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CHIPS Articles: Meet the Scientists: Dr. Susan Berggren

Meet the Scientists: Dr. Susan Berggren
Mathematician working in SPAWAR’s S&T in-house laboratory
By Jessica Tozer, Armed with Science Blog - April 29, 2015
WHO: Dr. Susan Berggren. Her background is in mathematics, but she got her PhD in Computational Science from a joint program between San Diego State University and Claremont Graduate University. Dr. Berggren’s master’s degree is in applied mathematics from San Diego State University, and she also has undergraduate degrees in mathematics and in physics from Oregon State University. She also met her husband and got married in Oregon. They moved to San Diego in 2006 and have a four-month-old boy named Dashel.

TITLE: Government scientist at the Advanced Concepts and Applied Research Branch at the Space and Naval Warfare (SPAWAR) Systems Center Pacific (SSC Pacific). Susan joined SSC Pacific in December 2012 through the new professionals (NP) program.

“The NP program allows you to do three month rotations with different groups to find a job that really suits you,” she explains. “It is a great opportunity for a mathematician, since we are not specialized with a particular subject as an engineer can be.”

MISSION: There are no rigid job descriptions at SSC Pacific, Susan says. “We can work on pretty much anything we can get funding for, as long as it is aligned with the needs of the Navy.”

Prior to 2012, she was an NREIP intern for two summers at SSC Pacific and worked on SQUID array modeling with the CERF group for her PhD dissertation.

So, basically, she’s pretty amazing.

What is your role as a subject matter expert in Superconducting Quantum Interference Device (SQUID) array modeling and design?

“I am the principal investigator on a project investigating different methods to do direction finding and noise estimation with SQUID arrays, which is supported by SPAWAR’s science and technology in-house laboratory initiative for research programs. My main tasks are to simulate array configurations, coupling schemes and external parameters to determine the optimal design for fabrication.

“The SQUIDs can be coupled in different fashions, in one and two dimensions. I take the circuit diagram and create a mathematical model, which I solve using the Euler-Maruyama method in Matlab. There are multiple different parameters that can be adjusted, such as junction critical currents, junction capacitance, loop sizes, and number of loops in each dimension. Also there are parameters that can be modeled to see their effects, such as fabrication spreads and external noise. “

What is the goal/mission of the SQUID and what do you hope it will achieve?

“Our application of the SQUID arrays will revolutionize the way signals are received. The SQUID array sensor is on a 1cm by 1cm chip. We anticipate a very wideband flat response in frequency from Hz to GHz, unlike today’s resonant antennas. Because of this we are not wavelength dependent and will be able to receive signals with very large wavelengths on our small device.

“We plan to dramatically increase listening capabilities and reduce the physical size of antennas so that they can be used on UAV’s and to streamline the topside of Navy ships, reducing the Radar Cross Section (RCS).”

In your own words, what is it about this technology that makes it so significant?

“It is a whole new way of thinking. Completely different physics than what is currently used. We actually have problems talking and relating between the two technologies. Superconductors are metals that lose all resistance to current when cooled below a critical (material dependent) temperature. This lossless current flow allows for much more efficient systems.

“The cold temperatures allow for lower noise systems. The SQUIDs themselves are tiny loops of superconductor with two weak links called Josephson junctions that create a circulating current when a field is applied. They sense the magnetic field of an incoming signal, rather that the electric field like a present-day antenna does. The SQUIDs are sensitive enough to sense the magnetic fields being given off by your brain and heart.”

“The possibilities with this technology, and using cryogenic applications in general, are really exciting. Especially now that there are closed cycle coolers the size of coffee cups that have almost a century shelf life and can cool to below 77 Kelvin.”

You’re a theorist of the Cryogenic Exploitation of Radio Frequency (CERF) group at SSC Pacific. What does that mean and how does it connect to the SQUID mission?

“The CERF group is made up of members of different disciplines; we have physicists, a materials scientist, an electrical engineer, a device expert, a digitals signals processing expert, and a RF engineer. I am the mathematician supporting the team.

“I support different projects, including the SQUID work, doing mathematical modeling tasks. We are trying to investigate the entire receive chain from antenna, through analog preprocessing and conditioning, to digital conversion and digital signal processing. We have projects in each of these areas ongoing at the CERF lab. A couple of our analog conditioning units have transitioned to the fleet.”

How could you use your work to aid the military or help with military missions?

“My work at the CERF lab will be used to reduce the size, weight, power and cost of traditional shipboard antenna requirements, thereby reducing the RCS and sustainability costs of a ship’s topside.

“Also it will be used to gain HFDF capabilities on small UAV’s for covert intelligence gathering. The use of cryogenically cooled electronics will increase the number of signals detected, the range at which they can be detected and the accuracy with which they can be detected. It will help ensure information dominance in the Navy. “

What do you think is the most impressive/beneficial thing about what you do and why?

“For my particular piece of the puzzle, not the applications the technology will be used for, I feel that the biggest benefit I bring is cost and time savings. Mathematical modeling of a device or system before we build it allows us to narrow down the options and answer operational questions. A simulation takes much less time and costs a lot less than a fabrication run. I can run hundreds of simulations so that when we do fabricate a device it is close to optimal and we know what to expect.”

What got you interested in this field of study?

“I have always liked math, but not so much proofs with their theorems, assumptions and lemmas. I preferred my applied mathematics and physics classes for their real world applicability. I also didn’t want to be a teacher. A lot of people think that the only profession there is for a mathematician is to teach.

“I was more interested in becoming a research scientist. I wanted whatever my career was to work on something tangible, something that would be of use to someone and would benefit people’s lives. I think I get that with my job at the Navy. Everything we work on is in response to a direct warfighter need.”

If you could go anywhere in time and space, where would you go and why?

“I am having trouble answering this one. My mind goes all over. So the short of it is that I would like to go to the Tardis from Doctor Who so I could go all over!”

“First I would like to go 50 years in the future to see our inventions in action. I also would like to go back to a time before electricity to a cabin in the woods where I could gold pan and gem hunt all day without the bustle and distractions of today.

“Next, I would go to an alien planet to meet an extraterrestrial.

“Finally, I would travel through the past meeting all the people whose formulas and theorems I use today. However, these would all be temporary trips. Right now is the place I want to stay. What we are working on is so cutting-edge and exciting, SSC Pacific is where I want to be.”

Do you have anything else you’d like to add? Any advice you’d like to give?

“Don’t let people tell you that you can’t do something. Use it as motivation to prove them wrong.”

For more information about Dr. Berggren’s work, read her recent public releases:

Investigation of the Effects of Oxygen Content in YBa2Cu3Ox on the Depth and Profile of Direct Ion Trenches

Making the Effects of Varying the Capacitance, Resistance, Temperature, and Frequency Dependence for HTS Josephson Junctions, DC SQUIDS, and DC bi-SQUIDs

Meet the Scientists is an Armed with Science segment highlighting the men and women working in the government realms of science, technology, research and development. The greatest minds working on the greatest developments of our time. If you have someone you’d like AWS to highlight for this segment, email Jessica L. Tozer at

Dr. Berggren is observing the RF experimental test setup of a chip fabricated from optimal designs determined from her modeling of systems of differential equations derived from SQUID array circuit diagrams. Photo by Alan Antczak.
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