分布式光纤管道泄漏检测及预警技术灵敏度分析

针对管道安全存在的问题,提出了一种基于Mach-Zehnder光纤干涉仪原理的分布式光纤管道泄漏检测及预警技术,利用与管道同沟敷设的光缆中的3条单模光纤构成分布式光纤微振动传感器检测管道沿线的振动信号,可以有效地检测管道沿线所发生泄漏和异常事件．分析和研究了检测系统的测试灵敏度影响因素,并采用不同光缆结构和埋设方式对检测系统的检测灵敏度进行测试．实验结果表明,该检测技术可以检测到1m范围内的人工挖掘信号,在气体管道压力不小于0．2MPa的条件下,可以检测到0．4m^3／min的气体管道泄漏．     

Enhancement in sensitivity for fiber-optic torsion sensors

We demonstrate a simple fiber-optic torsion sensor with enhanced sensitivity. The sensor is based on the combination of a Malus and a Fabry-Perot (MFP) interferometer and allows for the sensitive detection of changes in the polarization of the guided beam due to torsion applied to the fiber. The basic idea behind this optical arrangement is to enhance the sensitivity for the measurements of intracavity anisotropies due to multiple passes of the beam through the sensing area. Theoretical analysis based on Jones calculus for a fiber-optic MFP interferometer shows that small twists in the fiber can be monitored through variations on the transmission of the arrangement. Experimental results with a hybrid MFP arrangement of bulk optical components and optical fibers show that, compared to single-pass polarimeter measurements, an enhancement in sensitivity up to 116 can be effectively achieved.     

Phase detection sensitivity enhancement of surface plasmon resonance sensor in a heterodyne interferometer system

We propose a method of rotating the analyzer in front of the photodetector in a heterodyne interferometer system to implement optical phase shift and detection sensitivity enhancement of surface plasmon resonance (SPR) sensors. When the analyzer is rotated to shift the phase curve to be near the phase jump point, the phase detection sensitivity of the SPR sensor can be greatly enhanced. Theoretical calculations of a prism-coupled SPR device were performed using this method. Experimental result using an electro-optic heterodyne interferometer is reported.     

Detection of gold nanoparticles using an immunoglobulin-coated piezoelectric sensor

Since the existence of nanoparticles in our environment has already attracted considerable attention due to their possible toxic impact on biological systems, the field detection of nanoparticles is becoming a technology that will be much in need. We have constructed a piezoelectric sensor with an antibody-coated electrode. The antiserum can bind gold nanoparticles with a high degree of selectivity and sensitivity. The biosensor thus constructed can detect 4, 5, or 6?nm gold nanoparticles (GNPs) depending on the coated antiserum. The sensitivity for the detection of 5?nm GNPs was 10.3 ± 0.9?ng?Hz(-1), with the low limit of detection at 5.5?ng. A quartz crystal microbalance (QCM) sensor was capable of detecting GNPs and other types of nanoparticle, such as ZnO, or Fe(3)O(4). The current study provides, for the first time, a platform for detecting nanoparticles in a convenient, economical manner.     

Sensitivity analysis for PCA-based chiller sensor fault detection

This paper presents an algebraic solution of erroneous sensor's undetectable boundary to evaluate the sensitivity of chiller sensor fault detection based on principal component analysis. Q-statistic of PCA is normally applied as a collective statistical index to detect sensor fault by comparing its value with the threshold. However, Q-statistic has no specific physical meaning and cannot evaluate the sensitivity of the provided method for sensor fault detection. We analyzed the definition of Q-statistic and derived the numerical value of the minimum range not to detect sensor fault. Bias sensor fault of a fielded screw chiller was studied for each sensor in PCA model by introducing different severity levels. Results showed that each sensor has different fault detection sensitivity using the same PCA model. The undetectable boundary can be a criterion used to evaluate the detection sensitivity of PCA-based method easily.     

Drift correction in a multichannel integrated optical young interferometer

We demonstrate that in a sensor based on a multichannel Young interferometer, the phase information obtained for different pairs of channels can be used to correct the long-term instability (drift) due to temperature differences between measuring and reference channels, the drift in the alignment of the setup, etc. Experiments show that the nature of a major part of the drift is such that the drift present in one of the channels can be determined by interpolation of the drift measured in the two adjacent channels. It is shown that a drift reduction of 10 times can be achieved as compared with the situation in which no correction is applied. We anticipate that these findings will permit the exploitation of the extreme sensitivity of interference-based sensors to a much greater extent.     

External phase-modulation interferometry

We analyze and test a laboratory benchtop version of a compound interferometric phase sensor, a Michelson interferometer whose output is combined coherently with a phase-modulated local oscillator beam tapped off the Michelson input beam. This configuration models a whole class of external-modulation interferometers designed to shift signals, obscured by low-frequency intensity noise of the light source, into a shot-noise-limited region of the photocurrent spectrum. We find analytically that the shot-noise-limited sensitivity achievable with this system is comparable with that obtained by using internal phase modulation, with both schemes suffering (for different reasons) approximately a 22% sensitivity penalty compared with ideal shot-noise-limited direct detection. Experimentally we achieve true shot-noise-limited sensitivity, and we investigate trade-offs necessitated by commonly encountered nonideal features in any external-modulation system. Our analytic model, which specifically accounts for Michelson fringe contrast, electronic receiver noise, phase-modulation depth, and the local oscillator tap-off fraction, is sufficiently accurate to predict the absolute sensitivity of our benchtop instrument to within 0.5 dB.     

Amplification-Free Detection of SARS-CoV-2 Down to Single Virus Level by Portable Carbon Nanotube Biosensors (Small 34/2023)

The rapid and sensitive detection of trace-level viruses in a simple and reliable way is of great importance for epidemic prevention and control. Here, a multi-functionalized floating gate carbon nanotube field effect transistor (FG-CNT FET) based biosensor is reported for the single virus level detection of SARS-CoV-2 virus antigen and RNA rapidly with a portable sensing platform. The aptamers functionalized sensors can detect SARS-CoV-2 antigens from unprocessed nasopharyngeal swab samples within 1 min. Meanwhile, enhanced by a multi-probe strategy, the FG-CNT FET-based biosensor can detect the long chain RNA directly without amplification down to single virus level within 1 min. The device, constructed with packaged sensor chips and a portable sensing terminal, can distinguish 10 COVID-19 patients from 10 healthy individuals in clinical tests both by the RNAs and antigens by a combination detection strategy with an combined overall percent agreement (OPA) close to 100%. The results provide a general and simple method to enhance the sensitivity of FET-based biochemical sensors for the detection of nucleic acid molecules and demonstrate that the CNT FG FET biosensor is a versatile and reliable integrated platform for ultrasensitive multibiomarker detection without amplification and has great potential for point-of-care (POC) clinical tests.     

Lead silicate fiber-based,refractive index-independent temperature sensor

Thee fabrication is reported of a simple, compact, and stable refractive index (RI)-independent temperature sensor based on a soft glass fiber (SGF) interferometer. Because the SGF has a high thermal expansion coefficient and a high RI, it is sensitive to temperature change but not sensitive to the RI change of liquids with lower RI. It thus can be used to detect the temperature change of aqueous solutions accurately. As an example, a temperature sensor with a temperature sensitivity of ～17?pm/°C and a negligible RI sensitivity of only about ?1?nm/RIU (RI unit) in the range 1.32–1.43 is demonstrated. In addition, our SGF interferometer has potential applications and advantages in detecting liquids such as liquid crystals with higher RI.     

Solid-contact electrochemical polyion sensors for monitoring peptidase activities

We report here on improved solid-contact electrochemical polyion sensors for the detection of polyion protamine. The polymeric membrane sensors were fabricated with a conducting polymer as an ion-electron transduction layer. We observed that decreasing the magnitude of the applied current pulse caused a significant improvement of the sensor sensitivity to low protamine levels. The protamine sensors exhibited a stable and reversible response to protamine concentrations ranging from 0.05 to 30 mg L-1. The sensors were used for monitoring peptidase activities utilizing galvanostatically controlled solid-contact membrane sensors. The polyion protamine was used as a substrate to detect the activity of the protease trypsin. The enzyme activity was continuously monitored by measuring the protamine concentration as it is cleaved by enzyme into smaller fragments to which the sensor is less sensitive. In the presence of a given level of protamine the initial rate of reaction can be linearly related to the trypsin activity within a 0-5 U mL-1 concentration range. The interference with the enzymatic reaction product arginine was specifically examined.     

Improving the phase sensitivity of a Mach–Zehnder interferometer via a nonlinear phase shifter

We propose a scheme to improve the phase sensitivity of a Mach–Zehnder interferometer. In this scheme, a Kerr nonlinear phase shifter is used to replace the traditional linear phase shifter. We consider two detection approaches: the direct homodyne detection (DHD) and the indirect homodyne detection (IHD). We find that the Kerr nonlinear phase shifter can improve the phase sensitivity of the interferometer, and the DHD is better than the IHD. In addition, we also find that the phase sensitivity of the Kerr nonlinear interferometer is robust against photon losses.     

Surface Plasmon Resonance Biosensor Incorporated in a Michelson Interferometer WithEnhanced Sensitivity

A novel double-pass phase-sensitive surface plasmon resonance (SPR) biosensor based on a Michelson interferometer with differential phase interrogation is presented. The new setup provides an intrinsic resolution enhancement of up to two times in terms of achievable detection sensitivity due to an amplification effect in the SPR phase change when we place the SPR sensor head in the signal arm of the interferometer so that the interrogating optical beam traverses the sensor surface twice. Experimental results obtained from saltwater mixtures and antibody-antigen binding reactions confirmed the expected sensitivity enhancement as compared to the conventional SPR biosensor based on a Mach-Zehnder interferometer     

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer

This paper describes a fiber optic sensor suitable for noncontact detection of ultrasonic waves. This sensor is based on the fiber optic Sagnac interferometer, which has a path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. Ultrasonic oscillations produced by conventional ultrasonic piezoelectric transducers were successfully detected, and the performance of this interferometer was investigated by a power spectrum analysis of the output signal. Based on the validation of the fiber optic Sagnac interferometer, noncontact detection of laser-generated surface waves was performed. The configured Sagnac interferometer is very effective for the detection of small displacement with high frequency, such as ultrasonic waves used in conventional nondestructive testing (NDT)     

High sensitivity of taper-based Mach-Zehnder interferometer embedded in a thinned optical fiber for refractive index sensing

A taper-based Mach-Zehnder interferometer (MZI) embedded in a thinned optical fiber is demonstrated as a highly sensitive refractive index (RI) sensor. A RI sensitivity of 2210.84 nm/RIU (refractive index unit) is obtained at the external RI of 1.40, which is ten times higher than that of normal taper- and long-period fiber grating (LPFG)-based sensors. The sensitivity can be further improved by decreasing the diameter of the thinned fiber and increasing the interferometer length of the MZI. The proposed MZIs have lower temperature sensitivities compared with normal fiber sensors, which is a desirable merit for RI sensors to reduce the cross sensitivity caused by thermal drift.     

Aptamer-based viability impedimetric sensor for viruses

The development of aptamer-based viability impedimetric sensor for viruses (AptaVISens-V) is presented. Highly specific DNA aptamers to intact vaccinia virus were selected using cell-SELEX technique and integrated into impedimetric sensors via self-assembly onto a gold microelectrode. Remarkably, this aptasensor is highly selective and can successfully detect viable vaccinia virus particles (down to 60 virions in a microliter) and distinguish them from nonviable viruses in a label-free electrochemical assay format. It also opens a new venue for the development of a variety of viability sensors for detection of many microorganisms and spores.     

Performance improvement in Mach–Zehnder interferometer-based refractive index sensor using elliptical photonic nanowires

We propose a modified Mach–Zehnder interferometer design based on elliptical silica photonic nanowires. The use of the interferometer as an evanescent field-based refractive index (RI) sensor was numerically investigated. Single-mode operation, maintaining polarization and very high sensitivity, is achieved at short optical wavelengths by simply using elliptical nanowires. The proposed sensor is capable of determining the RI of benzene solutions with different concentrations in water and detecting a RI variation of the order of 10^?6 RI units in only a 1-mm length sensitive area. Extremely high sensitivity of 4.63?rad/μm is achieved using an 800?nm elliptical silica nanowire diameter. The operating wavelengths (λ = 650?nm and 970?nm) were chosen to avoid high water absorption. The sensor is shown to be an alternative solution to small circular-nanowire-based sensor whose core size needs to be significantly reduced below 400?nm to achieve comparable performance.     

Boosting sensitivity of organic vapor detection with silicone block polyimide polymers

We demonstrate that silicone block polyimide polymers have an unusually high sensitivity to nonpolar organic vapors, including chlorinated organic solvent vapors. When 0.18-5.34-microm-thick films of silicone block polyimide polymers were deposited onto 10-MHz thickness shear mode (TSM) oscillators, these films were implemented to detect parts-per-billion concentrations of trichloroethylene (TCE) with a detection sensitivity of 0.5-23.5 Hz per 500 ppb of vapor. With a film thickness of 3.4 microm (91.5-kHz frequency shift upon film deposition), optimized for the minimal sensor noise of 0.04 Hz, the calculated detection limit of sensor response (S/N = 3) was 3 ppb of TCE. Detection limits for other chlorinated organic solvent vapors, such as perchloroethylene (PCE), cis-1,2-dichloroethylene (DCE), trans-1,2-DCE, 1,1-DCE, and vinyl chloride (VC) were 0.6, 6, 6, 11, and 13 ppb, respectively. Assuming only the mass-loading response when deposited onto the TSM devices, silicone block polyimide polymers have partition coefficients of over 200 000 to parts-per-billion concentrations of TCE that make them at least 100 times more sensitive than other known polymers for TCE detection. We observed that unlike conventional polyimides, water sensitivity of the new hybrid polyimides is suppressed because of the silicone soft block. Water sensitivity is comparable with the sensor response to nonpolar organic vapors. The high sensitivity and long-term stability of these sensor materials make them attractive for ultrasensitive practical sensors.     

Optical-fiber copolymer-film electric-field sensor

Characteristics of a fiber-optic sensor for the detection of external electric fields are presented. This device utilizes a single-mode fiber that is embedded in a poled vinylidene fluoride-tetrafluoroethylene copolymer film and incorporated as the sensor arm of a Mach-Zehnder interferometer. A low-frequency intrinsic sensitivity of (0.20 +/- 0.03) x 10(-12) m/V is measured which compares well with our projected theoretical static sensitivity. This sensitivity implies a minimum detectable field of 33 microAV/m for a 1.0-km length of activated fiber and a 10(-7)-rad phase-shift detection capability.