We discuss a novel approach that would lead to the development of an ultrasonic optical force-fee... more We discuss a novel approach that would lead to the development of an ultrasonic optical force-feedback measurement microphone.
IEE Colloquium on Terahertz Technology and its Applications, 1997
It is now over two decades since the resonant tunnelling effect in semiconductor barrier structur... more It is now over two decades since the resonant tunnelling effect in semiconductor barrier structures was reported, and since then a considerable number of actual or potential applications of this principle as an active terahertz frequency device have emerged. The semiconductor double barrier structure acts as an energy filter which exhibits peaks in electron transmission and consequently in the current-voltage characteristic. The resonamt tunnel diode (rtd) characteristic displays a negative differential resistance (ndr) which implies that power may be extracted from the device when it is embedded into a suitable circuit. Furthermore, the rtd characteristics may be adjusted by judicious choices of the size and properties of the various semiconductor layers within the device leading to other applications such as mixers, multipliers and detectors. From the viewpoint of high frequency operation, the important issue is that these devices respond rapidly to changes in applied voltage; the upper frequency limit is set by the "RC" time constant (7rc) dominated by the contact resistance and device depletion capacitance. Considerable attention has been paid to the control of 7rc by appropriate choice of material system; for example, InAs exhibits a negative Schottky barrier which implies exceptionally low contact resistance leading to calculated maximum operating frequency,&, , values exceeding lTHz for a 2pm rtd. In practice, the highest recorded2 operating frequency for an rtd, 712GHz, was achieved in the InAs/AlSb material system which exploits the aforementioned ultralow contact resistance, and also talces advantage of a variety of subtle effects which favour tunnelling through the barrier in this staggered-bandgap material. Elementary considerations suggest that the maximum power obtainable from the device is a simple fraction (3/16) of the product [AI.Av] where AI and AV are the current and voltage range of the ndr region. AV may be improved for a given device structure by the insertion of a depletion region; to increase AI (the so-called peak-tovalley ratio) requires careful control of the growth process to reduce scattering effects and the implementation of material-design strategies (as noted above) which increase the device peak current. In practice, the value of maximum power deduced from this simple formula greatly exceeds actual output values; "typical" power levels3 drop from around 6OpW
Tenth International Conference on Optical Fibre Sensors, 1994
The potential of optical fibers in monitoring water uptake from plants is considered. Application... more The potential of optical fibers in monitoring water uptake from plants is considered. Applications include an optical potometers that monitors water uptake from individual roots, the detection of xylem cavitation using audio acoustic emission with an interferometric force feedback microphone, an optical displacement transducer that detects changes in leaf thickness in relation to leaf water potential, and the use of
Trends in Optical Fibre Metrology and Standards, 1995
A novel, dual plastic optical fibre amplitude modulating displacement transducer of improved sens... more A novel, dual plastic optical fibre amplitude modulating displacement transducer of improved sensitivity is presented. Results of different fibre optic configurations and the merits of cutting the fibres twice so as to improve coupling and make full use of the critical angle are shown.
... REFERENCES 1. Treen, AS & Cronin, NJ 1993, 18th International Conference on Infrared and ... more ... REFERENCES 1. Treen, AS & Cronin, NJ 1993, 18th International Conference on Infrared and Millimeter Waves eds. Birch, J. R & Parker, TJ, SPLE Vol 2104, Coichester, 470-471 2. Miles, R E., Steenson, DP, Pollard, It D., Chamberlain, JM & Henini, M. 1995, Inst. Phys. ...
The monitoring of water uptake in plants is becoming increasingly important. Optical sensors offe... more The monitoring of water uptake in plants is becoming increasingly important. Optical sensors offer considerable advantages over conventional methods and several sensors have been developed including an optical potometer that monitors water uptake from individual roots, the detection of xylem cavitation using audio acoustic emissions with an interferometric force feedback microphone, and an optical fiber displacement transducer that detects changes in leaf thickness in relation to leaf-water potential.
International Conference on Informatics in Control, Automation and Robotics, 2009
This paper investigates the roundoff noise effect in the digital controller on the closed-loop ou... more This paper investigates the roundoff noise effect in the digital controller on the closed-loop output for a discrete-time feedback control system. Based on a polynomial parametrization approach, a sparse controller structure is derived. The performance of the proposed structure is analyzed by deriving the corresponding expression of closed-loop roundoff noise gain and the problem of finding optimized sparse structures is solved. A numerical example is presented to illustrate the design procedure and the performance of the proposed structure compared with those of some existing well-known structures.
The first S-parameter measurements of micro-machined 100 μm high air-filled rectangular waveguide... more The first S-parameter measurements of micro-machined 100 μm high air-filled rectangular waveguides are reported, which have been performed at W-band using a specially designed test fixture connected to a standard vector network analyser. The ...
This paper presents a monolithically fabricated microelectromechanical piezoelectric cantilever b... more This paper presents a monolithically fabricated microelectromechanical piezoelectric cantilever beam with a T-shaped cross section capable of in-plane and out-of-plane displacements and sensing. High-aspect-ratio T-beams are achieved by direct micromachining of bulk lead zirconate titanate (PZT-4) via reactive ion etching of 65-$ muhbox {m} $-deep features. Electrodes deposited on the top and bottom web and flange regions of the T-shaped structure allow in-plane and out-of-plane motion actuation and ...
Proceedings of the 6th International Conference on Informatics in Control, Automation and Robotics, 2009
This paper investigates the roundoff noise effect in the digital controller on the closed-loop ou... more This paper investigates the roundoff noise effect in the digital controller on the closed-loop output for a discrete-time feedback control system. Based on a polynomial parametrization approach, a sparse controller structure is derived. The performance of the proposed structure is analyzed by deriving the corresponding expression of closed-loop roundoff noise gain and the problem of finding optimized sparse structures is solved. A numerical example is presented to illustrate the design procedure and the performance of the proposed structure compared with those of some existing well-known structures.
1Physics Department, University of Nottingham, Nottingham, NG7 2RD, UK. 2Dept. of Electronic and ... more 1Physics Department, University of Nottingham, Nottingham, NG7 2RD, UK. 2Dept. of Electronic and Elec. Eng., University of Leeds, Leeds, LS2 9JT, UK. 3Dept. of Cybernetics, University of Reading, Whiteknights, Reading, RG6 6AI.: UK. 4School of Physics, University of Bath, ...
A new type of horn antenna for operation at 1.6 THz, that can be fabricated monolithically with 1... more A new type of horn antenna for operation at 1.6 THz, that can be fabricated monolithically with 1=4-height micromachined waveguide, is described. Height limitations imposed by the micromachining process are overcome by removing a tapered slot in the upper surface of a scalar horn, allowing the E-plane fields to extend outside the confines of the metallic structure before radiation, with a consequent reduction in E-plane beamwidth. 1.6 THz radiation pattern measurements for different designs show that, while there is scope for further optimisation, 3 dB beamwidths of 24 and 17.5 in the E-and H-planes, respectively, can be achieved.
International Conference on Informatics in Control, Automation and Robotics, 2009
This paper investigates the roundoff noise effect in the digital controller on the closed-loop ou... more This paper investigates the roundoff noise effect in the digital controller on the closed-loop output for a discrete-time feedback control system. Based on a polynomial parametrization approach, a sparse controller structure is derived. The performance of the proposed structure is analyzed by deriving the corresponding expression of closed-loop roundoff noise gain and the problem of finding optimized sparse structures is solved. A numerical example is presented to illustrate the design procedure and the performance of the proposed structure compared with those of some existing well-known structures.
An optical tiltmeter has been developed. It comprises a force-feedback pendulum device in which b... more An optical tiltmeter has been developed. It comprises a force-feedback pendulum device in which both the sensing and feedback are by means of optical fibres, so that there are no external electrical connections. Optical fibres of two different types are used, polymer fibres to detect the angular error and glass fibre bundles to convey light power.
We discuss a novel approach that would lead to the development of an ultrasonic optical force-fee... more We discuss a novel approach that would lead to the development of an ultrasonic optical force-feedback measurement microphone.
IEE Colloquium on Terahertz Technology and its Applications, 1997
It is now over two decades since the resonant tunnelling effect in semiconductor barrier structur... more It is now over two decades since the resonant tunnelling effect in semiconductor barrier structures was reported, and since then a considerable number of actual or potential applications of this principle as an active terahertz frequency device have emerged. The semiconductor double barrier structure acts as an energy filter which exhibits peaks in electron transmission and consequently in the current-voltage characteristic. The resonamt tunnel diode (rtd) characteristic displays a negative differential resistance (ndr) which implies that power may be extracted from the device when it is embedded into a suitable circuit. Furthermore, the rtd characteristics may be adjusted by judicious choices of the size and properties of the various semiconductor layers within the device leading to other applications such as mixers, multipliers and detectors. From the viewpoint of high frequency operation, the important issue is that these devices respond rapidly to changes in applied voltage; the upper frequency limit is set by the "RC" time constant (7rc) dominated by the contact resistance and device depletion capacitance. Considerable attention has been paid to the control of 7rc by appropriate choice of material system; for example, InAs exhibits a negative Schottky barrier which implies exceptionally low contact resistance leading to calculated maximum operating frequency,&, , values exceeding lTHz for a 2pm rtd. In practice, the highest recorded2 operating frequency for an rtd, 712GHz, was achieved in the InAs/AlSb material system which exploits the aforementioned ultralow contact resistance, and also talces advantage of a variety of subtle effects which favour tunnelling through the barrier in this staggered-bandgap material. Elementary considerations suggest that the maximum power obtainable from the device is a simple fraction (3/16) of the product [AI.Av] where AI and AV are the current and voltage range of the ndr region. AV may be improved for a given device structure by the insertion of a depletion region; to increase AI (the so-called peak-tovalley ratio) requires careful control of the growth process to reduce scattering effects and the implementation of material-design strategies (as noted above) which increase the device peak current. In practice, the value of maximum power deduced from this simple formula greatly exceeds actual output values; "typical" power levels3 drop from around 6OpW
Tenth International Conference on Optical Fibre Sensors, 1994
The potential of optical fibers in monitoring water uptake from plants is considered. Application... more The potential of optical fibers in monitoring water uptake from plants is considered. Applications include an optical potometers that monitors water uptake from individual roots, the detection of xylem cavitation using audio acoustic emission with an interferometric force feedback microphone, an optical displacement transducer that detects changes in leaf thickness in relation to leaf water potential, and the use of
Trends in Optical Fibre Metrology and Standards, 1995
A novel, dual plastic optical fibre amplitude modulating displacement transducer of improved sens... more A novel, dual plastic optical fibre amplitude modulating displacement transducer of improved sensitivity is presented. Results of different fibre optic configurations and the merits of cutting the fibres twice so as to improve coupling and make full use of the critical angle are shown.
... REFERENCES 1. Treen, AS & Cronin, NJ 1993, 18th International Conference on Infrared and ... more ... REFERENCES 1. Treen, AS & Cronin, NJ 1993, 18th International Conference on Infrared and Millimeter Waves eds. Birch, J. R & Parker, TJ, SPLE Vol 2104, Coichester, 470-471 2. Miles, R E., Steenson, DP, Pollard, It D., Chamberlain, JM & Henini, M. 1995, Inst. Phys. ...
The monitoring of water uptake in plants is becoming increasingly important. Optical sensors offe... more The monitoring of water uptake in plants is becoming increasingly important. Optical sensors offer considerable advantages over conventional methods and several sensors have been developed including an optical potometer that monitors water uptake from individual roots, the detection of xylem cavitation using audio acoustic emissions with an interferometric force feedback microphone, and an optical fiber displacement transducer that detects changes in leaf thickness in relation to leaf-water potential.
International Conference on Informatics in Control, Automation and Robotics, 2009
This paper investigates the roundoff noise effect in the digital controller on the closed-loop ou... more This paper investigates the roundoff noise effect in the digital controller on the closed-loop output for a discrete-time feedback control system. Based on a polynomial parametrization approach, a sparse controller structure is derived. The performance of the proposed structure is analyzed by deriving the corresponding expression of closed-loop roundoff noise gain and the problem of finding optimized sparse structures is solved. A numerical example is presented to illustrate the design procedure and the performance of the proposed structure compared with those of some existing well-known structures.
The first S-parameter measurements of micro-machined 100 μm high air-filled rectangular waveguide... more The first S-parameter measurements of micro-machined 100 μm high air-filled rectangular waveguides are reported, which have been performed at W-band using a specially designed test fixture connected to a standard vector network analyser. The ...
This paper presents a monolithically fabricated microelectromechanical piezoelectric cantilever b... more This paper presents a monolithically fabricated microelectromechanical piezoelectric cantilever beam with a T-shaped cross section capable of in-plane and out-of-plane displacements and sensing. High-aspect-ratio T-beams are achieved by direct micromachining of bulk lead zirconate titanate (PZT-4) via reactive ion etching of 65-$ muhbox {m} $-deep features. Electrodes deposited on the top and bottom web and flange regions of the T-shaped structure allow in-plane and out-of-plane motion actuation and ...
Proceedings of the 6th International Conference on Informatics in Control, Automation and Robotics, 2009
This paper investigates the roundoff noise effect in the digital controller on the closed-loop ou... more This paper investigates the roundoff noise effect in the digital controller on the closed-loop output for a discrete-time feedback control system. Based on a polynomial parametrization approach, a sparse controller structure is derived. The performance of the proposed structure is analyzed by deriving the corresponding expression of closed-loop roundoff noise gain and the problem of finding optimized sparse structures is solved. A numerical example is presented to illustrate the design procedure and the performance of the proposed structure compared with those of some existing well-known structures.
1Physics Department, University of Nottingham, Nottingham, NG7 2RD, UK. 2Dept. of Electronic and ... more 1Physics Department, University of Nottingham, Nottingham, NG7 2RD, UK. 2Dept. of Electronic and Elec. Eng., University of Leeds, Leeds, LS2 9JT, UK. 3Dept. of Cybernetics, University of Reading, Whiteknights, Reading, RG6 6AI.: UK. 4School of Physics, University of Bath, ...
A new type of horn antenna for operation at 1.6 THz, that can be fabricated monolithically with 1... more A new type of horn antenna for operation at 1.6 THz, that can be fabricated monolithically with 1=4-height micromachined waveguide, is described. Height limitations imposed by the micromachining process are overcome by removing a tapered slot in the upper surface of a scalar horn, allowing the E-plane fields to extend outside the confines of the metallic structure before radiation, with a consequent reduction in E-plane beamwidth. 1.6 THz radiation pattern measurements for different designs show that, while there is scope for further optimisation, 3 dB beamwidths of 24 and 17.5 in the E-and H-planes, respectively, can be achieved.
International Conference on Informatics in Control, Automation and Robotics, 2009
This paper investigates the roundoff noise effect in the digital controller on the closed-loop ou... more This paper investigates the roundoff noise effect in the digital controller on the closed-loop output for a discrete-time feedback control system. Based on a polynomial parametrization approach, a sparse controller structure is derived. The performance of the proposed structure is analyzed by deriving the corresponding expression of closed-loop roundoff noise gain and the problem of finding optimized sparse structures is solved. A numerical example is presented to illustrate the design procedure and the performance of the proposed structure compared with those of some existing well-known structures.
An optical tiltmeter has been developed. It comprises a force-feedback pendulum device in which b... more An optical tiltmeter has been developed. It comprises a force-feedback pendulum device in which both the sensing and feedback are by means of optical fibres, so that there are no external electrical connections. Optical fibres of two different types are used, polymer fibres to detect the angular error and glass fibre bundles to convey light power.
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Papers by Lucas Karatzas