Laser-interferometric analysis of surface acoustic wave resonators

The research work described in this Thesis concentrates on studying surface acoustic wave (SAW) resonators, in particular resonators which utilize the leaky surface acoustic wave (LSAW) mode. Such resonators constitute building blocks for radio-frequency SAW bandpass filters, which are widely employed in modern cordless and cellular telecommunication systems. The number of radio frequency SAW filters produced presently exceeds 3 billion per year. The work is carried out with an optical Michelson laser interferometer developed at the Materials Physics Laboratory specifically for the purpose of studying SAW components. In the course of this work the interferometer was equipped with a high-speed photodetector and state-of-the-art detection electronics, enabling the measurement of surface vibrations at frequencies as high as 2 GHz with amplitudes on the order of a few picometers. Furthermore, the setup was equipped with high-precision motorized scanning stages and computer control in order to facilitate automatically performed two-dimensional scans with a large number of scanning points and measuring speeds up to 50 000 points per hour. The optical setup features a spatial resolution better than one micrometer, enabling measurement of surface waves with wavelengths down to 2 micrometers. The interferometer can be used for analysis of surface acoustic wave devices as well as for thin-film bulk acoustic wave resonators and radio-frequency microelectromechanical systems (RF-MEMS). Laser-interferometric measurements were performed on LSAW resonators and filters on rotated Y-cut lithium tantalate (LiTaO3). As a result, an unexpected acoustic field distribution was observed. Further measurements and simulations showed that the observed field distributions resulted from LSAWs escaping outside the resonator into the busbars. This acoustic loss mechanism can significantly degrade the performance of an LSAW filter. The obtained results have been acknowledged by SAW filter manufacturers in Japan and in Europe. In addition, measurements of bulk acoustic wave (BAW) radiation from LSAW resonators were carried out. Such radiation is inherent for LSAW resonators. Theoretical models and numerical simulations characterizing the phenomenon exist but very few direct measurements have been reported. Here, direct measurement results of BAW radiation fields generated by an LSAW resonator on LiTaO3 are reported revealing both fast shear and slow shear bulk waves. Furthermore, two coupling mechanisms, backscattering and direct excitation, were identified. Such information can be used in the development of more accurate simulation models.reviewe

Joint Polish–Finnish sampling of surface waters around the phosphogypsum waste stacks in Gdańsk and Police from 1 to 3 July 2013 – Results of the expedition

The report describes the results of the joint Polish–Finnish sampling expedition aimed at estimating the possible effects of the two Polish phosphogypsum stacks located in Wislinka (Gdańsk) and Police on the loading of the Baltic Sea and the nearby watercourses. The joint expedition was based on the agreement between the Polish and Finnish Ministers of the Environment in June 2013. The results indicate a clear effect of the phosphogypsum stack on phosphate and total phosphorus concentrations in the Martwa Wisla. The physical nature of the basin with no permanent flow into the sea weakens mixing and dilution and may cause a local enrichment of pollutants from external sources, compared with a normal river having a constant water flow into the sea. Our suggestion is that a comprehensive study should be carried out in the stack area of Wislinka, as well as in the Martwa Wisla and its catchment area, to be able to calculate water and phosphorus mass balances in the area, and the magnitude of inputs of phosphorus to the Baltic Sea caused by the stack. The role of sediments as sinks and sources of phosphorus and other pollutants in the Martwa Wisla should be studied as well. In Police the effects of the phosphogypsum stack were less obvious. This could be expected as a result of effective mixing and dilution due to the high flow in the Oder River. Additionally, measures have been implemented to prevent leakage, by means of a hydraulic barrier and by collecting runoff water and directing it to the local wastewater treatment plant (WWTP). However, the results of the present expedition and also the results of the local monitoring programme from 2008 to 2012 indicate that the effects of the phosphogypsum stack on the quality of the recipient water cannot be ruled out. In order to estimate possible leakages in Police we suggest that an intensive monitoring programme for both groundwater and surface waters would be initiated. The sampling frequency for monitoring the leakage from the phosphogypsum stack should be increased to at least 12 annual samples at both the upstream and downstream stations. In addition, the water flow of the Oder between the stack and the nearby island should be continuously monitored. This would enable a reliable estimation of the potential phosphorus load into the Baltic Sea caused by the stack

Auroral imaging with combined Suomi 100 nanosatellite and ground-based observations: A case study

Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground-based and, nowadays more and more, also by space-based measurements. Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on Dec. 3, 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground-based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a cubesat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modelling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground-based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modelling demonstrate how even a small 1-Unit (size: 10 cm x 10 cm x 10 cm) CubeSat and its camera, build using cheap commercial off-the-shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground-based observations.Comment: Accepted manuscript 34 pages, 17 figure

Radar—CubeSat Transionospheric HF Propagation Observations: Suomi 100 Satellite and EISCAT HF Facility

Radio waves provide a useful diagnostic tool to investigate the properties of the ionosphere because the ionosphere affects the transmission and properties of high frequency (HF) electromagnetic waves. We have conducted a transionospheric HF-propagation research campaign with a nanosatellite on a low-Earth polar orbit and the EISCAT HF transmitter facility in Tromsø, Norway, in December 2020. In the active measurement, the EISCAT HF facility transmitted sinusoidal 7.953 MHz signal which was received with the High frEquency rAdio spectRomEteR (HEARER) onboard 1 Unit (size: 10 × 10 × 10 cm) Suomi 100 space weather nanosatellite. Data analysis showed that the EISCAT HF signal was detected with the satellite's radio spectrometer when the satellite was the closest to the heater along its orbit. Part of the observed variations seen in the signal was identified to be related to the heater's antenna pattern and to the transmitted pulse shapes. Other observed variations can be related to the spatial and temporal variations of the ionosphere and its different responses to the used transmission frequencies and to the transmitted O- and X-wave modes. Some trends in the observed signal may also be associated to changes in the properties of ionospheric plasma resulting from the heater's electromagnetic wave energy. This paper is, to authors' best knowledge, the first observation of this kind of “self-absorption” measured from the transionospheric signal path from a powerful radio source on the ground to the satellite-borne receiver

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