Researchers make tiny, yet complex fiber optic force sensor

Date:
September 8, 2020
Source:
The Optical Society
Summary:
Researchers have developed a tiny fiber optic force sensor that
can measure extremely slight forces exerted by small objects. The
new light- based sensor overcomes the limitations of force sensors
based on micro- electro-mechanical sensors (MEMS) and could be
useful for applications from medical systems to manufacturing.



FULL STORY ========================================================================== Researchers have developed a tiny fiber optic force sensor that can
measure extremely slight forces exerted by small objects. The new
light-based sensor overcomes the limitations of force sensors based
on micro-electro-mechanical sensors (MEMS) and could be useful for
applications from medical systems to manufacturing.


========================================================================== "Applications for force sensing are numerous, but there is a lack
of thoroughly miniature and versatile force sensors that can perform
force measurements on small objects," said research team leader Denis
Donlagic from the University of Maribor in Slovenia. "Our sensor helps
meet this need as one of the smallest and most versatile optical-fiber
force sensors designed thus far." In The Optical Society (OSA) journal
Optics Letters, Donlagic and Simon Pevec describe their new sensor,
which is made of silica glass formed into a cylinder just 800 microns
long and 100 microns in diameter -- roughly the same diameter as a human
hair. They demonstrate the new sensor's ability to measure force with a resolution better than a micronewton by using it to measure the stiffness
of a dandelion seed or the surface tension of a liquid.

"The high resolution force sensing and broad measuring range could be
used for sensitive manipulation and machining of small objects, surface
tension measurements on very small volumes of liquid, and manipulating
or examining the mechanical properties of biological samples on the
cellular level," said Donlagic.

Creating an all-glass sensor Although MEMS-based sensors can provide
miniature force sensing capabilities, their applications are limited
because they require application-specific protective packaging and
multiple electrical connections. Without proper packaging, MEMS devices
also aren't biocompatible and can't be immersed in water.



==========================================================================
To develop a more versatile miniature force sensor, the researchers
created an all-optical fiber optic sensor completely made of glass. The
complex undertaking was made possible by a special etching process the researchers had previously developed to create complicated all-fiber microstructures. They used this micromachining process to create a
sensor based on a Fabry-Perot interferometer -- an optical cavity made
from two parallel reflecting surfaces.

The end of the sensor's lead-in fiber together with a thin flexible silica diaphragm were used to create the tiny interferometer. When external force
is exerted onto a silica post with either a round or cylindrical force
sensing probe on the end, it changes the length of the interferometer
in a way that can be measured with subnanometer resolution.

The way the sensor's structures were fabricated created an air-sealed
cavity that is protected from contamination and amenable for use in
biochemical environments. Not only can it be immersed in a variety of
liquids, but it can also measure positive and negative forces and doesn't
need any additional packaging for most applications.

Measuring tiny forces After evaluating and calibrating the sensor, the researchers used it to measure Young modulus -- a measure of stiffness --
of a human hair and common dandelion seed. They also measured surface
tension of a liquid by measuring the retraction force when a miniature
cylinder was removed from a liquid. The researchers were able to measure
force with a resolution of about 0.6 micronewtons and a force range of
about 0.6 millinewtons.

"The force sensing tip can be made substantially smaller -- down to
about 10 microns in diameter -- and can be adapted to perform various
force sensing tasks," said Donlagic. "The miniature force sensor can
also be used to create more complex sensors such as sensors that measure magnetic and electric fields or determine the surface tension or flow of
a liquid." The researchers say that the current version of the sensor
is ready for use.

However, improving the overload robustness, producing probe tips with
other shapes or adding miniaturized packaging could further expand
potential applications. The researchers are also working to automate
the processes used to fabricate the sensor to make it more practical.


========================================================================== Story Source: Materials provided by The_Optical_Society. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Simon Pevec, Denis Donlagic. Miniature all-fiber force
sensor. Optics
Letters, 2020; 45 (18): 5093 DOI: 10.1364/OL.401690 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200908162123.htm

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