Turning Surfaces into Touch Panels:
A Granite-Touch Pad
Hatem Elfekey and Shogo Okamoto

Abstract Touch sensing interfaces are used in many human to machine applications with the natural feeling to the touch missing. We propose the use of humantenna
touch technique to turn surfaces of natural or artiﬁcial conductive or semi-conductive
materials into passive touch pads. Because of the conductivity of the human body,
AC power lines induce a voltage on the human body which is used as the touch trigger. By the use of electrodes mounted at the edges of the surface, the ratio of voltage
detected is used to compute the touch location. Granite touch pad was implemented
as an example, and the voltage detected at the electrodes due to various touch locations is presented.
Keywords Humantenna ⋅ Granite ⋅ Touch pad ⋅ Human body

1 Introduction
Touch sensing applications are in ever high demand as touch sensing interfaces areused in most human-machine interfaces. On the other hand, touch pads require special surface that is manufactured for touch sensing. Consequently, the feeling of touchis limited. For example, touching the screen of a smart phone may not feel as richas touching an actual wall or table top. To enhance the feeling of touch, many haptic feedback technologies have been implemented with the goal of creating artiﬁcial
sense of surfaces. In this paper, we propose a diﬀerent approach. We propose turning
surfaces into touch pad instead of recreating particular textures via texture displays.
As a result, the rich natural texture of surfaces is preserved, while serving as a touchsensing interface.

H. Elfekey (✉) ⋅ S. Okamoto
Graduate School of Engineering, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya, Aichi Prefecture, Japane-mail: elfekey.hatem.mahmoud@h.mbox.nagoya-u.ac.jp
S. Okamoto
e-mail: okamoto-shogo@mech.nagoya-u.ac.jp© Springer Nature Singapore Pte Ltd. 2018
S. Hasegawa et al. (eds.), Haptic Interaction, Lecture Notes
in Electrical Engineering 432, DOI 10.1007/978-981-10-4157-0_51

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H. Elfekey and S. Okamoto

For the aforementioned purpose, many touch technologies are available. Candidates comprise infra-red, camera, acoustic and capacitive technologies. Infra-red
based touch sensing technology demands the use of many transmitters and receivers
to extract the location of the touch, which may not be prefered for some applications[1]. Although the acoustic pulse recognition (APR) technique use only four microphones and an easy algorithm to precisely locate the touch position, the “touch andhold” feature is unavailable [1, 2]. On the other hand, surface acoustic wave (SAW)
touch technology can detect “touch and hold”, yet, the accuracy of the touch detection
is dependent on the geometry of the surface [3]. Capacitive touch techniques makeuse of the capacitance change of the surface due to touch to calculate the position ofthat touch. Consequently, transmitters and receivers of electrical signals are required
to measure the change of capacitance. For example, the user is asked to wear, holdor use a device that acts as the transmitter of an electrical signal [4]. In an earlier
study [5], a mat was used as a transmitter of high frequency signals to travel though
the human body. When the human touches a surface with four electrodes mounted
on the corners, four high frequency currents are detected by the corner electrodes.
Depending on the ratios of these currents, the touch location is identiﬁed. Such amat demands additional space and speciﬁc installation requirements which are notavailable for general objects and materials [5].
We propose the use of the induced voltage on the human body from the AC powerlines as the touch input, instead of the aforementioned transmitter device. Thus, theproposed touch-sensing technique is passive. Furthermore, the proposed techniqueturns conductive/semi-conductive surfaces into a touch panel. As a result, materials
with desirable mechanical or thermal qualities could be touch sensitive. Also, thegeometrical properties of the touch surface does not interfere with touch signals,
unless the electrical path between the touch location and the electrode is altered. As
proof of concept, a passive granite touch panel is proposed in this paper.

2 Operation Principle
Due to the fact that the human body contains minerals and salts, it exhibits conductive
qualities, and hence, is aﬀected by nearby line’s 100/220 V, inducing a potential on
the human body [6]. The induced voltage on the human body will be used as thetouch trigger for the proposed touch panel.
Granite tiles have relative permittivity range of 5 to 8 F/m [7], hence, it was used
to implement a touch ﬂoor [8]. However, multiple tiles were used to implement thattouch ﬂoor. In the present study, using only one tile and four electrodes and a signal
conditioning circuit, we implemented a touch pad. The voltage detected at the eachcorner of the tile has an inverse relation to the distance between the touch locationand the respective electrode. Thus, by calculating the ratios of the voltage detected,
the touch location is computed.

Turning Surfaces into Touch Panels: A Granite-Touch Pad303Fig. 1 The voltage detected at the corners of a granite surface while the tile is touched from near
the four electrodes and in the middle of the granite tile

3 Experimentation and Results
A regular ﬂat granite tile of 30 × 30 cm with electrodes mounted on the four cornersof the tile was used. A user was asked to touch the granite tile using a bare ﬁnger ina typical experimental room. The voltage from the four corners was connected to an
oscilloscope for signal evaluation. Figure 1 shows the user touching the tile at speciﬁclocations in speciﬁed time periods. At time 6 s the user touched the granite tile at thecenter while at times 1.5, 2.5, 3.5 and 4.5 s the user touched near the ﬁrst, second,
third and fourth electrode receptively. Upon each touch event, a 60 Hz voltage signal
was observed at each electrode. The electrode nearest to the touch location received
the largest signals. Furthermore, the ﬁnger was placed at the center of the tile; the fourelectrodes received nearly equal level of signals. The voltage of “no touch” received
at the four electrodes was signiﬁcantly smaller than the voltage of touch, as seenin Fig. 1. The above mentioned observation indicates that the location of touch is
calculated based on the output of the four electrodes.

4 Conclusion
In this paper, a methodology of turning a regular surface into a passive touch sensing
panel was proposed. The system is simple, cost-eﬀective, and of low power, as it ispassive.

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Acknowledgements This study was in part supported by JSPS Kakenhi (15H05923).

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