Imperial College London

DrMunirAhmad

Faculty of EngineeringDepartment of Electrical and Electronic Engineering

Research Fellow
 
 
 
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Contact

 

+44 (0)20 7594 6260m.m.ahmad

 
 
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Location

 

707Electrical EngineeringSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

64 results found

Watts C, Hanham S, Armstrong J, Ahmad M, Stevens M, Klein Net al., 2020, Microwave dielectric sensing of free-flowing, single, living cells in aqueous suspension, IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, Vol: 4, Pages: 97-208, ISSN: 2469-7249

Dielectric measurements offer the possibility of highly sensitive detection of physical cell properties, and are of interest for clinical applications due to their non-destructive nature and the lack of need for cell labelling. Here we report sensitive measurements on single, living, free-flowing cells (not electrostatically or dielectrophoretically trapped, cultured or fixed directly on sensing elements) in aqueous medium at ~9.8 GHz taken using a coupled dielectric-split ring resonator assembly. Inductive coupling between the two resonators enabled separation of microfluidic chips from RF connectors and allowed for time-resolved continuous-wave measurements on flowing single cells via the coaxial ports of a dielectric-loaded microwave cavity. Analysis via an equivalent circuit model showed that the novel resonator assembly maintained the permittivity-dependent sensitivity of a split ring resonator while operating at quality factors >1000 with lossy aqueous media (typically ~1900). Using a microfluidic channel with a 300 x 300 μm cross section, at a water-loaded resonant amplitude of ~-22 dB at 0 dBm input power level, shifts in amplitude due to individual cells passing through the sensing region of up to -0.0015 dB were observed. Correlations between averaged amplitude shifts and cell size as well as material properties demonstrate the diagnostic potential of this technique.

Journal article

Hanham S, Watts C, Ahmad M, Otter W, Lucyszyn S, Klein Net al., 2019, Photonic crystal resonators as bio-liquid sensing platforms in the terahertz band, META 2019

We describethe development of high quality(Q)factor photonic crystal resonators(PCRs)integrated with microfluidic systems to formthe basis ofhighly sensitive liquid sensing platformsforthe terahertz band.The strong confinement of the terahertz fieldincombinationwith the high Q-factor provided bythe PCR allows the measurement of thedielectric properties of sub-nanoliter liquid volumes. We demonstrate the utility of thisapproach by measuring the complex permittivity of several bio-liquids at 100 GHz.

Conference paper

Hanham S, Watts C, Ahmad M, Otter W, Lucyszyn S, Klein Net al., 2018, Photonic crystal resonators for terahertz sensing applications, Progress in Electromagnetics Research Symposium, Publisher: IEICE, Pages: 803-803

Conference paper

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.

Journal article

Hanham SM, Ahmad MM, Lucyszyn S, klein Net al., 2017, LED-switchable High-Q Packaged THz Microbeam Resonators, IEEE Transactions on Terahertz Science and Technology, Vol: 7, Pages: 199-208, ISSN: 2156-342X

This paper describes the design, fabrication and experimental characterization of photonic crystal microbeam cavity resonators for the terahertz band implemented using suspended dielectric rectangular waveguide (DRW) in high resistivity silicon. Electrical quality factors of up to 11,900, combined with small modal volumes of 0.28 mm3 and 0.077 mm3, are demonstrated for devices operating at 100 and 200 GHz, respectively. The devices are found to be extremely light-sensitive, opening up new opportunities for light-controlled switching devices at terahertz frequencies. It is shown that the quality factor of the resonator can be tuned and the resonance extinguished through photo-illumination with an infrared light-emitting diode (IR LED). Additionally, the questions of thermal tunability and thermal stability of the resonators are examined. The demonstrated resonators are inherently suited to integration with DRW and by silicon bulk micromachining represent an attractive approach for realizing microphotonic integrated circuits for terahertz systems-on-a-substrate.

Journal article

Watts C, Hanham SM, Ahmad MM, Adabi M, Klein Net al., 2017, Coupled Dielectric-Split Ring Microwave Resonatorfor Liquid Measurements in Microfluidic Channels atNanoliter Volumes, European Microwave Conference, Publisher: IEEE

A microwave dielectric resonator based sensor system has been investigated with respect to its sensitivity for the assessment of aqueous liquids. The system exploits the field enhancement of a split ring structure while retaining high and tunable quality factors due to weak and adjustable coupling between a planar split-ring and a dielectric resonator. The proposed sensor with integrated microfluidic channel allows investigation of volumes of liquids less than 1 nL and is capable of detecting small changes in relative permittivity, as demonstrated by measurements of water-ethanol solutions.

Conference paper

Klein N, Watts C, Hanham SM, Otter WJ, Ahmad MM, Lucyszyn Set al., 2016, Microwave-to-terahertz dielectric resonators for liquid sensing in microfluidic systems, Conference on Terahertz Emitters, Receivers, and Applications VII, Publisher: Society of Photo-optical Instrumentation Engineer, ISSN: 0277-786X

The microwave-to-terahertz frequency range offers unique opportunities for the sensing of liquids based on the degree of molecular orientational and electronic polarization, Debye relaxation due to intermolecular forces between (semi-)polar molecules and collective vibrational modes within complex molecules. Methods for the fast dielectric characterization of (sub-)nanolitre volumes of mostly aqueous liquids and biological cell suspensions are discussed, with emphasis on labon- chip approaches aimed towards single-cell detection and label-free flow cytometry at microwave-to-terahertz frequencies. Among the most promising approaches, photonic crystal defect cavities made from high-resistivity silicon are compared with metallic split-ring resonant systems and high quality factor (Q-factor) whispering gallery-type resonances in dielectric resonators. Applications range from accurate haemoglobin measurements on nanolitre samples to label-free detection of circulating tumor cells. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Conference paper

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

Conference paper

Syms RRA, Young IR, Ahmad MM, Taylor-Robinson SD, Rea Met al., 2013, Magneto-Inductive Catheter Receiver for Magnetic Resonance Imaging, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol: 60, Pages: 2421-2431, ISSN: 0018-9294

Journal article

Syms RRA, Young IR, Ahmad MM, Taylor-Robinson SD, Rea Met al., 2013, Endoscopically Compatible MR-safe Magneto-inductive Imaging Catheter, 2013 7TH INTERNATIONAL CONGRESS ON ADVANCED ELECTROMAGNETIC MATERIALS IN MICROWAVES AND OPTICS (METAMATERIALS 2013), Pages: 25-27

Journal article

Fobelets K, Ahmad MM, Roumyantsev S, Shur Met al., 2013, Influence of ambient on conductivity and 1/f noise in Si nanowire arrays, ICNF International Conference on Noise and Fluctuations

Conference paper

Syms RRA, Young IR, Ahmad MM, Rea Met al., 2012, Magnetic resonance imaging using linear magneto-inductive waveguides, JOURNAL OF APPLIED PHYSICS, Vol: 112, ISSN: 0021-8979

Journal article

Syms RRA, Taylor-Robinson S, Ahmad MM, Young IRet al., 2012, Radiofrequency Detector Coils

A resonant radiofrequency (RF) detector assembly comprising a substrate, a coil formed on a front surface of the substrate, and two capacitors, each capacitor having a front plate which is formed on the front surface of the substrate and a rear plate formed on a rear surface of the substrate, the two front plates each being electrically connected to a different end of the coil, and the two rear plates being electrically connected to each other.

Patent

Koellensperger PA, Karl WJ, Ahmad MM, Pike WT, Green Met al., 2012, Patterning of platinum (Pt) thin films by chemical wet etching in Aqua Regia, JOURNAL OF MICROMECHANICS AND MICROENGINEERING, Vol: 22, ISSN: 0960-1317

Journal article

Syms RR, Young IR, Ahmad MM, Rea M, Wadsworth CA, Taylor-Robinson SDet al., 2010, Thin-film detector system for internal magnetic resonance imaging, Sensors and Actuators A:Physical, Vol: 163, Pages: 15-24, ISSN: 0924-4247

Journal article

Wadsworth CA, Young IR, Rea M, Ahmad MM, Khorsandi SE, Davidson B, Khan S, Taylor-Robinson SD, Syms RRet al., 2009, A CATHETER-MOUNTED MAGNETIC RESONANCE DETECTOR COIL FOR BILIARY IMAGING: FIRST EX VIVO HUMAN HEPATOBILIARY IMAGES, 60th Annual Meeting of the American-Association-for-the-Study-of-Liver-Diseases, Publisher: JOHN WILEY & SONS INC, Pages: 740A-741A, ISSN: 0270-9139

Conference paper

Choonee K, Syms RRA, Ahmad MM, Zou Het al., 2009, Post processing of microstructures by PDMS spray deposition, SENSORS AND ACTUATORS A-PHYSICAL, Vol: 155, Pages: 253-262, ISSN: 0924-4247

Journal article

Ahmad MM, Syms RA, Young IR, Mathew B, Casperz W, Taylor-Robinson SD, Wadsworth CA, Gedroyc WMet al., 2009, Catheter-based flexible microcoil RF detectors for internal magnetic resonance imaging., Publisher: IOP Publishing, Pages: 1-10

Conference paper

Howe FA, Syms RRA, Ahmad MM, Rodrigues LM, Griffiths JR, Young IRet al., 2009, In Vivo (31)P Magnetic Resonance Spectroscopy Using a Needle Microcoil, MAGNETIC RESONANCE IN MEDICINE, Vol: 61, Pages: 1238-1241, ISSN: 0740-3194

Journal article

Wadsworth CA, Syms RRA, Khan SA, Dickinson RJ, Gedroyc WMW, Thursz MR, Ahmad MM, Awan SA, Caspersz W, Taylor-Robinson SD, Young IRet al., 2009, A CATHETER-MOUNTED MAGNETIC RESONANCE DETECTOR COIL FOR BILIARY IMAGING: FIRST IN VITRO BILIARY IMAGES, Annual Meeting of the British-Society-of-Gastroenterology, Publisher: B M J PUBLISHING GROUP, Pages: A147-A147, ISSN: 0017-5749

Conference paper

Li Y, Ahmad MM, Hand JW, Syms RRA, Gilderdale D, Collins DJ, Young IRet al., 2007, Microcoils on structured silicon substrates for magnetic resonance detection, IEEE SENSORS JOURNAL, Vol: 7, Pages: 1362-1369, ISSN: 1530-437X

Journal article

Syms RRA, Ahmad MM, Young IR, Gilderdale DJ, Collins DJet al., 2006, Microengineered needle micro-coils for magnetic resonance spectroscopy, JOURNAL OF MICROMECHANICS AND MICROENGINEERING, Vol: 16, Pages: 2755-2764, ISSN: 0960-1317

Journal article

Syms, R R A, Ahmad M M, Young I R, Gilderdale D, Collins D Jet al., 2006, Microengineered needle micro-coils for magnetic resonance spectroscopy, Journal of Micromechanics and Microengineering, Vol: 16, Pages: 2755-2764

Journal article

Larsson MP, Ahmad MM, 2006, Improved polymer–glass adhesion through micro-mechanical interlocking, Journal of Micromechanics and Microengineering, Vol: 16, Pages: S161-S168

Journal article

Fobelets K, Vincent B, Christofi A, Ahmad M M, McPhail D S, Zhang Jet al., 2006, Visualisation of Ge condensation in SOI

Conference paper

Syms RRA, Ahmad MM, Young IR, Gilderdale D, Collins DJ, Leach MOet al., 2006, Needle microcoils for MRS, 19th IEEE Conf. on Microelectromechanical Systems (MEMS' 06), 22 - 26 January 2006, Istanbul, Turkey, Publisher: IEEE

Conference paper

Syms RRA, Ahmad MM, Young IR, Gilderdale D, Collins DJ, Leach MOet al., 2006, Needle microcoils for MRS, 19th IEEE Conf. on Microelectromechanical Systems (MEMS' 06), 22 - 26 January 2006, Istanbul, Turkey, Publisher: IEEE

Conference paper

Howe FA, Griffiths JR, Rodrigues L, Syms RRA, Ahmad MM, Young IRet al., 2006, 31P spectroscopy using a silicon-based needle coil, 14th Scientific Meeting of the International Society for Magnetic resonance in Medicine (ISMRM '06)

Conference paper

Syms RRA, Ahmad MM, Young IR, Gilderdale D, Collins DJ, Leach MOet al., 2005, Batch fabrication of micro-coils for MR spectroscopy on silicon, 4th IEEE International Conference on Sensors, 31 October - 1 November 2005, Irvine, CA, Pages: 227-230

Conference paper

Syms RRA, Ahmad MM, Young IR, Gilderdale D, Collins DJ, Leach MOet al., 2005, Batch fabrication of micro-coils for MR spectroscopy on silicon, 4th IEEE International Conference on Sensors, 31 October - 1 November 2005, Irvine, CA, Pages: 227-230

Conference paper

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