Raspberry Pi and smartphone-based interferometric measurement

29 June 2018

Epigem have announced its improved quality control of transparent electronic film, thanks to research on surface measurement – based on inexpensive fibre-optics, phone cameras, and a Raspberry Pi SBC.

As a partner in the University of Loughborough-led project, ‘Synthetic aperture interferometry: High-resolution optical measurement over an exceptionally large field of view’, the Redcar-based company challenged the University to develop instrumentation to inspect and measure precision-embossed thin film and microfluidic devices.

Loughborough’s solution is an array of cameras and sources that produces a sequence of digital holographic images, which can be combined to synthesise the output of an interference microscope – but with 10,000 times the field of view.

In order to meet this challenge, the University has developed methods to micro-machine the tip of optical fibres and has exploited additive manufacturing (or 3D printing) to produce miniature, digital holographic cameras.

Each camera is connected to a Raspberry Pi single board computer to pre-process the images before the data is combined to give a map of surface height.

Using this technology, Loughborough researchers have now demonstrated surface height measurements with a precision of 10 nanometres, a lateral resolution of 1.7 micrometres, and a field of view of almost 50 x 50 mm2.

The next step is to produce an array of 225 cameras, which could achieve similar measurement precision with a lateral resolution of 0.85 micrometres and a field of view of 100 x 100 mm2.

Tim Ryan, Epigem’s managing director, said: “This is a fantastic achievement, going in a very short time from idea, to design, converting to hardware – through to development. It has huge potential for quality control of electronic films and our microelectrode-enabled products.

“Working with Loughborough University, state-of-the-art micro fabrication techniques have been deployed throughout the project.

“Interferometry can tell us a lot about the roughness of a surface. As Epigem expands its measurement for the life sciences capability, we are now asking ourselves where else the technology can be applied in relation to serious disease diagnosis.”

Jeremy Coupland, Professor of Applied Optics and Associate Dean (Research) at the Wolfson School of Mechanical, Electrical and Manufacturing Engineering, said: “We have made a huge step forward here using inexpensive over-the-counter technology to build what is essentially a gigantic interference microscope and are now looking to exploit this technology in real-world applications.

“You could say that we are developing cutting-edge metrology with a few mobile phones and Christmas tree lights!”

The project is a partnership between Loughborough University, Taylor Hobson, the National Physical Laboratory (NPL), The Manufacturing Technology Centre (MTC), and Epigem, and is funded by the EPSRC.

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