Volume 78, Issue 10, October 2007
Index of content:
- THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL AND PHOTOACOUSTIC
78(2007); http://dx.doi.org/10.1063/1.2793501View Description Hide Description
We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the sample under study. An optical angle sensor is used to measure the laser deflection providing a simple and experimental arrangement. We demonstrate its principle and a simple procedure to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.
Optimally accurate thermal-wave cavity photopyroelectric measurements of pressure-dependent thermophysical properties of air: Theory and experiments78(2007); http://dx.doi.org/10.1063/1.2793503View Description Hide Description
An experimental technique for the measurement of thermal properties of air at low pressures using a photopyroelectric (PPE) thermal-wave cavity (TWC) was developed. In addition, two theoretical approaches, a conventional one-dimensional thermal-wave model and a three-dimensional theory based on the Hankel integral, were applied to interpret the thermal-wave field in the thermal-wave cavity. The importance of radiationheat transfer mechanisms in a TWC was also investigated. Radiation components were added to the purely conductive model by linearizing the radiationheat transfer component at the cavity boundary. The experimental results indicate that the three-dimensional model is necessary to describe the PPE signal, especially at low frequencies where thermal diffusion length is large and sideways propagation of the thermal-wave field becomes significant. Radiation is found to be the dominant contributor of the PPE signal at high frequencies and large cavity lengths, where heat conduction across the TWC length is relatively weak. The three-dimensional theory and the Downhill Simplex algorithm were used to fit the experimental data and extract the thermal diffusivity of air and the heat transfer coefficient in a wide range of pressures from . It was shown that judicious adjustments of cavity length and computational best fits to frequency-scanned data using three-dimensional photopyroelectric theory lead to optimally accurate value measurements of thermal diffusivity and heat transfer coefficient at various pressures.
A hot-wire probe for thermal measurements of nanowires and nanotubes inside a transmission electron microscope78(2007); http://dx.doi.org/10.1063/1.2785848View Description Hide Description
A hot wire probe has been developed for use inside a transmission electron microscope to measure the thermal resistance of individual nanowires,nanotubes, and their contacts. No microfabrication is involved. The probe is made from a platinum Wollaston wire and is pretensioned to minimize the effects of thermal expansion, intrinsic thermal vibrations, and Lorentz forces. An in situ nanomanipulator is used to select a particular nanowire or nanotube for measurement, and contacts are made with liquid metal droplets or by electron-beam induced deposition. Detailed thermal analysis shows that for best sensitivity, the thermal resistance of the hot-wire probe should be four times that of the sample, but a mismatch of more than two orders of magnitude may be acceptable. Data analysis using the ratio of two ac signals reduces the experimental uncertainty. The range of detectable sample thermal resistances spans from approximately . The probe can also be adapted for measurements of the electrical conductance and Seebeck coefficient of the same sample. The probe was used to study a multiwalled carbon nanotube with liquid Ga contacts. The measured thermal resistance of had a noise level of approximately and was repeatable to within upon breaking and re-making the contact.
78(2007); http://dx.doi.org/10.1063/1.2800776View Description Hide Description
Precision temperature measurements are required in the LTP, the LISA technology package, for various diagnostics objectives. In this article, we describe in detail the front-end electronics design and the associated temperature sensors to achieve the LTP requirements: noise equivalent temperature of in the frequency range from at room temperature. We designed an ac Wheatstone bridge and a subsequent digital demodulation to minimize noise. We show experimental results where the required sensitivity in the measurement bandwidth is fulfilled.