UB Physicist Develops Concept Of An Inkjet Printer That Prints Documents Invisible To The Naked Eye

BUFFALO, N.Y. -- It sounds like something out of a James Bond movie: an electronic inkjet printer that prints with invisible ink.

But earlier this month, University at Buffalo physicists published a paper in Applied Physics Letters that describes a device that could do just that.

"The proposed printing technology, when ready, should be capable of producing fine-resolution images that are invisible to the naked eye and that could be used for the purpose of encryption," said Surajit Sen, Ph.D., assistant professor of physics at UB and lead author.

Potential applications include any situation where something needs to be identifiable by some secure or covert means, such as imprinting currency with an identifiable mark that could be seen only when used with a powerful microscope.

At the same time, because the technology would, for the first time, allow for extremely precise regulation of the size of the ink drop, it also would make high-resolution, visible images possible.

"You could even think about using such a technology to produce extremely tiny, hard copies of large documents, like books," said Sen. "You could prepare documents that are very tiny and so can be easily transported, but which could be accessed in their entirety by being run through a computer. A 200-page book might be able to be packed into just a few sheets of paper."

The UB physicists have proven a theoretical concept and a design for a potential inkjet printer that could make ink drops as much as 100 times smaller than the size that is possible with today's best inkjet printers, making them invisible to the naked eye. At the same time, the concept includes ways to cluster inkdrops together, creating visible images with extremely high resolution.

"If our research pans out, a device like this could make feasible unusual applications that, right now, are simply impossible to accomplish," said Sen.

A provisional patent application has been filed by UB on the concept and design.

The "Holy Grail" of higher-resolution images in inkjet printing is the ability to squeeze out tinier and tinier drops of ink. But because the printers use a nozzle to spray ink drops onto the paper, the drops only can be as small as the size of that nozzle.

Not anymore, say the UB physicists, whose research proposes a way to do away completely with inkjet printer nozzles.

"In our paper, we present the concept and calculations that describe the method of designing inkjet printers that are nozzle-free and, therefore, capable of attaining unprecedented resolution with inkdrop sizes that can be as small as 15 or 20 nanometers," explained Sen.

A nanometer is a billionth of a meter. The very smallest inkdrop size now available in state-of-the-art inkjet printers is, at best, a millionth of a meter, said Sen.

According to the paper's authors, technology based on this research would allow drops of ink to come out of a printer at variable speeds, eliminating the need for expensive, specially coated papers that now are necessary with inkjet printers.

It also would allow for invisible -- or visible -- images to be printed on things other than paper, Sen said, such as dollar bills, or even electronic devices.

The concept is based on printing with inks made of ferrofluid particles that form a stable colloid in colored water. The particles are aligned along the direction of an applied magnetic field.

"When an appropriately orchestrated mechanical impulse is applied along the direction of that magnetic field, a tight bundle of energy called a solitary wave is generated in the chain of ferrofluid particles," Sen explained. "This solitary wave travels along the chain and pushes a particle out of the liquid and onto the paper, or whatever is being imprinted, and the image is made."

The mechanical impulse eliminates the need for nozzles, which ordinarily provide the impetus for spraying the ink onto paper.

The study's co-authors and co-investigators in the provisional patent application are Felicia S. Manciu and Marian Manciu, both doctoral candidates in the UB Department of Physics.

The work was funded partially by Sandia National Laboratories of the Department of Energy. The idea for the research grew out of a UB Multidisciplinary Pilot Project Program grant to Sen; Bernard Weinstein, Ph.D., professor of physics, and Nassir Ashgriz, Ph.D., professor of mechanical and aerospace engineering.