Determination of blood glucose level is a frequently occurring procedure in diabetes care. As the most common method involves collecting blood drops for chemical analysis, it is invasive and liable to afflict a degree of pain and cause a skin injury. To eliminate these disadvantages, this thesis focuses on pulsed photoacoustic techniques, which have potential ability in non-invasive blood glucose

/pdf/pulsed-photoacoustic-techniques-and-glucose-determination-in-51acwfklpg.pdf

Pulsed Photoacoustic Techniques and Glucose Determination in Human Blood and Tissue

Optical detection of ultrasound has numerous advantages over traditional piezoelectric methods. These systems offer noncontact inspection, rapid scanning capabilities, fine spatial sampling, and large bandwidths. In addition, difficulties associated with conventional ultrasound imaging systems such as cross-talk between elements, electrical connections, and electromechanical resonances are greatly reduced or even eliminated. Because of this, high frequency phased arrays for ultrasound detection can be emulated by accurately positioning and focusing optical beams on a suitable surface, which defines array elements. However, optical systems have lower sensitivity than their piezoelectric counterparts, limiting their widespread use in ultrasound imaging. Active optical detection offers a solution. An active ultrasound detector consisting of a neodymium-doped glass waveguide laser with an optical demodulation system, was built demonstrating enhanced sensitivity while preserving the benefits of traditional passive optical detection.

High frequency ultrasound imaging using an active optical detector

Practical considerations for the rapid inspection of composite materials using laser-based ultrasound

This paper presents a comprehensive overview of Laser Ultrasonic Testing (LUT) and its applications in composite materials. The working principles of LUT are thoroughly explained, and an assessment of its advantages and drawbacks is provided. The mechanisms of wave generation and detection are described, along with their influence on the capabilities and limitations of LUT. The paper includes an inclusive overview of each LUT application in composite materials, highlighting their potential, challenges, and research gaps. LUT is a noncontact and nondestructive technique that utilizes lasers to generate and detect ultrasonic waves, with the material itself acting as an emitting transducer. This unique noncontact approach offers an accurate, versatile, convenient, and rapid method for inspecting and characterizing materials. However, some challenges and research gaps have hindered its widespread adoption. One significant challenge in LUT is the low signal-to-noise ratio (SNR), which becomes more pronounced in composite materials due to their low ablation threshold and high wave attenuation. Furthermore, the characterization and inspection of composite materials are more intricate due to their anisotropy and complex damage patterns. Despite these challenges, the combination of ultrasonic waves capable of characterizing and inspecting materials, coupled with the capabilities of lasers and optics for noncontact and real-time operation, presents a promising outlook for the widespread implementation of LUT in Smart Industries and harsh industrial environments, including those with high temperatures, high pressures, or radioactive conditions. This paper contributes to the understanding of LUT's potential and limitations, paving the way for further advancements in its applications. 

Laser Ultrasonics for Nondestructive Testing of Composite Materials and Structures: A Review

Knowledge of the permeability tensor in liquid composite molding is important for process optimization. Unfortunately, experimental determination of permeability is difficult and time consuming. Numerical calculation of permeability from a model reinforcement can circumvent experimentation. However, permeability predictions often rely on a model reinforcement that does not accurately mimic the actual microstructure. A rapid, nondestructive technique called optical coherence tomography (OCT) can image the microstructure of a composite in minutes. Actual microstructural information can be then used to improve the accuracy of the model and therefore the predicted permeability. Additionally, the influence on fiber volume fraction and microstructural variability on permeability can be systematically studied.



In this work, binary images were generated from the low contrast OCT data through image de-noising, contrast enhancement and feature recognition. The resulting data were input to a lattice-Boltzmann model for permeability prediction. The influence of the fiber volume fraction, tow surface area, average mean free channel path, and variable microstructure are discussed in terms of their individual and synergistic effects on permeability. The calculated axial and transverse permeabilities from the images show very good agreement with the experimental values.

/pdf/the-prediction-of-permeability-for-an-epoxy-e-glass-33v56m1h2u.pdf

The prediction of permeability for an epoxy/E-glass composite using optical coherence tomographic images

To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Perot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of signals derived from optical back reflection, and optical transmission, through the interferometer. Theoretical analysis and experimental results have demonstrated that the new scheme has a higher sensitivity than those described previously. Sensitivity enhancements between 2 and 17 times can be expected. Depending on mirror reflectivity, the frequency response is approximately flat in the range of 10 MHz and above, limited only by the free spectral range of the interferometer device.

https://iopscience.iop.org/article/10.1088/0957-0233/6/7/010/pdf

A conjugate optical confocal Fabry-Perot interferometer for enhanced ultrasound detection

A non-contact scanning system is described which is capable of producing two-dimensional ultrasonic images of defects in opaque materials. Lasers are used both for generation and detection of ultrasound. Short-duration high-power ( approximately 2 MW) laser pulses are used to generate ultrasound on the surface of a sample. Such ultrasound in the form of steps or pulses propagates through the sample and after interaction with defects are monitored by a 50 cm confocal Fabry-Perot interferometer. The interferometer uses back-scattered laser light from the sample's surface, which can be diffuse in nature. System sensitivity is sufficient for applications on optically rough surfaces. Two-dimensional scans have been performed, leading to computer-generated images of artificial defects in aluminium.

A non-contact scanning system for laser ultrasonic defect imaging

A non-contacting laser ultrasound system has been developed to visualize laminar defects in carbon fiber composite materials. Laser-generated ultrasound (LGU) was produced from a Nd:YAG Q-switched laser. Ultrasound was detected with the use of an actively stabilized Fabry-Perot interferometer using a 400 mW argon-ion laser source. It detected ultrasound in a typical frequency range of 1 to 10 MHz. Through-transmission C-scan measurements were made in carbon fiber composite materials of thickness 1 to 20 mm. Peak-to-peak amplitudes of the first longitudinal ultrasonic pulse were measured, with attenuation used as the basis of defect examination. Digital filtering was adopted to enhance defect visibility. Results showed that images with size resolution better than 1 mm can be achieved. Such measurements take into account any variation of surface reflectivity which can arise in industrial materials.

Defect visualization in carbon fiber composite using laser ultrasound

Through-transmission ultrasonic imaging of sub-surface defects using non-contact laser techniques

The invention provides a non-destructive test (NDT) method and apparatus for remote detection of ultrasound, particularly from industrial rough surfaces. The technique enables the measurement of ultrasonic velocity, in-plane and out-of-plane ultrasonic displacements within Lamb wave frequencies. The technique is particularly applicable to chemical and nuclear industry process pipes and the like. The system provides high light gathering power, similicity in alignment, vibration tolerance, fibre compatibility and is suitable for use in hazardous environments, giving it particular relevance to NDT in the chemical and nuclear industry. The technique provides a method of investigating an item, the method comprising the steps of: generating ultrasound waves in the item; generating a first laser beam, forming a first probe beam and a first reference beam from the first laser beam, applying the first probe beam to a location on the item to generate a first return beam; applying the first reference beam and the first return beam to first detection means; generating a second laser beam, forming a second probe beam and a second reference beam from the second laser beam, applying the second probe beam to a location on the item to generate a second return beam; applying the second reference beam and second return beam to second detection means; analysing the output of the first and second detector means. The technique can also be implemented using a single probe beam to produce a first and second return beam and first and second reference beams.

Improvements in and relating to inspection

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