sma proposal

8/2/2019 Sma Proposal

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SMART MATERIALS AND STRUCTURE(06-89-440) BY DR STOILOV

Proposal to Design an

Energy Scavenger usingPyroelectric MaterialsPresented by

Chukwuma D Ugwu (102792360)

11/2/2011

The main objective of this project is to design a portable scavenging device that will convert thermal

energy into electrical energy through the use of pyroelectric material.


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Table of Contents

Objectives -------------------------------------------------------------------------------------- 1

Introduction --------------------------------------------------------------------------------------- 1

Problem Description ----------------------------------------------------------------------------- 2

Design Concept -------------------------------------------------------------------------------- 3

Conclusion ------------------------------------------------------------------------------------------ 12

Appendix --------------------------------------------------------------------------------------------13

References --------------------------------------------------------------------------------------- 16


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1

Objective:

The main objective of this project is to design a scavenger device that could convert thermal

energy into electrical Energy using Pyroelectric materials with reasonable efficiency (about 5%).

Introduction:

There is an increasing demand to explore methods for energy harvesting and scavenging. Due to

recent advances in electronics coupled with the fact that the price of energy is skyrocketing, there

is an increasing push to make devices more effective by either conserving or recapturing low

forms of energy such as mechanical vibrations, light and thermal energy back into the system.

(Sodano et al., 2004). Industry, world-wide, discharges over 1001012 joules (TJ) annually of

low-grade waste heat (10C to250C) from electric power stations, pulp and paper mills,

steel and other metal foundries, glass manufacturers and petrochemical plants( Ikura,2008). Inthe U.S. around 55% of the energy generated from all sources in 2009 was lost as waste-heat

(Lawrence, 2010). A technology to recover or convert this low-grade waste heat to

usable electricity could save industrial sectors tens of billions of dollars annually, through

increased process efficiencies and reduced fuel costs, while substantially reducing greenhouse

gas emissions. Therefore, this paper will be focussing on converting thermal energy emitted from

engines.

Thermal energy in the environment is a potential source of energy for low-power electronics

(Xie et al., 2010). The pyroelectric effect is popular for its use in detecting radiation first

proposed by Ta as early as 1932. Most pyroelectric detectors are made of thin wafers ofpyroelectric crystals in which when exposed to time varying radiation will produce an electrical

response (Liu et al.., 1978). There has been notable research in thermal energy scavenging.

Researchers at the University of Minnesota have come up with a new alloy-Ni45Co5Mn40Sn10

which undergoes a reversible phase transformation, in which one type of solid turns into another

type of solid when the temperature changes, according to a news release from the University of

Minnesota. Specifically, the alloy goes from being non-magnetic to highly magnetize. The

temperature only needs to be raised a small amount for this to happen (Boyle, 2011).


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Problem Description:

The aim of this research is to view, analyse and design a small scale energy harvesting system

using ferroelectric materials with special focus on pyroelectric materials. A material is said to

exhibit pyroelectric effect when a change in the materials temperature with respect to time result

in the production of electric charges (Bauer, 2006). If the temperature change is uniform over

the crystal, then the pyroelectric effect is described by a pyroelectric coefficient vector p given

by

Where Ps is the spontaneous polarization vector and T is the temperature (Nye p.78, 1957).

In order to harvest this energy, it would undergo four stages namely:

1. Conversion of raw input energy into effective energy that can be transferred to the activematerial

2. Conversion of energy available in the material into electrical energy3. Extraction of electrical energy available on the material4. Storage of the extracted energy.

Fig. 1 Energy harvesting flow cycle.

There are several physical limitations in regards to how efficient heat can be converted into

electricity. The useful work of all thermal engines is limited thermodynamically by Carnot

efficiency, given by:

carnot = 1 - TL/TH --------------- (1)

Where TH is temperature of heat source and TL is temperature of heat sink

Host

Structure

Energy

Conversion

Energy

extraction

Energy

Storage


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=

=

---------------------- (2)

Where WE is generated electricity, WP = energy lost in temp cycle, CV = heat capacity of

pyroelectric device, Qint =heat loss in thermal cycle and Qleak= heat leakages between the hot

and cold sources.

The actual energy conversion efficiency for any thermal scavenging device will depend on the

temperature difference between the hot and cold sources given by

Vmax =

------------------------- (3)

The resultant current will be given as

I =

------------------------------------- (4)

Where Afis the surface area of pyroelectric thin film capacitor, Ps(C/m2) is the pyroelectic thin

film polarization and p is the pyroelectric coefficient in C/m2K

The output power will simply be

PN = Vmax I ------------------------------------------ (5)

The resultant work done in converting thermal energy into electrical energy is given as

W =

Design Concept:

There are three design concepts that will be explored. Before getting into those concepts, various

design problems will be discoursed and tentative solution given pursued. One of the major draw

backs for using Pyroelectic materials in a scavenging device is the amount of electricity it could

generate upon heating. Pyroelectric materials like piezoelectric material do suffer from small

power output. To increase the power output, pyroelectric materials are stacked in series as shown

in fig 2a. Each of these stacks are placed in rows all connected in series (fig 2b). The resultant

voltage will be a lot higher thereby increasing the resultant power output.


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Fig 2a:Pyroelectric materials stacked in series Fig 2b: pyroelectric material stacked in series

Concept 1:

To create an effective pyroelectric generator, there has to a constant flow of electrons. This isachieved by varying the temperature on the material itself. To do this, an actuator in the form of

a cantilever beam is used to move the pyroelectric elements constantly from a hot plate to a cold

plate (shown in fig 3). The cantilever beam will be made up of a thin layer of a suitable shape

memory effect like NiTi or a dielectric material. These will enhance heat transfer through

conduction. Heat transfer through convection and conduction will be used for the cold plate.

Fig 3 showing the energy scavenger

Pyroelectric Generator

Anchor

SMP

Actua

Metallic plates

Hot and cold

surfaces


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Fig 4 showing the cantilever beam.

Concept 2:

Instead of using a cantilever beam as an actuator in moving the pyroelectric material between

plates, a SMA spring is used. The pyroelectric plate starts directly on the hot plate. As it heats

up, it also transfers that heat energy to the SMA actuator which triggers an upward movement

(fig 5). At this second stage, a stream of coolants such as air and water will be used to enhance

the heat transfer. As the pyroelectric plate gets cool, the SMA goes back to its original position.

Since the voltage produced is dependent on the cycle per unit time, the goal will be to make this

as efficient as possible.

A SME

material

BimetalElectrode

Bottom

Electrode

Top

Electrode

Anchor

Bottom

ElectrodeAnchor


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Fig 5 showing the energy scavenger concept II

Final Design Concept:

The final concept as shown in figure 6 utilizes demagnetization of magnets with increase in

temperature for its actuation system. The pyroelectric material PVDF is first coated with a

dielectric material. Note fig 7 below shows displacement due to temperature change

SMA

Actuators

Hot Body

Pyroelectric plate


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This dielectric material not only increases the heat conduction of the pyroelectric material but

also acts as poles used to remove the electric charge produced. Another layer of Neodymium

Iron Boron (N4914 used for the hot plate and N4321 used for the cold plate) magnets with

properties as shown in table 1 are utilized for the actuators.

Magnet Br(T) H(A/m) %Br(O

C) %H(O

C) Max Temp(O

C)

N4914 13.9 160.8495 -0.11 -0.61 130

N4321 13.1 158.336 -0.10 -0.05 160Table1: Show magnetic and mechanical properties of two types of NbFeb magnets. Data gotten from integrated magnetics

Neodymium Iron Boron magnets was preferred to other type of magnets because of its instability

with change in temperature. The strength of the magnet and the rate of demagnetization were

carefully chosen such that the magnet attached to the hot plate is stronger magnetically. As there

is a change in temperature, it slowly loses its magnetism faster than the magnet on the opposite

surface. Initially the force of N4914 is calculated as 0.16N (details of the calculated provided in

appendix) with N4321 0.149N. However when there is a 40oC change in temperature due to the

heating, N4914 magnetic force degrades to just 0.11N with N4312 at 0.14N. With greater force

being applied upwards, the pyroelectric material moves from the hot plate to the cold plate as

shown in figure 6. Rollers connected to a lead rail helps constrain the pyroelectric material to

ensure smooth actuation. The lead rail not only helps guide the PVDF actuation for but also acts

as the poles for each pyroelectric material and helps reduce the magnetic interaction between

systems (Fazeng, et.al, 1992). With cooling comes re-magnetization of the magnets which

returns the system back to its starting point. Its important to note that Nd-Fe-B based magnets

are not recommended for applications above 150o

C. The time taken for one complete actuationdepends on the rate of heating in terms of time rather because the response time of PVDF is

virtually instantaneous.


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As shown in figure 8, each PVDF has a separate actuation system. With an area of 1.44cm2, the

temperature profile is even all around each PVDF thereby increasing the efficiency in electric

voltage production. The maximum electric field which arises due to a temperature shift is:

V(to) =

where V (t0) is the induced electric field in volts/meter, is the pyroelectric coefficient in

Coulomb/C meter2, t is the thickness of the PVDF (in this case 110m), T is the temperature

difference in C, K3is the dielectric constant, and 0 is the dielectric permittivity of free space.

is typically ~ 400x10-6

coulomb/C meter2.

Table 2: Material properties of Pyroelectric Material

Sample Dielectricconstant

(KHz)

Area

(cm2)

Pyroelectric

coefficient(C/m2/K)

Capacitance

(nF)

Curie Temp(oC) o(F/m)

PVDF 10.46 1.44 9 0.090 165 8.85*E-12*table from Xie, 2010, dielectric constant from Westlake product bulletin

The current generated by the PVDF is given as

ip(t) = p`A

Where ip(t) is the induced electric current in A/m, p` is the component of the pyroelectric

coefficient orthogonal to the electrode surface area A; and T(t) denotes the temperature with

respect to time.

Figure 8 shows the graph of voltage generated in terms of time correlating with the temperature

change in terms of time. The voltage generated by PVDF depends on the rate of heat transfer.

The energy scavenger is treated with insulating gas such as argon to reduce the internal heat

transfer between plates. Detailed calculations provided at the appendix. At a temperature

difference at body temperature (assumed to be 40C), the average voltage produced per unit

actuator is 19mV. Given that the total number of actuators is 50, the total amount of voltage

produced by the scavenger is 0.95V. When the temperature difference is 100C, the voltage

produced by the scavenger is about 2V/0.5sec.


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A control system is developed with a temperature controller that controls the voltage output by

the scavenger device as shown in figure 9. The operational amplifier does amplify the voltage

produced by the device and also prevents the voltage going back into the system. A capacitor(10nF) is utilized to temporarily store and steady the fluctuating voltage being produced turning

it into a DC voltage. A very large resistor (1M) is used to limit the amount of current that enter

the operational amplifier.


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Conclusion:

At the end of the research, an energy scavenging design for the conversion of thermal energy

into electrical energy using pyroelectric materials was made. We have developed a new

innovative concept for the conversion of low temperature thermal waste heat into electrical

energy using electromechanically based microstructures, which convert thermal energy gradientsinto temporally varying energy gradients across these millimeter sized structures. These

millimeter sized energy harvester structures can be fabricated in 2D arrays and scaled up in size

allowing these devices to generate sizable amounts of electrical power for many applications.

The design, modeling and experimental work outlined in this report describes the initial studies

we have performed to demonstrate the utility of this technique. Although these studies are in

their initial stages, an actuation system that achieves a complete cycle in 0.5secs has for the firsttime, modeled and demonstrated a steady flow of voltage operating in a relatively low

temperature gradient. These operating frequencies (and resultant rates of temperature change in

the cantilever structures) are several orders of magnitude greater than have previously beenachieved in pyroelectric energy harvesting devices.

With extensive temperature cycling studies on fabricated thin film pyroelectric capacitivestructures and the testing of various operational amplifiers, a portable charging device powered

purely by the human body temperature could be designed in the near future.


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Appendix:

>> % Neodymium Iron Boron N4914

>> % F = AB^2/2u0

>> Area = 1.44; Br = 13.9; H= (12800*4*pi)/1000 %Area =m^2, Br =T, H=T

H =

160.8495

>> Area = 1.44*10^-4

Area =

1.4400e-004

>> F= (Area*Br^2)/(2*(Br/H)) %F in N

F =

0.1610

>> % in force due to temperature rise

>> Br_new =((13.9*0.11*40)/100)

Br_new =

0.6116

>> Br_new2= 13.9 - Br_new

Br_new2 =

13.2884

>> Hnew= (160.8495*0.611*40)/100

Hnew =

39.3116

>> Hnew2=(160.8495-Hnew)

Hnew2 =


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2

121.5379

>> Fnew= (Area*Br_new2^2)/(2*(Br_new2/Hnew2))

Fnew =

0.1163

>> %Magnetic property for upper level magnet using Neodymium Iron Boron N4316

>> Br = 13.1; H= (12600*4*pi)/1000

H =

158.3363

>> Fn= (Area*13.1^2)/(2*(13.1/158.336))

Fn =

0.1493

>> % change in force due to temperature rise

>> BrN =13.1-((13.1*0.10*40)/100)

BrN =

12.5760

>> Hnew= 158.336-(158.336*0.05*40)/100

Hnew =

155.1693

>> Fn= (Area*BrN^2)/(2*BrN/(Hnew))

Fn =

0.1405

>> for t=(1:10) % calculating voltage generated in respect to temperature change

>> for t = (1:10:100)

V_t0=(400*10^-6*t*110*10^-6)/(10.46*1000*8.85*10^-9)


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end

V_t0 =

4.7531e-004

V_t0 =

0.0052

V_t0 =

0.0100

V_t0 =

0.0147

V_t0 =

0.0195

V_t0 =

0.0242

V_t0 =

0.0290

V_t0 =

0.0337

V_t0 =

0.0385

V_t0 =

0.0433

>> plot (V_t0, t)

>> t=(1:100);

>> V_t0=(400*10^-6*t*110*10^-6)/(10.46*10008.85*10^-9);


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Reference:

J.Xie, X.P.Mane, et.all, 2010. Performance of Thin Piezoelectric Materials for pyroelectric

Energy Harvesting, published in Journal of Intelligent Material Systems and structures, Vol 21-Feb 2010.

J.F.Nye, Physical Properties of Crystals. London, England: Oxford University Press, 1957

Rebecca Boyle, New Allow can convert heat directly into electricity, 2011

http://www.popsci.com/technology/article/2011-06/new-alloy-can-convert-heat-directly-

electricity

Ikura, M., Conversion of Low-grade waste heat to electricity, CANMET Energy Technology

Centrehttp://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/publications.html?2008-56

Lawrence Livermore National Laboratory, Estimated U.S. energy use in 2009,

https://flowcharts.llnl.gov/

Lallart, Guyomar, Ferroelectric Materials for small-scale Energy Harvesting Devices and Green

Energy Products, LGEF, INSA-Lyon.

LIU, Long, Pyroelectric Detectors and Materials, Proceedings of the IEEE, Vol. 66, No.1,

January 1978

Wu, Hagelstein, Chen, Sinha, Meulenberg, Quantum-coupled single-electron thermal to electric

conversion scheme, Journal of Applied Physics, 2009.

J. F. Liu, Y. Ding, Y. Zhang, D. Dimitrar, F.Zhang and G. C. Hadjipanayis, New rare-earthpermanent magnets with an intrinsic coercivity of 10kOe at 500oC, Journal of Applied Physics,

85, 5660(1999)

L Fazeng, Ren Jianjun, et al, 1991. Thermal Stability ofLow Cost Nd-Fe-B Magnets,University of Shenyang, China.

PVDF Films mechanical properties, Published in Western lake Product Bulletin, Westlake

plastic Company P.O. Box 127, Lenni, PA 19052 USAhttp://www.westlakeplastics.com/pdf/film_pvdf.pdf
http://www.popsci.com/technology/article/2011-06/new-alloy-can-convert-heat-directly-electricityhttp://www.popsci.com/technology/article/2011-06/new-alloy-can-convert-heat-directly-electricityhttp://www.popsci.com/technology/article/2011-06/new-alloy-can-convert-heat-directly-electricityhttp://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/publications.html?2008-56http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/publications.html?2008-56http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/publications.html?2008-56https://flowcharts.llnl.gov/https://flowcharts.llnl.gov/https://flowcharts.llnl.gov/http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/publications.html?2008-56http://www.popsci.com/technology/article/2011-06/new-alloy-can-convert-heat-directly-electricityhttp://www.popsci.com/technology/article/2011-06/new-alloy-can-convert-heat-directly-electricity

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