OPTICAL DESIGN: Made by Tibi
|Record created date||Feb. 3, 2013|
|Record created by||None|
We don't know.
03, JUNE 2013
I discovered this new sensor by playing with the microfiber transducer.
Ideas were there before from discussions with Frederic about the constriction transducer. Frederic thought that the mechanism of the constriction transducer was leakage, and suggested to plunge it in water to see how the signal changes. The microfilament is a constricted optical fiber on a longer length, so the connection was easy to make, I plunged one microfiber transducer into water and it worked.
I also tested it to see a difference between water and alcohol, and it worked. I tested saturated salted water, and the signal difference with pure water was too small to make a conclusion.
I published the results in this video http://youtu.be/oA-0UgrdPBU
I believe that the working principle is leakage: the fiber is pulled to a smaller core, some light transferred into the cladding, which propagates if the fiber is in air. If the fiber is immersed in a fluid with higher refraction index some light escapes. We're measuring intensity fluctuations. So yes, it depends on the difference between the index of refraction of the cladding and the external media. Nothing out of the ordinary. There is some specific know how for the fabrication of the fiber, which has to be tapered and pulled with a certain geometry, the tip has to be melted to a ball and coated with silver (we're using our in-house low cost silver coating method) to send the light back to the detector.
I marked some time for documenting the work, communicating to SENSORICA and publishing it on social media.
I used 125/63.5 MM glass Infinicor300 Corning fiber, pulled with the microsplicer, voltage used 8.5V, max current. I pulled the fiber by hand using the manual micrometers on the device. One can diminish the voltage down to 8V. 7V is not enough to melt the glass fiber. At 8 one can do finer stretches.
The tip of the pulled micro fiber was melted to round it, and was coated using our inhouse wet silver coating method. Only the very tip was coated. I made 2 devices, 1 to 2 mm long, 40 and 20 microns diameter. Only the 20 microns diameter was sensitive when immersed into water.
I used the 850nm LED to test it, before it was improved with filter and amplifier.
TODO: try different diameters. It seems that the critical diameter is between 40 and 20 microns. Also try multiple constrictions to see if we can have a discrete level sensor.