Ji Yan Dai

The Hong Kong Polytechnic University, Hong Kong, Hong Kong

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Publications (2)4.8 Total impact

  • Jun Ma · Wei Jin · Hoi Lut Ho · Ji Yan Dai
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    ABSTRACT: A miniature fiber-tip pressure sensor was built by using an extremely thin graphene film as the diaphragm. The graphene also acts as a light reflector, which, in conjunction with the reflection at the fiber end-air interface, forms a low finesse Fabry-Perot interferometer. The graphene based sensor demonstrated pressure sensitivity over 39.4 nm/kPa with a diaphragm diameter of 25 μm. The use of graphene as diaphragm material would allow highly sensitive and compact fiber-tip sensors.
    Optics Letters 07/2012; 37(13):2493-5. DOI:10.1364/OL.37.002493 · 3.29 Impact Factor
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    ABSTRACT: High-frequency (25 MHz) ultrasonic transducers with Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub>-BaTiO<sub>3</sub> (NBT-BT) lead-free piezoelectric single crystal as the active elements are fabricated and characterized. The impedance measurement reveals that the poled [001]-oriented NBT-BT single crystal exhibits a high thickness electromechanical coefficient k<sub>t</sub> of 0.52 and a low clamped dielectric constant of 80. The -6-dB bandwidth of the transducer is 46.16% and the insertion loss at the center frequency is -31.89 dB. The good performance of the transducer indicates that the NBT-BT single crystal would be a promising lead-free material for ultrasonic transducer applications.
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 12/2010; 57(11-57):2601 - 2604. DOI:10.1109/TUFFC.2010.1727 · 1.51 Impact Factor