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.
Remotely-Piloted Helicopter Citrus Yield Map Estimation
A remotely-piloted Gas Xcell mini-helicopter with GPS, wireless Ethernet, and a machinevision system was flown over orange trees to take overhead images. The individual tree images were processed to estimate the number of orange pixels in the images. The fruit yield of individualtrees at harvest a month later had an r-squared value of 0.373 with the number of orange pixels onthe irrigated tree images. While it was demonstrated that a remotely-piloted mini-helicopter could beused to acquire useful overhead images of citrus trees, substantial further research is needed toimprove the accuracy of estimates of individual tree yields or health.