Tech Briefs Magazine - August 2022 - 30

Materials & Coatings
a
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45 °C
b
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c
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23 °C
a) Temperature distribution image of the bioinspired thermotherapy patch affixed to the human wrist in normal, inward, and outward bending conditions.
(b, c) The patch affixed to the cubital fossa area and elbow, respectively. (Image: Tampere University)
treatment of arthritis, stiff joints, cervical
spondylosis, and physical injuries.
Traditional thermotherapy pads are
known to have caused burns, mainly
among people who fall asleep with
their heating pads on or among the elderly
who might not be very sensitive to
heat. Part of the problem is that commercial
heating pads are opaque and
users cannot see how their skin is reacting
to the therapy.
As the thermotherapy patch is made
entirely of plant-based materials, it can
help reduce carbon footprint and electronic
waste. All the materials used in
the fabrication process are eco-friendly,
economical, easily accessible, and easy to
fabricate. Electronics, especially flexible
electronics, are increasingly integrated
into medical devices, textiles, wellness
trackers, and other portable devices.
For more information, contact the
Communications
Office
at
tau@tuni.fi; +358 294 520 800.
Piezoelectric Material Remains Effective at High Temperatures
The material remains effective as an energy harvester or sensor at temperatures to well
above 572 °F.
The Pennsylvania State University, University Park, PA
P
iezoelectric materials hold great
prom ise as sensors and as energy
harvesters but are normally much less
effective at high temperatures, limiting
their use in environments such as
engines or space exploration. A new
piezoelectric device was developed
that remains highly effective at elevated
temperatures.
Piezoelectric materials generate an
electric charge when rapidly compressed
by a mechanical force during
vibrations or motion such as from machinery
or an engine. This can serve
as a sensor to measure changes in
pressure, temperature, strain, or acceleration.
Potentially, piezoelectrics
could power a range of devices from personal
electronics like wristband devices
to bridge stability sensors.
Researchers integrated the material
into a version of a piezoelectric energy
harvester technology called a bimorph
that enables the device to act as a sensor,
an energy harvester, or an actuator.
A bimorph has two piezoelectric layers
30
Schematic of a piezoelectric energy harvester that transforms
mechanical vibrations to electrical energy. (Image:
Elizabeth Flores-Gomez Murray/Penn State)
shaped and assembled to maximize efficient
energy harvesting. Sensors and
energy harvesters, while bending the
bimorph structure, generate an electrical
signal for measurement or act as a
power source.
Unfortunately, these functions work
less effectively in high-temperature environments.
Current state-of-the-art piezoelectric
energy harvesters are normally
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limited to a maximum effective operating
temperature range of 176 °F
(80 °C) to 248 °F (120 °C).
The new piezoelectric material
composition showed a near-constant
efficient performance at temperatures
up to 482 °F (250 °C). In addition,
while there was a gradual dropoff
in performance above 482 °F (250
°C), the material remained effective
as an energy harvester or sensor at
temperatures to well above 572 °F.
Another benefit of the material was
an unexpectedly high level of electricity
production. While at present,
piezoelectric energy harvesters are not
at the level of more efficient power producers
such as solar cells, the new material's
performance was strong enough to
open possibilities for other applications;
for example, as a continuous, battery-free
power supply in dark or concealed environments
such as inside an automotive
system or even the human body.
For more information, contact David
Pacchioli at dap1@psu.edu.
Tech Briefs, August 2022
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Tech Briefs Magazine - August 2022

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