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Hermetically Packaged Capacitive Silicon Resonators on LTCC Substrate
Published in Nguyen Van Toan, Takahito Ono, Capacitive Silicon Resonators, 2019
Figure 4.15 shows the measured electrostatic frequency tuning characteristic for the two-arm-type resonator after the packaging process, indicating a frequency tuning range of 700 Hz, by changing the polarization voltage from 40 V to 80 V. The measured electrical tuning slope is 17.5 Hz/V, showing an effective capacitive gap size of 500 nm after packaging.
Parametric analysis of hybrid tribo-piezoelectric energy harvester
Published in Mechanics Based Design of Structures and Machines, 2022
Shyam Kishor Sharma, Satish Kumar, Rajeev Kumar
The surface charge density (σ) and the relative permittivity (ϵr) are two significant parameters for the HTPEH. The power output of the piezoelectric unit does not depend on the surface charge density (σ). However, the triboelectric output power is directly proportional to the surface charge density (σ), as shown in Fig. 5(a). The effect of increasing relative permittivity has a favorable impact on the power output of TEH, as shown in Fig. 5(b). In contrast, the effect of increasing relative permittivity (ϵr) on the PEH unit is adverse, as shown in Fig. 5(c). The surface charge density of the triboelectric layer can be increased by different methods like surface morphology, dynamic charge transfer, and surface modifications to increase the power output of the TEH unit (He et al. 2015; Mahmud et al. 2016; Cui et al. 2020). The large relative permittivity of piezoelectric material facilitates electrical tuning and reduces their piezoelectric voltage coefficients (Jain et al. 2015; Tian et al. 2018). Therefore, the material with lower relative permittivity is generally suitable for the piezoelectric energy harvester.
Voltage-induced pseudo-dielectric heating and its application for color tuning in a thermally sensitive cholesteric liquid crystal
Published in Liquid Crystals, 2019
Po-Chang Wu, Guan-Wei Wu, Chia-Hua Yu, Wei Lee
Extending our previously suggested pathway toward effective λc tuning of CLC bandgap by an externally applied AC voltage, we have studied the influence of the cell parameters. Based on the electro-thermal effect derived from the pseudo-dielectric relaxation, our technique is characterized by significantly lower operating voltage required for a wider tuning range in comparison with other alternatives relying on electrical tuning. This method entails two prerequisites involving the LC material itself and the empty cell. We designed a – Δε CLC with thermally responsive bandgap properties by doping a proper amount of the chiral additive S-811 into the negative nematic MLC-6608. By means of temperature-dependent dielectric spectroscopy, it was found that the temperature range of the CLC phase decreases with increasing S-811 content until the CLC phase disappears at 50 wt%. The CLC with 45-wt% S-811, possessing the phase transition temperature between CLC and SmA at room temperature (TSmA-CLC = 21°C), was demonstrated as the optimized sample for further investigations. Following Keating’s theory, the spectral feature of this CLC exhibits a very wide thermally tunable λc range from 1392 nm (IR) at 22°C to 340 nm (UV) at 39°C. For the second prerequisite to allow effective temperature elevation achieved by external voltages via the pseudo-dielectric heating, the CLC was injected into a standard sandwich-type planar-aligned cell with ITO electrodes. It was confirmed that the observed dielectric relaxation, dominating the pseudo-dielectric heating behavior in this study, is not attributable to the dipole rotation of LC molecules but the cell geometry which can be regarded as an equivalent circuit consisting of a resistance from the electrode layer (i.e., RITO) and a capacitance from the LC layer (C = ε0εsA/d) in series. On this basis, key factors affecting the tuning efficacy were further investigated by introducing the CLC into empty cells with different cell conditions. It was evidenced that the change in cell temperature as a function of the voltage frequency of the cell well follows the model established by Schadt [22], indicating that the operating voltage amplitude and frequency can readily be reduced by reducing the cell gap and employing a host LC material with larger dielectric permittivity. Specifically, the maximum tunable temperature range (ΔTmax) can simply be controlled by optimizing the values of specific heat conductivity (h) and resistivity (RITO) of the substrates, following the relation ΔTmax ∝ (h⋅RITO)–1.