Circularity in Energy Harvesting Computational "Things"

Abstract

We have witnessed explosive growth in computing devices at all scales, in particular with small wireless devices that can permeate most of our physical world. The IoT industry is helping to fuel this insatiable desire for more and more data. We have to balance this growth with an understanding of its environmental impact. Indeed, the ENSsys community must take leadership in putting sustainability up front as a primary design principle for the future of IoT and related areas, expanding the research mandate beyond the intricacies of the computing systems in isolation to encompass and integrate the materials, new applications, and circular lifecycle of electronics in the IoT. Our call to action is seeded with a circularity-focused computing agenda that demands a cross-stack research program for energy-harvesting computational things.

CCS CONCEPTS • Computer systems organization → Embedded systems; • Hardware → Analysis and design of emerging devices and systems; Impact on the environment; Circuit substrates.

Full text

Circularity in Energy Harvesting Computational "Things"
Nivedita Arora1, Vikram Iyer2, Hyunjoo Oh1, Gregory D. Abowd3, Josiah D. Hester1
1Georgia Institute of Technology, 2University of Washington, 3Northeastern University,USA
Figure 1: Motivating Applications i) Compostable physiological sensing facemask ii) Dandelion-like wireless smoke sensors
that degrade in soil iii) Gameboy with easily recyclable/upcycled components
.
ABSTRACT
We have witnessed explosive growth in computing devices at all
scales, in particular with small wireless devices that can permeate
most of our physical world. The IoT industry is helping to fuel
this insatiable desire for more and more data. We have to balance
this growth with an understanding of its environmental impact.
Indeed, the ENSsys community must take leadership in putting
sustainability up front as a primary design principle for the future
of IoT and related areas, expanding the research mandate beyond the
intricacies of the computing systems in isolation to encompass and
integrate the materials, new applications, and circular lifecycle of
electronics in the IoT. Our call to action is seeded with a circularity-
focused computing agenda that demands a cross-stack research
program for energy-harvesting computational things.
CCS CONCEPTS
•Computer systems organization
→
Embedded systems;•
Hardware
→
Analysis and design of emerging devices and systems;
Impact on the environment;Circuit substrates.
KEYWORDS
Sustainability, Intermittent Computing, Transient Electronics, Re-
cycle, Upcycle, Circular Electronics, sustainable HCI
ACM Reference Format:
Nivedita Arora
1
, Vikram Iyer
2
, Hyunjoo Oh
1
, Gregory D. Abowd
3
, Josiah D.
Hester
1
. 2022. Circularity in Energy Harvesting Computational "Things".
In The 20th ACM Conference on Embedded Networked Sensor Systems (SenSys
’22), November 6–9, 2022, Boston, MA, USA. ACM, New York, NY, USA, 3 pages.
https://doi.org/10.1145/3560905.3568106
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©2022 Association for Computing Machinery.
ACM ISBN 978-1-4503-9886-2/22/11.. .$15.00
https://doi.org/10.1145/3560905.3568106
1 INTRODUCTION
The development of energy harvesting and energy-neutral systems
(ENS) over the past decade has largely been driven by a push for
functionality and low-power operation at scale: to enable a vision
of wireless sensing devices that can last for years on a single battery
or run battery-free. The conuence of technologies developed by
the ENSsys community, including ultra-low power wireless com-
munication [
19
], advances in energy harvesting [
15
,
20
], and the
ability to run sophisticated programs on harvested energy with
intermittent computing, [
14
] has begun to make this vision a reality.
With commercial adoption, they have the potential to further fuel
the rapid growth of the internet of things (IoT) industry which is
expected to increase to a trillion by 2035 [
18
]. The ability to place
computing devices everywhere, however, raises a new question:
what will happen to them at the end of their life? Even the
most robust device will eventually become electronic waste
(e-waste). Global e-waste exceeded is the fastest-growing waste
stream and will exceed 74 million metric tons (Mt) by 2030 [
6
].
E-waste includes hazardous materials like heavy metals and ame
retardants, with the potential to pollute groundwater if buried and
air when incinerated and pose environmental justice concerns to
the surrounding communities [16].
We propose that the ENSsys community integrate environ-
mental sustainability as a core objective for the next decade
to develop devices with a fully circular life cycle. For example,
intermittent computing objects that are transient in nature can
degrade to dust, be recycled, or be recaptured after use. Imagine
a computational face mask that measures health data powered by
human breath and can be composted after use (Figure 1 a). Like-
wise, visualize dandelion-like wireless smoke sensors that can be
dropped into the forest to detect res and then disintegrate into
the soil (Figure 1 b). Think about playing an interaction-powered
game-boy that can be up-cycled back into other electronic devices
(Figure 1c) Facemasks [
4
], Dandelion-sensors [
10
], and the Battery-
Free Gameboy[
5
] now exist as Energy Neutral Systems (ENS) but
do not yet have a circular life cycle. Currently, both the creation
and adoption of such circular, battery-free, computationally sophis-
ticated objects is a non-trivial research problem for three reasons:

SenSys ’22, November 6–9, 2022, Boston, MA, USA Arora, et al.
(1)
Use of non-biodegradable/ hard-to-recycle materials
in functional devices: Traditional semiconductor processors
contain silicon and/or germanium, with plastic substrates and
encasing. Similarly, sensors, displays, and harvesters also heavily
rely on inorganic material composites. These materials are non-
biodegradable and are hard to recycle/upcycle.
(2)
Lack of developer tool-kits to create circular life cycle
battery-free circuits and systems: While developer toolkits for
energy-neutral computing and wireless communicating systems
is an active area of research [
11
,
17
], there is a complete lack of
electronic design and prototyping toolkits for embedded system
developers to create circular computational objects that simulta-
neously balance circular life cycle concepts like biodegradability,
recycling with low/unreliable power operation.
(3)
Lack of product and interaction design that inspires
computational object’s recycle/reuse/degradation: While
advances in intermittent computing have inspired a new gen-
eration of battery-free, sophisticated, interactive computational
objects and wearables, they still generate e-waste. Achieving cir-
cularity requires thinking beyond circuits and systems. There is
a need for sustainable product design and interaction guidelines
to inspire the user to properly recycle/reuse/degrade dierent
electronic/non-electronic parts of the computational object.
Figure 2: Circular Computing Stack (CCS)
Our Position: In this position paper, we project that overcoming
the above limitations requires rethinking the entire computing
stack with circular lifecycle as equally important system
design criteria as low/unreliable power operation and func-
tional performance (Figure 3). The ENSsys community is well
positioned to make a signicant impact in this domain. Intermit-
tent computing and low-power wireless technologies have already
shown that we can eliminate batteries and the challenges they pose
for circularity. To go beyond this, we introduce two emerging elds
of research that each focus on circularity at a dierent layer of the
computing stack – Transient Electronics at the bottom and Sus-
tainable Interaction Design at the top (section 2). Energy Neutral
Systems (ENS) sit in the middle layer and are focused on power
and function. We discuss open research question and strategies for
bridging the gaps between these three layers as a way to realize
circular energy-neutral computational objects (section 3). Finally,
we end with a call to action for the ENSsys Community (section 4).
Figure 3: System Design Parameters
2
CIRCULARITY-FOCUSED RESEARCH FIELDS
Transient Electronics
Researchers in chemistry and materials science have explored tran-
sient electronics with a focus on identifying or synthesizing biodegrad-
able materials that can be employed for high-performance func-
tional devices [
13
]. These include fundamental P-type, N-type, di-
electric, and substrate materials made from plant material (cellulose,
paper, leaves, wood, starch, and alginate), animal (chitosan/chitin,
egg whites, silk, gelatin, and peptides) and synthetic protein poly-
mers (PLA, PLGA, PVA, PCL, PHB/V). Interconnects are built using
benign metals (Mg, Zn, Mo, Fe, W) or organic conductive polymers
(PEDOT: PSS, Mxene)[
21
]. All these materials chemically or physi-
cally dissolve, disintegrate, and degrade into harmless by-products
[
7
]. Examples of transient functional devices include – organic thin
lm transistors on PLGA substrates, electrochromic displays using
gelatin, biodegradable LRC passive elements and memristors, recy-
clable thermoelectric generators, and super-capacitors. Such rich
growing body of work provides a set of physical primitives to serve
as the bottom layer in the circular computing stack.
Sustainable Interaction Design
The eld of Sustainable Interaction Design focuses on creating
products and their life cycle frameworks that enhance recyclability,
reusability, and degradability [
2
,
3
]. For targeting the circularity of
everyday objects the selection of materials can be made based on the
desired life-cycle of the product. Further, sustainable product design
adopts materials and parts that are reusable during fabrication
[
12
] or at the end of the product lifecycle [
8
]. Some strategies
have now been applied to electronic objects like mobile phones[
9
]
and peripherals like computer mice[
1
]. These design principles
and applications highlight the technology gaps for the ENSsys
community to target.
3 OPEN RESEARCH CHALLENGES
Enabling circularity for the functional computational objects will
require intra-disciplinary and iterative dialogue between the Tran-
sient Computing, Energy Neutral Systems, and Sustainable Indus-
trial Design researchers to solve the research challenges below.
(1)
Developer toolkit for transient device, circuit and sys-
tem performance modeling: Transient devices can show large
uctuations in conventional system metrics (e.g performance,
power) over time. Thus, scaling the creation and adoption of

Circularity in Energy Harvesting Computational "Things" SenSys ’22, November 6–9, 2022, Boston, MA, USA
circular energy-neutral systems requires building circuit design
toolkits that can predict degradation of parameters over the sys-
tem’s lifetime. For this, transient devices should be rst individu-
ally modeled for their degradation with age and then together
as a circuit. We hope that such a toolkit can enable creation of
complex circuitry like biodegradable microprocessors for inter-
mittent computing applications. It can also help match circular
computational objects with appropriate power harvester and
harvesting conditions as well as inform the duration of reason-
able use of the circular computational object for a particular
application scenario.
(2)
Tuning transience: Longevity vs. Degradability Enabling
circularity requires carefully balancing the trade-o of making
a device robust enough for functional use while still allowing
it to be easily disassembled and degraded at the end of life. Ad-
dressing this challenge requires combining novel materials with
system-level innovations. For example, if the frequency of a
biodegradable transistor is limited, can we design dierent al-
gorithms and architectures to work within these constraints?
Circularity introduces a new set of physical constraints beyond
minimizing power for the ENSsys community to explore.
(3)
Adaptive runtime programming platform for circular
systems. In addition to designing systems that can run with
novel performance constraints, can we also design systems that
will adapt to changing conditions? For example, if degradation af-
fects timing functions, could we adjust its algorithm parameters
(e.g. FFT window) to compensate? Similarly, these techniques
could upcycle degraded components by combining them in novel
architectures. This presents an opportunity to build on intermit-
tent computing techniques to enable circularity.
(4)
Product design for circularity Circular life cycle concepts
are not limited to just transient functional devices, circuits and
systems but need to be expanded to the product design of the
computational object. For example, having a modular assembly
of electrical parts and mechanical bodies can ease the complexity
of steps and types of processes that are required at the end of
the lifecycle. Substrate Materials used in the physical body of the
computational object should be biodegradable/Eco-friendly simi-
lar to substrates of the functional devices. Further, the physical
form factor and interaction design of the computational object
should inspire circular interactions like reuse, upcycle, or degra-
dation. For example, a computational face mask can have a quote
hidden inside it, just like a fortune cookie, to motivate cutting
and decomposition in soil.
4 CALL TO ACTION
In this position paper, we introduce circular computing stack (CCS)
as a call to action for the ENSsys community to the rising health
and climate perils of electronic waste. It provides a road map for
ENSsys researchers to be ag-bearers in bridging the gap with
two emerging research elds, namely, Transient Electronics and
Sustainable Interaction Design, to be able to create usable battery-
free computationally sophisticated circular objects that can be easily
degraded to dust, be recycled, or be recaptured after use.
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