EPILOGUE SCIENCE, SCIENCE! SsTd E=+tDdTεE=+StrainPermittivityMatrix for direct piezoelectric eectElectric displacementElectric ledElastic complianceStressThe Complicated and BizarreWorld of PiezoelectricityIt was due to the inuence of my pro-fessor in college that I originally became in-terested in investigating piezoelectric con-stants and ferroelectric substances, mate-rials that exhibit dielectric polarization in their natural state that can be inverted by applying an external voltage. In short, I was doing research useful in materials develop-ment. I mainly studied polyvinylidene flu-oride, a thermoplastic uoropolymer use-ful for applications that require high puri-ty, high strength, high chemical resistance, and high thermal resistance. Polyvinylidene fluoride offers superior workability com-pared to other uoroplastics. It’s also a fa-miliar resin used to make shing lines and guitar strings. The resin characteristical-ly generates a voltage in response to the strain produced when pressure is applied, a phenomenon called piezoelectricity. We also have piezoelectric ceramics, a piezo-electric material used in many fields, in-cluding cassette stoves, speakers, and un-derwater sonars. The two differ in that polyvinylidene uoride has the advantage of reversibly stretching about 10 times as much as piezoelectric ceramics. This ad-vantage allows polyvinylidene fluoride to generate electricity at levels comparable to piezoelectric ceramics.* *After all my research, I remain fasci-nated by the piezoelectric equations. The piezoelectric equations are essential for the development of various devices that use piezoelectric materials.Piezoelectricity is a complex phenome-non that involves many factors and el-ements, including anisotropy, frequen-cy characteristics, and complex compo-nents, in addition to the three compo-nents of force. I found it fascinating from the start that these equations could de-scribe materials having complex piezo-electricity. Furthermore, when considering piezo electric materials using these equa-tions, I found myself straddling both sci-ence and mathematics. I love performing the calculations while considering both as-pects. Piezoelectric calculations follow a complicated and bizarre process that in-volves first determining the components to some extent based on calculations, then deriving a certain value by performing cal-culations based on the estimated compo-nents. It gives you the impression that you are unraveling the elements one by one from the phenomena and materials, and then organizing them using the equations.* *At rst glance, the piezoelectric equa-tions appear very simple. But when you follow the process of calculation through actual experiments, you come to under-stand that extremely complex factors are involved. When I ask myself why I contin-ue to be so fascinated by the piezoelectric equations, I come to the conclusion that it’s because, quite contrary to appearanc-es, the phenomena unfolding before my eyes involve very complex events. It’s made me aware of the obligation to think deeply about everything, even when things seem simple. It’s not a life-changing realization, but I do feel the piezoelectric equations have changed the way I think about vari-ous phenomena.Linear piezoelectricity is the effect of both electrical and elastic mechanical actions. These actions are dened by mathematical formulas. S is strain, s is elastic compliance, T is stress, D is elec-tric displacement,εis permittivity, and E is electric eld. These equations give us a peek into the complex phenomenon known as piezoelectricity.Hajime IshiiS&V Sensor Development Group, Technical Development Center. Joined Rion in 2019. His current work involves sensors, main-ly for seismometers. He is also involved in developing sensors that calculate ac-celeration using piezoelectric elements.No. 006The Intersection of Science and MathematicsRion is supported by many science-loving and math-loving staff mem-bers. In this series, our science-minded staff members write about their enthusiasm for their respective elds of interest. Part 6 is about the piezoelectric equations.Because We’re Science and Math LoversColumn by Rion’s staff on their obsession with scienceInterview and article by Kana Yokota20
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