1) The document discusses micro-vibrational energy harvesting using piezoelectric transducers. It notes that piezoelectric transducers have the potential to power wireless electronics by harvesting ambient vibrational energy. 2) A cantilever beam design with piezoelectric plates bonded to the beam and a tip mass is proposed as the most effective configuration for capturing vibrational energy. 3) The document also examines energy harvesting circuits, noting the importance of matching the circuit design to the application to optimize power efficiency and output performance.

1. .
Conversion of Energy
MICRO VIBRATIONAL ENERGY HARVESTING USING PIEZOELECTRIC TRANSDUCER
JOSEPH M. RICHARDS, REZAUL KARIM NISHAT, AND SHAIKH AHMED
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
SOUTHERN ILLINOIS UNIVERSITY, CARBONDALE, IL 62901, USA
Motivation
 Energy harvesting systems have existed for decades in the form of:
 Wind Turbines
 Hydro-electric generators
 Solar Power systems
 Micro-energy harvesting has drawn increased interest as the need for a
wireless electrical power supply increases.
 Virtually inexhaustible source
 Little or no adverse environmental effects
 Energy harvesting that converts ambient energy available in the
environment into electrical energy offers the potential of renewable
power sources
 Potential to directly replace the battery and ultimately dampen the
environmental impact caused by the disposal of batteries.
Challenges for Energy Harvesting
Micro-Energy Harvesting
Conclusions References
1) Priya, S. Advances In Energy Harvesting Using Low Profile Piezoelectric Transducers.Journal of Electroceramics, March 2007, pp. 167-184.
2) Raju, M., & Grazier, M. ULP meets energy harvesting: A game-changing combination for design engineers. Texas Instruments: White Paper. April 2010
3) Beeby,S. O’Donnel, T. Roy, S. A micro electromagnetic generator for vibration energy harvesting. Journal of Micromechanics and Microengineering, June 2007,
pp. 1257-1265.
4) Wright, P. K. A piezoelectric vibration based generator for wireless electronics. Smart Materials and Structures, Aug 2004, pp. 1131-1142
5) Priya, S. (2008). Energy harvesting technologies. New York: Springer.
 Harvested power is derived from ambient sources so it tends to be
unregulated, intermittent and small
 Energy storage is required (I.e thin-film batteries, capacitors…)
 Energy cannot be stored indefinitely
 Energy Harvesting Circuits vary in efficiency
 Energy harvesting circuits do not have rules for realizing the best
power efficiency in circuit design.
 In general, the design goal is to match the energy harvesting
circuit to the application of the circuit to achieve the best overall
performance
 The direct piezoelectric effect converts mechanical
energy into electrical energy.
 Pressure generates charges on the surface of
piezoelectric materials.
 The approximate mechanical power of a
piezoelectric transducer vibrating assuming:
 The mass of the vibration source is much
greater than the seismic mass (m) in the
generator
 The vibration source is an infinite source of
power.
 The piezoelectric generates maximum power when
the operating frequency is also the natural
frequency.
Transducer Design
 The transducer design consists of an energy harvesting
generator and an energy harvesting circuit
 The energy harvesting circuit (LTC-3588) is a low-loss
full-wave bridge rectifier with a high efficiency buck
converter
 The generator is a cantilevered beam with piezoelectric
plates bonded on a substrate and a tip mass at one end
Energy Harvesting Circuit
 A piezoelectric transducer is proposed which can generator usable
electrical energy. The model provides some design intuition, which is
summarized as follows:
 The system should be designed to resonate at the dominant driving
frequency of the target vibrations if possible.
 Power output is proportional to the proof mass attached to the
system.
 Conversion efficiency of the energy harvesting circuit can be
greatly increased through carful design of the circuit.
 As systems decrease in size and power consumption, the possibility of
powering these wireless micro-electronics by ambient energy
harvesting increases.
Generator Configuration
 Macro-scale energy harvesting generates megawatts of energy for reducing oil dependency.
 Micro-energy harvesters scavenges milli-watts of ambient energy from surrounding sources.
 Ambient energy exists in various forms such as human activity, vehicles, and environmental sources.
 The most prominent micro-energy harvesting technologies extract energy from vibration,
temperature gradients and light
 Solar energy has proven to be capable of providing high power densities of 10,000 μW/cm3
 Light intensity can drop the efficiency and power density significantly.
 Solar energy density drops down significantly inside buildings and is dependent on weather
 Temperature gradients are another alternative power source that has been proposed
 While power generated from temperature gradients is abundant in some applications, it is
unsatisfactory in many others.
 Vibrational generators have been proposed using electromagnetic, electrostatic, and
piezoelectric conversion methods.
 Each method for transforming energy has benefits for certain applications. However, a quick
comparison of methods is possible by considering the average energy density between each of
the conversion methods.
 It is clear that piezoelectric transducers have the greatest potential for producing higher
power outputs than other conversion methods.
 A few configurations for constructing piezoelectric transducers have been proposed
 a cantilevered beam with piezoelectric plates bonded on a substrate and a tip mass at one
end (a)
 a multilayer piezoelectric plates (b)
 equivalent lumped spring mass with external excitation (c)
 The cantilevered beam configuration for the transducer is most favorable for a given force input.
 The cantilever configuration results in the highest average strain in the piezoelectric.
 The power output is closely related to the average strain developed in the bender.
 The cantilevered beam structure results in the lowest resonance frequency for a given size
 The target input vibrations are low frequency
 The conversion from mechanical low frequency stress into usable
electrical energy using a piezoelectric transducer can be outlined in
three primary steps:
 Firstly, the mechanical ac stress must be trapped from the
piezoelectric source.
 The mechanical energy is then converted into electrical energy
with the piezoelectric transducer directly through the
piezoelectric effect.
 The processed electrical energy is then stored. An energy
storage mechanism with significant energy density or power
density is required.
 Lithium ion batteries are generally chosen if high energy
density is needed and ultracapacitors are chosen if high
power density is needed.
 Energy harvesting circuits do not have rules for realizing the best power efficiency in
circuit design.
 In general, the design goal is to match the energy harvesting circuit to the application of
the circuit to achieve the best overall performance
 A simple energy harvesting circuit consists of a diode rectifier (AC/DC) and a DC–DC
converter.
 The addition of DC–DC converter has been shown to improve energy harvesting by a
factor of 7.
LT Spice IV Simulation
 LT spice IV is a high performance
simulator, schematic capture and
waveform viewer
 Using the simulator, it is possible to
ensure the waveform of a circuit for a
given input
 In our simulation, we achieved the
expected output waveform for the
energy harvesting circuit.
Diagram of the piezoelectric plates bonded to cantilever beam
Block Diagram of energy harvesting circuit
Simulated waveform output for LTC-3588 using LT Spice IV
Waveform output for LTC-3588
Micro-energy Harvesting estimates. [2]
Micro-energy Harvesting estimates. [2]
Energy density estimates for three vibrational transducers. [4]
(a) Cantilever beam with tip mass, (b) multilayer PZT subjected to transverse vibration and
(c) equivalent lumped spring mass system of a vibrating rigid body. [5]
A two-layer bender mounted as a cantilever. S is strain, V
is voltage, M is mass, and z is vertical displacement [4].
Schematic representation of the piezoelectric energy harvesting circuit [1].