Effect of geometry on the characteristics of a drum actuator

This study presents a large displacement, piezoceramic and metal composite-based actuator, named drum piezoceramic-actuator. The drum actuator consists of a short, thick-walled steel cylinder sandwiched by two thin composite disks, which are fabricated from a brass disk bonded with one piezoceramic disk. The piezoceramic disk polarized in its thickness direction is of a large diameter to thickness ratio, thus, produces a large radial displacement under an applied voltage in the thickness direction, and consequently results in a large transverse deflection of the composite disks in the drum. Some original results are obtained in the drums with the geometrical changes in the short, thick-walled steel cylinder. The drum (outer diameter: 12.0 mm) demonstrates displacement output 7 times as large as that of a cymbal actuator with the same ceramic material and comparable dimensions under the same DC driving voltage of 78 V. The effective piezoelectric charge coefficient d33 of the drum is measured and is about 3 times as large as that reported for the cymbal. The drums also showed first resonance frequency of the transducer from 15.68 to 32.57 kHz and faster response time of about tens microseconds which are mainly based on the dimensions of the short, thick-walled steel cylinder

Hollow Gaussian beam generation through nonlinear interaction of photons with orbital-angular-momentum

Hollow Gaussian beams (HGB) are a special class of doughnut shaped beams that do not carry orbital angular momentum (OAM). Such beams have a wide range of applications in many fields including atomic optics, bio-photonics, atmospheric science, and plasma physics. Till date, these beams have been generated using linear optical elements. Here, we show a new way of generating HGBs by three-wave mixing in a nonlinear crystal. Based on nonlinear interaction of photons having OAM and conservation of OAM in nonlinear processes, we experimentally generated ultrafast HGBs of order as high as 6 and power >180 mW at 355 nm. This generic concept can be extended to any wavelength, timescales (continuous-wave and ultrafast) and any orders. We show that the removal of azimuthal phase of vortices does not produce Gaussian beam. We also propose a new and only method to characterize the order of the HGBs.by N. Apurv Chaitanya, M. V. Jabir, J. Banerji, G. K. Samant