Allen H. Meitzler

Mode Coupling Occurring in the Propagation of Elastic Pulses in Wires

The propagation of elastic pulses in wires of circular cross section has been studied for conditions in which pulses having carrier frequencies ranging from 0.5 to 4.0 Mc were transmitted in wires having diameters between 0.1 and 0.2 cm. The pulses used in the experiments were shaped to have relatively narrow frequency spectra. At certain frequencies, herein called critical frequencies, pulses propagating in certain modes were observed to undergo pronounced distortion in which the peak amplitude of an affected pulse was reduced and the duration of the pulse was increased many times its original length. This pulse distortion associated with the presence of critical frequencies is shown to be caused by coupling between two modes of propagation. In agreement with predictions of the general theory of mode coupling, the critical frequencies are frequencies at which two modes of propagation have the same phase velocity.

Structural transformations occasioned by crystallographic shear in PLZT and TiO2 ceramics

Fine-grained PLZT and TiO2 ceramics subjected to applied electric fields can, depending upon composition and temperature, undergo disorder-order structural transformations that carry the materials from non-polar to polar structures. This paper proposes that the observed transformations are the result of crystallographic shear processes that depend upon the presence of ordered, planar defect structures in the materials.

Ultrasonic wave interferometers

An acoustic or ultrasonic device includes two ultrasonic energy transmission paths having substantially identical transmission characteristics for a neutral condition of the device. One or both of the transmission paths include path altering structure(s) or coating(s) for changing the transmission characteristics of one or both of the paths in response to a physical phenomenon to be sensed or monitored. The paths have input transducers coupled thereto for transmitting ultrasonic energy into the paths. The input transducers are driven by a single oscillator such that the ultrasonic energy waves generated in the two paths are substantially identical to one another. A drive adjusting circuit compensates for any differences between the two paths and/or the ultrasonic waves in the two paths. An output transducer is coupled to the two paths for receiving ultrasonic waves from the paths and generating an output signal which is the result of combining the acoustic or ultrasonic waves from the two paths. By combining the waves from the two paths, the output signal is effectively the interference pattern generated by the waves in the two paths and hence the device operates as an acoustic or ultrasonic energy interferometer to sense or monitor physical phenomena to which the path altering structure(s) or coating(s) respond.

Ultrasonic Delay Lines for Digital Data Storage

This paper describes the design features and performance characteristics of a delay line design which is specifically intended for digital data applications. The design consists basically of a delay medium in the form of a long, thin strip with piezoelectric ceramic, thickness‐shear mode transducers bonded to the end faces. The strip acts as an elastic waveguide in which the energy contained in an input elastic pulse is propagated by a number of modes with varying amounts of dispersion. By the proper use of absorbing material along the edges of the strip, it is possible to suppress selectively the more dispersive modes and thereby reduce the width of the output pulse to the extent that megacycle bit rates may by used even in lines with delays of the order of 10 msec. Since the medium acts as a waveguide, long delays may be obtained at relatively low loss. In a typical design, to be described in detail, the line has a delay of 4.3 msec, an insertion loss of 34 db, and a maximum bit rate (on a nonreturn‐to‐...

Selective Attenuation of Elastic Wave Motions in Strips of Polycrystalline Metals

Longitudinal and flexural waves in an infinite plate of an isotropic elastic material can be analytically synthesized from a single dilatational potential function and a single rotational potential function. If A is the amplitude of the former and B is the amplitude of the latter, it is possible to calculate the ratio A/B for a particular mode as a function of frequency once the values of the roots of the appropriate frequency equation are at hand. Calculations of this kind have been carried out for the lowest three longitudinal and lowest three flexural modes and show that, in general, these modes are composite wave motions involving varying combinations of dilatational and rotational components such that A/B varies in amplitude and phase in a given mode as a function of frequency. The primary purpose of this paper is to introduce the “character” of the various modes, defined as [(A/B)(A/B)*], as a concept useful in understanding the selective attenuation of high‐frequency elastic modes in polycrystallin...

Unusual microstructures in TiO2 ceramic pellets with asymmetrical electrical conductivity

Ceramic pellets of TiO2 (rutile), with embedded Pt wire electrodes, have been heat treated in a manner that changed the normal electrical properties of rutile at room temperature from those of an insulator to those of a semiconductor with rectifying characteristics. This change in electrical properties was accompanied by the development of unusual microstructures in the rutile grains which were analyzed by a combination of techniques including transmission electron microscopy and scanning transmission electron microscopy. These analyses indicated that, under the applied conditions of heat treatment, Pt diffused into the rutile and reacted initially with the TiO2 at oxygen vacancy sites to form point‐defect agglomerates and that these point defects blocked the normal formation of crystallographic shear planes. As the process proceeded by continued Pt diffusion, thin planar precipitates of PtTi3 were formed in epitaxial relation to the surrounding rutile matrix.

Electrical rectification caused by lamellar microstructures in platinum‐doped TiO2−x ceramics

A heat treatment combining cyclic oxidation/reduction with an applied electric field is described that enhances the diffusion of Pt into TiO2−x ceramics and causes a reaction product of PtTi3 to be formed. The PtTi3 forms as lamellar microstructures within the TiO2−x rutile grains. The ceramics produced by this heat treatment have markedly altered electrical properties showing room‐temperature conductivities increased several orders of magnitude and asymmetrical conductivity (rectification) characteristics.

Determination of Elastic Constants of Isotropic Materials at Megacycle Frequencies

The frequency dependence of the phase and group velocities for longitudinal and flexural waves in a plate provides the basis for several convenient methods of determining elastic constants. In these methods two independent elastic constants are determined in strip‐shaped samples from measured values of certain special frequencies and delay times. One set of data is determined by the frequencies at which certain pairs of modes have either equal group or phase velocities. At other frequencies the delay vs frequency characteristics of various modes have extrema, and the frequencies at which these occur along with the measured delays provide another set of data. Theoretical calculations have been carried out which show the dependence of these measured quantities on Poissons ratio. The shear wave velocity and Poissons ratio are determined for a sample behaving essentially as an isotropic, elastic solid by selecting values that bring calculated and measured quantities into agreement. The methods to be discuss...

Acoustic wave transmission media using silicon plates with micromachined cavities

The author describes the application of micromachining techniques to form two types of cavities useful in silicon acoustic wave oscillators for sensor applications. Under the design conditions described, it is possible in one processing operation to form two kinds of rectangular cavities in the interior of a silicon die: (1) cavities with long perpendicular walls that are suitable for acting as reflecting surfaces for an ultrasonic beam, and (2) cavities with long sloping walls that are suitable for acting as boundary surfaces, confining the divergent lobes of an ultrasonic beam and dissipating unwanted wave energy by a combination of mode conversion and absorption. By combining these two types of cavities with transducers directing an acoustic beam in <110> directions, it is possible to form an acoustic wave oscillator with a relatively long, multisegment propagation path.<<ETX>>

Polar behavior of the platinum/zirconia interface

Abstract Oxygen sensors using yttria-doped zirconia in combination with platinum electrodes can store relatively large amounts of charge if cooled from high temperatures with a potential difference of 1.0 V applied to the terminals. On reheating the sensors, peak discharge currents are obtained at 350°C.