CMOS image sensors traditionally have used a pinned photodiode with a transfer gate to achieve low dark signal and noise. One drawback of the pinned photodiode is the inability to achieve good Modulation Transfer Function (MTF) as the sensor thickness is increased beyond epitaxial thicknesses greater than 10μm as required for higher red response. This is due to the pinned photodiode providing only a very small voltage to deplete the silicon, which results in significant lateral charge diffusion and poor resolution. The limitation in device thickness means that the QE at longer wavelengths (>600nm) is limited for conventional CMOS pixel technologies. A way to increase the depletion depth is to apply a back bias from the rear of the device, however if one were to do this on standard CMOS image sensors then there would be significant leakage current between the back bias and components on the device causing it to not function. A new patented DDE (Deep Depletion Extension) implant helps diode depletion regions to merge laterally creating a “pinch-off” and prevent leakage from in-pixel transistors. This enables epitaxial thickness of up to 50μm to be fully depleted with negligible leakage. The CIS220 is a new ESA GSTP funded derivative of the CIS120 Capella Space Imager platform which incorporates this patented HiRho back bias structure allowing full depletion of the sensor thickness. This paper will present initial results from back-thinned CIS220 devices with 17μm and 33μm thicknesses and will explore the effect of the back bias on electro-optical test results.

A dynamic fibre Bragg grating interrogation scheme is investigated using two-wave mixing in erbium-doped fibre, capable of adapting to quasistatic strain and temperature drifts. An interference pattern set up in the erbium-doped fibre creates, due to the photorefractive effect, a dynamic grating capable of wavelength demodulating the FBG signal. The presence of a dynamic grating was verified and then dynamic strain signals from a fibre stretcher were measured. The adaptive nature of the technique was successfully demonstrated by heating the FBG while it underwent dynamic straining leading to detection unlike an alternative arrayed waveguide grating system which simultaneously failed detection. Two gratings were then wavelength division multiplexed with the signal grating receiving approximately 30dB greater signal showing that there was little cross talk in the system.

Dynamic strain signals are important for many structural monitoring applications, but the high-speed interrogation of strain sensors based on fibre Bragg gratings (FBGs) remains a challenge. Arrayed waveguide grating (AWG) interrogation schemes have been proposed, and by using modelling and validation experiments several design considerations are investigated and their relationship to system performance indicators determined. The Bragg grating length has an impact on the ability of the grating to 'observe' the transient strain field, while the spectral widths of both the FBG and AWG influence the recovered strain resolution. The system performance was examined for both high frequency noise as well as the long-term drifts over an hour, with a strain resolution of 1.4 mu epsilon observed and drift of less than 3.1 mu epsilon h(-1). The noise dependence on the relative overlap of the AWG and FBG spectra was found to be significant and the inclusion of a semiconductor optical amplifier to boost light intensity at the detectors was found to significantly improve performance with an improvement in the signal-to-noise ratio up to 200%.

Structural Health Monitoring (SHM) techniques have been developed as a cost effective alternative to currently adopted Non-Destructive Testing (NDT) methods which have well understood levels of performance. Quantitative performance assessment, as used in NDT, needs to be applied to SHM techniques to establish their performance levels as a basis for technique comparison and also as a requirement for practical aerospace application according to set regulations. One such measurand is Probability of Detection (POD). This paper reports experiments conducted to investigate the location accuracy of the Acoustic Emission (AE) system in monitoring events from Hsu- Nielson and fatigue crack AE sources as a route to establish the POD of AE in SHM. It was found that fatigue crack tips could be located at 90% POD within 10 mm accuracy.

Aircraft that employ composites are prone to impact damage that can degrade structural performance and yet leave little visible sign. Manual inspection to detect such damage can be costly and time consuming. In this paper we investigate the use of damage detection sensors to discriminate between damaging and non-damaging impacts. In use it is likely that the impact magnitude and location will be unknown. To simulate this, a range of impact energies were performed at a varying distances from a piezoelectric acoustic sensor on composite panels. The sensor output was analysed to find distance invariant features that could be used to indicate whether an impact caused damage. In damaging impacts, a secondary signal burst, with amplitude significant when compared to the initial burst, was observed. An algorithm was produced to differentiate signals based on this feature which has the potential to contribute to a structural monitoring system and thus reduce the inspection burden ultimately leading to lower aircraft maintenance costs.

Minimizing the temporal jitter in ultrafast oscillator systems is key to successful pump-probe spectroscopy. Recently, synchronization between two independent oscillators has been applied to higher-energy, amplified systems and has achieved sub-200 fs synchronization between two amplifiers.

Damage detection systems for structural health monitoring have been successfully demonstrated in flight trials utilising a BAE Systems Hawk jet aircraft leased from the Royal Air Force. The trials were part of a joint European MoD project called AHMOS II.An integrated system comprising structural flight test specimens and a range of damage detection systems linked into a common hardware and software architecture was successfully operated during a series of flight tests in the summer of 2007. The experimental system was built into a specially engineered pod mounted on the wing inboard pylon. This paper describes the background to the experiment and gives results from one of the flight test systems that used AE during the flights to detect the presence and growth of cracks in a metallic flight test specimen. The system was able to detect crack growth against very high levels of background acoustic noise (estimated as greater than 135 dB) and electronic interference. The equipment functioned without fault for the duration of the flights which used the full flight envelope of the aircraft including high g-turns, air combat manoeuvres and aerobatics at altitudes up to nine kilometres and seven take-off and landing cycles.The trials demonstrated that the system could clearly distinguish between undamaged and damaged states in a specimen (essential if false calls are to be avoided) and that crack growth, subsequently verified by microscopic inspection, could be detected in flight.(1)

In this talk we will present an overview of recent development of ultrafast lasers sources and their applications. This talk will highlight some recent state of the art ultrafast pulse results from Ti:Sapphire and Ytterbium based laser systems. There are significant advantages in being able to directly diode pump Ytterbium materials resulting in more compact bulk solid state and fiber based laser systems. Several newly emerging technologies such as Optical Parametric Chirped Pulse Amplification, and Supercontinuum Generation have generated great excitement in recent years. The evolution of more compact and user friendly ultrafast laser systems has enabled completely new fields that take advantage of the extremely high peak powers and very short time duration of ultrafast laser pulses. Recent results in the fields of multiphoton microscopy, micromachining, 3-D fabrication, and spectroscopy will be discussed.

In this talk we first review the historical development of commercial mode-locked lasers based on titanium doped sapphire, including experimental and theoretical data highlighting the limits of these lasers, especially average output power and tuning range. Commercially available one-box systems are rapidly approaching these limits, with the latest systems offering an average power of more than 2.9W at 800nm, corresponding to more than 350kW peak power. In addition, systems are now becoming available with an extremely wide tuning range, extending from just under 700nm to over 1020nm, using only a single set of optics. These achievements enable further advancements of applications, such as micromachining, which require the highest peak power with increased throughput rates, and multi-photon microscopy where increased tunability and higher average power are of particular benefit. Some of the remaining challenges and the innovative techniques used to address them will also be discussed during the presentation.

We report on the latest advances at Spectra-Physics in tunability and average power for automated and manual Ti:Sapphire laser Sources that can be used for multiphoton rnicroscopy - the Mai Tai (R) HP and Tsunami (R) HP. We also present new performance data for a fully automated Optical Parametric Oscillator - the Opal (R) pumped using the automated Ti:Sapphire pump source - Mai Tai HP.

We describe the characterization of the temperature and strain responses of fiber Bragg grating sensors by use of an interferometric interrogation technique to provide an absolute measurement of the grating wavelength. The fiber Bragg grating temperature response was found to be nonlinear over the temperature range -70 degrees C to 80 degrees C. The nonlinearity was observed to be a quadratic function of temperature, arising from the linear dependence on temperature of the thermo-optic coefficient of silica glass over this range, and is in good agreement with a theoretical model.

Chapter 6 Structural Health Monitoring Evaluation Tests P. A. Lloyd, P. A. Lloyd DSTL, Room 1052 A2 Building, Farnborough, Hampshire GU14 0LX, UKSearch for more papers by this authorR. Pressland, R. Pressland A380 Landing Gear, Airbus UK, P.O. Box 77, Bristol BS99 7AR, UKSearch for more papers by this authorJ. McFeat, J. McFeat BAE SYSTEMS, Airframe Engineering, Military Aircraft, Warton Aerodrome W427C, Preston, Lancashire, PR4 1AX, UKSearch for more papers by this authorI. Read, I. Read Sowerby Research Centre, BAE SYSTEMS, FPC 267, PO Box 5, Filton, Bristol BS12 7QW, UKSearch for more papers by this authorP. Foote, P. Foote Sowerby Research Centre, BAE SYSTEMS, FPC 267, PO Box 5, Filton, Bristol BS12 7QW, UKSearch for more papers by this authorJ. P. Dupuis, J. P. Dupuis EADS, Corporate Research Centre, France, P.O. Box 76, 12 Rue Pasteur, 92152 Suresnes, FranceSearch for more papers by this authorE. O'Brien, E. O'Brien Experimental Stress Analysis, Airbus UK, P.O. Box 77, Bristol BS99 7AR, UKSearch for more papers by this authorL. Reithler, L. Reithler EADS, Corporate Research Centre, France, P.O. Box 76, 12 Rue Pasteur, 92152 Suresnes, FranceSearch for more papers by this authorS. Grondel, S. Grondel Institut D'Electronique et de Microélectronique du Nord (IEMN), Départment Opto-Acousto-Electronique, Université de Valenciennes, Le Mont Houy, Valenciennes Cedex F-59304, FranceSearch for more papers by this authorC. Delebarre, C. Delebarre Institut D'Electronique et de Microélectronique du Nord (IEMN), Départment Opto-Acousto-Electronique, Université de Valenciennes, Le Mont Houy, Valenciennes Cedex F-59304, FranceSearch for more papers by this authorK. Levin, K. Levin Structures Department, The Aeronautical Research Institute of Sweden (FOI/FFA), P.O. Box 11021, 172 90 Stockholm, SwedenSearch for more papers by this authorC. Boller, C. Boller Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UKSearch for more papers by this authorC. Biemans, C. Biemans DaimlerChrysler Sales Germany, Salzufer 6, 10587 Berlin, GermanySearch for more papers by this authorW. J. Staszewski, W. J. Staszewski Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UKSearch for more papers by this author P. A. Lloyd, P. A. Lloyd DSTL, Room 1052 A2 Building, Farnborough, Hampshire GU14 0LX, UKSearch for more papers by this authorR. Pressland, R. Pressland A380 Landing Gear, Airbus UK, P.O. Box 77, Bristol BS99 7AR, UKSearch for more papers by this authorJ. McFeat, J. McFeat BAE SYSTEMS, Airframe Engineering, Military Aircraft, Warton Aerodrome W427C, Preston, Lancashire, PR4 1AX, UKSearch for more papers by this authorI. Read, I. Read Sowerby Research Centre, BAE SYSTEMS, FPC 267, PO Box 5, Filton, Bristol BS12 7QW, UKSearch for more papers by this authorP. Foote, P. Foote Sowerby Research Centre, BAE SYSTEMS, FPC 267, PO Box 5, Filton, Bristol BS12 7QW, UKSearch for more papers by this authorJ. P. Dupuis, J. P. Dupuis EADS, Corporate Research Centre, France, P.O. Box 76, 12 Rue Pasteur, 92152 Suresnes, FranceSearch for more papers by this authorE. O'Brien, E. O'Brien Experimental Stress Analysis, Airbus UK, P.O. Box 77, Bristol BS99 7AR, UKSearch for more papers by this authorL. Reithler, L. Reithler EADS, Corporate Research Centre, France, P.O. Box 76, 12 Rue Pasteur, 92152 Suresnes, FranceSearch for more papers by this authorS. Grondel, S. Grondel Institut D'Electronique et de Microélectronique du Nord (IEMN), Départment Opto-Acousto-Electronique, Université de Valenciennes, Le Mont Houy, Valenciennes Cedex F-59304, FranceSearch for more papers by this authorC. Delebarre, C. Delebarre Institut D'Electronique et de Microélectronique du Nord (IEMN), Départment Opto-Acousto-Electronique, Université de Valenciennes, Le Mont Houy, Valenciennes Cedex F-59304, FranceSearch for more papers by this authorK. Levin, K. Levin Structures Department, The Aeronautical Research Institute of Sweden (FOI/FFA), P.O. Box 11021, 172 90 Stockholm, SwedenSearch for more papers by this authorC. Boller, C. Boller Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UKSearch for more papers by this authorC. Biemans, C. Biemans DaimlerChrysler Sales Germany, Salzufer 6, 10587 Berlin, GermanySearch for more papers by this authorW. J. Staszewski, W. J. Staszewski Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UKSearch for more papers by this author Book Editor(s):W. J. Staszewski, W. J. Staszewski Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UKSearch for more papers by this authorC. Boller, C. Boller Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UK Formerly with European Aeronautic Defence and Space Company – EADS, Munich, GermanySearch for more papers by this authorG. R. Tomlinson, G. R. Tomlinson Department of Mechanical Engineering, Sheffield University, Mappin Street, Sheffield S1 3JD, UKSearch for more papers by this author First published: 19 December 2003 https://doi.org/10.1002/0470092866.ch6 Formerly with European Aeronautic Defence and Space Company – EADS, Munich, Germany AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Large-scale Metallic Evaluator Large-scale Composite Evaluator Flight Tests Summary References Health Monitoring of Aerospace Structures: Smart Sensor Technologies and Signal Processing RelatedInformation