Event Type:
Pritchett Lecture
Talk Title:
Novel electro-mechanical devices based on the Compliant Capacitor
GTMI (MARC) Building Auditorium

David R. Clarke

Extended Tarr Family Professor of Materials

School of Engineering and Applied Sciences

Harvard University, Cambridge, MA 02138


Dielectric elastomers are an exciting class of new materials whose properties are only just being explored and exploited.  One way of thinking about them is that they are highly compliant and flexible capacitors, whose dimensions can be controlled by an applied voltage to give dimensional changes orders of magnitude greater than piezoelectric materials or metals.  Although a very simple concept, its’ implementation to create new devices offers many opportunities for highly inter-disciplinary engineering research, bringing together materials, non-linear mechanics, electrical engineering and control. As I hope to describe, it also provides new ways to think about the imaginative use of materials.

In this talk I will describe some of the applications we are exploring as well as some of the scientific and technical challenges to our understanding of materials and devices that become evident in using them. We are particularly interested in applications of compliant capacitors, such as for adaptive optics, energy harvesting, displays and soft robotics.  Common to them all, is creating very large, reversible strains, upwards of several hundred percent, by applying a voltage. This poses a major challenge: how to achieve these strains in complaint and conformable electrodes when the strains are much larger than the rupture or fracture strains (~ 0.2 %) of any known metal or transparent electrode material, such as standard ITO conductors?  I will describe our approach and a new figure-of-merit for comparing different transparent conducting electrodes. A second challenge is to prevent dielectric breakdown since the attainable stretch depends on the applied electric field.  Surprisingly, the breakdown field depends not just on thickness – as in other dielectrics – but also on the pre-strain suggesting that the breakdown strength depends on molecular conformations in an incompressible polymer even though there is no spectroscopic evidence for any changes. 

Bio:  David R. Clarke is the inaugural holder of the Extended Tarr Family Professor of Materials Chair in the John A. Paulson School of Engineering and Applied Sciences (SEAS) at Harvard University. He holds a PhD in Physics from the University of Cambridge, a B.Sc. in Applied Sciences from Sussex University, and a ScD from the University of Cambridge.

A member of the National Academy of Engineering since 1999, he is also a Fellow of both the American Physical Society and the American Ceramic Society, and recipient of the Alexander von Humboldt Foundation Senior Scientist Award in 1993. He shared the 2008 Japanese NIMS Award for Recent Breakthroughs in Materials Science for Energy and Environment. He is a Distinguished Life Member of the American Ceramic Society and was recently listed as author of one of the 11 best papers in the 110 years of publications on ceramics and glasses.  

 His long-term interests in materials range from the fundamentals to the applied, from ceramics to metals to semiconductors and polymers. He has published over 450 papers in areas of materials ranging from thermal barrier coatings, to dielectric elastomers to fundamentals of oxidation to microelectronics reliability, and the electrical and optical properties of ZnO and GaN. 

At Harvard, he enjoys interacting with students in a Freshmen seminar course on “Materials, Energy and Society”, and teaching graduate courses in composites and deformation of materials. He recently introduced a new undergraduate course in SEAS on “Fundamentals of Heat Transfer”, a required course for students studying Mechanical Engineering.