Sillas Hadjiloucas

Research projects

Current research projects

• Co-investigator in an International (4 year) project funded by FAPESP (Brazilian Government) Grant Title: PROJETO TEMTICO Espectroscopia Terahertz no Domnio do Tempo: Desenvolvimento de Mtodos Analticos, Tcnicas de Processamento de Sinais, Estudos Bioqumicos e Fundamentais, Coordenador: Celio Pasquini, Instituto de Qumica Universidade Estadual de Campinas, UNICAMP and Instituto Tecnolgico de Aeronutica, So Jos dos Campos (ITA), Brazil.

Research in instrumentation and measurement

Development of novel amplitude modulated reflectance fibre-optic displacement sensors and novel feedback based optoelectronic stabilization schemes for accurately measuring displacement, velocity, acceleration, force and pressure. These are suitable for a range of automotive and robotic applications, and have been also used for flow measurement and the measurement of relative humidity in the atmosphere (through the development of a feedback dew-point sensor).

Development of optical force feedback microphones (this is a continuation of work performed by L. Karatzas, D. Keating and M. Usher). The innovation in the work lies in the use of force feedback to control the motion of the diaphragm in the capsule, with the sensing performed interferometrically. By measuring the amount of effort needed to keep the capsule in a set position in the presence of a disturbance (staying at the mid-point of a single fringe in a Fabry-Perot interference pattern), a very accurate (shot noise limited) estimate of the acoustic disturbance is obtained. The work required the design of a novel capsule topology that linearizes the feedback system. Applications include non-destructive testing, biomedical applications, audio research, echo-location and photoacoustic spectrometry.

Collaboration with the Department of Electronic and Electrical Engineering (Optoelectronics Division, headed by Prof. B.Culshaw) and the Department of Pure and Applied Chemistry, the University of Strathclyde led to work towards the development of a hydrogel (hydrophilic polymer) based distributed fibre optic microbend sensor for measuring of soil moisture and the water potential (a component of the chemical potential) in solutions. This sensor was based on measurements of quasi-sinusoidal distortions of fixed periodicity on a multimode graded index optical fibre using Optical Time Domain Reflectometry.

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I worked as visiting researcher at RWTH Aachen with the fast-pulse (femtosecond) THz spectroscopy group (currently considered as one of the best group in the world in THz spectroscopy) and characterised polymers and waveguide structures at frequencies ranging from 100 GHz to 3.0 THz. This work led to a collaboration with GigaOptics GmbH, Mhlheim/Main Germany for the development of a novel dual frequency comb THz spectrometer, this is now known in the fast pulse community as the ASOPS modality. My knowledge of optics, femtosecond systems and the related research disciplines has led to my appointment to the position of 'Ultrafast Laser Lab committee member for the University until its re-deployment at Imperial College.

Research in signal processing, system identification and control

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Under development are novel system identification tools in the wavelet domain for the further processing of spectroscopic transients. Defining the background and sample interferograms as the input and output signals, the frequency response of an identified model provides an estimate of the complex insertion loss (CIL). A wavelet-packet formulation is adopted and sub-band models Mi,j(z) are identified from the sample and background interferograms by following a least-squares procedure.

The wavelet-packet model structure consists of a decomposition tree, which defines frequency sub-bands. H(z), G(z) denote low-pass and high-pass decomposition filters, respectively, with reconstruction counterparts represented by Hr(z), Gr(z). The sub-band models are represented by the transfer functions M0,2(z), M1,2(z), M2,2(z), M3,2(z).

Model identification of a sample interferogram for a given frequency sub-band.

The signal processing work has also been extended to Wiener-Hammerstein systems to provide an identification window related to receiver motion dynamics using information from the non-linear addition of electric field amplitudes associated with multiple propagation channels (direct line-of-sight, ground/wall reflections, diffractive components) from multiple emitters. This is of interest from a mobile communications perspective. We have also performed analysis and classification of ECG signals using Linear Discriminant Analysis Classifiers as well as non-linear neural network based classifiers. A novelty in the work is the representation of the input signals to the classifiers in compact support wavelet bases. Wavelets are used to de-noise the signal and minimize the number of inputs to the neural network. The approach facilitates network training and provides a better framework for feature extraction. Furthermore, the generalization ability of the classifier is improved.

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Research in genetic algorithms for femtosecond pulse shaping experiments

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Research skills map

A summary of research skills mapped to a range of application areas is provided below.

Past project support and donations in kind

• EPSRC GR/R36213/01 award for 'Cavity Ringdown Far-Infrared Absorption Spectroscopy' Individual Grant Review Overall Assessment:'Good' Communication of Research Outputs 'Tending to Outstanding' (PI).
• EPSRC CASE AWARD 'Future terahertz mesh network architectures for mobile telecommunications' (project co-sponsored by VODAFONE (PI).
• CCLRC AWARD 'Heterodyne cavity ringdown absorption spectroscopy for atmospheric chemistry studies at THz frequencies,' (PI).
• HEFCE funded: 'Establishment of the Ultrafast Laser Laboratory at Reading University' (with John Bowen in Cybernetics, Dr. L,. Frasinski and Dr. S. O'Leary in Physics), (Co-I).
• GREEK GOVERNMENT: PhD studentship on 'Terahertz measurement techniques for plant water relations' (PI).
• NATIONAL INSTRUMENTS donation in kind: Hardware and LABVIEW software from National Instruments towards the 'Flying Brains' student project (PI).
• MAX-PLANCK Institute for Biochemistry, Munich (Prof. Keilmann) donation in kind: a custom-made close cycle temperature control incubator which is integrated with microwave components to perform in vivo studies of the biological effects of THz radiation on yeast cell cultures (PI).
• UoR, Department of Physics donations in kind: A laser (Nd:YAG, 1 Joule 10 ns pulse), with harmonic generator crystal, polarization optics and dedicated heat exchanger, an Argon ion laser (14W) with close cycle heat exchanger, an ultrasonic scanner for biomedical applications and various optoelectronic and microwave (10 GHz) equipment and lasers (PI).
• UoR RETF three year PhD Studentship for 'Biological Investigations Using Terahertz Radiation' (PI).
• Travel and subsistence visiting Scholarships in 2006 and 2010 to Instituto Tecnolgico de Aeronutica, So Jos dos Campos Brazil for projects titled 'Control of Dynamic systems' sponsored by PRONEX/CNPq (Brazilian government) and 'Spectro-analytical Instrumentation and Methodologies' sponsored by PROCAP/CAPES (Brazilian government), (PI for UK).
• Travel and subsistence funds for Xiaoxia (Sunny) Yin to visit Reading University as Pysden Memorial Fellow to conduct research in the summer term of 2007. Collaboration with Prof. Abbott's group (Department of Electrical and Electronic Engineering, University of Adelaide) in the area of signal processing of THz transients.
• Travel and subsistence grant from RIKEN Institute to Japan for collaborations on 'Investigations on the effects of non-thermal levels of terahertz radiation in yeast cells'.
• INTAS travel and subsistence grant for collaboration with Russian Academy of Sciences, Nizhny Novgorod, Russia on 'Prospects for Cavity Ringdown Spectroscopy at THz frequencies'.
• Collaborative agreement with GigaOptics GmbH, Mhlheim/Main Germany for the development of a novel dual frequency comb THz spectrometer based around two Ti:Sapphire oscillators producing 30 femtosecond duration pulses and operated at 1 GHz repetition rate. Prototype delivered at cost price.