research article infrared thermography in the...

Hindawi Publishing CorporationThe Scientific World JournalVolume 2013 Article ID 323948 8 pageshttpdxdoiorg1011552013323948

Research ArticleInfrared Thermography in the Architectural Field

Carosena Meola

Department of Industrial Engineering Aerospace Division University of Naples Federico II Via Claudio 21 80125 Napoli Italy

Correspondence should be addressed to Carosena Meola carmeolauninait

Received 28 August 2013 Accepted 26 September 2013

Academic Editors J Kim and B Kumar

Copyright copy 2013 Carosena Meola This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Infrared thermography is becoming ever more popular in civil engineeringarchitecture mainly due to its noncontact characterwhich includes two great advantagesOnone side it prevents the object under inspection fromany alteration and this isworthwhileespecially in the presence of precious works of art On the other side the personnel operate in a remote manner far away from anyhazard and this complies well with safety at work regulations What is more it offers the possibility to quickly inspect large surfacessuch as the entire facade of a building This paper would be an overview of the use of infrared thermography in the architecturaland civil engineering field First some basic testing procedures are described and then some key examples are presented owing toboth laboratory tests and applications in situ spanning from civil habitations to works of art and archaeological sites

1 Introduction

Infrared thermography (IRT) is being used in an ever morebroad number of application fields and for many differentpurposes indeed any process which is temperature depen-dent may benefit from the use of an infrared device In otherwords an infrared imaging device should be considered aprecious ally to consult for diagnostics and preventative pur-poses for the understanding of complex fluid dynamics phe-nomena or for material characterization and proceduresassessment which can help improve the design and fabrica-tion of products Infrared thermography may accompany theentire life of a product since it may be used to control themanufacturing process to nondestructively assess the finalproduct integrity and to monitor the component in-service

The first use of infrared thermography as a nondestruc-tive testing technique dates back to the beginning of the lastcentury [1 2] but it was only recently accepted amongst stan-dardized techniques Initially IRT suffered from perplexitiesand incomprehension mainly because of difficulties in theinterpretation of thermograms It received renewed attentionstarting from the 1980s when the importance of heat transfermechanisms [3 4] in image interpretation was understoodNow infrared thermography is a mature technique and isbecoming ever more attractive in an ever more increasingnumber of application fields This has also led to a prolifer-ation of infrared devices which differ in weight dimensions

shape performance and costs to fulfil desires of a multitudeof users in a vast variety of applications [5] In fact an infraredimaging system can be now tailored for specific requirementsand it can be advantageously exploited for process control andmaintenance planning without production stops and withconsequent money saving Of course complete exploitationof infrared thermography requires understanding of basictheory and application of standard procedures

Of relevant interest is the application of an infrared imag-ing device in architecture and civil engineering after BuildingRegulations for Conservation of Fuel and Energy (2007)However infrared thermography can be used also to discoverdefects in buildings envelope to monitor reinforcing steelin concrete to detect moisture inside building walls and soforth [6ndash8]

It is known that masonry structures deteriorate over timemainly due to natural forces of decay due to thermal stressesand due to water infiltration the main degradation effectsinclude variations in concrete compaction and voiding spall-ing or microcracking in masonry and reinforcement dete-rioration and this may be of great concern if the structurebelongs to the cultural heritage Indeed IRT represents avaluable tool for nondestructive evaluation of architectonicstructures and artworks because it is capable of giving indi-cation about most of the degradation sources of artworks andbuildings of both historical interest and civil use In particu-lar by choosing the most adequate thermographic technique

2 The Scientific World Journal

it is possible to monitor the conservation state of artworks intime and to detect the presence of many types of defects (egvoids cracks disbonding etc) in different types of materials[9 10] It is possible to inspect either a large surface such asthe facade of a palace or a very small surface of only fewsquare millimetres The main advantages of infrared ther-mography when dealing with precious artworks may be sum-marized in three words noncontact noninvasive and twodimensional

Long-term conservation of artworks involves periodicinspection to evaluate existing conditions to discover defi-ciencies at an incipient stage and to plan restoration beforecatastrophic failure occurs In this context infrared thermog-raphy (IRT) as a remote imaging system represents a power-ful tool to be used for quick periodic inspection The imagescan be stored in a digital format and a history of the materialdegradation can be easily examined and visualized as well ascompared to a previous situation by retrieval of archivedimages It is known that IRT has some limitations when deal-ing with deep and low thermal resistance defects but it hasproved to still be useful in conjunction with high-depth tech-niques [11ndash13]

This work would be an overview of some of the appli-cations of infrared thermography to the architectural fieldperformed at the Aerospace Engineering Section of theDepartment of Industrial Engineering University of NaplesFederico II to which the author belongs The results shownherein come from laboratory tests as well as in situ inspectionof civil buildings and of important artworks such as themosaic of the Battle of Issus in the Archaeological Museumof Naples and frescoes in the Villa Imperiale in Pompeii

2 Instrumentation and Test Procedure

Tests were carried out by using pulse and lock-in tech-niques and different cameras which include both cooled anduncooled detectors A brief description of the two techniquesand infrared cameras is given as follows

21 Pulse Thermography Pulse thermography (PT) consistssimply in the stimulation of the object (under evaluation) andmonitoring of its surface temperature variation during thetransient heating or cooling phase Heating is generally per-formed by lamps flash lamps scanning lasers or hot air jetsCooling can be practically attained by cold air jets Of courseair jets (hot or cold) can be used only on a massive surfacesince jet impingementmaydamage delicate objects for exam-ple artworks

For the case of slabs analysis with PT can be performedin two different modes transmission and reflection In thetransmission mode the infrared camera views the rear facethat is the face opposite to the heatingcooling source How-ever since the opposite side is not always accessible andoravailable the reflection mode for which both heating (cool-ing) source and camera are positioned on the same side ismainly applied

The thermal energy propagates by diffusion under thesurface while the infrared camera monitors the temperature

variation over the viewed surface Obviously for a uniformlyheated surface the temperature distribution is uniform incase of a homogeneous material The presence of a defect at acertain depth interferes with the heat flow causing local sur-face temperature variations The visibility of a defect can beevaluated by the following parameter119863

119879[14]

119863119879=|Δ119879|

1003816100381610038161003816Δ1198791199041003816100381610038161003816

=

1003816100381610038161003816119879119904 minus 1198791198891003816100381610038161003816

1003816100381610038161003816119879119904 minus 1198791199031003816100381610038161003816

(1)

where 119879119889is the temperature over a defective zone 119879

119904is the

temperature in a sound zone and 119879119903is a reference temper-

ature More specifically 119879119903is the temperature of the sound

material before starting transient heating or cooling 119879119903=

119879119904 (119905 = 0)

(ie the temperature of the first thermal image takenat 119905 = 0 s in the time sequence) Indeed the quantity119879

119904minus119879119903=

Δ119879119904plays an important role because it indicates the optimal

temperature variation to which the material has to be sub-jected for good defect visibility

The defect detection is limited by the signal-to-noise ratio(SNR) [15] or by the noise equivalent temperature difference(NETD) of the infrared detector In addition the surfacefinish is of great importance since variations in surface rough-ness cleanliness uniformity of paint and other surface con-ditions can cause variations in the emissivity coefficient andaffect the temperature measurement These drawbacks areovercome using lock-in thermography

22 Lock-InThermography In this work lock-in thermogra-phy is performedwith halogen lamps and is simply referred toas LTThe energy generated by halogen lamps is delivered tothe object surface in the form of periodic thermal waves Thethermographic system is coherently coupled to the thermalwave source which is operated in such a way that a sinusoidaltemperature modulation resultsThis modulation is obtainedfrom a nonlinear electrical signal produced by the lock-inmodule which also allows for frequency variation The ther-mal wave propagates inside the material and gets reflectedwhen it reaches parts where the heat propagation parameterschange (inhomogeneities)

The reflected wave interferes with the surface wave pro-ducing an oscillating interference pattern which can be mea-sured in terms of amplitude or phase angle that respectivelyproduces amplitude or phase imagesThedepth range for theamplitude image is given by 120583 which is calculated from thethermal diffusivity 120572 and the wave frequency 119891 = 1205962120587 asfollows

120583 = radic120572

120587119891 (2)

The maximum depth 119901 which can be reached for the phaseimage corresponds to 18120583 [16ndash19] The material thicknesswhich can be inspected depends on the wave period (thelonger the period the deeper the penetration) and on thematerial properties (eg thermal diffusivity)

23 Infrared Cameras Different infrared cameras by FLIRsystems are used which include either high performance

The Scientific World Journal 3

800

800

200

Plexiglas

Tuff

p = 20mm

p = 70mm

p = 120mm

Figure 1 Sketch of one-layer specimen

cooled detector cameras which are suitable for the researchfield or handheld cameras that are more appropriate for insitu inspections All the handheld cameras are equipped withmicrobolometer detectors working in the long wave infraredband generally from 8 up to 12 microns They differentiatefor thermal sensitivity and mainly for spatial resolution Inparticular the B4 andB360 have both 320times 240 pixels but theB360 offers the advantage of a more ergonomic configurationwith the possibility to rotate the lens and take images also inpresence of problematical optical access Of the same ergo-nomic configuration but of better resolution is the T640which has 640 times 480 pixels the same number of pixels bothP640 and P660 also have the latter being an upgrade ofthe P640 with obviously a better performance As a generalcharacteristic for all the new generation handheld camerasimages are stored on flash memory cards

The cooled detector cameras used by the author for archi-tectural applications include four cameras Two camerasequipped with a single MCT detector working in the 8ndash12microns and cooled with liquid nitrogen are the Agema 880of 140 times 140 pixels and digitalization at 8 bits and the Agema900 of 272 times 136 pixels and digitalization at 12 bits Two cam-eras including FPA QWIP second generation sensors work-ing in the 8-9 microns with Stirling cooler are the SC3000 of320times 240 pixels and the SC6000 of 640times 512 pixels (FLIR sys-tems) Herein only some peculiar results obtained by eitheruncooled or cooled detector cameras are shown as examples

3 Tests and Data Analysis

Tests were carried out partly in laboratory to assess testingprocedures and data analysis and partly in situ includingeither civil habitations or archaeological sites as well as worksof art

31 Laboratory Tests Laboratory tests are carried out byconsidering two types of specimens which simulate one- andtwo-layer structures with defects of different geometry andnature located at different depths [20]

The one-layer specimen of square section 800times 800mm2and of thickness 200mm is made of concrete (a mixture ofcement sand and water) with buried defects (air-filled Plex-iglas boxes and pieces of tuff) at depth from 119901 = 20mmup to120mm (Figure 1) More specifically the four circular insertsare 70mm in diameter while the central square-shaped inserthas a side of 100mm the thickness of all is 30mm

The other type of square section 900 times 900mm2 is com-posed of a plaster layer (one half is 10mm and the other halfis 20mm thick) over a support of brick marble or tuff withcork disks and air-filled plastic bags (in total 12) between theplaster and the support to simulate detachments (Figure 2)The inserts are 1mm thick and of diameter ranging between40mm and 100mm

The results herein reported are obtained with the cooledFPA detector SC3000 and by using the PT technique Twothermal images of two-layer specimens are shown in Figure 3for the support made of marble (Figure 3(a)) and of brick(Figure 3(b)) As can be seen all defects are visible but thehigher contrast is caused by the larger air-filled Plexiglasboxes It is worth noting that the images in Figure 3 are takenat a certain time instant during the cooling phase for whichall defects are visible in fact shallow defects (at depth 119901 =10mm) appear first but they tend to vanish later when thedeeper (119901 = 20mm) ones become visible Indeed thevisibility of a defect depends strongly on its thermal resistancewhich in turn depends on both geometrical (ie diameterthickness and depth) and thermal characteristics (ie con-ductivity diffusivity and effusivity) an important role is ofcourse played by the characteristics (resolution) of the usedinstrumentation [20]


450450

900

Plastic insert

Cork insert

Support

Plaster

Cork

Plastics

2010

30

Figure 2 Sketch of two-layer specimen

p = 20mmp = 10mm

(a) Marble support

239∘C

195∘C

p = 20mm p = 10mm

(b) Brick support

Figure 3 Thermal images of two two-layer specimens

The contrast 119863119879(see (1)) is plotted against the defects

diameter over depth ratio 119889119901 in Figure 4 for the one-layerspecimen considering both completely dry and partially wetconcrete (tests are carried out two times three months afterfabrication and six months later) As can be seen the tuffinserts display higher contrast for wet conditions on theother hand tuff in presence of water gets soaked modify-ing its thermal properties with respect to the surrounding

masonry structure Plexiglas instead being waterproof hasthe same thermal contrast independent of the moisture con-tent of the hosting material

32 Inspection In Situ Infrared thermography was widelyused for in situ inspection of architectonic structures andworks of art [9 11ndash14] Only a few examples are reportedherein


1 102 505dp

001

01

1

10

WetPlexiglasTuff

DryPlexiglasTuff

DT

Figure 4119863119879against 119889119901 for the one-layer specimen

321 Inspection of Civil Edifices Some thermal imagesaccounting for infiltration of water and presence of humidityare shown in Figure 5 for outside (Figure 5(a)) and inside(Figures 5(b)ndash5(e)) All images are taken with handheld cam-eras more specifically with the B4 (the images shown in Fig-ures 5(a) 5(d) and 5(e)) with the B360 (the image shown inFigure 5(b)) and with the P640 (the image shown inFigure 5(c)) Figure 5(a) shows the underneath surface of abalcony the dark stains indicate degradation of concretebecause of infiltration of water most probably due to poortightness of the upside surface Figure 5(b) represents thecorner between walls of a house in which a humidity stain isclearly evident Humidity stains are also present on the wallof the public edifice which is a sports centre as shown inFigure 5(c) In the latter it is possible to see humidity stainsdeveloping on the top due to not only poor tightness of theexternal wall envelope but also humidity raising from thebottom through capillary suction Figure 5(d) shows a por-tion of a garage roof in which there is water infiltrationFigure 5(e) represents the same scene as Figure 5(d) but afterforced infiltration of water with the aim of locating theentrance pathway From a comparison between images it ispossible to distinguish infiltration in progress or better thewater pouring out as in Figure 5(e) from the effects of infil-tration like the damp patches in Figures 5(a)ndash5(c)

Water infiltration is a complex task to deal with since it isvery difficult or impossible to precisely locate the entry pointwithout disruption of the roof or pavement this is becausefrom entrance and exit often there may be a tortuous path-way In addition often water infiltration remains impercep-tible to naked eyes for a long time becoming noticeable whenthe unpleasant damp patches appear this happens because ofthe diffusion aptitude of water An infrared imaging devicemay help solve the problem through a suitable procedureinvolving forced water entrance this is the approach pursued

to discover water infiltration in the roof of the garage(Figure 5(e))

An example of buried structures is given in Figure 6 Thefirst image (Figure 6(a)) is taken at a distance of 3m withpulse thermography and with the SC3000 camera It refersto a roof ferroconcrete beam in a warehouse the thicker darkhorizontal lines represent the buried steel rods while the ver-tical milder lines indicate brackets The beam under study is40 cm wide and about 15m long and it is tapered along thethird dimension It is interesting to see that infrared thermog-raphy offers the possibility to ascertain the presence of steelbars inside ferroconcrete beams and to evaluate their diam-eter This of course is of paramount importance since itprevents from destructive tests and is time andmoney savingThe second image taken with the B360 camera (Figure 6(b))displays irregular dark bands that indicate the presence ofburied duct cables there Often as in this case conduits forelectrical cables do not follow straight directions while find-ing their exact location is vital to avoid troubles when drillinga hole in the wall

322 Application to the Cultural Heritage The increasingsensitivity towards the conservation of cultural properties islooking at infrared thermography as an excellent aid [10]Themain causes of degradation of art treasures lie in exposureto adverse environmental conditions including thermal andmechanical stresses and variation of humidity which give riseto microcracks disbonding and formation of mould It is ofutmost importance to detect defects at an incipient stage andto understand modifications induced by variation of envi-ronmental parameters to plan the most adequate program ofprevention from decay of artworks Infrared thermographyhas proved its capability to help find detached tiles inmosaicsand degradation of plaster and frescoes [9] to measure ther-mal properties like diffusivity and effusivity of materials forthe solution of the inverse problem [10] and to monitormicroclimatic conditions [21] which often represent themajor hazard issue for the conservation of precious works ofart

Herein some phase images collected during campaigns oftests in situ in the Archaeological Museum of Naples and inthe archaeological site of Pompeii are shown Such images aretakenwith cooled detector cameras (Agema 900 and SC3000)equipped with the IR lock-in option In particular phaseimages reported in Figure 7 are taken with the Agema 900camera while phase images reported in Figure 8 are takenwith the SC3000 camera

Figure 7 shows a picture of a portion of the famousmosaicof the Battle of Issus (ArchaeologicalMuseum inNaples) withtwo phase images This is a masterpiece of inestimable valuewhich was created with the opus vermiculatum techniquetiles of miniature size (about 20 tiles in a cm2) were gluedwith rosin which is sensitive to temperature rise Then theinspection of such artwork poses serious problems in terms ofits safeguard As a general comment the PT technique is notsuitable since it is affected by nonuniform emissivity distribu-tion which is a major problem in the evaluation of mosaicsbecause to obtain the desired chromatic effects tiles of differ-ent materials colours and brightness are generally used and


267∘C

216∘C

26

25

24

23

22

(a)

230∘C

210

(b)

127∘C

108∘C

12

11

(c)

301∘C

268

(d)

301∘C

268

(e)

Figure 5 Examples of water infiltration (a) Underneath surface of a balcony (b) Wall corner inside a house (c) Wall surface inside a gym(d) Garage roof (e) Garage roof during forced infiltration

(a) Roof ferroconcrete beam (b) Buried electrical conduit

Figure 6 Examples of thermal images in presence of buried structures

(A)

(B)

(A)

(B)

Figure 7 A part of the Battle of Issus mosaic (ArchaeologicalMuseum in Naples)

this causes local variation of emissivity Thus the evaluationis made with the LT technique and with special care to avoid

undesired temperature rise the lamp is positioned far enoughfrom the mosaic surface The variation of the phase anglewith varying heating frequencies provides information usefulto discriminate between tiles made of different materials tolocate disbonded tiles and detachments in the plaster supportunderneath the tiles and to discover restored plaster in areaswithout tiles In particular the twophase images taken both at119891 = 0019Hz which refer the one on the right top side to thesurface encircled by rectangleA and the other one on the rightbottom side to the surface encircled by rectangle B supplyrelevant details More specifically the variation of colour(variation of phase angle) indicates variation ofmaterial com-paction with presence of detachments in the encircled zones

Figure 8(a) shows a picture of a frescoed wall of the oecusroom of Villa Imperiale in Pompeii while Figures 8(b)ndash8(d) show phase images taken at decreasing frequency ofthe surface inscribed inside the rectangle in Figure 8(a) It is


(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz

Figure 8 Phase images ((b)ndash(d)) on the wall (a) in the oecus room in Villa Imperiale (Pompeii)

possible to see a crack networkwhich is present on the surface(Figure 8(b)) and propagates underneath in the support(Figure 8(d)) The lighter colour in Figure 8(c) indicates ageneral degradation of the support underneath the frescoessuch a degradation ismore important on the left corner as thelighter colour intensity shows (Figure 8(d)) From a compari-son between the three images it is also possible to gain infor-mation about the junction between the central panel and theleft wall In particular the phase image in Figure 8(c) whichwas taken at the heating frequency of 0005Hz (depth119901 about12 cm) shows in agreement with GPR data [13] a consolida-tion structure across the junction of the left wall part to thecentral panel

4 Conclusions

Some of the results obtained while applying infrared ther-mography to the inspection of architectonic structures andworks of art have been illustrated with also a brief introduc-tion to the basic procedures As main findings the appliedtechniques allow for the detection of hidden structuresas well as for the identification of areas damaged by in-depth ingression of moisture andor by disaggregation of theconstituent materials The attention herein has been mainlydevoted to the conservation conditions of masonry struc-tures while an infrared camera can be advantageouslyexploited also for the control of microclimatic conditions

Indeed infrared thermography as a remote imagingdevice represents a powerful tool to be used for quick peri-odic inspection of both civil habitations and historic build-ings to discover defects in buildings envelope to monitor

reinforcing steel in concrete to detect moisture inside build-ing walls to check indoor microclimate and so forth All thisinformation is useful to deal with conservation measuresand to improve microclimatic conditions for the comfort ofhuman beings and for the safeguard of the works of art

Conflict of Interests

The author declares no conflict of interests

References

[1] W S Beller ldquoNavy sees promise in infrared thermography forsolid case checkingrdquo Missiles and Rochets vol 16 no 22 pp1234ndash1241 1965

[2] D R Green ldquoPrinciples and applications of emittance-independent infrared non-destructive testingrdquo Applied Opticsvol 7 pp 1779ndash1786 1968

[3] C Cattaneo ldquoA form of heat conduction equation which elimi-nates the paradox of instantaneous propagationrdquo ComptesRendues vol 247 pp 431ndash433 1958

[4] H S Carslaw and J C Jaeger Conduction of Heat in SolidsClarendon Press Oxford UK 1959

[5] R Rinaldi ldquoInfrared devices short history and new trendspprdquoin Infrared Thermography Recent Advances and Future TrendsC Meola Ed chapter 2 pp 29ndash59 Bentham Science Publish-ers Sharjah UAE 2012

[6] V Vavilov T Kauppinen and E Grinzato ldquoThermal character-ization of defects in building envelopes using long square pulseand slow thermal wave techniquesrdquo Research in NondestructiveEvaluation vol 9 no 4 pp 181ndash200 1997


[7] D Bjegovic DMikulic andD Sekulic ldquoNon-destructivemeth-ods for monitoring reinforcing steel in concreterdquo in Proceedingsof the 9th International Conference Structural Faults Repair Lon-don 2001

[8] M Milazzo N Ludwig and V Redaelli ldquoEvaluation of evap-oration flux in building materials by infrared thermogra-phyrdquo in Proceedings of the Quantitative Infrared Thermography(QIRT rsquo02) D Balageas G Busse and G M Carlomagno Edspp 150ndash155 Dubrovnik Croatia 2002

[9] G M Carlomagno and C Meola ldquoInfrared thermography inthe restoration of cultural propertiesrdquo in Thermosense XXIIIvol 4360 of Proceedings of SPIE pp 203ndash216 usa April 2001

[10] E Grinzato ldquoThermography in cultural heritage conservationrdquoin Recent Advances in non Destructive Inspection C Meola Edchapter 5 pp 125ndash160 Nova Science Publisher New York NYUSA 2010

[11] G M Carlomagno R di Maio C Meola and N RobertildquoInfrared thermography and geophysical techniques in culturalheritage conservationrdquo Quantitative InfraRed ThermographyJournal vol 2 pp 5ndash24 2005

[12] CMeola R diMaioN Roberti andGMCarlomagno ldquoAppli-cation of infrared thermography and geophysical methods fordefect detection in architectural structuresrdquo Engineering FailureAnalysis vol 12 no 6 pp 875ndash892 2005

[13] G M Carlomagno R di Maio M Fedi and C Meola ldquoInte-gration of infrared thermography and high-frequency electro-magnetic methods in archaeological surveysrdquo Journal of Geo-physics and Engineering vol 8 no 3 article S93 2011

[14] C Meola and G M Carlomagno ldquoApplication of infrared ther-mography to adhesion sciencerdquo Journal of Adhesion Science andTechnology vol 20 no 7 pp 589ndash632 2006

[15] V P Vavilov D P Almond G Busse et al ldquoInfrared thermo-graphic detection and characterization of impact damage incarbon fibre composites results of the round robin testrdquo in Pro-ceedings of the Quantitative Infrared Thermography (QIRT 98)D Balageas G Busse and G M Carlomagno Eds pp43ndash52 Akademickie Centrum Graficzno-Marketingowe ŁodzPoland 1998

[16] A Lehto J Jaarinen T TiusanenM Jokinen andM LuukkalaldquoMagnitude and phase in thermal wave imagingrdquo ElectronicsLetters vol 17 no 11 pp 364ndash365 1981

[17] C A Bennett Jr and R R Patty ldquoThermal wave interferometrya potential application of the photoacoustic effectrdquo AppliedOptics vol 21 no 1 pp 49ndash54 1981

[18] G Busse ldquoOptoacoustic phase anglemeasurement for probing ametalrdquo Applied Physics Letters vol 35 no 10 pp 759ndash760 1979

[19] R LThomas J J Pouch Y HWong L D Favro P K Kuo andA Rosencwaig ldquoSubsurface flaw detection inmetals by photoa-coustic microscopyardquo Journal of Applied Physics vol 51 no 2pp 1152ndash1156 1980

[20] C Meola ldquoInfrared thermography of masonry structuresrdquoInfrared Physics and Technology vol 49 no 3 pp 228ndash233 2007

[21] E Grinzato ldquoState of the art and perspective of infrared ther-mography applied to building sciencerdquo in Infrared Thermogra-phy Recent Advances and Future Trends C Meola Ed chapter9 pp 200ndash229 Bentham Science Publishers Sharjah UAE2012

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



it is possible to monitor the conservation state of artworks intime and to detect the presence of many types of defects (egvoids cracks disbonding etc) in different types of materials[9 10] It is possible to inspect either a large surface such asthe facade of a palace or a very small surface of only fewsquare millimetres The main advantages of infrared ther-mography when dealing with precious artworks may be sum-marized in three words noncontact noninvasive and twodimensional

Long-term conservation of artworks involves periodicinspection to evaluate existing conditions to discover defi-ciencies at an incipient stage and to plan restoration beforecatastrophic failure occurs In this context infrared thermog-raphy (IRT) as a remote imaging system represents a power-ful tool to be used for quick periodic inspection The imagescan be stored in a digital format and a history of the materialdegradation can be easily examined and visualized as well ascompared to a previous situation by retrieval of archivedimages It is known that IRT has some limitations when deal-ing with deep and low thermal resistance defects but it hasproved to still be useful in conjunction with high-depth tech-niques [11ndash13]

This work would be an overview of some of the appli-cations of infrared thermography to the architectural fieldperformed at the Aerospace Engineering Section of theDepartment of Industrial Engineering University of NaplesFederico II to which the author belongs The results shownherein come from laboratory tests as well as in situ inspectionof civil buildings and of important artworks such as themosaic of the Battle of Issus in the Archaeological Museumof Naples and frescoes in the Villa Imperiale in Pompeii

2 Instrumentation and Test Procedure

Tests were carried out by using pulse and lock-in tech-niques and different cameras which include both cooled anduncooled detectors A brief description of the two techniquesand infrared cameras is given as follows

21 Pulse Thermography Pulse thermography (PT) consistssimply in the stimulation of the object (under evaluation) andmonitoring of its surface temperature variation during thetransient heating or cooling phase Heating is generally per-formed by lamps flash lamps scanning lasers or hot air jetsCooling can be practically attained by cold air jets Of courseair jets (hot or cold) can be used only on a massive surfacesince jet impingementmaydamage delicate objects for exam-ple artworks

For the case of slabs analysis with PT can be performedin two different modes transmission and reflection In thetransmission mode the infrared camera views the rear facethat is the face opposite to the heatingcooling source How-ever since the opposite side is not always accessible andoravailable the reflection mode for which both heating (cool-ing) source and camera are positioned on the same side ismainly applied

The thermal energy propagates by diffusion under thesurface while the infrared camera monitors the temperature

variation over the viewed surface Obviously for a uniformlyheated surface the temperature distribution is uniform incase of a homogeneous material The presence of a defect at acertain depth interferes with the heat flow causing local sur-face temperature variations The visibility of a defect can beevaluated by the following parameter119863

119879[14]

119863119879=|Δ119879|

1003816100381610038161003816Δ1198791199041003816100381610038161003816

=

1003816100381610038161003816119879119904 minus 1198791198891003816100381610038161003816

1003816100381610038161003816119879119904 minus 1198791199031003816100381610038161003816

(1)

where 119879119889is the temperature over a defective zone 119879

119904is the

temperature in a sound zone and 119879119903is a reference temper-

ature More specifically 119879119903is the temperature of the sound

material before starting transient heating or cooling 119879119903=

119879119904 (119905 = 0)

(ie the temperature of the first thermal image takenat 119905 = 0 s in the time sequence) Indeed the quantity119879

119904minus119879119903=

Δ119879119904plays an important role because it indicates the optimal

temperature variation to which the material has to be sub-jected for good defect visibility

The defect detection is limited by the signal-to-noise ratio(SNR) [15] or by the noise equivalent temperature difference(NETD) of the infrared detector In addition the surfacefinish is of great importance since variations in surface rough-ness cleanliness uniformity of paint and other surface con-ditions can cause variations in the emissivity coefficient andaffect the temperature measurement These drawbacks areovercome using lock-in thermography

22 Lock-InThermography In this work lock-in thermogra-phy is performedwith halogen lamps and is simply referred toas LTThe energy generated by halogen lamps is delivered tothe object surface in the form of periodic thermal waves Thethermographic system is coherently coupled to the thermalwave source which is operated in such a way that a sinusoidaltemperature modulation resultsThis modulation is obtainedfrom a nonlinear electrical signal produced by the lock-inmodule which also allows for frequency variation The ther-mal wave propagates inside the material and gets reflectedwhen it reaches parts where the heat propagation parameterschange (inhomogeneities)

The reflected wave interferes with the surface wave pro-ducing an oscillating interference pattern which can be mea-sured in terms of amplitude or phase angle that respectivelyproduces amplitude or phase imagesThedepth range for theamplitude image is given by 120583 which is calculated from thethermal diffusivity 120572 and the wave frequency 119891 = 1205962120587 asfollows

120583 = radic120572

120587119891 (2)

The maximum depth 119901 which can be reached for the phaseimage corresponds to 18120583 [16ndash19] The material thicknesswhich can be inspected depends on the wave period (thelonger the period the deeper the penetration) and on thematerial properties (eg thermal diffusivity)

23 Infrared Cameras Different infrared cameras by FLIRsystems are used which include either high performance


800

800

200

Plexiglas

Tuff

p = 20mm

p = 70mm

p = 120mm











450450

900

Plastic insert

Cork insert

Support

Plaster

Cork

Plastics

2010

30


p = 20mmp = 10mm

(a) Marble support

239∘C

195∘C

p = 20mm p = 10mm

(b) Brick support







1 102 505dp

001

01

1

10

WetPlexiglasTuff

DryPlexiglasTuff

DT










267∘C

216∘C

26

25

24

23

22

(a)

230∘C

210

(b)

127∘C

108∘C

12

11

(c)

301∘C

268

(d)

301∘C

268

(e)




(A)

(B)

(A)

(B)






(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz



4 Conclusions






References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










800

800

200

Plexiglas

Tuff

p = 20mm

p = 70mm

p = 120mm











450450

900

Plastic insert

Cork insert

Support

Plaster

Cork

Plastics

2010

30


p = 20mmp = 10mm

(a) Marble support

239∘C

195∘C

p = 20mm p = 10mm

(b) Brick support







1 102 505dp

001

01

1

10

WetPlexiglasTuff

DryPlexiglasTuff

DT










267∘C

216∘C

26

25

24

23

22

(a)

230∘C

210

(b)

127∘C

108∘C

12

11

(c)

301∘C

268

(d)

301∘C

268

(e)




(A)

(B)

(A)

(B)






(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz



4 Conclusions






References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










450450

900

Plastic insert

Cork insert

Support

Plaster

Cork

Plastics

2010

30


p = 20mmp = 10mm

(a) Marble support

239∘C

195∘C

p = 20mm p = 10mm

(b) Brick support







1 102 505dp

001

01

1

10

WetPlexiglasTuff

DryPlexiglasTuff

DT










267∘C

216∘C

26

25

24

23

22

(a)

230∘C

210

(b)

127∘C

108∘C

12

11

(c)

301∘C

268

(d)

301∘C

268

(e)




(A)

(B)

(A)

(B)






(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz



4 Conclusions






References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










1 102 505dp

001

01

1

10

WetPlexiglasTuff

DryPlexiglasTuff

DT










267∘C

216∘C

26

25

24

23

22

(a)

230∘C

210

(b)

127∘C

108∘C

12

11

(c)

301∘C

268

(d)

301∘C

268

(e)




(A)

(B)

(A)

(B)






(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz



4 Conclusions






References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










267∘C

216∘C

26

25

24

23

22

(a)

230∘C

210

(b)

127∘C

108∘C

12

11

(c)

301∘C

268

(d)

301∘C

268

(e)




(A)

(B)

(A)

(B)






(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz



4 Conclusions






References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










(a) Picture

(b) f = 00125Hz (c) f = 0005Hz (d) f = 000085Hz



4 Conclusions






References

























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation



























RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









research article infrared thermography in the...

Documents