Metal working – Piezoelectric device making
Reexamination Certificate
1999-08-12
2002-09-17
Vo, Peter (Department: 3729)
Metal working
Piezoelectric device making
C029S852000, C029S830000, C439S067000, C439S077000
Reexamination Certificate
active
06449821
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a design and the method of constructing ultrasonic transducers and, in particular, a design and method for interconnecting elements in multiple elevation transducers.
BACKGROUND OF THE INVENTION
Ultrasonic transducers are used in many medical applications and, in particular, for the non-invasive acquisition of images of organs and conditions within a patient, typical examples being the ultrasound imaging of fetuses and the heart. The ultrasonic transducers used in such applications are generally hand held, and must meet stringent dimensional constraints in order to acquire the desired images. For example, it is frequently necessary that the transducer be able to obtain high resolution images of significant portions of a patient's chest cavity through the gap between two ribs when used for cardiac diagnostic purposes, thereby severely limiting the physical dimensions of the transducer.
As a consequence, and because of the relatively small aperture between human ribs and similar constraints upon transducer positioning when attempting to gain images of other parts of the human body, there has been significant development of linear or phased array transducers comprising multiple transmitting and receiving elements, with the associated electronics and switching circuits, to provide relatively narrowly focused and “steerable” transmitting and receiving “beams”. The most common of such transducers comprises a one element wide by multiple element long linear array of transmitting and receiving elements arranged in line along a flat plane or, preferably, along a concave or convex arc, thereby providing a greater scanning arc.
The transmitting and receiving beams of such transducers are formed and steered by selecting individual transducers elements or groups of transducer elements to transmit or receive ultrasonic energy, wherein each such individual transducer element or group of transducers elements forms an “aperture” of the transducer array. Such an array is thereby formed of a single row of apertures extending along the face of the array and such transducers are consequently referred to as “single aperture” transducers.
While such azimuth scanning single aperture arrays are advantageous for many applications, single aperture transducers have the disadvantage that they can scan only along the single plane of the transducer elements. As a consequence, there have been many attempts to construct transducers that are also capable of steering or focusing in elevation as well as azimuth, that is, along the axis at right angles to the azimuth plane along which the elements are arrayed as well as along the azimuth plane.
As is well understood, the formation and steering and/or focusing of the transmitting and receiving beams of a transducer are controlled by selection and use of the various separate physical divisions or areas of transducer material comprising the transducer array, which, as described above, are referred to as “apertures”. In contrast to “single aperture” transducers, however, in which each aperture is formed by an element or group of elements extending across the face of the array as a single unitary area or division or the array, each corresponding element in a transducer capable of scanning in elevation is divided into multiple sub-elements, or segments. For this reason, and because each element position along such an array can form multiple apertures, that is, using different combinations of the sub-elements or segments of each of the transducer elements, such transducers are consequently referred to as “multiple aperture” transducers.
The shape, focus and direction of the transmitting and receiving beams of a multiple aperture transducer are again controlled by selection of the apertures of the array. In a multiple aperture array, however, each aperture is formed by one or more of the sub-elements, or segments, of the transducer elements, so that the apertures of a multiple aperture array can be used to steer and focus the transducer scan beam along the elevation axis as well as along the azimuth axis and can define multiple azimuthal scan planes, each being at a different angle of elevation.
It should be noted that in both single aperture transducers and in multiple aperture transducers the apertures may be either driven actively, or simply de-activated to reduce the size of the acoustic aperture, thereby controlling the shape, direction and focus of the transmitting and receiving beams formed by the transducer array.
The transducer elements of both single aperture and multiple aperture transducers are generally made of a piezoelectric material and the array of elements or sub-elements is generally mounted onto a body made of a backing material. Connections between the individual transducer elements and the associated electronics and switching elements are usually provided through various arrangements and combinations of thick and thin film circuits, flexible printed circuits and wires, which are generally located on the back of the array, between the array and the body, with leads running along the body to the transducer electronics. One or more layers of impedance matching material, generally considered to be a part of the elements themselves, is often superimposed upon the transducer elements to match the acoustic impedance of the transducer to the body or material being scanned, and a lens comprised of a suitable material may be additionally superimposed upon the impedance matching material to shape or focus the beams generated by the transducer elements. In some implementations, the impedance matching layers may have suitable acoustic characteristics and may be shaped to operate as an acoustic lens.
Single aperture transducers are generally constructed from a single piece of transducer material having a width equal to the length of one element and a length equal to the widths of the total number of elements plus spaces between the elements. One or more thin or thick film circuits or flexible printed circuits having connections and paths for the individual elements, or the like implemented in any of several other ways, are bonded to one side of the piece of transducer material and a layer or layers of matching material may be bonded to the radiating and receiving side of the transducer material to form a “stack” of the transducer material, circuits and matching layers. A temporary or permanent layer of backing material of some form, such as a flexible material, may also be bonded to the back of the stack to aid in handling the stack during manufacture.
Successive cuts are then made across the width of the transducer stack on the radiating/receiving side of the stack and at intervals corresponding to the widths of the elements and the spacing between the elements to divide the single piece of material into the individual elements. This operation is generally referred to as “dicing” and is usually done with a device referred to as a dicing saw, but may be done with other techniques, such as lasers. These cuts may extend only through the transducer and matching material layers, or partly or completely through the circuit layer, or through the circuit layer and at least a part of any backing layers, depending upon the detailed design and implementation of the circuit layers.
The assembly of individual transducer elements with the circuit and matching layers are then bonded to the backing body, which may have a flat, concave or convex face, as described above, with any temporary backing layers being removed as necessary. It should be noted that in certain instances the dicing may be done after the assembly of transducer elements, matching materials, and circuits is bonded to the backing material and that the dicing cuts may extend into the layers of backing material or even into the backing body.
Connections between the thin or thick film circuits connecting to the transducer elements and wires or printed circuits, such as flexible circuits, which in turn connect to the electronics and switching elements ma
Gurrie Francis E.
Sudol Wojtek
Koninklijke Philips Electronics , N.V.
Tugbang A. Dexter
Vo Peter
Vodopia John
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