Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-06-14
2002-05-28
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S327000
Reexamination Certificate
active
06396198
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wave transmission-reception element for use in an ultrasound probe, a method of manufacturing the element and an ultrasound probe incorporating the element to be inserted into, for example, a blood vessel for ultrasound diagnosis.
2. Description of Related Art
Ultrasound diagnosis, particularly ultrasonogram information, is essential in every field of present-day clinical medicine. For example, in examination of the interior of a blood vessel for an anomaly, such as arterial sclerosis, which is a serious disease derived from a clot resulting from accumulation of cholesterol, direct observation from inside a blood vessel can be expected to yield higher-resolution, more effective imaging than can observation from outside a blood vessel. In this case, since a blood vessel is full of blood, imaging cannot be performed by optical means. In such a case, ultrasound imaging is an effective means for visualization. In ultrasound imaging, an ultrasound probe is inserted into a blood vessel so as to enable visualization of the interior of the blood vessel for diagnosis.
In most conventional methods, an ultrasound beam is transmitted in a radial direction of a blood vessel to thereby obtain a two-dimensional image (as disclosed in, for example, U.S. Pat. Nos. 4,917,097 and 5,603,327 and Japanese Patent Application Laid-Open (kokai) No. 152800/1992). From the viewpoint of medical practice, obtaining a three-dimensional image in real time is preferred. According to a proposed method for obtaining a three-dimensional image, a plurality of piezoelectric elements are arranged in a circle at an end of a probe. One of the elements transmits spherical waves forward, and the remaining elements receive reflections of the spherical waves. The elements sequentially take turns transmitting spherical waves to thereby obtain a three-dimensional image.
In order to obtain a three-dimensional image, this method employs a probe capable of transmitting spherical waves forward. A plurality of fine elements formed from a piezoelectric material are arranged at an end of the probe in order to transmit/receive ultrasound waves.
A practically available material for such an element is a piezoelectric polymer, such as PVDF (polyvinylidene fluoride), which permits fine processing. However, from the viewpoint of sensitivity, piezoelectric ceramic, which has a higher electromechanical coupling coefficient, is preferred as material for the element. Thus, piezoelectric ceramic, such as PT (lead titanate) or PZT (lead zirconate titanate), is used as material for the element. An electrode is formed on each of the front and back faces of an annular piezoelectric ceramic piece. The annular piezoelectric ceramic piece is divided into a plurality of divisions by means of a dicing saw to thereby form a plurality of unit vibration elements, which constitute an ultrasound probe.
According to the above-mentioned method, the annular piezoelectric ceramic piece is divided into elements x serving as unit vibration elements. From the viewpoint of manufacture of elements, the method has an advantage in that a piezoelectric ceramic piece of relatively large size may be formed by a conventional method, since unit vibration elements of small size can be formed through cutting of the piezoelectric ceramic piece as mentioned above. However, as shown in
FIG. 22
, each element x has a complex shape, such as a portion of a sector. Thus, angle &thgr; of beam spread becomes small. Further, a spherical wave cannot be obtained, and a visualization range A becomes distant and narrow. Since the unit vibration elements are of a complex shape, their vibration modes become complicated, causing difficulty in signal processing. In this case, each of the piezoelectric elements may conceivably be formed into a circular shape. However, since the angle of beam spread as measured in a far sound field is reciprocal to the diameter of a sound source, in order to increase the angle of beam spread, a very fine element must be manufactured. A conventional method for manufacturing a piezoelectric ceramic piece encounters great difficulty in manufacturing a fine element applicable to ultrasound diagnosis effected from inside a blood vessel.
An object of the present invention is to provide a wave transmission-reception element for use in an ultrasound probe capable of solving the above problems, a method for manufacturing the wave transmission-reception element, and a probe incorporating the wave transmission-reception element.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a wave transmission-reception element for use in an ultrasound probe, comprising a base member and a plurality of unit vibration elements embedded in the base member. Each of the unit vibration elements comprises a piezoelectric ceramic piece polarized in a direction extending between its front and back faces, a front electrode formed on the front face of the piezoelectric ceramic piece, and a back electrode formed on the back face of the piezoelectric ceramic piece.
The piezoelectric ceramic piece may assume any of various forms, such as a short cylinder or a quadrangular prism. In the case of a form having a noncircular end face, such as a quadrangular prism, partial electrodes formed on the front and back faces may assume circular shapes so as to produce directivity characteristics substantially similar to those of a cylindrical piezoelectric ceramic piece.
The form of an end face of the piezoelectric ceramic piece is not limited to planar, but may be spherical so as to produce an action of a convex or concave lens. Employment of a spherical end face changes directivity accordingly.
The unit vibration elements having the thus-improved angle-of-beamspread characteristics may be arranged, for example, in a circle and may be operated such that one unit vibration element transmits spherical waves forward while the remaining vibration unit elements receive reflections of the spherical waves and such that the unit vibration elements sequentially take turns transmitting spherical waves to thereby create a three-dimensional image.
Preferably, the plurality of unit vibration elements are embedded in the base member such that each of the electrodes is exposed at the front or back face of the base member. Also, a portion of the base member may serve as an acoustic matching portion or a backing portion.
Specifically, the base member in which the plurality of unit vibration elements are embedded is formed of a member capable of matching the acoustic impedance of a medium, such as blood, within which detection is to be performed; the base member thickly covers the front electrodes of the unit vibration elements so as to form a thick cover portion; and the thick cover portion of the base member serves as an acoustic matching portion. This structure does not require employment of an acoustic matching layer in manufacture of an ultrasound probe from the wave transmission-reception element. The base member may be formed of, for example, an epoxy resin.
Preferably, the plurality of unit vibration elements are embedded in the base member capable of blocking transmission of incident sound waves; the base member thickly covers the back electrodes of the unit vibration elements so as to form a thick cover portion; and the thick cover portion of the base member serves as a backing portion. This structure does not require employment of a backing layer in manufacture of an ultrasound probe by use of the wave transmission-reception element. The base member may be, for example, a mixture of a resin material, such as epoxy resin, fluororesin, or silicone resin; aggregate; and a metallic powder, so as to be able to eliminate incident sound waves through conversion to thermal energy.
Preferably, the front or back electrodes are integrated into a common electrode covering all of the exposed faces of the piezoelectric ceramic pieces, and the common electrode serves a grounding electrode. Employment of the common electrode
Ohbayashi Kazushige
Okimura Yasuyuki
Brinks Hofer Gilson & Lione
Dougherty Thomas M.
NGK Spark Plug Co. Ltd.
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