EAST LANSING (WWJ) — Nelson Sepúlveda, assistant professor in the Michigan State University Department of Electrical and Computer Engineering, is investigating a phase-changing “smart material,” looking for new ways to move things at the micro level.

Funding for the research comes from three National Science Foundation grants, totaling $860,000 to advance his work on Vanadium Dioxide.

Sepúlveda is working to enable VO2-based technologies that can allow for the integration of this smart, multifunctional material into micrometer-sized devices.

“My research group works on very small stuff,” Sepúlveda said. “Think about taking the motor of a car and making it fit inside a hair. You want to scale down and integrate all the individual parts so you can make the best use of the fully assembled system. “With the help from a very talented group of graduate students – who basically do all the work — we take an actuator and make it fit within the thickness of two hairs – a device that is about 200 microns. When perfected, it could allow for very precise microsurgery and help surgeons pinpoint tissue for selective treatment… The collaboration with my colleague, Professor Xiaobo Tan, will be key in advancing the control of VO2-based devices. Any breakthroughs at the micro level will be very impactful.”

Sepúlveda added that other areas likely to be impacted by this research include radio frequency circuits — antennas and transceivers — and biomedical devices, sensors, actuators and imagers.

An actuator is a type of device for moving or controlling a mechanism or system. It is operated by a source of energy and converts that energy into motion. A microactuator does the same thing on a microscale.

Vanadium dioxide is a complex, strongly correlated “smart” material that experiences solid-to-solid phase transition when induced by temperature, ultrafast optical radiation or an electric field. It is considered “smart” because it remembers what its previous state was. When induced thermally, the phase change occurs at approximately 68 °C – not far from room temperature — making the material very attractive for practical applications.

Scientists have been working with VO2 since the 1950s. Early research focused on its electrical resistance change across the phase transition and its use as an electric switch. In the 1960s and 1970s, its thermochromic properties for optical uses were discovered. By the 1990s, the practical applications expanded to smart windows and optical filters.

Since 2008, Sepúlveda has looked at vanadium dioxide’s mechanical properties across phase transition.

“A good example of a phase change is applying heat to ice,” he said. “As you know, the physical properties of water are different from the properties of ice. The ice begins as a solid and goes through a phase change when temperature is applied and it turns to liquid. We are studying solid-to-solid phase transitions, where a solid becomes another type of solid. The change is very abrupt, fast and it has hysteresis; which means that it has memory. If you translate the capabilities of our VO2-based micro-actuators to the macro-scale, it would be similar to a human arm lifting 250 pounds at the speed of 1,000 times per second. The National Science Foundation is very interested in this new material.”

The first of the NSF grants, valued at $200,000, is meant to understand how phase-change materials could create a wireless, reconfigurable antennas and radio frequency front-end systems to improve reception and provide more channels for transmitting data.

The second grant, for $360,000, will create a comprehensive research plan for making the technology more applicable by improving its precision, speed and strength.

“We’re looking for ways to demonstrate larger ranges of actuation at the micro level,” he said.
The devices to be developed are monolithically integrated smart Micro Electrical Mechanical System actuators, with potential applications on micro-robotics, micro-surgery and micro-manipulation.

The third grant is for $300,000. Xiaobo Tan, an MSU associate professor of ECE, as the principal investigator and Sepúlveda as the co-principle investigator, will investigate modeling and control methods for VO2-based microactuators to enable precise, efficient control of the micro devices.


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