Research Interests:
Electromagnetic and acoustic properties of complex materials, metamaterials, wave-matter interactions, material systems tunable electronically, smart and programmable materials, embedded systems, computational methods, optimization methods.

Curriculum VitaeList of publicationsGoogle Scholar

Current Research:
1. Active metamaterials. Active metamaterials are artificial media having active elements embedded in their structure in order to enhance the material functionality. I have developed an active metamaterial platform that enables in principle any kind of material response allowed by the laws of physics. I am currently exploring the range of unusual wave behavior achievable in these materials and difficult to obtain using other approaches. Specific accomplishments include: electromagnetic and acoustic one-way mirrors that are transparent for one direction of wave propagation and opaque for the opposite direction (Popa&Cummer, Phys. Rev. B, 2012; Popa&Cummer, Nat. Comms., 2014); materials whose acoustic properties are reconfigurable in real-time (Popa et al, Phys. Rev. B, 2015); time reversal media (Popa et al, submitted). The figure on the right illustrates the latter: a diverging wave is incident on an active metamaterial mirror; the mirror responds in real-time with a second harmonic time reversal wave converging back towards the source.

2. Transformation optics/acoustics. Transformation optics and its close relative transformation acoustics comprise a set of tools that specify the properties of materials needed to implement a wide range of remarkable devices such as the invisibility cloak. The invisibility cloak is a shell that, placed around an object, guides acoustic waves around the object with minimal or no scattering. I have led the effort to design, fabricate, and demonstrate experimentally the first acoustic cloaks in air (Popa et al, Phys. Rev. Lett., 2011; Zigoneanu et al, Nat. Mater., 2014). I have also introduced optimization algorithms to the general theory that significantly reduce the complexity of transformation optics/acoustics designs (Popa et al, Phys. Rev. A, 2009; Popa et al, J. Opt., in press).

3. Water-based acoustic metafluids. Hiding objects from sound detection require fluid-like materials (called metafluids) having a large degree of mass anisotropy. Acoustic systems find most applications underwater, but designing metafluids for water environments is tricky. I have led the effort to demonstrate experimentally the first solid anisotropic materials for water-based operation (Popa et al, submitted), and I am exploring new ways to increase the anisotropy of these materials to the levels required by cloaking.

Other Projects:
4. General game playing. General game playing is a branch of artificial intelligence that strives to develop general algorithms that enable computers to play any game. The computer reads the rules of the game after the game has started and devises a strategy based entirely on these rules. No algorithms specialized for a particular game are permitted. I am currently developing a competitive player written in C++ and Java. So far, it won the 2015 edition of the competition organized by Coursera's General Game Playing course. The chronicle of the playoffs can be found here.