Measurement of Heating Rates in a Microscopic Surface-Electrode Ion Trap

We report measurement of heating rates of 40 Ca＋ ions confined in our home-made microscopic surface-electrode trap by a Doppler recooling method. The ions are trapped with approximately 800 μm above the surface, and are subjected to heating due to various noises in the trap. There are 3-5 ions involved to measure the heating rates precisely and efficiently. We show the heating rates in variance with the number and the position of the ions as well as the radio-frequency power, which are helpful for understanding the trap imperfection.

Heat transfer enhancement in MOSFET mounted on different FR4 substrates by thermal transient measurement

Miniaturization of electronic package leads to high heat density and heat accumulation in electronics device, resulting in short life time and premature failure of the device. Junction temperature and thermal resistance are the critical parameters that determine the thermal management and reliability in electronics cooling. Metal oxide field effect transistor（MOSFET）is an important semiconductor device for light emitting diode-integrated circuit（LED IC） driver application, and thermal management in MOSFET is a major challenge. In this study, investigations on thermal performance of MOSFET are performed for evaluating the junction temperature and thermal resistance. Suitable modifications in FR4 substrates are proposed by introducing thermal vias and copper layer coating to improve the thermal performance of MOSFET. Experiments are conducted using thermal transient tester（T3ster） at 2.0 A input current and ambient temperature varying from25℃ to 75℃. The thermal parameters are measured for three proposed designs： FR4 with circular thermal vias, FR4 with single strip of copper layer and embedded vias, and FR4 with I-shaped copper layer, and compared with that of plain FR4 substrate. From the experimental results, FR4I-shaped shows promising results by 33.71% reduction in junction temperature and 54.19% reduction in thermal resistance. For elevated temperature, the relative increases in junction temperature and thermal resistance are lower for FR4I-shaped than those for other substrates considered. The introduction of thermal vias and copper layer plays a significant role in thermal performance.

AN AUTOMATIC HEAT FLUX-TEMPERATURE MEASURING SYSTEM AND ITS APPLICATION

An automatic heat flux-temperature measuring system can be used to measure local body heat flux, local skin temperature, body core temperature, and ambient temperature, as well as mean body heat flux, mean skin temperature, physiological shell thermal insulation and suit thermal insulation. This paper describes the measuring principle, hardware construction, software program and the application in thermal measurements on divers.

Sb_(2)Te_(3)/graphite nanocomposite: A comprehensive study of thermal conductivity

Thermoelectric performance largely depends on the reduction of lattice thermal conductivity(kL).The study of the thermal conductivity(k)of a Sb_(2)Te_(3)/graphite nanocomposite system demonstrates-40%reduction in kL with graphite incorporation.A plausible explanation of intrinsic low kL observed in Sb_(2)Te_(3) based system is presented by modeling experimental specific heat(Cp)data.Raman spectroscopy measurement combined to X-Ray diffraction data confirms the presence of graphite as separate phase in the composite sample.It is found that phonon scattering dominates heat transport mechanism in the nanostructured Sb_(2)Te_(3)/graphite composite.Large reduction in kL is accomplished by intensifying scattering rate of phonons via various sources.Graphite introduces effective scattering sources,i.e.,defects of different dimensionalities in synthesized nanocomposite sample.Furthermore,graphite mediates phonon-phonon coupling and enhances lattice anharmonicity,which causes an intrinsic scattering of phonons with all frequencies in the Sb_(2)Te_(3)/graphite nanocomposite sample.Dislocation density and phonon anharmonicity of the synthesized samples are estimated from in depth analysis of temperature dependent synchrotron powder diffraction and Raman spectroscopic data.kL value as low as 0.8 W m1 K1 at 300 K,achieved with graphite dispersion in Sb_(2)Te_(3) based composite system makes the present comprehensive study an interesting concept to be developed in thermoelectric materials.