Elizabeth K. Reilly

Performance limits of the three MEMS inertial energy generator transduction types

In this paper, trends from the last 10 years of inertial micro-generator literature are investigated and it is shown that, although current generator designs are still operating well below their maximum power, there has been a significant improvement with time. Whilst no clear conclusions could be drawn from reported fabricated devices with respect to preferred transducer technology, this paper presents operating charts for inertial micro-generators which identify optimal operating modes for different frequencies and normalized generator sizes, and allows comparison of the different transduction mechanisms as these parameters vary. It is shown that piezoelectric generators have a wider operating range at low frequency than electromagnetic generators, but as generator dimensions increase, the frequency to which piezoelectric transducers outperform electromagnetic transducers decreases.

Modeling, fabrication and stress compensation of an epitaxial thin film piezoelectric microscale energy scavenging device

This paper focuses on a renewable power source for wireless sensor nodes via energy scavenging using thin film piezoelectrics. The novelty of this research is the growth of epitaxial PZT on a Si platform. The films were grown with good consistency using pulsed laser deposition. Using the optimized piezoelectric film properties, an analytical model was generated to predict the output power for a single cantilever, 5.5 nW/beam. Further, if arrays of the cantilevers were packed into a cubic centimeter, the output power would be 80–200 µW cm−3. A microfabrication technique was developed to manufacture the cantilevers using standard low-temperature procedures. As the devices demonstrated a significant residual stress upon release, an analytical model was created to predict the residual stress in the films from the high-temperature growth step. A neutral argon bombardment technique was then established to compensate for these stresses and to develop a planar usable device. The initial device fabrication was successful and testing was done to determine resonant frequency, quality factor and output power. The experimental resonant frequency response compared well with what was determined by the model, but the quality factor was 95, which was lower than expected. The output power per cantilever was 24.5 pW over a 510 MΩ load operating over an input vibration of 10 m s−2 and at resonant frequency (976 Hz).

Thin film piezoelectric energy scavenging systems for long term medical monitoring

For small, inexpensive, ubiquitous wireless sensors to be realized, all constituents of the device, including the power source, must be directly integratable. For long term application the device must be capable of scavenging power from its surrounding environment. An apparent solution lies in conversion of mechanical energy to electrical output via the growth and direct integration of piezoelectric thin film unimorphs with the wireless electronics

Technologies for an Autonomous Wireless Home Healthcare System

We present a design study highlighting our recent technological developments that will enable the implementation of autonomous wireless sensor networks for home healthcare monitoring systems. We outline the power requirements for a commercially available implantable glucose sensor which transmits measurements to an external wireless sensor node embedded in the home. A network of these sensor nodes will relay the data to a base station, such as a computer with internet connection, which will record and report this data to the user. We explore the feasibility of powering these sensors using energy scavenging from both body temperature gradients and vibrations in the home, and discuss our developments in energy storage and low power consuming hardware.

Energy Scavenging in Support of Ambient Intelligence: Techniques, Challenges, and Future Directions

Ambient intelligence (AmI) depends on the existence of vast quantities of wireless sensors distributed throughout the environment. While advances in IC fabrica- tion technologies, circuit designs, and networking techniques have greatly reduced the cost, size, and power consumption of potential wireless sensor platforms, the development of suitable power sources for many applications lags. The purpose of this chapter is both to review technologies for scavenging energy from the environment to power wireless sensors, and to discuss challenges and future research directions for vibration-based energy scaven- ging. Many potential energy scavenging technologies are presented along with current state of research and theoretical maximum power densities. Special focus is given to scavenging energy from mechanical vibrations extant in many environments. Results from vibration- based energy scavengers using piezoelectric structures developed by the authors are pre- sented demonstrating power production of approximately 375 mW=cm 3 . While wireless sensor nodes have successfully been powered by vibration-based energy scavengers, several improvements are possible, and indeed necessary, for widespread deployment. Three areas

Optimizing On-Chip Piezoelectric Energy Scavenging for Integration of Medical Sensors with Low-Power Wireless Networks

Vibrational energy scavenging using piezoelectric material is a viable method to provide sufficient energy for low-power wireless sensor networks. The applications for such devices in hospital settings as well as in vivo are abundant. Current devices are limited by both their design and material selection. This paper will address optimizing the design of microscale devices by showing how the device strains under input vibrations are directly proportional to its power output, and by proposing alternate designs which increase the strain distribution over more of the device volume. Finite element modeling (ANSYS®) was used to determine the strain distribution in a cantilever, modified cantilever, trapezoid, and spiral shaped piezoelectric microscale energy scavenging system. The increase in strain under uniform acceleration was determined to be 0, 29.2, 37.8, and 87.0%, respectively, over that of a simple cantilever.