This procedure aims to inexpensively fabricate metamaterials on a potentially industrial scale. First, fabricate the PMMA jacketing tube in the primary draw. Then include the indium in the hole and draw the indium filled fiber using a primary draw process.
Assemble the stacked indio, filled preform and a knee in a 90 degree Celsius oven. Proceed with a secondary draw process to draw the stacked indium filled, preform into a fiber. The resulting metamaterials contain wires of five micron separated by 50 microns that can be fabricated inexpensively on a potentially industrial scale and show plasmonic response in the terahertz frequency range.
Other methods for fabricating metamaterials such as lithographic, nano, and microfabrication techniques are expensive and can produce samples that are most a few centimeters in size. The main advantage of our technique is that we can fabricate hundreds of meters of metamaterials in fiber form. This allows us to address important questions in the field, such as whether metamaterials can be fabricated and technologically and practically relevant quantities.
The particular method we're demonstrating here yields metamaterials with a plasmonic response in the te hertz. The process can in principle, be scaled down to the nanoscale yielding metamaterials with a response in the visible spectrum. The inspiration for this method was our earlier work on drawing fibers with internal electrodes to make electro optic modulators.
We recently realized that this technique significantly extended, could be used to create metamaterials. Fabricating metamaterials by drawing preforms of stacked Indian filled fibers is difficult to learn. We hope that this visual demonstration will show what the various elements look like and the conditions required to draw these complex structures down to micron scale.
Demonstrating this process will be Richard Luin an engineer, and Alessandro T is a PhD student from our research group. This fabrication method of metamaterials involves two stages of drawing where each stage involves miniaturizing. A macroscopic object called a preform by drawing it in a furnace into a filament.
The primary draw process is used to stretch or sleeve preforms down to an outer diameter of greater than one millimeter. As a guide, use the primary drawing conditions in table one of the accompanying text To load the preform onto the draw tower. Clamp the top extender to the three jaw chuck, feed the preform into the hot zone of the furnace and align it using the XY micrometer stage.
Then close the top plate of the furnace. Increase the temperature to 185 degrees Celsius. Start the feed rate at five millimeters per minute.
Draw rate at six millimeters per minute and close the draw unit clamps. Monitor the behavior of draw tension over time. If sleeving, then vacuum is required.
Attach a vacuum tube to the vacuum sealed top preform extender using blue tack. Start the feed and draw units and then apply vacuum monitor the furnace temperature and the ratio between the feed and draw rates to maintain constant outer diameter and the drawing tension.Well. The polymethyl methacrylate jacketing tube used to structure the one millimeter indium wire is produced by stretching and sleeving.
Standard PMMA tubes in the primary draw process to produce a final PMMA jacketing tube of one millimeter in a diameter and 12 millimeter outer diameter. First cut 600 millimeter lengths of PMMA tubes with a six millimeter inner diameter and a 12 millimeter outer diameter. Prepare several PMMA tubes for future use during the sleeping process.
Place the PMMA tubes in an annealing oven at 90 degrees Celsius for a minimum of five days. After the Anil tubes have cooled to room temperature, clean the surface of the PMMA tube with isopropanol wipes and allow to dry. Next, attach the PMMA tube to the top extender using reflective tape.
Also attach the PMMA tube to the primary draw bottom extender. Now we draw the PMMA tube from an outer diameter of 12 millimeters to six millimeters in the primary drawing process shown earlier. Heat crimp one side of the resulting tube with a hot air gun and insert it into a new PMMA tube.
To create the PMMA tube assembly seal the bottom gap between the stretched tube and the new PMMA tube assembly. With PTFE tape, attach the top end of the PMMA tube assembly to the top extender using an inner layer of sticky tape, a middle layer of PTFE tape and an outer layer of reflective tape. Ensure the PTFE tape is tight and all gaps between the PMMA two assembly and the top extender are sealed, Stretch and sleeve.
The resulting PMMA tube assembly in the primary draw process under vacuum as shown earlier from an outer diameter of 12 millimeters to six millimeters, resulting in an inner diameter to outer diameter ratio of approximately 0.25. Repeat this process until the final PMMA jacketing tube has inner to outer diameter ratio of approximately 0.1 with an inner diameter of one millimeter. The secondary draw process is used to stretch preforms to an outer diameter smaller than one millimeter.
When the drawing temperature is reached, the preform begins to neck down out of the furnace due to the weight of the bottom extender. Providing the initial drawing force start the feed rate at 2.5 to five millimeters per minute and start by increasing the furnace temperature to 170 degrees Celsius. Then slowly increase the temperature by 2.5 to five degrees Celsius up to 220 degrees Celsius.
To control the speed of the dropdown, maintain the fiber diameter around 250 to 500 microns. To prevent the fiber snapping, attach the fiber to the capstan wheel that is spinning at a slow rate of under one meter per minute. Wind the fiber around the dancer wheels and attach to the fiber spool.
Use the secondary drawing conditions in the accompanying manuscript as a guide to obtain the steady state drawing conditions and final fiber dimensions To maintain constant outer diameter and the drawing tension, monitor the furnace temperature and the ratio between the feed and draw rate. The one millimeter indium wire will now be sleeved and stretched in the PMMA jacketing tube in the secondary draw process to produce an Indio filled fiber without a diameter one millimeter, Cut the indium wire to 550 millimeter lengths and insert into the PMMA jacketing tube to create the indium filled preform assembly, stretch and sleeve the filled preform assembly in the secondary drawing process with vacuum to make an indio filled fiber of a final outer diameter. One millimeter drawn under 15 to 20 grams tension.
After the draw process is complete, remove the spool of indium filled fiber from the tower, inspect the end face and along the longitudinal length of the Indio filled fiber under a light microscope. Problematic defects can include separation between the indium wire and PMA tubing interface, fluctuations in wide diameter or fracture cracks along the fiber length Bundle, many indium filled fibers using rubber bands and insert into the PMMA preformed jacketing tube, ensuring the fibers are straight and are of a tight fit, stretch and sleeve. The stacked preform assembly in the secondary drawing process with vacuum to make indium stacked fiber of final outer diameter 0.6 millimeters and drawn under 80 grams Tension.
The desired product is a metamaterial fiber containing five micron wires separated by 50 micron. This cross section schematic of a multiple sleeved jacket shows a single Indio wire sleeved in three successive jacketing PMMA tubes. The preform of one millimeter PMMA fiber contains continuous indium wire of 100 micron in diameter.
This microscope image is an example of the cross section of a metamaterial fiber with plasmonic response in the terahertz range. The plasmonic response manifests itself such that at low frequencies, the material behaves like a metal, and at high frequencies like a dielectric with the plasma frequencies defining the boundary between the two behaviors here. Experimental measurements characterize this fiber type drawn to three different dimensions.
In both cases, the plasma frequency dependence on diameter is apparent. After watching this video, you should have a good understanding of how to fabricate metamaterial structures inexpensively and on a potentially industrial scale. Remember to draw the Indian field fibers under high tension to prevent the Indian from breaking up along the fiber length.
This is achieved by maintaining a low temperature, which results in a high viscosity for the polymer, and thus preserves the structure that contains the liquid metal.
