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  • Open access
  • 99 Reads
Recent Advances on SHM of Reinforced Concrete and Masonry Structures Enabled by Self-Sensing Structural Materials

Structural Health Monitoring is aimed at transforming civil structures into self-diagnosing systems able to automatically reveal the occurrence of a fault or a damage after a critical event such as an earthquake. While data science is presently experiencing a tremendous development, leading to the availability of powerful tools and algorithms that extract relevant information by effectively fusing data provided by different types of sensors, one of the main bottlenecks still limiting the development of SHM in the filed of civil engineering is the general lack of reliable sensing technologies that are effectively applicable to the large scale. A very promising solution to such a large scale challenge would be using the same construction materials for strain sensing and direct damage detection. In this view, the authors have recently proposed smart concretes and smart bricks that are piezoresistive concretes and clay bricks obtained by doping traditional construction materials with conductive nano- or micro inclusions. These novel multifunctional materials have the ability to provide measurable electrical output under application of a mechanical load and to provide information useful for damage detection, localization and quantification. The paper introduces both technologies, discusses their potentials and illustrates their application to paradigmatic structural elements arranged in the laboratory. The presented results contribute to showing the revolutionary impact that smart concretes and smart bricks may have in the near future on SHM of concrete and masonry structures.

  • Open access
  • 115 Reads
Elastic Dry-Type Solar Cell Rubber with Photovoltaics and Piezoelectricity for Compressive Sensing

Ordinary solar cell is too hard to bend or be squashed by compression, and to be extended by tensile strength. Because it is generally made of plastic polymer. However, if the one has elastic, flexible and extensible property as well as sensing of piezoelectricity, it is useful and effective on the artificial skin installed over a human-like robot as a husk which generates electric power in itself by solar and perceives any forces or temperature. Or other varied engineering applications will be feasible. In addition, such hybrid functions of both photovoltaics and piezoelectricity does not need any power supply or battery to be equipped. The solar cell with sensing developed in the present paper is novel in solar cell and sensor fields. For the realization of the elastic solar cell, it was made of natural rubber and electrolytically polymerized with configuration of magnetic clusters of metal particles by aiding a magnetic field, corresponding to the MCF rubber which the present author had developed as an elastic, flexible and extensible sensor made of natural rubber. The principle of photovoltaics and piezoelectricity was elucidated. The photo-voltage and current were measured under the photo-excitation based on the p- and n-type semiconductor resulted from the electrolytic polymerization of MCF rubber or from the doping, or on the dye. For clarifying piezoelectricity the compressive sensing was measured under compression.

  • Open access
  • 64 Reads
Cost-benefit optimization of sensor networks for SHM applications

Structural health monitoring (SHM) is aimed to obtain information about the structural integrity of a system, e.g. via the estimation of its mechanical properties through observations
collected with a network of sensors. In the present work, we provide a method to optimally design sensor networks in terms of spatial configuration, number and accuracy of sensors. The utility of the sensor network is quantified through the expected Shannon information gain of the measurements with respect to the parameters to be estimated. At assigned number of sensors to be deployed over the structure, the optimal sensor placement problem is ruled by the objective function computed and maximized by combining surrogate models and stochastic optimization algorithms. For a general case, two formulations are introduced and compared: (i) the maximization of the information obtained through the measurements, given the appropriate constraints (i.e. identifiability, technological and budgetary ones); (ii) the maximization of the utility efficiency, defined as the ratio between the information provided by the sensor network and its cost. The method is applied to a large-scale structural problem, and the outcomes of the two different approaches are discussed.

  • Open access
  • 92 Reads
Planar localization of radio-frequency or acoustic sources with two receivers

In the localization of electromagnetic or acoustic emitters, generally, when a pulse is radiated from a source, the wave will arrive to two receivers at different times. One of the advantages of measuring these time differences of arrival or TDOA is that it is not required a common clock as in other localization techniques based on the time of arrival of the pulse to the receiver. With only two sensors, all the possible points in the plane that would give the same TDOA describe a hyperbola. Using an independent third receiver and calculating the intersection of the three hyperbolas will give the position of the source. Therefore, planar localization of emitters using multilateration techniques can be solved at least with three receivers. This paper presents a method to locate sources in a plane with only two receivers reducing the number of acquisition channels and hence, the cost of the equipment. One of the receivers is in a fixed position and the other describes a circumference around the first one. The TDOA are measured at different angles completing a total turn and obtaining a periodic function, angle versus TDOA, that has all the geometric information needed to locate the source. The paper will show how to derive this function analytically with the distance from the fixed receiver to the source and a bearing angle as parameters. Then, it will be demonstrated that it is possible to fit the curve with experimental measurements to obtain the parameters of the position of the source.

  • Open access
  • 65 Reads
Observability and Performance Analysis of Velocity Measurements with Lever Arm Aided INS

In most autonomous vehicles the navigation subsystem is based on Inertial Navigation System (INS). Regardless of the INS grade, its navigation solution drifts in time. To avoid such a drift, the INS is fused with external sensor measurements. Recent publications show that the lever-arm, the relative position between the INS and aiding sensor, has influence on the navigation performance.

Most published research in this field is focused on INS/GNSS fusion with GNSS position updates only where performance and analytical observability analysis were made to examine the consequence of vehicle maneuvers on the estimation of the lever-arm states.

Yet, besides position updates, a variety of sensors measuring the vehicle velocity vector are available including GNSS and a Doppler velocity log. As in position measurements, when performing INS/velocity measurements fusion, the lever-arm must be taken account for. In this paper, an analytical observability and performance analysis for velocity measurements with lever-arm aided INS is derived for stationary conditions. The observable and unobservable subspaces are derived for two error-stets models: 1) a 12 error-state model (the position and lever-arm error-states are not included) yet the lever-arm is present in the measurement equation and 2) a 15 error-state model including the lever-arm error-states. The analytical closed form expressions are verified by numerical simulation.

  • Open access
  • 57 Reads
Signal Acquisition from Piezoelectric Transducers for Impedance-Based Damage Detection

Damage detection in structural health monitoring (SHM) using piezoelectric transducers has received attention in recent decades for increasing safety and reducing maintenance costs of various types of engineering structures. Among the various methods to detect structural damage, the impedance-based method performs the measurement of the electrical impedance of piezoelectric transducers attached in the monitored structure, which is related to the mechanical properties of the structure due to the piezoelectric effect. Therefore, the impedance measurement is critical to ensure the correct diagnosis of the structure and this paper presents an analysis of the main techniques of signal acquisition from piezoelectric transducers that have been proposed in the literature to replace the conventional impedance analyzers. Experimental tests were carried out with a piezoelectric transducer attached to an aluminum bar and the acquisition techniques were analyzed and compared regarding the precision and sensitivity to damage. The analysis was performed using the real part of the impedance signatures and a basic damage index based on the correlation coefficient. The results indicate that the signal acquisition techniques have important differences regarding the precision and sensitivity to structural damage that should be considered in the development of impedance-based SHM systems.  

  • Open access
  • 75 Reads
Real-Time Audio Event Detection over a Low-Cost GPU Platform for Surveillance in Remote Elderly Monitoring

The average of life expectancy of the population and the prioritization of authorities in active and home aging has increased recently. This has led governments and private organizations to increase efforts in caring the elder and dependant segment of the population. The latest advances in technology and communications point out new ways to monitor those people with special needs at their own home, increasing their quality of life of the elderly or the dependant in a cost-affordable way. This same proposal can improve the quality of caring in retirement homes, giving support to the caring services. The purpose of this paper is to present an Ambient Assisted Living (AAL) able to identify, analyze and detect specific events in the daily life environment – mostly, at home or in a residence – defined by medical and assistant staff that can be considered as an emergency situation. It is designed to be deployed in controlled environments, where social services or medical staff are thought to be nearby. This hybrid network service is intended activate several alarms in the central services when certain situations occur in the monitored place. This tele-care proposal for certain predefined risk situations is validated through a proof of concept that takes benefit of the high performance computing capabilities of a NVIDIA Graphical Processing Unit on an embedded system named Jetson TK1 to be able to process and detect the events locally, even the situations that last in time. This platform holds the basic implementation of the acoustic event detection system, for both in-home or residence-based caring service. The system is nowadays designed to identify eight different situations along time, and set the correspondent alarm when one of the situations is detected.

  • Open access
  • 37 Reads
Analysis of Piezoelectric Diaphragms in Impedance-Based Damage Detection in Large Structures

The use of low-cost transducers such as piezoelectric diaphragms in structural health monitoring (SHM) applications based on the electromechanical impedance (EMI) method has grown in recent years. Although many studies report the feasibility of such transducers for impedance-based damage detection, the experiments are typically performed on small structures. Therefore, the objective of this work is to perform an experimental analysis of the feasibility of the piezoelectric diaphragms for the detection of damage in large structures. Several tests were carried out on a large aluminum plate in which a diaphragm was attached. The electrical impedance signatures of the transducer were collected and a basic damage index was calculated in order to verify the feasibility of quantifying the size of the damage at different distances from the transducer. The experimental results indicate that the piezoelectric diaphragms have a good sensitivity to provide a damage size classification in large structures. In addition, the sensitivity to damage detection and classification decrease as the distance between the transducer and the damage increases. Therefore, the results reported in this study indicate that low-cost piezoelectric diaphragms are feasible for impedance-based SHM applications in large structures.

  • Open access
  • 114 Reads
Detecting Anomalous Noise Events on a Low-Capacity Acoustic Sensor in Dynamic Road Traffic Noise Mapping

One of the main aspects affecting the life of people living in urban and suburban areas is their continued exposure to high road traffic noise (RTN) levels, traditionally measured by specialists working on the field. Nowadays, the deployment of Wireless Acoustic Sensor Networks (WASN) has allowed automatic noise mapping in Smart Cities. In order to obtain a reliable picture of the RTN levels affecting citizens, those anomalous noise events (ANE) unrelated to road traffic should be removed from the noise map computation. For this purpose, this paper introduces an Anomalous Noise Event Detector (ANED) designed to differentiate in real-time between RTN and ANE at every 1 second, using an algorithm running at a low-capacity $\mu$controller-based acoustic sensor developed within the DYNAMAP project. The low-cap ANED follows a binary audio event detection approach to discriminate between ANE and RTN. It is based on the computing of spectral differences of the input acoustic data in order to fit the computational capacity of the considered low-cap sensors. The experiments considering real-life acoustic data show the feasibility of the proposal as a means to complement the results obtained by the ANED developed for the high-cap acoustic sensors of the WASN.

  • Open access
  • 47 Reads
Deterministic Propagation Modeling for Intelligent Vehicle Communication in Smart Cities

Vehicular Ad Hoc Networks (VANETs) are envisaged to be a critical building block of Smart Cities and Intelligent Transportation System (ITS) where pollution and congestion reduction, vehicle mobility improving, accidents prevention, safer roads are some of VANETs expected benefits. The vehicular communications encompass three major approaches: Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I) and Vehicle-to-Pedestrian (V2P). Although there is a significant research effort in VANETs radio channel characterization, the use of more general methods than theoretical and empirical models is required to understand more accurately the propagation phenomena in urban environments. In this work, a deterministic computational tool based on an in-house 3D Ray-Launching algorithm and standard IEEE 802.11p, are used to measure and represent the spatial large-scale and small-scale urban radio propagation phenomena for V2I and V2P communications. Spatial analysis of the path loss (PL), Power Delay Profile (PDP), Coherence Bandwidth (CB), Doppler shift, Doppler spread along avenues is presented in order to characterize the impact that the obstacles (geometry, electromagnetic properties and relative position), distance, link frequency, placement of Road Side Units (RSUs) and location of wearable sensors, have in the V2I and V2P propagation channels. Results show the impact of the temporal and spatial variation in the received signal power, due to the time dispersive behavior and rapid changes between Line-of-sight (LoS), Quasi-line-of-sight (QLoS) and Non-line-of-sight (NLoS) of the urban environments. These results should be useful for radio-planning Wireless Sensor Networks (WSNs) designers in future V2V and V2P communication systems.