Research in a Vacuum: DARPA Tries to Tap Elusive Casimir Effect for Breakthrough Technology

Casimir forces on parallel plates. (Wikimedia Commons)

Adam Marcus writes in Scientific American: “Named for a Dutch physicist, the Casimir effect governs interactions of matter with the energy that is present in a vacuum. Success in harnessing this force could someday help researchers develop low-friction ballistics and even levitating objects that defy gravity. For now, the U.S. Defense Department’s Defense Advanced Research Projects Agency (DARPA) has launched a two-year, $10-million project encouraging scientists to work on ways to manipulate this quirk of quantum electrodynamics.

“Vacuums generally are thought to be voids, but Hendrik Casimir believed these pockets of nothing do indeed contain fluctuations of electromagnetic waves. He suggested, in work done in the 1940s with fellow Dutch physicist Dirk Polder, that two metal plates held apart in a vacuum could trap the waves, creating vacuum energy that, depending on the situation, could attract or repel the plates. As the boundaries of a region of vacuum move, the variation in vacuum energy (also called zero-point energy) leads to the Casimir effect. Recent research done at Harvard University, Vrije University Amsterdam and elsewhere has proved Casimir correct—and given some experimental underpinning to DARPA’s request for research proposals.

“Investigators from five institutions—Harvard, Yale University, the University of California, Riverside, and two national labs, Argonne and Los Alamos—received funding. “(View the full Scientific American article: http://www.scientificamerican.com/article.cfm?id=darpa-casimir-effect-research)

More Data from the Original Request for Proposals for this Funding

The Defense Advanced Research Projects Agency (DARPA) is soliciting innovative research proposals in the area of Casimir Effect Enhancement (CEE). The goal of this program is to develop new methods to control and manipulate attractive and repulsive forces at surfaces based on engineering of the Casimir Force. One could leverage this ability to control phenomena such as adhesion in nanodevices, drag on vehicles and many other interactions of interest to the DoD.

A specific goal of this single-phase DARPA program is to demonstrate the ability to manipulate and engineer the Casimir force including the ability to neutralize the Casimir force.

Possible approaches to these program goals could include the development of composite materials, engineered nanostructures, mixed-phase materials, or active elements. DARPA appreciates that research activities (models and experiments) have already identified manipulation of the Casimir force as an important challenge. DARPA is interested in supporting significant, focused effort to demonstrate the ability to neutralize the Casimir force.

Proposed research should investigate innovative approaches that enable revolutionary advances in science, devices, or systems. Specifically excluded is research that primarily results in evolutionary improvements to the existing state of practice.

Background and Description

Recent advances in the ability to fabricate nanomechanical devices and to measure nanometer-scale forces have led to applications for van der Waals forces (non-contact AFM uses the gradient in vdW force to detect proximity to the surface, for example). Van der Waals forces also play a role in attracting nanomechanical structures into contact, whereupon permanent adhesion can cause failure of the device.

In practical devices, roughened surfaces, Teflon-like coatings, and mechanical design are used to overcome vdW adhesion. For example, the corners of the Texas Instrument Digital Micromirror Device (TI DMD) have tiny springs which store potential energy during the application of the electrostatic drive force; removal of the electrostatic force leads to the stored potential energy being released, which causes the mirror to be sprung free of the adhesive force. This is important in the DMD, as there are more than a million mirrors making contact to the surface at more than 10,000 times/second, and adhesion of any of the mirrors results in a detectable defect in the display. In other MEMS devices, such as inertial sensors, a Teflon-like film is deposited on the released micromechanical structures to reduce the surface energy of adhesion, and helping to prevent final adhesion and device failure. New ways to reduce or eliminate adhesive forces would allow improvements in MEMS reliability.

As devices evolve from micro to nano-scale mechanical structures, the adhesive forces become relatively stronger (compared to the mechanical restoring forces available, which scale as second or third order in dimension). Researchers working to develop nanomechanical devices can mitigate adhesion by designing relatively stiff structures, but this leads to compromise in the range of motion or in the voltages required for actuation. The ability to reduce or eliminate adhesive forces would allow new designs and tradeoffs between all the other challenging issues in nanomechanical device design.

The vdW force results from correlations in the fluctuations of the dipole moments of atoms on the opposite sides of the interface. The physics of the vdW force relies only upon the polarizability of the material and on the separation between the sides of the interface. The Hamaker constant, which captures the polarizability and other materials properties of importance, varies by only a single order of magnitude over practical materials. As a result, there is little opportunity to adjust or manipulate the vdW force and reduce the adhesion-induced failure of devices.

The Casimir force arises from the interaction of the surfaces with the surrounding electromagnetic spectrum, and includes a complex dependence on the full dielectric function of both surfaces and the region between. The complexity of the Casimir force leads to significantly greater possibility for manipulation through materials, geometries, and other phenomena. The significantly greater complexity of the Casimir force potentially allows greater opportunity for neutralization or for use of Casimir forces to partially cancel vdW forces.

There has been considerable recent effort to study the Casimir force, arising from the improvements in the ability to measure small forces near surfaces and improvements in the ability to complete complex numerical computations efficiently. Included in this activity has been growing speculation about the possibility to manipulate Casimir forces. This speculation has been primarily based on models and computations, but there are many very interesting applications for such an ability. DARPA is interested in funding approaches that can lead to the ability to manipulate Casimir forces.

Because of the still-speculative nature of the current work on manipulation of Casimir forces, DARPA is interested in carrying out an exploratory basic research program. The primary goal of this program is to determine if it is possible to manipulate and to neutralize the Casimir force in an experimental system.

More information on the grant is available at: https://www.fbo.gov/download/8b4/8b458c6d69f55c347679679dfc2ad09c/darpa_baa_08_59_ceed_final_for_posting_9sep08.pdf

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