Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-13
2002-12-03
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06489706
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to ultrasound array transducers and methods for making such transducers. In particular, large transducers or transducers with large footprints are discussed below.
Transducers for medical ultrasound include a plurality of layers, such as an acoustic backing material layer, electrode layers, a layer of piezomaterial, an acoustic matching layer or layers, and a lens. The size of the largest manufacturable transducer is typically limited by the piezomaterial that is commercially available. The piezomaterial, such as polycrystalline PZT, is pressed and sintered or otherwise formed into a billet. The billet is sliced, and each slice is ground to a final thickness. The size of the ground slices is restricted by the fragility characteristics of piezomaterial as well as by the billet itself. As the slice size increases, the fragility characteristics lead to more manufacturing yield loss due to cracking and even destruction during use.
To prevent destruction of piezomaterial from handling and manufacturing, the ground slice of piezomaterial may be subjected to a compositing process. As disclosed in U.S. Pat. No. 4,412,148 to Klicker et al., the piezomaterial therein is formed or diced into isolated strips or posts, and the intervening gaps are filled with a polymer. The composited piezomaterial forms a flexible mat from the otherwise rigid billet or slice. However, the size of a composited piezomaterial is still limited by the size of the piezomaterial billet.
Other types of piezomaterials, such as monocrystalline PZT or PZN, often require further restriction of the size of the piezomaterial layer or slice. Monocrystalline PZT provides improved bandwidth for harmonic performance, but monocrystalline piezomaterials are made at present in single crystal billets of a much smaller size than pressed and sintered polycrystalline PZT powder (e.g. a maximum of ~1 cm×1 cm). Furthermore, monocrystalline piezomaterials are more prone to fracture during manufacture and use than polycrystalline materials. While compositing and other manufacturing processes, such as sintering, may result in more durable monocrystalline piezomaterials, the maximum available crystal size is still limited.
The piezomaterials discussed above are used to create an array of piezoelements for medical ultrasound image. Another use of piezomaterials is for non-destructive testing (NDT). It is known to create a crude mosaic of piezomaterials on a non-attenuative block, such as a metallic material, for allowing transmission of acoustic energy through the block into a workpiece under inspection. The block is placed against the material to be tested. Acoustic waves are generated by the piezomaterial and propagate through the nonattenuative block and into the material for testing. One prior art NDT transducer of this type has one mosaic “panel” of PZT per piezoelement and just a few elements in total. An attenuative backer is not used, but instead the sound beam is fired through the nonattenuative standoff—usually without any matching layer(s).
BRIEF SUMMARY
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a medical ultrasound transducer and a method for manufacturing the transducer.
A plurality of piezomaterial bodies, such as billets, slices or monocrystals, are merged together to form a larger piezomaterial body. For example, a 2 cm width×16 cm length footprint piezomaterial body is formed, from 8 2×2 cm subsections. The thickness, t, of the cojoined piezomaterial body is substantially less than either of the distances along first and second lateral dimensions, w and
1
, that define the footprint. t is usually chosen to be approximately ¼ wavelength of the transducers center frequency and may typically be on the order of 1 mm or a fraction thereof. Preferably, each piezomaterial body or subsection has a panel shape, and a plurality of such panels may be merged to form a large multi-panel such as the 2×16 cm multipanel of 8 2×2 cm subsections.
Since the cost of laterally small bodies of piezomaterial is less per unit area, a large piezomaterial body may be constructed for a lesser cost by merging a plurality of small panels. The panels are merged prior to or during manufacture and lamination of the transducer.
In one aspect, a plurality of panels are merged to form a whole-breast transducer. In this embodiment, each panel comprises a polycrystalline piezomaterial body. Monocrystalline panels or paneling of polycrystals having differing frequency constants may also be employed in order to improve acoustic harmonic performance or for other reasons.
In one embodiment, two piezomaterial bodies are placed adjacent each other along lateral edges. The resulting larger piezomaterial body has the same thickness as the two individual piezomaterial bodies but a larger footprint area than either of the two piezomaterial bodies.
In another embodiment, a medical ultrasound transducer includes a backing block and at least one matching layer. A multi-panel of piezomaterial comprises at least first and second abutted panels. The multi-panel also includes a backing material side and a matching layer side. The backing material side comprises first and second abutted panel sides of the first and second panels, respectively. The matching layer side comprises third and fourth abutted panel sides of the first and second panels, respectively.
In yet another embodiment, a medical ultrasound transducer is made by providing at least first and second panels of piezomaterial. The two panels are abutted to form an elongated multi-panel. The elongated multi-panel is stacked with at least the backing material and a matching layer.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.
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Edmiston Rick L.
Hossack John A.
Marian, Jr. Vaughn R.
Mohr, III John P.
Sliwa, Jr. John W.
Acuson Corporation
Brinks Hofer Gilson & Lione
Dougherty Thomas M.
Medley Peter
Summerfield Craig
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