Page 222 - Carbon Nanotube Fibres and Yarns

CHAPTER 9

Sensors based on CNT yarns

Jude C. Anike, Jandro L. Abot
Department of Mechanical Engineering, The Catholic University of America, Washington, DC, United States

9.1 Introduction

CNTs have excellent mechanical, electrical, thermal, and optical properties
that are being utilized individually or in combination to produce smart sen-
sors or multifunctional materials [1–11]. They have high aspect ratios that
are ideal for long and continuous sensing. Their high surface area, for in-
stance, can be exploited for depositing materials to create hybrid functional
materials or functionalized to create electrodes for a variety of applications
[1]. CNTs are also known to exhibit ballistic conductivity due to minimal
electron scattering in their 1D structure with mean free paths of the order
of tens of microns [2]. Mechanical strain may cause reproducible changes in
the electrical properties of CNT fibers, making it possible to exploit them
as electromechanical sensors [6, 7]. The associating changes include induc-
tance, capacitance, and resistance which can be correlated to the strain. Of
great importance is that CNT fibers are responsive to tensile, compressive,
flexural, and torsional strain. The working principles of sensors made from a
CNT macroscopic assembly include change of their electrical resistivity or
resistance due to mechanical strain known as piezoresistivity, change of their
inductance and capacitance due to mechanical strain, change of their elec-
trical resistivity due to variation in temperature known as thermoresistivity
[8], change of their electrical resistance due to variation in a magnetic field
known as magnetoresistance [9], and change in their electrical resistance
with change of their mechanical resonant frequency due to variation of
temperature, pressure, mass, and strain [10]. The change in conductance or
resistance is much more dominant than other variation in electrical prop-
erties [1–3]. This is partly because charge carriers are easily separated under
deformation leading to an increase in resistance. For very small strains, the
deformation has shown to be elastic and the conductive network is fully
recovered when the strain is removed, leading to a decrease in resistance.

Carbon Nanotube Fibers and Yarns Copyright © 2020 Elsevier Ltd.
https://doi.org/10.1016/B978-0-08-102722-6.00009-2 All rights reserved. 213