Metal working – Piezoelectric device making
Reexamination Certificate
1998-11-09
2001-02-06
Hall, Carl E. (Department: 3729)
Metal working
Piezoelectric device making
C174S034000, C310S336000, C600S459000
Reexamination Certificate
active
06182341
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to transducers and more particularly to broadband phased array transducers for use in the medical diagnostic field.
Ultrasound machines are often used for observing organs in the human body. Typically, these machines incorporate transducer arrays for converting electrical signals into pressure waves and vice versa. Generally, the transducer array is in the form of a hand-held probe which may be adjusted in position while contacting the body to direct the ultrasound beam to the region of interest. Transducer arrays may have, for example, 128 phased transducer elements for generating an ultrasound beam.
An electrode is placed at the front and rear portion of the transducer elements for individually exciting each element. The pressure waves generated by the transducer elements are directed toward the object to be observed, such as the heart of a patient being examined. Each time the pressure wave confronts tissue having different acoustic characteristics, a portion of the ultrasound wave is reflected backward. The array of transducers may then convert the reflected pressure waves into corresponding electrical signals. An example of a phased array acoustic imaging system is described in U.S. Pat. No. 4,550,607 granted Nov. 5, 1985 to Maslak et al. and is incorporated herein by reference. That patent illustrates circuitry for focusing the incoming signals received by the transducer array in order to produce an image on the display screen.
The elevation focus of most phased array transducers can generally be categorized as lens focused or mechanically focused. In the case of lens focused transducer arrays the emitting surface of the array is flat in the elevation direction and a material, the lens, is placed between the object to be imaged and the array. The lens material has a lower velocity of sound than the object being imaged for a convex shaped lens surface. The focusing of the ultrasound beam is achieved through the refraction at the lens/object interface. U.S. Pat. Nos. 4,686,408 and 5,163,436 describe lens focused phased array transducers and are specifically incorporated herein by reference.
Mechanically focused transducer arrays utilize a piezoelectric layer and matching layers which have a curved surface which face the object to be imaged. The surface is curved along the elevation direction and forms either a concave or convex structure. U.S. Pat. Nos. 4,184,094 and 4,205,686 described such a mechanically focused transducer array and are hereby specifically incorporated by reference. The curved surface of the top matching layer is then covered by an acoustic window which is usually formed from a low attenuation polymeric material. The polymeric material is considered an acoustic window and provides no focusing of the acoustic beam. Several two part castable polyurethane materials can be used as acoustic windows.
With reference to acoustic windows, it is possible to use polymeric materials with acoustic attenuation as low as 1.0 dB/mm at around 7 MHz and sound velocity very close to that of human body tissue, i.e. about 1,540 m/s. The use of low loss acoustic window materials in combination with a mechanically focused stack results in better depth penetration of the acoustic beam into the human body being imaged. With reference to the lens structure previously described, the lens material is much more attenuative than the acoustic window material, i.e. around 5.5 dB/mm at about 7 MHz, with velocity of sound far below that of water or the human body. Lower velocity materials such as these provide focusing of the acoustic beam in the elevation plane. Typically silicone RTV materials are used as these later lens materials.
Often a radio frequency interference (RFI) shield is provided underneath the lens or window. The RFI shield is used to reduce electromagnetic interference caused by the hospital or clinical environment which would produce noise in the ultrasound image or vice versa. There are various techniques for employing an RFI shield. One form of shield includes a polymeric shield substructure that has been sputtered with a thin metal. Often, the metal of choice is gold because gold has good conductivity and relative stability in the presence of various deleterious disinfecting solutions used by hospitals and clinics to disinfect the transducer between patient use.
A disadvantage associated with polymeric materials used to form windows or lenses is that they all absorb liquids to some extent, polyurethanes more so than silicones. The gold of the RFI shield acts as a relatively inert barrier to further ingress of these solutions that might occur as a result of repeated soaking of the transducer between patient uses to achieve a satisfactory level of disinfection or sterilization.
It is often difficult to achieve adequate adhesion between the window or lens material and the typically smooth metal surface of the RFI shield. In addition, it is often difficult to maintain adequate adhesion throughout the lifetime of the probe due to the repeated soakings of the transducer probe in disinfecting solution between patients. Transducer typically may be subjected to over 1,000 disinfecting cycles in a year, each cycle lasting anywhere from about 20 to 45 minutes. If the transducer probe is subject to sterilization, the soak time may be as long as 10 hours. The eventual ingress and diffusion of the disinfecting solutions through the window or lens of the transducer causes delamination of the window or lens from the underlying RFI shield. Delamination of this type results in poor image quality and typically the transducer must be returned to the manufacturer.
It is thus desirable to provide a method for optimizing the adhesion of the window or lens material to the underlying RFI shield so that repeated disinfection or sterilization cycles do not compromise the integrity of the transducer structure.
It is also desirable to promote the adhesion between the window or lens material with the underlying shield in a simple and inexpensive manner.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a shield for reducing the impact of radio frequency interference for an ultrasound transducer having a shield substructure including a polymeric film, a layer of metal disposed on the polymeric film and a layer of epoxy material coating the layer of metal.
According to a second aspect of the present invention there is provided a method of manufacturing a shield for reducing the influence of radio frequency interference for an ultrasound transducer. The method includes providing an acoustic stack, providing a shield substructure over a portion of the acoustic stack so that a top surface of the shield substructure faces an object to be imaged and treating the top surface of the shield substructure to promote adhesion with a covering.
REFERENCES:
patent: 4651310 (1987-03-01), Kaneko et al.
patent: 5327008 (1994-07-01), Djennas et al.
Ayter Sevig
Camacho Marilou F.
Shelley Oren
Sliwa, Jr. John William
Talbot Jim
Acuson Corporation
Brinks Hofer Gilson & Lione
Hall Carl E.
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