Page 37 - EE Times Europe Magazine – November 2023

EE|Times EUROPE 37

What’s Happening in the World of Micro-Energy Harvesting?

BEST EH TECHNOLOGIES FOR POWERING
IoT DEVICES
The micro-energy–harvesting technolo-
gies best suited to powering IoT devices
are photovoltaic (PV) cells; piezoelectric or
electrostatic converters, which harvest energy
from vibration; and Peltier thermoelectric
harvesters, which convert temperature gradi-
ents into electrical energy.
The power density of these sources ranges
from about 100 mW/cm for outdoor solar
2
to 10 mW/cm for a thermoelectric gener-
2
ator (TEG). The electrical characteristics
of the different harvesters vary widely. For
example, TEGs have low-impedance outputs,
producing continuous DC at a low voltage.
PV cells are similar, but the current, and
hence the impedance, varies with the level
of incident light. Piezoelectric harvesters
deliver shorter bursts of energy and usually Designed to help engineers quickly evaluate energy from several harvesting sources, the
at higher voltages than their TEG and PV demonstration platform shown comprises two PV harvesters, a piezoelectric harvester
counterparts. with a DC motor to generate vibration for it, two TEGs, and a heater and heatsinks to
This has led EH PMIC manufacturers to excite the TEGs.
offer a range of power management chips,
each designed to work with a particular there could be a lot of ambient vibration. In a System-level considerations come into
type of harvester. Some of these may also greenhouse, which may use smart, connected play, too. If wireless sensor modules are
need external components for impedance temperature and humidity sensors, the deployed close to hubs or routers, low-
transformation between the harvester and opposite is true. power, short-range radio protocols like
the chip. Bluetooth, Zigbee, Z-Wave or Wi-Fi can be
This presents a dilemma for the IoT device GAUGING HOW MUCH ENERGY used. The final selection is determined by
manufacturer. A slightly different device NEEDS TO BE HARVESTED the required data rate and signal range and
must be designed for each type of harvester. The nature of the end application, including costs. Where IoT devices are connected to a
Even then, there’s still the problem that the the wireless connectivity protocol or proto- network that spans a wide geographic area,
kinds of energy sources available to power cols used by IoT devices, are key determinants cellular or LPWAN connections may be the
the IoT device may not be known at the time of power consumption. For example, smart only options, both of which are power-
it’s being designed. For example, there’s not meters send tiny data packets infrequently, hungry compared with short-range systems,
much opportunity for solar PV in a railway whereas streaming video from security as the comparison table shows.
tunnel or inside an industrial plant, but cameras is data- and power-hungry. A detailed analysis of the power profile of
an IoT device when it’s deployed in the field is
the first step in determining the performance
required from an energy-harvesting system.

EH PMICs EVOLVE TO SIMPLIFY
MICRO-ENERGY HARVESTING
While IoT could be designed with multiple EH
PMICs to create a range of inputs, each suited
to a particular type of harvester, this adds
cost and wastes hardware resources in most
applications.
The most recent trend is toward smarter,
multiple-input EH PMICs. With these, two or
more types of harvesters can be connected to
the same power management chip.
Micro-energy harvesting has not yet
delivered on the promise of a battery-less
world for IoT devices, but it is certainly on
the cusp of doing so. As costs fall,
energy-harvesting systems become simpler
to design and use, and electronic engineers
show more commitment toward environ-
mental responsibility. ■
Comparison of data rates, bandwidth and power consumption for short-range and cellular
radios. A wireless subsystem can consume anywhere from 150 µW to 400 mW or more. Huw Davies is CEO and co-founder of
(Source: Voler Systems) Trameto.

www.eetimes.eu | NOVEMBER 2023