Power consumption is forecasted by the International Technology Roadmap of Semiconductors (ITRS) to pose long-term technical challenges for the semiconductor industry because power supplies do not adhere to Moore's Law. Miniaturization of power supplies alone, whether through capacitors, batteries or fuel cells, is unlikely to meet the needs for lifetime, robustness and scale of new devices. Examples of this can be seen in commercial devices where the present power supply (single battery electrochemistry, non-hybrid) comprise a large fraction of both mass (13-36%) and volume of devices. Majority of these portable devices are powered from secondary batteries that are powered via the GRID during recharge. As usage of these devices increases, so does power demand on the GRID (interconnected electric power network by which electrical power is distributed), which currently derives -85.9% of its power from fossil fuel, while only 14.1% from renewable energy sources. Hence the research goals are to extend product cycle life and reduce product volume and mass, while scavenging otherwise wasted mechanical energy that occurs during the operation of the device.
In this talk, an algorithm for designing hybrid power supplies will be discussed. The first part of the talk will focus on application of the algorithm using .battery technology, wherein a case study of the Wireless Integrated Microsystems (WIMS)-environmental monitor testbed (EMT) will be provided. The WIMS-EMT is a multicomponent microelectromechanical system (MEMS), incorporating complementary metal oxide semiconductor (CMOS) materials for high-precision circuits used for integrated sensors such as micro-g accelerometers, micro-gyroscopes, and pressure sensors.
The algorithm is comprised of three strategies for providing power, which include (I) specification of a single, aggregate power supply, resulting in a single battery electrochemistry and cell size; (2) specification of several power supplies, by a priori division of power sources by power range; and (3) specification of an arbitrary number of power "bundles," based on available space in the device.
The second part of the talk will focus on the expansion of the algorithm to include energetic piezoelectric materials. Piezoelectric materials generate electrical power when subjected to mechanical loading. Hybrid power generation, i.e. the use of two or more different power supply methods can, if done effectively, improve the lifetime (sustainability) and efficiency of single-source power supply systems such as batteries, fuel cells etc. The ability of piezoelectric devices to capitalize off of inherent device movements and acoustic wave production, offer opportunities to continuously charge secondary sources of power such as batteries, which could potentially increase host device operational lifetime until the activate materials of the battery are exhausted or the piezoelectric material cracks or breaks.
The talk will conclude with an analysis of future work required for realization of piezoelectric energy harvesting
Host: Dunbar Birnie x5-5605
Kimberly Ann Cook-Chennault is an Assistant Professor in the Mechanical and Aerospace Engineering Department at Rutgers University. She holds BS and MS degrees in Mechanical Engineering from the University of Michigan and Stanford University respectively; and a PhD in Biomedical Engineering from the University of Michigan.
Prior to receiving her doctorate, Dr. Cook worked at Ford Motor Company, Visteon and Lawrence Livermore National Laboratories. As a product engineer with Ford and Visteon, she designed automotive components and established design criterion for impending product platforms. While at Lawrence Livermore National Laboratory, she created dynamic and structural finite element numerical models of containers used to store and transport explosive materials, and validated the predictions of these models with experiments. Her research - hybrid power system design, is interdisciplinary, and allows for the combination of industrial, corporate and research experiences. For example, as a part of the Wireless Integrated Microsystems (WIMS) Environmental Test Monitor Test Bed (EMT) of the Engineering Research Center (ERC) at the University of Michigan; Dr. Cook solved a real-world problem - powering an environmental monitor, by developing the first algorithm for the design hybrid power supplies for portable MEMS. This work culminated with the creation of a userfriendly MatLab code, .POWER (Power Optimization for Wireless Energy Requirements). This work was funded by NSF through the Wireless Integrated Microsystems (WIMS) Engineering Research Center (ERC) at the University of Michigan, and introduced a new area of research, hybrid power supply design.
As an Assistant Professor at Rutgers University, Dr. Cook-Chennault continues her work in the design of hybrid power systems, and plans to incorporate energetic materials, such as piezoelectric energy harvesting devices into POWER. The challenges associated with energy harvesting via piezoelectric devices are related to their electrical properties: high voltage, low current and high impedance, which are characteristics usually optimal for actuator, sensor and ultrasonic applications, but not for generation of power and energy. However, reduction of power consumption of MEMS devices and advances in fabrication techniques, present new opportunities for materials once overlooked as power sources.