Application of active elements in artificial electromagnetic structures

doctoral thesis

• Title (croatian): Primjena aktivnih elemenata u umjetnim elektromagnetskim strukturama
• Author: Josip Lončar
• Mentor: Silvio Hrabar (mentor)
• Committee member: Silvio Hrabar (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; (Department of Communication and Space Technologies); Zagreb
• Defense date and country: 2017, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering; Radio Communications
• Universal decimal classification (UDC): 621.3 - Electrical engineering

Abstract

Active metamaterials are a group of artificial electromagnetic structures that employ active electronic circuits. They are characterized by specific properties, such as amplification, non-reciprocal response, dynamic reconfigurability and dynamic tunability, in addition to properties associated with passive metamaterials. Instability is the most challenging problem facing active metamaterials, especially those incorporating negative elements. The thesis includes a detailed stability analysis of lumped and distributed networks commonly used in modeling of active non-Foster metamaterials. The proposed stability analysis is applied to the model of metasurface-based PT-symmetric system. Finally, the analysis, synthesis, fabrication and experimental verification of passive and active reflective polarization converting metasurfaces are presented. The detailed stability analysis reveals that closed-form stability criterion can be derived only for specific types of distributed networks with negative elements. Some distributed networks are proven to be inherently unstable. Dispersion of a negative element is proposed as a solution to the stability problem. Furthermore, a closed-form stability criterion is derived for the model of PT-symmetric system. The analysis shows that every PT-symmetric system is necessarily marginally stable. Finally, stable operation of the active metasurface was ensured and verified. The desired effects of amplification, polarization conversion, polarization selectivity and non-reciprocal response were successfully demonstrated.

Abstract (croatian)

Aktivni metamaterijali su grupa umjetnih elektromagnetskih struktura koja rabi aktivna elektronička sklopovlja. Uz svojstva pasivnih metamaterijala, karakteriziraju ih dodatna specifična svojstva, kao što su pojačanje, nerecipročni odziv, dinamička rekonfigurabilnosti i dinamičko ugađanje. Osnovni problem aktivnih metamaterijala, naročito onih s negativnim elementima, je stabilnost. Disertacija predstavlja detaljnu analizu stabilnosti koncentriranih i distribuiranih mreža uobičajeno rabljenih u modeliranju aktivnih nefosterovskih metamaterijala. Predložena analiza stabilnosti primijenjena je na model PT-simetričnog sustava temeljenog na metapovršinama. Naposljetku, predstavljena je analiza, sinteza, izrada i eksperimentalna verifikacija pasivne i aktivne reflektirajuće metapovršine za konverziju polarizacije. Detaljna analiza stabilnosti otkriva da je kriterij stabilnosti moguće izvesti samo za specifične tipove distribuiranih mreža s negativnim elementima. Pokazano je da su neke distribuirane mreže inherentno nestabilne. Disperzija negativnog elementa je predložena kao rješenje problema nestabilnosti. Nadalje, izveden je kriterij stabilnosti za model PT-simetričnog sustava. Analiza pokazuje da je svaki PT-simetrični sustav nužno margninalno stabilan. Naposljetku, osiguran je i potvrđen stabilan rad aktivne metapovršine. Željeni efekti pojačanja, konverzije polarizacije, selektivnosti polarizacije i nerecipročnog odziva su uspješno demonstrirani.

• Keywords: negative elements; stability analysis; PT symmetry; metasurfaces
• Keywords (croatian): negativni elementi; analiza stabilnosti; PT simetrija; metapovršine
• Language: english
• URN:NBN: urn:nbn:hr:168:758673
• Study programme: Title: Electrical Engineering and Computing; Study programme type: university; Study level: postgraduate; Academic / professional title: Doktor znanosti elektrotehnike i računarstva (Doktor znanosti elektrotehnike i računarstva)
• Type of resource: Text
• Extent: 172 str. ; 30 cm.
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2019-04-05 14:28:13