Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-03-17
2001-04-24
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S344000, C250S351000
Reexamination Certificate
active
06222190
ABSTRACT:
Photo acoustic techniques are based on the heat effect being known as the photo-thermal effect. These techniques take advantages of the principle that absorbed radiation energy, in particular from infrared (IR) radiation results in pressure variations in a constant gas volume, whereby the pressure variations are proportional to the amount of energy absorbed. These pressure variations can then be detected by means of a sensitive pressure sensor.
This invention is directed to a photo acoustic infrared (IR) detector comprising a chamber for receiving a gas or gas mixture, a window for pulsed or modulated IR radiation into the chamber, and a pressure sensor adapted to detect or measure pressure changes in the chamber as a consequence of absorbed IR radiation. In the practical use of such a detector there can be the question of measuring or detecting infrared radiation in general, but a specific and important field of use relates to detection or measurements of gas or gas mixtures, e.g. with respect to air quality or air pollution.
Examples of known uses of such photo acoustic techniques are found, inter alia, in patent publication U.S.-H651 and in an article by C. F. Dewey Jr., R. D. Kamm and C. E. Hackett: Acoustic amplifier for detection of atmospheric pollutants, Appl. Phys. Lett., Vol. 23, No. 11, December 1973.
The present invention aims at substantial improvements in a photo acoustic detector as referred to above. An important object of the invention is to provide a detector design that can be manufactured in a simple and rational manner, among other things by employing standard components being in common use within the semiconductor technology and within electronics in general. It is possible to make photo acoustic detectors based on the invention, in miniature designs, being based upon the construction of the actual pressure sensor element by means of silicium i.e. silicon or similar materials, which e.g. are employed within the semiconductor technology.
On the above background the photo acoustic infrared detector according to the invention comprises novel and specific features in the form of a generally plate-shaped main part having a recess or bore for substantially forming the chamber, whereby the window closes the chamber at one side of the main part and whereby the pressure sensor is of the miniature type and is located at the opposite side of the main part in relation to said one side, so that the pressure sensor communicates with and closes the chamber at the opposite side, except for a venting channel for the chamber, and a cap being provided at said opposite side of the main part so that it encloses the pressure sensor and forms a gas space communicating with the chamber through the venting channel and being substantially larger than the gas volume in the chamber.
In a preferred embodiment of the detector according to the invention, the pressure sensor is manufactured of silicium in planar technology, i.e. a technology being well known and well developed within the semiconductor field.
In a further particularly preferred embodiment of the invention, the main part and the cap are in the form of components known per se for a standard encapsulation, whereby the main part is formed by the bottom of the standard capsule. In such a bottom the chamber can be formed in various ways, inter alia as an opening bored through the bottom.
Normally the pressure sensor will comprise a membrane structure with sensor elements incorporated therein or applied thereto. In order to generate a measuring signal corresponding to the membrane oscillations resulting from pressure changes in the chamber, various sensor principles can be contemplated, e.g. a piezo-resistive or capacitive measurement principle. In the exemplary embodiment to be described more closely below, piezo-resistive sensor elements are provided. Such principles and techniques are well known in connection with silicium pressure sensors and microphones or the like, and will not be discussed more closely here.
The design and manufacture of photo acoustic infrared and gas sensors based on silicium micromechanics involve several substantial advantages. These gas sensors are cheap in production and can be utilized advantageously for providing highly miniaturized photo acoustic detectors.
REFERENCES:
patent: 4740086 (1988-04-01), Oehler et al.
patent: 4866681 (1989-09-01), Fertig
patent: 4903248 (1990-02-01), Fertig
patent: 5616826 (1997-04-01), Pellaux et al.
patent: 6006585 (1999-12-01), Forster
patent: 41 16 280 A1 (1991-12-01), None
patent: 2 218 198A (1989-08-01), None
patent: WO 96/24831 (1996-08-01), None
Patent Abstracts of Japan, vol. 10, No. 19-P-42, Abstract of JP 60-173443A (Jun. 09, 1985).
Bernstein Ralph
Ferber Alain
Duane Morris & Heckscher LLP
Gabor Otilia
Hannaher Constantine
Leiv Eiriksson Nyfotek AS
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