Biomedical Engineering Reference
In-Depth Information
prostheses (Gage et al., 2005; Johnson et al., 2004; Oweiss et al.,
2005), are also dependent on microsystems for their operation. The use
of radio frequency (RF) induction for power and radio telemetry is
the best alternative when wires or batteries are not an option, which is
the case for some integrated neural stimulation microsystems (Najafi,
2000). This approach uses an external flat antenna and an implanted
on-chip antenna. These types of microsystems could also benefit from
energy harvesting to avoid battery limitations. To address the need for
more efficient technology, researchers have tried to employ energy har-
vesters for powering biomedical devices, as evidenced by investigations
of automatic self-winding wristwatches for powering pacemakers
(Gorge et al., 2001; Goto et al., 1998, 1999) or by using generators
placed in shoes for powering artificial organs (Antaki et al., 1995).
The decrease in power consumption by electronic devices has been
well documented over the years. A custom digital signal processing
(DSP) unit consumed about 18
μ
W of power by 1998 (Amirtharajah
and Chandrakasan, 1998). An updated version from the same group
presented a power consumption of 500 nW by 2005 (Amirtharajah
et al., 2005), while another group in 2008 presented a processor called
Phoenix using only 30 pW of power (Seok et al.; 2008). Therefore,
low-power electronics are making progress to extend battery life or
even use energy harvesting as the sole energy source. If electronic self-
winding wristwatches can harness body motion to power themselves,
in the near future hybrid approaches using energy harvesters and
rechargeable batteries could power more portable applications or even
implantable devices. It is anticipated that hybrid power supplies will be
critical for a wide range of autonomous microsystems (Bharatula
et al., 2005; Harb et al., 2002).
Another concern is the environmental panorama of battery disposal
around the world. Millions of batteries are discarded into sanitary
landfills where heavy metals can result in groundwater contamination.
Therefore, solutions that minimize or avoid battery disposal will cer-
tainly provide an environmental advantage.
s operation.
In addition, the larger the device, the larger the power consumption.
Cardiac pacemakers consume around 100
Power consumption is intrinsically attached to the device
'
W of electrical power in
average, while hearing aids, on the other hand, require around 50
μ
μ
Wof
power. The latter, although consuming less power,
involve frequent
