Siga di idetificaioe Distrib. Pago di ~ Ricerca Sistea ettrico XCIRTN - LP5 - L Titoo Rapporto suo studio di etodoogie iovative di prova e di itegraioe tra prove di tipo e etodo aaitico per e quaifice abietai eccaice sisice ed eettroagetice di copoeti e sistei per e cetrai uceari Parte /I : Caera riverberate per prove MC te eittete CIRTN PAGINA DI GUARDIA Descrittori Tipoogia de docueto: Coocaioe cotrattuae: Rapporto Tecico Accordo di prograa NA-MS: tea di ricerca "Nuovo uceare da fissioe" Argoeti trattati: Igegeria uceare: Sicurea uceare Igegeria eettroica: Apparati e copoeti eettroici Soario I presete docueto è focaiato sugi aspetti dea quaifica e copatibiità eettroagetica di struetaioe e sistei destiati a'ipiego i abiete specifico uceare. Nea pria parte vegoo evideiati gi aspetti teorici su cui si basa i fuioaeto di ua Caera Riverberate e e etodoogie di cacoo appicate per a defiiioe di iportati paraetri. La secoda parte riguarda e procedure operative ed i dettagi ecessari per a caibraioe e a caratteriaioe dea Caera Riverberate presete ei Laboratori de C.R. NA Casaccia secodo e orative iteraioai (IC 6-4-. Note RPORT PAR 8-9 LPS.D CRS-POLITO RL 3/ Autori: F.Caavero L.Cristiei R.Serra Poitecico di Torio - Dipartieto di ettroica Copia. I carico a: o MISSION Z.~..o NOM FIRMA NOM FIRMA NOM FIRMA P. Meoi RV. DSCRIZION DATA CONVALIDA VISTO APPROVAZION
CIRTN Cosorio Iteruiversitario per a Ricerca Tcoogica Nuceare POLITCNICO DI TORINO Dipartieto di ettroica Rapporto suo studio di etodoogie iovative di prova e di itegraioe tra prove di tipo e etodo aaitico per e quaifice abietai eccaice sisice ed eettroagetice di copoeti e sistei per e cetrai uceari. Part II: AUTORI F. Caavero L. Cristiei R. Serra CRS-POLITO RL 3/ TORINO AGOSTO Lavoro svoto i esecuioe dea iea progettuae LP5- D AdP MS NA Ricerca di Sistea ettrico - PAR8-9 Progetto.3 Nuovo Nuceare da Fissioe
ecutive Suar of te Docuet Tis report deas it a geera descriptio of Reverberatio Cabers for MC use. Te first part presets a overvie of te Reverberatio Caber fuctioig pricipes ad preiiar cacuatios of soe iportat paraeters of te ept caber suc as te first resoat frequecies ad te estiated Q factor. Tis basic but crucia aasis serves as a essetia startig poit for uderstadig basic operatig processes. Te secod part cocers operatig procedures ad detais ecessar for te caibratio ad caracteriatio of te NA reverberatio caber accordig to te iteratioa stadard IC 6-4-. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
Tabe of Cotets List of Abbreviatios 4. Reverberatio Caber Pricipes 5. Reverberatio Caber Teor 6 Modes iti a Idea Cavit 6 Loest Useabe Frequec Nuber of Cavit Modes Stirrig Ratio 4 Quait Factor 5 3. Fied Statistics i a Reverberatio Caber 8 rgodicit 8 Probabiistic Distributios 9 Correatio Fuctio Statistica Ucertait ad stiator Accurac 4. Operatig Procedure for te NA Reverberatio Caber Caibratio Measureet Sste Stirrer fficiec 4 Revie of IC 6-4- 7 Fied Uiforit 9 Caveats for Caibratio 9 Maiu Caber Loadig Verificatio 9 5. Refereces 3 Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 3 of 3
List of Abbreviatios M........ ectroagetic MC........ ectroagetic copatibiit UT........ quipet Uder Test RC........ Reverberatio caber OATS........ Ope Area Test Site AC........ Aecoic Caber TM........ Trasverse ectroagetic TX........ Trasittig (atea RX........ Receivig (atea LUF........ Loest Usabe Frequec SR........ Stirrig Ratio Q........ Quait Factor IL........ Isertio Loss ACF........ Atea Caibratio Factor CCF........ Caber Caibratio Factor CLF........ Caber Loadig Factor Τ........ Caber tie costat Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 4 of 3
. Reverberatio Caber Pricipes A eectroagetic reverberatio caber is a eectrica arge ig coductive cosed cavit or caber used to perfor M easureets (bot eissios ad iuit o eectroic equipet. A faciit tat fits tis descriptio ca be cosidered a reverberatio caber (aso caed a ode-stirred caber. A rotatig padde or oter eas of aterig te geoetr of te roo is aost aas used i a reverberatio caber for ode-stirrig or ode-tuig. Soeties a frequec-oduated source is used to acieve eectroic ode-stirrig. A cosed cavit as a propagatig odes ic for 3-diesioa stadig ave patters it a arge uber of resoat odes. Tis gives rise to regios ere te fied is sa ad oter ocatios ere it is arge. Tpica variatios are of te order of 4 db akig te perceived test fied ver strog depedet o te eact ocatio iside te cavit. At sufficiet ig frequecies te coupig betee a equipet ad a atea varies rapid it positio ad frequec. We a arge uber of odes are preset (as i a reverberatio caber te fied patter becoes ig detaied (atoug reguar but tere are sti arge ad rapid variatios i fied vaues it positio ad frequec. Te ode stirrer or tuer aters te boudar coditios tus ovig te positio of te aia ad iia of te fied agitude. Te sape of a reverberatio caber is b ad arge uiportat ver differet sapes ave so to perfor equa e. Istead te voue of te caber is te ke factor for satisfactor perforace. We coosig a rectaguar roo as a basis for buidig a reverberatio caber idea te diesios soud ot be sipe utipes or ratioa fractios of eac oter tis gives te argest uber of odes it differet resoace frequecies ad i pricipe iproves te roo perforace particuar at oer frequecies. Modeig te operatio of a reverberatio caber is of iterest because it aos te rapid copariso of differet scearios ad te deteriatio of uc greater iforatio about te fied structure ta is easi possibe it easureets. Hoever odeig eectrica arge ig-q structures suc as reverberatio cabers is ot a trivia eercise. For tis sort of ode fu ave uerica eectroagetic odeig etods are suitabe; Ra tracig etods ave aso bee used ad are suitabe for odeig te ig frequec beavior of reverberatio cabers. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 5 of 3
. Reverberatio Caber Teor Modes iti a Idea Cavit I order to defie te distributio of odes iside a idea cavit it is ecessar to start fro te geera idea of a resoator. I geera a resoator ca be obtaied b sort-circuitig a rectaguar aveguide ad tis operatio ust be doe at to sufficiet separated eds. We at a give frequec te geoetrica diesios of a resoator reac a specific egts a M fied iside te resoator fors a stadig ave patter. B usig Mae s equatios it is possibe to ateatica describe te fied distributio iside a cavit: jωµ H H H jωε + j ere ad H are te eectric ad te agetic fied stregt j is te eectric curret desit ε deotes te dieectric perittivit ad µ is te agetic pereabiit. B appig te propert of vector idetit to te first to Mae s equatios ( X ( X X it is possibe to derive te eectrica ad agetic ave equatios. Tese equatios ca be used to describe te fieds iside a cavit: c H c t H t ere c is te propagatio speed of te M aves iti te resoator ad c is te speed of te M aves i te vacuu: Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 6 of 3
c c ε µ r r Te eectrica ad agetic ave equatios ca be soved b usig te boudar coditios tat are derived for te tagetia copoets of te eectric ad agetic fieds: ( ad: H H ta ta for ( H H k < for ( H H j k s H H ta H H ta ta ta j for k < s for k ere is a ora vector tat poits fro regio ito regio ad js is te surface curret desit. It is aso possibe to derive te boudar coditios for te ora copoets of te eectric fied: ad te agetic fied: D D or D or B ( D D η B or B or ( B B η ere η is te surface carge. To of te equatios of te boudar coditios i te case of a idea cavit ca be approiated i tis a: H ta V or V Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 7 of 3
Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 8 of 3 Tese ast to equatios are vaid o te PC a surface V of te cavit for te ora copoet of te agetic fied ad for te tagetia copoet of te eectric fied. Appig tese cocepts to te rectaguar geoetr of a idea cavit resoator te obtaied resuts are: H H H B eas of te first ad te tird equatio te eectrica ad agetic ave equatios derived before ca be fufied b certai M fied stadig ave patters iside te cavit tose are caed as te cavit odes. Te cavit odes are divided i to ai parts te first categor is caed trasverse eectric(t ad it represets te odes ic ave a ero eectric fied copoet aog te -directio ( ie te secod categor is te trasverse agetic (TM ad it idicates te odes ic do ot ave a agetic fied aog te -directio (H. I te case of te fied copoets of TM p odes i a idea rectaguar cavit resoator: p p k si si cos ( p p k si cos si ( p cos si si ( p k j H ωε cos cos si ( p k j H ωε cos si cos ( ( H Te idices ad p are iteger ubers (ere 3. ad p.. Suc idices are used to idicate te uber of af aveegts i te tree directio ad. Te factor is te idt is te eigt ad is te egt of cavit.
Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 9 of 3 Te sae cocusios ca be aso derived for te T p odes: p H k j ωµ si si cos ( p H k j ωµ si cos si ( ( p H p k H cos cos si ( p H p k H cos si cos ( p H H si cos cos ( I tis secod case ad are equa to 3 ie p is equa to. Bot for te T ad te TM case te costat K is equa to: + + k k It is aso ecessar to defie te aguar frequec ω: + + p k c p ω I a cavit i ic te as are PC ad tere are o osses due to dissipative eeets preset iside te cavit it is possibe to defie te forua used to evauate te cut-off frequecies for a idividua odes: + + p c f p It is ot ipossibe to ave odes avig te sae cut-off frequec ad tis is true for a T p ad TM p cavit odes it > > ad p>. Tese odes it te sae cut-off frequec are caed degeerate odes.
B appig tese teoretica cocepts to a rea case ike te NA sieded roo it is possibe to fid te oda structure of tis caber for te T ad TM case. I te grap of Fig. te asterisks ad te ies are used to idetif te presece of a ode. Te ie represetatio is used o for odes tat are sufficiet separated fro te oters. Fig.:Teoretica oda structure for te caber uder stud (NA sieded roo diesios: 3.4 3.6 5.4. Te first odes are represeted. It is possibe to see ore i detais te oda structure for te first odes as iustrated i Fig.. It is possibe to ote tat o degeerate odes are preset sice te ad diesios of te NA caber ave differet vaues. I practice a reverberatio caber is ot a idea cavit but it is doiated b osses i te as. As a cosequece if te coditio of k>>ωε is vaid te sape of te fied distributio iside te cavit is ot odified but te agitude of te fied is reduced. B cosiderig a k vaue tat is saer ta te idea vaue (ifiite te fied distributio is a scaed versio of te oe obtaied for k tat goes to ifiite. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
Fig : Teoretica oda structure for te first eigt odes of te NA sieded roo. Loest Usabe Frequec Te frequec at ic a RC is abe to satisf te basic operatioa requireets is caed te oest usabe frequec (LUF. Differet defiitios app e.g. te LUF is te vaue of frequec fro ic at east.5 odes/mh are preset or for ic tere are 6- odes iside a idea cavit of te diesios of te RC. Te LUF ca aso be foud b koig te cutoff frequec f c of te fudaeta ode of a idea cavit it te sae sies of te RC. Te frequec f LUF is equa to 3 f c. Tese first to defiitios are quaitative ad te give a geera idea o o e a RC of a certai diesio i ork. Nuber of Cavit Modes Startig fro te assuptio of a ept RC itout a stirrer device it is possibe to evauate te cuuated uber of odes te ode desit ad aso te oda gap. Tose vaues are used to fid fro ic vaue of f LUF te caber fufis te fudaeta RC requireets. A epressio ca be used to fid a approiatio of te cuuated uber of odes tat are above cutoff for a specific vaue of frequec f: 8 N( f 3 f c 3 ( + + f c + Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
I order to satisf te LUF coditio te vaue of N(f ust be betee 6 ad odes. Te ode desit represets te uber of odes per frequec iterva; it ca be foud b appig te forua beo N f f 8 c 3 ( + + c At east.5 odes/mh above cutoff are required to ave a sufficiet statistica fied uiforit ad isotrop iside a RC. Aoter iportat factor tat it is iterestig to ko is te cutoff frequec of a idividua ode ito a idea rectaguar cavit: f i ( p c + p + Te factors p are itegers vaues tat are positive or equa to ero but o oe of tese factors ca be equa to ero at te sae tie. It is ecessar to arrage i a ascedig order a te vaues of cutoff frequecies ad after tat operatio it is possibe to cage te ide i it a e cosecutive ide i. B doig tis operatio te obtaied resut is: f i' + i' ( p ( p ' f i' Te set (p is differet fro (p ad it represets a differet ode. B subtractig te previous vaue fro te successive oe te oda gap betee cosecutive odes is evauated: f i' + ; i' f i' + f i' ( p ( p ' Te obtaied vaue is rea iportat to copare differet RCs ad to uderstad te quait of caber; te rue is: te saer te vaue of te oda gap te iger te quait of te RC is. It is possibe to app te cocepts tat are described i tis sectio to a rea caber i tis particuar case te caber used for te evauatio is a RC tat as bee buit startig fro a NA sieded roo. Te itera diesios of te sieded roo are: Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
Heigt 34 Widt 36 Dept 54 I order to fid te oest usabe frequec te cuuated uber of odes is set equa to (coditio tat is epaied i te sectio cocerig te LUF ad te te equivaet vaue of frequec is foud b sovig: 8 3 f c LUF 3 ( + + f c LUF + 8 f LUF 83 H To ceck if obtaied frequec fufis aso te oter coditios for te LUF te ode desit ust ave at east a vaue of.5 odes/mh above cutoff: N f 8 ( 83 8 3 ( 3 8 54 36 34 8 3 ( 54 + 36 + 34 75 od/ MH Aoter iterestig poit is to fid te vaues of cutoff frequec for soe idividua odes: 8 3 7 f( + 536 H 5 36MH 54 36 8 3 7 f( + 6443 H 64 43MH 36 34 8 3 7 f( + 574 H 57 4MH 54 34 8 3 7 f( + 75 H 7 5MH 54 36 34 It is aso possibe to fid te teoretica curve tat idicates te uber N of odes above cutoff for te NA sieded roo (iustrated i Fig. 3. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 3 of 3
5 5 N 5.5.5 3 Freq[MH] 3.5 4 4.5 5 8 Fig 3: Teoretica uber of odes N above cutoff i te NA sieded roo. B appig te forua used to fid te vaue of te ode desit it is possibe to sketc te grap represetig te idea curve of te ode desit for te NA sieded roo (Fig. 4. 4 8 dn/df 6 4 X:.8e+8 Y:.699.5.5 3 3.5 4 4.5 5 Freq 8 Fig 4: Teoretica ode desit for te NA sieded roo. Stirrig Ratio I order to evauate te efficiec of te stirrer iside a RC te stirrig ratio (SR is defied; aso SR ca be defied as te paraeter used to uderstad o uc te fied is odified b a rotatig stirrer. It is ecessar to evauate ad to store a vaues of te received poer of a atea iside te cavit for differet positios of te stirrer device. Te trasitted poer is ot odified for a rotatioa stirrer ages. We a te easures are copeted b ookig at te arcived data o te aiu ad te iiu vaues of received poer are used to copute te SR: Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 4 of 3
SR a PR ( i PR ( ϕ j ϕ... ϕ ϕ j ϕ... ϕ I tis etod te stirrer is ot rotatig cotiuous but it rotates it discrete stirrer steps (tis etod is caed ode-tued. Te case of a cotiuous stirrer rotatio is caed ode-stirrig ad for tis case a sort of tie averagig is required. Aoter possibe defiitio for te stirrig ratio is te et oe: SR a ϕ j ϕ... ϕ i ϕ j ϕ... ϕ ( ( I tis case te SR is evauates b te ratio betee te aiu ad te iiu vaue of te eectric fied stregt at a fied poit over oe revoutio of te stirrer. Usua te stirrer ratio is idicated i db te oer acceptabe iit for te SR beig db. If te SR is ig it idicates tat te stirrer is rea efficiet. Quait Factor Te quait factor Q is used to give a idea of te abiit of a RC to store eerg. If te vaue of Q is ig it idicates tat te caber is efficiet ad it as o osses. I order to fid te caber Q usua a TX ad a RX atea are positioed iside te caber ad te vaues of trasitted poer P TX ad of received poer P RX are easured. I tis a it is possibe to copute te epressio beo for differet ages of te stirrer: 6 V λ Q 3 P P RX TX Tere are differet coditios tat are abe to odif te quait factor of a RC for eape: Loadig itroduced b te cabes probes ad tripods of te ateas tat are iside te caber Loadig due to te presece of te UT Presece of apertures doors ad a oter particuar costructios Itrisic caber properties ike te coductivit of te a ateria Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 5 of 3
It is aso possibe to fid a forua for Q startig fro teoretica cosideratios: te quait factor is based o te tie averaged stored eerg W S ad o W d ic is te eerg dissipated i oe period iti a resoator. W S is defied as: Te epressio of Q is: W s D dv ε V V dv Q W W s d ωw W d s B isertig te forua of W s i Q ad takig ito accout tat te dissipated poer is equa to te et iput poer P i : Q ωε P i To evauate Q i a practica case it is ecessar to ko a te osses of te caber as te a osses aperture due to doors ad cotacts betee te paes of te a osses due to te ateas ad to te UT. Te previous forua icudes a tese osses. Aoter possibe easier forua tat takes ito accout o for oic osses of te as ca be derived: V dv 3V Q µ rδ s A 3λ + + + 6 δ s µ fk ere V idicates te caber voue ie A is te ier RC surface. I te IC 6-4- stadard for tpica vaues of ad for aveegts oer ta oe eter a approiatio for Q is give b: 3V Q µ r δ s A Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 6 of 3
Te to ast epressios are ofte used but te quait factor obtaied b te direct easureets i practica cases is saer b a factor 5 ad tis is due to te presece of oss ecaiss ad of te Joue eatig of te as. B eas of te forua tat approiates te quait factor takig ito accout te oic osses it is possibe to sketc te grap of te quait factor i te case of te NA sieded roo (Fig. 5. Te red curve sos o te Q factor is odified b avig a sa reductio of agetic pereabiit ie te gree oe represets te Q factor for a iger vaue of agetic pereabiit. 8 Q 6 4 3 4 5 6 7 8 9 Freq 8 Fig 5:Teoretica Quait factor for te NA sieded roo. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 7 of 3
3. Fied Statistics i a Reverberatio Caber Tere are to tpes of approac tat are used to describe teoretica a idea M eviroet iti a RC. Oe assues tat a RC ca be studied as a M cavit caracteried b a quasistatioar fieds structures correspodig to te cavit resoat odes; ufortuate if te sape of te cavit is too cope te structures of te resoat fieds sa be ver difficut to sove aatica. Te secod approac is to cosider te pae ave itegra represetatio for fieds based o te aguar pae ave spectru. B usig tis cocept it is possibe to represet te aguar spectru of a iited portio of te orkig voue i a probabiistic a based o sipe correatio assuptio. It is possibe to deterie te probabiistic ode for M fieds if te cosidered voue is far fro as ad stirrers. It is aso iportat to sa tat tis ode is iited to ig ecitatio frequec because o i tis case te rado properties of te pae ave spectru are assured. I a case bot te approaces ead te sae fied probabiistic descriptio. rgodicit Te rgodicit propert ca be described b cosiderig a RC ecited b te M fied i tree differet cases. Te first case is e te stirrer is ot ovig ad o a sige frequec M fied is ecited; accordig to tis assuptio it is possibe to cosider a set S of vaues tat represet te M quatit easured i differet ocatios iside te orkig voue. I te secod case te stirrer is sti fied ad o oe ocatio is used to copute te easureet; tis tie a set F of vaues is defied to cotai te M quatit easured at differet ecitatio frequecies. I te tird case o a sige frequec M fied is ecited iside te RC but te stirrer is ot fied. A set R is used to represet te M quatit easured i a fied ocatio but for differet positios of te stirrer. No cosiderig te propert of rgodicit it is possibe to ote tat te sets S F ad R ave te sae statistica properties e easureet sapes are idepedet. I cocusio e a Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 8 of 3
spatia sift a frequec sift or a stirrer rotatio are cosidered te M quatities are caracteried b te sae probabiistic distributio. Probabiistic Distributios Te startig poit of te probabiistic ode is tat te rea ad iagiar parts of te tree rectaguar copoet of te eectric ad agetic fied are idepedet fro eac oter ad te ave a Nora (Gaussia distributio. It is possibe to coect i te fooig Tabe I te distributios for eectric ad agetic fieds apitude ad square apitude. Tabe I M quatit X Distributio Probabiit desit fuctio f( Mea vaue Variace Re I { } { } Nora (Gaussia ep σ σ σ χ (Raeig* ep σ σ σ σ χ (poetia σ ep σ σ 4 4σ Magetic fied quatities ave te sae distributio of te eectric oes; te poer ad te curret received b a atea ave te sae distributios of te square apitude ad of te apitude respective as so i Tabe I (secod ad tird ro. It is iportat to ote tat statistica odes of Tabe I are obtaied for sapes costituted of idepedet easureets. Correatio Fuctio Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 9 of 3
For sige frequec cotiuous ave fieds tat are ecaica stirred te above probabiistic descriptio caracteries te fieds i a give spatia poit durig te stirrer rotatio. I order to give a copete probabiistic descriptio it is aso iportat to ko soetig about spatia correatio of te M fieds. Te spatia correatio fuctios for fieds ad eerg desit are foud startig fro te itegra pae ave represetatio. Statistica Ucertait ad stiator Accurac It is iportat to ko te statistica beavior of te M fieds iside te caber to be abe to evauate te ucertait of a test doe i a RC. Ofte i te RC easureets it is iterestig to evauate te iterva i ic a certai percetage p of te vaues fro a stadard Gaussia distributio are cotaied. Tis operatio ca be doe b sovig: p F ( t µ σ ( µ σ σ Te so caed aiu ikeiood estiator (ML ca be used as a estiator of te M-fied. I fact te ML estiator is aas asptotica ubiased ad its accurac ca be easi evauated. Asptotica ubiased eas tat its ea is te true vaue for arge aouts of data. I order to evauate te aout of data required to get a certai estiator accurac te fooig forua appies: e dt + ~ d k bn k bn ad i db otatio: ~ d og + k bn k bn Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
ere b is te uber of diesios of te fied data to be estiated k is used to deterie te cofidece eve (e. k±.96σ for p.95 ad fia N is te uber of statistica idepedet stirrer positios tat are required. If b it eas tat te fied probe is sesitive to a sige copoet of te fied. Te forua used to evauate N is: k + N ~ d b Te oest acievabe ucertait ± d ~ is depedet o N so it is essetia to ake sure tat a RC i cobiatio it a stirrer are abe to provide at east N idepedet distributios. It is ecessar to evauate te correatio coefficiet for te cose step age of te stirrer assuig tat ucorreated stirrer positio ied idepedet sapes. It is rea iportat to ceck if a stirrer is ot capabe to provide a required uber N of ucorreated fied distributio over a copete rotatio; at o frequec it is ore difficut to satisf te requireets. ~ d Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
4. Operatig Procedure for te NA Reverberatio Caber Caibratio Te ai of a caibratio is to ceck if te geerated fieds defied uder certai iits ave te sae agitude for a poariatios ad for a give uber of tuer steps. Oe procedure is te so caed ept caber caibratio ad it cosists i te copariso betee te peak fieds easured b te -probes it respect to te ea received poer of te referece atea. I order to perfor te caibratio it is ecessar to use isotropic probes. Te ea data of te atea is evauated for eigt differet paces iside te caber i order to icrease te accurac (Fig. 6. Fig 6: Te test voue ad caibratio ocatios i a RC. Te caibratio procedure soud be perfored o oce i te ife of te caber or o i te cases of reevat odificatios. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page of 3
Measureet Sste Te easureet sste as to be abe to geerate te proper poer iside te caber ad acquire iforatio o te eectric fied te poer beig trasitted ad refected b te trasittig atea te poer received b te receivig atea ad te stirrer aguar positio. Tpica te fooig ist of test equipet is recoeded for te easureet sste: Screeed roo NA RC itera diesios: 3.4 3.6 5.4 (eigt. Voue: 57.66 3. Oe ai access door of..44 ; ad a secodar oe of.9.4. TX/RX ateas Te ateas ust be efficiet i te frequec rage of utiiatio of caber. Tpica og-periodic or ad/or sort dipoes ateas are used. Te ateas ust be outed to reduce te ifuece o te fied distributio iti te cavit: - A cabes feedig te ateas ust be o-oss oes ad routed as cose as possibe to te cavit as. - Te tripods odig te ateas ust be etire ade i o-epsio pastic or ood tus avoidig uated oadig ad distortio of te M fied. Siga geerator Must cover te frequec bad of iterest. Poer Apifier(s Must cover te frequec bad of iterest ad ave a o aroic distortio. Spectru aaer Necessar to easure ad record te received poer. Directioa Coupers Te (bi-directioa coupers are used to easure te forard ad refected poer at te trasittig atea terias. Te ust cover te operatig frequec rage. Poer Meter ad Probe Heads Te poer eter is used to easure te forard ad refected poer provided b te bidirectioa coupers. Te to caes ust be copete idepedet fro eac oter ad be abe to easure poer siutaeous tus te et poer deivered to te RC ca be cacuated fro tese easureets. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 3 of 3
Fied Probe Te fied probe is utiied to easure te tree copoets of te eectric fied ad is epfu o durig caibratio of te RC. For actua MC easureets a fied probe is ot ecessari eeded but sti recoeded []. ectroagetic Absorbers A sufficiet aout of absorbers (efficiet at te desired frequec bad is eeded i order to perfor te oadig verificatio of te caber ic is a crucia vaidatio paraeter. Atteuator cabes ad adaptors Sice ig refectios are ofte preset i reverberatio cabers atteuators are eeded to protect sesitive equipet ike i.e. te apifier(s ad te spectru aaer. A coaia cabes ust be o-oss. Data acquisitio ad iterfacig A active devices of te RC equipet setup (siga geerator poer eter fied probe spectru aaer ad stirrer drive cotroer igt be abe to be reote cotroed fro a coputer. Data acquisitio progras ust aso be icuded. Te progras soud be especia adapted to te requireets of easureets used for perforace assesset ad caibratio: te ust ao to defie a cubic test grid for te fied probe sste b settig 8 differet spatia positios iti te RC te frequec rage of iterest (tat ca be spit ito differet frequec bads i case a cage of te apifiers ad/or te ateas ust be perfored te desired rotatioa stirrer steps de tie for te stirrer ad a te settigs of te spectru aaer. Te acquired easureet data ust saved ito a coveiet forat. To faciitate data adig it is advised tat resuts are post processed after easureets. If te caibratio ad caracteriatio of te NA RC is iteded to be perfored usig odetuig teciques (uder static coditios te a tie te stirrer is oved te easureet as to be paused to ao a ecaica osciatios to die out. Te geera easureet procedure is represeted as a fo diagra i Fig. 7. Stirrer fficiec I order to correct app te iteratioa stadard IC 6-4- [] te assesset of te stirrer efficiec soud be ko. Tis is perfored b eas of te autocorreatio coefficiet. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 4 of 3
Stirrer perforace data ust be obtaied b easurig te received poer at severa (tpica 45 eve spaced itervas over oe stirrer rotatio ad for differet frequec poits (tpica 5 ogaritica spaced i te frequec bad of iterest (tpica fro up to ties te first resoace. Te ai of tis procedure is tat b koig te first order autocorreatio for eac frequec te uber of stirrer itervas required b te stadard i te differet frequec bads ca be esured to be correct. I oter ords caibratio accordig to te iteratioa stadard IC 6-4- requires a iiu of idepedet fied sapes for ever frequec bad (e.g. 5 stirrer steps fro te start frequec to tree ties te start frequec. It soud be oted tat te start frequec is ot te LUF it is just a approiate startig frequec poit give i []. To assure tat te stirrer is abe to provide suc a uber of idepedet fied sapes te first order autocorreatio as to be easured. Usig te sae easured data soe data ratios as te stirrig ratio ad te poer deviatio to te ea ca be furter coputed. Te serve as iportat epirica-based perforace idicators. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 5 of 3
Fig 7: Measureet fo diagra. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 6 of 3
Revie of IC 6-4- Te oest useabe frequec fro ic a RC ca be used is ai deteried b te sie ad sape of te caber ad te effectiveess of te stirrer [ 3 4]. A procedure for caibratig a RC (tus koig its LUF is described i []. Caibratio. Te procedure of deteriig te LUF ad caracteriig iportat factors (suc as e.g. te aiu toerabe oadig of te caber te isertio oss etc. is ko as te caibratio process []. Te caibratio procedure soud be perfored o oce i te ife of te caber or o i te cases of reevat odificatios. For te caibratio te fieds ust be recorded at eigt positios iti te orkig voue (tese positios ust be te corer poits of te orkig voue. Te orkig voue ust keep a iiu distace of λ LUF /4 aa fro RC as stirrers ateas ad a oter eectroagetica reevat objects. Fied uiforit ust be tested at 45 ogaritica spaced frequecies over te first decade after o frequecies per decade are required. Te uber of stirrer positios goes fro a tota of 5 for te oer frequecies to a tota of for te iger frequecies. Te step-b-step procedure is cear detaied i Ae B sectio. i te IC 6-4- stadard []. Te aiu of eac sige-ais eectric fied copoet occurrig durig oe fu rotatio of te stirrer is deteried ad te oraied to te ea et iput poer P i ere ξ or tota j is te stirrer positio ad i is te spatia positio i 8. It soud be poited out tat tota refers to a data togeter ot to te tota vectoria fied stregt []. I te secod editio of te IC stadard ic is b te oet of ritig tis operatig procedure uder revie te ord vaidatio i repace tat of caibratio for beig ore suitabe ad appropriate. Neverteess i te fooig e i adopt te terioog as e as te oecature ad sbo of te first editio of []. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 7 of 3
Subsequet te stadard deviatio (deviatio betee te eigt positios i space is cacuated for te fied copoets ad aso for a te data togeter (i.e. a tota of 4 fied vaues cosistig of eigt positios for eac of ad. I order to copute te idividua ( ad copoets ad te cobied (tota stadard deviatios usig te tree aritetic per-ais average vaues ad te cobied aritetic average are cacuated. Fia te idividua per-ais stadard deviatios as e as te cobied stadard deviatio ca be derived. For coveiece te stadard deviatio is epressed i ters of db reative to te ea: Te IC 6-4- stadard requires aso te deteriatio of soe oter paraeters suc as te atea caibratio factor te isertio oss etc. Te are cacuated usig te poer received b te referece atea. Tese factors caracterie te caber for furter easureets ad ca be easi cacuated fooig te equatios i [] ae B. Te caibratio detaied i tis sectio eeds o to be perfored after te costructio of te caber ad after ajor odificatios i.e. cagig te stirrer is cosidered to be a Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 8 of 3
ajor odificatio if te cage resuts i cages i stirrer efficiec or cagig te ateas. Hoever it is a good practice to perfor a caibratio of te caber ear. Fied Uiforit For acceptabe ode-stirrig te four stadard deviatios i db reative to te ea potted agaist frequec soud a beo a toerace eve defied i [] ic is: Te IC stadard aso states tat tree frequecies per octave a eceed te iits above b o ore ta db. Caveats for Caibratio Appig te requireets ad usig te procedures itroduced i sectio 5 a statistica descriptio of RCs ca be perfored b eas of a fied uiforit easureet. Hoever soe precautios eed to be take e perforig suc easureets ad as bee reported i [5]. Specifica te refer to te uber of frequec poits ad te aroic distortio produced b te apifiers. ve toug a te requireets are et ueducated appicatio of te stadard a give resuts tat are ot satisfactor. Maiu Caber Loadig Verificatio Oe iportat part of te caibratio process described i [] is te aiu caber oadig verificatio. Reca tat poor reverberatio coditios ca be foud i a good perforig caber if te Q-factor is oered up to a uacceptabe eve. Sice a UT ca potetia oad te caber e iserted for perforig easureets te idea of te aiu caber oadig verificatio process is to easure up to at poit te caber ca be oaded itout degradig too uc its perforace. As a resut of tis oce-i-a-ifetie process RC users are abe to idetif if a particuar UT i oad te caber up to a uacceptabe eve or ot b perforig a quick caibratio before eac easureet []. Tis is doe b te ssteatica isertio of absorbers Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 9 of 3
iside te caber ad te easureet of te fied uiforit. B a tria-ad-error approac oe soud fid te aout of absorber ecessar to degrade te caber up to a uacceptabe eve. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 3 of 3
5. Refereces [] CISPR/A ad IC SC 77B: IC 6-4- - ectroagetic Copatibiit (MC - Part 4- : Testig ad Measureet Teciques - Reverberatio Caber Test Metods Iteratioa ectrotecica Coissio (IC Iteratioa stadard August 3. [] C. Brus: Tree-diesioa siuatio ad eperieta verificatio of a reverberatio caber PD Dissertatio Siss Federa Istitute of Tecoog Zuric Siterad 5. [3] J. Cegg A. C. Marvi J. F. Daso S. J. Porter: Optiiatio of Stirrer Desig i a Reverberatio Caber I Trasactios o ectroagetic Copatibiit vo. 47 o. 4 pp. 84-83 Noveber 5. [4] O. Lude L. Jasso M. Backstro: Measureets of Stirrer fficiec i Mode-stirred Reverberatio Cabers FOA Tecica Report: FOA-R-99-39-6-S Likopig Sede Ma 999. [5] R. Serra M. Boetti F. G. Caavero: Miseadig Issues tat Cae Up e Caibratig te Aeia Aeroautica Reverberatio Caber Iteratioa Coferece o ectroagetics i Advaced Appicatios pp. 93-96 Torio Ita Septeber 9. [6] D. Hi: ectroagetic Fieds i Cavities: Deteriistic ad Statistica Teories Piscataa I Press 9. Tite : Date : August ID uber : CRS-POLITO RL 3/ Page 3 of 3