Measuring and testing – Vibration – Sensing apparatus
Patent
1997-08-15
2000-08-01
Williams, Hezron
Measuring and testing
Vibration
Sensing apparatus
310313R, 310365, G01H 1100
Patent
active
060949880
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an ultrasound detector, and in particular to an array type detector for detecting in the 150 kHz to 30 mHz range which is typically used in medical and high definition sonar applications.
It is known to have ultrasound detectors which comprise a two-dimensional array of discrete detector elements, which may number from 20 or so to several hundred. Aside from the complexity of handling the information output from the individual elements, the known detectors suffer from a very complex or intricate manufacturing process. Typically each element in an array has a discrete electrical coupling.
Some prior art devices utilise a sheet of piezoelectric material, such as polyvinylidenediflouride (PVDF), which has an array of discrete electrodes formed on one surface of the PVDF film, however this still requires sophisticated manufacturing techniques for forming the electrode pattern on the PVDF surface.
EP-A-506733 describes an invasive instrument using an ultrasound detector utilizing a PVDF film which is electrically coupled to an electrode by an ohmic or capacitive coupling.
We have now realized that this principle can be applied to the formation of an array of elements on an ultrasound detector.
The present invention provides an ultrasound detector comprising a layer of piezoelectric material having first and second major surfaces, and an array of electrodes adjacent and facing one of the major surfaces, the electrodes being electrically coupled to the material by an ohmic or capacitive coupling.
Preferably the other major surface has a conductive film extending across it to form an electrode pair with each of the electrodes of the array.
The array may be one-dimensional, but the invention is particularly suited to providing a two dimensional array. The preferred materials for forming the detector are PVDF,a homopolymer or co-polymer incorporating PVDF, or a piezo electric composite material.
The detector of the invention may be readily manufactured by embedding an array of wire or conductive polymer electrodes in an electrically insulating material. The piezoelectric film is then bonded to the surface of the electrode/insulating material matrix. The piezoelectric film may also be deposited on the matrix, or, particularly in the case of a piezo composite material, it may be injection moulded onto the matrix surface.
It is desirable to reduce reflection losses at the piezoelectric layer surfaces, and also the effect of acoustic reverberations within the body of the detector.
A matching layer may be provided in front of the piezoelectric material layer to minimize acoustic mismatch between the propagation medium in front of the detector and piezoelectric layer. A layer of anechoic material may be provided to dissipate or absorb the ultrasound which is transmitted through the piezoelectric layer, to prevent reflection back towards the piezoelectric layer.
Very preferably an anechoic material with a high acoustic fractional power dissipation is used. The conductive polymer electrodes, if used, may also be made of a polymeric material with acoustically engineered properties. Silicone, polyurethane and polybutadiene based polymers can be used to provide anechoic and acoustically engineered materials.
The insulating material with the electrodes embedded in it may be machined or moulded to provide a surface in which the ends of the electrodes are exposed.
Another aspect of the invention provides an ultrasound detector comprising a layer of piezoelectric material having first and second major surfaces, and an array of electrodes adjacent and facing one of the major surfaces, wherein the electrodes are formed of conductive polymer material.
The conductive polymer electrodes may be in direct electrical contact with the piezoelectric layer or separated from it by an ohmic or capacitive coupling. The piezoelectric layer should be in intimate contact with the electrode array and its surrounding matrix. This could be achieved by depositing the piezoelectric material layer onto the electrode/matr
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patent: 4469978 (1984-09-01), Hamada et al.
patent: 4555953 (1985-12-01), Dario et al.
patent: 4755708 (1988-07-01), Granz et al.
patent: 4914565 (1990-04-01), Schnoeller et al.
Precision Acoustics Limited
Tran Thuy Vinh
Williams Hezron
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