Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-09-10
2003-12-30
Iman, Ali M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06669636
ABSTRACT:
RELATED APPLICATION
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ultrasound transmitting and receiving system, or transceiver, including an ultrasound transducer, an ultrasound waveguide and a jacket-type enclosure, said ultrasound waveguide being housed within the enclosure while the ultrasound transducer is positioned at one end of the ultrasound waveguide, whereby at said end of the ultrasound waveguide the ultrasound transducer can receive and transfer ultrasound waves from/to the ultrasound waveguide.
Ultrasound transceivers of this type are employed for instance in ultrasonic flowmeters and in vortex flowmeters. The ultrasound transducers typically used in these designs are piezoelectric crystals that are capable of generating as well as detecting ultrasonic waves.
In principle, it would be possible to equip an ultrasound transceiver with only one ultrasound transducer for generating as well as receiving ultrasonic waves. That, however, would require positioning the ultrasound transducer directly at the point where the ultrasonic waves are to be injected or detected. This would be difficult insofar as piezoelectric crystals, typically serving as ultrasound transducers as stated above, cannot be used above a certain temperature referred to as the Curie temperature. The reason is that above this Curie temperature, the crystal no longer possesses a ferroelectric or ferromagnetic phase, the very prerequisite for the piezoelectric properties of the crystal. Yet in cases where the moving fluid whose flow rate is to be measured with the ultrasonic flowmeter is very hot to a point where its temperature exceeds the Curie temperature of the piezoelectric crystal, any reliable operation requires a certain thermal insulation of the ultrasound transducer from the hot fluid. This is why ultrasound transceivers employ ultrasound waveguides that are designed to offer both best possible thermal insulation of the ultrasound transducer from the hot fluid and, to the extent possible, a loss-free and unimpeded transfer of the ultrasound signal. In that fashion, the ultrasound waveguide can inject ultrasonic waves generated by the ultrasound transducer into the flowing fluid and the ultrasound transducer can extract ultrasonic waves from the hot fluid while the ultrasound transducer is at a spatial distance from the hot fluid and is thermally insulated from the latter at least to a certain extent.
2. Description of the Prior Art
Conventional ultrasound transceivers employ ultrasound waveguides for instance of the type described in WO 96/41157. The ultrasound waveguide in that case is constituted of a plurality of very thin, mutually parallel rods whose individual diameter is substantially smaller than the wavelength of the ultrasound signal to be transferred. The rods are typically bundled close together and fitted into a tube that provides lateral support for the rods and thus constitutes an enclosure, or jacket, for the ultrasound waveguide, the result being a compact ultrasound waveguide. For an ultrasound waveguide, WO 96/41157 also describes a design where metal plates, bent in essentially circular fashion, are interleaved at a distance from one another. These, too, are housed in a tube that constitutes an outer jacket for the ultrasound waveguide. Finally, EP 1 098 295 discloses an ultrasound waveguide that consists of a rolled-up foil tightly fitted into a metal tube. To permit the transfer of ultrasonic waves in the frequency range from 15 kHz to 20 MHz, the thickness of each layer of the foil is less than 0.1 mm. The foil typically consists of a metallic material.
What the ultrasound transceivers incorporating ultrasound waveguides of the type described have in common is that the ultrasound transducer is positioned at one end of the ultrasound waveguide in such fashion that ultrasonic waves can be injected by the ultrasound transducer into the ultrasound waveguide and/or can be received by it from the latter. The typical approach involves the direct attachment of the ultrasound transducer to one end of the ultrasound waveguide, meaning physical contact between the two. Where the ultrasound waveguide is in the form of a rolled foil as described above, the ends of the ultrasound waveguide are usually welded up and butt-faced and the ultrasound transducer is mounted on this welded-up and level end face of the ultrasound waveguide.
However, the problem with ultrasound transmitters of the type described above is that ultrasonic waves generated by the ultrasound transducer enter not only the ultrasound waveguide but the jacket encasing it as well. A similar problem is encountered when the ultrasound transducer also serves to detect ultrasonic waves, i.e. as an ultrasound receiver, in which case ultrasonic waves travel to the ultrasound transducer not only via the ultrasound waveguide but by way of the jacket as well. As a consequence, when the system includes both an ultrasound transmitter and an ultrasound receiver, it is not only ultrasonic waves transmitted and received via the ultrasound waveguide that are measured but also ultrasonic waves that travel through the jacket of the waveguide. Now if on top of that the ultrasound transceiver system is installed with its jacket, for instance, into the wall of a pipe through which flows the fluid whose flow rate is to be measured, such measurements will include not only the ultrasonic waves that penetrate the fluid, but also those waves that have propagated through the wall of the pipe from the ultrasound transmitter to the ultrasound receiver. This phenomenon is referred to as cross coupling or crosstalk and may lead to a heterodyning or even complete suppression of the actual measuring signal of interest.
The problem associated with this manifests itself even more when one realizes that, when ultrasonic waves are switched between two mutually different media, the coefficient of transmission will be as follows, disregarding any geometric factors:
T
=4(
z
1
/z
2
)/(1+
z
1
/z
2
)
2
where z
1
and z
2
are the characteristic impedances of the first and, respectively, second medium between which the transition takes place. In the case of a transition from steel to air, the aforementioned coefficient of transmission T is approximately 0.004%. This means that a significant part of the acoustic energy, 99.996% to be exact, is lost. A major portion of this lost energy reappears in the undesirable cross coupling. Accordingly, this cross coupling or crosstalk severely affects the signal-to-noise ratio of a flowmeter that operates with an ultrasound transceiver.
SUMMARY OF THE INVENTION
It is therefore the objective of this invention to introduce an ultrasound transmitting and receiving system by means of which any undesirable cross coupling or crosstalk can be largely avoided.
With reference to the ultrasound transceiver design described above, the invention achieves that objective by means of an impedance step between the ultrasound transducer and the side of the jacket facing away from the ultrasound transducer.
This impedance jump as provided for by the invention thus covers an area of the jacket of the ultrasound transmitter in which the undesirable entry of ultrasonic waves from the ultrasound transducer into the jacket is significantly attenuated. Correspondingly, an ultrasound receiver according to the invention includes an area in which ultrasonic waves impinging on the jacket of the ultrasound receiver and conducted to the ultrasound transducer are significantly attenuated. This is because in both cases the ultrasonic waves travelling through the jacket must pass the impedance step, either as they come from or move toward the ultrasound transducer, with the magnitude of the impedance jump determining the degree of attenuation of the intensity of the ultrasonic waves essentially along the formula shown above for the coefficient of transmission.
An impedance step as provided for by the invention in the jacket of the ultrasound transceiver can be implemented in various ways. For e
Cesari and McKenna LLP
Iman Ali M.
Krohne A.G.
LandOfFree
Ultrasound transmitter and/or receiver system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ultrasound transmitter and/or receiver system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultrasound transmitter and/or receiver system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3181742