IEEE SENSORS JOURNAL, VOL. 14, NO. 7, JULY 2014 2355 Energy Center Detection in Light Scanning Sensors for Structural Health Monitoring Accuracy Enhancement Wendy Flores-Fuentes, Moises Rivas-Lopez, Oleg Sergiyenko, Julio C. Rodríguez-Quiñonez, Daniel Hernández-Balbuena, and Javier Rivera-Castillo Abstract—This paper introduces a novel electronic circuit that has to be embedded in a photodiode sensor as an integrated circuit board for electronic signal processing that detects the energy center of an optical signal, which represents the most accurate position measurement from a light emitter source mounted on a structure (such as a building, a bridge, or a mine). The optical scanning sensor for structural health monitoring proposed is a flexible system that can operate with a coherent or incoherent light emitter source. It is conformable to any kind of structure surfaces and data storage budget thanks to the signal processing stage being embedded into the sensor and does not require additional software processing, which reduces the time and memory spacing requirements for information recording. The theoretical principle of operation, as well as the technological and experimental aspects of design, development, and validation is presented. Index Terms—Centroid, energy signal centre, estimation error, light source, optical scanning, optical signal detection, optical signal processing, peak detection, SHM, SVMR. I. I NTRODUCTION S TRUCTURES experience deterioration and damage through their lifetimes due to environmental and excessive load conditions such as humidity, corrosion, earthquakes, gust waves, and traffic, among others. This results in structure deformation, cracking, dislocation and even collapse. Struc- tures play an important role in safety and economy. Thus, the increasing demand for the safest and most functional structures has driven the SHM research of data acquisition and its analysis to the obtention of indicators of the structure health. Nowadays, there are SHM systems with sensors based on a wide variety of technologies such as optical fiber, video cameras or optical scanner sensors. Each one has their own Manuscript received April 18, 2013; revised October 18, 2013 and March 1, 2014; accepted March 1, 2014. Date of publication March 6, 2014; date of current version May 29, 2014. This work was supported by the Engineering Institute of Autonomous University, Baja California, Mexicali, Mexico. The associate editor coordinating the review of this paper and approving it for publication was Dr. David Hecht. The authors are with the Engineering Institute, Autonomous University of Baja California, Mexicali 21280, Mexico (e-mail: wendy. flores6@uabc.edu.mx; mrivas@uabc.edu.mx; srgnk@uabc.edu.mx; julio. rodriguez37@uabc.edu.mx; dhernan@uabc.edu.mx; javier.rivera.castillo@ uabc.edu.mx). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2014.2310224 advantages and disadvantages depending on the type of struc- ture and the variables to be monitored and analyzed, which in turn depend on the kind of potential damage that they are intended to prevent. This work introduces a position measurement method based on an optical scanning sensor consisting of a light emitter source mounted on a structure together with an optical scan- ning aperture. The light beam is deflected through a lens and directed into a photodiode that converts it into a voltage output signal. Such output signal is electronically processed in order to detect the light energy centre, that is, its most accurate position measurement. This measurement is used to finally determine if a displacement has occurred [1]. The concept of energy signal centre has been used previ- ously in different applications with signals from several types of transducers, and many mathematical methods have been developed to do the post processing [2]–[14]. Some of these mathematical methods have been evaluated for optical scan- ning sensing; like the Geometric Centroid, the Power Spectrum Centroid and Peak Detection but all of them require digital signal post processing time and memory storage [15]–[21]. Instead of a digital signal post processing, a real time electronic signal processing, embedded into the photodiode sensor, is developed. II. THEORETICAL PRINCIPLE OF OPERATION The light scanning system sensor presented for SHM is a position measurement system. It is composed of a light emitter source installed on the structure under monitoring and an optical scanning aperture that is scanning the structure in the search of the light emitter source in order to determine if it has undergone a displacement. A. Position Indicator A light emitter source, mounted on the structure under monitoring, is used as a position indicator. This can be a coherent light emitter source such as a laser or an incoherent light source such as a bulb like the ones used in motor vehicles. We assume that for any light emitter source there is only one energy centre that represents its point position. B. Optical Scanning Aperture The rotating optical aperture is designed as a 45° slanted mirror surface attached to a cylindrical rod that deflects 1530-437X © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.