Ferroelectric Conversion
Ferroelectric conversion makes use of the peculiar properties of dielectric[12] materials. Barium titanate, for example, has good dielectric properties at low temperatures, but, when its temperature is raised to more than 120°C, the properties get worse rapidly. We cannot discuss dielectric behavior thoroughly in this booklet; suffice it to say that in this process heat is absorbed in a realignment of molecules within the barium titanate latticework.
If we now place a slab of barium titanate between the two plates of an electrical condenser and charge the condenser, as shown in [Figure 14], we have a unique way of converting heat into electricity directly. When the barium titanate is heated above its Curie point[13] of 120°C, the condenser’s capacitance is radically reduced as the dielectric constant falls. The condenser is forced to discharge and move electrons through an external circuit consisting of the load and the original source of charge. Useful electrical energy is delivered during this step. [Figure 14] shows the process schematically and mathematically. When the dielectric is cooled, waste heat is given up by the barium titanate, and the cycle is complete.
Figure 14 FERROELECTRIC ENERGY CONVERSION
The ferroelectric converter is really an electrical capacitor whose capacitance is changed by temperature. When heat is added, capacitance drops, voltage rises, and the capacitor is made to discharge through the load. CYCLE: ① Switch #1 closed, #2 open. Condenser charges from battery to charge Q₂ at voltage V₁ with capacity C₁. ② All switches open. Heat added, capacity changes from C₁ to C₂, charge remains constant, so voltage changes from V₁ to V₂. ③ Switch #2 closed, #1 open. Condenser discharges through load and battery to charge Q₁ at voltage V₁ with capacity C₂. ④ All switches open. Heat rejected, capacity changes from C₂ to C₁, charge remains constant, so voltage changes from V₁ to V₀. CYCLE THEN REPEATS. Energy supplied from battery each cycle is E₁. Energy delivered to load and battery each cycle is E₂. Net energy converted is then E₂ - E₁, the difference in the shaded areas.
(a) CIRCUIT HEAT IN BARIUM TITANATE DIELECTRIC WASTE HEAT OUT SWITCH #2 LOAD SWITCH #1 BATTERY (b) CYCLE DIAGRAM charge volts Q₂, Q₁, E₁, E₂, V₀ V₁ V₂ GENERAL INFORMATION: C₂ < C₁ V = Q/C