探测大气压下的水汽, 获得的噪声等效吸收系数为1.13×10^-6 cm^-1W/√Hz. 进一步讨论了优化系统和提升其探测灵敏度的途径. 关键词： 石英增强光声光谱 音叉式石英晶振 气体传感     

Nanocrystalline ZnO coated fiber optic sensor for ammonia gas detection

A cladding modified fiber optic sensor coated with nanocrystalline ZnO is proposed for ammonia gas detection. As-prepared and annealed zinc oxide (500 and 1200 °C) samples are used as the gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the ammonia concentration. The characteristics of the sensor when exposed to ethanol and methanol gases are also studied for gas selectivity. The time response characteristics of the sensor are reported.     

单根Sb掺杂ZnO微米线非平衡电桥式气敏传感器的制作与性能

通过使用化学气相沉积法,成功制备出超长、大尺寸的Sb掺杂ZnO微米线.基于非平衡电桥原理,利用单根Sb掺杂ZnO微米线作为非平衡电桥的一个桥臂,制作出了可以在室温环境下工作的气敏传感器原型器件.结果表明:室温下测得该传感器对20,50,100和200 ppm(1 ppm=10^-6)不同浓度的丙酮及乙醇气体的响应-恢复曲线均呈现为矩形形状,在空气及被测气体中均有稳定的电流值,并随着探测气体浓度的增大,器件的响应值也在逐渐增加.此外,还发现器件对丙酮气体具有更好的选择性,当丙酮气体浓度为200 ppm时,该传感器的响应时间为0.2 s,恢复时间为0.3 s,响应度高达243%.通过与普通电导式气敏传感器对比发现,采用这种非平衡电桥结构传感器可以明显地提高响应度,使响应和恢复时间更快.此外,还研究了器件的气体探测机理.     

Single-ended mid-infrared laser-absorption sensor for time-resolved measurements of water concentration and temperature within the annulus of a rotating detonation engine

A novel single-ended mid-infrared laser-absorption sensor for time-resolved measurements of water mole fraction and temperature was developed and deployed within the annulus of a hydrogen/air-fed rotating detonation engine (RDE). The sensor transmitted two laser beams targeting mid-infrared water transitions through a single optical port on the outer wall of the cylindrical RDE annulus and measured the backscattered radiation from the RDE inner surface using a photodetector for a round-trip path of 1.52?cm. Optimizing the sensor's optical arrangement using numerical ray tracing to minimize interference from optical emission, beam steering, and scattered laser light from window surfaces was essential to sensor performance. Scanned-wavelength-modulation spectroscopy with second-harmonic detection and first-harmonic normalization was implemented to allow for frequency-domain multiplexing of the two lasers and to suppress non-absorbing interference sources such as beam-steering and emission. Tunable diode lasers near 2551 and 2482?nm were modulated at 100 and 122?kHz, respectively, and sinusoidally scanned across the peaks of their respective water transitions at 10?kHz to provide a measurement rate of 20?kHz and detection limit of 0.5% water by mole. Experimentally derived spectroscopic parameters enabled water and temperature sensing with respective uncertainties of 7.3% and 5.3% relative to the measured values. Time-resolved and time-averaged sensor measurements of gas temperature and water vapor mole fraction allow quantitative evaluation of the combustion progress at the measurement location and thus provide a design tool for RDE optimization. Broadly, this single-ended laser sensor should find applications in other combustion systems where optical access is limited.     

Synthesis and gas sensing properties of high porosity n-type nickel ferrite thin film assisted by altering magnetic field

NiFe₂O₄ thin film with high porosity based gas sensors had been prepared and their microstructure and gas sensing property were investigated. The sensing layer, consisted of perpendicular overlapped NiFe₂O₄ chains which were induced by altering magnetic field to self-assemble, had high porosity. The phase character and porous microstructure were characterized by X-ray diffraction (XRD) and a polarizing optical microscopy. The gas sensing tests results indicated that the sensor presented a high sensitivity to NH₃ at 150 °C, and was selective to NH₃ below 200 °C. The large porosity microstructure should benefit the reaction between target gas and sensing material and the detection of low concentration gas at low working temperature. In repeatability tests, the response and recovery time values had only narrow fluctuations.     

A review of mixed-potential type zirconia-based gas sensors

A robust and reliable gas sensing device is considered as a convenient and practical solution for gas concentration monitoring that has become a mandatory requirement in different field of applications. For in situ hazardous gases detection, a mixed-potential type gas sensor has been regarded as a promising solid-state gas sensor. For the past three decades, there has been a significant progress in achieving high performance in mixed-potential type sensors. Therefore, this review is focused on reporting the development of mixed-potential type gas sensors with combined yttria-stabilized zirconia (YSZ) as the base solid electrolyte material and various classes of electrode materials for their potential utilization as a high-performance sensing electrode. The underlying sensing mechanism of a mixed-potential type YSZ-based sensor is elaborated here in detail. Transformation in design and configuration of this type of sensor is also covered in this report. In addition, recent progresses on mixed-potential type gas sensors development for detection of several target gases, such as carbon monoxide, hydrocarbons, nitrogen oxides, hydrogen, and ammonia, are reviewed. Strategies to improve the sensing characteristic, particularly gas sensitivity and selectivity, are also reported. Based on the understanding of the fundamental sensing mechanism and the requirements for high-performance gas sensors, challenges and future trends for this type of gas sensor development are discussed.     

Nanocrystalline cerium oxide coated fiber optic gas sensor

A clad-modified fiber optic sensor with nanocrystalline CeO₂ is proposed for gas detection. As-prepared and annealed CeO₂ (500 °C) samples have been used as gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia, ethanol and methanol gases (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the gas concentration. The characteristics of the sensor are also studied for gas selectivity. The time response characteristics of the sensor are reported.     

Molecular gas sensing below parts per trillion: radiocarbon-dioxide optical detection

Radiocarbon ((14)C) concentrations at a 43 parts-per-quadrillion level are measured by using saturated-absorption cavity ringdown spectroscopy by exciting radiocarbon-dioxide ((14)C(16)O(2)) molecules at the 4.5 μm wavelength. The ultimate sensitivity limits of molecular trace gas sensing are pushed down to attobar pressures using a comb-assisted absorption spectroscopy setup. Such a result represents the lowest pressure ever detected for a gas of simple molecules. The unique sensitivity, the wide dynamic range, the compactness, and the relatively low cost of this table-top setup open new perspectives for ^{14}C-tracing applications, such as radiocarbon dating, biomedicine, or environmental and earth sciences. The detection of other very rare molecules can be pursued as well thanks to the wide and continuous mid-IR spectral coverage of the described setup.     

大尺度区域水汽浓度激光检测方法的研究

为了实现大尺度区域下大气中水汽浓度的高灵敏度、高精确性、快速响应检测,与遥感反演的数据进行校正,采用了TDLAS直接吸收技术结合开放式监测的方法。选择水汽分子在1.27 μm附近的单根吸收谱线为目标谱线,设计了大尺度区域水汽激光检测系统。结合多次反射池验证了系统性能,40 m光程下极限灵敏度为14.803 mmol·mol-1。利用本系统在中国科学院禹城综合试验站完成了1 420 m光程下的连续外场实验,系统工作稳定,并与同场地涡度相关观测系统中的气体分析仪LI-7500的测量数据进行了对比,数据一致性较好。为在复杂野外非均匀下垫面的水汽浓度变化的监测提供新方法。     

Trace gas sensor based on quartz tuning fork enhanced laser photoacoustic spectroscopy

A compact photoacoustic gas sensor based on a quartz tuning fork and fiber-coupled distributed feedback (DFB) diode laser for detection of trace gas at atmospheric pressure has been developed. The sensor performance was evaluated by detection of water vapor in ambient air at normal atmospheric pressure. A normalized noise equivalent absorption coefficient of 1.68×10⁻⁸ cm⁻¹ W/Hz^1/2 was achieved. Influence of different acoustic microresonators and sample pressure on the sensor performance, and the characterization of the sensor response time were investigated. Approaches to improve the current sensor performance are discussed.     

Enhanced transduction of photonic crystal dye lasers for gas sensing via swelling polymer film

We present the enhanced transduction of a photonic crystal dye laser for gas sensing via deposition of an additional swelling polymer film. Device operation involves swelling of the polymer film during exposure to specific gases, leading to a change in total effective refractive index. Experimental results show an enhancement of 16.09 dB in sensing ethanol vapor after deposition of a polystyrene film. We verify different responses of the polystyrene film when exposed to either ethanol vapor or increased humidity, indicating selectivity. The concept is generic and, in principle, straightforward in its application to other intracavity-based detection schemes to enable gas sensing.     

基于单个量子级联激光器的大气多组分测量方法

利用单个新型中红外量子级联激光器作为激光光源,结合长程光学吸收池技术开展了大气多组分同时测量方法的研究.通过结合基于自适应性Savitzky-Golay滤波的数据处理算法,有效地提高了系统检测灵敏度和光谱分辨率.研究结果表明,在1 s的时间分辨率和1 atm压力条件下,采用二次微分探测技术可实现CO,N_2O和H_2O测量精度分别为8.20 ppb,7.90 ppb和64.00 ppm(1 ppb=10~(-9),1 ppm=10~(-6));通过提高信号平均时间,在最佳的积分时间(85 s)时,系统可实现的最小检测限分别为1.25 ppb(CO),1.15 ppb(N_2O)和35.77 ppm(H_2O).整个系统具有结构紧凑,成本相对较低,通过选择其他波段的量子级联激光器的激光光源,即可实现对其他分子的实时分析.本系统可广泛应用于大气化学等领域的应用研究.