11 April 2007 The influence of the radius of the electrodes employed in Coulomb excitation of acoustic waves in piezoelectric materials
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Abstract
Coulomb excitation and detection of ultrasonic waves in piezoelectric crystals by spherical electrical probes is discussed in view of the opening angle of the cone of longitudinal waves coupling to such a probe. The electric field distribution in the piezoelectric crystal under the probe is modeled by means of finite elements in order to determine the effective size of the probe normalized to the sphere radius. The dynamic impedance of the probe is estimated, and it is shown that a probe of a size appropriate to illuminate or detect from the piezoelectric half space has a frequency-independent impedance of about 3 k&OHgr; under idealizing assumptions. Measurements of the directionality of ultrasound emission and detection at a frequency of about 100 MHz are presented for three probes with different tip radii, varying from about 30 &mgr;m to 2.5 mm. As expected, larger probes yield a higher directionality. A relatively large forward contribution is observed even for small spheres.
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Anowarul Habib, Evgeny Twerdowski, Moritz von Buttlar, Reinhold Wannemacher, Wolfgang Grill, "The influence of the radius of the electrodes employed in Coulomb excitation of acoustic waves in piezoelectric materials", Proc. SPIE 6532, Health Monitoring of Structural and Biological Systems 2007, 653214 (11 April 2007); doi: 10.1117/12.715716; https://doi.org/10.1117/12.715716
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KEYWORDS
Crystals

Optical spheres

Acoustics

Ultrasonography

Dielectrics

Gold

Wave propagation

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