Alternative Caloric Energy Conversions - Magnetocaloric Energy Conversion: From Theory to Applications - page 425

Table 10.9 Characteristics of the self-driven pyroelectric energy converters
Authors Material Δ T ( ° C) Power ( µ W) References

Cuadras et al. PZT 30 0.5 [ 65 ]

Zhang et al. PZT 16 2.7 [ 68 ]

Mane et al. PMN-0.3PT / / [ 63 ]

Mane et al. PZT / / [ 63 ]

Ravindran et al. Piezoceramic vibrit 1100 80 3.0 [ 69 ]

Ravindran et al. PZT 96 4.4 [ 70 ]

material is attached to the bimetallic strip, its temperature oscillates as well and a
pyroelectric current is generated. To test the concept, a 250-

µ m-thick PZT ceramic

10 mm 2 was attached to a bimetal strip (type MS, Rau
GmbH) with dimensions 40 × 6 × 0.28 mm 3 . Peltier elements were used to simulate
the heat source and the heat sink of the device. The experiment was performed for
various values of the temperature difference between the heat sink and the heat
source. Based on the measured voltage and electrical current, the generated power
was calculated. At a temperature difference of 96 K between the heat source and the
heat sink and a frequency of 0.2 Hz, a maximum power of 4.4

material with an area of 10 ×

W was achieved.
In Table 10.9 , the main characteristics of the above-presented, self-driven,
pyroelectric, energy harvesting prototypes are presented. The generated electrical
power of the devices is in the range of a few

µ

W. For example, this could be
enough to power an electronic watch [ 71 ]. However, it has to be taken into account
that the mass of the pyroelectric materials used in the prototypes presented was
relatively low since in almost all the cases only one pyroelectric element was used.
A further increase in the generated power could also be achieved by increasing the
frequency of the devices. This calls for better heat-transfer mechanisms and the use
of thermal diodes.

µ

Pyroelectric Energy Harvesters Based on the Ericsson Cycle

The most common way to realize the pyroelectric Ericsson thermodynamic cycle is
by performing a so-called dipping experiment. In this case, two thermal baths, one
having the temperature T high and the other the temperature T low , are prepared. The
pyroelectric material is further connected to a voltage source and alternatively
moved from the hot to the cold thermal bath. Furthermore, the voltage applied to
the electrodes of the pyroelectric material is changed so that the material undergoes
the pyroelectric Ericsson cycle. The performance of the material is usually
expressed as the electrical energy generated per litre of pyroelectric material in one
thermodynamic cycle constrained by the prede ned temperatures (T high ,T low ) and

the electric elds (E high ,E low ). Many different authors reported on the pyroelectric
material

s performance measured using the dipping experiment. The results of some
of these experiments are gathered in Table 10.10 ; however, only the maximum

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