Tools of the Trade

Pictured above: from left, Ryszard Pryputniewicz, professor of mechanical engineering; Xiuping Chen, '12; Jason Parker, '12; and Vu Nguyen, '12.

A Shining Light in the World of Reliability

By Michael Dorsey

Tiny cantilevers barely 10 microns across that vibrate more than a million times a second to transmit signals from cell phones. Minute gyroscopes almost invisible to the naked eye that keep cars from skidding. These are just two of the products of the relentless drive to make technology smaller, faster, lighter, cheaper — and more capable.

An endless string of new materials and manufacturing techniques that have stretched the boundaries of engineering and physics. At each step along the way, and with each breakthrough, the same question has been asked: “Will it work . . . reliably?”

For more than three decades, they have come to WPI from corporations, government agencies, and national laboratories seeking that answer. Specifically, they have sought out the expertise of Ryszard Pryputniewicz, Kenneth G. Merriam Professor of Mechanical Engineering. The founder and director of WPI’s Center for Holographic Studies and Laser micro-mechaTronics, Pryputniewicz is an internationally recognized pioneer in holographic interferometry.

Invented in 1947, holography is a method for creating three-dimensional images of objects using lasers. Pryputniewicz became intrigued by holograms while growing up in his native Poland; by the time he began his doctoral studies at the University of Connecticut, American engineer Karl Stetson had discovered how to use holography to measure instantaneous stresses, strains, and vibrations. Stetson’s career eventually brought him to United Technologies in Connecticut, where Pryputniewicz met him, beginning a lifelong friendship.

Stetson discovered that if a hologram of an object under stress is combined with another of the same object at rest or in a different state of stress, differences in the object’s displacement or deformation will appear as dark and light bands called fringes. The spacing and direction of these fringe lines can be directly translated into the forces acting on the object. As a measurement tool, holography offers some important advantages. For example, it measures forces acting on an entire object, all at once; and it is noninvasive, which makes it ideal for studying the behavior of fragile objects.

Pryputniewicz first used holographic interferometry while a graduate student at UConn for groundbreaking work that helped identify the best way to move teeth with orthodontic appliances. When he came to WPI as an assistant professor in 1978, he set up one of the earliest university laboratories in the field.

Chen and Pryputniewicz with an environmental chamber for measuring microscopic structures.

Over time, the laboratory grew into a center, expanding ultimately to include 14 individual laboratories, and took on an increasingly complex series of challenges in aviation, microelectronics, MEMS (micro-electro-mechanical systems), and, more recently, nanotechnology. This work has been sponsored by a veritable who’s who of technology giants, from government agencies like NASA, DARPA, and the Missile Defense Agency, to companies like AMP, Honeywell, Boeing, and General Motors, to such national research centers as Draper Laboratory, Los Alamos National Laboratory, and Sandia National Laboratories.

Along the way, Pryputniewicz and his students and collaborators have helped advance holographic interferometry itself, developing new techniques and new technology that enabled the center to accomplish feats not even dreamed of just few decades ago. “There have been certain basics about the science and our techniques from the beginning,” Pryputniewicz says, “but with each new challenge, we have had to take it a little further.”

For example, in the 1980s Pryputniewicz and Stetson helped pave the way for the use of CCDs (charge-coupled devices) to replace photographic plates for recording holograms. Where it was once necessary to laboriously trace each fringe with digitizing tables, images are now recorded and processed on the fly. “Back then we could process two images a day,” he says. “Today we record a million points of information 30 times every second, and we are still not satisfied.” 

For example, in the 1980s Pryputniewicz and Stetson helped pave the way for the use of CCDs (charge-coupled devices) to replace photographic plates for recording holograms. Where it was once necessary to laboriously trace each fringe with digitizing tables, images are now recorded and processed on the fly. “Back then we could process two images a day,” he says. “Today we record a million points of information 30 times every second, and we are still not satisfied.”

Such fast recording speeds, coupled with ultrafast laser pulses that can freeze blindingly fast action, have enabled the center to study the forces acting on microscopic machines built by Sandia Labs, which have gears one-third the diameter of a human hair that spin at more than a million revolutions per minute.

Most recently, Pryputniewicz and 15 teams of undergraduates, working with graduate students, developed and refined a unique chamber that permits microscopic devices to be studied under precisely controlled environmental conditions. A foot across and just 10 inches high, it sits on an air suspension system that, in turn, rests on a large slab of granite, thus isolating the chamber from external vibrations. Computer-controlled systems can create a vacuum inside the chamber and cool or heat objects inside to precise temperatures. A window on top of the chamber permits laser beams to illuminate the objects inside.

With support from several government and industrial sponsors, students are currently using the chamber to measure the quality of high-performance dynamic sensors used in everything from medical devices to Mars rovers. They are also learning an approach that has been Pryputniewicz’s mantra for more than three decades. It’s called ACES, which stands for the unification of analytical, computational, and experimental solutions. It means comparing the experimental results obtained in the laser labs with finite element studies and computer models of the same objects and phenomena.

“We combine all three to verify the results and make sure the circle closes,” he says. “That way, everything is comparable, verifiable, and reliable.”

It is an approach that, for more than 30 years, has made WPI a required stop for agencies, companies, and laboratories striving to break new ground in technology, and Pryputniewicz himself, one of the most respected authorities on what makes things work . . . reliably.

 
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