Institute of Paper Science and Technology, Inc.

Georgia Tech Research Corporation

Pierre H Brodeur

Theodore G Jackson

Maclin S Hall

Emmanuel F LaFond

Charles C Habeger, Jr

Yves H Berthelot

Joseph P Gerhardstein

Mont A Johnson

The present invention provides a system and method to reduce motion-induced noise in the detection of ultrasonic signals in a moving sheet or body of material. An ultrasonic signal is generated in a sheet of material and a detection laser beam is moved along the surface of the material. By moving the detection laser in the same direction as the direction of movement of the sheet of material the amount of noise induced in the detection of the ultrasonic signal is reduced. The scanner is moved at approximately the same speed as the moving material. The system and method may be used for many applications, such in a paper making process or steel making process. The detection laser may be directed by a scanner. The movement of the scanner is synchronized with the anticipated arrival of the ultrasonic signal under the scanner. A photodetector may be used to determine when a ultrasonic pulse has been directed to the moving sheet of material so that the scanner may be synchronized the anticipated arrival of the ultrasonic signal.

System and method of reducing motion-induced noise in the optical detection of an ultrasound signal in a moving body of material

An apparatus and method for non-contact measurement of ultrasonic waves on moving paper webs employs a photorefractive interferometer. The photorefractive interferometer employs an optical head in which the incident beam and reflected beam are coaxial, thus enabling detection of both in-plane and out-of-plane waves with a single apparatus. The incident beam and reference beams are focused into a line enabling greater power to be used without damaging the paper.

Non-contact measurements of ultrasonic waves on paper webs using a

Methods and apparatus for acoustic fiber fractionation using a plane ultrasonic wave field interacting with water suspended fibers circulating in a channel flow using acoustic radiation forces to separate fibers into two or more fractions based on fiber radius, with applications of the separation concept in the pulp and paper industry. The continuous process relies on the use of a wall-mounted, rectangular cross-section piezoelectric ceramic transducer to selectively deflect flowing fibers as they penetrate the ultrasonic field. The described embodiment uses a transducer frequency of approximately 150 kHz. Depending upon the amount of dissolved gas in water, separation is obtained using a standing or a traveling wave field.

Methods and apparatus for acoustic fiber fractionation

A non-destructive, non-contact testing apparatus and method which generally includes an ultrasonic signal generator for inducing one or more ultrasonic signals in a material and an optical interferometer that includes a laser for illuminating a section of the material and for detecting beat frequencies resulting from reflected light from the material. Deformations in the material as a result of the ultrasonic signal cause the beat frequency to be shifted as a result of the Doppler effect. Such differences in the beat frequency are detected by the system and used as an indication of a characteristic of the material.

Material characteristic testing method and apparatus using

A method for improving the accuracy of measuring the velocity and time of flight of ultrasonic signals through moving web-like materials such as paper, paperboard and the like, includes a pair of ultrasonic transducers disposed on opposing sides of a moving web-like material. In order to provide acoustical coupling between the transducers and the web-like material, the transducers are disposed in fluid-filled wheels. Errors due to variances in the wheel thicknesses about their circumference which can affect time of flight measurements and ultimately the mechanical property being tested are compensated by averaging the ultrasonic signals for a predetermined number of revolutions. The invention further includes a method for compensating for errors resulting from the digitization of the ultrasonic signals. More particularly, the invention includes a method for eliminating errors known as trigger jitter inherent with digitizing oscilloscopes used to digitize the signals for manipulation by a digital computer. In particular, rather than cross-correlate ultrasonic signals taken during different sample periods as is known in the art in order to determine the time of flight of the ultrasonic signal through the moving web, a pulse echo box is provided to enable cross-correlation of predetermined transmitted ultrasonic signals with predetermined reflected ultrasonic or echo signals during the sample period. By cross-correlating ultrasonic signals in the same sample period, the error associated with trigger jitter is eliminated.

Out-of-plane ultrasonic velocity measurement

A system for relatively accurately measuring the velocity and time of flight of ultrasonic signals in the thickness direction through moving web-like materials, such as paper, paperboard and the like, includes a pair of ultrasonic transducers disposed on opposing sides of the moving web-like material. The ultrasonic transducers are disposed in fluid-filled wheels to provide acoustical coupling between the transducers and the web-like material. In order to eliminate errors, known as trigger jitter, inherent in systems used to digitize ultrasonic signals for manipulation by a digital computer, a pulse echo box is provided to enable the capture of a reflected ultrasonic signal in addition to the ultrasonic signal transmitted through the web. By cross-correlating the transmitted and reflected ultrasonic signals in the same sample period, the error associated with trigger jitter is eliminated.

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Smyrna, GA, United States of America

Pierre H Brodeur