The aim of this study is to examine how small amounts of ambient energy, such as in vibrations or wind flow, can be converted to electrical energy and to build a working design. The different energy harvesting principles found in literature are studied first. Piezoelectric energy harvesting was found suitable for both energy harvesting out of ambient vibrations and wind flow. A cantilevered beam setup with a piezopatch (MFC patch) is chosen because it has good power conversion characteristics, it is robust and versatile. Both vibration and wind flow harvesting devices can be constructed with this setup. Vibration harvesting setups were constructed with both a commercially available bimorph piezoceramic harvester and with an unimorph harvester consisting of a stainless steel plate and a composite-reinforced piezoceramic patch attached to it. The power output is reported. The parameters that are of importance to optimize the setup are discussed. The possibilities to use the beam for wind flow harvesting were explored. Different aeroelastic phenomena were studied to give insight into possible working principles. A number of designs are proposed and some are tested using the stainless steel plate with the MFC patch. The possibility of using aeroelastic stability to harvest energy is shown, and suggestions for further improvements are given.

1. Design and validation of
piezoelectric energy
harvesting systems
Ilyas Caluwé
ilyas.caluwe@gmail.com
20-12-2012 Herhaling titel van presentatie 1

2. Contents
• Literature study
• Vibration energy harvesting
• Wind flow energy harvesting
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.2

3. Part 1
LITERATURE STUDY
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.3

4. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.4

5. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.5

6. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.6

7. Part 2
VIBRATION HARVESTING
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.7

8. Vibration harvesting beam setup
Bimorph harvester MFC patch harvester
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.8

9. Vibration harvesting setup
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.9

10. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.10

11. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.11

12. Bimorph harvester
Power output 9
8
– No tip mass 7
Power output [mW]
– Acceleration rms 2,5 g 6
5
– Optimal external load resistance
4
equals internal resistance of the
3
piezo: Parallel theoretic
2 Series theoretic
– Series: 46,2 kΩ
1 Parallel measured
– Parallel: 12,5 kΩ Series measured
0
– Pout, parallel ≈ Pout,series 0 20000 40000 60000 80000 100000
– Vopt,parallel = ½ . Vopt, series Resistance [Ω]
– Iopt, parallel = 2 . Iopt, series
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.12

13. Bimorph harvester
Power output in function of the tip mass
– Acceleration rms: 1 g
Tip mass Pout/Pin 16
[gram] [-] 14
Output power
12
Input power
0 0,37
Power [mW]
10
1 0,36 8
6
2 0,30 4
3 0,31 2
0
4 0,29 0 1 2 3 4
Tip mass [gram]
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.13

14. MFC harvester
Power output
No tip mass Tip mass of 4 grams
– Acceleration rms: 1 g – Acceleration rms: 1 g
– fres = 36,8 Hz – fres = 18 Hz
– Max power output: 1,43 mW – Max power output: 3,78 mW
1.6 16
1.4 14
Output power [mW]
1.2 12
Voltage [V]
1.0 10
0.8 Power (left axis) 8
0.6 Voltage (right axis) 6
0.4 4
0.2 2
0.0 0
0 50000 100000 150000 200000
Electrical resisitive load [Ω]
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.14

15. Comparison
Comparison of energy densities of the
different harvesting devices for the same
input power
Output power Output power /
[mW] active area
[mW/cm²]
Bimorph 2,87 0,28
MFC patch 1,42 0,36
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.15

16. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.16

17. Part 3
WIND FLOW HARVESTING
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.17

18. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.18

19. 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:
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.19

20. Upstream cylinder
Power 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 fres ≈ 19 Hz
– Comparable power output
Disadvantages:
– Separate cylinder
– No stable output
– Frequency
– Amplitude
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.20

21. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.21

22. Two plates with tip cylinder
Long tip cylinder, two plates
– Eliminate torsional movement
– More MFC patches can be added
– Importance of clamming
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.22

23. Two plates with tip cylinder
Power 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.23

24. 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
Design and validation of piezoelectric energy harvesting systems
1 Jul 2011 Pag.24

25. 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
1 Jul 2011 Pag.25