Search

A Lock-In Amplifier (LIA), or phase sensitive detector, is an instrument capable of providing high frequency selectivity allowing the user to distinguish a signal of interest from background noise, and has become an important component in the instrumentation for the study of many different physical phenomena. In this work a LIA is implemented using digital signal processing techniques on a field programmable gate array, or FPGA, and is compared against a commercial counterpart with the objective of showing that homebrewed instruments can produce reliable and trustworthy results. For this comparison experimental tests have been performed which are based on the photoacoustic effect, given that LIAs are cornerstones of many techniques based in this and other related effects. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a photoacoustic method is proposed for specific heat capacity measurements in solids using a heat transmission configuration, where illumination takes place at the reference–sample interface. The method involves the use of a liquid reference sample so that it becomes free of instrumental function influence due to effects dependent on the detection cell, the frequency dependence of the microphone response and of the involved electronics. The method is validated with measurements performed in test samples of different materials. [Copyright &y& Elsevier]

• A method is presented for thermal conductivity measurements in fluids. • The fluid fills a narrow gap between two solids. • Interfacial thermal resistance is measured by laser spot lock-in thermography. • Thermal conductivity is recovered from linear curve of gap thickness versus thermal resistance. In this work, we propose a new method to retrieve the thermal conductivity of fluids, k f , using laser spot lock-in infrared thermography. The measurement cell consists in two paralepidid blocks separated by a narrow gap of variable and known width, L. This gap can be filled with a gas or a liquid, producing a thermal contact resistance, R th , which quantifies the thermal barrier to heat propagation. By focusing the laser spot close to the interface between the two solids, this thermal contact resistance can be obtained by fitting the temperature field recorded by the infrared camera to its analytical expression. Using the well-known relationship R th = L / k f , the thermal conductivity of the fluid is obtained from a simple linear relation. Measurements performed in test samples show a good agreement between determined thermal conductivities and literature reported values, demonstrating the validity of the method. [ABSTRACT FROM AUTHOR]