Design and validation of piezoelectric energy harvesting systems

12-04-2023 1Herhaling titel van presentatie

Design and validation of piezoelectric energy harvesting systems

Ilyas Caluwé[email protected]

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Contents

• Literature study• Vibration energy harvesting• Wind flow energy harvesting

Design and validation of piezoelectric energy harvesting systems1 Jul 2011

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LITERATURE STUDY

Part 1

1 Jul 2011Design and validation of piezoelectric energy harvesting systems

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Energy harvesting

Energy harvesting– Process of deriving and capturing energy from external sources and

storing it to power autonomous wireless devices– Example: power wireless sensor network nodes– Energy sources: Solar, thermal, mechanical– Extensive literature study:

– Different principles– Advantages and disadvantages– Explore possibilities for implementation in this work

– Purpose of the work: – find feasible setups to extract energy from vibrations or wind flow – derive the parameters important for optimization


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Mechanical energy harvesting

Availability of mechanical vibrations:– Pipe ducts, engines, near roads and railways, …

Conversion principles:– Electrostatic

– Variable capacitor

– Electromagnetic– Permanent magnet and coil

– Piezoelectric– Convert mechanical strain into electrical charge


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Piezoelectric energy harvesting

Piezobeam– The piezoelectric effect in combination with a cantilevered

beam was found a well performing and versatile setup– Piezolayers compressed / strained– Unimorph or bimorph– Series or parallel connection


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VIBRATION HARVESTING

Part 2


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Vibration harvesting beam setup

Bimorph harvester MFC patch harvester


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Vibration harvesting setup


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Vibration harvesting

Setup allows:– Clamming of both the bimorph

and MFC harvester– Different tip masses– Different electrical loads– Parallel and series connection

of the piezolayers– Different excitation frequencies– Measurement of output power– Measurement of input power


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Bimorph harvester

Resonant frequency– Good agreement with theoretic formula for a mass-

spring system without damping

– Most ambient vibrations are low frequent: 20 Hz to 200 Hz


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Bimorph harvester

Power output– No tip mass– Acceleration rms 2,5 g– Optimal external load resistance

equals internal resistance of the piezo:

– Series: 46,2 kΩ– Parallel: 12,5 kΩ

– Pout, parallel ≈ Pout,series

– Vopt,parallel = ½ . Vopt, series

– Iopt, parallel = 2 . Iopt, series


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Parallel theoreticSeries theoreticParallel measuredSeries measured

Resistance [Ω]Pow

er

outp

ut

[mW

]

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Bimorph harvester

Power output in function of the tip mass– Acceleration rms: 1 g


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Output powerLinear (Output power)

Tip mass [gram]

Pow

er

[mW

]

Tip mass [gram]

Pout/Pin

[-]

0 0,37

1 0,36

2 0,30

3 0,31

4 0,29

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MFC harvesterPower output

No tip mass– Acceleration rms: 1 g– fres = 36,8 Hz– Max power output: 1,43 mW

Tip mass of 4 grams– Acceleration rms: 1 g– fres = 18 Hz– Max power output: 3,78 mW


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Power (left axis)Polynomial (Power (left axis))

Electrical resisitive load [Ω]

Outp

ut

pow

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[mW

]

Volt

age [

V]

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Comparison

Comparison of energy densities of the different harvesting devices for the same input power


Output power [mW]

Output power / active area [mW/cm²]

Bimorph 2,87 0,28

MFC patch 1,42 0,36

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Conclusions on vibration harvesting

– Design has a power output that is comparable with literature– Caution when comparing: same parameters?

– Results are in agreement with theoretic harvester models– Importance of parallel / series connection of the piezolayers– Important to obtain optimal power output:

– Match resonant frequency to driving frequency– Is a distinct driving frequency present?

– Use optimal electrical load– Rigid clamming– Increasing tip mass:

– Increase in input and output power– Decrease in efficiency

– Geometry of plate and material choice– Further optimization is possible


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WIND FLOW HARVESTING

Part 3


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Wind flow harvesting

– Wind flow → Mechanical vibration → Electrical energy– Wind flow harvesting based on the experience gathered with the vibrating

beam setup in combination with aeroelastic effects:– Flutter:

– Vortex shedding:

– Structure is too stiff to obtain flutter– Emphasis is put on vortex shedding


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Vortex shedding

Upstream cylinder– 2 controllable parameters:

– Cylinder diameter– Distance cylinder and tip of plate

– Match resonant frequency with vortex shedding frequency to obtain lock in

– Estimation of the shedding frequency by using the Strouhal number:


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Upstream cylinderPower output


2,8 cm cylinder diameter– Optimal power output at 3 m/s– Optimal cylinder distance 10 – 15 cm

4 cm cylinder diameter– Optimal power output at 6 m/s– Optimal cylinder distance 20 – 25 cm– Comparable power output

Disadvantages:– Separate cylinder– No stable output

– Frequency– Amplitude

fres ≈ 19 Hz

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Tip cylinder


Long tip cylinder– fres 11,7 Hz

– Popt= 3 mW at 3,5-4 m/s– Torsional movement of tip– Voltage frequency and amplitude not stable

Short tip cylinder– Try to eliminate torsion– fres ≈ 17 Hz

– Popt= 0,75 mW at 6-6,5 m/s– Reduction in power output not in proportion

with area reduction– Power output peak at higher wind speed

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Two plates with tip cylinder


Long tip cylinder, two plates– Eliminate torsional movement– More MFC patches can be added– Importance of clamming

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Two plates with tip cylinderPower output

– Linear increase in power output in between 3,8 and 4,9 m/s– Steady sinusoidal voltage output– Lock in at rather high wind speed– fres ≈ 15 Hz


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Conclusions on wind flow harvesting


– Combination of clamped beam / piezoelectricity / aeroelasticity is feasible

– Lock-in phenomenon clearly observable– Long tip cylinder attached to two plates gives good results:

– Stable frequency– Stable amplitude– Power output is readily increased by adding piezoelectric patches– Linear increase in power output with wind speed

– Power output remains in the order of magnitude of milliwatts– Importance and interrelation of:

– Wind speed– Cylinder diameter

– Importance of a rigid clamming

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Future work


– Material choice– More flexible structural material

– Optimization of dimensions– Width / height of piezopatch and structural plate

– Electromechanical coupling– Damping because of the plate dimensions

– Thickness of the structural plate

– Conversion circuitry

Design and validation of piezoelectric energy harvesting systems

Technology

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