Leong Keey Seah

Cure monitoring of smart composites using Fiber Bragg Grating based embedded sensors

A sensor embedded in the composite laminate can act as a temperature transducer during the composite cure mechanism. Once the composite is cured, the same sensor can be used to provide the information about the mechanical changes that influence the performance of the material. Fiber Bragg Grating (FBG) sensor is one such sensor which one can use for the composite cure monitoring. We present here the results obtained with an associated FBG sensor system for the cure monitoring of smart composites. The performance of the embedded FBG sensor smart composite specimens under 3- and 4-point bending conditions are also being investigated. Finally, the performance analysis has been extended to cantilever specimens.

Formulation and implementation of a phase-resolved fluorescence technique for latent-fingerprint imaging: theoretical and experimental analysis

A theoretical and experimental study of the imaging of latent fingerprints by a phase-resolved fluorescence technique along with associated signal-processing analysis is described. The system configuration is optimized by incorporation of a novel approach of homodyne-assisted even-step phase shifting in a signal-processing concept. The excitation laser source and gain of the detection device, which are modulated at megahertz frequency followed by sensitive signal-processing concepts, are employed to separate the fingerprint fluorescence from background fluorescence. Experiments are carried out with fingerprints deposited upon different types of substrate surfaces. Later, a quantitative image-quality assessment is carried out, which confirms the improvement in the quality of the phase-resolved fingerprint image. Imaging of older fingerprints with better contrast is also carried out with the proposed novel technique.

An all fiber optic system modeling for the gastrointestinal endoscopy: design concepts and fluorescent analysis

A theoretical model, which describes both the spatial distributions of photons in fluorescence endoscopic images for the detection of abnormalities/defects in the intracavities of human body, specifically gastrointestinal path is presented. The design concept of the image probe, which was developed for collecting the low fluorescent emission using an excitation laser source and the imaging done through an image fiber bundle, are discussed here. A band-pass/neutral density filter combination was used to separate the fluorescence emission from the normal coherent background induced by the laser. Finally, a quantitative analysis done by varying the different parameters affecting the tissue fluorescence is discussed in this paper.

Homodyne and heterodyne signal processing assisted phase resolved optical technique for latent fingerprint imaging: a theoretical study

A general theory for phase-resolved fingerprint imaging and background suppression based on laser-induced fluorescence is developed and presented in this paper. Novel approaches of incorporating an even-step phase shifting method with a homodyne-assisted phase-resolved method as well as the camera exposure control approach for the heterodyne-assisted phase-resolved method are proposed, theoretically formulated and discussed. Theoretical results imply that the fluorescence from latent fingerprints can be extracted effectively, irrespective of whether its lifetime is longer than that of the background or not. Furthermore, it is shown that there exists an optimum modulation frequency, which is dependent on the fluorescence lifetimes of both the background and the fingerprint, to obtain a fingerprint image with better contrast.

An efficient phase analysis-based wavenumber linearization scheme for swept source optical coherence tomography systems

This letter reports an efficient phase analysis-based direct time domain resampling scheme for swept source-based optical coherence tomography (SS-OCT) systems. The unwrapped phase values, representing non-linear frequency sweeping of the laser, are extracted from the calibration signal generated by a Mach?Zehnder interferometer. Equidistant wavenumber spaces are calculated by normalizing obtained phase values followed by scaling to the maximum number of sampling points. The non-uniform fractional time index values corresponding to the uniformly distributed phase values are computed directly from the linearizer coordinates in order to eliminate the use of the polynomial fitting approach that is used in existing phase-based time domain resampling methods. This proposed linearization scheme shows a significant improvement in performance in terms of accuracy and speed in comparison with the major existing schemes. The robustness of the algorithm, as well as its impact on the resolution and sensitivity, are illustrated using an in-house-developed SS-OCT system and by performing imaging of a human finger nail and an eye model as test samples.

Theoretical analysis of phase-resolved fluorescence emission from fingerprint samples

Basic theory for the detection and imaging of latent fingerprints using phase-resolved optical method is described. In this work, extraction of single fluorescence emission from fingerprint samples deposited on non-fluorescing substrate is described. Also, the significance of incorporating the heterodyne concept in the signal-processing scheme in the formulated theoretical model is explained.

The accuracy of some codes of practice in predicting the load capacity of cold-formed columns

Abstract The accuracy of existing codes of practice for the design of cold formed steel sections, namely, from AISI [American Iron and Steel Institute. The Specification for the Design of Cold-formed Steel Structural Members (Aug. 1986)], BS (British Standards Institution. BS5950: Part 5—Structural Use of Steelwork in Building. Code of Practice for Design of Cold Formed Sections (1987).] and EUR [European Convention for Constructional Steelwork, ECCS. European Recommendations for the Design of Light Gauge Steel Members. Design of Cold Formed Steel Sheeting and Sections (1987).] is examined. Selected experimental results (ultimate load capacity) on columns with different cross-sections were used to compare with the predictions by the codes of practice. Results show that the accuracy of all the codes of practice examined varies from section to section. Some recommendations and proposed modifications to the codes were also made.

Electronically tunable external-cavity laser diode using a liquid crystal deflector

A novel external-cavity wavelength tunable laser based on a liquid crystal (LC) deflector is proposed. This device consists of a gain chip, collimating lens, LC deflector, and diffraction grating. By controlling the voltage applied to the LC deflector, a maximum wavelength variation of 12 nm and a sidemode suppression ratio higher than 30 dB are obtained

Measurement of interlaminar fracture properties of composites using the J-integral method:

This study explored the use of J-integral approach for characterizing mode I, mode II and mixed-mode I/II interlaminar fracture toughness of composites materials. Delamination tests were conducted to measure the fracture toughness and the resistance curve (R-curve) for double cantilever beam, end-notched flexure and mixed-mode bending specimens. The J-integral approach and the well-established ASTM standard methods based on LEFM were compared in this work. The results obtained from both methods are in very good agreement. However, the J-integral method has the advantages of being applicable to materials with large fracture process zone (e.g., composites with fiber bridging) and provides a simpler experimental procedure with fewer inputs. More importantly, the presented method avoids the ambiguity in visual measurements of delamination length required by the ASTM standard methods. In this study, an image-processing program based on Hough transform was developed to obtain the rotation angles of the specimen. The method provides good accuracy and has lower requirements for image resolution, light and material surface compared to previous methods.

Gold nanorods with higher aspect ratio as potential contrast agent in optical coherence tomography and for photothermal applications around 1300 nm imaging window

Over the past few years, plasmon-resonant nanorods of gold (AuNRs) have been used as the contrast agent in optical imaging and for photothermal applications. However, most of these studies were limited to AuNRs whose spectral peaks fall below 1000 nm. Recently, optical coherence tomography (OCT) imaging around 1300 nm has become one of the niche research areas due to its potential for many diagnostics imaging applications. In this paper, we have investigated plasmon-resonant AuNRs with higher aspect ratio as a potential contrast agent in OCT and for photothermal applications around the 1300 nm window. The AuNRs with an aspect ratio of 8.8, and longitudinal plasmon-resonance peak at 1320 nm have been used for the study. The AuNR used in the study has an average dimension of 88 nm (length) × 10 nm (diameter), and an effective size (R eff) of 11.8 nm. The optical extinction of plasmon-resonant AuNRs has been characterized by OCT using a new cross-correlation approach. The extinction cross-section estimated using the OCT method is in good agreement with the values obtained via finite difference time domain-method and UV–vis–NIR spectroscopy. Both the simulation and phantom based experimental studies have shown that AuNRs exhibit a large absorption to scattering cross-section ratio, making them ideal for absorption based contrast enhancement in OCT imaging around 1300 nm. Ex vivo studies on the pig adipose tissue also illustrate the efficiency of AuNRs with identified aspect ratio as a potential photothermal agent around 1300 nm.