Light-based Sensor Research Articles

Label-free detection of formaldehyde in water by titanium doped MoS2 gold nanoislands LSPR sensor

Formaldehyde is a known human carcinogen widely present in various industrial processes. Dissolved formaldehyde in water poses a significant threat to human health, not solely gases. Here, a novel label-free detection scheme of formaldehyde in aqueous environment via Ti-doped MoS2 as the functionalized layer on a localized surface plasmon resonance (LSPR) sensor is reported. It has been found that the strong adsorption of formaldehyde on Ti-doped MoS2 attached on gold nanoislands induces a strong local refractive index change and enables sensitive detection. Besides, the characterization and LSPR experimental results also highlight the contribution of the nanoislands morphology to facilitate improved surface attachment of Ti-doped MoS2, and in turn improves the sensing performance. Along with experimental work, density functional theory (DFT) calculation has shown the strong formaldehyde adsorption on Ti-doped MoS2 with water molecules included, therefore confirming its feasibility and effectiveness for sensing. The sensor has successfully achieved an excellent detection limit of 0.104 ppb with its selectivity studied and confirmed using DFT calculations and experiment. The practical value of this research lies in its potential development of this light-based sensor for water quality monitoring with the major advantages of facile synthesis, fast detection, and label-free sensing offered by LSPR.

Advances in borophene based photodetectors for a sustainable tomorrow: a comprehensive review.

Borophene, with its unique properties such as excellent conductivity, high thermal stability, and tunable electronic band structure, holds immense promise for advancing photodetector technology. These qualities make it an attractive material for enhancing the efficiency and performance of photodetectors across various wavelengths. Research so far has highlighted borophene's potential in improving sensitivity, response time, and overall functionality in optoelectronic devices. However, to fully realize the potential of borophene-based photodetectors, several challenges must be addressed. A major hurdle is the reproducibility and scalability of borophene synthesis, which is essential for its widespread use in practical applications. Furthermore, understanding the underlying physics of borophene and optimizing the device architecture are critical for achieving consistent performance under different operating conditions. These challenges must be overcome to enable the effective integration of borophene into commercial photodetector devices. A thorough evaluation of borophene-based photodetectors is necessary to guide future research and development in this field. This review will provide a detailed account of the current synthesis methods, discuss the experimental results, and identify the challenges that need to be addressed. Additionally, the review will explore potential strategies to overcome these obstacles, paving the way for significant advancements in solar cells, light-based sensors, and environmental monitoring systems. By addressing these issues, the development of borophene-based photodetectors could lead to substantial improvements in optoelectronic technology, benefiting various applications and industries.

Machine Learning Method and Visible Light-Based Sensors for Multiinterface Level Measurement

Machine Learning Method and Visible Light-Based Sensors for Multiinterface Level Measurement

Intensity-Based Identification of Reflective Surfaces for Occupancy Grid Map Modification

The presence of mobile robots in indoor environments is becoming increasingly significant. While there are algorithms such as SLAM that allow robots to navigate these environments, they do not take into account structural elements of modern buildings such as large glass areas. Due to the use of light-based sensors such as laser scans, these elements are only visible at few incident angles, so they are seen as noise by SLAM algorithms. In this work, reflective surfaces are detected by analyzing laser scan intensity values in order to build a reflection-aware map for safe indoor robot navigation. The main novelty of the proposed method is the usage of a single sensor to gather environment information and a single parameter to determine where reflective zones are. Experiments are carried out in multiple complex real scenarios, quantitatively testing how well the method performs against state of the art works and against factors such as changes in robot orientation, a large number of reflective areas or changes in illumination.

Single-phase high-entropy oxide-based chemiresistor: Toward selective and sensitive detection of methane gas for real-time applications

Detecting methane (CH4) with good selectivity is one of the most important safety precautions to prevent catastrophic incidents in the current industrial environment. Detection of small molecular size, inert and nonpolar characteristic gases at trace levels using chemiresistive technique at room temperature is still challenging because of weak adsorption between gas and sensing material. Therefore, we fabricated a single-phase high entropy oxide based chemiresistor and tested it towards the various gases and several hydrocarbons at room temperature, but the sensor displayed a higher selectivity to CH4 gas than other gases. Further, the sensor characteristics revealed a significant response to CH4 gas, good response and recovery time, good long-term stability, and an experimental detection limit of 25 ppm. Besides, the as-fabricated sensor is low-cost, small in size and consumes 50 nW power, much lower than the other commercialized light-based sensors. As proof of concept, the fabricated sensor was utilized to measure CH4 gas in a real-time atmosphere. The sensor reflected response characteristics similar to the controlled environment and recovered without carrier gas. This facile approach sheds light on the rational design of high-entropy oxides, paving the way for mass production and commercialization of ultra-trace gas detection sensors with superior sensing capability.

Slit Beam Shaping Technique for Femtosecond Laser Inscription of Symmetric Cladding Waveguides

In recent years, the Industry 4.0 paradigm has gained special relevance, focused on the integration of smart structures to increase the efficiency of processes. Photonics, with laser advanced manufacture and light-based sensors, can offer great possibilities in this field. Within advanced manufacturing, femtosecond lasers allow inscribing different optical structures. Waveguides are one of the most widely used structures in photonic sensors. This work proposes the design, simulation and manufacture of symmetric cladding waveguides in optical fibers using the slit beam shaping technique. Cladding waveguides characterized by their low losses (0.21 dB$/cm), quasi-step-index refractive index profile, and circular cross-section are used to couple evanescent light from the core of a single-mode fiber to each of the four cores of a multicore fiber.

These light-based sensors make glass recycling possible

These light-based sensors make glass recycling possible

Reconstruction of refractive index maps using photogrammetry

Large volume metrology is a key enabler of autonomous precision manufacturing. For component positioning, the optical-based metrology technique of photogrammetry could be used more widely if its accuracy was improved. These positional measurements are subject to uncertainties which can be greater than manufacturing tolerances. One source of uncertainty is due to thermal gradients, which cause the refraction of the light rays in large-scale industrial environments. This paper uses light-based sensor data to reconstruct a heterogeneous spatial map of the refractive index in air. We use this reconstructed refractive index map to discount the refractive effects and thereby reduce the uncertainty of this positioning problem. This new inverse problem employs Voronoi tessellations to spatially parameterize the refractive index map, the Fast Marching Method to solve the forward problem of calculating the light rays through this medium, and a Bayesian approach in the inversion. Using simulated data, this methodology leads to positioning improvements of up to 37.

Aluminum-Based Deep-Ultraviolet Surface Plasmon Resonance Sensor

An aluminum-based deep-ultraviolet surface plasmon resonance (DUV-SPR) sensor is promising for biological applications. Design aspects of a DUV-SPR sensor are here considered by using Fresnel multilayer model. Angular and wavelength interrogation modes are used, where fused silica, sapphire, and acrylic solacryl ultraviolet transmittance (acrylic SUVT) are used as optical substrates. Aluminum at its oxidized state (alumina) is also considered as an aluminum overlayer. Our 4-layer Kretschmann-Raether-based SPR sensor is applied for gaseous and aqueous solutions, where some figures of merit are used to analyze the sensor performance. Values for sensitivity, linewidth (FWHM, full width at half maximum), and FOM (figure of merit or quality factor) are calculated. Resolution is also found and compared with other devices by using a known formulation. The results indicate that our sensor has a higher sensitivity for both gaseous and aqueous solutions when compared with the visible light-based sensor. For aqueous solutions, analyte is simulated as a bulk or a monolayer. Therefore, DUV-SPR sensors are a good alternative to the conventional visible-based SPR devices, where the performance is similar or higher for some conditions, having a higher affinity for some proteins.

Development of Light Sensors to Measure Defoliation

Sensors have become valuable tools in agriculture when decisions regarding inputs require precision and speed. For example, factors in estimating defoliation in row crops, such as intensive labor and, in particular, subjectivity, are greatly reduced with the use of sensors that can remove these limitations and biases. Estimates of defoliation are almost always overestimated due to human error and biased, unconscious efforts to locate injury. To address these issues, the accuracy and preciseness of a light-based sensor to detect defoliation was tested by measuring simulated levels of defoliation (0-100%) on paper “leaves” at seven light intensities. Results indicated that higher lux values were detected through thinner paper (filter paper) than through thicker paper (cardstock), demonstrating that leaf thickness could potentially affect accuracy of the light-sensor system. Despite some light penetrating the thinner paper with simulated defoliation levels, the two light sensors tested yielded accurate and precise predictions of defoliation (R2 > 0.95). This light-sensor approach could potentially be used in the field to report real-time measurements of defoliation in row crops, such as soybeans, or in other plant-based systems where losses of leaf area require monitoring in order to prevent economic injury.

Autonomous safe landing-area determination for rotorcraft UAVs using multiple IR-UWB radars

In recent years, the important advances that have been made in unmanned aerial vehicles (UAVs) are being widely applied for civil purposes. However, several difficulties continue to exist in the implementation of missions, such as delivery and surveillance, in the private sector. Autonomous safe landing-area determination for small rotorcraft UAVs (RUAVs) is one of these unresolved issues, for the successful implementation of which adequate terrain information on the potential landing area is necessary. Previously, vision and light detection and ranging (LIDAR)-based methods were investigated for solving this problem. However, these light-based sensors have the disadvantage of being affected by weather or light conditions. The impulse radio ultra-wide band (IR-UWB) radar is a radar sensor with a wide frequency band that generates short-wavelength pulses. It has advantages such as light weight, small size, low power consumption, robustness to external environmental changes, and high range and distance resolutions. In this paper, we propose a novel safe landing-area determination system based on multiple IR-UWB radars, suitable for small RUAVs. Methods for detecting the ground and obstacles and estimating the ground slope and roughness values, based on the signals acquired by multiple IR-UWB radars are proposed. Through experiments, we demonstrate the feasibility and performance of the proposed method.

Novel Approach to Non-Invasive Blood Glucose Monitoring Based on Transmittance and Refraction of Visible Laser Light

Current blood glucose monitoring (BGM) techniques are invasive as they require a finger prick blood sample, a repetitively painful process that creates the risk of infection. BGM is essential to avoid complications arising due to abnormal blood glucose levels in diabetic patients. Laser light-based sensors have demonstrated a superior potential for BGM. Existing near-infrared (NIR)-based BGM techniques have shortcomings, such as the absorption of light in human tissue, higher signal-to-noise ratio, and lower accuracy, and these disadvantages have prevented NIR techniques from being employed for commercial BGM applications. A simple, compact, and cost-effective non-invasive device using visible red laser light of wavelength 650 nm for BGM (RL-BGM) is implemented in this paper. The RL-BGM monitoring device has three major technical advantages over NIR. Unlike NIR, red laser light has ~30 times better transmittance through human tissue. Furthermore, when compared with NIR, the refractive index of laser light is more sensitive to the variations in glucose level concentration resulting in faster response times ~7–10 s. Red laser light also demonstrates both higher linearity and accuracy for BGM. The designed RL-BGM device has been tested for both in vitro and in vivo cases and several experimental results have been generated to ensure the accuracy and precision of the proposed BGM sensor.

High-Resolution 3D Laser Imaging Advances to Subcentimeter Precision

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 23006, ’SS MTS: Subsea Monitoring - High-Resolution 3D Laser Imaging for Inspection, Maintenance, Repair, and Operations,’ by C. Embry, M. Hardy, and B. Nickerson, 3D at Depth; N. Manning, CDL; D. Goodyear, UTEC Survey; and D. Richardson, SPE, and J. Pappas, SPE, RPSEA, prepared for the 2012 Offshore Technology Conference, Houston, 30 April-3 May. The paper has not been peer reviewed. 3D laser imaging is a powerful data-collection system that provides 3D information for a specific region of interest. Developing the technology to provide high-definition subsea laser imaging enables the deepwater industry to use the current state of the art in 3D metrology and related best practices developed for the terrestrial market. Terrestrial laser scanners commonly produce centimeter spatial and range accuracy at the several-hundred-meter range. Because of the absorption of water, realizable deepwater systems are limited to tens-of-meters range, depending on the target and water conditions. Here, subcentimeter accuracy from greater than 6 m is demonstrated for an underwater laser system. Introduction Sonar systems have been the main tools for measurement and survey for many years and have become very sophisticated. Many companies have developed high-resolution multibeam sonar systems that can produce angular resolutions as small as 0.2°. However, the resolution of these systems is fundamentally limited by the underlying physics; a wave-length of light is more than 108 times smaller than ultrasonic wavelengths and can achieve angular resolutions of less than 100 Μrad (0.006°). Therefore, light-based sensors inherently have higher spatial resolutions than sonar systems. The underwater 3D laser sensor presented here has the fundamental advantage of providing subcentimeter precision from greater than 7 m, a capability that, to the authors’ knowledge, has not been demonstrated previously. The Sensor The optical head [laser imaging unit (LIU)] consists of the transmitter subsystem (laser and accompanying optics), the receiver subsystem (detector and accompanying optics), and the scanner. These subsystems can be optimized for different operational scenarios and environ-mental conditions. For this prototype system, we used a diode-pumped, passively Q-switched, Nd:YAG laser with an external nonlinear crystal to perform the frequency doubling to 532-nm laser light. The receiver is a high-speed silicon photo diode, and the scanning subsystem is a two-axis galvanometer scanner to allow programmable scanning in two orthogonal directions. Along with the LIU are multiple electronic control systems. These include the control subsystem for controlling the LIU and monitoring-system health; the central processing unit and bus for general system control and operation; the data subsystem for data collection, transformation, and processing; the data-storage system for housing data locally; the power and environmental monitoring system to convert the host-vehicle power to the various voltages required by the sensor; and the input/output (communication) subsystem. All of these systems are housed within the subsea sensor (Fig. 1). The prototype sensor is 8.2 in. in diameter and 28 in. long and weighs 76.1 lbm in air.

Active infrared sensors for mobile robots

Sensors based on the ultrasonic, pulse-echo technique for measuring range have been the mainstay for robotic collision avoidance systems. Although these sensors have been successfully applied to both indoor and outdoor mobile robotic applications, certain disadvantages of these systems prompted our investigation of inexpensive sensors that use light to determine the range or presence of targets. A number of commercially available, light-based sensors are analyzed for application in a mobile robotic space application. The objective of the analysis is to develop a cost-effective, light-based ranging sensor for a collision avoidance system for an experimental Mars Rover. This paper presents some results from our investigation. >