Publications
372 results found
Kamel H, Syms R, Kardoulaki EM, et al., 2017, Metamaterial MRI-based Surgical Wound Monitor, 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS), Publisher: IEEE, Pages: 334-336
Syms R, 2017, Rapid evaporation-driven chemical pre-concentration and separation on paper., Biomicrofluidics, Vol: 11, ISSN: 1932-1058
Airflow-enhanced evaporation is investigated as a method for rapid chemical preconcentration on a thin porous substrate. The mechanism is described by combining 1D models of capillary rise, chromatography, and pervaporation concentration. It is shown that the effective length of the column can be shorter than its actual length, allowing concentrate to be held at a stagnation point and then released for separation, and that the Péclet number, which determines the concentration performance, is determined only by the substrate properties. The differential equations are solved dynamically, and it is shown that faster concentration can be achieved during capillary filling. Experiments are carried out using chromatography paper in a ducted airflow, and concentration is quantified by optical imaging of water-soluble food dyes. Good agreement with the model is obtained, and concentration factors of ≈100 are achieved in 10 min using Brilliant Blue FCF. Partial separation of Brilliant Blue from Tartrazine is demonstrated immediately following concentration, on a single unpatterned substrate. The mechanism may provide a method for improving the sensitivity of lab-on-paper devices.
Syms RRA, Liu D, Ahmad MM, 2017, Nanostructured 2D cellular materials in silicon by sidewall transfer lithography NEMS, Journal of Micromechanics and Microengineering, Vol: 27, ISSN: 0960-1317
Sidewall transfer lithography (STL) is demonstrated as a method for parallel fabrication of 2D nanostructured cellular solids in single-crystal silicon. The linear mechanical properties of four lattices (perfect and defected diamond; singly and doubly periodic honeycomb) with low effective Young's moduli and effective Poisson's ratio ranging from positive to negative are modelled using analytic theory and the matrix stiffness method with an emphasis on boundary effects. The lattices are fabricated with a minimum feature size of 100 nm and an aspect ratio of 40:1 using single- and double-level STL and deep reactive ion etching of bonded silicon-on-insulator. Nanoelectromechanical systems (NEMS) containing cellular materials are used to demonstrate stretching, bending and brittle fracture. Predicted edge effects are observed, theoretical values of Poisson's ratio are verified and failure patterns are described.
Syms RRA, Floume T, 2017, Parasitic coupling in magneto-inductive cable, Journal of Physics D: Applied Physics, Vol: 50, ISSN: 0022-3727
Magneto-inductive (MI) waveguides are linear arrangements of magnetically coupled L–C resonators that propagate electrical energy at radio frequency without direct connection. To achieve the strong magnetic coupling needed for low-loss propagation, adjacent elements must be in such close proximity that electric coupling arises. In contrast to electric coupling in split ring resonators, the coupling occurs between the inductive tracks of adjacent resonant loops. Parasitic capacitance is demonstrated in flexible magneto-inductive cable, and shown to introduce additional propagation bands above the MI band. Simple models are developed to predict this effect, and strategies discussed to improve high-frequency isolation.
Kardoulaki EM, Syms RRA, Young IR, 2016, MRI for noninvasive thermometry, eMagRes, Vol: 5, Pages: 1203-1217, ISSN: 2055-6101
MRI was recognized for its potential use as a noninvasive in vivo thermometer 30 years ago. Today, the most popular application of MR thermometry is the guidance of thermal therapies for the treatment of cancer and other pathologies. These minimally invasive operations are routinely performed on patients who are not eligible for surgery in approximately 40 medical centers globally. The aim is to deliver or abduct thermal energy in order to cause local tissue necrosis or to sensitize a lesion to chemotherapy or radiotherapy without causing harm to the surrounding healthy tissue. Here we explain the principles of operation of MR thermometry and provide a critical review of the proposed methods, highlighting remaining fundamental and technical issues as well as recent progress. Emphasis is placed on hardware advances (RF receivers) for improved signal-to-noise ratio (SNR) which would lead to better accuracy, spatiotemporal resolution, and precise calibration. We conclude with a general outlook for the field.
Kardoulaki EM, Syms RRA, Young IR, et al., 2016, SNR in MI catheter receivers for MRI, IEEE Sensors Journal, Vol: 16, Pages: 1700-1707, ISSN: 1530-437X
Internal coils have a signal-to-noise ratio (SNR) advantage during magnetic resonance imaging. However, coils with continuous cables are generally unsafe, due to the risk of RF heating. Segmented cables, such as magneto-inductive waveguides, should introduce inherent safety at the price of increased noise, from both the cable and the body. Here, we derive analytical SNR expressions for both types of noise, develop a model to compare the SNR of different types of receiver, and validate the model with data from imaging experiments at 3T. Experiments and theory confirm that body noise does not prevent an SNR gain compared with an eight-element external coil, even when a long section of waveguide is loaded with tissue.
Syms R, Wright S, 2016, MEMS Mass Spectrometers: the Next Wave of Miniaturization, Journal of Micromechanics and Microengineering, Vol: 26, ISSN: 1361-6439
This paper reviews mass spectrometers based on micro-electro-mechanical systems (MEMS) technology. The MEMS approach to integration is first briefly described, and the difficulties of miniaturizing mass spectrometers are outlined. MEMS components for ionization and mass filtering are then reviewed, together with additional components for ion detection, vacuum pressure measurement and pumping. Mass spectrometer systems containing MEMS sub-components are then described, applications for miniaturized and portable systems are discussed, and challenges and opportunities are presented.
Syms R, Solymar L, 2015, A dynamic competition model of regime change, Journal of the Operational Research Society, Vol: 66, Pages: 1939-1947, ISSN: 1476-9360
A dynamic competition model for an oppressive government opposed by rebels is proposed, based on coupled differential equations with constant coefficients. Depending on their values, the model allows scenarios representing a stable, oppressive government and violent regime change. With constant coefficients, there can be no limit cycles. However, cycles emerge if rebels and governments switch characteristics after a revolution, if resources change hands and rebel motivations switch from grievance to greed. This mechanism is proposed as an explanation for the establishment of a new repressive regime after the overthrow of a similar regime.
Mokhtar MHH, Syms RRA, 2015, Tailored fibre waveguides for precise two-axis Lissajous scanning, Optics Express, Vol: 23, Pages: 20804-20811, ISSN: 1094-4087
A two-axis optical imaging system using a Lissajous scan pattern with non-integer frequency ratio is presented. A waveguide with precisely tuned mechanical resonant frequencies is constructed by dip coating two fibres with a transparent polymer. Motion is achieved by mounting a waveguide cantilever at 45° on a single piezoelectric actuator with a dual-frequency drive. Confocal signal collection is achieved using a mode-stripping detector, and feedback signals needed for frequency and phase locking are derived from intermittent reflection from an apertured mirror. The first scan axis is locked to the resonance of one of the modes, while the second scan axis is locked to the correct phase at the desired frequency ratio. Accurate acquisition of two-dimensional images is demonstrated.
Kardoulaki EM, Syms RRA, Young IR, et al., 2015, Thin-film micro-coil detectors: Application in MR-thermometry, Sensors and Actuators A: Physical, Vol: 226, Pages: 48-58, ISSN: 1873-3069
Kardoulaki EM, Syms RRA, Young IR, et al., 2015, Optothermal profile of an ablation catheter with integrated microcoil for MR-thermometry during Nd:YAG laser interstitial thermal therapies of the liver-An in-vitro experimental and theoretical study, Medical Physics, Vol: 42, Pages: 1389-1397, ISSN: 0094-2405
Purpose: Flexible microcoils integrated with ablation catheters can improve the temperature accuracyduring local MR-thermometry in Nd:YAG laser interstitial thermal therapies. Here, the authors areconcerned with obtaining a preliminary confirmation of the clinical utility of the modified catheter.They investigate whether the thin-film substrate and copper tracks of the printed coil inductor affectthe symmetry of the thermal profile, and hence of the lesion produced.Methods: Transmission spectroscopy in the near infrared was performed to test for the attenuationat 1064 nm through the 25 µm thick Kapton substrate of the microcoil. The radial transmissionprofile of an infrared high-power, light emitting diode with >80% normalized power at 1064 nmwas measured through a cross section of the modified applicator to assess the impact of the copperinductor on the optical profile. The measurements were performed in air, as well as with the applicatorsurrounded by two types of scattering media; crystals of NaCl and a layer of liver-mimicking gelphantom. A numerical model based on Huygens–Fresnel principle and finite element simulations,using a commercially available package (COMSOL Multiphysics), were employed to compare withthe optical measurements. The impact of the modified optical profile on the thermal symmetry wasassessed by examining the high resolution microcoil derived thermal maps from a Nd:YAG laserablation performed on a liver-mimicking gel phantom.Results: Less than 30% attenuation through the Kapton film was verified. Shadowing behind thecopper tracks was observed in air and the measured radial irradiation correlated well with the diffractionpattern calculated numerically using the Huygens–Fresnel principle. Both optical experimentsand simulations, demonstrate that shadowing is mitigated by the scattering properties of a turbidmedium. The microcoil derived thermal maps at the end of a Nd:YAG laser ablation performed on agel phantom in a 3 T s
Wright S, Malcolm A, Wright C, et al., 2015, A microelectromechanical systems-enabled, miniature triple quadrupole mass spectrometer, Analytical Chemistry, Vol: 87, Pages: 3115-3122, ISSN: 1086-4377
Syms RRA, Floume T, Solymar L, et al., 2015, Parametric Amplification of Magneto-Inductive Waves, NONLINEAR, TUNABLE AND ACTIVE METAMATERIALS, Vol: 200, Pages: 35-58, ISSN: 0933-033X
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- Citations: 1
Syms RRA, 2015, STATUS AND FUTURE TRENDS OF THE MINIATURIZATION OF MASS SPECTROMETRY, 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), Publisher: IEEE, Pages: 134-139, ISSN: 1084-6999
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- Citations: 2
Liu D, Syms RRA, Ahmad MM, 2015, NEMS BY MULTILAYER SIDEWALL TRANSFER LITHOGRAPHY, 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS), Publisher: IEEE, Pages: 288-291, ISSN: 1084-6999
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- Citations: 1
Mokhtar MHH, Syms RRA, 2014, Resonant fiber scanner with optical feedback, Optics Express, Vol: 22, Pages: 25629-25634, ISSN: 1094-4087
The addition of an apertured mirror before the imaging lens is proposed as a method of providing feedback in a single-axis resonant fiber scanner. Reflection at the scan extremities generates timing signals interlaced with back-scattered data, and a phase locked loop and a proportional controller then adjust the drive frequency and amplitude. The capture range and stability of the system are examined. Verification is obtained using a confocal scanner based on mechanically biaxial fiber.
Choonee K, Syms RRA, 2014, Robust cylindrical plasmonic nano-antennas for light-matter interaction, Progress in Electromagnetics Research, Vol: 148, Pages: 129-139, ISSN: 1559-8985
A cylindrical metallic plasmonic nano-antenna consisting of a shell supporting a disk, namedcapped shell, is proposed and studied by frequency domain finite element analysis. This new topology isshown to be weakly dependent on the radius of the structure and is therefore suitable for fabrication byparallel processes such as island lithography which generates a pseudo-random array with a distributionof diameters. Furthermore, compared to similar resonators such as rods, disks and shells, the cappedshell generates a larger volume with high fields, and is hence useful as a nano-antenna for light-matterinteraction.
Wiltshire MCK, Syms RRA, 2014, Noise performance of magneto-inductive cables, Journal of Applied Physics, Vol: 116, Pages: 034503-1-034503-7, ISSN: 0021-8979
Magneto-inductive (MI) waveguides are metamaterial structures based on periodic arrangements of inductively coupled resonant magnetic elements. They are of interest for power transfer, communications and sensing, and can be realised in a flexible cable format. Signal-to-noise ratio is extremely important in applications involving signals. Here, we present the first experimental measurements of the noise performance of metamaterial cables. We focus on an application involving radiofrequency signal transmission in internal magnetic resonance imaging (MRI), where the subdivision of the metamaterial cable provides intrinsic patient safety. We consider MI cables suitable for use at 300 MHz during 1H MRI at 7 T, and find noise figures of 2.3–2.8 dB/m, together with losses of 3.0–3.9 dB/m, in good agreement with model calculations. These values are high compared to conventional cables, but become acceptable when (as here) the environment precludes the use of continuous conductors. To understand this behaviour, we present arguments for the fundamental performance limitations of these cables.
Syms RRA, Solymar L, 2014, Loss and thermal noise in plasmonic waveguides, Journal of Applied Physics, Vol: 115, ISSN: 1089-7550
Rytov’s theory of thermally generated radiation is used to find the noise in two-dimensionalpassive guides based on an arbitrary distribution of lossy isotropic dielectric. To simplifycalculations, the Maxwell curl equations are approximated using difference equations that alsopermit a transmission-line analogy, and material losses are assumed to be low enough for modallosses to be estimated using perturbation theory. It is shown that an effective mediumrepresentation of each mode is valid for both loss and noise and, hence, that a one-dimensionalmodel can be used to estimate the best achievable noise factor when a given mode is used in acommunications link. This model only requires knowledge of the real and imaginary parts of themodal dielectric constant. The former can be found by solving the lossless eigenvalue problem,while the latter can be estimated using perturbation theory. Because of their high loss, the theory ismost relevant to plasmonic waveguides, and its application is demonstrated using single interface,slab, and slot guide examples. The best noise performance is offered by the long-range plasmonsupported by the slab guide.
Segkhoonthod K, Syms RRA, Young IR, 2014, Design of magneto-inductive magnetic resonance imaging catheters, IEEE Sensors Journal, Vol: 14, Pages: 1505-1513, ISSN: 1530-437X
A catheter-based RF receiver for internal magnetic resonance imaging is described. The device consists of a double-sided thin-film circuit, mounted on a hollow catheter. The system was originally designed for biliary ductal imaging, but is also potentially useful for vascular imaging. Signals are detected using a resonant L-C circuit at the catheter tip, transmitted along the catheter using an array of coupled L-C resonators, and coupled into a conventional RF system using a demountable inductive transducer. Protection against external B1 and E fields is obtained by using figure-of-eight-shaped elements with an electrical length shorter than that of an immersed half-wave dipole. Electromagnetic modeling software (AWR Microwave Office) is used to analyze a system designed for 1 H imaging at 1.5T, determine the effect of the tissue surround, demonstrate signal detection and transmission and verify intrinsic safety.
Liu D, Syms RRA, 2014, NEMS by sidewall transfer lithography, Journal of Microelectromechanical Systems, Vol: 23, Pages: 1366-1373, ISSN: 1057-7157
A batch fabrication process for nanoelectromechanicalsystems (NEMS) based on sidewall transfer lithography(STL) is demonstrated. The STL is used to form nanoscaleflexible silicon suspensions entirely by conventional photolithography.A two-step process for combining microscale andnanoscale features is used to fabricate double-ended and singleendedelectrothermal actuators with a minimum feature width of100 nm and an aspect ratio of 40:1. All devices are fabricated bydeep reactive ion etching in 4.5-µm-thick silicon using bondedsilicon-on-insulator material. The process could allow low costfabrication of nanoscale sensors and actuators.
Wiltshire MCK, Syms RRA, 2014, Measuring trapped noise in metamaterials, Journal of Applied Physics, Vol: 115, ISSN: 1089-7550
Metamaterials constructed from conductive elements are lossy, and the structures act as sources ofnoise, whose spectrum is modified by the resonant nature of the medium itself. Furthermore, insidethe medium, the noise is present as waves, which are standing waves for finite length samples. Wepresent direct measurements of the noise spectra for a simple metamaterial comprising arrays ofLC resonator elements, and compare them with the predictions of a circuit model incorporatingJohnson noise. We find excellent agreement between the measured data and the model,reproducing both the resonant structure and the bandwidth of the noise spectrum, thus confirmingthe concept of noise waves in these metamaterials. These noise features match the frequencyranges where the metamaterial properties are useful, showing that noise is an inevitable companionto metamaterial performance in practical situations.
Syms R, Wadsworth C, Young IR, et al., 2014, MR endoscopy vs EUS: a comparison, ISMRM-ESMRMB Joint Annual Meeting
Mokhtar MHH, Syms RRA, 2014, OPTICAL FEEDBACK CONTROL OF RESONANT FIBRE SCANNERS, International Conference on Optical MEMS and Nanophotonics (OMN), Publisher: IEEE, Pages: 93-94, ISSN: 2160-5033
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Syms RRA, Young IR, Rea M, 2013, Frequency scaling of catheter-based magneto-inductive MR imaging detectors, Pages: 594-597
Frequency scaling rules are introduced for catheter-based magneto-inductive magnetic resonance imaging detectors, intended for in vivo imaging of the vascular and biliary ductal systems. The design is based on a cascade of magnetically coupled L-C resonators, fabricated as a thin-film circuit and mounted on a catheter. Intrinsic safety is introduced using resonant elements designed to avoid coupling to uniform RF magnetic and electric fields. Mapping of reception patterns and high-resolution 1H imaging are demonstrated in a 3 T clinical scanner. © 2013 IEEE.
Syms RRA, 2013, The development of MEMS mass spectrometers, Pages: 2749-2754
Lab-on-a-chip devices have had a major impact on analytical chemistry. Integration allowed manipulation of minute quantities of reagent, reduced dead volumes and minimised peak broadening. Integrated electrospray nozzles allowed analysis immediately after separation. By comparison, the effort devoted to mass spectrometers has been small. Although attempts were made to miniaturise most common filters, fabrication involves the formation of complex electrodes that generate precise electric fields. Consequently, mass resolution has been poor. High voltages also limited mass range, while poor sample introduction limited sensitivity. Consequently, little progress was made until recently in miniaturizing the electrospray mass spectrometer. These difficulties have been overcome. Greatly improved filters have been developed, vacuum interfaces have been constructed and bench-top ESI-MS is commercially available. This paper summarizes recent developments. © 2013 IEEE.
Syms RRA, Young IR, Wadsworth CA, et al., 2013, Magnetic Resonance Imaging Duodenoscope, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol: 60, Pages: 3458-3467, ISSN: 0018-9294
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- Citations: 7
Choonee K, Syms RRA, 2013, Folded dipole plasmonic resonators, OPTICS EXPRESS, Vol: 21, Pages: 25841-25850, ISSN: 1094-4087
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- Citations: 2
Syms RRA, Young IR, Ahmad MM, et al., 2013, Magneto-Inductive Catheter Receiver for Magnetic Resonance Imaging, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol: 60, Pages: 2421-2431, ISSN: 0018-9294
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- Citations: 16
Syms RRA, Sydoruk O, Solymar L, 2013, Noise in one-dimensional metamaterials supporting magnetoinductive lattice waves, PHYSICAL REVIEW B, Vol: 87, ISSN: 2469-9950
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- Citations: 7
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