Silicon carbide diodes for neutron detection

In the last two decades we have assisted to a rush towards finding a He3-replacing technology capable of detecting neutrons emitted from fissile isotopes. The demand stems from applications like nuclear war-head screening or preventing illicit traffic of radiological materials. Semiconductor detectors stand among the stronger contenders, particularly those based on materials possessing a wide band gap like silicon carbide. We review the workings of SiC-based neutron detectors, along with several issues related to material properties, device fabrication and testing. The paper summarizes the experimental and theoretical work carried out within the E-SiCure project, co-funded by the NATO SPS Programme. Among the achievements, we have the development of successful Schottky barrier based detectors and the identification of the main carrier life-time-limiting defects in the SiC active areas, either already present in pristine devices or introduced upon exposure to radiation fields. The physical processes involved in neutron detection are described. Material properties as well as issues related to epitaxial growth and device fabrication are addressed. The presence of defects in as-grown material, as well as those introduced by ionizing radiation are reported. We finally describe several experiments carried out at the Jozef Stefan Institute TRIGA Mark II reactor (Ljubljana, Slovenia), where a set of SiC-based neutron detectors were tested, some of which being equipped with a thermal neutron converter layer. We show that despite the existence of large room for improvement, Schottky barrier diodes based on state-of-the-art 4H-SiC are closing the gap regarding the sensitivity offered by gas-based and that of semiconductor detectors

Development of a new neutron probe for borehole research

Neutronska proba za ispitivanje naftnih bušotina razvijena je na Institutu Ruđer Bošković u okviru HRZZ projekta IP-2018-01-4060 \u27\u27Nove primjene 14 MeV neutrona\u27\u27. U ovom istraživanju ispitane su daljnje mogućnosti redukcije šuma u mjerenju C/O omjera metodom pridružene alfa čestice. Mješavina kvarcnog pijeska i grafitnog praha korištena je kao materijal od interesa , dok su plastične bočice ispunjene dizel gorivom korištene kao šum (smetnja) i predstavljaju tekućinu unutar naftne bušotine (npr. nafta). Podjela alfa detektora na četiri jednaka segmenta, omogućila je podjelu volumena oko osi neutronske probe na četiri kvadranta. Materijal od interesa i dizel smješteni su u različite kvadrante i pokazano je da su C/O vrijednosti u slučajevima kad je smetnja prisutna unutar statističke greške u odnosu na slučaj kada smetnje nema.The neutron probe for testing oil wells was developed at the Ruđer Bošković Institute within the HRZZ project IP-2018-01-4060 "New applications of 14 MeV neutrons". In this study, further possibilities of noise reduction in C/O ratio measurement by the associated alpha particle method were investigated. A mixture of quartz sand and graphite powder was used as the material of interest, while plastic bottles filled with diesel fuel were used as noise (interference) and represent the liquid inside the oil well (e.g. oil). Dividing the alpha detector into four equal segments, allowed portioning the volume around the neutron probe axis into four quadrants. The material of interest and diesel were located in different quadrants and it is shown that the C/O values in cases where interference is present are within statistical errors compared to the case where there is no interference

Radiofrequency replica of plasmonic nanosphere

U ovom radu analizirana je radiofrekvencijska struktura (RF replika) koja u potpunosti oponaša elektromagnetska svojstva plazmoničke nano-kugle u optičkom području frekvencija. Analizirane strukture su Stuartov i Bestov sferni rezonator koje su se do sada upotrebljavale samo u antenskoj tehnologiji. Elektromagnetska svojstva ovih RF replika istražena su teorijski, numeričkom punovalnom simulacijom pomoću metode konačnih razlika u vremenskoj domeni i mjerenjima na prototipovima u frekvencijskom području 100-500 MHz. Simulacijom i mjerenjima potvrđena je inverzija smjera vektora električnog polja unutar RF replika u usporedbi s vektorom električnog polja u okolnom prostoru, što je osnovno svojstvo plazmoničke kugle. Pokazalo se da polje ima uniformniju razdiobu unutar Bestovog rezonatora, što ga čini pogodnijim za izradu RF replike od Stuartovog rezonatora. U cilju testiranja upotrebljivosti ovako izrađenih RF replika u skaliranim plazmoničkim eksperimentima, izrađen je model plazmoničkog valovoda sastavljen od četiri Bestova rezonatora. Valovod je pobuđen pomoću kratkog dipola u transverzalnom i longitudinalnom modu, a mjerenjem razdiobe faze incidentnog vala utvrđeno je postojanje povratnog i direktnog vala što se u potpunosti slaže s teorijskim predviđanjima. Time je pokazano da se razvijene RF replike plazmoničkih kugli zaista mogu koristiti za istraživanje osnovnih EM svojstava budućih plazmoničkih struktura za vođenje vala i plazmoničkih metamaterijala bez potrebe za skupom nanotehnologijom.electromagnetic properties of a plasmonic nanosphere at optical frequencies is analysed. Two structures, based on well known small spherical antennas (Stuart and Best’ spherical resonators), are considered as the possible candidates for the RF replicas. The electromagnetic properties of these RF replicas are investigated analytically, numerically, and experimentally in 100-500 MHz RF frequency range. The basic property of a plasmonic sphere is the inversion of the electric field vector direction inside the sphere compared to the electric field vector direction outside the sphere. This phenomenon, is confirmed by FDTD simulations and the measurements on experimental RF replicas. It was found that the electric field inside Best resonator is more uniform than the electric field inside Stuart resonator. Thus, it appears that Best resonator is more suitable for the construction af an RF replica of plasmonic nanosphere. In order to test the possible application of developed RF replicas in scaled experiments, the prototype of RF plasmonic wavegude consisted of four Best resonators was constructed. The waveguide was excited in both transversal and longitudinal modes with the help of a short dipole. The phase of the incident electric field was scanned along the waveguide and the results revealed the existence of the backward and forward waves, which is consistent with the theorethical analysis. Therefore, it was shown that developed RF replicas of plasmonic nanospheres can indeed be used for the investigation of the basic electromagnetic properties of future plasmonic structures and metamaterials. This approach elegantly avoids the use of advanced and very expensive nanotechnology

Radiofrequency replica of plasmonic nanosphere

U ovom radu analizirana je radiofrekvencijska struktura (RF replika) koja u potpunosti oponaša elektromagnetska svojstva plazmoničke nano-kugle u optičkom području frekvencija. Analizirane strukture su Stuartov i Bestov sferni rezonator koje su se do sada upotrebljavale samo u antenskoj tehnologiji. Elektromagnetska svojstva ovih RF replika istražena su teorijski, numeričkom punovalnom simulacijom pomoću metode konačnih razlika u vremenskoj domeni i mjerenjima na prototipovima u frekvencijskom području 100-500 MHz. Simulacijom i mjerenjima potvrđena je inverzija smjera vektora električnog polja unutar RF replika u usporedbi s vektorom električnog polja u okolnom prostoru, što je osnovno svojstvo plazmoničke kugle. Pokazalo se da polje ima uniformniju razdiobu unutar Bestovog rezonatora, što ga čini pogodnijim za izradu RF replike od Stuartovog rezonatora. U cilju testiranja upotrebljivosti ovako izrađenih RF replika u skaliranim plazmoničkim eksperimentima, izrađen je model plazmoničkog valovoda sastavljen od četiri Bestova rezonatora. Valovod je pobuđen pomoću kratkog dipola u transverzalnom i longitudinalnom modu, a mjerenjem razdiobe faze incidentnog vala utvrđeno je postojanje povratnog i direktnog vala što se u potpunosti slaže s teorijskim predviđanjima. Time je pokazano da se razvijene RF replike plazmoničkih kugli zaista mogu koristiti za istraživanje osnovnih EM svojstava budućih plazmoničkih struktura za vođenje vala i plazmoničkih metamaterijala bez potrebe za skupom nanotehnologijom.electromagnetic properties of a plasmonic nanosphere at optical frequencies is analysed. Two structures, based on well known small spherical antennas (Stuart and Best’ spherical resonators), are considered as the possible candidates for the RF replicas. The electromagnetic properties of these RF replicas are investigated analytically, numerically, and experimentally in 100-500 MHz RF frequency range. The basic property of a plasmonic sphere is the inversion of the electric field vector direction inside the sphere compared to the electric field vector direction outside the sphere. This phenomenon, is confirmed by FDTD simulations and the measurements on experimental RF replicas. It was found that the electric field inside Best resonator is more uniform than the electric field inside Stuart resonator. Thus, it appears that Best resonator is more suitable for the construction af an RF replica of plasmonic nanosphere. In order to test the possible application of developed RF replicas in scaled experiments, the prototype of RF plasmonic wavegude consisted of four Best resonators was constructed. The waveguide was excited in both transversal and longitudinal modes with the help of a short dipole. The phase of the incident electric field was scanned along the waveguide and the results revealed the existence of the backward and forward waves, which is consistent with the theorethical analysis. Therefore, it was shown that developed RF replicas of plasmonic nanospheres can indeed be used for the investigation of the basic electromagnetic properties of future plasmonic structures and metamaterials. This approach elegantly avoids the use of advanced and very expensive nanotechnology

Radiofrequency replica of plasmonic nanosphere

U ovom radu analizirana je radiofrekvencijska struktura (RF replika) koja u potpunosti oponaša elektromagnetska svojstva plazmoničke nano-kugle u optičkom području frekvencija. Analizirane strukture su Stuartov i Bestov sferni rezonator koje su se do sada upotrebljavale samo u antenskoj tehnologiji. Elektromagnetska svojstva ovih RF replika istražena su teorijski, numeričkom punovalnom simulacijom pomoću metode konačnih razlika u vremenskoj domeni i mjerenjima na prototipovima u frekvencijskom području 100-500 MHz. Simulacijom i mjerenjima potvrđena je inverzija smjera vektora električnog polja unutar RF replika u usporedbi s vektorom električnog polja u okolnom prostoru, što je osnovno svojstvo plazmoničke kugle. Pokazalo se da polje ima uniformniju razdiobu unutar Bestovog rezonatora, što ga čini pogodnijim za izradu RF replike od Stuartovog rezonatora. U cilju testiranja upotrebljivosti ovako izrađenih RF replika u skaliranim plazmoničkim eksperimentima, izrađen je model plazmoničkog valovoda sastavljen od četiri Bestova rezonatora. Valovod je pobuđen pomoću kratkog dipola u transverzalnom i longitudinalnom modu, a mjerenjem razdiobe faze incidentnog vala utvrđeno je postojanje povratnog i direktnog vala što se u potpunosti slaže s teorijskim predviđanjima. Time je pokazano da se razvijene RF replike plazmoničkih kugli zaista mogu koristiti za istraživanje osnovnih EM svojstava budućih plazmoničkih struktura za vođenje vala i plazmoničkih metamaterijala bez potrebe za skupom nanotehnologijom.electromagnetic properties of a plasmonic nanosphere at optical frequencies is analysed. Two structures, based on well known small spherical antennas (Stuart and Best’ spherical resonators), are considered as the possible candidates for the RF replicas. The electromagnetic properties of these RF replicas are investigated analytically, numerically, and experimentally in 100-500 MHz RF frequency range. The basic property of a plasmonic sphere is the inversion of the electric field vector direction inside the sphere compared to the electric field vector direction outside the sphere. This phenomenon, is confirmed by FDTD simulations and the measurements on experimental RF replicas. It was found that the electric field inside Best resonator is more uniform than the electric field inside Stuart resonator. Thus, it appears that Best resonator is more suitable for the construction af an RF replica of plasmonic nanosphere. In order to test the possible application of developed RF replicas in scaled experiments, the prototype of RF plasmonic wavegude consisted of four Best resonators was constructed. The waveguide was excited in both transversal and longitudinal modes with the help of a short dipole. The phase of the incident electric field was scanned along the waveguide and the results revealed the existence of the backward and forward waves, which is consistent with the theorethical analysis. Therefore, it was shown that developed RF replicas of plasmonic nanospheres can indeed be used for the investigation of the basic electromagnetic properties of future plasmonic structures and metamaterials. This approach elegantly avoids the use of advanced and very expensive nanotechnology

Graphene characterisation for application in electromagnetic metasurfaces

Predmet istraživanja ove dizertacije su elektromagnetska svojstva grafena. U tu svrhu, korišten je numerički model električne vodljivosti grafena temeljen na Kubovoj jednadžbi koja uzima u obzir frekvenciju signala, kemijski potencijal, gubitke zbog raspršenja naboja, i temperaturu. Pokazano je da je vodljivost grafena moguće utvrditi analitički pomoću Kubove jednadžbe samo ako je frekvencija signala znatno niža od frekvencije raspršenja naboja. Usporedba analitički utvrđenog riješenja i numeričkih vrijednosti dobivenih rješavanjem Kubo jednadžbe pokazala je dobro slaganje. Analiza je pokazala da vodljivost grafena u radiofrekvencijskom području ima izraženu realnu komponentu vodljivosti dok je imaginarna komponenta vodljivosti manja od realne komponente za četiri reda veličine. Zbog ovoga svojstva se impedancija grafena u radiofrekvencijskom području može aproksimirati realnim otporom. Nadalje je pokazano da je u optičkom području frekvencija realna komponenta električne vodljivosti grafena veća od imaginarne komponente za jedan red veličine. Stoga se i u optičkom području frekvencija impedancija grafena može aproksimirati realnim otporom. U THz području impedancija grafena ima kompleksnu vrijednost u skladu s Lorentz-Drudeovim disperzijskim modelom. Najzanimljivije svojstvo grafena, s aspekta primjene, je efekt polja: U nekim slučajevima vanjsko električno polje može promijeniti realni i imaginarni dio kompleksne impedancije grafena. Opisano svojstvo koristi se za postizanje negativne permitivnosti u upravljivim metamaterijalima i metapovršinama. Eksperimentalno istraživanje utjecaja vanjskog električnog polja na električnu vodljivost grafena pokazalo je kako se vodljivost materijala može povećati nekoliko puta. U okviru ovog rada razvijen je reaktor za sintezu uzoraka jednoslojnog i višeslojnog grafena. Postupak sinteze je kemijska depozicija iz parne faze. Reaktor je izrađen upotrebom lako dobavljivih komponenti niske cijene što ga čini dostupnim većini istraživačkih grupa. Sintezirani grafen je visoke kvalitete što je potvrđeno karakterizacijom uz pomoć Ramanove spektroskopije i elektronske mikroskopije. Dizajnirana je i praktično realizirana upravljiva grafenska metapovršina koja je u osnovi mikrovalni apsorber baziran na Salisburyjevom zastoru. Punovalne numeričke simulacije i mjerenja u području frekvencija od 10 GHz pokazuju efikasnu apsorpciju mikrovalne energije iako njegova debljina iznosi samo jedan atom. Posebnost razvijenog apsorbera je mogućnost jednostavnog podešavanja njegovih parametara promjenom upravljačkog visokonaponskog signala.Focus of this thesis is the analysis of electromagnetic properties of graphene for use in electromagnetic metasurfaces at room temperature. Analysis of intrinsic graphene electric conductivity model based on Kubo formula in wide frequency range shows that real and imaginary part of complex electric conductivity change significantly with signal frequency and bias voltage. Below the THz, a real part of conductivity dominates over imaginary part by more than two orders of magnitude. Therefore, the lumped element model of the graphene can be approximated as a simple resistor with typical value of 1 k. In the visible part of electromagnetic spectrum, a real part of graphene conductivity is more than an order of magnitude higher than imaginary part. Thus, a lumped element model can again be simplified to a simple resistor of 10 k. In the infrared region, however, graphene has a complex impedance in accordance with Lorentz-Drude model and, therefore, complete RLC lumped model has to be used. In addition, an external bias voltage can be applied to graphene to vary both the real and imaginary part of its complex impedance. This phenomenon is called "field effect" and it is used to realize a negative permittivity in reconfigurable metamaterials and metasurfaces. The low-cost CVD reactor for graphene synthesis was designed and manufactured. Synthesized graphene samples were characterised by Raman spectroscopy and scanning electron microscopy. Measurement results revealed high quality of single-layer and multi-layer samples adequate for use in graphene-based metasurface devices. A simple contactless metod for measuring a surface resistance of single-layer and multi-layer graphene samples was designed and tested. This method is preferable over existing contact methods due to lack of variable contact resistance. In this method a graphene sample is supported by thin dielectric substrate and such composite material is placed within a rectangular waveguide. The scattering parameters were measured with calibrated network analyzer and the surface resistance was determinated using simple mathematical postprocessing. This method is similar to other published methods for measuring surface conductivity of thin conductive films although the mathematical postprocessing has a different form. Measurement results of various graphene samples were found to be in a good agreement with numerical simulation based on Kubo eqauation. The metasurface based on Salisbury screen was designed, constructed and measured. A conductive film needed for absorption was composed of single graphene layer whereas the section of WR-90 wavegude was used as a quater-wave transformer. Measurements and numerical simulations showed that the surface resistance of graphene should be optimised for the efficient absorption. If optimised, graphene-based absorber has a high-efficiency (>99% absorption) although the thickness of a conductive layer is only one-atom. Reconfigurable microwave absorber based on a single-layer graphene was designed, constructed and measured. It has a form of parallel-plate capacitor with the dimensions of WR-90 flange. A single-layer graphene of high-quality was used as first electrode (an active layer), a poor-quality graphene was used as a second electrode (bias layer) and the PET (polyethylene terephtalate) was used as a dielectric. The controll of absorption is performed by modifying active layer impedance with polarity and magnitude of applied high voltage at bias layer. To produce graphene-on-dielectric-based devices, a novel method for graphene transfer is developed using laminating pouches. This method, to the best of authors knowledge, has not been published in the literature so far. A transfer process using laminating pouches is faster, simpler and of lower cost than currently popular methods found in literature

Graphene characterisation for application in electromagnetic metasurfaces

Predmet istraživanja ove dizertacije su elektromagnetska svojstva grafena. U tu svrhu, korišten je numerički model električne vodljivosti grafena temeljen na Kubovoj jednadžbi koja uzima u obzir frekvenciju signala, kemijski potencijal, gubitke zbog raspršenja naboja, i temperaturu. Pokazano je da je vodljivost grafena moguće utvrditi analitički pomoću Kubove jednadžbe samo ako je frekvencija signala znatno niža od frekvencije raspršenja naboja. Usporedba analitički utvrđenog riješenja i numeričkih vrijednosti dobivenih rješavanjem Kubo jednadžbe pokazala je dobro slaganje. Analiza je pokazala da vodljivost grafena u radiofrekvencijskom području ima izraženu realnu komponentu vodljivosti dok je imaginarna komponenta vodljivosti manja od realne komponente za četiri reda veličine. Zbog ovoga svojstva se impedancija grafena u radiofrekvencijskom području može aproksimirati realnim otporom. Nadalje je pokazano da je u optičkom području frekvencija realna komponenta električne vodljivosti grafena veća od imaginarne komponente za jedan red veličine. Stoga se i u optičkom području frekvencija impedancija grafena može aproksimirati realnim otporom. U THz području impedancija grafena ima kompleksnu vrijednost u skladu s Lorentz-Drudeovim disperzijskim modelom. Najzanimljivije svojstvo grafena, s aspekta primjene, je efekt polja: U nekim slučajevima vanjsko električno polje može promijeniti realni i imaginarni dio kompleksne impedancije grafena. Opisano svojstvo koristi se za postizanje negativne permitivnosti u upravljivim metamaterijalima i metapovršinama. Eksperimentalno istraživanje utjecaja vanjskog električnog polja na električnu vodljivost grafena pokazalo je kako se vodljivost materijala može povećati nekoliko puta. U okviru ovog rada razvijen je reaktor za sintezu uzoraka jednoslojnog i višeslojnog grafena. Postupak sinteze je kemijska depozicija iz parne faze. Reaktor je izrađen upotrebom lako dobavljivih komponenti niske cijene što ga čini dostupnim većini istraživačkih grupa. Sintezirani grafen je visoke kvalitete što je potvrđeno karakterizacijom uz pomoć Ramanove spektroskopije i elektronske mikroskopije. Dizajnirana je i praktično realizirana upravljiva grafenska metapovršina koja je u osnovi mikrovalni apsorber baziran na Salisburyjevom zastoru. Punovalne numeričke simulacije i mjerenja u području frekvencija od 10 GHz pokazuju efikasnu apsorpciju mikrovalne energije iako njegova debljina iznosi samo jedan atom. Posebnost razvijenog apsorbera je mogućnost jednostavnog podešavanja njegovih parametara promjenom upravljačkog visokonaponskog signala.Focus of this thesis is the analysis of electromagnetic properties of graphene for use in electromagnetic metasurfaces at room temperature. Analysis of intrinsic graphene electric conductivity model based on Kubo formula in wide frequency range shows that real and imaginary part of complex electric conductivity change significantly with signal frequency and bias voltage. Below the THz, a real part of conductivity dominates over imaginary part by more than two orders of magnitude. Therefore, the lumped element model of the graphene can be approximated as a simple resistor with typical value of 1 k. In the visible part of electromagnetic spectrum, a real part of graphene conductivity is more than an order of magnitude higher than imaginary part. Thus, a lumped element model can again be simplified to a simple resistor of 10 k. In the infrared region, however, graphene has a complex impedance in accordance with Lorentz-Drude model and, therefore, complete RLC lumped model has to be used. In addition, an external bias voltage can be applied to graphene to vary both the real and imaginary part of its complex impedance. This phenomenon is called "field effect" and it is used to realize a negative permittivity in reconfigurable metamaterials and metasurfaces. The low-cost CVD reactor for graphene synthesis was designed and manufactured. Synthesized graphene samples were characterised by Raman spectroscopy and scanning electron microscopy. Measurement results revealed high quality of single-layer and multi-layer samples adequate for use in graphene-based metasurface devices. A simple contactless metod for measuring a surface resistance of single-layer and multi-layer graphene samples was designed and tested. This method is preferable over existing contact methods due to lack of variable contact resistance. In this method a graphene sample is supported by thin dielectric substrate and such composite material is placed within a rectangular waveguide. The scattering parameters were measured with calibrated network analyzer and the surface resistance was determinated using simple mathematical postprocessing. This method is similar to other published methods for measuring surface conductivity of thin conductive films although the mathematical postprocessing has a different form. Measurement results of various graphene samples were found to be in a good agreement with numerical simulation based on Kubo eqauation. The metasurface based on Salisbury screen was designed, constructed and measured. A conductive film needed for absorption was composed of single graphene layer whereas the section of WR-90 wavegude was used as a quater-wave transformer. Measurements and numerical simulations showed that the surface resistance of graphene should be optimised for the efficient absorption. If optimised, graphene-based absorber has a high-efficiency (>99% absorption) although the thickness of a conductive layer is only one-atom. Reconfigurable microwave absorber based on a single-layer graphene was designed, constructed and measured. It has a form of parallel-plate capacitor with the dimensions of WR-90 flange. A single-layer graphene of high-quality was used as first electrode (an active layer), a poor-quality graphene was used as a second electrode (bias layer) and the PET (polyethylene terephtalate) was used as a dielectric. The controll of absorption is performed by modifying active layer impedance with polarity and magnitude of applied high voltage at bias layer. To produce graphene-on-dielectric-based devices, a novel method for graphene transfer is developed using laminating pouches. This method, to the best of authors knowledge, has not been published in the literature so far. A transfer process using laminating pouches is faster, simpler and of lower cost than currently popular methods found in literature

Graphene characterisation for application in electromagnetic metasurfaces

Predmet istraživanja ove dizertacije su elektromagnetska svojstva grafena. U tu svrhu, korišten je numerički model električne vodljivosti grafena temeljen na Kubovoj jednadžbi koja uzima u obzir frekvenciju signala, kemijski potencijal, gubitke zbog raspršenja naboja, i temperaturu. Pokazano je da je vodljivost grafena moguće utvrditi analitički pomoću Kubove jednadžbe samo ako je frekvencija signala znatno niža od frekvencije raspršenja naboja. Usporedba analitički utvrđenog riješenja i numeričkih vrijednosti dobivenih rješavanjem Kubo jednadžbe pokazala je dobro slaganje. Analiza je pokazala da vodljivost grafena u radiofrekvencijskom području ima izraženu realnu komponentu vodljivosti dok je imaginarna komponenta vodljivosti manja od realne komponente za četiri reda veličine. Zbog ovoga svojstva se impedancija grafena u radiofrekvencijskom području može aproksimirati realnim otporom. Nadalje je pokazano da je u optičkom području frekvencija realna komponenta električne vodljivosti grafena veća od imaginarne komponente za jedan red veličine. Stoga se i u optičkom području frekvencija impedancija grafena može aproksimirati realnim otporom. U THz području impedancija grafena ima kompleksnu vrijednost u skladu s Lorentz-Drudeovim disperzijskim modelom. Najzanimljivije svojstvo grafena, s aspekta primjene, je efekt polja: U nekim slučajevima vanjsko električno polje može promijeniti realni i imaginarni dio kompleksne impedancije grafena. Opisano svojstvo koristi se za postizanje negativne permitivnosti u upravljivim metamaterijalima i metapovršinama. Eksperimentalno istraživanje utjecaja vanjskog električnog polja na električnu vodljivost grafena pokazalo je kako se vodljivost materijala može povećati nekoliko puta. U okviru ovog rada razvijen je reaktor za sintezu uzoraka jednoslojnog i višeslojnog grafena. Postupak sinteze je kemijska depozicija iz parne faze. Reaktor je izrađen upotrebom lako dobavljivih komponenti niske cijene što ga čini dostupnim većini istraživačkih grupa. Sintezirani grafen je visoke kvalitete što je potvrđeno karakterizacijom uz pomoć Ramanove spektroskopije i elektronske mikroskopije. Dizajnirana je i praktično realizirana upravljiva grafenska metapovršina koja je u osnovi mikrovalni apsorber baziran na Salisburyjevom zastoru. Punovalne numeričke simulacije i mjerenja u području frekvencija od 10 GHz pokazuju efikasnu apsorpciju mikrovalne energije iako njegova debljina iznosi samo jedan atom. Posebnost razvijenog apsorbera je mogućnost jednostavnog podešavanja njegovih parametara promjenom upravljačkog visokonaponskog signala.Focus of this thesis is the analysis of electromagnetic properties of graphene for use in electromagnetic metasurfaces at room temperature. Analysis of intrinsic graphene electric conductivity model based on Kubo formula in wide frequency range shows that real and imaginary part of complex electric conductivity change significantly with signal frequency and bias voltage. Below the THz, a real part of conductivity dominates over imaginary part by more than two orders of magnitude. Therefore, the lumped element model of the graphene can be approximated as a simple resistor with typical value of 1 k. In the visible part of electromagnetic spectrum, a real part of graphene conductivity is more than an order of magnitude higher than imaginary part. Thus, a lumped element model can again be simplified to a simple resistor of 10 k. In the infrared region, however, graphene has a complex impedance in accordance with Lorentz-Drude model and, therefore, complete RLC lumped model has to be used. In addition, an external bias voltage can be applied to graphene to vary both the real and imaginary part of its complex impedance. This phenomenon is called "field effect" and it is used to realize a negative permittivity in reconfigurable metamaterials and metasurfaces. The low-cost CVD reactor for graphene synthesis was designed and manufactured. Synthesized graphene samples were characterised by Raman spectroscopy and scanning electron microscopy. Measurement results revealed high quality of single-layer and multi-layer samples adequate for use in graphene-based metasurface devices. A simple contactless metod for measuring a surface resistance of single-layer and multi-layer graphene samples was designed and tested. This method is preferable over existing contact methods due to lack of variable contact resistance. In this method a graphene sample is supported by thin dielectric substrate and such composite material is placed within a rectangular waveguide. The scattering parameters were measured with calibrated network analyzer and the surface resistance was determinated using simple mathematical postprocessing. This method is similar to other published methods for measuring surface conductivity of thin conductive films although the mathematical postprocessing has a different form. Measurement results of various graphene samples were found to be in a good agreement with numerical simulation based on Kubo eqauation. The metasurface based on Salisbury screen was designed, constructed and measured. A conductive film needed for absorption was composed of single graphene layer whereas the section of WR-90 wavegude was used as a quater-wave transformer. Measurements and numerical simulations showed that the surface resistance of graphene should be optimised for the efficient absorption. If optimised, graphene-based absorber has a high-efficiency (>99% absorption) although the thickness of a conductive layer is only one-atom. Reconfigurable microwave absorber based on a single-layer graphene was designed, constructed and measured. It has a form of parallel-plate capacitor with the dimensions of WR-90 flange. A single-layer graphene of high-quality was used as first electrode (an active layer), a poor-quality graphene was used as a second electrode (bias layer) and the PET (polyethylene terephtalate) was used as a dielectric. The controll of absorption is performed by modifying active layer impedance with polarity and magnitude of applied high voltage at bias layer. To produce graphene-on-dielectric-based devices, a novel method for graphene transfer is developed using laminating pouches. This method, to the best of authors knowledge, has not been published in the literature so far. A transfer process using laminating pouches is faster, simpler and of lower cost than currently popular methods found in literature