Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1994-08-22
1996-01-02
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310327, H01L 4108
Patent
active
054811538
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the non-destructive testing of materials, and in particular of materials such as concrete which are essentially non-homogeneous and which, at conventional ultrasound frequencies, would produce such a high degree of scattering that commonly used ultrasound techniques are not suitable.
2. Related Art
Ultrasound frequencies used in non-destructive testing of materials and in medical investigations are commonly greater than 1 MHz, whereas in highly scattering media only relatively low frequencies, below 1 MHz in any event and, in the case of concrete for example, preferably below 500 KHz, can be used. At these lower frequencies plane wave transducers would need to be unreasonably large and, moreover, when detecting incoherent waves produced in scattering media would be subject to phase cancellation effects. Hence new techniques and devices are required which are suitable for use in connection with scattering media; and it is an object of the present invention to provide an effectively point-source transmit/receive transducer suitable for such applications and, preferably, capable of wideband operation and suitable for short pulse or chirp operation, at low-ultrasound frequencies.
SUMMARY OF THE INVENTION
According to the invention there is provided an acoustic probe comprising a piezoelectric ceramic transducer element adapted to emit ultrasonic signals in a first direction and in a second direction opposite to the first, and mountable on a sample to be tested so as to transmit thereto signals emitted in the said first direction, wherein the probe also includes a rod-shaped acoustic waveguide having one end coupled to the transducer element to receive signals emitted by the transducer element in the said second direction and to transmit them along the waveguide, lossy cladding material acoustically coupled to the surface of the waveguide at least at a part thereof remote from its one end, and coupling means surrounding and mechanically secured and acoustically coupled to the ceramic element and the one end of the waveguide, the coupling means having a surface adapted to be secured to the sample to be tested and to transmit thereto signals emitted by the transducer element.
In preferred embodiments of the invention, in which the transducer element has the shape of a circular disc and the rod-shaped waveguide is also of circular cross-section and is arranged co-axial with the transducer element, the diameter of the waveguide is in the range 50% to 10% greater than that of the transducer element.
Preferably, also, the transducer element is partially set into a recess in the one end of the waveguide and partially projects therefrom, and the coupling means is a collar which surrounds and is mechanically secured and acoustically coupled to the one end of the waveguide and the part of the transducer element which projects therefrom.
In certain embodiments of the invention, the coupling means and the lossy cladding material together cover the whole of the exterior surface of the waveguide. In other embodiments, part of the length of the waveguide is free of cladding and a second transducer element is provided within the waveguide or spaced ring-shaped piezoelectric transducers are provided surrounding and acoustically coupled to that part of the waveguide.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described and explained more fully with reference to the accompanying drawings in which:
FIG. 1 is a diagrammatic longitudinal sectional view of a first embodiment of an acoustic waveguide probe according to the invention, secured in position on a surface of a sample under test;
FIG. 2 is a perspective view, on a larger scale, of a piezoelectric ceramic transducer element comprised by the probe shown in FIG. 1;
FIG. 3 is a scrap sectional view, also on a larger scale, showing the mounting of the transducer element in relation to an acoustic waveguide comprised by the probe shown in FIG. 1;
FIG. 4 shows acoustic velocity and disper
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Journal of the Acoustic Society of America, vol. 71, No. 5, May 1982, New York, USA, pp. 1163-1168 Thomas Proctor, Jr. "The improved Piezoelectric Acoustic Emission Transducer" see the whole document.
British Technology Group Ltd.
Budd Mark O.
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