Biomedical Engineering Reference
In-Depth Information
FIGURE 10.13
Elastic resistive transducer.
EXAMPLE PROBLEM 10.6
A 0.1 m long by 0.005 m diameter elastic resistive transducer has a resistance of 1 k
. (1) Cal-
culate the resistivity of the electrically conductive material inside the transducer, and (2) calculate
the resistance of the transducer after it has been wrapped around a patient's chest having a cir-
cumference of 1.2 m. Assume that the cross-sectional area of the transducer remains unchanged.
O
Solution
1.
The cross-sectional area of the transducer (
(0.0025)
2
m
2
10
5
m
2
. From
A
) is equal to
p
¼
1.96
10
3
10
5
m
2
1
O
1
:
96
¼
RA
Eq. (10.5), r
¼
0
:
196
O
m
l
¼
0
:
1m
2.
1
:
2m
R
stretched
¼
0
:
196
O
m
¼
12 k
O
10
5
m
2
1
:
96
EXAMPLE PROBLEM 10.7
Calculate the change in voltage that is induced across the elastic transducer in Example Prob-
lem 10.6 assuming that normal breathing produces a 10 percent change in chest circumference and
a constant current of 0.5 mA is passed through the transducer.
Solution
From Ohm's law (
V
¼
I
R
),
V
¼
0.5 mA
12 k
O¼
6V.If
changes by 10 percent,
D
V
¼
0.6 V.
R
