Dielectric Spectroscopy of Biological Samples

For the first time, the impedance spectrum of live Jurkat T-lymphocytes human cells was characterized in a single sweep spanning six decades of frequency from 9 kHz to 9 GHz. The ultrawide bandwidth bridged the traditional impedance spectroscopy at kilohertz to megahertz frequencies with the recently developed microwave dielectric spectroscopy, which can probe the cell interior without being hindered by the cell membrane. Based on the measured scattering parameters and a simple cell model, an equivalent circuit of four nondispersive elements, including membrane resistance, membrane capacitance, cytoplasm resistance, and cytoplasm capacitance, was extracted and found sufficient to explain the so-called β relaxation over the frequencies measured. The extracted cell parameters were in general agreement with the literature. However, the presently extracted membrane capacitance of 0.4 pF and cytoplasm resistance of 0.75 MΩ are on the low and high end of the literature, respectively. This could be explained by having separated out the shunt effects of the membrane resistance and cytoplasm capacitance, respectively. In fact, the present membrane resistance and cytoplasm capacitance, at 2.8 MΩ and 10 fF, respectively, are believed to be more reliable due to the low-conductivity solution and the microwave frequency used. Meanwhile, sensitivity analysis was carried out for extracting lumped cell characteristics such as membrane resistance and cytoplasm capacitance from the scattering parameters. The scattering parameters were measured on a coplanar waveguide with a Jurkat cell trapped by dielectrophoresis either in a series or shunt configuration. The sensitivity analysis validated our previous empirical observation that the insertion loss of a series-trapped cell and the return loss of a shunt-trapped cell were most sensitive to the cell impedance. Additionally, the membrane resistance and cytoplasm capacitance were most sensitive to low- and high-frequency scattering parameters, respectively. Furthermore, the dissertation presents a novel in situ single-connection calibration using biocompatible solutions, which is demonstrated in single-cell characterization from 0.5 GHz to 9 GHz for the first time as well. The characterization is based on quickly trapping and detrapping the cell by dielectrophoresis on a coplanar waveguide (CPW) with a small protrusion in one of its ground electrodes, which doubles as the calibration standard when covered by different liquids. Consistent with theoretical analysis, the difference in the transmission coefficient increases with increasing frequency and is generally smaller than the difference in the reflection coefficient. With improved accuracy and throughput, the calibration technique may enable broadband electrical characterization of single cells in a high-speed cytometer

Nonlinear mechanisms in passive microwave devices

Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria de les TICThe telecommunications industry follows a tendency towards smaller devices, higher power and higher frequency, which imply an increase on the complexity of the electronics involved. Moreover, there is a need for extended capabilities like frequency tunable devices, ultra-low losses or high power handling, which make use of advanced materials for these purposes. In addition, increasingly demanding communication standards and regulations push the limits of the acceptable performance degrading indicators. This is the case of nonlinearities, whose effects, like increased Adjacent Channel Power Ratio (ACPR), harmonics, or intermodulation distortion among others, are being included in the performance requirements, as maximum tolerable levels. In this context, proper modeling of the devices at the design stage is of crucial importance in predicting not only the device performance but also the global system indicators and to make sure that the requirements are fulfilled. In accordance with that, this work proposes the necessary steps for circuit models implementation of different passive microwave devices, from the linear and nonlinear measurements to the simulations to validate them. Bulk acoustic wave resonators and transmission lines made of high temperature superconductors, ferroelectrics or regular metals and dielectrics are the subject of this work. Both phenomenological and physical approaches are considered and circuit models are proposed and compared with measurements. The nonlinear observables, being harmonics, intermodulation distortion, and saturation or detuning, are properly related to the material properties that originate them. The obtained models can be used in circuit simulators to predict the performance of these microwave devices under complex modulated signals, or even be used to predict their performance when integrated into more complex systems. A key step to achieve this goal is an accurate characterization of materials and devices, which is faced by making use of advanced measurement techniques. Therefore, considerations on special measurement setups are being made along this thesis.Award-winningPostprint (published version

Piezoelectric units with self-tuning multi-resonant shunts for vibration absorption

This thesis is focused on a lightweight and modular control system formed by a piezoelectric patch connected to either a single-resonant or a multi-resonant self-tuning shunt, which can be used to mitigate the resonant response of one or multiple low-order flexural modes of a hosting structure. The aim of the study is to develop a self-contained unit, which can be bonded in batches on thin structures to decrease the low frequency flexural response generated by stationary stochastic disturbances. To this end, the study investigates the optimal tuning of both single-resonant and multi-resonant shunts with reference to a global and a local cost function. Two configurations of the single-resonant shunt are considered, which are formed by a resistance-inductance (RL) connected respectively in series and in parallel. Instead, a single configuration of the multi-resonant shunt is investigated, which is formed by an array of parallel branches encompassing a resistance-inductance-capacitance (RLC) connected in series. The global cost function, given by the minimisation of the hosting structure time-averaged total flexural kinetic energy, is used as a reference metric to assess the optimal tuning of the shunt. Instead, the local cost function, given by the maximisation of the time-averaged electric power absorbed either by the RL single-resonant shunt or by each RLC branch of the multi-resonant shunt, is employed for the practical implementation of the self-tuning shunt. The study shows that, with respect to the resistance and inductance shunt parameters, the two cost functions are characterised by mirror bell surfaces. Hence, the optimal shunt resistance and inductance values that would minimise the global cost function coincide with those that would maximise the local cost functions. As a result, both the single-resonant and multi-resonant shunts can be suitably tuned within the shunt itself by maximising the time-average electric power absorbed by the single-resonant shunt or by each branch of the multi-resonant shunt. The study also shows that, the tuning can be effectively implemented with a recursive two-paths tuning approach, whereby the inductance is first tuned along a constant-resistance path characterised by a bell shaped curve of the cost function and then the resistance is tuned along a constant-inductance path characterised by a bell shaped curve of the cost function too. This two-paths tuning sequence can be run recursively online such that the shunt can be adapted to variations of the electro-mechanical response of the hosting structure and piezoelectric transducer as well as to variations of the electric response of the shunt components, which can both occur in presence of temperature variations or other exogenous physical effects. Since the optimisations along the constant resistance and constant inductance paths are characterised by non-convex cost functions, the study proposes to employ the extremum seeking algorithm to find the optimal shunt parameters that would maximise the electric power absorption. This is a model-free gradient driven search algorithm, which asymptotically leads to the maximum of the non-convex bell-shaped paths. The algorithm is based on a periodic dithering signal that perturbs the inductance and resistance tuning signals such that the resulting electric power absorbed by the shunt equally shows such a periodic signal, which is either in phase or out-of-phase with the dithering signal depending the tuning is under or over estimating the shunt parameter with respect to the optimal one that maximises the power absorption. The study shows that this algorithm suitably leads to the optimal shunt values regardless the structure is excited by a stochastic disturbance such that the power cost function undergoes significant variations over time

Modular Nonlinear Characterization System and Large-Signal Behavioral Modelling of Unmatched Transistors for Streamlined Power Amplifier Design

This thesis provides a comprehensive approach to the characterization and modelling of large-signal nonlinear RF/microwave devices, circuits and systems. This research is moti- vated by the increased linearity and power-efficiency requirements of modern power ampli- fier technology for wireless communications. For instance, maximizing the power amplifier’s efficiency can only be achieved by operating RF transistors under strong nonlinear condi- tions, however this is contradictory to maximizing PA linearity. Simultaneously designing for efficiency and linearity is a challenging trade-off in today’s fragmented design process, therefore the advancement of computer-aided design (CAD) tools is essential for achieving an optimal solution. The successful and effective CAD tool based PA design relies on the availability of accurate nonlinear models to mimic the electro-thermal behaviour of RF transistors. The accuracy of these models depends on three factors: 1. The formulation of the model. 2. The model extraction procedure. 3. The accuracy of the measurement data. While prior work focuses separately on the improved model formulations or improving characterization accuracy, this thesis provides a comprehensive analysis of all three factors. This thesis proposes a modular large-signal RF device characterization system, and a non- linear behavioral model capable of handling strongly nonlinear unmatched RF transistors, each necessary to streamline the design process and achieve a first-pass PA design. iii As a first step, a large-signal characterization system has been developed to measure the multi-harmonic frequency response of RF transistors and has the ability to i) Perform high-power measurements, ii) Characterize unmatched transistors, iii) Operate the DUT under any possible operating condition, iv) Synthesize any multi-harmonic stimulus, and v) Reconstruct the time-domain I/V waveforms at the ports of the DUT. The proposed characterization system eliminates fragmentation between measurement and simulation environments by providing seamless integration with Harmonic Balance simulations. This provides a common framework that integrates all steps of the PA design process from device-level characterization, to circuit-level measurement and validation. This system is implemented using modular instruments consisting of mixer-based receivers, arbitrary waveform generators, impedance tuners, and a multi-harmonic phase-coherent reference source. It also integrates sequential calibration routines to provide receiver, port match, and source-power corrections to the DUT measurement plane and measurement routines for automated data collection. The second part of the thesis researches black-box frequency-domain behavioral mod- els that can approximate strongly nonlinear, unmatched devices. Our investigation yielded two complimentary solutions to ensure the targeted modelling accuracy. First, improving the accuracy of a first-order expansion-based Poly-Harmonic Distortion (PHD) model by 5dB, in terms of Normalized Mean-Squared Error (NMSE), by minimizing multi-harmonic reflections that artificially increase the order of the nonlinear system. While this addresses the fictitious need for higher-order models due to the deficiencies in the model extraction procedure, strongly nonlinear devices will require high-order models to achieve the targeted accuracy over a larger measurement distribution. Hence, a variable order Multi-Harmonic Volterra (MHV) model is proposed to extend the PHD model formulation to strong non- linear devices. This model is extracted by utilizing the proposed characterization system to extract higher-order multi-variate model coefficients not included in the PHD model. The resulting model improves DC drain current prediction by 5dB and improves funda- mental output-power prediction by 2dB. The MHV model improves the vector power-gain prediction by 3.4dB in realistic PA design applications, thereby providing better emulation of linearization techniques within a simulation environment. Finally, a concurrent dual-band PA design is studied as an example of how the pro- iv posed nonlinear characterization system and behavioural modelling approach can be used to enable complex PA designs. First, a 10W Class-AB PA is designed using dual-band matching-network theory, however it is difficult to implement because the design technique does not control the matching fractional bandwidth as a design parameter. Therefore, an alternative Class-J 45W dual-band PA was designed using a low-impedance matching network, combined with a trans-impedance dual-band filter. Although the dual-band PA can achieve comparable performance to an equivalent single-band PA at each separate fre- quency, further development of characterization, modeling, and circuit design techniques is needed to achieve high-efficiency during concurrent operation

Estimation and detection of transmission line characteristics in the copper access network

The copper access-network operators face the challenge of developing and maintaining cost-effective digital subscriber line (DSL) services that are competitive to other broadband access technologies. The way forward is dictated by the demand of ever increasing data rates on the twisted-pair copper lines. To meet this demand, a relocation of the DSL transceivers in cabinets closer to the customers are often necessary combined with a joint expansion of the accompanying optical-fiber backhaul network. The equipment of the next generation copper network are therefore becoming more scattered and geographically distributed, which increases the requirements of automated line qualification with fault detection and localization. This scenario is addressed in the first five papers of this dissertation where the focus is on estimation and detection of transmission line characteristics in the copper access network. The developed methods apply model-based optimization with an emphasis on using low-order modeling and a priori information of the given problem. More specifically, in Paper I a low-order and causal cable model is derived based on the Hilbert transform. This model is successfully applied in three contributions of this dissertation. In Paper II, a class of low-complexity unbiased estimators for the frequency-dependent characteristic impedance is presented that uses one-port measurements only. The so obtained characteristic impedance paves the way for enhanced time domain reflectometry (a.k.a. TDR) on twisted-pair lines. In Paper III, the problem of estimating a nonhomogeneous and dispersive transmission line is investigated and a space-frequency optimization approach is developed for the DSL application. The accompanying analysis shows which parameters are of interest to estimate and further suggests the introduction of the concept capacitive length that overcomes the necessity of a priori knowledge of the physical line length. In Paper IV, two methods are developed for detection and localization of load coils present in so-called loaded lines. In Paper V, line topology identification is addressed with varying degree of a priori information. In doing so, a model-based optimization approach is employed that utilizes multi-objective evolutionary computation based on one/two-port measurements. A complement to transceiver relocation that potentially enhances the total data throughput in the copper access network is dynamic spectrum management (DSM). This promising multi-user transmission technique aims at maximizing the transmission rates, and/or minimizing the power consumption, by mitigating or cancelling the dominating crosstalk interference between twisted-pair lines in the same cable binder. Hence the spectral utilization is improved by optimizing the transmit signals in order to minimize the crosstalk interference. However, such techniques rely on accurate information of the (usually) unknown crosstalk channels. This issue is the main focus of Paper VI and VII of this dissertation in which Paper VI deals with estimation of the crosstalk channels between twisted-pair lines. More specifically, an unbiased estimator for the square-magnitude of the crosstalk channels is derived from which a practical procedure is developed that can be implemented with standardized DSL modems already installed in the copper access network. In Paper VII the impact such a non-ideal estimator has on the performance of DSM is analyzed and simulated. Finally, in Paper VIII a novel echo cancellation algorithm for DMT-based DSL modems is presented

Characterisation of spectral and angular effects on photovoltaic modules for energy rating

This thesis presents work aimed at the development of practical and simplified methods for advanced characterisation of PV modules while reducing energy yield estimation uncertainties, focusing on the spectral and angular effects. In this work, practical characterisation method to measure the spectral response (SR) curve of PV modules have been developed based on the polychromatic method. Improvement of the method have been achieved through the development of new measurement setup and detail evaluation of the polychromatic fitting algorithm. Set of coloured plate with unique transmission profiles supplemented with a smaller number of optical bandwidth filters used in the measurement setup resulted in high throughput irradiance (the lowest is measured at 150 W/m2). High uniformity of the throughput irradiance over the measurement plane contribute to low uncertainty in the measurement of short-circuit current where the highest estimated uncertainty lays within the uncertainty margin for the STC measurement, at 2.5%. Measurement of optical/electrical of device under test with associated uncertainty are combined with the fitting algorithm through the Monte-carlo simulation method. The uncertainty in the final determination of SR characteristic gave the value of 7%, with about ±10% agreement between the SR curves obtained through the polychromatic method to the conventional monochromatic method. The measurement of angular response developed in this method employed the indoor measurement setup with the additional turn table attachment. The evaluation of divergent light of the non-ideal light source and the accuracy in angle adjustment of the turn table have been quantified and incorporated into the angular response measurement as uncertainties. Partial illumination method are applied for a reliable extraction of operating current in the measurement of PV modules with the uncertainty estimated at 1%. 4% variation in the measurement of angular dependency of various PV devices at high tilt angle have been realised which translate to about 1.5% difference in the simulated annual energy performance. The application of the same simulator in the development of spectral and angular response measurement in this work creates the potential for the angle-dependent spectral response characterisation on module scale. This have been realised through a simulation. Low uncertainty in energy yield is important as this indicate the risk in the investment of PV project. Detail evaluation with accuracy and uncertainty analysis of the works to be described will further improve the uncertainty in the measurement of spectral and angular response of PV modules, hence better accuracy in the assessment of energy yield can be achieved