Measuring and testing – Probe or probe mounting
Reexamination Certificate
1999-12-16
2001-11-06
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Probe or probe mounting
Reexamination Certificate
active
06311573
ABSTRACT:
BACKGROUND OF THE INVENTION
It is highly desirable to transmit ultrasonic energy into gases to be able to analyze the gases for their composition, flow and other properties and to conduct remote and level sensing of objects through air. It is also highly desirable to transmit ultrasonic energy into air to perform non-contact testing upon products, such as paper, wood, low acoustic impedance green ceramics and powder metals, plastics and composites as well as high acoustic impedance ceramics, metals, etc. In medical applications, it is also highly desirable to conduct non-contact diagnostics of skin and other parts of the body of humans or animals, fetus monitoring, blood flow measurements, and for non-contact and non-invasive therapeutical and surgical applications, such as for malignant skin removal, lipotirpsy, unwanted mole removal, etc. It is also highly desirable in agricultural applications, such as for plant and tree diagnostics, as well as for fruit, vegetable and seed analysis.
It is well understood that the acoustic impedance of gases is several orders of magnitude from the acoustic impedance of typical piezoelectric materials. Also, the larger the difference in acoustic impedance of two adjacent layers, the more difficult it is to transmit ultrasonic energy across the boundary between the two layers. Finally, it is known that gases rapidly absorb ultrasonic energy especially as the frequency of the ultrasound is increased.
It has been possible with a certain degree of success to transmit ultrasound into gases, such as air, by placing a low impedance material in front of the piezoelectric element. The transmission of ultrasound into gases has nevertheless been far less than desired.
It is an advantage, according to this invention, to provide a greatly improved ultrasonic transducer and method of using same which transmits ultrasonic energy into gases with much greater efficiency.
SUMMARY OF THE INVENTION
Briefly, according to this invention, there is provided an ultrasonic transducer for transmitting and receiving ultrasonic energy to and from a gaseous medium. The transducer comprises a piezoelectric element comprising a ceramic/piezoelectric material, an electrically conductive plating over the front and back sides of the piezoelectric element, a transmission layer of low acoustic impedance material adjacent the electrically conductive plating on the front side of the piezoelectric element, electrical connections for applying an exciting electrical signal to the piezoelectric element and a facing layer of fibers attached to the surface of the transmission layer. Preferably, the acoustic impedance of the transmission layer is between about 1×10
6
kg/m
2
·s and 20×10
6
kg/m
2
·s, the acoustic impedance of the piezoelectric material is between about 2×10
6
kg/m
2
·s and 50×10
6
kg/m
2
·s. According to one embodiment, the facing layer comprises a fibrous material, such as a mat, paper, felt or fabric that is bonded to the transmission layer without substantial penetration of the bonding agent into the fibrous material.
According to a preferred embodiment, the fibrous facing layer is comprised of fibers the substantial portion of which are oblique or perpendicular to the front face of the piezoelectric element.
Briefly, according to this invention, there is provided a method for transmitting sound and ultrasound through a gaseous medium into and out of a solid specimen comprising the steps of bonding a facing layer of a fibrous material to the transmission surface of a transducer for converting one form of energy to vibrations, for example, a piezoelectric transducer, without substantial penetration of the bonding agent into the fibrous material; bonding a facing layer of a fibrous material to a surface of the solid specimen without substantial penetration of the bonding agent into the fibrous material; and exciting the transducer directed at the surface of the solid specimen with the facing layer bonded thereto.
There is also provided a method for transmitting ultrasound through a gaseous medium into and through a solid specimen comprising the steps of bonding a facing layer of a fibrous material to the transmission surface of first and second transducers without substantial penetration of the bonding agent into the fibrous material; bonding a facing layer of a fibrous material to opposite surfaces of the solid specimen without substantial penetration of the bonding agent into the fibrous material; and exciting the first transducer directed at the surface of the solid specimen with the facing layer bonded thereto and detecting the ultrasound transmitted through the solid specimen with the second transducer.
REFERENCES:
patent: 4122725 (1978-10-01), Thompson
patent: 4197920 (1980-04-01), Cluzel et al.
patent: 5159838 (1992-11-01), Lynnworth
Fuller Benjamin R.
Thompson Jewel V.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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