Performance Of Optical Sensor Research Articles

Highly Sensitive Fiber Optic Current Sensors with Integrated λ/4 Retarder

ABSTRACTFiber optic current sensors have made unprecedented contributions to the safety and security of power grids. The λ/4 retarder, as a key component for generating circular polarization, can significantly enhance the performance of fiber optic current sensors (FOCS) due to its superior characteristics. However, traditional methods of fabricating homemade λ/4 retarders have inherent flaws. This study replaced the traditional λ/4 retarder in the all‐fiber current sensor with an integrated λ/4 retarder, which is proposed to convert linearly polarized light into circularly polarized light by controlling different spin rates of the spun fiber. The current sensitivity was increased from 0.235 to 0.404 mV/mA, and the noise was suppressed.

Deflection estimation of reinforced concrete beams using long-gauge optic sensors

Deflection is a crucial indicator in structural health monitoring, directly impacting the service life, safety, and economic viability of structures. However, current indirect methods for measuring deflection, such as multi-element FBG sensors or accelerometers, often have limitations. While they may be suitable for flexure-dominated reinforced concrete (RC) specimens in the elastic stage, they neglect the significant influence of nonlinearity and shear deformation. This paper introduces a new approach for estimating the deflection of reinforced concrete (RC) beams using distributed long-gauge optic sensors. The method tackles the limitations of current methods by incorporating the crucial factors of shear deformation, neutral axis position variation and shear stiffness degradation. Experimental studies are first conducted to validate the accuracy and stability of long-gauge optic sensors in small-scale RC members. Algorithms are then utilized the measurement data to estimate the deflection. The results demonstrate the excellent performance of long-gauge optic sensors in measuring shear deformation and vertical deflection of RC beams, as evidenced by comparisons with LVDT measurements. Additionally, a method for decoupling flexural and shear deformation is proposed. This method offers a preliminary assessment of the reinforced concrete (RC) beam type by quantifying the relative significance of shear deformation.

Improving the performance of resonator-based optical sensors using time-lagged correlation and Fourier phase shift analysis

The performance of time-lagged correlation and Fourier phase shift analysis in resonator-based optical sensors was evaluated and compared to centroiding algorithms. 100 emission spectra of an Er3+ oxyfluoride microsphere were recorded and the average of all data was used as a noiseless spectrum. The Whispering Gallery Mode (WGM) signal, superimposed on the Er3+ emission band, was subtracted and shifted to simulate sensor measurements. Additive random Gaussian noise with different values of the variance was added to the original and WGM-shifted spectra, and the WGM shift was estimated using time-lagged correlation, Fourier phase shift analysis and centroiding algorithms. The procedure was repeated 10000 times to evaluate the accuracy and precision of all numerical methods, and different values of the noise level and WGM shift were considered. These pseudo-experimental studies show that the use of time-lagged correlation and Fourier phase shift analysis can improve the accuracy and precision of the sensor when compared to traditional centroiding algorithms. Additionally, signal analysis can be automated without the need for peak identification and matching.

Corrections to “Static and Dynamic Performance of z-LiNbO₃ Optical Temperature Sensor”

Corrections to “Static and Dynamic Performance of z-LiNbO₃ Optical Temperature Sensor”

Investigation of membrane stress continuously adjustable fiber optic acoustic sensor based on inverse piezoelectric effect

In this paper, a fiber optic acoustic sensor with continuously adjustable membrane stress technology is proposed, in which the stress exerted on the membrane can be flexibly adjusted by employing the inverse piezoelectric effect of lead zirconate titanate (PZT) tubular pedestal. First, the response mechanism of stress on the membrane is investigated theoretically. Based on this principle, the effect of adjustable stress on the flat response region and sensitivity of a single mode-multimode-single mode (SMS) fiber optic acoustic sensor are studied experimentally. The experimental results reveal that the flat response region of the sensor extends from 250 Hz to 450 Hz following the continuous increase in the membrane stress by changing the positive direct current voltage applied on PZT from 0 V to 100 V; meanwhile, the sensitivity decreases gradually from 336.5 mV Pa−1 to 162.7 mV Pa−1. The results also verify that the average minimum detectable pressure of the sensor is maintained at 0.54 mPa Hz−1/2 with a fluctuation of 0.08 mPa Hz−1/2 during the tuning process of membrane stress, which provides a flexible method for performance and applicability improvement of membrane-based fiber optic acoustic sensors.

Photonic crystal fiber sensors to excite surface plasmon resonance based on elliptical detection channels are used for highly sensitive magnetic sensing

To improve the detection performance of fiber optic magnetic field sensors a new photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) was designed and investigated. The designed sensor uses an elliptical detection channel, and the modal transmission characteristics and magnetic field sensing characteristics of this fiber optic sensor are analyzed using the full vector finite element method (FVFEM). In addition, the effect of the detection channel on the detection accuracy at different curvatures was investigated. Compared with previous optical fiber magnetic field (MF) sensors, the designed sensor meets the requirements of both refractive index (RI) and MF measurements, and the MF sensitivity, RI sensitivity, and amplitude sensitivity (AS) of the sensor reach 0.739 nm/Oe, 12043.8 nm/RIU, and 754.88RIU−1, respectively. The designed sensor expands the application range of optical fiber sensors and reduces the cost. It has great potential for application in complex environments.

Performance Comparison of Lossy Mode Resonance Refractive Index Sensors on Structures Based on Graphene and MoS2

Abstract 2D materials such as graphene and MoS2 have a crucial role in improving the performance of optical sensors. In this work, we investigated a lossy mode resonance (LMR) sensor composed of MgF2 and 2D materials. The transfer matrix method has been chosen to determine the reflectance curve of the sensor with different thicknesses of MgF2 and 2D materials. The computational results show that the LMR sensor generated with s-polarized light has a better resonance. The existence of exciton in MoS2 also has a very dominant contribution to the resulting resonance. There are two absorption peaks around the wavelengths of 610 and 652 nm which are caused by the presence of excitons A and B in MoS2. When graphene- and MoS2-based chips are compared, MoS2-based chips display a wider detection range with better signal stability. A sensitivity of 70.37°/RIU can be achieved with MgF2 (200 nm)/MoS2 (5 layers). In addition, the proposed LMR sensor has a penetration depth that is two times higher than conventional SPR sensors, making it possible to replace SPR sensors which rely heavily on gold as their transducer.

High performance of SPR-based optical fiber pressure sensor: role of silicone rubber diaphragm

High performance of SPR-based optical fiber pressure sensor: role of silicone rubber diaphragm

A test performance of optical fibre sensors for real-time investigations of rotational seismic events: a case study in laboratory and field conditions

A test performance of optical fibre sensors for real-time investigations of rotational seismic events: a case study in laboratory and field conditions

Experimental study of SPR sensor performance enhancement by metal oxides

With the widespread application of fiber surface plasmon resonance (SPR) sensors in the field of biochemical sensing, especially in the detection of large molecules such as proteins, the sensitivity of traditional fiber SPR sensors has made it difficult to meet the requirements of detection accuracy in practical applications. This article proposes and proves an effective method for selecting the optimal metal oxide material to improve the sensing performance of SPR sensors. Metal oxides (TiO2 and ZnO) can improve the sensitivity by enhancing the evanescent field of fiber SPR phenomenon. Through simulation, it was found that when the metal oxide film of the composite film sensor maintains the same thickness, the metal oxide with a high effective refractive index (RI) has a better improvement effect on the sensitivity of the SPR sensor. Experimental results show that the maximum RI sensitivity of TiO2 composite film sensors and ZnO composite film sensors in the RI range of 1.333–1.420 is 15,200 nm/RIU and 13,600 nm/RIU, respectively. Compared to silver-based sensors, RI sensitivity has increased by 16.92 % and 4.62 %, respectively. To further verify the enhancement effect of different metal oxides on fiber sensors, another layer of PDMS film is deposited on TiO2 and ZnO films. Within the temperature sensing range, the maximum temperature sensitivity of these two composite film temperature sensors is 4.9 nm/°C and 4.3 nm/°C, respectively. Overall, metal oxides with high RI can improve the sensing performance of fiber optic sensors.

Influence of the reference surface and AFM tip on the radius and roundness measurement of micro spheres

The performance of tactile and optical surface sensors for nano and micro coordinate measuring machines is currently limited by the lack of precisely characterised micro spheres, since established strategies have mainly been developed for spheres in the range of millimetres or above. We have, therefore, recently focused our research efforts towards a novel strategy for the characterisation of spheres in the sub-millimetre range. It is based on a set of atomic force microscope (AFM) surface scans in conjunction with a stitching algorithm. To obtain an uncertainty statement, the uncertainty about the shape of the reference surface needs to be propagated via the shape of the AFM tip to the actual measurement object. However, the sampling process of an AFM is non-linear and the processing of AFM scans requires complex algorithms. We have, therefore, recently begun to model the characterisation of micro spheres through simulations. In this contribution, this model is extended by the influence of the tip and reference surface. The influence of the tip’s shape and reference surface is investigated through virtual and real experiments. The shape of the tip is varied by using tips with mean radii of 200 nm and 2 μm while sampling the same ruby sphere with a mean radius of 150 μm. In general, the simulation results imply that an uncertainty of less then 10 nm is achievable. However, an experimental validation of the model is still pending. The experimental investigations were limited by the lack of a suitable cleaning strategy for micro parts, which demonstrates the need for further investigations in this area. Although the characterisation of a full sphere has already been demonstrated, the investigations in this contribution are limited to equator measurements.

MmPose-NLP: A Natural Language Processing Approach to Precise Skeletal Pose Estimation Using mmWave Radars.

In this article, we presented mmPose-NLP, a novel natural language processing (NLP) inspired sequence-to-sequence (Seq2Seq) skeletal key-point estimator using millimeter-wave (mmWave) radar data. To the best of our knowledge, this is the first method to precisely estimate up to 25 skeletal key points using mmWave radar data alone. Skeletal pose estimation is critical in several applications ranging from autonomous vehicles, traffic monitoring, patient monitoring, and gait analysis, to defense security forensics, and aid both preventative and actionable decision making. The use of mmWave radars for this task, over traditionally employed optical sensors, provides several advantages, primarily its operational robustness to scene lighting and adverse weather conditions, where optical sensor performance degrade significantly. The mmWave radar point-cloud (PCL) data are first voxelized (analogous to tokenization in NLP) and N frames of the voxelized radar data (analogous to a text paragraph in NLP) is subjected to the proposed mmPose-NLP architecture, where the voxel indices of the 25 skeletal key points (analogous to keyword extraction in NLP) are predicted. The voxel indices are converted back to real-world 3-D coordinates using the voxel dictionary used during the tokenization process. Mean absolute error (MAE) metrics were used to measure the accuracy of the proposed system against the ground truth, with the proposed mmPose-NLP offering < 3 cm localization errors in the depth, horizontal, and vertical axes. The effect of the number of input frames versus performance/accuracy was also studied for N = {1,2, ... ,10} . A comprehensive methodology, results, discussions, and limitations are presented in this article. All the source codes and results are made available on GitHub for further research and development in this critical yet emerging domain of skeletal key-point estimation using mmWave radars.

Modulation of optical oxygen sensitivity of H2(TPP) by using Eu3+, Gd3+ and Yb3+ ions doped silicate-based bioactive glass powders immersed in simulated body fluid

Improving the performance of optical oxygen sensors can be accomplished by adding additives to the composition comprising an oxygen-sensitive probe encapsulated in a polymeric matrix. In this study, to advance the oxygen sensing ability, free meso-tetraphenyl porphyrin (H2(TPP)) was chosen as a luminophore. The sol-gel based 13–93 bioactive glass powders (BG) co-doped with ytterbium (Yb3+), gadolinium (Gd3+), and europium (Eu3+) and immersed in simulated body fluids (SBF) were also used as additives. After being immersed in SBF, bioactive glasses containing Eu3+, Gd3+, and Yb3+ were found to be able to convert hydroxyapatite corresponding to in vitro bioactivity tests. The optimum additive concentration for all glass samples is 3 wt%, based on photoluminescence-based properties. The luminescence dye was incorporated into poly(trimethylsilylpropyne) [poly(TMSP)] matrices in the form of a thin film along with bioactive glass additives to improve oxygen sensitivity. Emission-based intensity values of all porphyrin complexes have been followed as a signal drop during oxygen sensing measurements. The H2(TPP) along with the additive of BG:Eu3+ showed a 6.88 fold of I0/I ratio compared to the undoped and Gd3+ and Yb3+-doped BG forms in terms of the relative signal change. Large Stoke's shift (Ksv) values, high luminescence abilities, and linear spectral response make them promising candidates as oxygen sensing agents. It was concluded that prepared bioactive glass powders are suitable to use as additive materials for improving the oxygen sensitivity of meso-tetraphenyl porphyrin dye.

Sensitivity Performance of Optical Waveguide Sensors with Different Shapes of Cladding Layer for Microplastics Detection

With microplastics pollution becoming a global concern, there comes a need for sensors to attain an optimal level of sensitivity to detect microplastics in water. This work investigated the effects of cladding layer shapes on the sensitivity performance of an optical waveguide sensor for microplastics detection in water. In this research, three different cladding shapes—C-shaped fiber, D-shaped fiber, and rectangular waveguide with circular core—were simulated by using Wave Optics Module-COMSOL Multiphysics® software. The results indicated that the C-shaped fiber exhibited significantly higher sensitivity, with a sensitivity value of 1.070x10−3 compared to the D-shaped fiber and rectangular waveguide with 3.845x10−4 and 3.842x10−4, respectively. The sensitivities of the D-shaped fiber and rectangular waveguide were relatively similar and did not exhibit any significant difference. The higher sensitivity of the C-shaped fiber is attributed to its larger exposed core area to the analyte, resulting in higher interaction of the evanescent wave with the analyte. However, fabricating the C-shaped fiber is more challenging compared to the other two shapes. This research highlights the significance of cladding shapes in optical waveguide sensor sensitivities and provides design optimization insights for microplastics detection in water.

Evaluation of ultrasound sensors for transcranial photoacoustic sensing and imaging

Photoacoustic imaging through skull bone causes strong attenuation and distortion of the acoustic wavefront, which diminishes image contrast and resolution. As a result, transcranial photoacoustic measurements in humans have been challenging to demonstrate. In this study, we investigated the acoustic transmission through the human skull to design an ultrasound sensor suitable for transcranial PA imaging and sensing. We measured the frequency dependent losses of human cranial bones ex vivo, compared the performance of a range of piezoelectric and optical ultrasound sensors, and imaged skull phantoms using a PA tomograph based on a planar Fabry–Perot sensor. All transcranial photoacoustic measurements show the typical effects of frequency and thickness dependent attenuation and aberration associated with acoustic propagation through bone. The performance of plano-concave optical resonator ultrasound sensors was found to be highly suitable for transcranial photoacoustic measurements.

Design of Surface Plasmon Resonance-Based D-Type Double Open-Loop Channels PCF for Temperature Sensing.

Here, we document a D-type double open-loop channel floor plasmon resonance (SPR) photonic crystal fiber (PCF) for temperature sensing. The grooves are designed on the polished surfaces of the pinnacle and backside of the PCF and covered with a gold (Au) film, and stomata are distributed around the PCF core in a progressive, periodic arrangement. Two air holes between the Au membrane and the PCF core are designed to shape a leakage window, which no longer solely averts the outward diffusion of Y-polarized (Y-POL) core mode energy, but also sets off its coupling with the Au movie from the leakage window. This SPR-PCF sensor uses the temperature-sensitive property of Polydimethylsiloxane (PDMS) to reap the motive of temperature sensing. Our lookup effects point out that these SPR-PCF sensors have a temperature sensitivity of up to 3757 pm/°C when the temperature varies from 5 °C to 45 °C. In addition, the maximum refractive index sensitivity (RIS) of the SPR-PCF sensor is as excessive as 4847 nm/RIU. These proposed SPR-PCF temperature sensors have an easy nanostructure and proper sensing performance, which now not solely improve the overall sensing performance of small-diameter fiber optic temperature sensors, but also have vast application prospects in geo-logical exploration, biological monitoring, and meteorological prediction due to their remarkable RIS and exclusive nanostructure.

Performance of optical sensors for cloud measurements deployed by the ARM Aerial Facility during ACE-ENA.

During the Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA), a variety of in situ optical sensors using shadow imaging, scattering and holography were deployed by the Atmospheric Radiation Measurement (ARM) Aerial Facility to determine cloud properties. Taking advantage of the wide, overlapping range of instrumentation, we compare in situ cloud data from several different measurement methods for droplets up to 100µm. Data processing was tailored to the encountered conditions, leading to good agreement. Improvements include noise reduction for holography and better out-of-focus correction for shadow imaging. Comparison between direct liquid water content measurements and optical sensors showed better agreement at higher droplet number concentrations (>120/c m 3).

Improving the Width of Lossy Mode Resonances (LMRs) in Double-Clad Fibers

In this work, the characteristics of lossy mode resonances (LMRs) in double-clad fibers where the refractive index (RI) of the second cladding is lower than that of the first cladding are analyzed both numerically and experimentally. In the first place, the LMRs spectra obtained with a 75 nm TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film are simulated, and it is observed that a thicker second cladding improves the width of the resonances, making them narrower. Then, two experimental cases (no second cladding, and second cladding with thickness of 1.13 µm) are assessed, showing a good agreement with the previous simulations. Finally, an experimental refractometric study is carried out in liquids (surrounding medium refractive index in the 1.34 - 1.40 range) for both fibers, calculating the full width at 1dB (FW <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> ), the sensitivity, and the figure of merit (FOM). The FW <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> is better for the LMR obtained on the fiber with second cladding while the sensitivity is slightly greater for the fiber without second cladding. In the case of the FOM, it is higher for the double-clad fiber as the narrowing of the resonances outweighs the lower sensitivity. These results show that the performance of LMR-based optical fiber sensors can be improved by employing double-clad fibers.

Pr3+-doped perovskite niobate ceramics towards improving performance of optical temperature sensor by second harmonic generation (SHG) combined with lanthanide luminescence

Pr3+-doped perovskite niobate ceramics towards improving performance of optical temperature sensor by second harmonic generation (SHG) combined with lanthanide luminescence

Fiber Optic based Localized SPR for Nutrients Detection in Modern Agricultural Applications

Detection of nutrients in the hydroponics system, particularly nitrogen, phosphorus, and potassium (NPK) are critical to ensure the good production of crops. Currently, nutrients are analyzed using spectroscopy and electrochemical techniques, which are tedious and sophisticated. This study was conducted to develop a localized surface plasmon resonance (LSPR) fiber optic sensor technique to measure how much content of these nutrients should be added in the soil to increase crop fertility. The main objectives of this study are to study the LSPR fiber sensor technology on NPK in hydroponic systems, to create a fiber optic sensor technique for measuring NPK in hydroponic systems, and finally to characterize the performance of fiber optic sensors for measuring NPK in hydroponic systems. The utilization of the sensing materials, chitosan in this work is to improve the sensitivity feature of the sensor. Chitosan is coated on the surface of the tapered optical fiber prior to the LSPR NPK detection. The results of the absorption spectra will be visible at the end of the experiment where the obtained data are analyzed using SpectraSuite software. The results show that a good linearity was obtained when used AgNP/chitosan as the sensing material with the sensitivity of 0.041 nm ppm-1 in comparison to that of AgNP with the sensitivity of 0.039 nm ppm-1. A better limit of detection (LOD) and limit of quantification (LOQ) was also observed for AgNP/chitosan which are 35.61 ppm and 107.91 ppm, respectively. Meanwhile, AgNP exhibits LOD and LOQ of 106.16 ppm and 494.43 ppm, respectively. It is expected that this work will be a good contributor to the United Nations Sustainable Development Goals (UN SDG), No. 2: Zero Hunger.