Hiroshi Maiwa

By Hiroshi Maiwa

Part of the book: Advances in Ceramics

By Hiroshi Maiwa

The electrocaloric properties of (Pb,La)(Zr,Ti)O3 (PLZT) and BaTiO3 ceramics were investigated by the indirect estimation and direct measurement of temperature–electric field (T–E) hysteresis loops. The measured T-E loops showed a similar shape to strain–electric field (s–E) loops. The adiabatic temperature change ∆T due to electrocaloric effects was estimated from the polarization change of these samples. ∆Ts of 0.58 and 0.36 K were estimated for the (Pb,La)(Zr,Ti)O3 (PLZT)(9.1/65/35) ceramics and BaTiO3 ceramics sintered at 1400°C, respectively. The measured temperature changes ∆Ts in these samples upon the release of the electric field from 30 kV/cm to zero were 0.26 and 0.29 K, respectively.

Part of the book: Advanced Ceramic Processing

By Hiroshi Maiwa

The piezoelectric material selection and the circuit design in vibrational energy harvesting are discussed. The performances of the energy-harvesting unimorph devices that captured frequencies of 60 Hz by using piezoelectric PZT-based and BT-based ceramics were evaluated. Output voltages and power from the devices depend on the amplitude and the frequency of the oscillations, and depend on the load resistance. Generally, PZT-based ceramics are superior for piezoelectric energy-harvesting applications. The figures of merit of the materials are discussed in order to provide the guidelines of the piezoelectric material selections. Piezoelectric voltage coefficient, g31, is considered to be good parameter to predict the maximum voltages. On the other hand, d31g31/tanδ, k312Qm and d31g31 are close to the behavior of the maximum power. Combination of the piezoelectric unimorph and power management circuit produced the constant voltage output, which would be used as the power sources.

Part of the book: Piezoelectric Materials