Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1997-08-28
1999-02-09
Williams, Hezron
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
310358, 310334, 310345, 310800, G01L 100, H01L 4104, H01L 4108, H01L 4118
Patent
active
058697675
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to ultrasonic transducers, and in particular to ultrasonic transducers for use in conjunction with non-planar test specimens. In addition, the invention relates to a piezo-electric composite for use in such transducers.
DESCRIPTION OF THE PRIOR ART
Ultrasonic transducers are typically rigid devices due to the inherent physical properties of most piezo-electric materials, such as the PZT family and lead metaniobate. These ceramic materials are normally employed in the construction of piezo-electric devices owing to their high electro-mechanical coupling coefficient although they are not ideally suited for applications operating into a fluid medium or through a couplant material, due to acoustic mismatch. However, there is another family of piezo-electric materials, including the polymer polyvinylidene fluoride (PVDF), that possess the necessary properties for good electrical matching for operation in fluid based media, moreover they also offer a high degree of physical flexibility. Additionally, PVDF, due to its electrical properties, may provide high bandwith reception properties when operating into a very high input impedance receiver. However such materials are less sensitive than their piezo-electric ceramic counterparts.
In efforts to provide an improved ultrasonic transducer, ideally incorporating the favourable properties of both forms of piezo-electric materials, piezo-electric composites have been developed. Such composites consist of an array of piezo-ceramic rods embedded within a polymer matrix, manufactured using a `dice and fill` process; a sheet of ceramic is cut longitudinally and transversely to produce a plurality of square pillars which are then spaced apart and located in the polymer matrix. In such composites, the application of an electric, or pressure field causes the ceramic rods to vibrate, the surrounding polymer moving with the rods to give the appearance of a homnogeneous material. This combination of materials serves to provide reduced acoustical impedance properties when compared to pure ceramic and has increased electro-mechanical sensitivity.
Various polymer fillers have been adopted to fabricate such piezo-electric composites, and the use of flexible composites has allowed the forming of curved ultrasonic devices, which may be used to provide good coupling Of acoustic energy between the ultrasonic devices and test specimens, such as pipes, with correspondingly curved surfaces. However, efforts to provide flexible ultrasonic devices which are capable of reliable use with test specimens of a variety of curvatures have, as yet, proved unsuccessful.
It is an object of the present invention to provide a flexible ultrasonic transducer suitable for use in conjunction with non-planar test specimens.
SUMMARY OF THE INVENTION
According to the present invention there is provided a flexible ultrasonic transducer for use with test specimens of a variety of curvatures, the transducer including a flexible transmitter in the form of a piezo-electric composite comprising a combination of active piezo-ceramic elements embedded within a flexible substrate and mounted on a flexible stiffening layer, a flexible receiver array, and flexible electrodes for the transmitter and receiver.
Preferable also, the transmitter and receiver may be integral but are preferably separate, and most preferably the transmitter is located upwardly of the receiver, that is further from the face of the transducer for contact with the test specimen.
The transmitter is of a piezo-electric composite, which most preferably forms a single transmit element for good transmission sensitivity. Such piezo-electric composites comprise a combination of active piezo-ceramic elements embedded within a passive polymer phase. The elements may be of any suitable form, the dimensions tending to be a compromise between desired flexibility and ease of manufacture. The elements may be in the form of rods but preferably are in the form of platelets having a width:height aspect ratio suc
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Abstract-"Ultrasonic Probe and its Manufacture", Nakatani Chitose et al, vol. 12, No. 329, Patent No. JP63090759, Apr. 21, 1988.
Hayward Gordon
Powell David James
Moller Richard A.
University of Strathclyde
Williams Hezron
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