Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0076—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means
  • G01L9/0077—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means for measuring reflected light
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
  • A61B5/021—Measuring pressure in heart or blood vessels
  • A61B5/0215—Measuring pressure in heart or blood vessels by means inserted into the body
  • A61B5/02154—Measuring pressure in heart or blood vessels by means inserted into the body by optical transmission

Definitions

• the present invention relates to a miniaturized pressure sensor with a shell of an eleastic material, an elastic diaphragm arranged over an opening situated in the surface of the shell, a light conductor arranged inside the shell, a silicon body arranged inside the shell and a reflecting surface arranged on the body such as to be opposite of the light conductor.
• the known pressure transducer is a so-called relative pressure transducer, which means that it measures the pressure dif ⁇ ference between ambient pressure and a reference pressure.
• the reference pressure is in contact with the atmospheric pressure via an air duct inside the shell.
• This air duct has a constriction formed by a silicon body situated in the region of the diaphragm.
• the present invention has the object of providing a minia ⁇ turized pressure sensor of the kind described in the introduc ⁇ tion, which allows maintenance of atmospheric pressure in the distal air volume nearest the diaphragm in spite of the diaphragm moving quickly.
• Another object of the invention is to achieve a pressure sensor of the kind described in the introduction, and which has reduced compliance. Compliance is herein defined as volume change per pressure change.
• a small deflection or movement of the diaphragm shall provide a small volume change. This can be accomplished by either reducing the deflection or the size of the diaphragm.
• the above-mentioned objects are achieved by the body comprising a thin, cantilevering, short beamlike structure of silicon arranged for actuation by the diaphragm, and by the reflecting surface being arranged at the free end of the cantilever part of the beam structure, and upstanding from it, such that the pressure changes acting on the diaphragm will move the beam structure and thereby the reflecting surface, which then will move in front of the end of the light conductor or optical fibre.
• the adhesion effect associated with a reduced opening is avoided by the cantilevering beam structure having a hump on its back part situated under the diaphragm, this hump projecting into the opening in the shell surface of the sensor.
• Figure 1 illustrates a miniaturized pressure sensor according to the state of the art as appears in the above- mentioned Swedish patent
• Figure 2 is a cross-sectional view of a miniaturized pressure sensor in accordance with the present invention
• Figure 3 is a perspective view of an assembly means for ensuring a free path for the volume of air deciding reference pressure
• Figure 4 is a cross-sectional view of a miniaturized pressure sensor having a reduced area of an opening for a diaphragm
• Figure 5 is a cross-sectional view of a miniaturized pressure sensor in accordance with a second embodiment of the present invention.
• the known pressure sensor includes a shell 1 of elastic material, and an elastic diaphragm 2 arranged over an opening 3 situated in the shell surface.
• a light conducor 4 and a silicon body 5 are arranged inside the shell.
• a reflecting surface 6 is arranged opposite the end surface of the light conductor 4. The amount of reflected light in the light conduc ⁇ tor 4 is responsive to the amount with which the ambient pressure P deflects the diaphragm 2 and thereby the end surface of the light conductor or optical fibre 4 in relation to the reflecting surface 6.
• the silicon body 5 forms a constriction between the air volume 7 at the distal end of the diaphragm and the air duct 8 inside the proximal part of the shell. This constriction is a disadvantage in miniaturization.
• Figure 2 illustrates the pressure sensor in accordance with the present invention.
• the silicon body 5 is provided with a thin, cantilevering, short beam structure 10 arranged for actuation by the diaphragm 2.
• the structure is produced from single crystalline silicon by anisotropic etching of the 100- plane or the Ill-plane, which have a lower etching rate than surrounding crystal planes.
• a vertical mirror can be etched in this way at the end of the beam structure. By selective etching, the thickness of the beam can be defined within the area of magnitude from about 5 to about 30 ⁇ m.
• the beam structure is provided with extremely good bending properties, and since it can have the mentioned thickness its length can be made less than the length of the free end of the optical fibre in the embodiment according to Figure 1. The length of the complete sensor can thus be reduced in this way.
• the silicon body 5 is cemented to the light conductors or optical fibre 4, which is in turn cemented to the shell 1.
• etching rate is dependent on doping.
• the silicon can be p-doped or p-doped silicon can be n-doped.
• Different etching liquids can be used, inter alia postassium hydroxide.
• the silicon body illustrated in Figure 3 is used to provide a well-defined air duct and for facilitating assembly of the optical fibre in the sensor.
• the body 5 is substantially quadratic in cross section and is formed partly by the beam structure 10, which is provided at its end with the reflecting surface 6, and partly by an upwardly open elongate box with a bottom wall 11 and two side walls 12, 13.
• the two side walls are each provided with an upwardly open cutaway part, of which only one, 14, is shown.
• These parts 14 only extend a short distance along the length of the side walls, this distance corresponding to the length of the cantilevering part of the beam structure 10.
• the beam structure is joined to the box by an atomic bonding process (see Tenerz, H ⁇ k, Electronic Letters, May 22, 1986, Vol. 22, No. 11, pages 615-616) or anodic bonding by deposit ⁇ ing a glass layer in the joint.
• the box 10-13 When the sensor is assembled, the box 10-13 is inserted in the shell 1 up to the position corresponding to the one in Figure 2, the beam structure then being fixed to the shell, e.g. by cementing, or in some other way.
• the light conductor or optical fibre is then inserted in the end opening of the box in the manner illustrated in Figure 3.
• the position of the fibre relative the reflecting surface is easy to determine with great precision since the bottom, side and roof walls of the box serve as guides.
• the air duct mentioned above is formed between the optical fibre and teh four walls 10-13. These walls are smooth and have well defined sizes, in comparision with the rather random constric ⁇ tions which can occur in the embodiment according to Figure 1 in connection with the body 5 being cemented in the shell.
• the side walls 12, 13 and bottom wall are either made from flat wafers which are joined to each other, or the walls 11, 12 and 13 are made integral using such a selective etching procedure of the kind mentioned above.
• Figure 4 illustrates a miniaturized pressure sensor similar to the one in Figure 2.
• the area of the opening 3 has been reduced in relation to the one in Figure 2, with the object of increasing the comp ⁇ liance of the sensor.
• This embodiment further affords the advantages that the diaphragm 2 will be stiffer compared with the one in Figure 2, and therefore provide good mechanical protection to the sensor.
• an adhesion effect occurs, i.e. the diaphragm tends to stick to the beam structure 5 in the region denoted by the arrow 15. This falsifies the measuring result.
• Figure 5 illustrates a miniaturized pressure sensor in accor ⁇ dance with a second preferred embodiment of the invention.
• the opening 3 for the diaphragm 2 has a reduced area compared with the embodiment in Figure 2.
• the diaphragm is substantially flat and does not bulge down into the opening as in Figure 2.
• the beam structure 10 of the body 5 has a hump 16 on its back part in the region of the latter situated under the opening 3, this hump projecting into the opening 3 such as to be in contact with the diaphragm 2.
• This configuration results in that the adhesion effect no longer occurs or is at least considerably reduced.
• the upper surface of the hump is flat and its contour, seen from above in relation to Figure 5 is somewhat less than the contour of the opening so that the hump does not jam in the wall of the opening 3 when the beam structure moves.
• the hump 16 is preferably made integral with the body and is preferably produced simultaneously with the beam structure 10 by selective etching of the silicon as described above.
• This embodiment of the body 5 can also have the form of a box similar to the one with open end walls, as illustrated in Figure 3, the beam structure 10 being provided with the hump 16 on its back.
• the beam structure 10 is only in contact with the diaphragm 2, and is not cemented to the diaphragm.

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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Cardiology (AREA)
• Heart & Thoracic Surgery (AREA)
• Medical Informatics (AREA)
• Biophysics (AREA)
• Pathology (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Vascular Medicine (AREA)
• Physiology (AREA)
• Molecular Biology (AREA)
• Surgery (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• General Physics & Mathematics (AREA)
• Measuring Fluid Pressure (AREA)

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Cited By (3)

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Citations (6)

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• 1989
  • 1989-01-13 SE SE8900121A patent/SE462631B/sv not_active IP Right Cessation
• 1990
  • 1990-01-12 WO PCT/SE1990/000027 patent/WO1990007906A1/en active IP Right Grant
  • 1990-01-12 EP EP90901923A patent/EP0473582B1/en not_active Expired - Lifetime
  • 1990-01-12 DE DE69022988T patent/DE69022988T2/de not_active Expired - Fee Related
  • 1990-01-12 US US07/721,508 patent/US5195375A/en not_active Expired - Lifetime
  • 1990-01-12 JP JP2502399A patent/JP2514749B2/ja not_active Expired - Lifetime

Patent Citations (6)

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