1、 英文翻译 下属学院 理工学院 专 业 电子信息工程 2015 年 3 月 8 日 Wireless sensor networks for temperature and humidity monitoring withinconcrete structures1 ABSTRACT:This paper presents the development of an automatic wireless sensor monitoring system for civil engineering structures. The objective is to provide a solutio
2、n to measure both temperature and humidity inside a concrete structure. The research has been focused in the early age and curing phase period. Four solutions have been addressed. The first one involves the use of a negative temperature coefficient (NTC) thermistor and an IRIS mote allowing for the
3、creation of an IEEE 802.15.4 network. However, the results have shown that the sensor measurements present a 5 !C standard deviation between the actual and the experimental values. The second one considers the use of the SHT15 (humidity/temperature) sensor,together with the PIC18F4680 microcontrolle
4、r or the Arduino platform. The third solution involves the use of the SHT21S (humidity/temperature) sensor and the eZ430-RF2500 wireless development tool platform for the MSP430 microcontroller. In this case, the temperature readings were successfully performed for the first 16 h, while the humidity
5、 values were successfully obtained for the first 24 h of the experiment.Although the set of measured values is very promising for the SHT15 and SHT21S sensors, both sensors have stopped working after some time, showing that direct contact between the sensor and the concrete alkaline environment caus
6、es its breakdown. Finally, the fourth solution considers both the SHT15 and SHT21S sensors completely shielded allowing for the creation of a long-term solution.As, the SHT15 and SHT12S sensors have not been affected by the alkaline environment for more than two months of operation, enabling real-ti
7、me and continuous monitoring with almost non-intrusive tiny devices, the potential of applying the proposed inexpensive wireless sensor network approach is verified. 1. INTRODUCTION It is now recognised that integrated monitoring systems and procedures have an important and promising role to play in
8、 the total management of concrete structures. Monitoring deterioration would provide an early warning of incipient problems enabling the planning and scheduling of maintenance programmes, hence minimising relevant costs. Furthermore, the use of data from monitoring systems together with improved ser
9、vice-life prediction models leads to additional savings in life cycle costs 1,2. Sensors and associated monitoring systems to assess materials performance form an important element in the inspection, assessment and management of concrete structures. There are more than fifty different types of senso
10、r whose deployment into practical devices facilitates long-term monitoring of structural changes, reinforcement corrosion, c1oncrete chemistry, moisture state and temperature 2. The development of new sensor concepts allows for a more rational approach to the assessment of repair options, and schedu
11、ling of inspection and maintenance programmes in different civil engineering structures. Currently, there is a growing number of recent studies for the development of sensors in concrete structures, to monitoring from earlier-age parameters to environmental conditions that can cause deterioration pr
12、ocesses,some of which may be highlighted. Providakis and Liarakos 3 studied an early-age concrete strength development miniaturised sensor system. The idea is to characterise the condition of the fresh concrete at very early stages. It consists of a reusable transducer being strong enough to easily
13、detach from the hardened concrete structure, and to monitor the concrete strength development at early ages and initial hydration stages. Cruz et al. 4 studied the performance of a fibre-optic sensor for monitoring cracks of concrete, masonry and bituminous elements. The proposed sensor does not req
14、uire prior knowledge of the locations of cracks, which is significantly advanced over existing crack monitoring techniques. Moreover, according to the authors, several cracks can be detected, located and monitored using a single fibre. Duff and Farina 5 developed an integrated cost-effective sensor
15、system to monitor the state of reinforced concrete structures from the corrosion point of view. The sensor provides measurements of the open circuit potential of rebars, corrosion current density of rebars, electrical 1 Norberto Barroca, Luis M.Borges, Fernando J.Velez, Filipe Monteiro, Marcin Gorsk
16、i, Joao Castro-Gomes. Wireless sensor networks for temperature and humidity monitoring within concrete structuresJ. Construction and Building Materials, 2013(40):1156-1166. resistivity of concrete, availability of oxygen, chloride ions concentration in the concrete, and temperature inside the struct
17、ure 5.i Insertion of small sensors inside or at the surface of the concrete can be considered as one of the most promising development in order to monitor the long-term behaviour of concrete structures.Corrosion monitoring is possible using different sensors and methods that can work in the alkaline
18、 media of concrete for several years. Recorded data for corrosion potential and electrical concrete resistance obtained in real structures exposed to the environment can be used to determine the corrosion rate that corresponds to the concrete structure 6. Embedded sensors in the concrete near the su
19、rface (depth of 50 mm) enable measurements of the spatial and temporal distribution of the electrical characteristics within the cover-zone. Thereby it allows for an integrated assessment of its performance. Regular monitoring can enable cover-zone response to different ambient environments, namely
20、changes in the temperature7. Advances in the study of concrete deterioration can be achieved if concrete technologists cooperate with scientists in the relevant sensor sciences, to take advantage of the development of wireless low power smart sensor nodes capable of measuring behaviour, filtering, s
21、haring and combining readings from a large variety of sensors. Key issues are calibration of embedded sensors, robustness of sensors cast into concrete elements and durability of sensors in relation to the long live required for thestructures 8. The monitoring of temperature and moisture level will
22、provide crucial information about the hardening and setting process of concrete as well as the progress of deterioration mechanisms such as corrosion of steel reinforcement, freezethaw cycles, carbonation and alkaliaggregate reaction. A new technique to monitor the moisture level and temperature has
23、 recently been proposed in 9. This innovative technique uses nanotechnology/microelectromechanical systems (MEMSs) to measure temperature and internal relative humidity by using microcantilever beams and a moisture-sensitive thin polymer. Based on the obtained results, it was found that the proposed
24、 MEMS survived the concrete corrosive environment, as well as to internal and external stresses. Also it was found that the MEMS output reflects the change in the concrete properties and can be used to effectively measure moisture content and temperature, with high sensitivity. However, serious issu
25、es, such as long-term behaviour and repeatability of MEMS embedded into concrete, require further investigation 9. Resulting from cross-disciplinary research between civil engineering and automatic control engineering, a new measurement technique was recently developed in 9 enabling direct, real-tim
26、e measurements and continuous monitoring of concrete internal temperature and humidity via wireless signal transmission. The results are very promising with temperature/humidity sensors which monitor the internal temperature and humidity of concrete wirelessly, directly, in real-time and continuousl
27、y. However, several limitations need to be overcome when embedding electronic components into concrete, such as the continuity and stability of signal transmission, protection of electronic components, as well as the design of encapsulation boxes 10. 2. Motivation and objectives The primary objectiv
28、e of this interdisciplinary research is to develop a prototype for Wireless Sensor Networks (WSNs) allowing for remotely monitoring certain concrete structures. WSNs are formed by tiny devices, known as motes, that incorporate a microcontroller,sensors, memory, a power unit and a communication modul
29、e. They are able to sense the environment and communicate the information gathered from the sensors to the sink node through wireless links. Their capabilities include reading the value of physical variables at a given location, detecting the events of interest, whilst performing collaborative signa
30、l processing.From the application perspective, WSNs are useful in situations that require quick or infrastructure-less deployment and continuously monitoring 1113. Besides, the research work was focused on studying the behaviour of a concrete cube immediately after casting and at earlier ages, whils
31、t monitoring all the temperature and moisture changes in real time. This is accomplished by using an IEEE 802.15.4 network enabling a significant reduction of the installation time and costs. The experiments to be carried out,also aims at expanding the output from this research to the monitoring of other structures regardless the type of material, and to develop a prototype that facilitates to measure several parameters inside a real concrete structure, e.g., humidity and Temperature. In the context of WSNs applied to civil engineering structures it is important to create a
