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SATURN: Technical and Design Challenges of Building a Self-sustaining Sound and Vibration Sensing Material



SATURN is a thin and flexible multi-layer material that can sense sound and other mechanical vibrations in the environment without any external power source. It is constructed of inexpensive materials (paper, copper, and plastic), so that it can be attached to a variety of objects and surfaces. When flat, SATURN's frequency response below 5000Hz is comparable to a powered microphone. When bent, SATURN has a comparable frequency response up to 3000Hz. As a sound power harvester, SATURN can harvest 7 microWatts, which allows the detection of loud sound events. We explore the space of potential applications for SATURN as part of self-sustaining interactive systems.
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September 2019 | Volume 23, Issue 3
ATURN is a thin and exible multi-layer material that can sense
sound and other mechanical vibrations in the environment without
any external power source. It is constructed of inexpensive materials
(paper, copper, and plastic), so that it can be attached to a variety
of objects and surfaces. When at, SATURNs frequency response below
5000Hz is comparable to a powered microphone. When bent, SATURN
has a comparable frequency response up to 3000Hz. As a sound power
harvester, SATURN can harvest 7 microWatts, which allows the detection
of loud sound events. We explore the space of potential applications for
SATURN as part of self-sustaining interactive systems.
Excerpted from “SATURN: A Thin and Flexible Self-powered Microphone Leveraging Triboelectric
Nanogenerator,” from Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous
Technologies with permission. © ACM 2018
Nivedita Arora, Jin Yu, HyunJoo Oh, Thad E. Starner and Gregory D. Abowd
Georgia Institute of Technology, Atlanta, GA.
Editors: Nic Lane and Xia Zhou
Technical and Design Challenges
of Building a Self-sustaining Sound
and Vibration Sensing Material
What if a paper-like material could sense
and transmit sound and other mechanical
vibrations wirelessly? Imagine an early
morning scene in Sal’s household. Sal has
installed a single voice home control device
in her living room with paper microphones
at dierent places to extend remote inter-
actions. Sal gets up hearing the alarm sound
from the smart home device and double
taps the sticky-note paper microphone on
her bedpost to stop it. She goes to her closet
to dress for the day, unsure yet about the
weather. Sal asks the microphone sticky note
on her closet wall about the temperature
outside. Next, as she comes out to the living
room, she hears the voice of her 7-year-old
child on the home assistant, calling for her
via the paper microphone placed on his toy
elephant. She goes to check on him as her
husband arrives from his workout to open
the main door using a unique password
combination of blows and taps. e smart
home device recognizes his arrival and
announces that he is home. To make this
scenario a reality, where a disposable paper-
like material can sense mechanical vibrations,
such as voice, taps, and blows, we built a
wireless audio sensing and communication
material: SATURN (Self-powered Audio
Triboelectric Ultra-thin Rollable Nano-
generator) [2]. SATURN is thin and exible
in form factor, cheap to manufacture and
self-sustaining in its power consumption.
It has comparable signal quality to active
microphones that consume power and are
more expensive and bulky.
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September 2019 | Volume 23, Issue 3
of applications. e acoustic sensitivity
of SATURN when bent reduces with
increasing bending angle due to the increase
in stiness of the structure which results in
lesser vibration of the layers. At a bending
angle of 45 degrees, SATURN is still a
usable microphone and comparable to an
active microphone till 3000 Khz, allowing
capture of more than 60% of sounds
associated with voice.
Sound Energy Harvester
SATURN in the presence of loud sound can
harvest enough energy that could be used
for doing computational tasks. We analyzed
the 4x4 cm SATURN microphone patch as
a power harvester under loud sound pressure
(100 dB). For a 1 Mohm load, SATURN
generates approximately 0.5 Vpp at 150 Hz,
which rises to a maximum at 2.5 Vpp at 250
Hz and then falls below 1.0 Vpp at 350 Hz.
e same behavior is shown in the power
curve, with 6499 nW being the maximum
power that can be harvested at 250 Hz.
In the previous section, we saw the
characterization of SATURN as both a
self-sustaining microphone and an energy
harvester. To use SATURN in a practical
application, it needs to be embedded in
a self-sustaining computational system
that can allow a transfer or storage of the
data. Figure 5 shows how a tag consisting
of SATURN, a transistor, and a exible
antenna can leverage radio backscatter
technology to passively communicate
sensed sound or vibration information [1].
Figure 6 demonstrates how SATURN, when
in the presence of a loud sound, generates
enough power that it can support ipping
of a bit in ash memory, which can be
interrogated later using radio waves [2].
In an alternate method, if the loud sound
is persistent for a few seconds, it can be
used to activate a low-power long-range
radio [3], which allows for real-time
communication of loud acoustic events.
e thin and exible form factor of SATURN
allows it to be placed on dierent surfaces
for self-sustaining audio sensing appli-
cations (Figure 7). We imagine scenarios
where many dierent inexpensive SATURN
patches in the home can extend the range of
audio input for home assistants. In addition
to speech sensing, SATURN can also be
used as a contact microphone to sense
simple input touches, such that dierent
force of taps could be detected. In more
industrial environments, SATURN can be
used for acoustic failure monitoring and
diagnostics in places where it is dicult
or dangerous for humans to access. For
example, SATURN patches might be
placed on turbines in a nuclear power
plant to monitor them for vibrations that
indicate damage or wear. SATURN as
a loud sound power harvester could be
used for inexpensive, battery-free ambient
monitoring of sources of noise pollution.
Applications include monitoring for sound
thresholds exceeding human hearing
tolerance, such as in construction zones,
mines, music venues, power stations,
airports, spaceports, and military environ-
ments. Similarly, SATURN-based sensors
might be used for monitoring events, such
as landslides and mine gas explosions.
is section gives an overview of some of
the challenges faced and future work for
this project to make it more concrete and
deployable in real-life scenarios.
1. System Challenges: SATURN is an early
prototype for the paper microphone
scenario from Sal’s home. ere is a
need to work on the robustness of the
radio backscatter architecture for the
communication of data. Large scale
deployment of such sensors requires
us to create innovation on both the
hardware and the soware side to be
able to distinguish dierent devices
in a single room. In addition, there is
a need to incorporate privacy-aware
design principles and come up with both
innovative technological and social
approaches to ensure user control over
when and where a SATURN patch
senses and transmits data. For example,
FIGURE 2. Cycle of electricity generation process in SATURN under external acoustic excitation
due to the combined eect of triboelectrication and electrostatic induction.
FIGURE 3. Structural device design optimization.
Recent advances in materials science dem-
onstrate the possibility of self-powered, easy-
to-manufacture sensors that take advantage
of the triboelectric nanogenerator (TENG)
eect, which converts mechanical vibrations
into electrical energy [4,6]. When made
in the right form factor, these mechanical
energy generators could be manufactured as
self-sustaining sound and vibration sensors.
We use these principles for the design and
fabrication of SATURN, as explained below.
Principle of Working: Triboelectric
Nanogenerator (TENG)
When two dierent materials come into
contact and separate, or rub alongside
each other, they tend to either gain or lose
electrons, based on their position relative
to each other in the triboelectric series [8].
is common phenomenon of exchange of
electrons is called triboelectrication. e
redistribution of charge creates an electric
potential between the layers. If there is a
conductive path between the two layers,
the charge dierence will balance due to
electrostatic induction. Repeated contact
and separation, therefore, produces an
alternating current [5]. is multilayer
structure, consisting of dierent materials
that are both conductive on one side,
is called a Triboelectric Nanogenerator
Device Design
SATURN is an example of a TENG and
consists of two layers (Figure 1). e rst
is the copper that acts as a triboelectrically
positive material. is layer is coated onto
paper for mechanical support. Paper is low
cost, exible, light, and easy to perforate,
making it a favorable medium to support
vibration in the presence of sound waves.
e second layer is a dielectric plastic,
PTFE(Polytetrauoroethylene). It is a
triboelectrically negative material coated
with copper on one side. e rst and second
layers are placed with the copper side of the
paper touching the non-copper-coated side
of the PTFE. e layers are anchored to each
other using glue in a specic grid dot pattern.
A potential dierence is caused by vibration
and is measured between the two copper-
coated surfaces.
is section explains how the change in
air pressure due to sound vibrations causes
constant contact and separation in the
multilayer structure of SATURN. When the
two layers of SATURN, paper and PTFE,
come in contact with each other, charges
are induced in the copper and the PTFE
due to triboelectrication (Figure 2a).
PTFE has a greater electron anity and
gains electrons from the copper to become
negatively charged. In parallel, the copper
layer on the paper becomes positively
charged. e subsequent separation of the
paper and the PTFE (Figure 2b) induces a
potential dierence across the two copper
electrodes. Such a separation causes current
to ow from the paper towards the PTFE
layer when the device is connected to an
external load. is ow of current reverses
the polarity (Figure 2c) of charges on the
two copper electrodes (i.e., now the copper
on PTFE has more positive charge than
the copper layer on the paper). e next
compression results in a reversal of the
current ow (Figure 2d) from the paper
towards the PTFE layer to complete the
cycle of electricity generation.
Device Optimization
We have optimized dierent device design
parameters in SATURN’s structure to increase
its electrical response across a wide frequency
of the audible range. Dierent structural
design parameters (Figure 3) – the hole size
and spacing of holes in paper, the geometry
of the patch, and the glue points to attach the
two layers – are varied to understand their
eect on signal quality, to nally come up with
a design that is both reliable and replicable.
Self-sustaining Sound Sensor
Aer optimizing SATURN’s structural
parameters, we are able to reach the best
acoustic sensitivity of -25.63 dB (re mV/Pa)
at 1000 Hz with a circular shape of 16 cm
area with a grid pattern of holes of 0.4 mm
diameter and 0.2 mm spacing glued at 8
equally distant points around the edges and
the center to the PTFE. In this conguration,
the SATURN microphone has a comparable
frequency response from 20-5000Hz to an
active microphone (Figure 4). Approximately
90% of the information related to human
voice is within this range, making SATURN
a good quality microphone for a variety
FIGURE 1. SATURN device design: Multiple layered structure of SATURN, consisting of paper with
holes coated with copper (triboelectrically positive material) and PTFE (triboelectrically negative
material) coated with copper.
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We would like to thank our collaborators
at Georgia Tech’s Nanotechnology Lab:
Prof. Zhong Lin Wang, Yi-Cheng Wang,
Steven L. Zhang and Zhengjun Wang for
their guidance on the original version of the
SATURN paper. We thank Diego Osorio
and Fereshteh Shahmiri for their help in
making diagrams for the original SATURN
paper, some of which have been adopted in
this article. We would like to thank GVU
Prototyping Lab and Georgia Tech IEN
Cleanroom facility for letting us use their
equipment and space for experiments.
Nivedita Arora is a PhD student at the School
of Interactive Computing at Georgia Institute
of Technology. She combines learnings from
HCI, material science, chemical, electrical
and mechanical engineering to develop
computational material that can self-sustainably
sense, compute, actuate and communicate.
Jin Yu is a master’s student at the School of
Architecture at Georgia Institute of Technology.
Her work focuses on developing a new medium
that bridges art, engineering, and computing
for expanding the creativity of individuals.
HyunJoo Oh is an assistant professor with a
joint appointment at the School of Industrial
Design and the School of Interactive Computing
at Georgia Institute of Technology. Her work
explores computational design tools that
integrate everyday materials with computing
and how these combinations can broaden
creative possibilities for designers and learners.
Thad E. Starner is a professor in the School
of Interactive Computing at Georgia Institute
of Technology and a sta research scientist at
Google Research and Machine Intelligence. His
work led to the Google Glass family of devices,
and his research continues to investigate how
wearable computing can assist users in face-
to-face conversations and everyday situations.
Gregory D. Abowd is Regents’ Professor and
J.Z. Liang Chair at the School of Interactive
Computing at Georgia Institute of Technology.
His research interests focus on how the
advanced information technologies of
ubiquitous computing (or ubicomp) impact
our everyday lives when they are integrated
seamlessly into our living spaces.
[1] N. Arora and G.D. Abowd. (2018). ZEUSSS:
Zero energy ubiquitous sound sensing surface
leveraging triboelectric nanogenerator and analog
backscatter communication. In ACM 31st Annual
ACM Symposium on User Interface Soware and
Technology Adjunct Proceedings, 81–83.
[2] N. Arora, S. L. Zhang, F. Shahmiri, D. Osorio,
Y.-C.Wang, M. Gupta, Z. Wang, T. Starner,
Z. L. Wang, and G. D. Abowd. (2018). SATURN:
A thin and exible self-powered microphone
leveraging triboelectric nanogenerator. Proceedings
of the ACM on Interactive, Mobile, Wearable and
Ubiquitous Technologies, 2(2), 60.
[3] V. Talla, M. Hessar, B. Kellogg, A. Naja, J. R.
Smith, and S. Gollakota. (2017). LoRa backscatter:
Enabling the vision of ubiquitous connectivity.
Proceedings of the ACM on Interactive, Mobile,
Wearable and Ubiquitous Technologies, 1(3),105.
[4] Z.L. Wang. (2015). Triboelectric nanogenerators
as new energy technology and self-powered
sensors – principles, problems, and perspectives.
Faraday Discussions, 176, 447–458.
[5] Z. L. Wang. (2017.) On Maxwell’s displacement
current for energy and sensors: e origin of
nanogenerators. Materials Today, 20(2), 74–82.
[6] Z.L. Wang and A.C. Wang. (2018). Triboelectric
nanogenerator for self-powered exible
electronics and Internet of ings. In Meeting
Abstracts, 26, 1533–1533. e Electrochemical
[7] M. Weiser. e computer for the 21st century.
(1991). Scientic American, 265(3), 94–105.
[8] H. Zou, Y. Zhang, L. Guo, P. Wang, X. He,
G. Dai, H. Zheng, C. Chen, A.C. Wang, C. Xu,
et al. (2019). Quantifying the triboelectric
series. Nature Communications, 10(1), 1427.
FIGURE 7. SATURN is exible and can be made in dierent shapes and sizes, allowing
instrumentation of everyday objects, such as a soda bottle, shirt, and paper crafts for interaction,
control, context sensing, and event detection applications.
SATURN microphone patches could
be constructed at a physical level that
requires tapping a nger on it to prime
the backscatter circuit before audio could
be transmitted (e.g., when a speaker
taps a microphone to ask, “Is this mic
on?”). Furthermore, the patch can be
constructed to have a limited sensing
range for the human voice. Another way
to design SATURN for privacy is to tune
the resonant frequencies of the patch to
focus on only certain types of sound or
vibration, excluding the human voice.
2. Design Challenges: SATURN is a
computational material that looks more
like paper and inspires creative uses,
such as being used as part of papercra.
Computation that looks and feels more
like everyday objects will change the way
that we as humans experience, understand
and build relationships with that techno-
logy. It also creates opportunities and
challenges for infusing computation with
values, such as sustainability, through
the deliberate choice of materials used
to create a computational eect.
3. Manufacturing C hallenges: In an ideal
situation, we would like these paper
microphones to be cheap and disposable,
so we would not worry if they are lost
or stolen. Currently, the bill of materials
for a single sticky note-size SATURN
microphone is less than a cent, but its
manufacturing cost is still high due to the
way we are depositing copper on paper
and PTFE. is pushes us to think about
the manufacturing process, so it can be
scaled. When SATURN is placed in a
self-sustaining computational scenario,
the cost gets higher, depending on the
active transistor component being used.
is expense begs the fundamental
question: does our traditional semi-
conductor industry provide the support
needed for large-scale ubiquitous sensing?
How can we change our traditional manu-
facturing techniques to be able to support
applications where objects and surfaces
have computation embedded in them?
4. Need for Multi-disciplinary Mindset:
Building SATURN involves solving
technical, system-level and design
challenges, which span many elds.
Materials science is required to design
SATURN patches; mechanical
engineering helps characterize the
eect of vibration on a patch; wireless,
low-power electronics is necessary for
building self-sustaining communication;
exible electronics are required for
manufacturing the prototype, and design
and HCI knowledge help us explore
applications in everyday settings. Using
a combination of self-sustaining sensors
and backscatter technique, there is an
opportunity for creating thin wireless
sensing solutions for many dierent
phenomena. Developing them will
require researchers who can adopt an
aggressively multi-disciplinary mindset
to collaborate and learn the language of
many dierent elds.
SATURN is an example of a self-sustaining
wireless mechanical vibration and sound
sensing computational material. Its simple
multilayer construction results in a compu-
tational device that resembles everyday
materials. It looks and feels like paper, yet it
behaves like a wireless microphone. Using
power (requiring no external power source),
cost (large-scale manufacturing with simple
materials), and form factor (looking more like
everyday objects) as driving factors in the
design of computational devices can lead
to a whole new generation of interesting
computational materials. ese materials may
nally allow us to create technologies that, in
the words of Mark Weiser, “weave themselves
into the fabric of our everyday lives until they
are indistinguishable from it.” [7] n
FIGURE 5. Self-sustaining computational systems for SATURN as a sound sensor.
FIGURE 6. Self-sustaining computational systems for SATURN as a loud sound energy harvester.
FIGURE 4. Spectrogram of speech signal recorded simultaneously by iPhone and SATURN
microphone. The acoustic sensitivity of a 16 cm SATURN patch is comparable to an active
microphone in acoustic sensitivity till 5000Hz.
Weiser inspired us by forcing us to think differently about the size and usage patterns of computers. This vision of computational materials is similarly motivated. Indeed, inspiration is critical at this time, because there are so many challenges to overcome and it will take a community to address them. Significant technical challenges and a desire to deliver meaningful value while guarding against violations of greater societal values can only happen if we are fueled by the passion of this vision.
Full-text available
Triboelectrification is a well-known phenomenon that commonly occurs in nature and in our lives at any time and any place. Although each and every material exhibits triboelectrification, its quantification has not been standardized. A triboelectric series has been qualitatively ranked with regards to triboelectric polarization. Here, we introduce a universal standard method to quantify the triboelectric series for a wide range of polymers, establishing quantitative triboelectrification as a fundamental materials property. By measuring the tested materials with a liquid metal in an environment under well-defined conditions, the proposed method standardizes the experimental set up for uniformly quantifying the surface triboelectrification of general materials. The normalized triboelectric charge density is derived to reveal the intrinsic character of polymers for gaining or losing electrons. This quantitative triboelectric series may serve as a textbook standard for implementing the application of triboelectrification for energy harvesting and self-powered sensing.
Conference Paper
Full-text available
ZEUSSS (Zero Energy Ubiquitous Sound Sensing Surface), allows physical objects and surfaces to be instrumented with a thin, self-sustainable material that provides acoustic sensing and communication capabilities. We have built a prototype ZEUSSS tag using minimal hardware and flexible electronic components, extending our original self-sustaining SATURN microphone with a printed, flexible antenna to support passive communication via analog backscatter. ZEUSSS enables objects to have ubiquitous wire-free battery-free audio based context sensing, interaction, and surveillance capabilities.
Full-text available
We demonstrate the design, fabrication, evaluation, and use of a self-powered microphone that is thin, flexible, and easily manufactured. Our technology is referred to as a Self-powered Audio Triboelectric Ultra-thin Rollable Nanogenerator (SATURN) microphone. This acoustic sensor takes advantage of the triboelectric nanogenerator (TENG) to transform vibrations into an electric signal without applying an external power source. The sound quality of the SATURN mic, in terms of acoustic sensitivity, frequency response, and directivity, is affected by a set of design parameters that we explore based on both theoretical simulation and empirical evaluation. The major advantage of this audio material sensor is that it can be manufactured simply and deployed easily to convert every-day objects and physical surfaces into microphones which can sense audio. We explore the space of potential applications for such a material as part of a self-sustainable interactive system. Video :
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The vision of embedding connectivity into billions of everyday objects runs into the reality of existing communication technologies --- there is no existing wireless technology that can provide reliable and long-range communication at tens of microwatts of power as well as cost less than a dime. While backscatter is low-power and low-cost, it is known to be limited to short ranges. This paper overturns this conventional wisdom about backscatter and presents the first wide-area backscatter system. Our design can successfully backscatter from any location between an RF source and receiver, separated by 475 m, while being compatible with commodity LoRa hardware. Further, when our backscatter device is co-located with the RF source, the receiver can be as far as 2.8 km away. We deploy our system in a 4,800 $ft^{2}$ (446 $m^{2}$) house spread across three floors, a 13,024 $ft^{2}$ (1210 $m^{2}$) office area covering 41 rooms, as well as a one-acre (4046 $m^{2}$) vegetable farm and show that we can achieve reliable coverage, using only a single RF source and receiver. We also build a contact lens prototype as well as a flexible epidermal patch device attached to the human skin. We show that these devices can reliably backscatter data across a 3,328 $ft^{2}$ (309 $m^{2}$) room. Finally, we present a design sketch of a LoRa backscatter IC that shows that it costs less than a dime at scale and consumes only 9.25 $\mu$W of power, which is more than 1000x lower power than LoRa radio chipsets.
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Self-powered system is a system that can sustainably operate without an external power supply for sensing, detection, data processing and data transmission. Nanogenerators were first developed for self-powered systems based on piezoelectric effect and triboelectrification effect for converting tiny mechanical energy into electricity, which have applications in internet of things, environmental/infrastructural monitoring, medical science and security. In this paper, we present the fundamental theory of the nanogenerators starting from the Maxwell equations. In the Maxwell's displacement current, the first term ε0∂E∂t gives the birth of electromagnetic wave, which is the foundation of wireless communication, radar and later the information technology. Our study indicates that the second term ∂P∂t in the Maxwell's displacement current is directly related to the output electric current of the nanogenerator, meaning that our nanogenerators are the applications of Maxwell's displacement current in energy and sensors. By contrast, electromagnetic generators are built based on Lorentz force driven flow of free electrons in a conductor. This study presents the similarity and differences between pieozoelectric nanogenerator and triboelectric nanogenerator, as well as the classical electromagnetic generator, so that the impact and uniqueness of the nanogenerators can be clearly understood. We also present the three major applications of nanogenerators as micro/nano-power source, self-powered sensors and blue energy.
Triboelectrification is an effect known to society ever since the ancient Greek era, but it is usually considered a negative effect and avoided in many technologies. We have recently invented a triboelectric nanogenerator (TENG) that is used to convert mechanical energy into electricity by a conjunction of triboelectrification and electrostatic induction. As for this power generation unit, in the inner circuit, a potential is created by the triboelectric effect due to the charge transfer between two thin organic/inorganic films that exhibit opposite tribo-polarity; in the outer circuit, electrons are driven to flow between two electrodes attached on the back sides of the films in order to balance the potential. Ever since the first report of the TENG in January 2012, the output power density of TENG has been improved for five orders of magnitude within 12 months. The area power density reaches 500 W/m ² , and a conversion efficiency of ~50-85% has been demonstrated. The TENG can be applied to harvest all kind mechanical energy that is available but wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water and more. Alternatively, TENG can also be used as a self-powered sensor for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage and current output signals of the TENG, respectively, with potential applications for touch pad and smart skin technologies. The TENG is possible not only for self-powered portable electronics, but also as a new energy technology with a potential of contributing to the world energy in the near future. [1] Z.L. Wang, Materials Today, 20 (2017) 74-82. [2] “Nanogenerators for Self-Powered Devices and Systems”, by Z.L. Wang, published by Georgia Institute of Technology (first book for free online download): [3] Z.L. Wang, L. Lin, J. Chen. S.M. Niu, Y.L. Zi “Triboelectric Nanogenerators”, Springer, 2016. [4] Z.L. Wang “Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors”, ACS Nano 7 (2013) 9533-9557. [5] Z.L. Wang, J. Chen, L. Lin “Progress in triboelectric nanogenerators as new energy technology and self-powered sensors”, Energy & Environmental Sci, 8 (2015) 2250-2282.
Triboelectrification is one of the most common effects in our daily life, but it is usually taken as a negative effect with very limited positive applications. Here, we invented a triboelectric nanogenerator (TENG) based on organic materials that is used to convert mechanical energy into electricity. The TENG is based on the conjunction of triboelectrification and electrostatic induction, and it utilizes the most common materials available in our daily life, such as papers, fabrics, PTFE, PDMS, Al, PVC etc. In this short review, we first introduce the four most fundamental modes of TENG, based which a range of applications have been demonstrated. The area power density reaches 1200 W/m2, volume density reaches 490 kW/m3, and an energy conversion efficiency of ~50-85% has been demonstrated. The TENG can be applied to harvest all kinds of mechanical energy that is available in our daily life, such as human motion, walking, vibration, mechanical triggering, rotation energy, wind, moving automobile, flowing water, rain drop, tide and ocean waves. Therefore, it is a new paradigm for energy harvesting. Furthermore, TENG can be a sensor that directly converts a mechanical triggering into a self-generated electric signal for detection of motion, vibration, mechanical stimuli, physical touching, and biological movement. After a summary of TENG for micro-scale energy harvesting, mega-scale energy harvesting, and self-powered systems, we will present a set of questions that need to be discussed and explored for TENG’s applications. Lastly, since the energy conversion efficiencies for each mode can be different although the materials are the same, depending on the triggering conditions and design geometry. But one common factor that determines the performance of all the TENGs is the charge density on the two surfaces, the saturation value of which may independent of the triggering configurations of the TENG. Therefore, the triboelectric charge density or the relative charge density in reference to a standard material (such as polytetrafluoroethylene (PTFE)), can be taken as a measuring matrix for characterizing the performance of the material for the TENG.
Specialized elements of hardware and software, connected by wires, radio waves and infrared, will be so ubiquitous that no one will notice their presence.