Apparatus:
Samples were prepared with a heater film on one side and a thermometer setup
on the other. An oscillating voltage was applied to the heater and the
temperature fluctuations of the sample were measured. The samples were Gold Seal
3010 microscope slides of dimensions 7.62x2.54x0.1 cm, composed of soda lime
glass with a mass of 0.5 g. An aluminum film was evaporated onto the
heater side. We used a paper clip to mark of a line at the center of the film,
splitting the it into two sections. An Hewlett-Packard HP33102A function
generator provided a sinusoidal voltage at a frequency w
to one section of the heater, while the other section served as a temperature
reference. To the opposite side of the sample, two Minco Ni-Fe thermistors were
glued to the slide with thermal epoxy directly below each section of the heater.
The thermistors were connected in a Wheatstone bridge configuration, and the
potential difference across the bridge was amplified and measured by a Stanford
Research SR830 lock-in amplifier. The frequency reference for the lock-in
amplifier was provided by the HP33102A TTL output. The setup is represented
below in Fig. 1.
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Fig.1: Schematic of the experimental
setup. |
A sinusoidal voltage is applied to the heater at a frequency
w, the heat flux from the resistive heater occurs
at a frequency 2w, because power is
proportional to the square of the voltage, as illustrated in Fig. 2. Therefore
the lock-in amplifier is set in 2w mode.
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Fig. 2: Power and voltage frequency
relation. The frequency of the power dissipated by the heater is twice
as large as the frequency of the voltage applied to it. |
The entire setup was computer controlled. The
software would set the frequency and voltage of the heater and read data from
the SR830 via the GPIB interface, thus allowing automated measurements. We
measured the frequency response of the magnitude of the temperature oscillations
at different ambient temperatures between 77 K and room temperature.
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| Photo 1: The evaporator employed to apply the
aluminum heater film onto the samples. |
Photo 2: Microscope slides prepared with the
heater film. Note: the lines at the center of the sample delimiting two
sections. |
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| Photo 3: Instrumentation amplifier. The 4
connectors on the left are the voltage and power supply connections. The
connector on the right is the output. |
Photo 4: The SR830 lock-in amplifier. |
Last Updated:
05/13/2008
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