Biomedical Engineering Reference
In-Depth Information
(A)
(B)
400
400
350
Gasoline
Ethanol
Aluminum
Steel
Water
Glass
350
300
300
250
250
200
200
150
150
100
100
50
50
0
0
25
0
0.2
0.4
0.6
0.8
1
0
5
10
15
20
B (T)
Temperature difference (°C)
(C)
(D)
50
400
350
40
PZN-8%PT
300
30
250
PMN-PT30
200
PMN-PT28
20
150
100
10
PZT-507
50
PZT-701
PZT-502
0
0
0
20
40
60
80
100
0.5
0.6
0.7
0.8
0.9
1
E (MV/m)
Electromechanical coupling factor
Figure 1.4 Transduction generation limits: (A) thermal expansion, (B) electromagnetic, (C) piezoelectric, and
(D) electrostatic (Romero, 2010).
provides energy densities of tens of milliwatt per cubic centimeter.
However, the requirement of a thermal gradient limits where such a
generator can be placed. Generators placed against the skin use the dif-
ference in temperature between the body and the surrounding environ-
ment. Inside the human body such a generator would be severely
limited as it is estimated that gradients will never exceed 0.2
C
(Luchakov and Nozdrachev, 2009). In addition, harvesting the thermal
expansion of a material for energy generation is not a simple task.
Thermoelectric energy conversion makes use of a temperature gra-
dient to create an electric potential for thermoelectric materials. The
Carnot efficiency
η
c
η
c
5
ðT
high
2
T
low
Þ
=
T
high
(1.4)
provides a limit for this generation (where T stands for temperature).
If body temperature (37
C) and a cool room (25
C) are considered, the
