[go: up one dir, main page]
More Web Proxy on the site http://driver.im/
You seem to have javascript disabled. Please note that many of the page functionalities won't work as expected without javascript enabled.
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
7.3
3.4
Journals
Sensors
Special Issues
Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology
sensors-logo
Submit to Special Issue Submit Abstract to Special Issue Review for Sensors Propose a Special Issue

Journal Menu

► Journal Menu

Journal Browser

► Journal Browser
share announcement

Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: 31 July 2025 | Viewed by 10067

Special Issue Editors

Prof. Dr. Michele Norgia

E-Mail Website
Guest Editor
Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Via Ponzio 34/5, 20133 Milano, Italy
Interests: optical sensors; interferometry; optoelectronics; optical measurements
Special Issues, Collections and Topics in MDPI journals
Dr. Elfed Lewis

E-Mail Website
Guest Editor
Optical Fibre Sensors Research Centre (OFSRC), University of Limerick, Limerick V94 T9PX, Ireland
Interests: optical fibre sensors; medical sensors; optical fibre instrumentation
Special Issues, Collections and Topics in MDPI journals
Dr. Alberto Vallan

E-Mail Website
Guest Editor
Politecnico di Torino, Department of Electronics and Telecommunications, corso Duca degli Abruzzi, 24, I-10129 Torino, Italy
Interests: measurement instruments; sensors; optical fiber sensors; plastic optical fibers
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Optical sensors have evolved to be one of the most studied and widely applied sensing techniques in industrial, engineering, medical, and biological applications.

This Special Issue, entitled "Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology", focuses on collecting and discussing novel and advanced research works in various fields of optical measurements and sensors.

It pursues recent developments and new applications of optical sensing, including significant improvements in sensitivity, precision, accuracy, measurement speed, miniaturization of systems, and integration to optimize systems. Moreover, innovative designs of optical sensors for novel and specific applications are sought to increase the value of the discussion. Submissions including original research papers as well as review articles that summarize recent technical developments are welcome. 

Topics of interest include, but are not limited to, the following:

  • General photonic sensors and measurement techniques;
  • Interferometric sensors;
  • Optical rangefinder;
  • Micro–opto–electro-mechanical systems (MOEMSs);
  • Novel optical sensing technologies;
  • Laser doppler velocimetry;
  • Optical fiber sensors;
  • Single-point, multi-point, and distributed measurements.

We expect many colleagues in the field of optical sensors and measurements to contribute to this Special Issue.

Prof. Dr. Michele Norgia
Prof. Dr. Elfed Lewis
Dr. Alberto Vallan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • optical sensors
  • interferometry
  • fiber optical sensors
  • optical measurements
  • laser doppler velocimetry
  • optical rangefinder

Benefits of Publishing in a Special Issue

  • Ease of navigation: Grouping papers by topic helps scholars navigate broad scope journals more efficiently.
  • Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
  • Expansion of research network: Special Issues facilitate connections among authors, fostering scientific collaborations.
  • External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
  • e-Book format: Special Issues with more than 10 articles can be published as dedicated e-books, ensuring wide and rapid dissemination.

Further information on MDPI's Special Issue polices can be found here.

Published Papers (7 papers)

Download All Papers
Order results
Result details
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:

Research

16 pages, 2617 KiB  
Article
Integrated Spectral Sensitivity as Physics-Based Figure of Merit for Spectral Transducers in Optical Sensing
by Felix L. McCluskey, Anne van Klinken and Andrea Fiore
Sensors 2025, 25(2), 440; https://doi.org/10.3390/s25020440 - 13 Jan 2025
Viewed by 495
Abstract
The design of optical sensors aims at providing, among other things, the highest precision in the determination of the target measurand. Many sensor systems rely on a spectral transducer to map changes in the measurand into spectral shifts of a resonance peak in [...] Read more.
The design of optical sensors aims at providing, among other things, the highest precision in the determination of the target measurand. Many sensor systems rely on a spectral transducer to map changes in the measurand into spectral shifts of a resonance peak in the reflection or transmission spectrum, which is measured by a readout device (e.g., a spectrometer). For these spectral transducers, figures of merit have been defined which are based on specific assumptions on the readout and the data analysis. In reality, however, different transducers achieve optimal performance with different types of readout. Additionally, some transducers present a more complex spectral response for which existing figures of merit do not apply. In this paper, we investigate an approach to quantifying the potential performance of a given transducer for a more general class of readout methods. Starting from the Cramér–Rao lower bound, we define a new figure of merit, the integrated spectral sensitivity, which is directly related to the physical limit of precision and applicable to a wide variety of sensing systems. We apply this analysis to two different examples of transducers. The results bring useful insights into the design of optical sensors. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Schematic representation of the sensing system. Reflectance spectrum (blue) of (<b>b</b>) a photonic crystal (insets with biolayer in red) and (<b>c</b>) a Si/SiO<sub>2</sub> multilayer (inset with biolayer in red) and its derivative with respect to the measurand (red).</p> Full article ">Figure 2
<p>(<b>a</b>,<b>b</b>) Reflectance spectrum of PhC transducer (blue line) with the transmission functions for the readout channels of a spectrometric readout (green lines) for (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>4</mn> </mrow> </semantics></math> and (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>20</mn> </mrow> </semantics></math>. (<b>c</b>) Calculated integrated spectral sensitivity for PhC sensor with spectrometric readout of various linewidths.</p> Full article ">Figure 3
<p>(<b>a</b>,<b>b</b>) Reflectance spectrum of multilayer stack (blue line) with the transmission functions for the readout channels of a spectrometric readout (green lines) for (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> and (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>50</mn> </mrow> </semantics></math>. (<b>c</b>) Calculated integrated spectral sensitivity for multilayer stack with spectrometric readout of various linewidths.</p> Full article ">Figure 4
<p>Reflectance spectrum of (<b>a</b>) the PhC transducer and (<b>b</b>) a multilayer transducer, together with the two respective transmission functions for the ideal readout.</p> Full article ">Figure 5
<p>Reflectance spectrum of (<b>a</b>) PhC transducer with different normalized radii <math display="inline"><semantics> <mrow> <mi>r</mi> <mo>/</mo> <mi>a</mi> </mrow> </semantics></math> and (<b>b</b>) multilayer structures with different thicknesses. In (<b>c</b>,<b>d</b>), the corresponding integrated spectral sensitivity for an ideal readout (red crosses, left axis) and a high-resolution spectrometric readout (blue circles, left axis) are shown in comparison with the traditional figure of merit <math display="inline"><semantics> <mrow> <mi>F</mi> <mi>o</mi> <msub> <mrow> <mi>M</mi> </mrow> <mrow> <mo>ν</mo> </mrow> </msub> </mrow> </semantics></math> (black squares, right axis).</p> Full article ">
13 pages, 3496 KiB  
Article
Label- and Reagent-Free Optical Sensor for Absorption-Based Detection of Urea Concentration in Water Solutions
by Carlo Anelli, Vanessa Pellicorio, Valentina Bello and Sabina Merlo
Sensors 2024, 24(9), 2754; https://doi.org/10.3390/s24092754 - 26 Apr 2024
Cited by 1 | Viewed by 1315
Abstract
Contactless and label-free detection of urea content in aqueous solutions is of great interest in chemical, biomedical, industrial, and automotive applications. In this work, we demonstrate a compact and low-cost instrumental configuration for label-free, reagent-free, and contactless detection of urea dissolved in water, [...] Read more.
Contactless and label-free detection of urea content in aqueous solutions is of great interest in chemical, biomedical, industrial, and automotive applications. In this work, we demonstrate a compact and low-cost instrumental configuration for label-free, reagent-free, and contactless detection of urea dissolved in water, which exploits the absorption properties of urea in the near-infrared wavelength region. The intensity of the radiation transmitted through the fluid under test, contained in a rectangle hollow glass tubing with an optical pathlength of 1 mm, is detected in two spectral bands. Two low-cost, low-power LEDs with emission spectra centered at λ = 1450 nm and λ = 2350 nm are used as readout sources. The photodetector is positioned on the other side of the tubing, in front of the LEDs. The detection performances of a photodiode and of a thermal optical power detector have been compared, exploiting different approaches for LED driving current modulation and photodetected signal processing. The implemented detection system has been tested on urea–water solutions with urea concentrations from 0 up to 525 mg/mL as well as on two samples of commercial diesel exhaust fluid (“AdBlue™”). Considering the transmitted intensity in presence of the urea–water solution, at λ = 1450 nm and λ = 2350 nm, normalized to the transmitted intensity in presence of water, we demonstrate that their ratio is linearly related to urea concentration on a wide range and with good sensitivity. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Figure 1

Figure 1
<p>Instrumental configuration for optical, label-free urea detection.</p> Full article ">Figure 2
<p>Examples of the 2 kHz signals provided by the photodiode (<b>a</b>) using LED1450 and when water is filling the tubing (solid line) and when urea–water solution at <span class="html-italic">C</span> = 0.4 g/mL is filling the tubing (dash line); (<b>b</b>) using LED2350 and when water is filling the tubing (solid line) and when urea–water solution at <span class="html-italic">C</span> = 0.4 g/mL is filling the tubing (dash line).</p> Full article ">Figure 3
<p>RMS values of the acquired signals with both LEDs and photodiode, normalized to the RMS value obtained when water is filling the channel as reference fluid, as a function of the tested concentrations. Circle markers <span style="color:red">●</span>, <span style="color:#0432FF">●</span> and the dashed line refer to data collected in the first experiment, covering the urea concentration range 0–0.400 g/mL, whereas square markers <span style="color:red">■</span>, <span style="color:#0432FF">■</span> and the solid line refer to the second experiment, covering the urea concentration range 0.400–0.525 g/mL. Markers in blue refer to LED1450 whereas markers in red refer to LED2350. The error bar around the markers represents the average value ± standard deviation.</p> Full article ">Figure 4
<p>Amplitude of the acquired signals with both LEDs, normalized to the value obtained when water is filling the channel as reference fluid, as a function of the tested concentrations. Circle markers <span style="color:red">●</span>, <span style="color:#0432FF">●</span> and the dashed line refer to data collected in the first experiment, covering the urea concentration range 0–0.400 g/mL, whereas square markers <span style="color:red">■</span>, <span style="color:#0432FF">■</span> and the solid line refer to the second experiment, covering the urea concentration range 0.400–0.525 g/mL. Markers in blue refer to LED1450 whereas markers in red refer to LED2350. The error bar around the markers represents the average value ± standard deviation.</p> Full article ">Figure 5
<p>Transmitted intensity ratio <span class="html-italic">R</span>(<span class="html-italic">C</span>) = <span class="html-italic">T1450</span>(<span class="html-italic">C</span>)/<span class="html-italic">T2350</span>(<span class="html-italic">C</span>) as a function of the urea concentration. (<b>a</b>) Ratio calculated between the RMS values shown in <a href="#sensors-24-02754-f003" class="html-fig">Figure 3</a>; (<b>b</b>) ratio calculated between the amplitude values shown in <a href="#sensors-24-02754-f004" class="html-fig">Figure 4</a>. Circle markers ● refer to data collected in the first experiment, covering the urea concentration range 0–0.400 g/mL, whereas square markers ■ refer to the second experiment, covering the urea concentration range 0.400–0.525 g/mL. Black solid line: linear fitting. The error bar around the markers represents the average value ± standard deviation.</p> Full article ">Figure 5 Cont.
<p>Transmitted intensity ratio <span class="html-italic">R</span>(<span class="html-italic">C</span>) = <span class="html-italic">T1450</span>(<span class="html-italic">C</span>)/<span class="html-italic">T2350</span>(<span class="html-italic">C</span>) as a function of the urea concentration. (<b>a</b>) Ratio calculated between the RMS values shown in <a href="#sensors-24-02754-f003" class="html-fig">Figure 3</a>; (<b>b</b>) ratio calculated between the amplitude values shown in <a href="#sensors-24-02754-f004" class="html-fig">Figure 4</a>. Circle markers ● refer to data collected in the first experiment, covering the urea concentration range 0–0.400 g/mL, whereas square markers ■ refer to the second experiment, covering the urea concentration range 0.400–0.525 g/mL. Black solid line: linear fitting. The error bar around the markers represents the average value ± standard deviation.</p> Full article ">Figure 6
<p>Examples of the 250 mHz signals provided by the thermopile (<b>a</b>) using LED1450 and when water is filling the tubing (solid line) and when urea–water solution at <span class="html-italic">C</span> = 0.4 g/mL is filling the tubing (dash line); (<b>b</b>) using LED2350 and when water is filling the tubing (solid line) and when urea–water solution at <span class="html-italic">C</span> = 0.4 g/mL is filling the tubing (dash line).</p> Full article ">Figure 7
<p>Amplitude of the acquired signals with both LEDs and thermopile, normalized to the value obtained when water is filling the channel as reference fluid, as a function of the tested concentrations. Circle markers <span style="color:red">●</span>, <span style="color:#0432FF">●</span> and the dashed line refer to data collected in the first experiment, covering the urea concentration range 0–0.400 g/mL, whereas square markers <span style="color:red">■</span>, <span style="color:#0432FF">■</span> and the solid line refer to the second experiment, covering the urea concentration range 0.400–0.525 g/mL Markers in blue refer to LED1450 whereas markers in red refer to LED2350. The error bar around the markers represents the average value ± standard deviation.</p> Full article ">Figure 8
<p>Transmitted intensity ratio <span class="html-italic">R</span>(<span class="html-italic">C</span>) = <span class="html-italic">T1450</span>(<span class="html-italic">C</span>)/<span class="html-italic">T2350</span>(<span class="html-italic">C</span>) as a function of the urea concentration, calculated between the amplitude values shown in <a href="#sensors-24-02754-f007" class="html-fig">Figure 7</a>. Circle markers ● refer to data collected in the first experiment, covering the urea concentration range 0–0.400 g/mL, whereas square markers ■ refer to the second experiment, covering the urea concentration range 0.400–0.525 g/mL. Black solid line: linear fitting. The error bar around the markers represents the average value ± standard deviation.</p> Full article ">
27 pages, 9834 KiB  
Article
Detection and Recognition of Voice Commands by a Distributed Acoustic Sensor Based on Phase-Sensitive OTDR in the Smart Home Concept
by Tatyana V. Gritsenko, Maria V. Orlova, Andrey A. Zhirnov, Yuri A. Konstantinov, Artem T. Turov, Fedor L. Barkov, Roman I. Khan, Kirill I. Koshelev, Cesare Svelto and Alexey B. Pnev
Sensors 2024, 24(7), 2281; https://doi.org/10.3390/s24072281 - 3 Apr 2024
Cited by 1 | Viewed by 1555
Abstract
In recent years, attention to the realization of a distributed fiber-optic microphone for the detection and recognition of the human voice has increased, whereby the most popular schemes are based on φ-OTDR. Many issues related to the selection of optimal system parameters and [...] Read more.
In recent years, attention to the realization of a distributed fiber-optic microphone for the detection and recognition of the human voice has increased, whereby the most popular schemes are based on φ-OTDR. Many issues related to the selection of optimal system parameters and the recognition of registered signals, however, are still unresolved. In this research, we conducted theoretical studies of these issues based on the φ-OTDR mathematical model and verified them with experiments. We designed an algorithm for fiber sensor signal processing, applied a testing kit, and designed a method for the quantitative evaluation of our obtained results. We also proposed a new setup model for lab tests of φ-OTDR single coordinate sensors, which allows for the quick variation of their parameters. As a result, it was possible to define requirements for the best quality of speech recognition; estimation using the percentage of recognized words yielded a value of 96.3%, and estimation with Levenshtein distance provided a value of 15. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Figure 1

Figure 1
<p>Scheme of DAS interrogation for a smart city (<b>left</b>) and smart home (<b>right</b>).</p> Full article ">Figure 2
<p>(<b>a</b>) Scheme of a distributed fiber microphone based on a φ-OTDR; (<b>b</b>) waterfall of backscattered intensity (in a fake color scale) as a function of time and coordinate; and (<b>c</b>) backscattered intensity as a function of time for a specific coordinate.</p> Full article ">Figure 3
<p>(<b>a</b>) Interference signal before preprocessing; (<b>b</b>) signal after preprocessing; (<b>c</b>) spectrum of simulated interference signal before (blue trace) and after (red trace) filtering; (<b>d</b>) the spectrogram of the speech signal after preprocessing.</p> Full article ">Figure 4
<p>Block diagram of the algorithm used for processing the φ-OTDR setup signals.</p> Full article ">Figure 5
<p>Generalized experimental setup.</p> Full article ">Figure 6
<p>Experimental setup for the quality of speech recognition depending on the sampling frequency for hollow PZT cylinder with sensing fiber and coil sensing fiber configurations: (<b>a</b>) components and their interconnection in the experimental setup; (<b>b</b>) photo of the experimental setup.</p> Full article ">Figure 7
<p>An experimental setup for experimental studies of the quality of speech recognition depending on the sampling frequency for the sensing fiber placed simply on a table: (<b>a</b>) an experimental setup circuit, (<b>b</b>) the use of a metal plate to increase the sensitivity of the system.</p> Full article ">Figure 8
<p>An experimental setup for studies of the quality of speech recognition depending on the sampling frequency using a sensing fiber with a length of 2.5 m wound around an elastic horn-like core, influenced by speakers with a sound volume of 72 dB(C): (<b>a</b>) with the bottle bottom influenced by the speakers; (<b>b</b>) with the bottle sidepiece influenced by the speakers; (<b>c</b>) with the horn-like bottle without a bottom influenced by speakers from inside.</p> Full article ">Figure 9
<p>An experimental setup circuit for experimental studies of the quality of speech recognition depending on the sampling frequency for the sensing fiber with a pair of wFBGs.</p> Full article ">Figure 10
<p>Spectral characteristics of the original audio recording: (<b>a</b>) Spectrum; (<b>b</b>) Spectrogram.</p> Full article ">Figure 11
<p>Spectrograms of signals obtained with a sampling frequency of 40 kHz: (<b>a</b>) a PZT-actuated disturbance; (<b>b</b>) a coiled sensing fiber, with a volume of 92 dB(C); (<b>c</b>) a sensing fiber placed simply on the table, with a volume of 89 dB(C); (<b>d</b>) a sensing fiber section 0.8 m long glued to a metal plate, with a volume of 89 dB(C); (<b>e</b>) a bottle bottom influenced by the speakers, with a volume of 72 dB(C); (<b>f</b>) a bottle sidepiece influenced by the speakers, with a volume of 72 dB(C); (<b>g</b>) a horn-like bottle without a bottom influenced by the speakers from inside, with a volume of 72 dB(C); (<b>h</b>) a sensing fiber with wFBGs 1 m apart with a preamplifier, influenced by speakers, with a volume of 108 dB(C); (<b>i</b>) a sensing fiber with wFBGs 1 m part without a preamplifier, influenced by speakers, with a volume of 108 dB(C).</p> Full article ">Figure 12
<p>Dependence of speech recognition quality on ADC sampling frequency for different sensing fiber configurations: (<b>a</b>) the percentage of words recognized by Yandex SpeechKit; (<b>b</b>) the Levenshtein distance of the words recognized with Yandex SpeechKit; (<b>c</b>) the percentage of words recognized by Whisper NN; and (<b>d</b>) the Levenshtein distance of the words recognized with Whisper NN.</p> Full article ">
16 pages, 2895 KiB  
Article
Dynamic Measurement of a Cancer Biomarker: Towards In Situ Application of a Fiber-Optic Ball Resonator Biosensor in CD44 Protein Detection
by Zhuldyz Myrkhiyeva, Kanagat Kantoreyeva, Aliya Bekmurzayeva, Anthony W. Gomez, Zhannat Ashikbayeva, Meruyert Tilegen, Tri T. Pham and Daniele Tosi
Sensors 2024, 24(6), 1991; https://doi.org/10.3390/s24061991 - 21 Mar 2024
Cited by 2 | Viewed by 1787
Abstract
The accuracy and efficacy of medical treatment would be greatly improved by the continuous and real-time monitoring of protein biomarkers. Identification of cancer biomarkers in patients with solid malignant tumors is receiving increasing attention. Existing techniques for detecting cancer proteins, such as the [...] Read more.
The accuracy and efficacy of medical treatment would be greatly improved by the continuous and real-time monitoring of protein biomarkers. Identification of cancer biomarkers in patients with solid malignant tumors is receiving increasing attention. Existing techniques for detecting cancer proteins, such as the enzyme-linked immunosorbent assay, require a lot of work, are not multiplexed, and only allow for single-time point observations. In order to get one step closer to clinical usage, a dynamic platform for biosensing the cancer biomarker CD44 using a single-mode optical fiber-based ball resonator biosensor was designed, constructed and evaluated in this work. The main novelty of the work is an in-depth study of the capability of an in-house fabricated optical fiber biosensor for in situ detection of a cancer biomarker (CD44 protein) by conducting several types of experiments. The main results of the work are as follows: (1) Calibration of the fabricated fiber-optic ball resonator sensors in both static and dynamic conditions showed similar sensitivity to the refractive index change demonstrating its usefulness as a biosensing platform for dynamic measurements; (2) The fabricated sensors were shown to be insensitive to pressure changes further confirming their utility as an in situ sensor; (3) The sensor’s packaging and placement were optimized to create a better environment for the fabricated ball resonator’s performance in blood-mimicking environment; (4) Incubating increasing protein concentrations with antibody-functionalized sensor resulted in nearly instantaneous signal change indicating a femtomolar detection limit in a dynamic range from 7.1 aM to 16.7 nM; (5) The consistency of the obtained signal change was confirmed by repeatability studies; (6) Specificity experiments conducted under dynamic conditions demonstrated that the biosensors are highly selective to the targeted protein; (7) Surface morphology studies by AFM measurements further confirm the biosensor’s exceptional sensitivity by revealing a considerable shift in height but no change in surface roughness after detection. The biosensor’s ability to analyze clinically relevant proteins in real time with high sensitivity offers an advancement in the detection and monitoring of malignant tumors, hence improving patient diagnosis and health status surveillance. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Figure 1

Figure 1
<p>The sequential procedure of fabricating an optical fiber ball resonator using the Fujikura LZM-100. The location in the splicer where the fiber is inserted to fabricate the ball resonator is indicated in the orange box in the bottom image. The upper image shows the schematic images of the fabrication procedures, which include aligning and splicing the optical fiber before heating and rotating it with a CO<sub>2</sub> laser. This process results in the formation of the ball resonator structure.</p> Full article ">Figure 2
<p>Pressure characterization setup for an optical fiber ball resonator. A 499 μm resonator is placed into the tip of a burette and then systematically filled with DI water at different levels. The pressure data recorded at water column heights ranging from 16 cm to 66 cm demonstrates that changes in pressure do not alter the detected signals.</p> Full article ">Figure 3
<p>An illustration of the setup for the dynamic measurement of the CD44 protein. The setup includes a Legato 100 KD Scientific syringe pump, which operates at a flow rate of 20 mL/min to mimic venous circulation, and a 20-gauge polyurethane cannula that protects the optical fiber ball resonator, coupled with a LUNA OBR 4600 device for accurate detection.</p> Full article ">Figure 4
<p>Example of a calibration of a ball resonator for RI detection. (<b>a</b>) Spectrum of the ball resonator probe, for various RI values. (<b>b</b>) Inset displaying the spectrum in proximity of the detected spectral feature. (<b>c</b>) Change of intensity as a function of the refractive index.</p> Full article ">Figure 5
<p>Analysis of pressure effects on the 499 μm optical fiber ball resonator.</p> Full article ">Figure 6
<p>Representative images of the biosensors’ surface morphologies obtained from AFM measurements at various stages of functionalization. Images of different stages of functionalization in a 1 μm × 1 μm section of an optical fiber ball resonator’s surface are displayed: (<b>a</b>) Piranha pre-treatment, (<b>b</b>) silanization with APTMS, (<b>c</b>) heat treatment, (<b>d</b>) cross-linking with GA, (<b>e</b>) immobilization of antibodies, (<b>f</b>) blocking with mPEG-amine, and (<b>g</b>) CD44 protein detected by a ball resonator.</p> Full article ">Figure 7
<p>Quantitative analysis of the height and surface roughness of various functionalization phases for optical fiber ball resonator biosensors. Assessing the variations in height (<b>a</b>) and RMS-roughness (<b>b</b>) at every stage of functionalization. * <span class="html-italic">p</span> ≤ 0.05, ** <span class="html-italic">p</span> ≤ 0.01, *** <span class="html-italic">p</span> ≤ 0.001, ns, <span class="html-italic">p</span> &gt; 0.05.</p> Full article ">Figure 8
<p>An optical fiber ball resonator biosensor’s efficacy in detecting CD44 was analyzed. The sensorgram shows the change in signal intensity over time, showing how a functionalized optical fiber ball resonator reacts to increasing amounts of CD44 in serum, ranging from 7.1 aM to 16.7 nM in diluted calf serum; results from the 497 μm diameter sensor are highlighted.</p> Full article ">Figure 9
<p>This 3D sensorgram shows the real-time detection of CD44 using a biosensor with a 497 μm optical fiber ball resonator. The sensorgram plots the spectral intensity against wavelength and time. The color gradient change from blue to yellow visually demonstrates the biosensor’s response to increasing concentrations of CD44 in serum, which range from 7.1 aM to 16.7 nM. Each peak correlates to a specific CD44 concentration, demonstrating the sensor’s ability to measure.</p> Full article ">Figure 10
<p>Evaluation of optical fiber ball resonator biosensors’ specificity for CD44 in comparison to thrombin and gamma-globulin. The bar graph illustrates how biosensors with diameters varying from 492 to 497 μm responded differently to CD44, while showing minimal responses to gamma-globulin (489 μm) and thrombin (518 μm) at concentrations ranging from 9.3 fM to 16.7 nM. This indicates the biosensor’s specific affinity for CD44. Error bars represent the measurements standard deviation, emphasizing the consistency and reliability of the sensor’s specificity.</p> Full article ">Figure 11
<p>Results for CD44 detection from three biological replicates. (<b>a</b>) The graph shows the sensor’s response percentages in a logarithmic range of CD44 concentrations, demonstrating the sensors’ consistent performance in several trials. This is visible from the overlapping data points and the shaded confidence interval. (<b>b</b>) The graph compares intensity change (dB) for three sensors with varying diameters (492 μm, 496 μm, and 497 μm) to the logarithmic concentration of CD44. It indicates that the sensors operate consistently when CD44 levels increase. Error bars are used to indicate the standard deviation, which highlights the accuracy of the sensors while taking several measurements.</p> Full article ">
15 pages, 4605 KiB  
Article
Diagnostics of Internal Defects in Composite Overhead Insulators Using an Optic E-Field Sensor
by Damiano Fasani, Luca Barbieri, Andrea Villa, Daniele Palladini, Roberto Malgesini, Giovanni D’Avanzo, Giacomo Buccella and Paolo Gadia
Sensors 2024, 24(5), 1359; https://doi.org/10.3390/s24051359 - 20 Feb 2024
Viewed by 1373
Abstract
Composite insulators for high-voltage overhead lines have better performances and are lighter than traditional designs, especially in heavily polluted areas. However, since it is a relatively recent technology, reliable methods to perform live-line diagnostics are still under development, especially with regard to internal [...] Read more.
Composite insulators for high-voltage overhead lines have better performances and are lighter than traditional designs, especially in heavily polluted areas. However, since it is a relatively recent technology, reliable methods to perform live-line diagnostics are still under development, especially with regard to internal defects, which provide few external symptoms. Thermal cameras can be employed, but their use is not always straightforward as the sun radiation can hide the thermal footprint of internal degenerative effects. In this work, an optical E-field sensor has been used to diagnose the internal defects of a set of composite insulators (bandwidth 200 mHz–50 MHz, min. detectable E-field 100 V/m). Moreover, a modelling activity using finite elements has been carried out to identify the possible nature of the defects by comparing experimental E-field profiles with those simulated assuming a specific defect geometry. The results show that the sensor can detect the presence of an internal defect, since its presence distorts the E-field profile when compared to the profile of a sound insulator. Moreover, the measured E-field profiles are compatible with the corresponding simulated ones when a conductive defect is considered. However, it was observed that a defect whose conductivity is not at least two orders of magnitude greater than the conductivity of the surroundings remains undetected. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Figure 1

Figure 1
<p>Section view of the insulator.</p> Full article ">Figure 2
<p>Thermographic images of two composite insulators: (<b>a</b>) a new insulator with no defects—the temperature along its axis is uniform; (<b>b</b>) a defective insulator, as evidenced by the region between the 3rd and the 7th shed and enclosed by the orange circle, which is at a higher temperature than the rest of the insulator.</p> Full article ">Figure 3
<p>Comparison of two setups of the optic E-field sensor: (<b>a</b>) 4-fiber bundle configuration—it can measure two components of the electric field; (<b>b</b>) 2-fiber bundle configuration (this work setup)—it can measure only one component.</p> Full article ">Figure 4
<p>Experimental setup: (<b>a</b>) overview; (<b>b</b>) detail of the sensor and the winch.</p> Full article ">Figure 5
<p>Experimental profiles of the 45° component of the electric field for the tested insulators.</p> Full article ">Figure 6
<p>Zoom-in view of the simulated distribution of the electric field (modulus) generated by an insulator for an axisymmetric geometry: (<b>a</b>) electric field distribution of a defect-free insulator; (<b>b</b>) electric field distribution of an insulator that has a 0.1 mm-thick delamination between the fiberglass rod and the silicone housing spanning from the lower end-fitting to the 4th–5th shed for a total height of 210 mm and having the electric properties (<span class="html-italic">σ<sub>d</sub></span> and <span class="html-italic">ε<sub>r,d</sub></span>) of water.</p> Full article ">Figure 7
<p>Electric field profiles obtained from the finite element model for different dimensions of the defect (solid lines) and for three different defect locations (<b>a</b>–<b>c</b>) compared with the profiles obtained experimentally. All three graphs also show the simulated profile for a new insulator (solid black line): (<b>a</b>) defect positioned at the HV terminal; (<b>b</b>) defect positioned 15 mm above the HV terminal; (<b>c</b>) defect positioned 135 mm above the HV terminal.</p> Full article ">Figure 8
<p>Electric field profiles obtained from the finite element model for a specific defect geometry (<span class="html-italic">z<sub>d</sub></span> = 2715, <span class="html-italic">H<sub>d</sub></span> = 210 mm) at three different distances from the insulator axis.</p> Full article ">Figure 9
<p>Simulated electric field profiles for a given defect geometry (<span class="html-italic">z<sub>d</sub></span> = 2715, <span class="html-italic">H<sub>d</sub></span> = 210 mm) for different values of the defect conductivity and for two extreme values of its permittivity.</p> Full article ">Figure 10
<p>Measurement of the relative distance between electric field profiles as the conductivity of the defect increases (<span class="html-italic">z<sub>d</sub></span> = 2715, <span class="html-italic">H<sub>d</sub></span> = 210 mm).</p> Full article ">
12 pages, 2721 KiB  
Article
Experimental Characterization of Polarized Light Backscattering in Fog Environments
by Maria Ballesta-Garcia, Sara Peña-Gutiérrez, Pablo García-Gómez and Santiago Royo
Sensors 2023, 23(21), 8896; https://doi.org/10.3390/s23218896 - 1 Nov 2023
Cited by 2 | Viewed by 1431
Abstract
This paper focuses on the experimental characterization of the polarization behavior of light backscattered through fog. A polarimetric orthogonal state contrast imager and an active, purely polarized white illuminator system are used to evaluate both linear and circular polarization signals. The experiments are [...] Read more.
This paper focuses on the experimental characterization of the polarization behavior of light backscattered through fog. A polarimetric orthogonal state contrast imager and an active, purely polarized white illuminator system are used to evaluate both linear and circular polarization signals. The experiments are carried out in a macro-scale fog chamber under controlled artificial fog conditions. We explore the effect of backscattering in each imaging channel, and the persistence of both polarization signals as a function of meteorological visibility. We confirm the presence of the polarization memory effect with circularly polarized light, and, as a consequence, the maintenance of helicity in backscattering. Moreover, the circular cross-polarized channel is found to be the imaging channel less affected by fog backscattering. These results are useful and should be taken into account when considering active polarimetric imaging techniques for outdoor applications under foggy conditions. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Final encapsulation. (<b>b</b>) Camera encapsulated inside IP68 housing case protection.</p> Full article ">Figure 2
<p>(<b>a</b>) Scheme of a macro pixel from the DOFP camera, comprising 4 micro-polarizers whose optical axes are oriented at 0°, 45°, 90°, and 135°. (<b>b</b>) Modification of the measuring states when placing the QWP (red border) in front of the DOFP camera. The channels corresponding to the angles 45° and 135° are modified by properly orienting the QWP to detect left and right-handed circular polarization, respectively. Linear channels 0° and 90° remain unchanged.</p> Full article ">Figure 3
<p>(<b>a</b>) Array of 4 active illuminators mechanically assembled around the camera housing. The final unit used in the tests. (<b>b</b>) The backscattering signal of the illuminator under dense fog conditions is produced by the illumination distribution received in the 4 polarization channels of the DOFP camera. The homogeneous light distribution in the ROI (red circle) is produced by the 2 × 2 configuration illuminator array.</p> Full article ">Figure 4
<p>Scheme of the experiment where active polarized illumination is backscattered by fog and reaches the DOFP camera. LS, light source; PSG, polarization state generator; PSA, polarization state analyzer; <math display="inline"><semantics> <mrow> <mover accent="true"> <mrow> <mi mathvariant="normal">S</mi> </mrow> <mo mathvariant="normal">→</mo> </mover> </mrow> </semantics></math>, input polarization illumination.</p> Full article ">Figure 5
<p>Irradiance detected in CO and CROSS channels for very dense fog (visibility &lt; 15 m) when the illumination and detection pairs are (<b>a</b>) circularly polarized and (<b>b</b>) linearly polarized. The saturation in the CO channels remarks the prevalence of the input polarization state.</p> Full article ">Figure 6
<p>Mean irradiance values—averaged over time in increments of 10 m of visibility—of the light backscattered by fog for each polarization channel (CO and CROSS), for both circular (CP) and linear polarization (LP), as a function of the visibility.</p> Full article ">Figure 7
<p>Images of the fog chamber with the presence of objects and dynamic fog for (<b>a</b>) CP and (<b>b</b>) LP illumination and detection pairs.</p> Full article ">Figure 8
<p>(<b>a</b>) The difference between the mean irradiance values of polarization channels (CROSS–CO) of the backscattered light by fog for each polarization state (C for circular and L for linear), as a function of the visibility. (<b>b</b>) The DOCP for the case of CP, and the DOLP for the case of LP, as a function of the visibility.</p> Full article ">
14 pages, 4613 KiB  
Article
Influence of Tilting Angle on Temperature Measurements of Different Object Sizes Using Fiber-Optic Pyrometers
by Salvador Vargas, Alberto Tapetado and Carmen Vázquez
Sensors 2023, 23(19), 8119; https://doi.org/10.3390/s23198119 - 27 Sep 2023
Cited by 1 | Viewed by 1196
Abstract
This article presents a new model of optical power gathered by a fiber-optic pyrometer when there is a tilting angle between the fiber longitudinal axis and the vector perpendicular to the tangent plane of the emitted surface. This optical power depends on the [...] Read more.
This article presents a new model of optical power gathered by a fiber-optic pyrometer when there is a tilting angle between the fiber longitudinal axis and the vector perpendicular to the tangent plane of the emitted surface. This optical power depends on the fiber specifications, such as the diameter and the numerical aperture (NA), as well as the object parameters, including its diameter, emissivity, and tilting angle. Some simulations are carried out using other pyrometers from the literature without tilting to validate the model. Additional simulations with different optical fibers, object sizes, and distances at different tilting angles allow us to describe the behavior of the pyrometer when the object is smaller than the optical fiber field of view (the light cone defined by its NA). The results show that for a finite surface object, the power collected by the optical fiber is affected by changes in the tilting angle, greater tilting lesser gathered power, and reaching the maximum power when the field of view of the fiber covers up the entire object, as expected. On the other hand, additional equations are presented to describe the maximum tilting angle, and distance that allow the maximum power gathered for a determined object diameter and fiber, avoiding temperature measurement errors. Full article
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Optical Measurements and Sensing Technology)
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic of a fiber-optic pyrometer aligned with the target surface, showing the model variables. Adapted from [<a href="#B24-sensors-23-08119" class="html-bibr">24</a>].</p> Full article ">Figure 2
<p>Schematic of the fiber-optic pyrometer with a tilting angle showing the model variables.</p> Full article ">Figure 3
<p>Cartesian coordinate systems (<span class="html-italic">x’</span>, <span class="html-italic">y’</span>, <span class="html-italic">z’</span>) and (<span class="html-italic">x</span>, <span class="html-italic">y</span>, <span class="html-italic">z</span>), and their relationship.</p> Full article ">Figure 4
<p>Geometry of the fiber end plane used to calculate the delta limits <span class="html-italic">δ<sub>min</sub></span> and <span class="html-italic">δ<sub>max</sub></span>, in the arc integration situation.</p> Full article ">Figure 5
<p>Power gathered by the pyrometer vs. distances to the target at 2000 °C, using our script with a tilting angle <span class="html-italic">θ</span> = 0°.</p> Full article ">Figure 6
<p>Power gathered by the pyrometer vs. distances to the target at 1000 °C, using our script with a tilting angle <span class="html-italic">θ</span> = 0°, for different target sizes from 5 to 100 μm diameter.</p> Full article ">Figure 7
<p>Coupled power vs. target diameter, at 1000 °C placed at 100 μm. Optical fiber with 0.29 NA and 100 μm core.</p> Full article ">Figure 8
<p>Coupled power vs. target diameter at 1000 °C placed at 150 μm. Optical fiber with 0.275 NA and 62.5 μm core. Tilting angles: 0, 15, 30, and 45°.</p> Full article ">Figure 9
<p>Coupled power vs. target-fiber distance at 1000 °C and a fixed target diameter of 250 μm, Optical fiber with 0.275 NA and 62.5 μm core. Tilting angles: 0, 15, 30, and 45°.</p> Full article ">Figure 10
<p>Coupled power vs. target-fiber distance at 1000 °C and a fixed target diameter of 100 μm, Optical fiber with 0.14 NA and 9 μm core. Tilting angles: 0, 15, 30, and 45°.</p> Full article ">Figure 11
<p>Geometry used to find the maximum tilting angle <span class="html-italic">θ<sub>max</sub></span> to keep the maximum gathered power.</p> Full article ">Figure 12
<p>Maximum angle <span class="html-italic">θ<sub>max</sub></span> to avoid errors vs. target-fiber distance for optical fiber with 0.275 NA and 62.5 μm core, and a circular target of 250 μm diameter.</p> Full article ">
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-7
Back to TopTop