Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-12-02
2004-08-03
Imam, Ali (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S459000
Reexamination Certificate
active
06770032
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to passive sensors in general and to ultrasonic passive sensors in particular.
BACKGROUND OF THE INVENTION
Passive sensors (for implanting into the human body or for mounting at some inaccessible location within a machine) are known in the art. These sensors are typically electromagnetic, providing an electromagnetic signal when activated.
The prior art sensor systems typically comprise a sensor, implanted into the machine, and an activating and detecting system. The sensor is typically an oscillating circuit whose vibration frequency changes in response to the physical variable to be measured. The oscillating circuit typically includes a capacitor and an inductor, one of which is built to vary in accordance with the physical variable being measured. As a result, the vibration frequency of the circuit is a function of the physical variable.
When the sensor is irradiated with electromagnetic energy from the activating system, some of the energy is absorbed by the oscillating circuit, depending on how close the incident frequency or frequencies are to the resonant frequency of the circuit (which, in turn, depends on the physical variable being measured). The change in the electromagnetic field due to the absorption of energy by the oscillating circuit is detected by the detecting system.
Electromagnetic sensors and systems are described in the U.S. Pat. No. 4,127,110 and in an article: Carter C. Collins, “Miniature Passive Pressure Transensor for Implanting in the Eye”, IEEE Transactions on Bio-Medical Engineering, Vol. BME-14, No. 2, April 1967.
Unfortunately, within living tissue, the passive sensor is detectable within a range of approximately 10 times the diameter of its antenna (part of the oscillating circuit). Furthermore, the sensor system is not operative within a conductive enclosure.
Methods, devices and systems, using ultrasonically activated passive sensors usable for sensing different physical parameters within a human body or in other environments and scientific and industrial applications, have been described. U.S. Pat. No. 5,619,997 to Kaplan discloses a passive sensor system using ultrasonic energy. An ultrasonic activation and detection system ultrasonically activates passive sensors which may be implanted in a body or disposed in any other environment. The activated passive sensors or parts thereof vibrate or resonate at a frequency which is a function of the value of the physical variable to be measured. The passive sensors thus absorb ultrasonic energy from the exciting ultrasonic beam mostly at the frequency of vibration (resonance frequency) of the sensor. The frequency (or frequency range) at which the passive sensor absorbs energy may be detected by a suitable detector and used to determine the value of the physical parameter.
Additionally, if the exciting ultrasonic beam is pulsed, the ultrasonic sensor may continue to vibrate after the excitation beam is turned off. The frequency of the ultrasonic radiation emitted by the activated passive sensor after turning the excitation beam off may be detected and used to determine the value of the physical parameter.
Since more than one physical variable may influence the vibration frequency of passive sensors, a correction may be needed in order to compensate for the effects of other physical parameters unrelated to the physical parameter which needs to be determined on the measured sensor vibration frequency. For example, if pressure is the physical parameter to be determined, changes in temperature may affect the vibration frequency of the sensor. U.S. Pat. Nos. 5,989,190 and 6,083,165 to Kaplan disclose compensated sensor pairs and methods for their use for compensating for the effects of unrelated different physical variables on the determined value of another physical variable which is being determined.
Alternative methods for constructing and using passive ultrasonic sensors for performing measurements of a physical parameters may further advance the possibilities of performing measurements of physical parameters inside living organisms and in closed systems in industrial applications.
SUMMARY OF THE INVENTION
There is therefore provided in accordance with an embodiment of the present invention a passive acoustic sensor for determining the value of a physical variable in a measurement region. The sensor includes a housing having two spaced apart substantially parallel and substantially flat acoustically reflecting surfaces. At least one of the acoustically reflecting surfaces is a surface on a movable member configured to be movable with respect to the housing, such that the distance between the acoustically reflecting surfaces varies as a function of the physical variable. The acoustically reflecting surfaces are configured such that when incident acoustic waves having a range of frequencies are directed at the sensor in a direction substantially orthogonal to the acoustically reflecting surfaces, a first portion of the incident waves is reflected from one of the acoustically reflecting surfaces to form a first reflected wave, and a second portion of the incident waves is reflected from the remaining acoustically reflecting surface to form a second reflected wave. The first reflected wave and the second reflected wave interfere to form a returning acoustic signal having at least one maximally attenuated frequency which is correlated with the value of the physical variable in the measurement region in which the sensor is disposed.
Furthermore, in accordance with an embodiment of the present invention, one or more of the physical parameters of the sensor is selected such that the intensity of the first reflected wave is equal or substantially similar to the intensity of the second reflected wave.
Furthermore, in accordance with an embodiment of the present invention, one of the acoustically reflecting surfaces is a static surface of one of the walls of the housing.
Furthermore, in accordance with an embodiment of the present invention, one of the acoustically reflecting surfaces is a static surface of a wall of the housing. The housing has an open recess therein. The movable member is sealingly attached within the recess to form a sealed chamber within the housing. The chamber has a pressure level therein. The two acoustically reflecting surfaces are exposed on the external surface of the sensor for contacting a fluid within the region of measurement.
Furthermore, in accordance with an embodiment of the present invention, one or more of the parameters selected from the acoustic impedance of at least one component of the sensor, the area of the first reflecting surface of the two acoustically reflecting surfaces, the area of the second reflecting surface of the two acoustically reflecting surfaces, and any combinations thereof is selected such that the intensity of the first reflected wave is equal or substantially similar to the intensity of the second reflected wave.
Furthermore, in accordance with an embodiment of the present invention, the at least one component of the sensor is selected from the movable membrane of a portion thereof, and the wall of the housing underlying the static surface or a portion thereof, and the combination thereof.
Furthermore, in accordance with an embodiment of the present invention, the housing has an opening therein and a back wall opposing the opening. At least a part of the surface of the back wall facing the opening is the second reflecting surface of the two acoustically reflecting surfaces. The movable member is sealingly attached to the opening to form a sealed chamber within the housing. At least a portion of the surface of the movable member outside of the sealed chamber is the first reflecting surface of the two acoustically reflecting surfaces. The chamber has a fluid therein. At least a first part of the chamber defined between the movable member and the second reflecting surface is filled with the fluid. The sealed chamber includes at least a second part thereof. The second part of the sealed chamber is at
Eitan, Pearl, Latzer & Cohen Zedek LLP
Imam Ali
Microsense Cardiovascular Systems 1996
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