Biomedical Engineering Reference
In-Depth Information
when turned over every second and generated 600
Wat10Hzfor
10 cm linear displacement amplitude. A similar approach was also pre-
sented by Cavallier et al. (2005) but using tin balls and several PZT can-
tilever beams in a circular package (2 mm high, 14 mm diameter). In
spite of the fact that the objective was to compare the efficiency of PZT
cantilever beams versus stacks of PZT
μ
PZT, the study demon-
strated the use of low frequencies to excite vibrations in structures at
higher frequency without the need of frequency tuning. The evaluation
of the prototype was performed using one element tested at a frequency
of 6 Hz generating 62 nW. The complete generator with all the elements
would generate around 0.5
Silicon
μ
W.
Prosthetic knee implants is another area where piezoelectric genera-
tion has been studied, as evaluated by Platt et al. (2005a,b). Piezoelectric
transduction benefits from the knee location because forces can be up to
three times higher than the body weight. A laboratory test was elabo-
rated using three piezoelectric stacks (1 cm
3
1cm
3
2cm).Theproto-
type was capable of producing 850
W of continuously regulated power
(19% electrical efficiency, 20% electromechanical efficiency).
μ
A muscle-powered piezoelectric generator was presented by
Lewandowski et al. (2007). The generator was devised to be positioned
in series with a muscle tendon to use the muscle contraction for piezo-
electric stack compression. Power generation would benefit more from
electrically stimulated muscle rather than natural muscle contractions.
Hence, individuals with extensive paralysis are preferable, as electri-
cally stimulated muscle would not interfere with natural muscle move-
ment or other activities. In addition, the power needed to electrically
stimulate the muscles is minimal in comparison with the power that a
muscle can generate when using this generator. The forearm muscle
(brachiocardialis), the dorso-lateral muscle on the trunk (latissimus
dorsi), and the calf muscle (gastrocnemius) are capable of forces of 50,
100, and 250 N, respectively. These forces on a piezoelectric stack
(5 mm
3
5 mm cross-sectional area, 1 Hz, and 250 ms) can produce
power outputs of 8
μ
W (2.5 cm long, at brachiocardialis), 54
μ
W(4cm
long, at latissimus dorsi), and 690
μ
W (8 cm long, at gastrocnemius). A
μ
PZT stack prototype (5 mm
W
for a 250 N force. Muscle, tendon, and bone attachments were not
mentioned in this investigation.
3
5mm
3
18 mm) produced up to 80
Tashiro et al. (2002) developed a variable-capacitance-type electro-
static generator for harnessing the ventricular wall motion of a dog
'
sheart
