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Herein, the systematic change in the self-polarization behavior against the post-heat treatment after film deposition was investigated to understand the origin of self-polarization in hydrothermally prepared (KxNa1−x)NbO3 films with x = 0.88 at 240 °C below the Curie temperature. The transverse piezoelectric constant, e31,f, was evaluated by the cantilever method. The as-prepared films and heat-treated films at 300 °C had an almost perfectly self-polarized state and showed e31,f of ∼−5.0 C m−2 without applying an electric field as a poling treatment. Also, the piezoelectric response shows good linearity with the asymmetric piezoelectric butterfly curves, showing imprint characteristics. The self-polarized states were maintained until the heat treatment above the Curie temperature. Moreover, the self-polarized film was successfully deposited on the post-heat-treated film without the self-polarized state. This result suggests that the self-polarized state is generated regardless of the polarized state of the underlying layer by the hydrothermal synthesis in which deposition temperature is below the Curie temperature. [ABSTRACT FROM AUTHOR]

(KxNa1−x)NbO3 films that were approximately 3 μm in thickness and with various x values were systematically deposited at 240 °C on (100)cSrRuO3//(100)SrTiO3 substrates using a hydrothermal method. Direct and inverse transverse piezoelectric coefficients, e31,f, near 0 kV cm−1 were approximately −5.0 C m−2 for the as-deposited films with a wide range of x values without any poling treatment. A large difference in e31,f value was not observed before or after poling treatment upon applying a positive electric field, suggesting that the as-deposited (KxNa1−x)NbO3 films with x = 0.36–0.88 were almost fully in a self-polarized state. (KxNa1−x)NbO3 films with x = 0.36–0.88 without any poling treatment showed a figure of merit for an energy harvester (FOM = e31,f2/εr) above 0.13, as calculated directly from e31,f. These FOM values are relatively high compared with the reported ones for other lead-free films that have a perovskite structure. [ABSTRACT FROM AUTHOR]

Using a hydrothermal method, (K0.88Na0.12)NbO3 films were deposited at 240 °C on (100) cSrRuO3//(100)SrTiO3 substrates. Moreover, without any poling treatment, direct and inverse transverse piezoelectric coefficients, e31,f, near 0 kV/cm were approximately −5.0 C/m2 for the as-deposited film. This value was nearly unchanged following the application of an electric field and poling treatment, suggesting that as-deposited films are almost in a fully self-polarized state without the application of an electric field. As-deposited films with a thickness of up to 22 μm showed constant piezoelectricity without any poling treatment. The films did not crack or peel because of substrates due to the small thermal strain originating from the low deposition temperature. The figures of merit (FOM) for the vibration energy harvester [FOM = e31,f2/(ε0εr)] and sensor [FOM = e31,f/(ε0εr)] were estimated to be good at 32.8 GPa and –5.9 GV/m, respectively, primarily because of the low relative dielectric constant of ∼110. Furthermore, the piezoelectric voltage coefficient g31 [= d31/(ε0εr)] was estimated and demonstrated a high value of 0.073 Vm/N. [ABSTRACT FROM AUTHOR]

We report the performance of a prototype 29 m long loop-tube-type thermoacoustic prime mover. The phase adjuster (PA) that succeeded in low-temperature oscillation was examined for the aforementioned prototype. The onset temperature when PA length and PA position were changed was calculated using stability analysis. The onset temperature was found to be 153 °C. Using the calculation results, a prototype that succeeded in oscillating at an onset temperature of 155 °C was developed. These results indicate that the thermoacoustic system was successfully enlarged. This will promote practical application of a large system that converts waste heat to effective energy. [ABSTRACT FROM AUTHOR]

Stacks are among the most important devices for influencing the energy-conversion efficiency of work flow to heat flow during thermoacoustic phenomena. An optimal stack design is indispensable for the practical application of thermoacoustic systems. To this end, it is necessary to estimate the heat flow generated in the stack. This study proposes to estimate this quantity based on the sound generated by a thermoacoustic phenomenon in a stack without any temperature gradient. The heat flow caused by a standing-wave component generated by this thermoacoustic phenomenon is successfully measured. [ABSTRACT FROM AUTHOR]

A setup and approach for simultaneous measurement of the inverse and direct transverse piezoelectric coefficients of piezoelectric films was constructed. A longitudinal vibration mode resonator with a hydrothermally synthesized (K,Na)NbO 3 film deposited on a SrRuO 3 /SrTiO 3 substrate was investigated. The fabricated vibrator consists of two upper electrodes, one for actuation and the other for sensing. A driving voltage was applied to the actuator electrode to generate mechanical vibration at its resonance frequency. The vibration velocity was measured with a laser Doppler vibrometer, and the output current from the shorted sensing electrode was also measured to simultaneously evaluate the inverse and direct piezoelectric responses. The obtained inverse piezoelectric coefficient e 31 ̅ was −3.60 C/m2, while the direct piezoelectric coefficient e 31 ̅ was almost same at −3.69 C/m2. From these values, the inverse and direct piezoelectric coefficients e 31 , f were −4.93 and −5.05 C/m2, respectively. [Display omitted] • Measurement method establishment of the inverse and direct transverse piezoelectric coefficients for piezoelectric films simultaneously. • Use longitudinal vibration mode resonator using a hydrothermally synthesized (K,Na)NbO 3 film deposited on SrRuO 3 /SrTiO 3 substrate • Almost similar inverse and direct piezoelectric coefficients ( e 31 ̅) value of −3.60 and −3.69 C/m2, respectively. [ABSTRACT FROM AUTHOR]

This brief proposes a frequency synchronization method for a full-digital self-oscillating pulsewidth modulation (PWM) signal generator. The self-oscillating PWM signal generator (PSG) generates a variable switching frequency, which results in poor drive performance for a three-phase power inverter or converter. The proposed frequency synchronization method utilizes an additional carrier signal, such as a triangular wave, to fix the switching frequency of a self-oscillating PSG. The switching frequency is synchronized by the triangular wave. As a test case, a switching frequency of 312.5 kHz is used for a performance evaluation of the proposed PSG with a sampling frequency of 12.5 MHz. A first-order noise-shaped output has been obtained. A high-precision PWM signal with low distortion and high resolution of the effective duty cycle has been achieved within the bandwidth. The proposed synchronized self-oscillating PSG is implemented in a three-phase brushless dc motor driver system to confirm the three-phase synchronization performance. Undesirable ripple current from asynchronous operation was not observed. The switching frequencies were synchronized among the three phases. [ABSTRACT FROM PUBLISHER]