New Generation Of Optical Sensors Research Articles

Automated variance modeling for three-dimensional point cloud data via Bayesian neural networks

Three-dimensional (3-D) point cloud data are increasingly being used to describe a wide range of physical objects in detail, corresponding to customized and flexible shape designs. The advent of a new generation of optical sensors has simplified and reduced the costs of acquiring 3-D data in near-real-time. However, the variation of the acquired point clouds, and methods to describe them, create bottlenecks in manufacturing practices such as Reverse Engineering (RE) and metrology in additive manufacturing. We address this issue by developing an automated variance modeling algorithm that utilizes a physical object’s local geometric descriptors and Bayesian Extreme Learning Machines (BELMs). Our proposed ensemble and residual BELM-variants are trained by a scanning history that is composed of multiple scans of other, distinct objects. The specific scanning history is selected by a new empirical Kullback–Leibler divergence we developed to identify objects that are geometrically similar to an object of interest. A case study of our algorithm on additively manufactured products demonstrates its capability to model the variance of point cloud data for arbitrary freeform shapes based on a scanning history involving simpler, and distinct, shapes. Our algorithm has utility for measuring the process capability of 3-D scanning for RE processes.

New Radiometric Approaches to Compute Underwater Irradiances: Potential Applications for High-Resolution and Citizen Science-Based Water Quality Monitoring Programs.

Measuring the diffuse attenuation coefficient () allows for monitoring the water body’s environmental status. This parameter is of particular interest in water quality monitoring programs because it quantifies the presence of light and the euphotic zone’s depth. Citizen scientists can meaningfully contribute by monitoring water quality, complementing traditional methods by reducing monitoring costs and significantly improving data coverage, empowering and supporting decision-making. However, the quality of the acquisition of in situ underwater irradiance measurements has some limitations, especially in areas where stratification phenomena occur in the first meters of depth. This vertical layering introduces a gradient of properties in the vertical direction, affecting the associated . To detect and characterize these variations of in the water column, it needs a system of optical sensors, ideally placed in a range of a few cm, improving the low vertical accuracy. Despite that, the problem of self-shading on the instrumentation becomes critical. Here, we introduce a new concept that aims to improve the vertical accuracy of the irradiance measurements: the underwater annular irradiance (). This new concept consists of measuring the irradiance in an annular-shaped distribution. We first compute the optimal annular angle that avoids self-shading and maximizes the light captured by the sensors. Second, we use different scenarios of water types, solar zenith angle, and cloud coverage to assess the robustness of the corresponding diffuse attenuation coefficient, . Finally, we derive empirical functions for computing from . This new concept opens the possibility to a new generation of optical sensors in an annular-shaped distribution which is expected to (a) increase the vertical resolution of the irradiance measurements and (b) be easy to deploy and maintain and thus to be more suitable for citizen scientists.

Multifunctional derivatives of pyrimidine-5-carbonitrile and differently substituted carbazoles for doping-free sky-blue OLEDs and luminescent sensors of oxygen

IntroductionEvolution of organic light-emitting diodes (OLEDs) reached the point, which allows to obtain maximum internal quantum efficiency of 100% partly using heavy-metal-free emitters exhibiting thermally activated delayed fluorescence (TADF). Such emitters are also predictively perfect candidates for new generation of optical sensors since triplet harvesting can be sensitive to different analytes (at least to oxygen). Although many organic TADF emitters have been reported so far as OLED emitters, the investigation of materials suitable for both OLEDs and optical sensors remains extremely rare. ObjectivesAiming to achieve high photoluminescence quantum yields in solid-state and triplet harvesting abilities of organic semiconductors with efficient bipolar charge transport required for application in both blue OLEDs and optical sensors, symmetrical donor–acceptor-donor organic emitters containing pyrimidine-5-carbonitrile electron-withdrawing scaffold and carbazole, tert-butylcarbazole and methoxy carbazole donor moieties were designed, synthesized and investigated as the main objectives of this study. MethodsNew compounds were tested by many experimental methods including optical and photoelectron spectroscopy, time of flight technique, electrochemistry and thermal analyses. ResultsDemonstrating advantages of the molecular design, the synthesized emitters exhibited sky-blue efficient TADF with reverse intersystem crossing rates exceeding 106 s−1, aggregation-induced emission enhancement with photoluminescence quantum yields in solid state exceeding 50%, hole and electron transporting properties with charge mobilities exceeding 10-4 cm2/V·s, glass-forming properties with glass transition temperatures reaching 177 °C. Sky-blue OLEDs with non-doped light-emitting layers of the synthesized emitter showed maximum external efficiency of 12.8% while the doped device with the same emitter exhibited maximum external efficiency of 14%. The synthesized emitters were also used as oxygen probes for optical sensors with oxygen sensitivity estimated by the Stern-Volmer constant of 3.24·10-5 ppm−1. ConclusionThe developed bipolar TADF emitters with pyrimidine-5-carbonitrile and carbazole moieties showed effective applicability in both blue OLEDs and optical sensors.

Real-Time Sensing with Patterned Plasmonic Substrates and a Compact Imager Chip.

Optical sensing is an important research field due to its proven ability to be extremely sensitive, nondestructive, and applicable to sensing a wide range of chemical, thermal, electric, or magnetic phenomena. Beyond traditional optical sensors that often rely on bulky setups, plasmonic nanostructures can offer many advantages based on their sensitivity, compact form, cost-effectiveness, multiplexing compatibility, and compatibility with many standard semiconductor nanofabrication techniques. In particular, plasmon-enhanced optical transmission through arrays of nanostructured holes has led to the development of a new generation of optical sensors. In this chapter we present a simple fabrication technique to use plasmonic nanostructures as compact sensors. We position the nanohole array, an LED illumination source, and a spacer layer directly on top of a standard complementary metal-oxide-semiconductor (CMOS) imager chip. This setup is a viable sensor platform in both liquid and gas environments. These devices could operate as low-cost sensors for environmental monitoring, security, food safety, or monitoring small-molecule binding to extract affinity information and binding constants.

Silicon photonic structures with embedded polymers for novel sensing methods

At present time research and development of a new generation of optical sensors using conjugated polymers, in particular sensors of explosives are actively underway. Nevertheless, the problems of the sensitivity, selectivity, and stability of such sensors are still of great interest. One of the ways to solve the problem is the creation of luminescence sensors based on photonic crystals with a high specific surface area, which have significant sorption ability and allow to effective modulate emission properties of luminophores. In this paper, porous silicon microcavities with embeded organic polyphenylenevinylene- (PPV) and polyfluorene- (PF) type polymers were created. It was shown that polymer infiltration in porous silicon microcavities leads to modification of their luminescence properties, which is expressed in narrowing of the emission spectrum and changing of its directional pattern. It was demonstrated that such structures exhibit sensitivity to saturated vapors of trinitrotoluene. The structures proposed can be treated as a basis for development of new type of sensors used for detection of vapors of nitroaromatic compounds.

Direct spectral imaging of plasmonic nanohole arrays for real-time sensing

Plasmon-enhanced optical transmission through arrays of nano-structured holes has led to the development of a new generation of optical sensors. In this paper, to dramatically simplify the standard optical setups of these sensors, we position the nanoholes, an LED illumination source and a spacer layer directly on top of a CMOS imager chip. Transmitted light diffracts from the nanohole array, spreading into a spectrum over the space of a millimeter to land on the imager as a full spectrum. Our chip is used as a sensor in both a liquid and a gas environment. The spectrum is monitored in real-time and the plasmon-enhanced transmission peaks shift upon exposure to different concentrations of glycerol-in-water solutions or ethanol vapors in nitrogen. While liquids provide good refractive index contrast for sensing, to enhance sensitivity to solvent vapors, we filled the nanoholes with solvatochromic dyes. This on-chip solution circumvents the bulky components (e.g. microscopes, coupling optics, and spectrometers) needed for traditional plasmonic sensing setups, uses the nanohole array as both the sensing surface and a diffraction grating, and maintains good sensitivity. Finally, we show simultaneous sensing from two side-by-side locations, demonstrating potential for multiplexing and lab on a chip integration.

Sensitivity Analysis of a Proposed Novel Opto-Nano-Mechanical Photodetector for Improving the Performance of LIDAR and Local Optical Sensors

We propose a novel approach to the development of a new generation of optical sensors with enhanced detection sensitivity for chemical species. The novelty comes from combining an extremely high Q cantilever sensor with an already well established very sensitive technique, frequency modulation (FM) spectroscopy. In existing implementations, this inherent sensitivity is limited by the inadequacy of current state-of-the-art electronic filters to differentiate the weak amplitude modulated (AM)signal from the inevitable high-frequency laser noise, a consequence of the deterioration in the quality factor with increasing frequency exhibited by these filters. Our approach combines FM techniques with the rapidly advancing technology of nano-mechanical resonator (cantilever) development. Here a cantilever functions as both a sensitive photodetector and a high-quality spectral or temporal filter. These ultra-low mass devices enable detection of the photon momentum rather than conventional detection by photon energy. At least one order of magnitude enhancement appears feasible with existing cantilever technology.

Preparation of a novel optical sensor for low pH values using agarose membranes as support

A simple and effective method for the preparation of a new generation of optical sensors based on optically transparent agarose membranes was developed. An optical pH sensor for low pH values was accordingly fabricated by immobilization of Congo Red on epoxy-activated agarose. In an optimized coupling pH of 10 and a dye concentration of 10−5molL−1, a sensitive sensor with long term stability was obtained.It was found that the acidity constant of Congo Red in the immobilized form is smaller than in solution. The sensor responds rapidly to the pH changes in a range of 0.5–5 with a response time of 3.0min and a reproducibility better than 0.30% (R.S.D). The sensor was mounted in a flow cell and successfully applied for on-line pH monitoring. No evidence of leaching of the dye or any signal drift was observed.

Fabrication Of Organic Dye-Coated High-Tc Superconductor Optical Devices: Interface Chemistry And Properties

ABSTRACTThe preparation and characterization of a new generation of optical sensors fabricated from high-temperature superconductor (HTSC) thin films is reported herein. These new hybrid devices are prepared using HTSC thin films which are coated with organic dye overlayers. These systems have been shown to respond selectively to those wavelengths which are absorbed strongly by the molecular dye. Methods for fabricating the superconductor element and depositing the dye layer are discussed. Moreover, scanning electron microscopy and resistivity versus temperature measurements are utilized to characterize these hybrid structures.