Dov Hazony

Ultrasonic transducer for monitoring acoustic emissions

An ultrasonic piezoelectric transducer for monitoring acoustic events in a medium is disclosed. The transducer includes an elongated body member having a blind bore therein, a piezoelectric crystal which is received in the blind bore within the body member and which contacts the bottom surface thereof, and a rod which is received in the blind bore and which firmly contacts the piezoelectric crystal compressing the crystal against the bottom of the blind bore. The tip of the elongated body member has a convex configuration forming a lens permitting the interception of acoustic events over a wide angle and the direction of same toward the piezoelectric crystal for monitoring and detection purposes.

Edge effects in short‐pulse piezoelectric transducers

The electroelastic properties of thin‐thickness‐driven piezoelectric transducers are analyzed when the passive edges are free. The principal signals are relatively short stress pulses. It will be seen that these pulses travel close to or at the speed of sound in an unbounded medium and that, like in the one‐dimensional space, circuit models, may be associated with these transducers. Special cases will be pointed out by examples.

Electromechanical modeling of distortionless piezoelectric transducers with nonuniform parameters

Ample analytical and experimental evidence shows that a nonuniformly poled piezoelectric medium may offer much advantage in transducer work. For example, ideal coupling sections may be matched between media of different impedance levels and transducers may be made with ideal pressure impulse response. However, the medium may interfere with sound transmission causing dispersion and spurious signals. These problems are avoided when the nonuniformity of the medium is controlled so as to render sound transmission distortionless. Properties of such media are studied. It is shown that it is possible to associate impedance matrices with these properties and electrical networks with these matrices.

Nonuniformly poled spherical shell piezoelectric transducers

Elastic and electric properties of the radial mode spherical shell piezoelectric transducer are studied in detail. It is shown that impedance matrices may be associated with these properties and electrical networks identified with these matrices.

Surface stress waves when the elastic constants are functions of depth

Of concern are distortionless surface stress waves propagating in a medium which may be nonuniform relative to depth. A similar problem was posed by Burke et al. [Q. Appl. Math. 183–194 (1976)] where a unidimensional electrical ladder network model, nonuniform along the principle axis, was used in the investigation. Presently, a two‐dimensional development is given based on Hooke’s law and Newton’s law leading to the well‐known Rayleigh‐waves formulation in a uniform medium. It will be seen that broadband high‐pass propagation modes exist along the principle surface. As these propagate along the surface, they are accompanied by a phase change, linear with distance, in the frequency domain, and an associated symmetry change, periodic with distance, in the time domain. Applications may be found in high‐frequency acousto‐optics, in situ ultrasonic monitoring of elongated bodies, high‐frequency SAW filters, and whenever surface acoustic waves are employed in an environment of high precision or relatively larg...

Plate volume probing in manufacturing (or, extension modes in thin plates excited by broad normal sound beams)

A thin plate is excited by a normal acoustic beam of a finite area. The beam forms a propagation channel across the plate. This propagation mode is analyzed when the driving signals are sharp pulses. But, the main emphasis is on leaks that radiate off the main channel. These contain extension modes that travel along the off‐channel axis in a coherent manner. Further, it will be seen that these may be singled out to monitor volumes of plates, walls of tubes, and inspection of welds; especially when access is restricted to a single surface. Experimental results will be presented and discussed. [Work supported by ONR and TecSonics, Inc.]

Edge‐less short‐pulse piezoelectric transducers

The behavior of a thin transducer is analyzed when the electroded section constitutes a small part of the available areas. The principal signals are relatively short stress pulses. It will be seen that these pulses may travel close to or at the speed of sound in an unbounded medium and that circuit models may be associated with these transducers. The results also apply to the analysis of elastic properties of thin plates when the aperture of the probing beam is wider than the thickness of the plate.

Ultrasonic monitoring of bearing wear insitu.

Of concern are wear measurements of surfaces of bearing seals and valves. It will be seen that these may be implemented in terms of ultrasonic transducer arrays, constructed so as to be an integral part of the wear surface, monitoring in situ the amount and rate of the material removed. The associated data are assembled and manipulated in real time allowing for computer control and prediction. Technical aspects of the device will be discussed including journal bearing oil film measurements and the displacement and orbit of the rotating shaft. [Work supported by TecSonics, Inc. of Twinsburg, Ohio, Ohio Edison, and EPRI.]

Mapping by means of nonspecular reflections

Nonspecular reflections radiate equally in all directions according to surface and not the effective aperture. Hence inclined planes or grain boundaries would make a stronger contribution to the reflected signal. A scanning ultrasonic method is demonstrated taking advantage of this effect. A single transducer is used in the scanning in conjunction with a signal processing method to cancel the specular reflections. Experimental results are given showing significantly improved resolution. [Work supported by NIH.]

Edge effects in standard shapes piezoelectric transducers—A new method for calculating elastic coefficients

An electrical network similar to the Mason model is constructed to conform with the electroelastic properties of thin isotropic piezoelectric ceramics of standard shapes under the condition of short stress pulses in this thickness mode. It will be seen that these pulses travel close to the speed of sound in an unbounded medium and that it is possible to calculate the elastic coefficients by setting the two active faces free. Specifically, both λ and μ, the Lame constants, may be calculated from one measurement.