60 GHz stepped impedance filter using Planar Goubau line technology

This paper presents a fifth order stepped impedance low-pass filter using low loss Planar Goubau Line (PGL) technology on high resistivity Silicon substrate at millimeter-wave frequencies. The filter is simulated and optimized using 3D full-wave electromagnetic field simulations performed on HFSS (High Frequency Simulator Structure). On-wafer measurements in the 50-65 GHz band are in good agreement with simulation results. At 60 GHz, the measured insertion loss is 3.6dB which includes the two coplanar waveguide-to-GPL transitions

Picosecond Pulse Measurements of Graphene

This thesis investigates Graphene, a gapless semi-conductor with relativistic-like electron behaviour, using on-chip terahertz time-domain spectroscopy (OC-THz-TDS). In this technique single-cycle THz frequency pulses are emitted, guided by waveguides, and detected on a single chip. The device fabrication is achieved by incorporating planar Goubau line waveguides with epitaxial GaAs and graphene grown by chemical vapour deposition. Spectroscopy of these devices, with graphene spanning a small gap between the waveguides, reveals large oscillations that are mainly attributed to the gap and other waveguide features. Optical-pump terahertz-probe measurements are used to isolate the contribution of the graphene sample, and to observe the (picosecond timescale) hot-carrier lifetime. The ultrafast carrier dynamics of graphene are then applied to demonstrate the first known measurements of graphene as an on-chip terahertz photoconductive detector; operating at frequencies up to 600 GHz. Pulsed terahertz emission from graphene is also demonstrated for a range of bias voltages, and considerations towards the design of all-graphene on-chip terahertz devices is discussed. The spatial dependence of picosecond pulse detection using graphene is also investigated, achieved by mapping the optical probe location for a variety of switch geometries. A better understanding of the interaction of the terahertz field with the graphene over distances of 50 to 200 um is obtained, which may be used to improve performance and build towards making graphene a viable option in commercial THz-TDS systems

Microwave response of tessellated metal surfaces and their constituent elements

Over the last century the electromagnetic (EM) spectrum has become ever more accessible with advances in technology. As a result, EM filters (or Frequency Selective Surfaces (FSSs)) have been developed for many applications. Such filters have been used on satellites and radomes. In this thesis, novel single layer and dual layer FSS have been studied and characterised, experimentally and using Finite Element Method (FEM) modelling, showing very good agreement between the data and models. The interesting transmission properties of these structurally complicated FSS are explained and the physics of the resonant modes that mediate transmission is explored. Enhanced transmission through an array of sub-wavelength apertures close to the diffraction limit has been a popular area of physics for many years. In addition enhanced reflection from metal patch arrays has been of great interest. This thesis studies original extensions of conventional FSS. The work is split into two main sections: single layer FSS and dual layer FSS. In the first experimental chapter (chapter 5) two new single layered FSS comprising complementary elements tessellated into composite arrays are explored (a connected array and a disconnected array). The behaviour of these arrays is compared with that of arrays of the constituent elements that either exhibit enhanced transmission or enhanced reflection phenomena. The behaviour of the connected composite array can be inferred from the behaviour of arrays of the constituent elements. Interestingly for the disconnected composite array, the behaviour can not be inferred from the constituent elements as without one or the other of the elements in situ, the modes supported on the composite array are not supported for the arrays of constituent elements. The second and third experimental chapters (Chapters 6 and 7) explore the transmission through dual layer arrays composed of either capped holes or capped annuli. Despite the holes being capped with a metal disc, the array exhibits a remarkably high transmission, mediated by the annular cavity formed between the caps and apertured metal sheet. In Chapter 7 concentrically nested annular patches above annular slots are used to achieve multiple transmission pass bands. For many applications it is often desirable to miniaturise resonant elements. Developing this concept further, chapter 8 explores the resonant frequency of a structured capped aperture. The internal structure of metal inclusions, give control over the resonant frequency of the cavity, reducing it's resonant frequency significantly and miniaturising the size of the cavity compared to the incident wavelength.Dst

Si Waveguide Technology for High Performance Millimeter-Wave/Terahertz Integrated Systems

The terahertz (THZ) spectrum (0.3 – 3 THz) offers new opportunities to a wide range of emerging applications which demand high-quality THz sources, detectors, amplifiers, and integrated circuits. On-chip integration of planar transmission line passive components degrades their performance due to the conduction loss. Therefore, a hybrid integrated technology in which all of the high-quality passive components are implemented using a suitable off-chip planar integrated technology and the active devices are placed on-chip, has become the most promising approach. In this thesis, a low-cost and low-loss silicon-on-glass (SOG) integrated circuit technology is proposed for THz/millimeter-wave (mmW) applications. Highly-resistive intrinsic silicon (Si) is selected as the main guiding region due to its high transparency at mmW/THz frequency ranges and the maturity of Si-devices fabrication. In the proposed technology, all of the passive components and waveguide connections are made of highly-resistive Si on a glass substrate. The proposed technique leads to a high-precision and low-cost fabrication process, wherein the alignment between the sub-structures is automatically achieved during the fabrication process. This is performed by photolithography and dry etching of the entire integrated passive circuit layout through the Si layer of the SOG wafer. The SOG dielectric ridge waveguide, as the basic component of the SOG integrated circuit, is theoretically and experimentally investigated. A test setup is designed to measure propagation characteristics of the proposed SOG waveguide. Measured dispersion diagrams of the SOG dielectric waveguides show average attenuation constants of 0.63 dB/cm, 0.28 dB/cm, and 0.53 dB/cm over the frequency ranges of 55 – 65 GHz, 90 – 110 GHz, and 140 – 170 GHz, respectively. Extending the SOG platform toward the THz range is achieved by new SOG waveguide structures wherein the glass substrates below the Si channels are etched to reduce the effect of greater glass material loss at higher frequencies (i.e., > 200 GHz). To fabricate these structures, the glass substrate is etched in hydrophilic acid before bonding to the Si. Four new SOG configurations, called the suspended SOG, corrugated SOG, rib SOG, and U-SOG waveguides are proposed with their respective fabrication techniques for the THz range of frequencies. In the suspended SOG waveguide, a periodic configuration of Si beams supports the Si guiding channel over the etched grove on the glass substrate. Measurements of two suspended SOG waveguides show low attenuation constants of 0.031 dB/λ0 and 0.042 dB/λ0 (on average) over the frequency ranges of 350 - 500 GHz and 400 - 500 GHz, respectively. It is theoretically demonstrated that the rib SOG and U-SOG waveguides are promising candidates for THz high-density and low-loss integrated circuits. Rib SOG waveguide and U-SOG waveguide test devices are designed over the frequency bands of 0.8 – 0.9 THz and 0.9 – 1.1 THz. The proposed SOG waveguide technology can easily be extended to several THz with no limitations. A new mmW low-loss dielectric phase shifter integrated in the corrugated SOG platform is designed, fabricated, and measured. Phase shifts of 111 ° and 129 ° at frequencies of 85 GHz and 100 GHz, with maximum insertion losses of 0.65 dB and 2.5 dB, are achieved during measurements of the proposed phase shifter. Millimeter-wave integrated SOG tapered antennas are developed and implemented. The idea of a suspended SOG tapered antenna is demonstrated to enhance the radiation efficiency and the gain of the SOG tapered antenna over 110 – 130 GHz. The suspended SOG tapered antenna, which can function under two orthogonal mode excitations, shows measured efficiencies of higher than 90 % for the two vertical polarizations

Characterization of Carbon Nanotubes and Nanowires and Their Applications

This thesis establishes comprehensive methodology for characterization of metallic nanowires (NWs) and carbon nanotubes (CNTs), and evaluation of their performance for interconnect applications at microwave/ mm-wave/THz frequencies. The research focus is on the development of modeling and measurement methods to determine constitutive material parameters, i.e. conductivity, and contact resistance of platinum (Pt) NWs, as well as on the development of modeling approaches to evaluate characteristic parameters for antennas, nano-coaxial lines, and single wire transmission lines composed of CNTs. Applicability of traditional two-port measurements is investigated for accurate determination of material parameters for Pt NWs over a broad frequency range. Two test-setups are developed. First, several configurations with directly contacted Pt NWs to a host coplanar waveguide (CPW) structure are designed and realized to determine the conductivity and contact resistance. Full-wave finite element and circuit models are used to determine the two parameters by fitting simulations to measurements. It is found that the single measurement setup with direct contacts cannot determine the two parameters simultaneously. To solve this problem, two approaches based on transmission line and lumped element models for Pt NWs are developed. Both approaches employ a set of two NWs with different lengths. The feasibility of both approaches is thoroughly studied and relevant conclusions are made. An approach based on lumped element models is validated experimentally, and it is shown that the contact resistance and conductivity of 300 nm diameter Pt NWs are about 50 W and 0.013sbulk, respectively. In the second setup, the capacitive coupling contact between the Pt NWs and the CPW structure is exploited to determine the NW’s conductivity. Two variations of this setup, specifically in-slot and on-dielectric configurations, are developed. Full-wave finite-element models are utilized to demonstrate suitability of the two configurations and to determine the conductivity of Pt NWs by fitting to measurements. Structural and elemental analyses of fabricated devices are conducted to assess fabrication and measurement issues. Full-wave modeling for individual CNTs and CNT bundles is performed by the use of method of moments and finite element method codes in order to CNTs as antennas, nano-coaxial lines, and single wire transmission lines. Characteristic parameters, such as impedance, gain, efficiency, and line loss for each interconnect are evaluated and compared to those of their copper-based counterparts. Results show better performance of CNTs over conventional metals at microwave frequencies. The extension of modeling and metrology for semiconducting NWs and CNTs, and the study of graphene at microwave frequencies are proposed as directions for future work

Wireless power transmission para drones

Mestrado em Engenharia Eletrónica e TelecomunicaçõesDrones are unmanned aerial vehicles that have proliferated the market due to their low cost and the many applications that can already be associated to them. Besides the common use of these devices for playful activities, as aerial event recording, they demonstrate an enormous potential in other applications, such as military, as search and rescue or reconnaissance missions, or commercial, for example: surveillance and inspection of crops. However, most commercial devices currently available suffer from a major drawback in terms of their dependence of batteries which, in consequence of the large energy demand supplied to the drone's engines, quickly discharge. In addition, the weight of these batteries typically implies that more power is needed to keep the drone flying. This drawback can be overcome, or attenuated, using dedicated wireless power transmission systems that enable the devices to maintain flight without the need of batteries or simply charging them while in use. Throughout this dissertation a microwave wireless power transmission system working at 5.8 GHz will be described in detail, with emphasis on the design of the microstrip antenna array developed to allow directive transmission and the rectenna proposed for reception and power conversion. The proposed system allows the used quadcopter to boot and link with its remote control and demonstrates the potential to be adapted for other purposes.Drone é a designação normalmente atribuída a veículos aéreos não tripulados que se têm proliferado no mercado devido ao seu baixo custo e inúmeras aplicações. Além do seu uso em actividades lúdicas, como o já comum registo aéreo de eventos, demonstram um enorme potencial noutras aplicações, tanto militares, missões de busca e salvamento e reconhecimento de terreno, como comerciais, sendo exemplo a vigilância e inspecção de campos de colheita. No entanto, maioria dos dispositivos comerciais actualmente disponíveis padecem de uma grande limitação no que toca à sua dependência de baterias que, de modo a alimentar os motores do drone, rapidamente se descarregam. Além disso, o peso que estas baterias implicam levam a que seja necessária uma maior potência para que o drone se mantenha a voar. Estes problemas podem ser contornados, ou atenuados, recorrendo a sistemas de transmissão dedicada de energia electromagnética que possibilitem aos dispositivos manter vôo sem recurso a baterias ou carregando-as quando em uso. Ao longo desta dissertação será descrito em detalhe um sistema de transferência de energia sem fios projectado para trabalhar à frequência de 5.8 GHz, dando ênfase ao desenho de um agregado de antenas microstrip, desenvolvido para possibilitar uma transmissão directiva, e a rectenna proposta para recepção da energia electromagnética e sua conversão em corrente contínua. O sistema proposto possibilita ao quadricóptero ter energia suficiente para se conseguir ligar e estabelecer comunicação com o seu controlo remoto sendo que a arquitectura proposta demonstra potencial para ser adaptada em futuras abordagens

Microwave and millimeter-wave rectifying circuit arrays and ultra-wideband antennas for wireless power transmission and communications

In the future, space solar power transmission and wireless power transmission will play an important role in gathering clean and infinite energy from space. The rectenna, i.e., a rectifying circuit combined with an antenna, is one of the most important components in the wireless power transmission system. To obtain high power and high output voltage, the use of a large rectenna array is necessary. Many novel rectennas and rectenna arrays for microwave and millimeter-wave wireless power transmission have been developed. Unlike the traditional rectifying circuit using a single diode, dual diodes are used to double the DC output voltage with the same circuit layout dimensions. The rectenna components are then combined to form rectenna arrays using different interconnections. The rectennas and the arrays are analyzed by using a linear circuit model. Furthermore, to precisely align the mainbeams of the transmitter and the receiver, a retrodirective array is developed to maintain high efficiency. The retrodirective array is able to track the incident wave and resend the signal to where it came from without any prior known information of the source location. The ultra-wideband radio has become one of the most important communication systems because of demand for high data-rate transmission. Hence, ultra-wideband antennas have received much attention in mobile wireless communications. Planar monopole ultra-wideband antennas for UHF, microwave, and millimeter-wave bands are developed, with many advantages such as simple structure, low cost, light weight, and ease of fabrication. Due to the planar structures, the ultra-wideband antennas can be easily integrated with other circuits. On the other hand, with an ultra-wide bandwidth, source power can be transmitted at different frequencies dependent on power availability. Furthermore, the ultra-wideband antenna can potentially handle wireless power transmission and data communications simultaneously. The technologies developed can also be applied to dual-frequency or the multi-frequency antennas. In this dissertation, many new rectenna arrays, retrodirective rectenna arrays, and ultra-wideband antennas are presented for microwave and millimeter-wave applications. The technologies are not only very useful for wireless power transmission and communication systems, but also they could have many applications in future radar, surveillance, and remote sensing systems

Electromagnetic Energy Harvesting Surfaces

The concept of wireless power transfer (WPT) was successfully demonstrated in the early years of the 20th century. One promising application of using the WPT concept is the WPT transmission utilizing a large array of solar cells outside the earth's atmosphere to collect solar energy and then converts it to microwave power for transmission to earth using highly directive antennas. Space solar power SSP transmission concept may play an important role in the near future in harvesting clean and sustainable energy from space. The SSP concept calls for the large rectenna (i.e., antennas and rectifying circuitry) arrays farms that receive the microwave power that is transmitted from space and convert it into usable DC power. To obtain high power and high output voltage, the use of a large rectenna array is necessary, and hence the focus of this thesis is on improving the harvesting efficiency of rectenna systems. The two main figures of merit to evaluate a WPT rectenna system are the radiation to AC efficiency, and the radiation to DC efficiency. The latter combines the efficiencies of the electromagnetic energy collectors or antenna, and that of the rectifying circuitry. In the progress towards improving the efficiency of a rectenna array system, efforts were heavily focused on improving the AC to DC conversion efficiencies. However, in most previous works, efforts to improve the efficiency of the antennas were not pursued. The majority of rectennas were in fact designed using conventional antennas because of their wide use in modern communications technologies but not for their particular ability or suitability to efficiently harvest electromagnetic radiation. The first part of this thesis introduces, for the first time, the use of dielectric resonator antenna (DRA) in an array form as an energy harvester. A single DRA and a 1x3 array were used to build foundation profiles for using DRAs in an array form as an energy harvester. The proposed structures were designed and fabricated to maximize energy reception around 5.5 GHz. The size of the ground plane and coupling between dielectric resonator (DR) elements in an array were studied with special focus on the overall efficiency of the antenna structure for different incident polarizations. A 5x5 array was built and tested numerically and experimentally. Measurements showed that energy absorption efficiency as high as 67% can be achieved using an array of DRAs. Then an extension of this finding was carried out considering the DRA's fabrication challenges. A complementary DRAs structure consisting of DR blocks backed by cut grounds is proposed. It was shown through numerical simulations that the complementary DR blocks resonator can efficiently deliver the incident power carried by an electromagnetic wave to a load with an efficiency of 80%. The concept of using an electromagnetic energy harvesting surface (EHS) structure is introduced in the second part of this thesis. A design of an electromagnetic EHS inspired by an array of printed metallic dipolar elements is introduced. The unit cell of the EHS is based on two printed asymmetric off-center fed dipoles. As a proof of concept, a finite array of 9x3 unit cells was analyzed numerically and experimentally to work at 3 GHz. The array was first analyzed for maximizing radiation to AC absorption where each dipole was terminated by a resistor across its gap. An overall radiation to DC harvesting efficiency of 76% was obtained experimentally. The third part of this dissertation presents a design for a multi-polarization electromagnetic EHS inspired by a multi-layer unit cell of printed asymmetrical metallic dipolar elements. The harvesting array features two layers that collectively capture the incident energy from various incident angles. The harvester was first analyzed for maximizing the radiation to AC absorption at 3 GHz where each dipole was terminated by a resistor across its energy-collecting gap. As a proof of concept, a multi-layer array consisting of 3x3 asymmetrical dipolar elements of the multi-layer unit cell was fabricated and measured experimentally. The experimental results yielded an overall radiation to DC harvesting efficiency of 70%for multiple incident polarizations. Next, an EHS is introduced for receiving multiple polarizations while using only one metallization layer. The EHS unit cell is based on two cross-dipoles that enable capturing the energy from various angles of illuminations at an operating frequency of 3 GHz. The simulation results yielded a radiation to AC efficiency of 94% at multiple angles of polarization. For validation, a finite array of 7x7 unit cells was fabricated and tested experimentally. The experimental results of the EHS energy harvesting array show an overall radiation to DC harvesting efficiency of 74% at various polarization angles. A critical design feature of the proposed cross-dipole EHS array is that it allows direct matching to a rectifying circuitry at the dipoles plane. The thesis concludes by introducing an efficient dual-band EHS array using two stacked-layer of cross-dipole elements for efficient harvesting at two frequency bands for multiple polarizations. The proposed EHS array introduces the concept of stacked surfaces that can be directly integrated with the rectification circuitry. The multilayer EHS array allows direct matching to a rectifying circuitry such that DC power is collected at the elements' plane for each layer. The total achieved harvested DC power is the collective contribution of the rectified DC power from the EHS's layers. A finite multi-layer array of 7x7 unit cells was fabricated and tested experimentally. The experimental results of the dual-band EHS energy harvesting array show an overall radiation to DC harvesting efficiencies of 77% and 70%, respectively, at various polarization angles at the desired operating frequencies of 2.7 GHz and 3.4 GHz

Microfluidic capillary in a waveguide resonator for chemical and biochemical sensing

This thesis presents a novel microwave sensor for the characterisation of fluids with the integration of a microfluidic capillary. Various designs and fabrication methods were investigated for the integrated microfluidic capillary. SU-8 and PDMS were investigated as possible materials, however proved difficult to produce large volumes of capillaries. PMMA a cheap readily available material was also investigated. Using an Epilog CO2 laser ablation machine rapid prototyping of microfluidic capillaries was achieved using PMMA. Two microwave resonator designs are proposed as non-contact sensing devices. The first design utilizes an E-plane filter in a split-block rectangular waveguide housing. This offers advantages in enhanced near fields and simple manufacturing techniques. Simulation and experimental results are presented, demonstrating sensitivity of such microwave sensors. Various materials under test were used: Methylated spirit/water concentrations, lubricant and motor oils and animal red blood cell concentrations. Resonant frequency shifts in the region of 10s of MHz were observed. However most notably in the methylated spirit concentrations there was no resonant frequency shift, only a shift in the return losses were observed. The integration of the E-plane filter and the microfluidic capillary resulted in poor repeatability due to alignment issues of the filter and capillary. The second design incorporates the use of Distributed Bragg Reflectors for a compact and fully integrated, no moving parts, device. The simulation results produced a Q-factor 1,942 at a resonant frequency of 23.3 GHz. The Bragg sensor produced promising simulation results as well as initial experimental results. There was up to 20 MHz resonant frequency shift between the samples. Samples included Eppendorf tubes filled with water and oil

A Compact Reconfigurable 1-D Periodic Structure in GaAs MMIC With Stopband Switching, Dual-Band Operation and Tuning Capabilities

This paper presents a systematic study of a compact and reconfigurable periodic structure in GaAs MMIC technology. Compactness is achieved by the introduction of spiral inductors in a conventional unit cell without disturbing the reactive loading mechanism. The proposed architecture exhibits a 28.3% wider stopband with 62.6% smaller footprint compared to a conventional structure. The compactness and bandwidth improvement in the proposed structure is explained with the help of dispersion and circuit analysis. The reconfigurability built into the design using PIN diodes allows stopband switching, dual-band operation and tuning capabilities with the mere use of a single reactive load in its unit cell. To the best of the authors knowledge, it is the first time a reconfigurable MMIC implementation is realized using the proposed structure or even the conventional design. As a guide to design, sensitivity analysis to filter performance is presented for important structure parameters. Switching element parasitics are discussed in two ways: firstly, with the design and measurement of structures with idealized switching conditions and in second, with the circuit and full-wave EM modelling of the finite periodic structure with the actual PIN diodes. The on-chip measurements of the fully reconfigurable filter show excellent agreement with simulations