Millimetre Wave Power Measurement

There is currently no traceable power sensor for millimetre wave frequencies above 110 GHz. This thesis investigates a novel approach to remove this limitation by combining the placement of a uniquely designed microchip directly in waveguide. The design of the chip is novel in that it does not rely on a supporting structure or an external antenna when placed in the waveguide. The performance of the design was primarily analysed by computer simulation and verified with the measurement of a scale model. The results show that it is feasible to measure high frequency power by placing a chip directly in waveguide. It is predicted that the chip is able to absorb approximately 60% of incident power. Any further efficiency would require modification of the chip substrate. However, this proposed design should allow the standards institutes a reference that will enable the calibration of equipment to beyond 110 GHz

Metrology State-of-the-Art and Challenges in Broadband Phase-Sensitive Terahertz Measurements

The two main modalities for making broadband phase-sensitive measurements at terahertz (THz) frequencies are vector network analyzers (VNA) and time-domain spectrometers (TDS). These measuring instruments have separate and fundamentally different operating principles and methodologies, and they serve very different application spaces. The different architectures give rise to different measurement challenges and metrological solutions. This article reviews these two measurement techniques and discusses the different issues involved in making measurements using these systems. Calibration, verification, and measurement traceability issues are reviewed, along with other major challenges facing these instrument architectures in the years to come. The differences in, and similarities between, the two measurement methods are discussed and analyzed. Finally, the operating principles of electro-optic sampling (EOS) are briefly discussed. This technique has some similarities to TDS and shares application space with the VNA

Reconfigurable optically-controlled waveguide for terahertz applications

The development of tunable waveguide components for systems that require multifunctionality, at terahertz frequencies is investigated using the photoconductivity e ect. Specifically, by the photo-generation of free charged carriers highly conducting plasma regions are created and by changing the light pattern in real time, various tunable components can be implemented. The aim of this thesis is to present a novel reconfigurable optically-controlled terahertz waveguide switch as an illustrative example of this approach, addressing the challenges and limitations involved in simulation, implementation and measurement of such devices and is organised in the following chapters. Chapter 1 gives the background theory of the fundamental principles of optoelectronic devices and presents a literature survey of existing optically-controlled structures across a wide frequency spectrum. Chapter 2 presents a comparative study of four commercial software packages with the aim to show that it is not always straightforward to select the most appropriate boundary conditions and define a material's parameter within a software when terahertz structures are modelled. A study of various modelling approaches using commercially-available software packages has been undertaken; a number of approaches have been identified and the most appropriate solutions are indicated. Chapter 3 presents a microwave plasma switch as a proof-of-concept scaled demonstrator. In this preliminary experiment a metal pipe rectangular waveguide (similar to WR-650 standard) has been implemented, which can be reconfigured as an ON-OFF switch using a plasma column formed by commercially available discharge tubes. This provides a good starting point for more sophisticated devices as presented in the following chapters. In Chapter 4 a novel optically-controlled waveguide plasma switch for terahertz applications is presented. The switch is excited by a continuous wave (CW) laser source and the photoconductivity profile, due to the laser illumination, is described in detail. The performance of the switch is studied by means of full-wave numerical simulations and various parametric studies are undertaken to provide physical insight in the device performance. The thermal characteristics of the device are also investigated. Chapter 5 gives in detail the processing steps for the microfabrication of various prototypes with the assembly of the prototypes being also discussed. The waveguide experimental setup is described in detail and the measurement results obtained are presented. In particular, emphasis has been given on the alignment of the devices with the Vector Network Analyser waveguide heads. Finally, Chapter 6 gives a summary of the work presented in this thesis and potentially new research directions are indicated as future work.Open Acces

Transmission and Reflection method with a material filled transmission line for measuring Dielectric properties

Measurement of the electromagnetic properties of a material sample with simpler procedures and greater accuracy is very desirable in the design of radio frequency and microwave equipment. Real-time complex calculations and instantaneous results are possible using modern measuring equipment such as the vector network analyzer. Measurement and analysis of various transmission line using S-parameters have been developed by others. In the thesis we have attempted to develop a simpler method to determine the complex permittivity and permeability using the transmission and reflection method with a material filled transmission line. Schemes for simultaneous measurement of the relative permeability and permittivity are developed using a combination of hardware and software tools to make the procedure simpler and efficient

Development of microwave NDT inspection techniques for large solid propellant rocket motors Final report

Microwave nondestructive testing techniques for large solid propellant rocket engine

Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy

Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation spanning 70 THz in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides significant spectral broadening and engineered spectra targeted at specific mid-infrared bands. We use this coherent light source for dual-comb spectroscopy at 5 um.Comment: 26 pages, 5 figure

Multi-chip module interconnections at microwave frequencies: electromagnetic simulation and material characterisation

In this work both the interconnections and materials used in multi-chip modules (MCMs) at microwave frequencies have been investigated. The electrical behaviour of the interconnections was studied using commercially available 2.SD and 3D electromagnetic simulators (HFSSTM, MDSTM and Momentum™). State-of-the-art conductive and dielectric film materials used in the fabrication of multi-layer MCM structures were characterized using microstrip/wave guide resonator techniques. The models chosen for simulation of interconnections are commensurate with those in current use in MCM technology. Crosstalk between microstrip conductors in multi-layer MCM structures was simulated and new knowledge leading to new design rules was obtained.Typical elements in MCM interconnect structures, such as vias, bends and airbridges were also investigated. The principal features of these elements were simulated and the results were obtained in S-parameter form. Based on the simulated results, these parasitic elements were modelled in terms of their equivalent circuits which can be used in circuit simulators to aid more rigorous MCM circuit design. A microstrip ring resonator, fabricated using the newly developed conductive material from Heraeus, was employed to measure the line loss. New techniques have been developed to measure the permittivity and loss tangent of thin dielectric films. In the previous methods for the measurement of these films, the accuracy in measuring the relative permittivity is limited and there is no available technique to measure the loss tangent. A novel cavity perturbation method was developed to accurately measure both the relative permittivity and loss tangent of the films deposited on a supporting substrate. An additional independent technique, derived from transmission line theory, for measuring the relative permittivity of dielectric film was also established. A particular feature of the new teclmiques, which led to high accuracy in measuring dielectric constant and loss tangent was the positioning of the dielectric film in the region of maximum electric field strength, thereby ensuring maximum interaction between the electric field and the film material. A rigorous error analysis was performed on the new techniques, which led to the establishment of practical measurement correction factors. A simple and rigorous method has also been developed to accurately measure the loss tangent of dielectrics with known dielectric constant using a resonant cavity. The novel method eliminates the need for any physical measurement of the dielectric sample. The new technique should permit the development of techniques for very high frequency characterisation of dielectric materials

Impedance Transformers

Non