Terahertz characterisation of UV offset lithographically printed electronic-ink

Inkjet-printed electronics are showing promising potential in practical applications, but methods for real-time, non-contact monitoring of printing quality are lacking. This work explores Terahertz (THz) sensing as an approach for such monitoring. It is demonstrated that alterations in the localised dielectric characteristics of inkjet-printed electronics can be qualitatively distinguished using quasi-optically-based, sub-THz reflection spectroscopy. Decreased reflection coefficients caused by the sintering process are observed and quantified. Using THz near-field scanning imaging, it is shown that sintering produces a more uniform spatial distribution of permittivity in the printed carbon patterns. Images generated using THz-TDS based imaging are presented, demonstrating the combination of high resolution imaging with quantification of complex permittivities. This work, for the first time, demonstrates the feasibility of quality control in printed electronic-ink with THz sensing, and is of practical significance to the development of in-situ and non-contact commercial-quality characterisation methods for inkjet-printed electronics

Design and Operation of a Microwave Flow Cytometer for Single Cell Detection and Identification

Microwave dielectric sensing has become a popular technique in biological cell sensing for its potential in online, label-free, and real-time sensing. At microwave frequencies probing signals are sensitive to intracellular properties since they are able to penetrate cell membranes, making microwave flow cytometry a promising technology for label-free biosensing. In this dissertation a microwave flow cytometer is designed and used to measure single biological cells and micro particles. A radio frequency (RF)/microwave interferometer serves as the measurement system for its high sensitivity and tunability and we show that a two-stage interferometer can achieve up to 20 times higher sensitivity than a single interferometer. A microstrip sensor with an etched microfluidic channel is used as the sensing structure for measuring single cells and particles in flow. The microwave flow cytometer was used to measure changes in complex permittivity, , of viable and nonviable Saccharomyces cerevisiae and Saccharomyces pastorianus yeast cells and changes in complex permittivity and impedance of two lifecycle stages of Trypanosoma brucei, a unicellular eukaryotic parasite found in sub-Saharan Africa, at multiple frequencies from 265 MHz to 7.65 GHz. Yeast cell measurements showed that there are frequency dependent permittivity differences between yeast species as well as viability states. Quadratic discriminate analysis (QDA) and k-nearest neighbors (KNN) were employed to validate the ability to classify yeast species and viability, with minimum cross-validation error of with cross validation errors of 19% and 15% at 2.38 GHz and 265 MHz, respectively. Measurements of changes in permittivity and impedance of single procyclic form (PCF) and bloodstream form (BSF) T. brucei parasites also showed frequency dependence. The two cell forms had a strong dependence on the imaginary part of permittivity at 2.38 GHz and below and a strong dependence on the real part of permittivity at 5.55 GHz and above. Three PCF cell lines were tested to verify that the differences between the two cell forms were independent of cell strain. QDA gave maximum cross-validation errors of 15.4% and 10% when using one and three PCF strains, respectively. Impedance measurements were used to improve cell classification in cases where the permittivity of a cell cannot be detected. Lastly, a microwave resistance temperature detector (RTD) is designed, and a model is developed to extract the temperature and complex permittivity of liquids in a microfluidic channel. The microwave RTD is capable of measuring temperature to within 0.1°C. The design can easily be modified to increase sensitivity be lengthening the sensing electrode or modified for smaller volumes of solute by shortening the electrode

Environmental high frequency characterization of fabrics based on a novel surrogate modelling antenna technique

Wearable antennas are mostly constructed from fabric or foam, whereas e-textiles are often used as conductive parts. A design obstacle is the lack of knowledge about the electromagnetic properties of these materials. Moreover, most of these fabrics exhibit electromagnetic properties that depend on prevailing atmospheric conditions. In this work, we present a dedicated characterization method to determine the complex permittivity of fabrics or foams, as well as the effective conductivity of e-textiles, and this as a function of relative humidity. The method extracts the constitutive parameters by comparing measured and simulated antenna figures of merit such as input impedance and antenna efficiency. This inverse problem is solved using a surrogate-based optimization technique as implemented in the Surrogate Modeling Toolbox, yielding a fast and accurate characterization. The method is evaluated by characterizing six materials which are exposed to relative humidity levels ranging from 10% to 90%. From the extracted complex permittivities of the six materials, two-phase dielectric mixing models based on the volumetric fractions of the absorbed moisture in the substrates are developed and evaluated in terms of accuracy. For the materials exhibiting a high sensitivity to moisture, the model is observed to be less accurate. However, the worst model accuracy is shown to be comparable with the estimated accuracy of the characterization procedure. For materials with low sensitivity to moisture, the model fits the measured values very well

Water-structuring molecules and nanomaterials enhance radiofrequency heating in biologically relevant solutions

For potential applications in nano-mediated radiofrequency cancer hyperthermia, the nanomaterial under investigation must increase the heating of any aqueous solution in which it is suspended when exposed to radiofrequency electric fields. This should also be true for a broad range of solution conductivities, especially those that artificially mimic the ionic environment of biological systems. Herein we demonstrate enhanced heating of biologically relevant aqueous solutions using kosmotropes and a hexamalonoserinolamide fullerene

On-chip terahertz characterisation of liquids

Spectroscopy at terahertz frequencies can be used in a wide range of applications including radio-astronomy, pharmaceutical manufacturing control, and the study of processes in molecular biology. Biomolecular samples should preferably be studied in their native environment, water, however, water poses extreme attenuation for THz-frequency waves, deteriorating or even impeding analysis using these waves. The most common THz spectroscopy method, time-domain spectroscopy, can measure water samples using free-space measurements, lacks sensitivity when trying to measure on a chip environment. To exploit the advantages that chip measurements offer, such as integration and cost, this thesis works on developing on-chip THz spectroscopy of aqueous samples using a frequency-domain approach, with vector network analysers. Vector network analysers exhibit a higher dynamic range than time-domain spectroscopy systems, making them a promising alternative for sensitive THz measurements. For maximising the sensitivity of the measurements, the losses must be minimised. One important source of losses at THz frequencies are conductor and radiation loss. In this thesis, two planar waveguides were designed, coplanar waveguide and planar Goubau line, minimising their losses at THz frequencies by avoiding the coupling to other parasitic modes, obtaining attenuation constants as low as 0.85 Np/mm for coplanar waveguide and 0.33 Np/mm for planar Goubau line. Additionally, planar Goubau line calibration structures were developed for setting the measurement plane along this planar waveguide. Finally, coplanar waveguides were integrated with microfluidic channels to perform spectroscopy measurements of water samples, showing good performances as THz sensors of high-loss liquids.This thesis is a first step towards a sensitive and miniaturised system for measuring the electrical properties of high-loss liquids, which could shed light on the fundamental biomolecular processes in the picosecond time-scale

Measurements and analysis of the microwave dielectric properties of tissues

Knowledge of the microwave dielectric properties of human tissues is essential for the understanding and development of medical microwave techniques. In particular, microwave thermography relies on processes fundamentally determined by the high frequency electromagnetic properties of human tissues. The specific aim of this work was to provide detailed information on the dielectric properties of female human breast tissue at 3-3.5GHz, the frequency of operation of the Glasgow microwave thermography equipment. At microwave frequences the frequency variation of the dielectric properties of biological tissues is thought to be determined mainly by the dipolar relaxation of tissue water. Water exists in different states of binding within the tissue; the relaxation of each component of this water may be parameterised by the Debye or Cole-Cole equations. At a single frequency an average relaxation frequency may be calculated for a given tissue type. Mixture equations may be used to describe the dielectric properties of two-phase mixtures in terms of the dielectric properties and volume fractions of the component phases. Biological tissues are very much more complex than these two phase models. However, comparisons of the observed dielectric properties as a function of water content, with models calculated from mixture theory allow some qualitative conclusions to be drawn regarding tissue structure. Human and animal dielectric data at frequencies between 0.1 and 10GHz have been collected from the literature and are displayed in tabular form. These comprehensive tables were used to examine the widely-held assumption an animal tissue is representative of the corresponding human tissue. This assumption was concluded to be uncertain in most cases because of lack of available data, and perhaps wrong for certain tissue types. The tables were also used to compare in vivo and in vitro dielectric data. These may be expected to be different because the tissue is in a physiologically abnormal state in vitro. However at microwave frequencies in vitro data was found to be representative of the tissue in vivo provided gross deterioration of the tissue is avoided. A new resonant cavity perturbation technique was designed for dielectric measurements of small volumes of lossy materials at a fixed frequency of 3.2GHz. This technique may be used to measure materials of a wide range of permittivities and conductivities with accuracies of 3-4%. The major sources of error were found to be tissue heterogeneity and sample preparation procedures. Using this technique in vitro dielectric measurements were made on human female breast tissues. A large number of data were gathered on fat and normal breast tissues, and on benign and malignant breast tumours. Each data set was parameterised using the Debye equation. Results from this suggest that all breast tissues measured in this work contain a component of bound water. A smaller proportion of water is bound in fat than is bound in other tissues. Comparisons were made of the dielectric properties of breast tissues with values calculated from mixture theories. Permittivity data largely fall within bounds set by mixture theory: conductivity data often fall outside these limits. This may imply that physiological saline is not a good approximation to tissue waters; or it may imply that another relaxation process is occurring in addition to the dipolar relaxation of saline. Comparisons of tissue type indicate that a dielectric imaging system could be designed which would detect breast diseases, but that severe problems could arise in distinguishing disease types from dielectric imaging alone

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

Radio-Frequency Sensors for Detection and Analysis of Chemical and Biological Substances

Dielectric spectroscopy (DS) is an important technique for scientific and technological investigations in various areas. DS sensitivity and operating frequency ranges are critical for many applications, including lab-on-chip development where sample volumes are small with a wide range of dynamic processes to probe. In this dissertation, the design and operation considerations of radio-frequency (RF) interferometers that are based on power-dividers (PDs) and quadrature-hybrids (QHs) is presented. The effective quality factor (Qeff) of the sensor is as high as ∼3.8×10^6 with 200 μL of water samples. Such interferometers are proposed to address the sensitivity and frequency tuning challenges of current DS techniques. A high-sensitivity and stable QH-based interferometer is demonstrated by measuring glucose-water solution at a concentration level that is ten times lower than some recent RF sensors and DNA solution at ~3×10^-15 mol/mL that is close to the previously reported lowest result while the sample volume is ~1 nL. Composition analysis of ternary mixture solutions are also demonstrated with a PD-based interferometer. Using a tunable liquid attenuator by accurately changing its liquid volume, the sensitivity of a RF interferometer is tuned automatically. The obtained Qeff of the interferometer is up to 1×10^8 at ~5 GHz, i.e., ~100 times higher than previously reported results. When material-under-test, i.e., methanol-water solution in this work, is used for the tuning, a self-calibration and measurement process is demonstrated from 2 GHz to 7.5 GHz at a methanol concentration level down to 5×10^-5 mole fraction, which is 100 times lower than previously reported results. A microwave scanning technique is reported for the measurement of floating giant unilamellar vesicles (GUV) in a 25 μm wide and 18.8 μm high microfluidic channel. The measurement is conducted at 2.7 GHz and 7.9 GHz, at which a split ring resonator (SRR) operates at odd modes. A 500 nm wide and 100 μm long SRR split gap is used to scan GUVs that are slightly larger than 25 μm in diameter. The smaller fluidic channel induces flattened GUV membrane sections, which make close contact with the SRR gap surface. The used GUVs are synthesized with POPC (16:0-18:1 PC 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), SM (16:0 Egg Sphingomyelin) and cholesterol at different molecular compositions. It is shown that SM and POPC bilayers have different dielectric permittivity values, which also change with measurement frequencies. The obtained membrane permittivity values, such as 73.64-j6.13 for POPC at 2.7 GHz, are more than 10 times larger than previously reported results. The discrepancy is likely due to the measurement of dielectric polarization responses that are parallel with, other than perpendicular to, the membrane surface. POPC and SM-rich GUV surface sections are also clearly identified from scanning measurement results. Further work is needed to enable accurate analysis of membrane composition and dynamics at high spatial resolutions