Dr. Shihong Jiang Profile

Dr. Shihong Jiang

Research Fellow at University of Nottingham

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Proceedings Article | 4 March 2013 Paper

Seeing hidden colors with acoustically modulated laser speckle sensing

Terence Leung, Shihong Jiang

Proceedings Volume 8581, 85813E (2013) https://doi.org/10.1117/12.2004620

KEYWORDS: Speckle, Modulation, Reflectivity, Spectroscopy, Digital cameras, Speckle pattern, Laser scattering, Scattering, Near infrared, Sensors

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A technique based on acoustically modulated laser speckle has been demonstrated which can quantify and classify 25 colored papers, even when they are hidden 5 mm behind an opaque slab barrier with a thickness of 5 mm and a reduced scattering coefficient of 1.8 mm^-1. A small vibration at 200 Hz was induced on the colored paper by attaching it to the central diaphragm of a loudspeaker. Two He-Ne lasers (green at 543 nm and red at 633 nm) illuminated the slab surface sequentially. Although the slab blocked most of the incoming light, a small proportion of light penetrated through, interacted with the vibrating colored paper and backscattered, causing a time-varying speckle pattern on the slab surface. A consumer grade digital camera was used to capture the speckle pattern from which the speckle contrast difference was calculated and shown to be indicative of the color of the hidden object. Using the speckle contrast difference measured at 543 nm and 633 nm, the nearest neighbor classification algorithm was employed to classify the 25 hidden colors (formed by different percentages of base colors magenta and cyan), achieving an accuracy of 72%. This work has demonstrated that the acoustically modulated laser speckle technique can increase the sensitivity of spectroscopic measurements in a deeper region, which has the potential to be translated into clinical applications such as cerebral oxygenation measurement in which a superficial layer (skull) is present.

Proceedings Article | 17 February 2011 Paper

Optical measurement of sound using time-varying laser speckle patterns

Terence Leung, Shihong Jiang, Jeremy Hebden

Proceedings Volume 7896, 789623 (2011) https://doi.org/10.1117/12.874707

KEYWORDS: Speckle pattern, Speckle, CCD cameras, Optical testing, Brain, Modulation, Head, Digital micromirror devices, Sensors, Dielectrophoresis

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In this work, we introduce an optical technique to measure sound. The technique involves pointing a coherent pulsed laser beam on the surface of the measurement site and capturing the time-varying speckle patterns using a CCD camera. Sound manifests itself as vibrations on the surface which induce a periodic translation of the speckle pattern over time. Using a parallel speckle detection scheme, the dynamics of the time-varying speckle patterns can be captured and processed to produce spectral information of the sound. One potential clinical application is to measure pathological sounds from the brain as a screening test. We performed experiments to demonstrate the principle of the detection scheme using head phantoms. The results show that the detection scheme can measure the spectra of single frequency sounds between 100 and 2000 Hz. The detection scheme worked equally well in both a flat geometry and an anatomical head geometry. However, the current detection scheme is too slow for use in living biological tissues which has a decorrelation time of a few milliseconds. Further improvements have been suggested.

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