Kaifeng Dong

Using maximum spectrum of continuous wavelet transform for demodulation of an overlapped spectrum in a fiber Bragg grating sensor network.

The maximum spectrum of the continuous wavelet transform (MSCWT) is proposed to demodulate the central wavelengths for the overlapped spectrum in a serial fiber Bragg grating (FBG) sensing system. We describe the operation principle of the MSCWT method. Moreover, the influence of the interval gap between two FBG wavelengths, 3 dB bandwidths, and optical powers of the reflected spectra are discussed. The simulation and experimental results indicate that the MSCWT can resolve an overlapped spectrum and decode the central wavelength with high accuracy. More importantly, the proposed peak detection method can enhance the sensing capacity of a wavelength division multiplexing FBG sensor network.

Effect of Amorphous/Crystalline Material Doping on the Microstructure and Magnetic Properties of FePt Thin Films

The effects of various doping materials (amorphous phases: TiO2, SiO2, MgO, and C and crystalline phases: HfO2 and ZrO2) on the microstructure and magnetic properties of FePt thin films have been investigated. It is found that FePt films with amorphous doping materials especially MgO and C have better (001) texture and grain isolation than doping with crystalline materials. Nevertheless, doping with crystalline materials, FePt films were preferred to form columnar structures with a larger aspect ratio compared with semi-spherical grain shape for amorphous doping materials. Moreover, all the FePt-X films exhibit better perpendicular anisotropy except for FePt-ZrO2 films due to some FePt (200) textured films epitaxial grown directly on tetragonal (002) textured ZrO2. For crystalline materials doping, the (001) texture and perpendicular anisotropy could be improved by tuning crystalline oxide materials with appropriate lattice structure, which may offer a method for application in FePt in heat-assisted magnetic recording media.

Theoretical Analysis of a Microring Resonator Array with High Sensitivity and Large Dynamic Range Based on a Multi-Scale Technique

By using a multi-scale measurement technique, a high-sensitivity and large dynamic-range sensor array, which consisted of a single resonator and a series of cascaded resonators with a sensing ring and a reference ring, was modeled, and its transmission properties were investigated theoretically and numerically. We also set forth the principle of a multi-scale measurement technique based on the transmission spectrum of a resonator. This sensor array could have a nearly tenfold increase in sensitivity, and an improved dynamic range in an arrow wavelength range. The simulated results were in good agreement with the theoretical analysis.

Giant Magneto-Impedance (GMI) Effect in Single-Layer Soft Magnetic Film Under Stress

The stress-induced magnetic anisotropy can significantly affect giant magneto-impedance (GMI) effect of the soft magnetic film. This paper is devoted to the GMI effect of the single layer soft magnetic film implied without and with a stress. By simulating a physical model with MATLAB and COMSOL software, the impedance expression of the single layer soft magnetic film and the relation between external magnetic field and magnetic permeability are deduced. We observed that, without a stress, the sensitive region increased firstly and then decreased with the increasing of the excitation current frequency from 1 MHz to 200 MHz. While the film was subjected to the stress in the direction of the current with one end stressed, the stress on the film was gradually reduced from stressed end to free end. Also, the impedance change rate of the film changed when the stress was added, which is similar to the effect of adding a bias magnetic field on the film. More importantly, the addition of stress σ can induce the bias of the GMI measurement range and improve its sensitivity near zero magnetic fields. This may provide a new way for designing a GMI sensor with higher sensitivity and adjustable measurement range.

Control of Microstructure and Magnetic Properties of FePt Thin Films with TiN–MgO Intermediate Layer

The effects of TiN-MgO intermediate layer on the microstructure and magnetic properties of FePt-SiNx-C films were investigated. With doping MgO into TiN, three components were formed, including titanium dioxide, titanium nitride and titanium oxynitride. This caused the decrease of the surface energy and the increase of the interface energy, and further induced the promotion of island growth of FePt, thus the improvement of the isolation and the decrease of FePt grains. On the other hand, the decrease of surface energy and the forming of some titanium dioxide with doping MgO would accompany the deterioration of epitaxial growth and thus the deterioration of the perpendicular magnetic anisotropy of FePt films in a certain degree. By optimizing the concentration of TiN and MgO, the FePt-SiNx-C films with small grain size of 5.86±1.03 nm and good perpendicular anisotropy would be obtained.

A novel pressure sensor based on series-coupled double microring resonators with a simple beam

ABSTRACT We propose and analyse a novel optical pressure sensor based on series-coupled double microring resonators (SDMRRs) on a simple beam. The pressure applied on the sensor is measured through the change of the optical transmission spectrum at the output port. The optical transmission performances of the SDMRRs have been analysed and compared with the single and paralleled-coupled structures by the method of finite element analysis and numerical simulation. The simulation results showed that the stress sensitivity is 0.0225u2009kPa–1 and linear measurement range of the sensor is 30u2009kPa. Furthermore, the influence of the amplitude transmission coefficient, half round phase shift and microring radius on the sensitivity have been investigated to optimize the sensor performance. This proposed sensor can be used for the smaller pressure detection in automotive, aerospace, oil/logging equipment and other harsh environmental application.

Improvement of perpendicular anisotropy of columnar FePt-ZrO2-C films with FePt insert layer

The effects of various thicknesses of FePt insert layer on the microstructure and magnetic properties of FePt-ZrO2-C thin films have been investigated. It is found that with inserting 0.4 nm FePt films between the TiON intermediate layer and FePt-ZrO2-C layer, the perpendicular anisotropy indicated by Hc⊥/Hc//ratio would increase from 4 to 13.1, suggesting the perpendicular anisotropy could be improved a lot with using FePt insert layer. Simultaneously, the FePt grains of FePt-ZrO2-C thin films maintained columnar structure and the grain isolation could also be improved in a certain degree. With further increase of the FePt insert layer thickness, although the perpendicular anisotropy was still larger than that without FePt insert layer, the grain size of the FePt-ZrO2-C films would increase and the isolation would be deteriorated.

Simulation of stress effect on GMI in soft magnetic amorphous film

Soft magnetic amorphous film not only has the giant magneto-impedance (GMI) effect, but also significantly affected by stress-induced magnetic anisotropy[1].