Numerical simulations of microacoustic resonators and filters

This dissertation discusses numerical simulations of microwave acoustic resonators and bandpass filters employed in wireless telecommunication systems. In the first part of the dissertation, tailored finite element method (FEM) software with efficient numerical techniques is implemented and applied in the modeling of thin-film bulk-acoustic wave resonators (FBARs). Simulations with 3D FEM models of FBARs are carried out to investigate the effect of the electrode shape on the spurious resonances that often are present in the electrical response. The modeling results are validated through comparison of simulated and measured mechanical vibration amplitudes. The usability of the FEM tool is further demonstrated in simulations of a resonator design that features a clean electrical frequency response, free of spurious resonance peaks caused by anharmonic modes. Additionally, a method is proposed for determination of the elastic constants of a piezoelectric thin-film material. The technique is based on fitting of the computed dispersion curves of Lamb-wave modes to those measured from an FBAR using a scanning laser interferometer. In the second part of this dissertation, numerical simulations are used to study propagation properties of longitudinal leaky surface acoustic wave (LLSAW) mode under periodic electrode array on YZ-cut lithium niobate (LN). A combined FEM/boundary element method is employed to compute the electric admittance of one-port synchronous LLSAW resonators. Simulations and experiments are used to derive the dependence of the resonator resonance frequencies and Q values on the electrode dimensions. Ladder-type bandpass filters exploiting the LLSAW mode are implemented on YZ-cut LN in the frequency range from 2.5 GHz to 5.2 GHz, with fundamental mode LLSAW resonators as building blocks. The results demonstrate that the high phase velocity of the LLSAW mode on YZ-cut LN allows inexpensive fabrication of wide-band, low-loss filters up to 5 GHz using conventional optical lithography. The third topic considered is comprehensive modeling of a SAW duplexer, including electromagnetic modeling of the ceramic package. The parasitic capacitive and inductive couplings in the package are obtained using rigorous computation, allowing one to estimate the package effects on the duplexer performance.reviewe

Regional carbon price floor in EU ETS – Case studies in the Nordic and Baltic energy markets

The CO2 emission allowances price level in EU ETS has fluctuated since the implementation of the scheme. The allowance price level influences short-term fuel switch decisions and profitability of investments and due to this, the fluctuation can slow down the implementation of low-carbon solutions. To give the markets a more stable signal of the development of the CO2 price, carbon price floor (CPF) has been discussed as a potential measure to complement the ETS. The CPF could be implemented in national, regional or EU level. In this report, the impact of regional CPF implemented either on Nordic or Nordic and Baltic level is analysed concentrating on electricity and heating sector perspectives. In case of electricity markets, the analysis is based on European-wide electricity market simulation with various scenarios. The aim in the analysis is to quantify the potential effects of CPF on electricity generation, electricity flows, CO2 emissions and wholesale prices. In case of heating sector, the aim is to analyse how CPF could potentially impact on the replacement of fossil fuels both in the short- and long-term. In the electricity sector, it could be argued that CPF would have only minor cost impacts in the Nordic region due to production mix being to large extent already mostly based on CO2-free technologies. On the other hand, due to the same fact, the impact of CPF on the electricity generation is likely to be less relevant as in many other regions, for example in Central Europe. Based on the analysis, Nordic CPF could under certain market conditions result in decrease in electricity production with fossil fuels and peat, with only a small impact on average wholesale prices. However, the electricity generation in the Nordics would slightly decrease, being replaced with generation in other market areas. In the heating sector, the implementation of CPF could also decrease the use of fossil fuels and peat, being replaced by biomass. However, the utilisation of fossil fuels could be expected to decrease with current market conditions and the potential achievable benefits could be further limited by technical constraints in production units

Properties of Nanocrystalline Silicon Probed by Optomechanics

Nanocrystalline materials exhibit properties that can differ substantially from those of their single crystal counterparts. As such, they provide ways to enhance and optimize their functionality for devices and applications. Here, we report on the optical, mechanical and thermal properties of nanocrystalline silicon probed by means of optomechanical nanobeams to extract information of the dynamics of optical absorption, mechanical losses, heat generation and dissipation. The optomechanical nanobeams are fabricated using nanocrystalline films prepared by annealing amorphous silicon layers at different temperatures. The resulting crystallite sizes and the stress in the films can be controlled by the annealing temperature and time and, consequently, the properties of the films can be tuned relatively freely, as demonstrated here by means of electron microscopy and Raman scattering. We show that the nanocrystallite size and the volume fraction of the grain boundaries play a key role in the dissipation rates through nonlinear optical and thermal processes. Promising optical (13,000) and mechanical (1700) quality factors were found in the optomechanical cavity realized in the nanocrystalline Si resulting from annealing at 950°C. The enhanced absorption and recombination rates via the intragap states and the reduced thermal conductivity boost the potential to exploit these nonlinear effects in applications including Nanoelectromechanical systems (NEMS), phonon lasing and chaos-based devices