Biomedical subjects

Donghui Zhao

Publications and source records attributed to Donghui Zhao.

6 recordsLinked to original sources

PubMed2006

Dynamic two-axis curvature measurement using multicore fiber Bragg gratings interrogated by arrayed waveguide gratings.

We describe the use of arrayed waveguide gratings (AWGs) in the interrogation of fiber Bragg gratings (FBGs) for dynamic strain measurement. The ratiometric AWG output was calibrated in a static deflection experiment over a +/-200 microepsilon range. Dynamic strain measurement was demonstrated with a FBG in a conventional single-mode fiber mounted on the surface of a vibrating cantilever and on a piezoelectric actuator, giving a resolution of 0.5 microepsilon at 2.4 kHz. We present results of this technique extended to measure the dynamic differential strain between two FBG pairs within a multicore fiber. An arbitrary cantilever oscillation of the multicore fiber was determined from curvature measurements in two orthogonal axes at 1125 Hz with a resolution of 0.05 m(-1).

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PubMed2005

Strain and temperature sensitivity of a single-mode polymer optical fiber.

We have measured the optical phase sensitivity of fiber based on poly(methyl methacrylate) under near-single-mode conditions at 632.8 nm wavelength. The elongation sensitivity is 131 +/- 3 x 10(5) rad m(-1) and the temperature sensitivity is -212 +/- 26 rad m(-1) K(-1). These values are somewhat larger than those for silica fiber and are consistent with the values expected on the basis of the bulk polymer properties.

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PubMed2005

Transverse load and orientation measurement with multicore fiber Bragg gratings.

We demonstrate the sensitivity of Bragg gratings in a multicore fiber to transverse load. The Bragg peaks are split because of stress-induced birefringence, the magnitude of which depends upon the load and grating position relative to the load axis. Experiments show that a set of gratings in a four-core fiber can measure a load axis angle to +/- 5 degrees and a load magnitude to +/- 15 N m(-1) up to 2500 N m(-1). We consider alternative designs of multicore fiber for optimal load sensing and compare experimental and modeled data.

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PubMed2004

Bend sensors with direction recognition based on long-period gratings written in D-shaped fiber.

The curvature- or bend-sensing response of long-period gratings (LPGs) UV inscribed in D-shaped fiber has been investigated experimentally. Strong fiber-orientation dependence of the spectral response when such LPGs are subjected to bending at different directions has been observed and is shown to form the basis for a new class of single-device sensor with vector-sensing capability. Potential applications utilizing the linear response and unique bend-orientation characteristics of the devices are discussed.

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PubMed2004

Differential birefringence in Bragg gratings in multicore fiber under transverse stress.

We present experimental measurements of the peak splitting of the reflection spectra of fiber Bragg gratings as a result of birefringence induced by transverse loading of a multicore fiber. Measurements show that the splitting is a function of the applied load and the direction of the load relative to the azimuth of the fiber. A model for calculating the stress in the fiber that is due to an applied load is in good agreement with our experimental observations.

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PubMed2004

Use of dual-grating sensors formed by different types of fiber Bragg gratings for simultaneous temperature and strain measurements.

We report on a systematic investigation of the dependence of both temperature and strain sensitivities on the fiber Bragg grating type, including the well-known Type I, Type IIA, and a new type that we have designated Type IA, using both hydrogen-free and hydrogenated B/Ge codoped fibres. We have identified distinct sensitivity characteristics for each grating type, and we have used them to implement a novel dual-grating, dual-parameter sensor device. Three dual-grating sensing schemes with different combinations of grating type have been constructed and compared, and that of a Type IA-Type IIA combination exhibits the best performance, which is also superior to that of previously reported grating-based structures. The characteristics of the measurement errors in such dual-grating sensor systems is also presented in detail.

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