Biomedical Engineering Reference
In-Depth Information
Table 2.4 ASTF Values Calculated from Various Motion Sources
Vibrating Source
σ
ω
(m
2
/s
3
)
Base of a three-axis machine tool
a
0.230
Blender casing
a
0.054
Cloth dryer machine
a
0.016
Washing machine
a
0.0004
Small microwave oven
a
0.007
Home breadmaker
a
0.001
Heating, ventilation, and air conditioning (HVAC) vents in office building
a
0.0001
0.006
Walking (measured on the head)
b
0.5
3.0
a
Calculated from Roundy (2003).
b
Calculated from Hirasaki et al. (1999).
Roundy (2003) provided some examples of the peak acceleration
and its corresponding frequency for several applications; these results
are tabulated for
σ
ω
values and summarized in
Table 2.4
. A study by
Hirasaki et al. (1999) provided values from acceleration and frequency
from human walking to tabulate the
σ
ω
term presented in
Table 2.4
.
From these results, the
ASTF
(or
σ
ω
values) for machine-based vibra-
tions are relatively low (
σ
ω
values from body activi-
ties, such as walking, are relatively high (
.
1).
{
1). In contrast,
Stephen (2006) reported that electromagnetic energy harvesting can
deliver a maximum power that corresponds to 50% of the maximum
available power. Therefore, the expression for maximum power that
can be delivered into the electrical load is
P
max elect
5
1
4
mσ
ω
Q
(2.9)
Arranging previous equation to be divided by the generator volume
V
to obtain volumetric power density, such as
V
5
m/
ρ
, where
ρ
is the
proof mass density, leads to
P
max elect
V
5
1
4
ρσ
ω
Q
(2.10)
A plot of the last equation is shown in
Figure 2.3
. A proof mass
density of 10 g/cm
3
was used (for simplicity and because it is similar to
that of molybdenum). Two distinct zones are displayed, the first is for
the human-based motion harvesters (assuming
Q
B
1 and
σ
ω
B
1), while
the second is
for machine-based vibration generators
(assuming
