OBNOVLJIVI IZVORI ENERGIJE U BEŽIČNIM SENZORSKIM MREŽAMA

The advances in the technology of cheap and low power consumption microelectronic components have lead to the expansion of wireless technologies in the past two decades. One of the most important shortcomings of all wireless devices, including sensor ones, are limited energy resources. This paper reviews common mechanism of energy harvesting and energy scavenging, which draw power from the environment to feed the energy reserves in wireless sensor networks. They include conversion of the energy of electromagnetic waves, vibrations and heat.Razvoj jeftinih mikroelektronskih komponenti niske potrošnje uslovio je ekspanziju bežičnih tehnologija u zadnje dve dekade. Jedna od glavnih mana svih bežičnih uređaja, uključujući senzorske, jesu ograničeni energetski resursi. U ovom radu opisani su uobičajeni mehanizmi koji se koriste u „energy harvesting“ i „energy scavenging“ procedurama, kojima se snaga iz okoline koristi za dopunjavanje energetskih rezervi u bežičnim senzorskim mrežama. Oni uključuju konverziju energije elektromagnetskih talasa, vibracija i toplote

Gravity satellite missions measurement data for atmospheric density estimation

Gravity satellite missions measurement data are primarily intended for use in the estimation of an accurate model of Earth’s gravity field. The satellites’ almost circular orbits with polar or near-polar inclination of the orbital planes, and low altitude (between 250 and 500 km), enable almost full coverage of the globe. Orbit tracking by precise high orbiting navigation satellite system provides the data about three-dimensional satellite position and its deviations. Precision accelerometers on the satellites extend the ability to monitor non-gravitational forces acting on them continuously. One of these forces, atmospheric drag along orbits, can be derived from the orbit track positions and their derivatives, and also from the precise accelerometer measurements, so it can be used for atmospheric mass density determination. On the other hand, the density of the atmosphere and its main constituents can be derived from the spectroscopic measurements. One of the examples is thermospheric mass density determination using neutral mass spectrometers on earlier satellite missions. Measurement of the Earth’s far ultraviolet (FUV) dayglow is used to infer number density profiles of N2, O, and O2. Combination of accelerometers measurements and spectroscopic data is the foundation of two widely used empirical models of thermospheric mass density. This contribution describes the basic measurements on gravity satellite missions and atmospheric drag estimation, gives the comparison and combination of obtained data with spectrometric measurements of atmospheric density, and lists potential improvements using the data from the recently launched satellite gravity missions

Walsh analysis - a convenient preprocessor for period detection in astronomy

Walsh analysis is practically analogous to Fourier analysis, except that square wave is used instead of the sine one. It has one major advantage over Fourier - it can be performed much faster. This may seem of little importance at first, since computers have gotten to the point where most programmers do not take any care about the size of their code or the speed of their calculations. However, LSST will provide astronomers with huge data sets, and searching for periodicity peaks with high resolution might require enourmous amount of calculations. To perform this analysis in real time (a matter of seconds) it is important to skip non-necessary mathematical operations and focus on applying complex period detection algorithms (such as line fitting, analysis of variance, and others) only in the vicinity of expected peaks, not on all arbitrary periods. To do this efficiently, we propose that Walsh analysis is applied on the data first. A simulation was conducted with artifiucially generated light curves for the three types of variable stars: RRLyr, Algols and classical cepheids. LSST current baseline cadence (enigma 1189) was used for the timing of samples

Influence of material surface roughness on backscattering in laser scanning

In this paper, the possibility of applying Kirchhoff 's scalar approximation model for determining the backscattering coefficient from rough surfaces is investigated. Surfaces of dielectric and metallic materials, which have low roughness are considered. Based on the roughness parameters and electrical properties of these materials, the backscattering coefficient is modelled as a function of the incident angle of electromagnetic radiation used in laser scanning. It was represented that the type of scattering and the range of backscattering radiation angles, in the case of seemingly smooth surfaces, vary significantly when the roughness parameters change

Stabilnost frekvencije kvarcnih oscilatora

Oscilatorna kola su neizbežni deo praktično svih elektronskih uređaja. Najčešće se koriste kola na bazi kvarcnih kristala. Prikazan je proces proizvodnje i princip rada kvarcnih oscilatora, kao i podele kristala i oscilatornih kola. Analizirane su metode kvantitativnog opisivanja greške odnosno nestabilnosti frekvencije. Efekti koji utiču na promene frekvencije su klasifikovani po fizičkom poreklu i vremenskom periodu u kom se dešavaju

Mreža bežičnih senzora za merenje vibracija na građevinskim objektima

Nedestruktivno praćenje stanja građevinskih objekata se bazira na merenju vibracija objekata pri dinamičkim ispitivanjima ili u toku njihove eksploatacije. U ovu svrhu se sve više koriste mreže bežičnih senzora (WSN) koje čine fleksibilan i jeftin merni sistem, jer nema razvlačenja kablova velikih dužina za povezivanje senzora. U ovom radu je ukratko prikazan sadašnji stepen razvoja i primene WSN i opisan je sistem za bežično merenje vibracija na objektima razvijen na Građevinskom fakultetu u Beogradu. Predstavljeni su struktura i karakteristike mernog sistema baziranog na elektronskim komponentama male potrošnje i originalnom softveru

Ispitivanje vremenske sinhronizovanosti mernih signala snimljenih MEMS akcelerometrima

U radu je opisano ispitivanje sinhronizovanosti podataka koji su uzorkovani putem odvojenih MEMS akcelerometara. Korišćeni su bežični senzorski uređaji razvijeni na Građevinskom fakultetu u Beogradu, namenjeni merenju vibracija građevinskih objekata. Poznato je da ovi uređaji mogu da postignu tačnost vremenskog označavanja uzoraka reda veličine10 μs za kraće merne periode (ispodminuta). Ovo znači da je greška koju elektronika unosi zanemarljiva za merenje mehaničkih veličina sa frekvencijom uzorkovanja reda veličine kHz. Analizirane su varijacije u fazi izlaznih signala različitih senzora prilikom identične pobude. Problem je ograničena mogućnost ostvarivanja identične mehaničke pobude na različitim mestima u prostoru, te je bez savršene opreme nemoguće razgraničiti koliki deo greške potiče od nepoklapanja ulaznih signala, a koliki od nesavršenosti senzorskog aparata. Pokazano je da je moguće dobiti standardnu devijaciju vremenskog ofseta između snimljenih signala reda veličine milisekunde

The problem of heritology abduction through instrumental analysis of cultural heritage materials

Heritološki fenomeni u oblasti istraživanja kompozitnih umetničkih dela, u vezi sa raznovrsnošću pristupa u kvalitativnim i kvantitativnim kriterijumima za izbor materijala, postavljaju složene zadatke u primeni instrumentalnih metoda, koje prethode izradi protokola za konzervaciju-restauraciju predmeta kulturne baštine. U ovom radu u fokusu je problem heritološke abdukcije, u heurističkoj proceni broja neophodnih analiza, odnosno deficita podataka u fragmentarnim strukturama koje su izraz umetničkog spontaniteta, a sa akcentom na fenomen praemissa minor u traganju za metodološki čvrstom platformom za interpretaciju podataka.Taking into account the diversity of approaches in qualitative and quantitative criteria for material selection heritology phenomena in the field of research of composite art works set complex tasks in the application of instrumental methods, which precede the development of protocols for conservation and restoration of cultural heritage. The focus of this paper is on the problem of heritology abduction, particularly in the domain of heuristic assessment concerning the number of necessary analyses, i.e. the deficit of data in fragmentary structures, these being expressions of artistic spontaneity. At the same time, the paper also tackles the phenomenon of minor assumptions while pursuing a methodologically sound platform for interpreting data

Serbian Virtual Observatory

We review the newly established project of Serbian Virtual Observatory. In the last few years Virtual Observatories are becoming a new concept in the world of astronomy. The main aim of Virtual Observatories is to make accessible astronomical data to astronomers regardless of their geographical location as well as provide them with tools for analysis. The project of Serbian Virtual Observatory aims to achieve the following goals: 1) establishing SerVO and join the EuroVO and IVOA 2) establishing SerVO data Center for digitizing and archiving astronomical data obtained at Serbian observatories 3) inclusion of BelData/STARK-B and other theoretical and simulated data in SerVO 4) development of tools for visualization of dat

Razvoj i analiza senzorskog sistema za merenje vibracija građevinskih objekata

Structural Health Monitoring (SHM) involves measurement techniques used in damage detection and estimation of usability of different kinds of structures. SHM is usually performed in civil engineering, to determine states of buildings and capital infrastructural objects, such as bridges, towers, dams and tunnels. Reasons for the rapid development of SHM in the past two decades are increasing needs to monitor aging structures, new requests to build cheaper and more complex objects on heavier terrain (which often demands monitoring during both construction and exploitation), and growing demands implied by safety and other standards. On the other hand, technological advances and price decrease in the areas of wireless technologies and micro-electro-mechanical (MEMS) sensors caused SHM techniques to become widely available. A wireless sensor system primarily designed to measure vibrations of civil engineering structures is described. SHM of capital civil engineering objects is often performed by modal analysis of vibrations, which includes comparison of amplitudes and phases of specific signal harmonics in different points. Wireless systems are commonly used for this, since they have significant advantages over the wired ones. There is no need to use impractical and expensive large cables, both the whole system and sensor nodes can be easily relocated, and sensors are easier placed at hard-to-reach spots. There are shortcomings as well, mainly lower data transfer bit rate, sensibility to different electromagnetic interferences, including openness of the medium for attack, and limited energy supply. Sensor devices of the developed system are made in surfacemount technology (SMT). They use MEMS accelerometers, with small energy consumption, suitable for battery powered wireless systems. A solar panel was constructed to harvest sun power and supply the devices with additional energy, in case they are placed on spots with sufficient intensity natural light. Radio modems of domestic production were used for communication...Nadzor stanja objekata ili structural health monitoring (SHM) obuhvata merne tehnike kojima se vrši akvizicija podataka relevantnih za otkrivanje oštećenja i procenu upotrebljivosti raznih vrsta struktura. SHM se najčešće primenjuje u građevinskoj struci, za određivanje stanja zgrada i kapitalnih infrastrukturnih objekata, kao što su mostovi, tornjevi, brane, tuneli, itd. Razlozi za nagli razvoj SHM u poslednjih par decenija su povećane potrebe za ispitivanjem ostarelih objekata, novi zahtevi za izgradnjom jeftinijih a kompleksnijih objekata na težim tipovima terena (što zahteva nadzor i za vreme gradnje i za vreme eksploatacije), i rast zahteva sigurnosnih i drugih standarda. S druge strane, tehnološki razvoj i pojeftinjenje bežičnih tehnologija i mikroelektromehaničkih (MEMS) senzora je uslovio da SHM postane dostupan širokom spektru korisnika. U radu je opisan bežični senzorski sistem prvenstveno dizajniran za merenje vibracija na građevinskim objektima. SHM kapitalnih građevinskih objekata se najčešće vrši analizom modova oscilacija, što podrazumeva upoređivanje amplituda i faza pojedinih harmonika signala u različitim tačkama. U ovu svrhu se skoro isključivo koriste bežični sistemi, koji imaju izražene prednosti u odnosu na žičane. Nije potrebno nepraktično i skupo razvlačenje kablova, ceo sistem i pojedinačni senzori su lakši za premeštanje, i senzori se lakše mogu postaviti na teško pristupačna mesta. Postoje i mane, a to su manja brzina prenosa podataka, osetljivost na smetnje različitog porekla, uključujući otvorenost medijuma za nameran napad sa strane, i problemi sa ograničenošću napajanja. Senzorski uređaji su realizovani u surface-mount tehnologiji (SMT). Koriste MEMS akcelerometre za merenje ubrzanja. Njihova potrošnja je mala što odgovara zahtevima baterijski napajanih bežičnih uređaja. Napravljen je solarni panel koji služi za energetsko dopunjavanje senzorskih uređaja u slučaju da se ovi postavljaju na mesta sa prirodnom svetlošću dovoljnog intenziteta. Korišćeni su radio modemi domaće proizvodnje za komunikaciju..