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12 pages, 4240 KiB

Open AccessArticle

One-Step Laser Encapsulation of Nano-Cracking Strain Sensors

by Chan Park, Hyunsuk Jung, Hyunwoo Lee, Sunguk Hong, Hyonguk Kim and Seong J. Cho

Sensors 2018, 18(8), 2673; https://doi.org/10.3390/s18082673 - 14 Aug 2018

Cited by 12 | Viewed by 5050

Abstract

Development of flexible strain sensors that can be attached directly onto the skin, such as skin-mountable or wearable electronic devices, has recently attracted attention. However, such flexible sensors are generally exposed to various harsh environments, such as sweat, humidity, or dust, which cause [...] Read more.

Development of flexible strain sensors that can be attached directly onto the skin, such as skin-mountable or wearable electronic devices, has recently attracted attention. However, such flexible sensors are generally exposed to various harsh environments, such as sweat, humidity, or dust, which cause noise and shorten the sensor lifetimes. This study reports the development of a nano-crack-based flexible sensor with mechanically, thermally, and chemically stable electrical characteristics in external environments using a novel one-step laser encapsulation (OLE) method optimized for thin films. The OLE process allows simultaneous patterning, cutting, and encapsulating of a device using laser cutting and thermoplastic polymers. The processes are simplified for economical and rapid production (one sensor in 8 s). Unlike other encapsulation methods, OLE does not degrade the performance of the sensor because the sensing layers remain unaffected. Sensors protected with OLE exhibit mechanical, thermal, and chemical stability under water-, heat-, dust-, and detergent-exposed conditions. Finally, a waterproof, flexible strain sensor is developed to detect motions around the eye, where oil and sweat are generated. OLE-based sensors can be used in several applications that are exposed to a large amount of foreign matter, such as humid or sweaty environments. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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21 pages, 10103 KiB

Open AccessArticle

Ultrasound Sensors for Diaphragm Motion Tracking: An Application in Non-Invasive Respiratory Monitoring

by Amirhossein Shahshahani, Carl Laverdiere, Sharmistha Bhadra and Zeljko Zilic

Sensors 2018, 18(8), 2617; https://doi.org/10.3390/s18082617 - 9 Aug 2018

Cited by 23 | Viewed by 7080

Abstract

This paper introduces a novel respiratory detection system based on diaphragm wall motion tracking using an embedded ultrasound sensory system. We assess the utility and accuracy of this method in evaluating the function of the diaphragm and its contribution to respiratory workload. The [...] Read more.

This paper introduces a novel respiratory detection system based on diaphragm wall motion tracking using an embedded ultrasound sensory system. We assess the utility and accuracy of this method in evaluating the function of the diaphragm and its contribution to respiratory workload. The developed system is able to monitor the diaphragm wall activity when the sensor is placed in the zone of apposition (ZOA). This system allows for direct measurements with only one ultrasound PZT5 piezo transducer. The system generates pulsed ultrasound waves at 2.2 MHz and amplifies reflected echoes. An added benefit of this system is that due to its design, the respiratory signal is less subject to motion artefacts. Promising results were obtained from six subjects performing six tests per subject with an average respiration detection sensitivity and specificity of 84% and 93%, respectively. Measurements were compared to a gold standard commercial spirometer. In this study, we also compared our measurements to other conventional methods such as inertial and photoplethysmography (PPG) sensors. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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13 pages, 3693 KiB

Open AccessArticle

Remote Cell Growth Sensing Using Self-Sustained Bio-Oscillations

by Pablo Pérez, Gloria Huertas, Alberto Olmo, Andrés Maldonado-Jacobi, Juan A. Serrano, María E. Martín, Paula Daza and Alberto Yúfera

Sensors 2018, 18(8), 2550; https://doi.org/10.3390/s18082550 - 3 Aug 2018

Cited by 5 | Viewed by 4234

Abstract

A smart sensor system for cell culture real-time supervision is proposed, allowing for a significant reduction in human effort applied to this type of assay. The approach converts the cell culture under test into a suitable “biological” oscillator. The system enables the remote [...] Read more.

A smart sensor system for cell culture real-time supervision is proposed, allowing for a significant reduction in human effort applied to this type of assay. The approach converts the cell culture under test into a suitable “biological” oscillator. The system enables the remote acquisition and management of the “biological” oscillation signals through a secure web interface. The indirectly observed biological properties are cell growth and cell number, which are straightforwardly related to the measured bio-oscillation signal parameters, i.e., frequency and amplitude. The sensor extracts the information without complex circuitry for acquisition and measurement, taking advantage of the microcontroller features. A discrete prototype for sensing and remote monitoring is presented along with the experimental results obtained from the performed measurements, achieving the expected performance and outcomes. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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13 pages, 6275 KiB

Open AccessArticle

Stand-Alone Wearable System for Ubiquitous Real-Time Monitoring of Muscle Activation Potentials

by Ivan Mazzetta, Paolo Gentile, Marco Pessione, Antonio Suppa, Alessandro Zampogna, Edoardo Bianchini and Fernanda Irrera

Sensors 2018, 18(6), 1748; https://doi.org/10.3390/s18061748 - 29 May 2018

Cited by 22 | Viewed by 4917

Abstract

Wearable technology is attracting most attention in healthcare for the acquisition of physiological signals. We propose a stand-alone wearable surface ElectroMyoGraphy (sEMG) system for monitoring the muscle activity in real time. With respect to other wearable sEMG devices, the proposed system includes circuits [...] Read more.

Wearable technology is attracting most attention in healthcare for the acquisition of physiological signals. We propose a stand-alone wearable surface ElectroMyoGraphy (sEMG) system for monitoring the muscle activity in real time. With respect to other wearable sEMG devices, the proposed system includes circuits for detecting the muscle activation potentials and it embeds the complete real-time data processing, without using any external device. The system is optimized with respect to power consumption, with a measured battery life that allows for monitoring the activity during the day. Thanks to its compactness and energy autonomy, it can be used outdoor and it provides a pathway to valuable diagnostic data sets for patients during their own day-life. Our system has performances that are comparable to state-of-art wired equipment in the detection of muscle contractions with the advantage of being wearable, compact, and ubiquitous. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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14 pages, 36779 KiB

Open AccessArticle

Effective Crack Detection in Railway Axles Using Vibration Signals and WPT Energy

by María Jesús Gómez, Eduardo Corral, Cristina Castejón and Juan Carlos García-Prada

Sensors 2018, 18(5), 1603; https://doi.org/10.3390/s18051603 - 17 May 2018

Cited by 35 | Viewed by 6743

Abstract

Crack detection for railway axles is key to avoiding catastrophic accidents. Currently, non-destructive testing is used for that purpose. The present work applies vibration signal analysis to diagnose cracks in real railway axles installed on a real Y21 bogie working on a rig. [...] Read more.

Crack detection for railway axles is key to avoiding catastrophic accidents. Currently, non-destructive testing is used for that purpose. The present work applies vibration signal analysis to diagnose cracks in real railway axles installed on a real Y21 bogie working on a rig. Vibration signals were obtained from two wheelsets with cracks at the middle section of the axle with depths from 5.7 to 15 mm, at several conditions of load and speed. Vibration signals were processed by means of wavelet packet transform energy. Energies obtained were used to train an artificial neural network, with reliable diagnosis results. The success rate of 5.7 mm defects was 96.27%, and the reliability in detecting larger defects reached almost 100%, with a false alarm ratio lower than 5.5%. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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16 pages, 5270 KiB

Open AccessArticle

Development of a Wireless Unified-Maintenance System for the Structural Health Monitoring of Civil Structures

by Gwanghee Heo, Byungjik Son, Chunggil Kim, Seunggon Jeon and Joonryong Jeon

Sensors 2018, 18(5), 1485; https://doi.org/10.3390/s18051485 - 9 May 2018

Cited by 7 | Viewed by 3858

Abstract

A disaster preventive structural health monitoring (SHM) system needs to be equipped with the following abilities: First, it should be able to simultaneously measure diverse types of data (e.g., displacement, velocity, acceleration, strain, load, temperature, humidity, etc.) for accurate diagnosis. Second, it also [...] Read more.

A disaster preventive structural health monitoring (SHM) system needs to be equipped with the following abilities: First, it should be able to simultaneously measure diverse types of data (e.g., displacement, velocity, acceleration, strain, load, temperature, humidity, etc.) for accurate diagnosis. Second, it also requires standalone power supply to guarantee its immediate response in crisis (e.g., sudden interruption of normal AC power in disaster situations). Furthermore, it should be capable of prompt processing and realtime wireless communication of a huge amount of data. Therefore, this study is aimed at developing a wireless unified-maintenance system (WUMS) that would satisfy all the requirements for a disaster preventive SHM system of civil structures. The WUMS is designed to measure diverse types of structural responses in realtime based on wireless communication, allowing users to selectively use WiFi RF band and finally working in standalone mode by means of the field-programmable gate array (FPGA) technology. To verify its performance, the following tests were performed: (i) A test to see how far communication is possible in open field, (ii) a test on a shaker to see how accurate responses are, (iii) a modal test on a bridge to see how exactly characteristic real-time dynamic responses are of structures. The test results proved that the WUMS was able to secure stable communication far up to nearly 800 m away by acquiring wireless responses in realtime accurately, when compared to the displacement and acceleration responses which were acquired through wired communication. The analysis of dynamic characteristics also showed that the wireless acceleration responses in real-time represented satisfactorily the dynamic properties of structures. Therefore, the WUMS is proved valid as a SHM, and its outstanding performance is also proven. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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19 pages, 2659 KiB

Open AccessArticle

Pido: Predictive Delay Optimization for Intertidal Wireless Sensor Networks

by Xinyan Zhou, Xiaoyu Ji, Bin Wang, Yushi Cheng, Zhuoran Ma, Francis Choi, Brian Helmuth and Wenyuan Xu

Sensors 2018, 18(5), 1464; https://doi.org/10.3390/s18051464 - 8 May 2018

Cited by 11 | Viewed by 4791

Abstract

Intertidal habitats are among the harshest environments on the planet, and have emerged as a model system for exploring the ecological impacts of global climate change. Deploying reliable instrumentation to measure environmental conditions such as temperature is challenging in this environment. The application [...] Read more.

Intertidal habitats are among the harshest environments on the planet, and have emerged as a model system for exploring the ecological impacts of global climate change. Deploying reliable instrumentation to measure environmental conditions such as temperature is challenging in this environment. The application of wireless sensor networks (WSNs) shows considerable promise as a means of optimizing continuous data collection, but poor link quality and unstable connections between nodes, caused by harsh physical environmental conditions, bring about a delay problem. In this paper, we model and analyze the components of delays in an intertidal wireless sensor network system (IT-WSN). We show that, by properly selecting routing pathways, it is feasible to improve delay. To this end, we propose a Predictive Delay Optimization (Pido) framework, which provides a new metric for routing path selection. Pido incorporates delay introduced by both link quality and node conditions, and designs a classifier to predict future conditions of nodes, i.e., the likely time of aerial exposure at low tide in this case. We evaluate the performance of Pido in both a real IT-WSN system and a large-scale simulation, the result demonstrates that Pido decreases up to 73% of delays on average with limited overhead. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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15 pages, 2478 KiB

Open AccessArticle

Compact FTICR Mass Spectrometry for Real Time Monitoring of Volatile Organic Compounds

by Joël Lemaire, Sébastien Thomas, Allan Lopes, Essyllt Louarn, Hélène Mestdagh, Hubert Latappy, Julien Leprovost and Michel Heninger

Sensors 2018, 18(5), 1415; https://doi.org/10.3390/s18051415 - 3 May 2018

Cited by 16 | Viewed by 5792

Abstract

In this paper, we present a compact Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) designed for real time analysis of volatile organic compounds (VOCs) in air or in water. The spectrometer is based on a structured permanent magnet made with NdFeB segments. [...] Read more.

In this paper, we present a compact Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) designed for real time analysis of volatile organic compounds (VOCs) in air or in water. The spectrometer is based on a structured permanent magnet made with NdFeB segments. Chemical ionization is implemented inside the ICR cell. The most widely used reaction is the proton transfer reaction using H₃O⁺ precursor ions, but other ionic precursors can be used to extend the range of species that can be detected. Complex mixtures are studied by switching automatically from one precursor to another. The accuracy obtained on the mass to charge ratio (Δm/z 5 × 10⁻³), allows a precise identification of the VOCs present and the limit of detection is 200 ppb without accumulation. The time resolution is a few seconds, mainly limited by the time necessary to come back to background pressure after the gas pulses. The real time measurement will be illustrated by the monitoring of VOCs produced during the thermal degradation of a polymer and by an example where three different precursor ions are used alternatively to monitor a gas sample. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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9 pages, 3776 KiB

Open AccessArticle

Demonstration of a Speckle Based Sensing with Pulse-Doppler Radar for Vibration Detection

by Nisan Ozana, Reuven Bauer, Koby Ashkenazy, Nissim Sasson, Ariel Schwarz, Amir Shemer and Zeev Zalevsky

Sensors 2018, 18(5), 1409; https://doi.org/10.3390/s18051409 - 3 May 2018

Cited by 6 | Viewed by 3457

Abstract

In previous works, an optical technique for extraction and separation of remote static vibrations has been demonstrated. In this paper, we will describe an approach in which RF speckle movement is used to extract remote vibrations of a static target. The use of [...] Read more.

In previous works, an optical technique for extraction and separation of remote static vibrations has been demonstrated. In this paper, we will describe an approach in which RF speckle movement is used to extract remote vibrations of a static target. The use of conventional radar Doppler methods is not suitable for detecting vibrations of static targets. In addition, the speckle method has an important advantage, in that it is able to detect vibrations at far greater distances than what is normally detected in classical optical methods. The experiment described in this paper was done using a motorized vehicle, which engine was turned on and off. The results showed that the system was able to distinguish between the different engine states, and in addition, was able to determine the vibration frequency of the engine. The first step towards real time detection of human vital signs using RF speckle patterns is presented. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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9 pages, 8248 KiB

Open AccessFeature PaperArticle

Development of a Waterproof Crack-Based Stretchable Strain Sensor Based on PDMS Shielding

by Seong Kyung Hong, Seongjin Yang, Seong J. Cho, Hyungkook Jeon and Geunbae Lim

Sensors 2018, 18(4), 1171; https://doi.org/10.3390/s18041171 - 12 Apr 2018

Cited by 35 | Viewed by 7846

Abstract

This paper details the design of a poly(dimethylsiloxane) (PDMS)-shielded waterproof crack-based stretchable strain sensor, in which the electrical characteristics and sensing performance are not influenced by changes in humidity. This results in a higher number of potential applications for the sensor. A previously [...] Read more.

This paper details the design of a poly(dimethylsiloxane) (PDMS)-shielded waterproof crack-based stretchable strain sensor, in which the electrical characteristics and sensing performance are not influenced by changes in humidity. This results in a higher number of potential applications for the sensor. A previously developed omni-purpose stretchable strain (OPSS) sensor was used as the basis for this work, which utilizes a metal cracking structure and provides a wide sensing range and high sensitivity. Changes in the conductivity of the OPSS sensor, based on humidity conditions, were investigated along with the potential possibility of using the design as a humidity sensor. However, to prevent conductivity variation, which can decrease the reliability and sensing ability of the OPSS sensor, PDMS was utilized as a shielding layer over the OPSS sensor. The PDMS-shielded OPSS sensor showed approximately the same electrical characteristics as previous designs, including in a high humidity environment, while maintaining its strain sensing capabilities. The developed sensor shows promise for use under high humidity conditions and in underwater applications. Therefore, considering its unique features and reliable sensing performance, the developed PDMS-shielded waterproof OPSS sensor has potential utility in a wide range of applications, such as motion monitoring, medical robotics and wearable healthcare devices. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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12 pages, 2288 KiB

Open AccessArticle

Estimation of Fine and Oversize Particle Ratio in a Heterogeneous Compound with Acoustic Emissions

by Ejay Nsugbe, Cristobal Ruiz-Carcel, Andrew Starr and Ian Jennions

Sensors 2018, 18(3), 851; https://doi.org/10.3390/s18030851 - 13 Mar 2018

Cited by 24 | Viewed by 4906

Abstract

The final phase of powder production typically involves a mixing process where all of the particles are combined and agglomerated with a binder to form a single compound. The traditional means of inspecting the physical properties of the final product involves an inspection [...] Read more.

The final phase of powder production typically involves a mixing process where all of the particles are combined and agglomerated with a binder to form a single compound. The traditional means of inspecting the physical properties of the final product involves an inspection of the particle sizes using an offline sieving and weighing process. The main downside of this technique, in addition to being an offline-only measurement procedure, is its inability to characterise large agglomerates of powders due to sieve blockage. This work assesses the feasibility of a real-time monitoring approach using a benchtop test rig and a prototype acoustic-based measurement approach to provide information that can be correlated to product quality and provide the opportunity for future process optimisation. Acoustic emission (AE) was chosen as the sensing method due to its low cost, simple setup process, and ease of implementation. The performance of the proposed method was assessed in a series of experiments where the offline quality check results were compared to the AE-based real-time estimations using data acquired from a benchtop powder free flow rig. A designed time domain based signal processing method was used to extract particle size information from the acquired AE signal and the results show that this technique is capable of estimating the required ratio in the washing powder compound with an average absolute error of 6%. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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1031 KiB

Open AccessArticle

A Direct Bicarbonate Detection Method Based on a Near-Concentric Cavity-Enhanced Raman Spectroscopy System

by Dewang Yang, Jinjia Guo, Chunhao Liu, Qingsheng Liu and Ronger Zheng

Sensors 2017, 17(12), 2784; https://doi.org/10.3390/s17122784 - 1 Dec 2017

Cited by 7 | Viewed by 5338

Abstract

Raman spectroscopy has great potential as a tool in a variety of hydrothermal science applications. However, its low sensitivity has limited its use in common sea areas. In this paper, we develop a near-concentric cavity-enhanced Raman spectroscopy system to directly detect bicarbonate in [...] Read more.

Raman spectroscopy has great potential as a tool in a variety of hydrothermal science applications. However, its low sensitivity has limited its use in common sea areas. In this paper, we develop a near-concentric cavity-enhanced Raman spectroscopy system to directly detect bicarbonate in seawater for the first time. With the aid of this near-concentric cavity-enhanced Raman spectroscopy system, a significant enhancement in HCO₃⁻ detection has been achieved. The obtained limit of detection (LOD) is determined to be 0.37 mmol/L—much lower than the typical concentration of HCO₃⁻ in seawater. By introducing a specially developed data processing scheme, the weak HCO₃⁻ signal is extracted from the strong sulfate signal background, hence a quantitative analysis with R² of 0.951 is made possible. Based on the spectra taken from deep sea seawater sampling, the concentration of HCO₃⁻ has been determined to be 1.91 mmol/L, with a relative error of 2.1% from the reported value (1.95 mmol/L) of seawater in the ocean. It is expected that the near-concentric cavity-enhanced Raman spectroscopy system could be developed and used for in-situ ocean observation in the near future. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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4257 KiB

Open AccessArticle

All-Solid-State Sodium-Selective Electrode with a Solid Contact of Chitosan/Prussian Blue Nanocomposite

by Tanushree Ghosh, Hyun-Joong Chung and Jana Rieger

Sensors 2017, 17(11), 2536; https://doi.org/10.3390/s17112536 - 3 Nov 2017

Cited by 29 | Viewed by 9009

Abstract

Conventional ion-selective electrodes with a liquid junction have the disadvantage of potential drift. All-solid-state ion-selective electrodes with solid contact in between the metal electrode and the ion-selective membrane offer high capacitance or conductance to enhance potential stability. Solution-casted chitosan/Prussian blue nanocomposite (ChPBN) was [...] Read more.

Conventional ion-selective electrodes with a liquid junction have the disadvantage of potential drift. All-solid-state ion-selective electrodes with solid contact in between the metal electrode and the ion-selective membrane offer high capacitance or conductance to enhance potential stability. Solution-casted chitosan/Prussian blue nanocomposite (ChPBN) was employed as the solid contact layer for an all-solid-state sodium ion-selective electrode in a potentiometric sodium ion sensor. Morphological and chemical analyses confirmed that the ChPBN is a macroporous network of chitosan that contains abundant Prussian blue nanoparticles. Situated between a screen-printed carbon electrode and a sodium-ionophore-filled polyvinylchloride ion-selective membrane, the ChPBN layer exhibited high redox capacitance and fast charge transfer capability, which significantly enhanced the performance of the sodium ion-selective electrode. A good Nernstian response with a slope of 52.4 mV/decade in the linear range from 10⁻⁴–1 M of NaCl was observed. The stability of the electrical potential of the new solid contact was tested by chronopotentiometry, and the capacitance of the electrode was 154 ± 4 µF. The response stability in terms of potential drift was excellent (1.3 µV/h) for 20 h of continuous measurement. The ChPBN proved to be an efficient solid contact to enhance the potential stability of the all-solid-state ion-selective electrode. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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Review

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26 pages, 2452 KiB

Open AccessReview

Real-Time Early Warning System Design for Pluvial Flash Floods—A Review

by Melisa Acosta-Coll, Francisco Ballester-Merelo, Marcos Martinez-Peiró and Emiro De la Hoz-Franco

Sensors 2018, 18(7), 2255; https://doi.org/10.3390/s18072255 - 12 Jul 2018

Cited by 95 | Viewed by 20787

Abstract

Pluvial flash floods in urban areas are becoming increasingly frequent due to climate change and human actions, negatively impacting the life, work, production and infrastructure of a population. Pluvial flooding occurs when intense rainfall overflows the limits of urban drainage and water accumulation [...] Read more.

Pluvial flash floods in urban areas are becoming increasingly frequent due to climate change and human actions, negatively impacting the life, work, production and infrastructure of a population. Pluvial flooding occurs when intense rainfall overflows the limits of urban drainage and water accumulation causes hazardous flash floods. Although flash floods are hard to predict given their rapid formation, Early Warning Systems (EWS) are used to minimize casualties. We performed a systematic review to define the basic structure of an EWS for rain flash floods. The structure of the review is as follows: first, Section 2 describes the most important factors that affect the intensity of pluvial flash floods during rainfall events. Section 3 defines the key elements and actors involved in an effective EWS. Section 4 reviews different EWS architectures for pluvial flash floods implemented worldwide. It was identified that the reviewed projects did not follow guidelines to design early warning systems, neglecting important aspects that must be taken into account in their implementation. Therefore, this manuscript proposes a basic structure for an effective EWS for pluvial flash floods that guarantees the forecasting process and alerts dissemination during rainfall events. Full article

(This article belongs to the Special Issue Smart Sensing System for Real-Time Monitoring)

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