A nonintrusive low-cost sensor based on silicon photodiode detectors has been designed to analyze the formation and behavior of excited CH(*) and C(2)(*) radicals in the combustion process by sensing the spectral emission of hydrocarbon flames. The sensor was validated by performing two sets of experiments for both nonconfined and confined flames. For a nonconfined oil flame, the sensor responses for the axial intensity were highly correlated with the measurements obtained with a radiometer. For confined gas flames the ratio between the signal corresponding to C(2)(*) and CH(*) was successfully correlated with the CO pollutant emissions and the combustion efficiency. These results give additional insight on how to prevent an incomplete combustion using spectral information. The fast response, the nonintrusive character, and the instantaneous measurement of the needed spectral information makes the proposed optical sensor a key element in the development of advanced control strategies for combustion processes. 相似文献
The properties of a CMOS-compatible pn-photodiode, phototransistor, and one-dimensional lateral-effect photodiode (LEP) for position-sensing applications are characterized. The photodiode and phototransistor seem to have properties that are comparable to typical commercial photodetectors despite the relatively large variations in their spatial and spectral responses and the lower responsivity in the near-infrared band. In addition to the above properties the LEP's show excellent linearity, but 3-4 times larger NEP than corresponding commercial LEP's due to low resistance of the current dividing layer. The responsivity variations have no effect on the linearity of the LEP, and the slightly lower responsivity at near-infrared has only a negligible effect on the achievable resolution (SNR). These properties, usually considered as weak points of CMOS-compatible photodetectors, are believed to have little or no effect on the properties of a position sensor, if the diameter of the light spot is small (<100 μm). CMOS-compatible photodetectors are therefore believed to be very suitable for industrial position-sensing applications 相似文献
Strain distribution of asphalt pavement varies in transverse and longitudinal directions, and distresses, such as cracks, ruts and settlements, often occur randomly, which can be efficiently measured by distributed optical fibre sensing technology. As bare optical fibre is weak to resist shear and torsion forces during pavement construction, the protective technique is required. Therefore, a flexible asphalt-mastic packaged optical fibre sensor was developed in this research for distributed strain monitoring of asphalt pavement. Theoretical analysis on strain transfer of the optical fibre-based sensors embedded in asphalt pavement was conducted to improve the design of the protective layer and remove the strain transfer error. Afterwards, laboratory tests on the asphalt concrete beam were carried out to validate the performance of the sensor. Finally, the proposed sensors were applied to detect the in situ performance of urban asphalt pavement under temperature and traffic loads. The results indicate that the proposed optical fibre sensor detects the distributed strain of asphalt pavement effectively, and the in situ data show significant effects of temperature and traffic loads on asphalt concrete course. This research contributes to the full-scale monitoring and health assessment of large-span pavement. 相似文献
In the aircraft industry the use of externally bonded composite repairs has become an accepted way of repairing fatigue, or corrosion, damaged metallic structural components. However, current NDI and damage assessment techniques for composite repairs are passive and generally performed on ground. The challenge is to develop new techniques utilising recent analytical and experimental tools. This report examines the use of optical fibre sensors. Optical fibres offer a means of monitoring the load transfer process in these repairs, and can therefore be used to provide an indication of the integrity of the repair. This paper describes the use of an array of fibre Bragg grating strain sensors (FBGs) for the in situ monitoring of bonded repairs to aircraft structures and, in particular, the monitoring of crack propagation beneath a repair. In this work the FBGs have been multiplexed using a combination of wavelength and spatial techniques employing a tunable Fabry–Pérot (FP) filter to track individual gratings. The multiplexed FBGs were then surface-mounted on a boron–epoxy unidirectional composite patch bonded to an aluminium component. The sensors were located so as to monitor the changing stress field associated with the propagation of a crack beneath the patch. The ability of relating experimental results to sensor readings is then confirmed using both a thermo-elastic scan of the patch and 3D finite element analysis. 相似文献
Flexible, wearable, and even stretchable sensors are the key components of smart electronic textiles. However, most reported flexible and wearable sensors for wearable electronics are usually fabricated in two-dimensional (2D) planar strip configurations, which cannot be properly integrated into textile structures and thus greatly degrade intrinsic properties such as the softness, flexibility, and air permeability of textiles and the aesthetic feeling of clothing. In this work, a new one-dimensional weavable strain sensing yarn consisting of an elastic polyurethane (PU) core, a conductive Ag-nanoparticles/graphene-microsheets composite sheath, and a silicone encapsulation layer was designed and fabricated through an easily manipulated protocol. Arising from the reasonable structural design and appropriate material selection, the as-fabricated strain sensor not only exhibited excellent flexibility, stretchability, and highly repeatable electromechanical stability (a repeatability error of 1.56%) but also possessed both high sensitivity (a gauge factor of nearly 500) and a relatively wide working range (0–50% applied strain) with good linearity (a correlation coefficient of 0.98). In addition, the facile, nearly all-solution-based fabrication protocol enabled the scalable production of long conductive yarns. Thus, the proper yarn length and superb mechanical properties endowed the stretchable conductive yarn with good weavability. The excellent wearability of the stretchable conductive yarn was derived from the outermost isolating, hydrophobic, and biocompatible silicone encapsulation layer. A wearable high-sensitivity strain sensing textile, fabricated by directly weaving the as-prepared yarn-based sensor, showed great potential for application to wearable textile sensors for real-time monitoring of human motions from vigorous walking to subtle and complex pronunciations.
The sensing of chemicals and biochemical molecules using several porous silicon optical microsensors, based both on single-layer interferometers and resonant-cavity-enhanced microstructures, is reported. The operation of both families of sensors is based on the variation of the average refractive index of the porous silicon region, due to the interaction with chemical substances either in vapor or liquid state, which results in marked shifts of the device reflectivity spectra. The well established single-layer configuration has been used to test a new chemical approach based on Si-C bonds for covalent immobilization of biological molecules, as probe, in a stable way on the porous silicon surface. Preliminary results on complementary oligonucleotide recognition, based on this technique, are also presented and discussed. Porous silicon optical microcavities, based on multilayered resonating structures, have been used to detect chemical substances and, in particular, flammable and toxic organic solvents, and some hydrocarbons. The results put in evidence the high sensitivity, the reusability, and the low response time of the resonant-cavity-enhanced sensing technique. The possibility of operating at room temperature, of remote interrogation, and the absence of electrical contacts are further advantages characterizing the sensing technique. 相似文献
提出了一种基于多元状态估计(Multivariate State Estimation Techniques,MSET)和序贯概率比检验(Sequential Probability Ratio Test,SPRT)的内燃机气阀机构振动监测方法.在该方法中,首先建立正常工况下各监测参数之间的关联模型;然后根据系统当前观测特征向量与各建模样本特征向量之间的相似性程度,使用MSET对当前观测特征向量进行估计,得到与观测特征向量相对应的估计残差;最后使用SPRT对观测特征向量的估计残差进行均值和方差检验,确定系统的工作状态.试验中,通过设置不同的气阀间隙大小来模拟内燃机气阀机构不同程度的异常工况,以整周期缸盖振动信号幅值域特征作为系统工况监测参数.试验结果表明,MSET可有效增强故障状态下的信号特征呈现,而SPRT可在较少的周期内实现内燃机气阀机构异常工况的识别,MSET和SPRT的结合有效地实现了对内燃机气阀机构异常工况的早期监测. 相似文献
Noncontact long-range position sensing is desirable for a number of applications. We have designed and fabricated a monolithically integrated vertical-cavity surface-emitting laser (VCSEL) and p-type/intrinsic/n-type (PIN) photodetectors for optical position sensing. Calculations using the reflection from a periodic metallic corrugation as a position gauge indicate resolution in the submicron regime. High device uniformity is obtained using novel fabrication techniques. We observe a threshold current of 0.52 mA for the VCSELs and a detector responsivity of 0.38 A/W at 840 nm. The optical cross talk between VCSELs and detectors is also quantified. 相似文献
A concept for optical temperature sensing based on the differential spectral reflectivity/transmittance from a multilayer dielectric edge filter is described and demonstrated. Two wavelengths, λ(1) and λ(2), from the spectrum of a broadband light source are selected so that they are located on the sloped and flat regions of the reflection or transmission spectrum of the filter, respectively. As temperature variations shift the reflection or transmission spectrum of the filter, they change the output power of the light at λ(1), but the output power of the light at λ(2) is insensitive to the shift and therefore to the temperature variation. The temperature information can be extracted from the ratio of the light powers at λ(1) to the light at λ(2). This ratio is immune to changes in the output power of the light source, fiber losses induced by microbending, and hence modal-power distribution fluctuations. The best resolution of 0.2 °C has been obtained over a range of 30-120 °C. Based on such a basic temperature-sensing concept, a wavelength-division-multiplexed, temperature-sensing system is constructed by cascading three sensing-edge filters that have different cutoff wavelengths along a multimode fiber. The signals from the three sensors are resolved by detecting the correspondent outputs at different wavelengths. 相似文献
Atmospheric corrosion monitoring(ACM)sensors were employed to study the initial atmospheric corrosion of carbon steels over a one-month period in six outdoor dynamic atmospheric environments in China.Based on the~250,000 corrosion data sets collected,the environmental impacts of relative humidity,temperature and rainfall on the initial corrosion behavior of carbon steels were investigated.The results showed that rainfall was the strongest environmental factor influencing the initial atmospheric corrosion rate.Relative humidity significantly influenced the corrosion of carbon steels in low-precipitation environments and non-rainfall period. 相似文献
A review of photodetectors for optical detection in biological applications is presented. The intent is to provide an overview of the performance metrics and trade-offs among popular photodetectors in order to facilitate an easier match among the photodetector, biological stimulus, and optical pathway. The characteristics and nonidealities of fluorescent and phosphorescent reporters, and the properties of optical components such as filters, lenses, and light sources, are reviewed. By accounting for sources of noise in these components, it is shown how to determine metrics for the optical system that can then be converted to photodetector metrics. Defined photodetector metrics include the quantum efficiency, responsivity, noise-equivalent power, detectivity, gain, dark current, response time, and noise spectrum. The operating principles and performance trade-offs of photodetectors are reviewed, and emphasis is placed on photodetectors for integrated compact systems. Top commercial candidates for photodetectors for detecting light emitted from reporters are the photomultiplier tube, avalanche photodiode, and charge-coupled device. Focus is placed on new developments in complementary metal-oxide-semiconductor structures that can provide low-cost, low-power, and low-voltage alternatives to traditional approaches to biological imaging. Reviewed device structures are presented in the context of supporting the development of laboratory-based instruments and compact fully-integrated systems. 相似文献
We present the first example of an integrated complementary metal-oxide-semiconductor (CMOS) photodetector coupled with a solid-state xerogel-based thin-film sensor to produce a compact chemical sensor system. We compare results using two different CMOS-based detector systems to results obtained by using a standard photomultiplier tube (PMT) or charge-coupled device (CCD) detector. Because the chemical sensor elements are governed by a Stern-Volmer relationship, the Stern-Volmer quenching constant is used as the primary comparator between the different detectors. All of the systems yielded Stern-Volmer constants from 0.042 to 0.049 O/sub 2/%/sup -1/. The results show that the CMOS detector system yields analytical data that are comparable to the CCD- and PMT-based systems. The disparity between the data obtained from each detector is primarily associated with the difference in how the signals are obtained by each detector as they presently exist. We have also observed satisfactory reversibility in the operation of the sensor system. The CMOS-based system exhibits a response time that is faster than the chemical sensor element's intrinsic response time, making the CMOS suitable for time-dependent measurements. The CMOS array detector also uses less than 0.1% the power in comparison to a standard PMT or CCD. The combined xerogel/CMOS system represents an important step toward the development of a portable, efficient sensor system. 相似文献