Trine engineering students present research at international workshop

Four Trine University mechanical engineering students presented their original research at an international conference focusing on microelectromechanical systems (MEMS) and microsystems technologies.

The Solid-State Sensors, Actuators, and Microsystems Workshop, held every two years, took place May 31 through June 4 in Hilton Head, South Carolina.

The Trine students work with James Miller, Ph.D., assistant professor in the Wade Department of Mechanical and Aerospace Engineering, to research ways to make MEMS resonators, which vibrate to allow devices to keep time and sense movement, work better.

The team is seeking to develop techniques to make the resonance frequencies of MEMS resonators more stable by utilizing controlled mechanical tension, nonlinear operation and amplifier circuit design to improve their performance.

They are investigating whether tuning the tension on the resonators — similar to tightening a guitar string to tune it — will make the resonators’ frequencies more stable. This work has applications for improved timekeeping devices, which are ubiquitous in modern technology such as smartphones, computers and data centers.

The research is funded by a grant from the National Science Foundation.

Controlling noise sources

Janna Wilson of Kokomo, Indiana, presented on "Amplifier gain limits for thermomechanical-noise-limited frequency stability in capacitive MEM resonators."

“I studied two different conditions a MEMS device can operate under,” she said. “In one, the circuit surrounding the device produces the noise limitations when a low bias voltage and low gain amplifier are used. In the other, the noise from the device’s own thermomechanical motion is the limiting factor when a high gain amplifier and high bias voltage are applied.”

She found that using high gain amplification and high biasing voltage to limit a device to its own thermomechanical noise resulted in improved frequency stability and better transduction (converting energy from one form to another) strength.

“These results are useful, seeing as most commercial MEMS devices are limited by noise from the amplifier and therefore have room for improvement,” she said.

She said it was “highly encouraging” to have her research accepted for the workshop and that she gained valuable experience as she looks ahead to applying to graduate school and conducting more research.

“The conversations I had at my presentation were the most rewarding part of the conference,” she said. “So many people wanted to hear more about the work our lab is doing, and it was great to hear so many new perspectives on my topic.”

More strain, more stability

The research conducted by Maranda Padfield of Kokomo, Indiana, was titled, “Variable mechanical strain improves frequency stability in MEM resonators."

Padfield’s research examined the effects of applied strain to a micromechanical beam in its operating environment.

“As the tension applied to the beam increases, so does the resonance frequency of the device, which should increase the quality factor and improve the resonance frequency stability,” she explained.

Her research found that increased tension did have the desired effects up to a point, yielding more than 40% improvement in frequency stability. However, this improvement plateaued, potentially due to external electrical damping in system.

Padfield is conducting follow-up experiments this summer to better understand this saturation effect.

“There were a couple of people in industry who were interested in the implications for their devices,” she commented.

She said she was honored that her work was accepted into the conference, especially as an undergraduate student, and having their entire team get accepted made it even better.

“I am incredibly grateful that Dr. Miller took on the challenge of teaching and mentoring us and giving us the opportunity to have published research at this stage in our education,” she said.

She plans to eventually earn a Ph.D. and said the experience of conducting and presenting research will help her both with graduate school and her eventual career.

“We were able to connect with many incredible professors from different universities across the country. Being able to meet and interact with them before applying to their labs helps make that decision a little bit easier, and them having a face to put to a name will hopefully help my acceptance chances,” she said.

“I also got to talk to some industry leaders that were interested in my work. That helps my internship chances during my educational career, as well as my career past the end of my education.”

Mitigating converted frequency noise

Nicholas Ewing of Wabash, Indiana, presented “Zero-dispersion parametric pumping in encapsulated micromechanical resonators.”

His research covered two concepts in the MEMS field: zero-dispersion points, specific points where amplitude noise in the team’s resonator does not result in frequency noise, which can improve stability; and parametric pumping, a method of actuation where the team modulates the spring constant of their resonator at double the frequency of the primary driving force in order to tune the dynamics of the response, also shown to provide improved frequency stability.

“We investigated the combination of these two concepts in a micromechanical resonator with the goal to study if the two methods could, together, provide improved frequency stability for application in commercial timing devices,” he said.

By applying parametric pumping, the team observed additional zero-dispersion points beyond what is typically seen with direct-drive only.

“We believe that these points may provide additional frequency stability improvements beyond the typically observed points,” Ewing said.

The team plans to expand upon these findings throughout this summer to determine the impact on frequency stability.

Ewing said he had many in-depth discussions with people who stopped by his poster.

He is looking to attend graduate school and said his research work is a big step toward that goal, since he will have two published conference papers and two journal papers under review by the time he will apply.

New behaviors

Nathan Stefanski of Almont, Michigan, researched “Higher order parametric resonance in encapsulated micromechanical resonators.”

By exciting a device designed by Dr. Miller and fabricated by fellow researchers at Stanford University at frequencies well below its normal operating level via higher-level parametric pumping, Stefanski was able to observe and characterize previously unexplored responses for devices fabricated using the same manufacturing process as commercial timekeeping devices.

“Understanding these behaviors may help researchers and industry professionals develop more stable and sensitive MEMS devices for future timing and sensing applications,” he said.

“In the days leading up to the conference, I was nervous about presenting my work,” he admitted. “However, the students, professors and industry professionals at the conference were supportive and offered valuable advice. During the poster session, I had constructive discussions with professors from major research universities as well as representatives from industry. Their feedback provided new perspectives on my work and will help guide my research efforts throughout the summer.”

He said attending the conference opened his eyes to the significant role MEMS devices play in everyday life.

“While my own research has been primarily theoretical, many conference presentations highlighted practical applications in defense, biomedicine, agriculture and acoustics,” he said.