Smoke detector chamber boundary surfaces
Device for optically detecting smoke and implementing thereof. Apparatus and methods for detecting the presence of smoke in a small, long-lasting smoke detector are disclosed. Specifically, the present disclosure shows how to build a very compact housing around the smoke detector while keeping the reflections from the housing structure to a very low value while satisfying all the other peripheral needs of fast response to smoke and preventing ambient light. This allows very small measurements of light scattering of the smoke particles to be reliable in a device resistant to the negative effects of dust. In particular, geometrical optical elements, e.g., cap and optical defection elements, are disclosed.
1 . An apparatus for detecting smoke within a compact footprint detector which propagates light substantially away from a smoke detector chamber, the apparatus comprising:
a cap having an upper surface and a lower surface extending from the upper surface, the lower surface configured to define a part of the smoke detector chamber and having an apex;
a printed circuit board (PCB), the PCB having one or more light emitting devices facing the lower surface of the cap; and
a circular sidewall having an inner surface,
wherein an upper surface of the PCB, the inner surface of the circular sidewall and a lower surface of the cap define a chamber configured to allow light traveling within the chamber to travel unimpeded in a direction parallel to the circular sidewall from the upper surface of the PCB to the lower surface of the cap, and
wherein the lower surface is at least shaped like a paraboloid with an arcuate wall emanating from a common point that forms the apex within the smoke detector chamber, wherein the apex is formed to be a closest point of the arcuate wall to a plane of the PCB.
2 . The apparatus according to claim 1 , wherein the cap comprises a first material.
3 . The apparatus according to claim 2 , wherein the first material has an index of refraction between 1.45 and 1.6.
4 . The apparatus according to claim 3 , wherein the cap comprises a polymer.
5 . The apparatus according to claim 3 , wherein the cap comprises glass.
6 . The apparatus according to claim 2 , wherein the first material is configured to absorb light centered about a first wavelength.
7 . The apparatus according to claim 6 , wherein absorption by the first material of the light centered about the first wavelength has a penetration depth on an order of tens of wavelengths.
8 . The apparatus according to claim 1 , wherein the cap includes an anti-reflective coating applied to at least part of the lower surface.
9 . The apparatus according to claim 8 , wherein the anti-reflective coating is configured to absorb light centered about a first wavelength.
10 . The apparatus according to claim 1 , wherein the lower surface of the cap has a matte finish, at least in part.
11 . The apparatus according to claim 1 , wherein the lower surface of the cap is configured to be highly reflective, at least in part.
12 . The apparatus according to claim 1 , wherein the lower surface of the cap has a parabolic shape as viewed from a cross-section, side view, at least in part.
13 . The apparatus according to claim 1 , wherein the lower surface of the cap has an elliptical shape as viewed from a cross-section, side view, at least in part.
14 . The apparatus according to claim 1 , wherein the cap is configured to mechanically couple to a printed circuit board.
15 . The apparatus according to claim 1 , wherein the arcuate wall terminates at a sidewall.
16 . The apparatus according to claim 1 , wherein the common point defines a center of the cap.
17 . The apparatus according to claim 1 , wherein the one or more light emitting devices are configured to emit light, and wherein the arcuate wall is configured to reflect the light emitted from the one or more light emitting devices in an orthogonal direction that is dependent on parabolic foci.
18 . The apparatus according to claim 1 , wherein the one or more light emitting devices are configured to emit light in a direction perpendicular to the PCB and parallel to an axial center of the cap.
19 . The apparatus according to claim 1 , wherein the lower surface of the cap is configured to receive the light directly from the one or more light emitting devices without intervening reflection.