Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Piezoelectric Charging for Smart Fabric
Applications
1
R. Hackworth , J. R. Moriera, R. Maxwell, R. Kotha, and A.A. Ayon, Member, IEEE
Abstract— Our current research includes an innovative design
and fabrication method for a wearable piezoelectric power
generating fabric. Rather than building a flexible piezoelectric
device and then applying it onto clothing as reported by other
groups, our approach is to integrate the devices directly with the
fabric while requiring no processing temperatures over 150 ˚C.
The device discussed here simply consists of a piezoelectric layer
encapsulated between a bottom electrode/wearable fabric and a
top layer electrode/conductive film layer.
Index Terms—Charge generation and storage, polyvinylidene
fluoride (PVDF), piezoelectric materials, smart fabrics.
I. INTRODUCTION
e report on the feasibility of employing flexible PVDF
Wpiezoelectric membranes to be used to generate
electrical charge for powering portable electronics. By
converting some of a person’s naturally expended mechanical
energy into useful electrical energy, the batteries currently in
use in portable electronic devices may be minimized, as well
as made efficiently green. Ideally, these devices will be
wearable and light-weight. The energy generation will
originate from the exploitation of the piezoelectric effect of
certain materials such as PVDF due to their naturally
occurring deformation as shown on Fig. 1.
a commercially available fabric enable greater comfort for the
end-user in a wearable energy harvester. Research has largely
focused on PVDF in cyclopentanone as a solvent due to its
natural flexibility compared with that of any other
piezoelectric materials we tested so far (which include zinc
oxide, barium titanate, et al..). For optimal piezoelectric
effects the PVDF film needs to be in the β-crystalline phase
[1]. PVDF is usually observed in one of the four main phases,
but only the β-phase is expected to possess strong d 31 ,
properties which are critical requirements in building a
practical prototype. The beta phase is generally formed by
poling the polymer at a high voltage while stretching it. When
the alpha phase is poled the dipoles align and for the delta
phase. Upon stretching the bonds in the chains will reorient
themselves into an all trans configuration. To convert the
largely α-phase PVDF into β-phase requires aligning the
polymer chains into the all trans phase structure as in Fig. 2.
To achieve this, the cured PVDF can be simultaneously
stretched and poled [2, 3] while at elevated temperature to
induce more of the bulk membrane into the stronger
piezolelectric β- phase [4].
Fig. 2. β-phase PVDF.
Fig. 1. The piezoelectric effect.
Multiple options for fabric substrates, bottom and top
electrodes, piezoelectric materials, as well as with the methods
by which they were fabricated were investigated. Our
observations indicate that the most successful bottom
electrode and fabric combination found so far consists of a
commercial polyester fabric coated through an electroless
deposition of nickel followed by copper. The characteristics of
Manuscript received April 8, 2011.
Thanks go to: Army Research Office
UTSA MEMs lab
II. MATERIALS
We start with the discussion of multiple options for fabric
substrates, bottom and top electrodes, and piezoelectric
materials, along with the methods [5] in which they are
fabricated.
Many commonly available fabrics and their melting points,
flash points, and decomposition temperatures were evaluated.
These fabrics were initially studied due to their ability to
withstand temperatures in excess of 150˚C, which is close to
the upper temperature range that any PVDF processing should
require. The curie temperature and melting point of PVDF are
close to each other. The currently accepted answer is a curie
temperature of about 150˚C and a melt temperature of 175˚C.
According to the manufacturer (Solef), devices made from
PVDF typically have a maximum usage temperature of about
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