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11 pages, 2471 KiB

Open AccessArticle

Single Transparent Piezoelectric Detector for Optoacoustic Sensing—Design and Signal Processing

by Elias Blumenröther, Oliver Melchert, Jonas Kanngießer, Merve Wollweber and Bernhard Roth

Sensors 2019, 19(9), 2195; https://doi.org/10.3390/s19092195 - 12 May 2019

Cited by 15 | Viewed by 4491

Abstract

In this article, we present a simple and intuitive approach to create a handheld optoacoustic setup for near field measurements. A single piezoelectric transducer glued in between two sheets of polymethyl methacrylate (PMMA) facilitates nearfield depth profiling of layered media. The detector electrodes [...] Read more.

In this article, we present a simple and intuitive approach to create a handheld optoacoustic setup for near field measurements. A single piezoelectric transducer glued in between two sheets of polymethyl methacrylate (PMMA) facilitates nearfield depth profiling of layered media. The detector electrodes are made of indium tin oxide (ITO) which is both electrically conducting as well as optically transparent, enabling an on-axis illumination through the detector. By mapping the active detector area, we show that it matches the design form precisely. We also present a straightforward approach to determine the instrument response function, which allows to obtain the original pressure profile arriving at the detector. To demonstrate the validity of this approach, the measurement on a simple test sample is deconvolved with the instrument response function and compared to simulation results. Except for the sputter instrumentation, all required materials and instruments as well as the tools needed to create such a setup are available to standard scientific laboratories. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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11 pages, 1542 KiB

Open AccessArticle

Microplastics Detection in Streaming Tap Water with Raman Spectroscopy

by Ann-Kathrin Kniggendorf, Christoph Wetzel and Bernhard Roth

Sensors 2019, 19(8), 1839; https://doi.org/10.3390/s19081839 - 18 Apr 2019

Cited by 106 | Viewed by 15808

Abstract

Microplastic particles have been found in drinking water sources worldwide and, thus, also in our food and beverages. Especially small microplastics, with sizes of 1 mm and less, cannot be identified reliably without spectroscopic means such as Fourier transform infrared spectroscopy (FTIR) or [...] Read more.

Microplastic particles have been found in drinking water sources worldwide and, thus, also in our food and beverages. Especially small microplastics, with sizes of 1 mm and less, cannot be identified reliably without spectroscopic means such as Fourier transform infrared spectroscopy (FTIR) or Raman spectroscopy, usually applied to the particles extracted from the samples. However, for drinking and tap water, with its comparatively low biological loads, direct observation may be possible and allows a point-of-entry monitoring for beverages and food to ensure uncontaminated drinking water is being used. In a proof of concept, we apply Raman spectroscopy to observe individual microplastic particles in tap water with added particulate and fluorescent contaminants streaming with 1 L/h through a custom-made flow cell. We evaluated several tubing materials for compatibility with microplastic suspensions containing three different polymers widely found in microplastic surveys worldwide. The experiment promises the monitoring of streaming tap water and even clear surface waters for microplastics smaller than 0.1 mm. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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8 pages, 50348 KiB

Open AccessArticle

Evaluating the Performance of Functionalized Carbon Structures with Integrated Optical Fiber Sensors under Practical Conditions

by Kort Bremer, Lourdes S. M. Alwis, Frank Weigand, Michael Kuhne, Yulong Zheng, Marco Krüger, Reinhard Helbig and Bernhard Roth

Sensors 2018, 18(11), 3923; https://doi.org/10.3390/s18113923 - 14 Nov 2018

Cited by 17 | Viewed by 3635

Abstract

An Optical Frequency Domain Reflectometry (OFDR) based fiber optic sensor scheme “embedded” in concrete for the purpose of structural health monitoring (SHM) of carbon concrete composites (C³) is presented. The design, while strengthening the concrete structure, also aims to monitor common [...] Read more.

An Optical Frequency Domain Reflectometry (OFDR) based fiber optic sensor scheme “embedded” in concrete for the purpose of structural health monitoring (SHM) of carbon concrete composites (C³) is presented. The design, while strengthening the concrete structure, also aims to monitor common SHM parameters such as strain and cracks. This was achieved by weaving the carbon fiber together with optical fiber, based on a specialized technique that uses an embroidery setup where both the carbon and optical fiber are woven on a water dissolvable polymer substrate. The performance of the sensing scheme was characterized in-situ utilizing the OFDR based technique and the results presented. The sensors embedded on a custom made concrete block were subjected to varying strain via a three point bending test to destruction and the results discussed. The intended dual-achievement of the scheme thus proposed in SHM and strengthening the C³ is demonstrated. The suitability of the OFDR scheme for C³ is combined with a fibre Bragg grating (FBG)-based approach, and discussed in detail. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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9 pages, 19501 KiB

Open AccessArticle

Polymer Based Whispering Gallery Mode Humidity Sensor

by Ann Britt Petermann, Thomas Hildebrandt, Uwe Morgner, Bernhard Wilhelm Roth and Merve Meinhardt-Wollweber

Sensors 2018, 18(7), 2383; https://doi.org/10.3390/s18072383 - 22 Jul 2018

Cited by 20 | Viewed by 4412

Abstract

Whispering gallery mode (WGM) resonators are versatile high sensitivity sensors, but applications regularly suffer from elaborate and expensive manufacturing and read-out. We have realized a simple and inexpensive concept for an all-polymer WGM sensor. Here, we evaluate its performance for relative humidity measurements [...] Read more.

Whispering gallery mode (WGM) resonators are versatile high sensitivity sensors, but applications regularly suffer from elaborate and expensive manufacturing and read-out. We have realized a simple and inexpensive concept for an all-polymer WGM sensor. Here, we evaluate its performance for relative humidity measurements demonstrating a sensitivity of 47 pm/% RH. Our results show the sensor concepts’ promising potential for use in real-life applications and environments. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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10 pages, 2589 KiB

Open AccessArticle

Investigating the Strain, Temperature and Humidity Sensitivity of a Multimode Graded-Index Perfluorinated Polymer Optical Fiber with Bragg Grating

by Yulong Zheng, Kort Bremer and Bernhard Roth

Sensors 2018, 18(5), 1436; https://doi.org/10.3390/s18051436 - 5 May 2018

Cited by 43 | Viewed by 4889

Abstract

In this work we investigate the strain, temperature and humidity sensitivity of a Fiber Bragg Grating (FBG) inscribed in a near infrared low-loss multimode perfluorinated polymer optical fiber based on cyclic transparent optical polymer (CYTOP). For this purpose, FBGs were inscribed into the [...] Read more.

In this work we investigate the strain, temperature and humidity sensitivity of a Fiber Bragg Grating (FBG) inscribed in a near infrared low-loss multimode perfluorinated polymer optical fiber based on cyclic transparent optical polymer (CYTOP). For this purpose, FBGs were inscribed into the multimode CYTOP fiber with a core diameter of 50 µm by using a krypton fluoride (KrF) excimer laser and the phase mask method. The evolution of the reflection spectrum of the FBG detected with a multimode interrogation technique revealed a single reflection peak with a full width at half maximum (FHWM) bandwidth of about 9 nm. Furthermore, the spectral envelope of the single FBG reflection peak can be optimized depending on the KrF excimer laser irradiation time. A linear shift of the Bragg wavelength due to applied strain, temperature and humidity was measured. Furthermore, depending on irradiation time of the KrF excimer laser, both the failure strain and strain sensitivity of the multimode fiber with FBG can be controlled. The inherent low light attenuation in the near infrared wavelength range (telecommunication window) of the multimode CYTOP fiber and the single FBG reflection peak when applying the multimode interrogation set-up will allow for new applications in the area of telecommunication and optical sensing. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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12 pages, 2448 KiB

Open AccessArticle

Long-Period Gratings in Highly Germanium-Doped, Single-Mode Optical Fibers for Sensing Applications

by Sebastian Schlangen, Kort Bremer, Yulong Zheng, Sebastian Böhm, Michael Steinke, Felix Wellmann, Jörg Neumann, Bernhard Roth and Ludger Overmeyer

Sensors 2018, 18(5), 1363; https://doi.org/10.3390/s18051363 - 27 Apr 2018

Cited by 12 | Viewed by 6063

Abstract

Long-period fiber gratings (LPGs) are well known for their sensitivity to external influences, which make them interesting for a large number of sensing applications. For these applications, fibers with a high numerical aperture (i.e., fibers with highly germanium (Ge)-doped fused silica fiber cores) [...] Read more.

Long-period fiber gratings (LPGs) are well known for their sensitivity to external influences, which make them interesting for a large number of sensing applications. For these applications, fibers with a high numerical aperture (i.e., fibers with highly germanium (Ge)-doped fused silica fiber cores) are more attractive since they are intrinsically photosensitive, as well as less sensitive to bend- and microbend-induced light attenuations. In this work, we introduce a novel method to inscribe LPGs into highly Ge-doped, single-mode fibers. By tapering the optical fiber, and thus, tailoring the effective indices of the core and cladding modes, for the first time, an LPG was inscribed into such fibers using the amplitude mask technique and a KrF excimer laser. Based on this novel method, sensitive LPG-based fiber optic sensors only a few millimeters in length can be incorporated in bend-insensitive fibers for use in various monitoring applications. Moreover, by applying the described inscription method, the LPG spectrum can be influenced and tailored according to the specific demands of a particular application. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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13 pages, 4541 KiB

Open AccessArticle

High-Precision Phenotyping of Grape Bunch Architecture Using Fast 3D Sensor and Automation

by Florian Rist, Katja Herzog, Jenny Mack, Robert Richter, Volker Steinhage and Reinhard Töpfer

Sensors 2018, 18(3), 763; https://doi.org/10.3390/s18030763 - 2 Mar 2018

Cited by 48 | Viewed by 10484

Abstract

Wine growers prefer cultivars with looser bunch architecture because of the decreased risk for bunch rot. As a consequence, grapevine breeders have to select seedlings and new cultivars with regard to appropriate bunch traits. Bunch architecture is a mosaic of different single traits [...] Read more.

Wine growers prefer cultivars with looser bunch architecture because of the decreased risk for bunch rot. As a consequence, grapevine breeders have to select seedlings and new cultivars with regard to appropriate bunch traits. Bunch architecture is a mosaic of different single traits which makes phenotyping labor-intensive and time-consuming. In the present study, a fast and high-precision phenotyping pipeline was developed. The optical sensor Artec Spider 3D scanner (Artec 3D, L-1466, Luxembourg) was used to generate dense 3D point clouds of grapevine bunches under lab conditions and an automated analysis software called 3D-Bunch-Tool was developed to extract different single 3D bunch traits, i.e., the number of berries, berry diameter, single berry volume, total volume of berries, convex hull volume of grapes, bunch width and bunch length. The method was validated on whole bunches of different grapevine cultivars and phenotypic variable breeding material. Reliable phenotypic data were obtained which show high significant correlations (up to r² = 0.95 for berry number) compared to ground truth data. Moreover, it was shown that the Artec Spider can be used directly in the field where achieved data show comparable precision with regard to the lab application. This non-invasive and non-contact field application facilitates the first high-precision phenotyping pipeline based on 3D bunch traits in large plant sets. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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13 pages, 5689 KiB

Open AccessArticle

Measuring Device for Air Speed in Macroporous Media and Its Application Inside Apple Storage Bins

by Martin Geyer, Ulrike Praeger, Ingo Truppel, Holger Scaar, Daniel A. Neuwald, Reiner Jedermann and Klaus Gottschalk

Sensors 2018, 18(2), 576; https://doi.org/10.3390/s18020576 - 13 Feb 2018

Cited by 13 | Viewed by 6685

Abstract

In cold storage facilities of fruit and vegetables, airflow is necessary for heat removal. The design of storage facilities influences the air speed in the surrounding of the product. Therefore, knowledge about airflow next to the product is important to plan the layout [...] Read more.

In cold storage facilities of fruit and vegetables, airflow is necessary for heat removal. The design of storage facilities influences the air speed in the surrounding of the product. Therefore, knowledge about airflow next to the product is important to plan the layout of cold stores adapted to the requirements of the products. A new sensing device (ASL, Air speed logger) is developed for omnidirectional measurement of air speed between fruit or vegetables inside storage bins or in bulk. It consists of four interconnected plastic spheres with 80 mm diameter each, adapted to the size of apple fruit. In the free space between the spheres, silicon diodes are fixed for the airflow measurement based on a calorimetric principle. Battery and data logger are mounted inside the spheres. The device is calibrated in a wind tunnel in a measuring range of 0–1.3 m/s. Air speed measurements in fruit bulks on laboratory scale and in an industrial fruit store show air speeds in gaps between fruit with high stability at different airflow levels. Several devices can be placed between stored products for determination of the air speed distribution inside bulks or bin stacks in a storage room. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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13 pages, 4319 KiB

Open AccessArticle

Using Acceleration Data to Automatically Detect the Onset of Farrowing in Sows

by Imke Traulsen, Christoph Scheel, Wolfgang Auer, Onno Burfeind and Joachim Krieter

Sensors 2018, 18(1), 170; https://doi.org/10.3390/s18010170 - 10 Jan 2018

Cited by 26 | Viewed by 5435

Abstract

The aim of the present study was to automatically predict the onset of farrowing in crate-confined sows. (1) Background: Automatic tools are appropriate to support animal surveillance under practical farming conditions. (2) Methods: In three batches, sows in one farrowing compartment of the [...] Read more.

The aim of the present study was to automatically predict the onset of farrowing in crate-confined sows. (1) Background: Automatic tools are appropriate to support animal surveillance under practical farming conditions. (2) Methods: In three batches, sows in one farrowing compartment of the Futterkamp research farm were equipped with an ear sensor to sample acceleration. As a reference video, recordings of the sows were used. A classical CUSUM chart using different acceleration indices of various distribution characteristics with several scenarios were compared. (3) Results: The increase of activity mainly due to nest building behavior before the onset of farrowing could be detected with the sow individual CUSUM chart. The best performance required a statistical distribution characteristic that represented fluctuations in the signal (for example, 1st variation) combined with a transformation of this parameter by cumulating differences in the signal within certain time periods from one day to another. With this transformed signal, farrowing sows could reliably be detected. For 100% or 85% of the sows, an alarm was given within 48 or 12 h before the onset of farrowing. (4) Conclusions: Acceleration measurements in the ear of a sow are suitable for detecting the onset of farrowing in individually housed sows in commercial farrowing crates. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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1627 KiB

Open AccessCommunication

Synergy Effect of Combining Fluorescence and Mid Infrared Fiber Spectroscopy for Kidney Tumor Diagnostics

by Andrey Bogomolov, Valeria Belikova, Urszula J. Zabarylo, Olga Bibikova, Iskander Usenov, Tatiana Sakharova, Hans Krause, Olaf Minet, Elena Feliksberger and Viacheslav Artyushenko

Sensors 2017, 17(11), 2548; https://doi.org/10.3390/s17112548 - 5 Nov 2017

Cited by 18 | Viewed by 5202

Abstract

Matching pairs of tumor and non-tumor kidney tissue samples of four patients were investigated ex vivo using a combination of two methods, attenuated total reflection mid infrared spectroscopy and fluorescence spectroscopy, through respectively prepared and adjusted fiber probes. In order to increase the [...] Read more.

Matching pairs of tumor and non-tumor kidney tissue samples of four patients were investigated ex vivo using a combination of two methods, attenuated total reflection mid infrared spectroscopy and fluorescence spectroscopy, through respectively prepared and adjusted fiber probes. In order to increase the data information content, the measurements on tissue samples in both methods were performed in the same 31 preselected positions. Multivariate data analysis revealed a synergic effect of combining the two methods for the diagnostics of kidney tumor compared to individual techniques. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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4124 KiB

Open AccessArticle

Development and Testing of an LED-Based Near-Infrared Sensor for Human Kidney Tumor Diagnostics

by Andrey Bogomolov, Urszula Zabarylo, Dmitry Kirsanov, Valeria Belikova, Vladimir Ageev, Iskander Usenov, Vladislav Galyanin, Olaf Minet, Tatiana Sakharova, Georgy Danielyan, Elena Feliksberger and Viacheslav Artyushenko

Sensors 2017, 17(8), 1914; https://doi.org/10.3390/s17081914 - 19 Aug 2017

Cited by 22 | Viewed by 7196

Abstract

Optical spectroscopy is increasingly used for cancer diagnostics. Tumor detection feasibility in human kidney samples using mid- and near-infrared (NIR) spectroscopy, fluorescence spectroscopy, and Raman spectroscopy has been reported (Artyushenko et al., Spectral fiber sensors for cancer diagnostics in vitro. In Proceedings of [...] Read more.

Optical spectroscopy is increasingly used for cancer diagnostics. Tumor detection feasibility in human kidney samples using mid- and near-infrared (NIR) spectroscopy, fluorescence spectroscopy, and Raman spectroscopy has been reported (Artyushenko et al., Spectral fiber sensors for cancer diagnostics in vitro. In Proceedings of the European Conference on Biomedical Optics, Munich, Germany, 21–25 June 2015). In the present work, a simplification of the NIR spectroscopic analysis for cancer diagnostics was studied. The conventional high-resolution NIR spectroscopic method of kidney tumor diagnostics was replaced by a compact optical sensing device constructively represented by a set of four light-emitting diodes (LEDs) at selected wavelengths and one detecting photodiode. Two sensor prototypes were tested using 14 in vitro clinical samples of 7 different patients. Statistical data evaluation using principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) confirmed the general applicability of the LED-based sensing approach to kidney tumor detection. An additional validation of the results was performed by means of sample permutation. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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Review

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53 pages, 18813 KiB

Open AccessFeature PaperReview

Raman Sensing and Its Multimodal Combination with Optoacoustics and OCT for Applications in the Life Sciences

by Merve Wollweber and Bernhard Roth

Sensors 2019, 19(10), 2387; https://doi.org/10.3390/s19102387 - 24 May 2019

Cited by 17 | Viewed by 5178

Abstract

Currently, many optical modalities are being investigated, applied, and further developed for non-invasive analysis and sensing in the life sciences. To befit the complexity of the study objects and questions in this field, the combination of two or more modalities is attempted. We [...] Read more.

Currently, many optical modalities are being investigated, applied, and further developed for non-invasive analysis and sensing in the life sciences. To befit the complexity of the study objects and questions in this field, the combination of two or more modalities is attempted. We review our work on multimodal sensing concepts for applications ranging from non-invasive quantification of biomolecules in the living organism to supporting medical diagnosis showing the combined capabilities of Raman spectroscopy, optical coherence tomography, and optoacoustics. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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2613 KiB

Open AccessReview

The Application of EM38: Determination of Soil Parameters, Selection of Soil Sampling Points and Use in Agriculture and Archaeology

by Kurt Heil and Urs Schmidhalter

Sensors 2017, 17(11), 2540; https://doi.org/10.3390/s17112540 - 4 Nov 2017

Cited by 87 | Viewed by 12491

Abstract

Fast and accurate assessment of within-field variation is essential for detecting field-wide heterogeneity and contributing to improvements in the management of agricultural lands. The goal of this paper is to provide an overview of field scale characterization by electromagnetic induction, firstly with a [...] Read more.

Fast and accurate assessment of within-field variation is essential for detecting field-wide heterogeneity and contributing to improvements in the management of agricultural lands. The goal of this paper is to provide an overview of field scale characterization by electromagnetic induction, firstly with a focus on the applications of EM38 to salinity, soil texture, water content and soil water turnover, soil types and boundaries, nutrients and N-turnover and soil sampling designs. Furthermore, results concerning special applications in agriculture, horticulture and archaeology are included. In addition to these investigations, this survey also presents a wide range of practical methods for use. Secondly, the effectiveness of conductivity readings for a specific target in a specific locality is determined by the intensity at which soil factors influence these values in relationship to the desired information. The interpretation and utility of apparent electrical conductivity (EC_a) readings are highly location- and soil-specific, so soil properties influencing the measurement of EC_a must be clearly understood. From the various calibration results, it appears that regression constants for the relationships between EC_a, electrical conductivity of aqueous soil extracts (EC_e), texture, yield, etc., are not necessarily transferable from one region to another. The modelling of EC_a, soil properties, climate and yield are important for identifying the location to which specific utilizations of EC_a technology (e.g., EC_a₋texture relationships) can be appropriately applied. In general, the determination of absolute levels of EC_a is frequently not possible, but it appears to be quite a robust method to detect relative differences, both spatially and temporally. Often, the use of EC_a is restricted to its application as a covariate or the use of the readings in a relative sense rather than as absolute terms. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Germany)

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