Simple and portable low frequency lock-in amplifier designed for photoacoustic measurements and its application to thermal effusivity determination in liquids

Abstract

The lock-in amplifier is a very useful instrument for observing very small signals under adverse signal-to-noise conditions. In this work, we describe a simple and portable lock-in amplifier designed to be used in photoacoustic measurements. The device was used to measure the thermal effusivity of eight different liquid samples (distilled water, glycerol, acetone, ethanol, 2-propanol, chloroform, hexane, and methanol), as well as the effusivity of acetone in aqueous solution at distinct concentrations, giving good results. The instrument has a bandwidth of 10 Hz-10 kHz and a sensitivity of 1 μV.

Low-Cost, High-Performance Lock-in Amplifier for Pedagogical and Practical Applications

“…Students with such backgrounds can develop and apply their knowledge to potentiostats for electrochemistry, , characterization of microelectrodes, measurement of pH, peak resolution, and photometry . Lock-in amplifiers (LIAs) are commonly used in research laboratories to improve signal-to-noise and to analyze time-dependent responses, and their construction provides a particularly good exercise for teaching undergraduate students about circuit principles and applications. − Previously reported LIA designs use prepackaged LIA integrated circuits such as ADA2200, which enable efficient construction but provide less opportunity for learning, or they use chips such as AD630, which provide a more open architecture but do not provide a means for measuring phase shifts that are critical in understanding time-dependent drive-response behavior (e.g., alternating current or AC circuits).…”

“…This allows us to describe exercises that students can conduct to learn about fundamental AC circuits by driving resistors (R’s) and capacitors (C’s) with an AC voltage, using the LIA to measure both the amplitude and phase shift of the response, and comparing with expected R/C behavior. We note that the present LIA design can be used not only for teaching, for example, in a senior analytical chemistry course or a senior instrumental analysis course, but also for research applications. , It is able to determine the phase shift of the device under test from . A phase shifter needed to determine V y is built-in the LIA and need not be added.…”

“…We note that the present LIA design can be used not only for teaching, for example, in a senior analytical chemistry course or a senior instrumental analysis course, but also for research applications. 8,15 It is able to determine the phase shift of the device under test from…”