FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Measurement Science and Systems Engineering Division
fields (electromagnetic waves) is based on the detection of the force on electrically charged
nanomechanical oscillators. Nanoscale mechanical structures have already proven potentially useful for
the detection of small (attonewton) forces, which will enable the measurement of small electric and
electromagnetic fields. To achieve both high dynamic range and wide spectral response, we need to
design a system where the cantilever operating frequency is tunable. During the project, we will design
and fabricate a nanomechanical oscillator for E-field detection. In addition, we will characterize the
fabricated nanomechanical oscillators by measuring their responses to time varying electric and
electromagnetic fields.
Mission Relevance
Highly sensitive nanomechacical E-field detectors will have a tremendous impact in many applications,
such as the detection of small strength fields from global positioning system signals inside buildings.
Specific Department of Defense needs for electric field sensing are described in the recent Defense
Advanced Research Projects Agency (DARPA) BAA 09-34. DARPA program manager Dr. Devanand
Shenoy has expressed great interest in utilizing micro/nanomechanical systems for electric field sensing.
The great promise of these devices in detecting both static and time varying electric fields stems from this
initial feasibility study. Other implications of this technology can be envisioned in environmental science,
homeland security, and DOE applications. A more efficient electric grid may be a result of the accurate
and inexpensive detectors of low frequency E-fields surrounding power lines. In addition, technologies
capable of identifying centrifuge locations as well as other counterproliferation technologies are likely to
result from this study.
Results and Accomplishments
The following research tasks were completed during FY 2010 to demonstrate the unique advantages of
the present dual wavelength imaging technique and to show the feasibility of the approach. The FY 2010
tasks focused primarily on fabrication and testing of nanomechanical oscillators and their adaptation for
detection for constant and time varying electric fields. We evaluated several designs of microfabricated
oscillators, including pillar-shaped and cantilever-shaped resonator structures. Gold-coated cantilever
structures fabricated using silicon nitride as a structural material were found to be most promising for
creating one-dimensional arrays of E-field detectors. Implemented devices relied on a straightforward
technological sequence suitable for scaled-up fabrication. We assembled a test rig based on optical
readout and tested a series of cantilever resonators in the frequency range 1 kHz to 30 MHz. An electrical
charge on the cantilever tips was created by applying a DC bias between the metal layer on the cantilever
and a metal counter electrode at 1–5 mm away from the cantilever. The value of the charge located on the
tip was evaluated using finite-element analysis modeling. Consistent with our analytical predictions, less
stiff cantilevers showed higher sensitivity and were selected for subsequent, more detailed studies. In
summary, we demonstrated the feasibility of the innovative concept of a cantilever-based E-field detector
that integrates an antenna, a high Q resonator, and a frequency mixer on a very compact platform. Using
heterodyning, we achieved detectability of E-fields in the sub-millivolt per meter range in the kilohertz to
megahertz frequency range. Further improved sensitivity can be obtained by integrating a high charge
density electrete into the resonating element.
Information Shared
Datskos, P., S. Rajic, N. Lavrik, and T. Thundat. 2010. “Nanomechanical Electric and Electromagnetic
Field Sensors.” UT-Battelle Invention Disclosure 201002376, DOE S-115,422. Patent application in
preparation.
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