Integrated smoke detection device

Abstract

The integrated smoke detection device comprises a carrier (1), a light source (2) arranged on or above the carrier, a light receiver (3) arranged on or above the carrier at a distance from the light source, and a polarizing member (7) arranged on or above the carrier, the light source emitting radiation (a, b) into the polarizing member. The polarizing member is configured to have a boundary surface (11) that linearly polarizes a reflected portion (d) of the radiation emitted by the light source, and an exit surface (12) that allows the reflected portion (d) to exit the polarizing member.

Claims

1. An integrated smoke detection device, comprising: a carrier, a light source arranged on or above the carrier, a light receiver arranged on or above the carrier at a distance from the light source, and a polarizing member arranged on or above the carrier, the light source emitting radiation into the polarizing member; the polarizing member being configured to have a boundary surface that linearly polarizes a reflected portion of the radiation emitted by the light source, and an exit surface that allows the reflected portion to exit the polarizing member, the light source and the polarizing member being configured such that the radiation emitted by the light source is redirected by total internal reflection of an emitted ray into an internally reflected ray; and the internally reflected ray being directed to the boundary surface.

2. The integrated smoke detection device according to claim 1, further comprising: a detection region contiguous with the polarizing member, the detection region and the polarizing member comprising indices of refraction, the index of refraction of the polarizing member being higher than the index of refraction of the detection region.

3. The integrated smoke detection device according to claim 2, further comprising: sidewalls limiting the detection region, the sidewalls being formed by a dark molding compound.

4. The integrated smoke detection device according to claim 1, wherein the polarizing member comprises a clear or semitransparent molding compound.

5. The integrated smoke detection device according to claim 1, wherein the light source emits directly into the polarizing member.

6. The integrated smoke detection device according to claim 1, wherein the light source is embedded in the polarizing member.

7. The integrated smoke detection device according to claim 1, further comprising: a planar top surface of the carrier, the light source, the light receiver and the polarizing member being arranged on the top surface, and the light source emitting in a direction normal to the top surface, away from the carrier.

8. The integrated smoke detection device according to claim 1, wherein the polarizing member has a shape of a triangular prism or a truncated triangular prism.

9. The integrated smoke detection device according to claim 1, wherein the boundary surface is arranged to generate a refracted portion and a reflected portion of the radiation emitted by the light source, a ray of the refracted portion and a ray of the reflected portion enclosing an angle of 90.

10. The integrated smoke detection device according to claim 1, further comprising: an upper layer of the light receiver, the upper layer including a polarization filter.

11. The integrated smoke detection device according to claim 10, further comprising: a band-pass filter in the upper layer.

12. The integrated smoke detection device according to claim 10, further comprising: a photodiode and a further photodiode being integrated in the light receiver, the polarization filter being arranged such that radiation passing the polarization filter is only received by the photodiode.

13. The integrated smoke detection device according to claim 1, further comprising: a shielding member arranged between the light source and the light receiver, the shielding member being formed by a dark molding compound.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross section of an embodiment of the integrated smoke detection device.

(2) FIG. 2 is a transparent perspective view of the embodiment according to FIG. 1.

DETAILED DESCRIPTION

(3) FIG. 1 is a cross section of an embodiment of the integrated smoke detection device. A light source 2 is arranged on or above a top surface 10 of a carrier 1, which may in particular be a semiconductor substrate, like a silicon substrate, for instance. A light receiver 3 is arranged on or above the top surface 10 of the carrier 1 at a distance from the light source 2. The use of a semiconductor substrate as carrier 1 facilitates external electric connections of the light source 2 and the light receiver 3, in particular connections with electric circuits for power supply and/or signal processing.

(4) The light source 2 may in particular be a light-emitting diode (LED) or a vertical-cavity surface-emitting laser (VCSEL), for instance. A vertical-cavity surface-emitting laser has the advantage that it provides a collimated and intense beam emitted in a relatively small solid angle.

(5) The light receiver 3 may especially be a semiconductor device, like a silicon die with an integrated photodiode and/or readout circuitry, for instance. More than one photodiode may be integrated in the light receiver 3. The light receiver 3 may comprise an upper layer 5 including a polarization filter 15 and/or a band-pass filter 16.

(6) FIG. 1 shows an embodiment comprising a photodiode 13 that is covered by the polarization filter 15 and a further photodiode 14 that is not covered by a polarization filter. This arrangement enables a differential measurement, which can compensate for obstructions of the light path by dirt or debris, for example.

(7) The polarization filter 15 can especially be a metal grid formed in a metallization layer of a wiring provided for the circuitry. The optional band-pass filter 16 may be a narrow band-pass interference filter, for instance, which reduces the influence of ambient light.

(8) A detection region 4 is present above the carrier 1. The detection region 4 may be limited by sidewalls 6, which may be formed by a dark molding compound absorbing radiation in the wavelength range of the light source 2, for instance. The detection region 4 is not closed and allows smoke 9 to enter from outside, especially from the environment. If no smoke is present, the detection region 4 may be filled with any gas from the environment that does not trigger the smoke detector, like ambient air, for instance. A smoke chamber may optionally be provided for the detection region 4 and may include the sidewalls 6, but a smoke chamber is not necessary for the integrated smoke detection device.

(9) A polarizing member 7 is arranged adjacent to the detection region 4. The light source 2 can be contiguous with the polarizing member 7, so that the light source 2 emits radiation directly into the polarizing member 7. The polarizing member 7 is configured to have a boundary surface 11 that linearly polarizes a reflected portion d of the radiation a, b emitted by the light source 2, and an exit surface 12 that allows the reflected portion d to exit the polarizing member 7 and to enter the detection region 4. The polarizing member 7 may especially have essentially the shape of a triangular prism or a truncated triangular prism.

(10) The polarizing member 7 may comprise a clear or semitransparent molding compound like epoxy resin, for instance, and may especially be directly molded over the light source 2. Its index of refraction may be typically about 1.5, for example.

(11) A shielding member 8 may optionally be arranged between the light source 2 and the light receiver 3 to shield the light emitted from the light source 2 and prevent stray light from reaching the light receiver 3. The shielding member 8 may be formed by a dark molding compound, for instance, especially the same kind of molding compound that is used for the sidewalls 6.

(12) The embodiment according to FIG. 1 shows an example of a suitable path of the radiation emitted by the light source 2. The radiation is emitted into the polarizing member 7 in a direction pointing away from the carrier 1. If the top surface 10 of the carrier 1 is planar, the direction of an emitted ray a may especially be perpendicular to the top surface 10 of the carrier 1.

(13) Total internal reflection within the polarizing member 7 may be employed to redirect the emitted ray a. To this end, the shape of the polarizing member 7 may be adapted so that the angle of incidence .sub.1 onto the first outer boundary surface of the polarizing member 7 that is reached by the emitted ray a is larger than the critical angle. Consequently, the emitted ray a is totally internally reflected into an internally reflected ray b as shown in FIG. 1. If the critical angle is assumed to be typically about 42 for a clear molding compound at an interface to ambient air, the angle of incidence .sub.1, which is equal to the angle of reflection .sub.1, may be typically 67, for instance.

(14) The shape of the polarizing member 7 is such that the radiation propagating within, either the emitted ray a or the internally reflected ray b as in the embodiment shown in FIG. 1, reaches a boundary surface 11 of the polarizing member 7 at an angle of incidence .sub.B that is smaller than the critical angle. Thus the boundary surface 11 splits the radiation into a refracted portion c and a reflected portion d. The reflected portion d is at least partially polarized.

(15) The refracted portion c is not employed for the detection of smoke and may be absorbed at the sidewall 6.

(16) The polarizing member 7 may especially be configured to yield Brewster's angle of incidence .sub.B at the boundary surface 11, so that a ray of the refracted portion c and a ray of the reflected portion d form an angle of 90, and the reflected portion d is linearly polarized. The right angle between the rays of the refracted portion c and the reflected portion d is indicated in FIG. 1 by an angle curve and a small dot.

(17) Brewster's angle is about 34 at an interface between a dielectric material having a refractive index of about 1.5 and ambient air. The reflected portion d may be sufficiently polarized if the angle of incidence .sub.B is not exactly but at least close to Brewster's angle.

(18) The angle of incidence .sub.B equals the angle of reflection .sub.B. As the detection region 4, which may be filled with ambient air, for instance, has a refractive index that is lower than the refractive index of the polarizing member 7, the angle of refraction .sub.2 may be assumed to be larger than the angle of incidence .sub.B.

(19) The polarized radiation exits the polarizing member 7 at an exit surface 12, from where it propagates into the detection region 4. If smoke 9 has entered the detection region 4 and the exiting ray e reaches the smoke 9, the radiation is scattered by the smoke 9, and scattered rays f, g propagating in different directions are observed.

(20) In FIG. 1 polarization is indicated on the rays with double arrows and circles. The double arrows indicate the presence of a polarization parallel to the plane of the drawing, while the circle indicates the presence of a polarization normal to the plane of the drawing. If .sub.B is Brewster's angle, the ray of the reflected portion d of the radiation is linearly polarized orthogonally to the plane of the drawing, as indicated by the presence of a circle and the absence of a double arrow. The exiting ray e maintains its linear polarization during its further propagation.

(21) The polarization filter 15 is arranged to block the component of polarization that is orthogonal to the plane of the drawing of FIG. 1. Hence radiation that is totally linearly polarized in the orthogonal direction, which is indicated in FIG. 1 by the absence of a double arrow, cannot pass the polarization filter 15 and is thus prevented from reaching the photodiode 13 of the light receiver 3. If the radiation is scattered by smoke 9, the linear polarization is not maintained during scattering, so that the scattered rays f, g comprise components of polarization parallel and orthogonal to the plane of the drawing, as indicated in FIG. 1 by the presence of both circles and double arrows. The depolarized radiation traverses the polarization filter 15 on the light receiver 3, is detected by the photodiode 13, and a signal is triggered accordingly.

(22) By way of example, FIG. 1 shows a scattered ray f that reaches the photodiode 13 through the polarization filter 15 and a further scattered ray g that reaches the photodiode 14 without traversing a polarization filter, thus enabling a differential measurement.

(23) If there is no smoke in the detection region 4, but only water vapor, the polarized radiation will be scattered as well, but its linear polarization is not altered.

(24) Consequently it will be blocked by the polarization filter 15 and cannot be detected by the photodiode 13. Triggering a false alarm in the absence of smoke is thus avoided.

(25) FIG. 2 is a transparent perspective view of the embodiment according to FIG. 1. Elements shown in FIG. 2 that correspond to elements shown in FIG. 1 are designated with the same reference numerals.

(26) The detection mechanism of the integrated smoke detection device does not rely on an accurate alignment of the scattering angle. This enables a short optical path at a relatively large scattering volume and thus a reduction of size. Because of the compact arrangement of the smoke detection device, without smoke chamber, no complex optical elements that require a special manufacturing process are required. The device can easily be tested during the manufacturing process. Further advantages are high reliability, stability against cross-sensing of water droplets, and a reduction of the influence of stray light.