Mid Sweden University

One of the applications for RFID technology is to monitor and position RFID-tagged objects over large volumes. To achieve this, one possible option is to implement RFID reader antennas, which are relatively thin but with significantly large areas, and place them beneath the RFID-tagged objects.  In order to realise RFID reader antennas with large-areas, circuit materials other than conventional rigid PCB materials should be investigated and utilized. Therefore, this thesis addresses how non-conventional PCB materials can be used to achieve large-area RFID reader antenna structures.

   Non-conventional PCB materials are firstly chosen, which comprises patterned Al-polyimide foil, printed conductive Ag inks onto paper, polyethylene foam as antenna substrate. The physical and electrical properties of the materials are measured. These properties are later used in antenna simulations. In addition, assembly methods, e.g. circuit lamination and VIA fabrication, for the chosen materials are developed. 

   Three novel surface mounting techniques are developed and characterized in this thesis. The techniques are developed for mounting SMD components onto tracks made by Al, a screen printed Ag flake ink, and an inkjet printed Ag nanoparticle ink. These techniques are characterized and evaluated by various methods, including contact resistance measurements, bonding strength tests, and microscopy studies. The characterizations show these techniques have achieved low contact resistance and sufficient bonding strength.

   Based on the previous efforts, two antenna systems, respectively operating on UHF (867 MHz) and HF (13.56 MHz) bands, are fabricated. The two antenna systems are designed into SP4T switching networks, using standard antenna elements as the loads of the network. The input RFID interrogation signals from commercial industrial RFID readers are directed into every antenna element periodically through the SP4T switching networks. Both antenna systems are characterized by means of various RF power attenuation measurements and passive RFID tag interrogation tests. It is shown in the results that both antenna systems have low RF attenuations, potentials to perform passive RFID tag positioning, and possibilities to be expanded to larger areas.

   In the end, based on the antenna system characterization results and design parameters, a great amount of calculation is performed in order to discuss how large the antenna system areas can be as well as how many antenna elements can be achieved in one antenna system. 

Flexible circuits, also known as flexible printed circuit boards, were originally developed in the 1950s for interconnection between multiple electronic devices when flexibility and movement were required. Nowadays, flexible circuits can be used for implementing electronic systems much more complicated than just interconnections. A commonly seen material combination of flexible circuits is copper foils laminated on polyimide substrates, although these solutions are both expensive and environmentally hazardous. With developments in printed electronics, many non-conventional materials can be used in fabricating flexible circuits that have advantages such as increased flexibility, low cost, a small environmental impact, etc. In addition, fast and efficient manufacturing methods can produce flexible electronics in large volumes. This opens a window of opportunity to create electronic systems over geometrically large areas. This thesis proposes methods and guidelines for how to implement largearea electronic devices using non-conventional flexible materials and technologies. The thesis specifically focuses on electronic systems that integrate both digital and analogue signals. Further, it demonstrates and provides examples of how signals in the microwave frequencies, commonly requiring expensive materials, can be handled with non-conventional materials and technologies. Several conductor-substrate material combinations are used, which are fabricated using industrial processes. The conductor materials include conductive inks, copper foils, and aluminium foils, while the substrate materials comprise papers, a nonwoven fabric, and a polyimide. In particular, methods are investigated in order to achieve a low DC resistance in printed conductiveink-based tracks, which opens the possibilities for them to be used in highcurrent applications. Several surface mounting techniques are developed for incorporating surface mount devices within the fabricated flexible circuits, including the use of low-temperature solder paste, isotropic conductive adhesives, and anisotropic conductive adhesives. Some of the techniques have achieved sufficiently low contact resistance and adequate component bonding strengths, and thus can be used in implementing hybrid electronic systems. In addition, most of the techniques have the potential to be used in automated component assembly lines. As demonstrators, two antenna systems for commercial RFID readers operating at high frequency (13.56 MHz) and ultra-high frequency (867 MHz) iv Abstract bands are implemented, which comprise both digital and analogue signals. The two antenna systems are designed as part of SP4T switching networks using standard antenna elements as the loads of the network. It is shown in the results that both antenna systems have low RF attenuations, the potential to perform passive RFID tag positioning, and the possibility to be expanded to larger areas. Based on the characterisations to the two antenna systems, discussions are made about how large the antenna system areas can be as well as how many antenna elements can be achieved in a single antenna system. This thesis provides a material-to-system approach and demonstrates that non-conventional flexible materials and printed electronic technologies are suitable choices for large-area electronics.

Flexibla kretsar, även kända som flexibla tryckta kretskort, utvecklades ursprungligen på 1950-talet för sammankoppling mellan flera elektroniska enheter när flexibilitet och rörelse var nödvändig. Numera kan flexibla kretsar användas för att implementera elektroniska system som är mycket mer komplicerade än bara sammankopplingar. En vanligt sett materialkombination av flexibla kretsar är kopparfolier laminerade på polyimid-substrat, även om dessa lösningar är både dyra och miljöfarliga. Med utvecklingen inom tryckt elektronik kan många icke-konventionella material användas för att tillverka flexibla kretsar som har fördelar såsom ökad flexibilitet, låg kostnad, en liten miljöpåverkan, etc. I tillägg kan snabba och effektiva tillverkningsmetoder producera flexibel elektronik i stora volymer. Detta öppnar ett fönster av möjligheter att skapa elektroniska system över geometriskt stora områden. Flera kombinationer av material för ledare och substrat används i denna avhandling, som tillverkas med industriella processer. Ledarmaterialen inkluderar ledande bläck, kopparfolier och aluminiumfolier, medan substraten innefattar papper, ett nonwoven-tyg och en polyimid. I synnerhet undersöks metoder för att uppnå låg DC-resistans i tryckta bläckbaserade ledare, vilket också möjliggör användning i högströmstillämpningar. Flera ytmonteringsmetoder utvecklas för att införliva ytmonterade komponenter i de tillverkade flexibla kretsarna, inklusive användning av lödpasta med låg temperatur, isotropa ledande lim och anisotropa ledande lim. Vissa av teknikerna har uppnått tillräckligt lågt kontaktmotstånd och adekvata komponentbindningsstyrkor och kan således användas vid implementering av hybridelektroniska system. Dessutom har de flesta tekniker potentialen att användas i automatiserade komponentmonteringslinjer. Som demonstrator implementeras två antennsystem för kommersiella RFID-läsare som arbetar med högfrekvensband (13.56 MHz) och ultrahögfrekvensband (867 MHz), som innefattar både digitala och analoga signaler. De två antennsystemen är konstruerade som en del av SP4T-nätverk med standardantennelement som nätverksbelastningar. Det visas i resultaten att båda antennsystemen har låga RF-dämpningar, potentialen att utföra passiv RFIDtaggpositionering och möjligheten att utökas till större områden. Baserat på resultaten diskuteras hur stora antennsystemområdena kan vara och hur många antennelement som kan uppnås i ett enda antennsystem. Sammanfattning vi Denna avhandling ger ett material-till-system-tillvägagångssätt och demonstrerar att icke-konventionella flexibla material och tryckt elektronisk teknik är lämpliga val för storskalig elektronik.