Measuring and testing – Volume or rate of flow – Using differential pressure
Reexamination Certificate
1999-06-01
2001-07-24
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Using differential pressure
C073S715000
Reexamination Certificate
active
06263741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow-restriction device and especially to a micromechanically produced flow-restriction device.
2. Description of Prior Art
Micromechanically produced fluid passages are known e.g. in the field of fluid dosage. A simple dosing system consists e.g. of a fluid reservoir, a pressure transducer and a fluid passage having a defined flow resistance.
In addition, micromechanically produced multisensors for flow, temperature and pressure measurements are known in the field of technology. Such systems are provided with a micro-mechanical capillary on the back of a substrate and with piezoelectric pressure sensors arranged on the front of a substrate. Such known systems are disadvantageous insofar as they are difficult to produce and, in addition, insofar as the piezoelectric pressure sensors are very expensive.
DD-A-285188 discloses a flow sensor provided with a capillary and used for continuous measurements of gas volume flows. In this known flow sensor, a differential pressure between an inlet reservoir and an outlet reservoir is caused by a pressure drop via a capillary. This differential pressure is detected by means of a membrane provided with a resistance bridge which is adapted to be unbalanced, and is then used as a measure of a gas volume stream.
In the Patent Abstracts of Japan, Sect. P, Vol. 17 (1993), No. 550 (P-1624), a flow rate detection element is described, which is provided with a small channel, a pressure detection element being arranged within the walls of said channel. The pressure detected serves to control the fluid flow rate, whereby a fine control of the transport speed of the fluid can be achieved.
The publication “Einsatz von Siliziumsensoren in Proze&bgr;me&bgr;-geräten zur Druckmessung—Stand und Tendenzen”, Technisches Messen 59 (1992) 9, pp. 340-346, contains an explanation of piezoresistive and capacitive silicon sensors and their fields of application.
EP-A-0435237 describes an electronic microvalve consisting of a silicon substrate and a freestanding, flexible, dielectric closure plate, a space being arranged between the closure plate and the silicon substrate. The silicon substrate is provided with an inlet opening, whereas the closure plate has provided therein outlet openings in such a way that said closure plate leaves the inlet opening open in a non-excited state and closes said inlet opening in an excited state.
DE-A-3814150 also refers to a valve arrangement consisting of microstructured components. In this valve arrangement, an actuating element is adapted to be moved relative to a flow path distributor for thus opening or closing fluid paths depending the respective switching position.
U.S. Pat. No. 5,377,524 discloses a microflow measurement device which makes use of a capacitive pressure sensor. In the known pressure measurement device, an inlet opening and an outlet opening are provided in a carrier plate. The carrier plate has a structured substrate arranged thereon. Said substrate is structured such that it defines, on the one hand, a channel together with the carrier plate and, on the other hand, a capacitive pressure sensor together with the carrier plate. The channel is implemented such that it defines a flow resistance. The capacitive pressure sensor is defined by a membrane and an associated membrane electrode as well as by a counterelectrode arranged on the carrier plate in spaced relationship with said membrane electrode. According to U.S. Pat. No. 5,377,524, the capacitive pressure sensor is arranged outside of the flow path, viz. in a lateral branch, so as to permit the measurement of a pressure difference between the pressure prevailing at the inlet opening and the pressure prevailing at the outlet openig.
In Boillat, M. A. et al: “A Differential Pressure Liquid Flow Sensor for Flow Regulation and Dosing Systems”, PROC. IEEE MICRO ELECTROC MECHANICAL SYSTEMS 1995, 29.1.95-2.2.95, NL-Amsterdam, pp. 350-352, a flow sensor is described in the case of which two piezoresistive low-pressure sensors are provided for detecting the pressure in the flow path in front of and behind a channel constituting a flow-restriction.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an economy-priced and simple micromechanically produced flow-restriction device with at least one integrated pressure sensor.
In accordance with the present invention, this object is achieved by a micromechanically produced flow-restriction device comprising:
a first passage opening formed in a first main surface of a substrate;
a channel which is formed in a second main surface of the substrate and one end of which is in fluid communication with said first passage opening;
a second passage opening which is in fluid communication with a second end of the channel,
said first passage opening, said channel and said second passage opening defining a flow path,
a membrane which is formed in the substrate and which is in fluid communication with said first passage opening;
a membrane electrode formed at least on said membrane;
a cover attached to the second main surface of the substrate in such a way that said cover defines together with said channel a flow resistance of the flow-restriction device, said cover being provided with a counterelectrode which is arranged in opposed, spaced relationship with said membrane electrode in such a way that said membrane electrode and said counterelectrode define a capacitive pressure sensors said capacitive pressure sensor being arranged on a wall of the flow path.
In a preferred embodiment of the present invention, the second passage opening or outlet opening is formed in the first main surface of the substrate, said second passage opening or outlet opening being in fluid communication with a second membrane which is formed in the substrate and which is provided with a membrane electrode. The cover is provided with a second counterelectrode which is arranged in opposed, spaced relationship with said second membrane electrode in such a way that said second membrane electrode and said second counterelectrode define a capacitive pressure sensor. It follows that, in the case of this embodiment, the micromechanically produced structure is provided with a flow-restriction device and two pressure sensors, one of said pressure sensors being formed in front of the channel defining the flow resistance, when seen in the direction of flow, whereas the other pressure sensor is formed behind the channel defining the flow resistance, when seen in the direction of flow.
In the micromechanically produced flow-restriction device according to the present invention, the cover serves to define the restriction of the flow-restriction device and it also serves as a counterelectrode of the at least one pressure sensor which is implemented as a capacitive sensor. Hence, only two chip components, viz. the substrate and the cover, are required. Preferably, the cover as well as the substrate are produced from silicon, another possibility being, however, to use Pyrex glass for the cover, said Pyrex glass having the same coefficient of thermal expansion as silicon.
The capacitive sensors formed in the flow-restriction device according to the present invention can be produced at a reasonable price and have a low temperature dependence. It follows that compensation electronics can be dispensed with. The flow measurement chip defined by the micromechanically produced flow-restriction device has preferably no further electronics arranged thereon, since a flow measurement chip of this type is disinfected with gamma rays. Such a gamma radiation would destroy electronics, e.g. MOS-FETs or the like, provided on the chip.
The flow-restriction device according to the present invention can advantageously be used e.g. in a dosing system which works on the overpressure principle. In a further embodiment according to the present invention, a temperature sensor is additionally provided in the area of the channel of the flow-restriction device so that the flow-restric
Beyer Weaver & Thomas LLP
Fraunhofer-Gesellschaft zur Förderung der Angewandten Forschung
Fuller Benjamin R.
Mack Corey D.
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