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Upper-Limb Prosthetic Devices 209

Table 1 Noncapacitive WPT Options
Options
Ultrasound [14]
Parameters Inductive Coupling [11] [12] RF [6] [13] [12]
Human Depends on energy Yes Yes
safety transferred
Efficiency 73% 48% 21%–35%
Max power Up to 10W <1W 100mW
Frequencies 1kHz–100MHz 30kHz– 10kHz–10MHz
300GHz
From Moutopoulou, E., Bertos, G.A., Mablekos-Alexiou, A., Papadopoulos, E.G., 2015. Feasibility of a
biomechatronic EPP upper-limb prosthesis controller. Conf. Proc. IEEE Eng. Med. Biol. Soc. 2015,
2454–2457. https://doi.org/10.1109/EMBC.2015.7318890.

separation and size of the coil pair, loop diameter, and frequency play a major
role in determining WPT performance (Celik and Aydin, 2017).
The noncapacitive WPT couplings, include the inductive, radio fre-
quency (RF), and ultrasound couplings. Of those, the inductive coupling
is characterized by high efficiency and power transfer capability and is there-
fore superior to the other two (Moutopoulou et al., 2015), see Table 1. Also,
according to Sun et al. (2013), inductive coupling is considered to be the best
choice for biomedical applications.
Candidate biomedical applications include artificial hearts, visual pros-
theses, ingestible devices (Kim et al., 2014), and upper-limb-embedded
biomechatronic devices (Kontogiannopoulos et al., 2018). Implantable neu-
ral prosthetic devices typically have power requirements that exceed the
capability of reasonably sized implantable batteries. Therefore, transcutane-
ous magnetic coupling remains the method of choice for powering
implanted neural prostheses (Troyk and DeMichele, 2003). A fully wireless
EMG recording system that can enable upper-limb prosthesis control while
achieving maximum power transfer efficiency through magnetic resonantly
coupled (inductive) WPT is described in Bercich et al. (2016). This solution
makes notable progress in the efficiency of WPT through loosely coupled
inductive links specifically for upper-limb prostheses. As an added benefit
of the inductive coupling, data can also be transmitted (Ghovanloo and
Najafi, 2004; Troyk and DeMichele, 2003).
For these applications, directivity, system stability, reliability, and effi-
ciency enhancement through the wireless transfer coil design enhancement
and operational tunings are required (Kim et al., 2014). Other important
parameters include human safety due to a rise in tissue temperature and min-
iaturization of the relevant electronics (Moutopoulou et al., 2015).