The simplicity of the Wankel engine makes it well-suited for mini, micro, and micro-mini engine designs. The Microelectromechanical systems (MEMS) Rotary Engine Lab at the University of California, Berkeley, has previously undertaken research towards the development of Wankel engines of down to 1 mm in diameter, with displacements less than 0.1 cc. Materials include silicon and motive power includes compressed air. The goal of such research was to eventually develop an internal combustion engine with the ability to deliver 100 milliwatts of electrical power; with the engine itself serving as the rotor of the generator, with magnets built into the engine rotor itself. Development of the miniature Wankel engine stopped at UC Berkeley at the end of the DARPA contract. Miniature Wankel engines struggled to maintain compression due to sealing problems, similar to problems observed in the large scale versions. In addition, miniature engines suffer from an adverse surface to volume ratio causing excess heat losses; the relatively large surface area of the combustion chamber walls transfers away what little heat is generated in the small combustion volume resulting in quenching and low efficiency.