Biomedical Engineering Reference
In-Depth Information
cases, voltage multipliers have been employed to increase and rectify
the output voltages. Some of the limitations faced by the use of semi-
conductor p
n junctions can be overcome by the use of active elec-
tronics (Amirtharajah et al., 2006; Makihara et al., 2006; Marzencki
et al., 2008; Peters et al., 2008; Siebert et al., 2005).
Because the energy generation process from energy harvesting is
heavily dependent on the availability of the external energy source, the
produced energy must be stored for use when the energy source is
unavailable. Capacitors and rechargeable batteries are the traditional
energy storage elements that have been used for this purpose.
Rechargeable batteries are preferable because of their high energy
storage capacity, but they have a limited number of charging cycles.
Capacitors can be charged quickly an infinite number of times,
although the energy storage capacity is relatively low. On the other
hand, electrochemical double-layer capacitors (supercapacitors or
ultracapacitors) provide almost unlimited recharges with relatively
high energy storage capacity. Supercapacitors with sizes resembling a
postage stamp with capacities of 5
19 F have been presented (Flipsen,
2005; van Donk, 2000). Thin-film lithium batteries can also reduce the
size of rechargeable power sources for biomedical applications
(Albano et al., 2007; Bates et al., 2000; Bharatula et al., 2005; Harb
et al., 2002). Studies reporting the successful use of rechargeable bat-
teries using piezoelectric energy harvesters have also been carried out
(Sodano et al., 2005a,b).
5.2 FUTURE
The increase in population ageing will take a toll on the developed econ-
omies. For sure, something will be done in order to minimize this
impact. Better health-care monitoring (treating before it gets more com-
plicated and/or expensive) as well as to keep the population more active
will surely be one of the keys to attack this problem. As a whole, this
panorama will be a priority, otherwise health care cost and economic
development will be jeopardized. Thus, physiological measurement is a
field that is likely to become more important in the near future.
Today the measurement of physiological parameters is something
that can be done at home with ease (body weight, heart rate, blood
pressure, blood glucose) with no medical supervision. Later on more
