Proceedings Article | 5 May 2012
KEYWORDS: Light emitting diodes, Particles, Cameras, CCD cameras, Sensors, LED lighting, Velocity measurements, Microfluidics, Imaging systems, CCD image sensors
Particle Image Velocimetry (PIV) is a non-invasive, full-field optical measurement technique that has become a
dominant tool for velocity measurement of fluids and gases at both macro (traditional PIV) and micro (microPIV) scales.
In PIV experiments, the fluid under the investigation is seeded with tracer particles, which are shining under an
excitation by a properly tuned light source. The idea behind the method is to precisely register the position of
corresponding particles in two shifted instances of time and then using these records calculating particle displacements,
i.e. flow velocity. In most PIV experimental setups, illumination is performed using dual cavity pulse lasers, whose
outputs reach several hundreds mJ at short pulse lengths (tens of nano-seconds). Unfortunately, such laser systems are
very expensive and bulky. In this work, we investigate a possibility to replace the laser illumination with a high power
LED illumination, aiming towards the development of the cost effective and portable microPIV systems.
We have developed an electronic circuit, which drives LEDs with a high current over short time duration. The driver
circuit is triggered by an internal electronics of the CCD camera, and is able to produce single or double current pulses
per camera trigger. Besides, the circuit also allows i) flexible adjustment of the pulse duration (from 1 μs up to tens of
msec), ii) the time delay within pulse pairs, which is crucial for double-frame mode, and iii) time delay between the
trigger signal and current pulses.
We present experimental results of flow velocity measurements obtained using the microPIV system and the developed
illumination setup. We have investigated the flow of water, which was seeded with the spherical-polystyrene-fluorescent
particles, inside rectangular microchannels. For illumination, a LumiLED LED with a peak wavelength at 470 nm was
used at the double-illumination mode, where current pulses of up to 10 A at duration of 5 μs were achieved.
