IEEE Power Electronics Magazine - September 2021 - 25

economic benefits can further be expanded (particularly
for modular designs and manufacturing processes), but is
beyond the scope of this article. The key takeaway message
is tiny system CAPEX improvements can lead to huge
CAPEX, OPEX and reliability gains.
Source vs Load: Where to Put the Focus
Higher energy density storage solutions for edge devices is
helpful but not enough - for most applications the difference
between required and available lifetime energy (based on
available battery space) is too large (typically 500%+). An
integration of multiple technologies is necessary.
Higher Density Energy Sources: This relates not only
to the 'primary battery' but also to functions assuring
steady voltage to the load, for example capturing ambient
energies, managing short-term transients (typically
jumping from μA to mA), facilitating wireless power
transfer (WPT) when available. Many next-generation
IoT devices will comprise multiple such devices with
integrated power management IC (PMIC) technology.
Smaller System Budgets: IoT devices typically
sleep for most of their operation so minimizing component
power consumption (sensors, MCUs, transceivers,
power management and storage devices) in
sleep/quiescent mode is critical. This then needs to be
augmented by close interaction with the system-integrators
and end-users to minimize active (sensing/
actuation, data processing and transceiving) where
power consumption typically jumps from µA to mA.
Fundamental 'fit for purpose' decisions on power and
communication architectures are needed on how data
is processed meeting application needs.
Energy Harvesting: This entails using ambient
energies where available (heat, vibrations, light).
They are typically sporadic so it needs to be complemented
by related energy storage and power management
devices/circuits to capture energy and make
available for use, minimizing the primary battery
drain. There is a sweet spot (~1-300 µW), where we
have a 'double impact' of less drain on the power
source and increased viability of use of reasonablysized
harvesters, sometimes leading to power autonomy.
A recent EU publication from the EnABLES EU
'power IoT' project [6] gives good insight into real-life
examples (Figure 3).
Wireless power transfer (WPT) is often perceived as a type
of EH and can be impactful, for example, for difficult-toaccess
embedded or implanted sensors. However, it is not
truly autonomous as it relies on the activation/positioning of
the wireless power source. Unless within 1-2 cm of the
load, the PCF for the edge node is &103, taking the wireless
power source into account.
The Power IoT Ecosystem of Stakeholders
All of this results in a complex mix of hardware and software
technologies as well as detailed understanding of usecases
so the IoT device can be power-optimized and ambient
energies exploited. It is critical for all stakeholders to
IoT Device Power Consumption
1 µW5 µW 20 µW 200 µW 500 µW1 mW
Autonomous
500
200
100
50
20
10
Temp,
Light
Sensor
RFID
Tag and
Pacemaker*
Low
Sense Rate
Accelerometer
* Low TEG Temp and Vibration Compatible Only
** High Temp TEG Source Unlikely
FIG 3 Energy harvesting sweet spot/battery life extension impact [6]. TEG: thermoelectric generator. (Source: courtesy of EnABLES)
September 2021 z IEEE POWER ELECTRONICS MAGAZINE 25
100 mm3 TEG Array 50° C Gradient (500 µW)
200 mm3 Indoor Solar Panel (60 µW)
100 mm3 TEG Array 5° C Gradient (100 µW)
200 mm3 Vibrational Harvester 0.1 G (2 µW)
Hearing Aid*
and CO2
Detector
Smart**
Bandage
Asset
Tracking
Tag
Battery Life Extension (%)

IEEE Power Electronics Magazine - September 2021

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