A technique based on an inexpensive process used to print electronic circuit boards has been developed for constructing complex three-dimensional devices, such as a micro-reformer for fuel cells. The new method could be a versatile way to more cheaply and easily create microscale devices, making it practical to fabricate fuel cells for recharging two-way radios. It could also help make some types of chemical manufacturing safer and more efficient, and produce wireless-tire air-pressure sensors inexpensive enough to be standard issue in new cars.
The process works by building up hundreds of layers of specially formulated inks containing various materials, such as polymers, metals, and ceramics, to form a three-dimensional structure, complete with hollow passages and chambers sealed inside, says Arthur Chait, CEO of EoPlex Technologies, in Redwood City, CA, the startup company that developed the new technique. For each layer, the technology prints both the materials that will make up components of the final device and space-holder materials that will help support the next printed layer.
Each layer is cured by a flash of ultraviolet light before the next layer is printed, and once all of the layers have been printed, the whole assembly is fired at high temperatures, about 850 degrees Celsius , depending on the materials used. These materials have to be carefully selected so that they shrink at the same rate during the firing, and so that the space-holding materials can diffuse through the other materials, leaving behind empty spaces.
One of the company’s first devices, a fuel-cell “reformer” for stripping hydrogen from methanol, will supply enough hydrogen for micro fuel cells that recharge 20-watt two-way radios used in emergency areas, where grid power isn’t reliably available. The 300-layer device shows the complexity possible with the printing technique, Chait says. The layers form a total of 33 discrete components, such as heating coils, catalyst beds, “chambers, passageways, a diffuser section, a reformer section, and a combustion section,” he says. Methanol is fed into the device, and the combination of steam and catalysts free the hydrogen. The entire reformer is the size of two dominoes.
Small reformers have been built before by researchers at MIT, the Pacific Northwest National Laboratories, and the University of Illinois. But so far, with the exception of a shoebox-size device, they have been inefficient, transforming only a “very small percentage” of the energy in the fuel into electricity, says Klaus Jensen, professor at the MIT Microsystems Laboratory. If EoPlex has indeed succeeded in making a small device that works well in a fuel cell, he says, “that would be a very important advance.”
Chait says his company is working with several others to create prototype devices based on the new technique, which can produce complex, three-dimensional structures out of multiple materials–and do so in a high-throughput process that can lower costs. The new method is an improvement over other printing-based techniques, Chait says, such as those that print designs on pre-formed ceramic sheets. The new method requires no pre-forms, which simplifies the process, cuts costs, and allows for more-complex designs, he says.
EoPlex is applying the concept to manufacturing micro-reactors, devices now often made from silicon, which quickly combine small amounts of precursor compounds to form high-value chemicals. Because they work with small amounts of chemcials at a time, such micro-reactors could be safer than conventional techniques when interacting with toxic or volatile chemicals. EoPlex has also designed an electrical generator smaller than a dime that uses piezoelectric materials to transform vibrations in a vehicle into electricity for powering wireless sensors. While wireless air-pressure sensors are now available on luxury cars, Chait says the new power source could lead to much smaller devices. The new printing technique would help make the sensors inexpensive enough to be put on all new cars.
Printing technologies have promise because “they are amenable to low-cost mass production,” says Michael Cima, materials-science and engineering professor at MIT. “If you’re talking about sensors for cars, you’ve got to make millions of them, and you’ve got to make them cheaply.”
But scaling up to actual production can be difficult, says Emanuel Sachs, an MIT professor of mechanical engineering with experience developing three-dimensional printing techniques. “Are their accuracies, tolerances, and production rates good enough to make real stuff? That’s what it’s going to come down to.”