Bio-inspired Sensors for Structural Health Monitoring - Biotechnologies and Biomimetics for Civil Engineering - page 257

Fig. 11.3 A mobile sensor
prototype (developed by
researchers at the Georgia
Institute of Technology,
USA) is crawling on a steel
pedestrian bridge. (Photo
courtesy of Prof. Yang Wang,
Georgia Institute of
Technology, USA)
hard-to-reach areas that an inspector or engineer would otherwise not be able to
access conveniently.
A prime example of a bio-inspired mobile sensor for SHM is work by Zhu et al.
( 2010 ). The mobile sensor was fabricated by connecting two two-wheeled vehicles
with a flexible beam (Fig. 11.3 ). The wheels were made with magnets so that it
could climb ferromagnetic structures. The design of the robot also included
infrared sensors and Hall effect sensors for the purposes of detecting boundaries
and for locomotion, respectively. For SHM, a Silicon Designs 2260-010 acceler-
ometer was located on the center of the robot's center flexible beam, and the
mobile sensor could control the attachment and detachment of the accelerometer
onto the structure (i.e., by moving the two two-wheeled cars closer or farther away
from each other, respectively). Two different experimental laboratory tests were
conducted in the laboratory for validating their performance. The mobile sensors
successfully crawled around a steel portal frame, and two robots collected struc-
tural vibration response (excited using impact hammer strikes) at 11 different
measurement points. Damage was simulated by adding a mass block or by loos-
ening bolts at connections. By analyzing the transmissibility function, damage
location was successfully identified. Other research groups have also developed
various types of crawling robots (Huston et al. 2005 ; Akiba et al. 2013 ; Oh et al.
2009 ).
While the aforementioned mobile sensor was more mechanical and resembled
that of a car, the design of the Geckobot was inspired by the gecko's ability to
climb almost any type of surface (Unver et al. 2006 ). In particular, the Geckobot
featured synthetic dry adhesive feet, made with polydimethyl siloxane (PDMS)
elastomer that mimicked the gait and climbing mechanism of real geckos. Like a
real gecko, when the PDMS toe was controlled to detach from the surface, the
PDMS was bent and peeled off in a way that minimized the detaching force.
Another unique design was its active tail that enhanced the robot's mobility during
climbing. With the existence of a tail, it could provide additional force that secured