Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-03-30
2003-11-04
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S628000, C073S862046, C600S459000
Reexamination Certificate
active
06640634
ABSTRACT:
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-159179 filed Mar. 31, 2000 and No. 2000-118572 filed Apr. 9, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to an ultrasonic probe to be used for ultrasonic diagnosis and ultrasonic flaw detection, a method of manufacturing such a probe and an ultrasonic diagnosis apparatus comprising such a probe.
Conventional ultrasonic probes utilized for ultrasonic diagnosis apparatus comprise a one-dimensional array probe formed by arranging short strip-shaped (narrow box-shaped) piezoelectric vibrators in an array. This is because a technique referred to as an electronic scanning method is generally used for ultrasonic scanning operations for good reasons. With the electronic scanning method, the ultrasonic vibrators of the array are provided with respective delay times when focussing the pulse to be transmitted or the received signal. Since this method allows high speed scanning and high speed alteration of the focal point of the ultrasonic beam to be transmitted or the received ultrasonic beam, it is in the main stream of ultrasonic scanning.
With the above electronic scanning method, in the case of a one-dimensional array probe, the operation of electronic focussing can be conducted on an ultrasonic wave in the direction of arrangement of the piezoelectric vibrators and an ultrasonic beam can be used for scanning. However, only an acoustic lens can be used for focussing in a direction perpendicular to the direction of arrangement (and hence to the surface to be scanned by the ultrasonic wave. This means that it is not possible to dynamically change the focal point. Additionally, any scanning operation using an ultrasonic beam cannot be conducted two-dimensionally (on a plane) because piezoelectric vibrators are arranged only one-dimensionally in conventional ultrasonic probes.
In recent years, efforts have been made to develop systems for three-dimensionally collecting and displaying ultrasonic images by arranging vibrators (ultrasonic vibrators) in the form of a matrix, dynamically focussing the ultrasonic beam in all directions and using the ultrasonic beam for three-dimensional scanning.
For such a system to be realized, it is necessary to use a two-dimensional array ultrasonic probe comprising two-dimensionally arranged vibrators. In other words, the use of a two-dimensional array ultrasonic probe is a prerequisite for realizing omnidirectional focussing and high speed three-dimensional scanning of ultrasonic waves.
Generally, in two-dimensional array probes, vibrators are arranged in the form of a matrix of m rows and n columns. In order to realize three-dimensional dynamic focussing and three-dimensional beam scanning to a satisfactory extent, a number greater than 50 have to be selected for m and also for n and vibrators have to be arranged at a micro-pitch of less than 0.5 mm. Then, more than 2,000 channels of wires have to be led out of an area of about 2 cm square.
Meanwhile, a number of proposals have been made for realizing two-dimensional array probes particularly in terms of process and configuration. For example, Japanese Patent Application KOKAI Publication No. 59-152800 discloses a method of manufacturing a two-dimensional array probe, which will be summarily described below.
Firstly, a grounding plate and a flexible printed circuit board (FPC) are connected respectively to the front and rear surfaces of a raw piezoelectric vibrator and a backing member and an acoustic adjustment layer are formed as in the case of a one-dimensional array probe. Then, the grounding plate and the FPC are bent in an appropriate manner. Subsequently, the vibrator is diced to produce array vibrators and signal leads and grounding wires are led out from the respective lateral sides of the vibrators to produce a one-dimensional array transducer. A two-dimensional array ultrasonic probe is produced by bonding a plurality of such one-dimensional array transducers.
Japanese Patent Application KOKAI Publication No. 2000-138400 discloses an ultrasonic probe comprising layer-built electronic components, including layer-built piezoelectric elements and a flexible printed circuit board bonded to the layer-built piezoelectric elements. In this ultrasonic probe, every other electrode is selected in the layer direction of the piezoelectric elements and the selected electrodes are electrically connected together by means of an electrode pattern of the flexible printed circuit board to form a first group of electrodes, while the remaining electrodes are connected together to form a second group of electrodes. An end of the electrode pattern of the flexible printed circuit board is used as the electrode section for external connection that is also electrically connected to the two groups of electrodes.
Besides the above probes, many other two-dimensional array ultrasonic probes have been proposed and include those obtained by two-dimensionally arranging electrode drawing out terminals in the form of a matrix, drawing out leads therefrom, connecting a piezoelectric vibrator plate onto a substrate and dividing the piezoelectric vibrator plate into matrix in such a way that each vibrator is found on an electrode drawing out terminal.
However, with any of the known methods, it is difficult to realize a two-dimensional array probe comprising a large number of vibrators that are arranged at a micro-pitch with a high productivity and low cost.
Meanwhile, PZT (lead zirconate-titanate) type piezoelectric ceramic materials and lead relaxa-titanate type piezoelectric monocrystalline materials are used as ultrasonic wave receiving materials in the field of medical ultrasonic diagnosis apparatus and non-destructive testing apparatus.
Additionally, as pointed out above, efforts have been made to develop two-dimensional probes comprising two-dimensionally arranged rod-shaped vibrators. By using rod-shaped vibrators, it is possible to use k33 corresponding to the longitudinal vibration of a rod for the vibration mode. The value of k33 is found between 60 and 80% in the case of PZT type ceramic materials and 80 and 94% in the case of relaxa-titanium type monocrystalline materials. These values are promising for realizing high sensitivity probes.
The technology of THI (Tissue Harmonic Imaging) is currently used to capture minute blood flow in the field of ultrasonic diagnosis apparatus. With the technology of THI, higher harmonics of the second degree of the transmitted ultrasonic wave (echo) are received and detected. Therefore, conventional ultrasonic probes realized by adopting the THI technology are forced to use the resonance frequency of the piezoelectric vibrators either for wave transmission or for wave reception or compromise the requirement of transmission and that of reception at the cost of sacrificing the frequency characteristics of the piezoelectric vibrators to a certain extent. As a result, problems arise including an undesired high drive voltage transmitted from the drive circuit and/or a reduced reception sensitivity.
Japanese Patent Application KOKAI Publication No. 11-234797 discloses a technology of using different sets of piezoelectric vibrators for ultrasonic wave transmission and reception. According to the patent document, piezoelectric vibrators are arranged in a single layer as reception vibrators while transmission vibrators are arranged to form a thin multilayer structure to raise the intensity of the transmitted ultrasonic wave. However, any two arrangements of piezoelectric vibrators of the same piezoelectric material formed at the same thickness show a substantially similar center frequency in the operating frequency band. Therefore, the use of the technology of Japanese Patent Application KOKAI Publication No. 11-234797 for THI does not significantly improve the reception sensitivity.
The above problems are particularly serious in two-dimensional array probes because down-sized vibrators are used
Hashimoto Shin'ichi
Itsumi Kazuhiro
Kobayashi Tsuyoshi
Saito Shiro
Tezuka Satoru
Kabushiki Kaisha Toshiba
Kwok Helen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Surin Jacques
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