Poster– Surface++: A Scalable and Self-sustainable Wireless
Sound Sensing Surface
Nivedita Arora1, Qiuyue Xue1, Dhruva Bansal1, Peter McAughan1, Ryan Bahr1, Diego Osorio1,
Xiaomeng Ma1, Alanson P. Sample2, Thad E. Starner1, Gregory D. Abowd1
1Georgia Institute of Technology, USA , 2University of Michigan, USA
Figure 1: Applications include (a) Interaction and control: adding Surface++ to objects and surfaces increases smart home as-
sistants’ listening range (b) Wearable control: attaching Surface++ to a shirt or jacket allows control using voice or tap gestures
(c) Context sensing and surveillance: a Surface++ array extends the acoustic sensing range to almost 10 meters allowing the
detection of coughing, laughing, talking, or a baby crying in a large-room setting (d) Outdoor localization: outdoor Surface++
patches can sense and communicate gunshot sounds to indoor transceivers for real-time triangulation of ring locations
We present Surface++, which leverages our previous work SAT-
], a self-powered exible acoustic sensor, and ZEUSSS [
a passive wireless sound communication technique using analog
backscatter, to create a scalable and self-sustainable wireless sound
sensing surface. Our new prototype allows for large area acoustic
sensing using modular fabrication techniques with the promise
of being fully printable. A single small Surface++ patch can be
used to extend voice and gesture input for everyday surfaces, while
our more sensitive Surface++ modular array allows for large-area
context sensing and localization.
•Human-centered computing →Interaction devices
ware →Power and energy
Communication hardware, inter-
faces and storage.
Self-sustainable; Sensing; Vibration; Sound; Triboelectric Nano-
generator; Flexible electronics, Backscatter Communication; Low-
power; Acoustic Localization; Interaction and control
ACM Reference Format:
Nivedita Arora, Qiuyue Xue, Dhruva Bansal, Peter McAughan, Ryan Bahr,
Diego Osorio, Xiaomeng Ma, Alanson P. Sample, Thad E. Starner, Gregory
D. Abowd. 2019. Poster: Surface++: A Scalable and Self-sustainable Wireless
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ACM ISBN 978-1-4503-6661-8/19/06.
Sound Sensing Surface. In The 17th Annual International Conference on
Mobile Systems, Applications, and Services (MobiSys
19), June 17–21, 2019,
Seoul, Republic of Korea. ACM, New York, NY, USA, 2 pages. DOI: https:
Power has long been a major design constraint for both mobile and
ubiquitous sensing applications. Ideally, sensing nodes would work
without the need of a wired or replaceable power source. In addi-
tion, they would be thin and exible so that they might conform
to the objects on which they are placed. We recently showed the
promise of such a self-sustaining acoustic sensor named SATURN
], and demonstrated its ability to leverage analog RF backscatter
to transmit the acoustic signal passively o the sensor [
Surface++, we explore how the performance of the SATURN sensor
can be improved to harvest more energy and/or increase its per-
formance as an acoustic sensor. This optimization enables a wide
variety of vibration and acoustic sensing applications. In addition,
we optimize our design making the system modular and printable.
2 SYSTEM ARCHITECTURE
The system architecture consists of two parts—a single or array of
self-sustainable acoustic sensors connected in series and a passive
communication component, which are explained below.
] (Figure 2a)
uses a Triboelectric Nanogenerator
] to convert tiny vibrations induced on its surface into
an electric signal (Figure 2b). Electrically, SATURN can be con-
sidered as a variable capacitor and voltage source. Since voltages
sources in series add, we connected multiple SATURN patches to
form a SATURN array structure (Figure 2c). Each SATURN patch
in this array includes a half-wave rectier (Figure 2d), resulting in
1SATURN video: www.youtube.com/watch?v=OLuZHpa_FIM
MobiSys ’19, June 17–21, 2019, Seoul, Korea
constructive addition of voltage generated from each patch. Con-
structing a 3x3 array improves acoustic sensitivity and is able to
detect sound sources which are almost 6 meters away, a 3X im-
provement in range from a single patch backscatter. This modular
design is scalable in performance with additional SATURN patches
connected in series.
Figure 2: Self-sustainable acoustic sensing (a) SATURN : a
thin and exible self-powered microphone  (b) Triboelec-
tric Nanogeneration (TENG) (c) Array of SATURN patches
connected together in series with (d) half-wave rectiers to
sum sound signal response
We add passive communication using analog RF backscatter. Our
experimental apparatus (Figure 3a) consists of the Surface++ tag
and a transmitter-receiver pair operating in the UHF (900 MHz)
frequency band. The Surface++ tag consists of a SATURN array and
a dipole antenna connected in two dierent designs, both of which
allow for change in impedance when sound is present. The rst
design (Figure 3b), exploits SATURN as a variable voltage source
connected to a JFET, a voltage controlled impedance device to ef-
fectively cause impedance change in the tag. The second design
(Figure 3c), leverages SATURN itself as a variable capacitor which
causes impedance change due to change in reactance of the tag.
According to backscatter theory [
], this change in tag impedance
causes change in the reection coecient of the tag which eec-
tively amplitude modulates the carrier wave signal, such that the
back-scattered signal would include the audio signal information,
which can be extracted at the receiver end with simple signal pro-
cessing techniques. Both the designs are impedance matched with
the antenna to allow maximum modulation on backscatter signal.
The components in the second design specically can be printed.
3 APPLICATIONS AND DISCUSSION
The self-sustainablity and thin form factor of Surface++ allows it
to be added to everyday objects and surfaces. Figure 1 illustrates
Figure 3: System Architecture: (a) Backscatter apparatus in-
cluding Surface++ tag and transceiver (b) Surface++ tag de-
sign exploiting SATURN as variable voltage source (c) Sur-
face++ tag design exploiting SATURN as variable capacitor
possible applications of Surface++; the applications in 1a and 1c
have been demonstrated in working systems. Future research will
optimize performance for dierent sound frequencies as well as for
dierent backscatter radio carriers. Creating a fully printable and
cheaply reproducible Surface++ is a priority as it enables dierent
applications. For example, a wide deployment of sensors will enable
a demonstration of large scale audio localization for gunshot detec-
tion. Surface++ could also be used for acoustic failure monitoring
and diagnostics of large scale equipment in areas that are dicult or
dangerous to access, such as the turbines in a nuclear power plant.
Another technical priority is an analysis of the privacy implications
of Surface++ to determine how challenges such as providing notice,
choice and consent, and a sense of proximity and locality of the
eective range of the device might aect the design .
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MobiSys ’19, June 17–21, 2019, Seoul, Korea