Biomedical Engineering Reference
In-Depth Information
Figure 2.5
Magneto-elastic sensor. The permeability of a magneto-elastic tape is changed if a
force/strain (wave or vibration) is applied to the magneto-elastic tape (recreated) [9]
the transformer windings to change (Figure 2.5). If a very small permanent magnet is
held above the detection device by a compliant medium, the change in flux caused by
the magnet's movement due to an applied force can be detected and measured. The field
intensity follows an inverse relationship, leading to a nonlinear response, but which can be
easily made linear by suitable processing. A tactile sensor using magneto-elastic material
consists of a material bonded to the substrate and is used as a core for an inductor. As
the core is stressed, the susceptibility of the material changes, which is measured as a
change in the coil inductance.
2.5 Optical Sensors
The rapid expansion of optical technology in recent years has led to the development of
a wide range of tactile sensors. The operating principles of optically based sensors are
well known and they fall into two classes: 'intrinsic,' where the optical phase, intensity,
or polarization of transmitted light is modulated without interrupting the optical path, and
'extrinsic,' where the physical stimulus interacts with the light external to the primary
light path.
Intrinsic and extrinsic optical sensors can be used for touch, torque, and force sensing.
For industrial applications, the most suitable will be that which requires the least optical
processing. For robotic touch and force-sensing applications, the extrinsic sensor, based
on intensity measurement, is the most widely used, due to the simplicity of its construction
and subsequent information processing. The potential benefits of using optical sensors are
immunity to external electromagnetic interferences, being far from the optical source due
to use of optical fibers, and low weight and volume.
