Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-07-31
2004-07-06
Chapman, John E. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C310S334000, C310S336000
Reexamination Certificate
active
06758094
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to ultrasonic transducers, and, more particularly, to an ultrasonic transducer wafer, or substrate, having variable acoustic impedance.
BACKGROUND OF THE INVENTION
Ultrasonic transducers have been available for quite some time and are particularly useful for non-invasive medical diagnostic imaging. Ultrasonic transducers are typically formed of either piezoelectric elements or of micro-machined ultrasonic transducer (MUT) elements. The piezoelectric elements typically are made of a piezoelectric ceramic such as lead-zirconate-titanate (abbreviated as PZT), with a plurality of elements being arranged to form a transducer array. A MUT is formed using known semiconductor manufacturing techniques resulting in a capacitive ultrasonic transducer cell that comprises, in essence, a flexible membrane supported around its edges over a silicon substrate. By applying contact material, in the form of electrodes, to the membrane, or a portion of the membrane, and to the base of the cavity in the silicon substrate, and then by applying appropriate voltage signals to the electrodes, the MUT may be energized such that an appropriate ultrasonic wave is produced. Similarly, when electrically biased, the membrane of the MUT may be used to receive ultrasonic signals by capturing reflected ultrasonic energy and transforming that energy into movement of the electrically biased membrane, which then generates a receive signal.
The transducer elements may be combined with control circuitry forming a transducer assembly, which is then further assembled into a housing possibly including additional control electronics, in the form of electronic circuit boards, the combination of which forms an ultrasonic probe. This ultrasonic probe, having either bulk wave piezoelectric elements or MUTs and which may include various acoustic matching layers, backing layers, and de-matching layers may then be used to send and receive ultrasonic signals through body tissue.
In the past, joining an acoustic sensor, such as a piezoelectric ceramic transducer element or a MUT element, to the electrical control circuitry required the use of many individual wires to connect each element of the transducer array to the control circuitry. In the case of large transducer arrays having many hundreds or thousands of elements, large wiring harnesses were required. Unfortunately, a large wiring harness increases the bulk and the cost of the ultrasonic probe. For ultrasonic probes that are designed to be used inside the human body, it is desirable to reduce the overall size of the ultrasonic probe and related cabling. One manner of reducing the size of the probe and the cabling is to provide the transducer control electronics on an integrated circuit (IC) assembly or on a circuit board. An IC in proximity to the transducer array may be used to transmit and receive from many small transducer elements and may also be used to multiplex the signals, thereby reducing or eliminating the bulky and expensive cables that typically connect the ultrasonic probe elements to the control electronics.
Placing the transducer array over the IC results in greater packaging efficiency, but often causes undesirable coupling of acoustic energy between transducer elements through the substrate material because the substrate material on which the IC is formed comes into contact with all of the transducer elements.
Therefore, it would be desirable to have a way to connect the elements of an ultrasonic transducer array directly to an integrated circuit or circuit board while reducing or eliminating the undesirable lateral propagation of acoustic energy through the substrate of the IC and the circuit board.
SUMMARY
The invention is directed to a wafer having variable acoustic properties. The wafer may be used as a substrate over which to form an ultrasonic transducer, an IC, or may be used as a circuit board. An ultrasonic transducer formed on the wafer may include piezoelectric ceramic transducer elements or MUT elements. By controlling the acoustic impedance of the wafer upon which the integrated control circuitry for an ultrasonic transducer is formed, the acoustic impedance of the wafer can be matched to the acoustic impedance requirements of the ultrasonic transducer Furthermore, by the addition of internal voids, the wafer reduces or eliminates the lateral propagation of acoustic energy through the wafer.
Other systems, methods, features, and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.
REFERENCES:
patent: 4277712 (1981-07-01), Hanafy
patent: 4672591 (1987-06-01), Breimesser et al.
patent: 5160870 (1992-11-01), Carson et al.
patent: 5511296 (1996-04-01), Dias et al.
patent: 5648942 (1997-07-01), Kunkel, III
patent: 5744898 (1998-04-01), Smith et al.
Chapman John E.
Koninklijke Philips Electronics , N.V.
Vodopia John
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