P.G. Kornreich

The metallization of silicone polymers in the rubbery and the glassy state

The vacuum deposition of metals onto poly (dimethylsiloxane) (PDMS) gels was studied as a function of the crosslink density and the polymer substrate temperature during the deposition. Reflectance and conductance measurements were used to characterize the quality of the resulting metal films. Variations in the measurements were found to depend on the substrate temperature during metallization and on the particular metal used. For most cases, the variations of conductance and reflectance can be accounted for by cracks in the metal film and the coarseness of the surface texture.

DEFT: Direct electronic Fourier transforms of optical images

A family of novel devices for electronic imaging is described and several different realizations age presented. Direct electronic Fourier transform (DEFT) cameras employ coupling between surface strain waves, the image intensity, and electrical charge to produce electronic signals representing the spatial Fourier transform of the image at a single pair of terminals. This signal can be easily processed to accomplish pattern recognition, all-electronic image magnification (zoom) and stabilization, motion detection, and focusing. Reproduction of the image is expected to be accomplished by a light valve employing strain-induced modulation of uniform light. Experimental results for light intensity variation in one dimension are reviewed for a silicon chip bulk acoustic wave camera and for a CdS surface wave camera. Some preliminary results are also reported for a fused quartz elastobirefringent light valve image reconstruction device.

A direct electronic Fourier transform device for imaging

A novel device employing elastophotoconductivity in CdS to create electronic signals representing the spatial Fourier transform of an image is described.

The Molecular and Macroscopic Anisotropy of PVF2

The elastic and loss constants of PVF2 films have previously been characterized by ultrasonic measurements according to 2mm symmetry. However, these films are semicrystalline with the crystalline content having three polymorphs, the a, B, and y phases. Measurements of the orientation distribution function for these phases were taken by infrared dichroism . The absorption bands indicate that the crystalline phases are not oriented along the preferred directions of the film as is normally assumed for ultrasonics applications. The anisotropy found by IR at the molecular level is compared with the macroscopic elastic anisotropy as found by acoustic measurements. The results reveal the correct macroscopic symmetry and are indicative of the sensitivity of the ultrasonic measurements to the crystalline phase anisotropy of the PVF2 film.

Experimental image alignment system

A microcomputer-based instrument forlimage alignment with respect to a reference image is described which uses the DEFT sensor (Direct Electronic Fourier Transform) for image sensing and preprocessing. The instrument alignment algorithm which uses the two-dimensional Fourier transform as input is also described. It generates signals used to steer the stage carrying the test image into the correct orientation. This algorithm has computational advantages over algorithms which use image intensity data as input and is suitable for a microcomputer-based instrument since the two-dimensional Fourier transform is provided by the DEFT sensor.

Spurious acoustic modes in two-dimensional Fourier transform devices

Experiments conducted on two-dimensional (2D) Fourier transform sensors using CdS films on z-cut LiNb03 show evidence for the presence of more than one acoustic velocity in the substrate. Pulsed experiments conducted with two transducers and detailed measurements of transducer frequency response confirm the presence of these additional modes. As a result, the Fourier transform of any image repeats itself in frequency space, the number of repetitions depending on the number of additional acoustic modes. The detrimental effects of these spurious modes can be eliminated entirely by suitable sampling of the image projected on the sensor.

Modulation of current in a thin film of lead tin selenide by bulk acoustic waves

We have measured a 0.1% modulation of electron current in a lead tin selenide film due to a bulk acoustic wave propagated in the barium fluoride substrate. This effect was observed as an ac component of the current at the acoustic frequency 0.6 MHz.

Electrodynamic instabilities in the deformation-potential interaction

This paper is concerned with several electrodynamic effects associated with the interaction of hypersonic waves with conduction electrons in crystals of n-type germanium. One aspect of this interaction involves the creation of coherent microwave current by a sound wave under the influence of a dc electric field. We study this aspect in relation to current oscillation, amplification, and traveling-wave effects with a view toward engineering applications. Electromagnetic radiation and internal transmission of energy are similarly discussed. We have constructed a model for the interaction of electron current with hypersonic waves ( w geq 10_{9} ) through shear-deformation potential coupling in moderately doped n-type germanium subject to a dc electric field. From a Boltzmann equation treatment of the charge transport, and a continuous-system Lagrange equation for the sound field, we obtained the dispersion relation. By means of the Bers-Briggs criteria, we found a convective instability (spatial growth) for 10_{10} for supersonic drift. Since no absolute instability (spontaneous oscillation) was detected, this interaction can provide stable amplification of ac electron current and of hypersonic waves. Or, if one is an input to the crystal, the other will be generated. The gain is of order hundreds of decibels per centimeter. Solving the eigenvalue problem yielded an infinite discrete set of complex frequencies whose imaginary parts indicated growth rates of order 107dB/s, which amounts to a usable gain of order 102dB. Finally, Maxwells equations were used to estimate the electro-magnetic effects of the various electrodynamic instabilities. Sample calculations indicated current densities of order 10-1A/cm2.