Basic Studies of Electrically Controlled Elasticity of Lead Zirconate Titanate (PZT) Ceramic and its Application to Intercepting Elastic Waves
We studied a novel technique for controlling the elastic coefficient of a piezoelectric lead zirconate titanate (PZT) ceramic by connecting a negative-capacitance circuit that behaves as a "negative capacitor". Thus, we can realize control through a mechanism in which PZT is softened and hardened. On the basis of this technology, we developed a simple experimental system for intercepting elastic waves in the frequency range from 8 kHz to 110 kHz. We determined the attenuation factor in transmission loss of the experimental system, which was more than 10 dB in this frequency range. The maximum attenuation factor in transmission loss was about 60 dB at a frequency of 91 kHz.
Sound isolation by piezoelectric polymer films connected with negative capacitance circuits
Sound pressure produces strain and polarization in piezoelectric polymer films. The electric charge induced by the polarization in the electrode of the films is introduced to a negative capacitance circuit and the resulting voltage is fed back to the electrode. The field-induced strain cancels the stress-induced strain, leading to the increase of the elastic coefficient of the films. If the capacitance of the circuit is controlled to be equal to that of the film, the elastic coefficient approaches infinity. Using this principle, the sound isolation by piezoelectric polymer films connected with a negative capacitance circuit was undertaken. A PVDF film with a curved plane was located in the middle of an acoustic tube and the transmission loss through the film was determined in the audio frequency range. At any single frequency, the complete isolation of sound was achieved by adjusting the feedback. The precise matching of complex capacitance of the circuit with that of the film was required to obtain the increase of the transmission loss over a broad frequency range.
Frequency distributions of the mixing height over an urban area from SODAR data
The height of the mixing-layer (MLH) is an important parameter in the assessment of the dilution of primarily emitted or secondarily formed air pollutants in the atmospheric boundary-layer. A continuous measurement of MLH is possible only by remote sensing. Here, 17 months of SODAR data have been analysed automatically to derive the MLH over the city of Hannover in Northern Germany. In contrast to earlier studies the MLH has been determined from vertical profiles of the acoustic backscatter intensity and from the variance of the vertical velocity component. The results are presented in form of monthly frequency distributions and mean daily courses of MLH. These statistical evaluations of MLH show a clear annual course and interannual variability. The study shows the possibility to derive meaningful climatological information from long-term SODAR measurements for air quality issues.