Page 211 - Handbook of Biomechatronics

208 Georgios A. Bertos and Evangelos G. Papadopoulos

11 bits. Together with a haptic input device, a setup was created allowing
palpation and force feeling.
Wearable systems posture sensors for upper body rehabilitation are
reviewed (Wang et al., 2017). These include mostly accelerometers and
IMUs measuring accelerations and angular velocities, as they yield relatively
accurate essential values, are easy to use, and are miniature in size. Similar
sensors can be used in upper-limb prostheses to track arm or hand motions,
and for safety reasons.

1.5.6 Wireless Power Transfer
Wireless power transfer (WPT) is the transmission of electrical power with-
out wires and is based on technologies using time-varying electric, magnetic,
or electromagnetic fields. WPT is useful to power electrical devices where
are inconvenient, or not possible, as is the case of body embedded sensors,
actuators, and communication devices.
Power can be transferred over short distances (near-field transfer) by
alternating magnetic fields and inductive coupling between coils, or by alter-
nating electric fields and capacitive coupling between metal electrodes.
Inductive coupling is the most common method of WPT and is used in
charging devices such as smart phones, electric shavers, visual prostheses,
and implantable medical devices (cardiac pacemakers, cochlear implants)
(Sun et al., 2013; Moorey et al., 2014)(Fig. 16). For 20mm distance

Fig. 16 Capacitive and inductive couplings for WPT. (From Sun, T.J., Xie, X., Wang, Z.H.,
2013. Design challenges of the wireless power transfer for medical microsystems. In: 2013
IEEE International Wireless Symposium (IWS).)