Biomedical Engineering Reference
In-Depth Information
battery energy density increased only 5
3
. This graph is an extension
of the one presented by Starner and Paradiso (2004) that covered the
period from 1990 to 2003. The reference point for the comparisons
was kept the same: a high-end portable computer from 1990, with an
80386 processor running at 16 MHz, 8 MB of RAM and 40 MB of
hard disk capacity, using a nickel
cadmium battery. The latest tech-
nologies were compared for each year as multiples of the reference lap-
top. Only disk capacity and available RAM data were kept from
Starner and Paradiso from the years 1990 to 2003. Specialized com-
puter magazines over the Internet were used to obtain most of the
information. As there are several central processing unit (CPU) bench-
marking comparisons, the number of million instructions per second
(MIPS) for Intel processors was used as a reference providing a similar
trend line as the one from the work of Starner and Paradiso. The bat-
tery energy density was based on the volumetric energy density (Wh/L)
data gathered from Panasonic
3
for nickel
cadmium, nickel
metal
hydride, and lithium
ion battery chemistries, because it was readily
available until 2010. Although Starner and Paradiso calculated the
energy density using joules per kilogram, the results are nearly identi-
cal. The IEEE 802.11 standard released in 1997 was included for the
wireless network speed trend.
On the other hand, energy sources other than batteries exist with
even higher power densities, as shown in
Figure 1.2
,butmostofthem
are designed for macroscale systems and/or require a combustible to
operate. The human body is also an alternative energy source that can
provide power densities under 1 W/kg (1 mW/g) or 1 W/L (1 mW/cm
3
)
as shown in the figure. Due to the decrease in power consumption of
electronic devices mentioned previously, the available power density
levels of 1 mW/cm
3
or 1 mW/g are an interesting option for low-power
applications. Because the power is generated by body motion, the appli-
cations that can directly benefit for this approach are portable electronics
and biomedical devices (wearable or surgically implantable).
Figure 1.3
highlights the power budget for some electronic applica-
tions within the human body generation range. For example, using the
previous reference of 1 mW/cm
3
(or 1 mW of power in a volume of
1cm
3
) only a few miniature low-power applications (such as pace-
makers, hearing aids, watches, and some consumer devices) can directly
