COMPACT OPTICAL SMOKE DETECTION SYSTEM AND DEVICE

Description

Field of the Disclosure

[0001] The present disclosure relates to smoke detection. More specifically, this disclosure describes apparatus and techniques relating to for detecting smoke within a compact footprint detector which mitigates deleterious effects of dust, thereby increasing longevity and efficacy.Background

[0002] A smoke detector is a device that senses smoke, typically as an indicator of fire. Commercial security devices issue a signal to a fire alarm control panel as part of a fire alarm system, while household smoke detectors, also known as smoke alarms, generally issue a local audible or visual alarm from the detector itself.

[0003] Smoke detectors are housed in plastic enclosures, typically shaped like a disk about 150 millimeters (6 in) in diameter and 25 millimeters (1 in) thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization), detectors may use either, or both, methods. Sensitive alarms can be used to detect, and thus deter, smoking in areas where it is banned. Smoke detectors in large commercial, industrial, and residential buildings are usually powered by a central fire alarm system, which is powered by the building power with a battery backup.

[0004] Domestic smoke detectors range from individual battery-powered units, to several interlinked mains-powered units with battery backup; with these interlinked units, if any unit detects smoke, all trigger even if household power has gone out. Optical smoke detectors tend to be larger in size. And consequently, 90% of domestic smoke detectors using ionization technology.

[0005] While ionization smoke alarms are generally more responsive to flaming fires, photoelectric smoke alarms are generally more responsive to fires that begin with a long period of smoldering (called "smoldering fires"). For each type of smoke alarm, the advantage it provides may be critical to life safety in some fire situations. Home fatal fires, day or night, include a large number of smoldering fires and a large number of flaming fires. One cannot predict the type of fire one may have in a home or when it will occur. Any smoke alarm technology, to be acceptable, must perform acceptably for both types of fires in order to provide early warning of fire at all times of the day or night and whether one is asleep or awake.

[0006] An ionization smoke detector uses a radioisotope, typically americium-241, to ionize air; a difference due to smoke is detected and an alarm is generated. The smoke detector has two ionization chambers, one open to the air, and a reference chamber which does not allow the entry of particles. The radioactive source emits alpha particles into both chambers, which ionizes some air molecules.

[0007] There is a potential difference (voltage) between pairs of electrodes in the chambers; the electrical charge on the ions allows an electric current to flow. The currents in both chambers should be the same as they are equally affected by air pressure, temperature, and the ageing of the source. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm.

[0008] A photoelectric, or optical smoke detector contains a source of infrared, visible, or ultraviolet light (typically an incandescent light bulb or light-emitting diode), a lens, and a photoelectric receiver (typically a photodiode). In spot-type detectors all of these components are arranged inside a chamber where air, which may contain smoke from a nearby fire, flows. In large open areas such as atria and auditoriums, optical beam or projected-beam smoke detectors are used instead of a chamber within the unit: a wall-mounted unit emits a beam of infrared or ultraviolet light which is either received and processed by a separate device, or reflected back to the receiver by a reflector.

[0009] In some types, particularly optical beam types, the light emitted by the light source passes through the air being tested and reaches the photosensor. The received light intensity will be reduced by absorption due to smoke, air-borne dust, or other substances; the circuitry detects the light intensity and generates the alarm if it is below a specified threshold, potentially due to smoke. In other types, typically chamber types, the light is not directed at the sensor, which is not illuminated in the absence of particles. If the air in the chamber contains particles (smoke or dust), the light is scattered and some of it reaches the sensor, triggering the alarm.

[0010] As stated, ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smoldering stage. Fire safety experts and the National Fire Protection Agency recommend installing what are called combination alarms, which are alarms that either detect both heat and smoke, or use both the ionization and photoelectric processes. Combination alarms that include both technologies in a single device are available, with some even including a carbon monoxide detection capability.

[0011] Unfortunately, the size and / or footprint of optical smoke detectors make them impermissible for the vast majority of home use, as well as a large proportion of business use. The inventor of the present disclosure has identified these shortcomings and recognized a need for a more compact, robust optical smoke detector system. That is, an optical smoke detector which is small enough for ubiquitous use while being robust enough for years of long life maintaining a sensitive state.

[0012] This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings. US 4,857,895 discloses a combined obscuration and scattered-light smoke detector which senses a reduced electrical signal in the presence of smoke and an increased electrical signal in the presence of smoke. GB 2397122 A discloses a smoke detector, where detection of a fire depends on correlating signals of two sensors, so as to minimise the response to effects other than aerosols.Summary of the Disclosure

[0013] The invention is defined by the appended claims. According to a first aspect of the invention, an apparatus for detecting smoke is defined in claim 1. According to a second aspect of the invention, a method for detecting smoke is defined in claim 7. Apparatus and methods for detecting smoke within a compact footprint detector which mitigates the deleterious effects of dust, thereby increasing longevity and efficacy 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 comprising opto-isolating structural chamber columns, are disclosed.Brief Description of the Drawings

[0014] For a fuller understanding of the nature and advantages of the present invention, reference is made to the following detailed description and in connection with the accompanying drawings, in which: Figure 1, not forming part of the claimed invention, shows a side view of an exemplary optical smoke detector boundary surface; Figure 2, not forming part of the claimed invention, depicts the top-down view of an exemplary optical smoke detector demonstrative of operation; Figure 3 depicts the top-down view of elements forming an exemplary optical smoke detection device, in accordance with some embodiments of the disclosure provided herein; Figure 4A demonstrates the shortcomings with regard to the state of the art in optical smoke detection devices in operation, in accordance with some embodiments of the disclosure provided herein; Figure 4B demonstrates the overcoming of aforementioned shortcomings with regard to the state of the art in optical smoke detection devices in operation and elements comprised by an exemplary optical smoke detector, in accordance with some embodiments of the disclosure provided herein; Figure 5 depicts the top-down perspective of an optical detection die comprised by an exemplary optical smoke detection device, in accordance with some embodiments of the disclosure provided herein; Figure 6 depicts the side view of an optical detection die comprised by an exemplary optical smoke detection device, in accordance with some embodiments of the disclosure provided herein; Figure 7 graphically illustrates an isometric view of an exemplary optical smoke detection device in operation, in accordance with some embodiments of the disclosure provided herein; Figure 8, not forming part of the claimed invention, depicts a top-down view of elements forming an exemplary optical smoke detection device; Figure 9A, not forming part of the claimed invention, illustrates a side view of an exemplary compact smoke detector cap; Figure 9B, not forming part of the claimed invention, depicts a top-down view of an exemplary compact smoke detector cap; Figure 9C, not forming part of the claimed invention, illustrates an isometric view of an exemplary compact smoke detector cap; Figure 10A, not forming part of the claimed invention, illustrates a side view of an exemplary compact smoke detector cap; Figure 10B, not forming part of the claimed invention, depicts a top-down view of an exemplary compact smoke detector cap Figure 10C, not forming part of the claimed invention, illustrates an isometric view of an exemplary compact smoke detector cap; and, Figure 11, not forming part of the claimed invention, shows a side view of an exemplary optical smoke detector boundary surface. Detailed Description

[0015] The present disclosure relates to smoke detection. More specifically, this disclosure describes apparatus and techniques relating to the optically identification of smoke within a compact and robust detector.

[0016] The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrative examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure are set forth in the proceeding in view of the drawings where applicable.

[0017] Fires can occur in a variety of ways. The two most common forms of fires are slow smoldering fires and fast flaming fires. A smoldering fire is a slow, low-temperature, flameless form of combustion. These fires develop slowly and generate a significant amount of smoke which is easily detected by an optical smoke detector. Smoldering fires are typically initiated on upholstered furniture by weak heat sources such as cigarettes or an electrical short-circuit.

[0018] Fast flaming fires develop rapidly, typically generating black smoke and toxic fumes and leave little time for escape. The characteristic temperature and heat released during smoldering (typically 600° C.) are low compared to those in a fast flaming fire (typically 1500° C.). Fast flaming fires propagate typically about ten times faster than smoldering fires. However, smoldering fires emit a high level of toxic gases such as carbon monoxide. These gases are highly inflammable and could later be ignited in the gas phase, triggering the transition to flaming combustion.

[0019] Smoke detectors for detecting smoke through detection of scattered light by smoke particles have conventionally been proposed and put into practice. Such a smoke detector detects a fire as follows. The smoke detector has a dark chamber for storing a photo emitter and a photo detector. Light emitted from the photo emitter is scattered by smoke particles having flowed into the dark chamber, to thus generate scattered light. The photo detector receives the scattered light.

[0020] Optical type smoke alarms have several systemic and operational disadvantages when compared with ionization type smoke alarms. In recent years, smoke detectors including light traps for inhibiting noise light (light generated by reflection, by an inner wall of the dark chamber, of light having been emitted from the photo emitter) from reaching the photo detector have been proposed.

[0021] There are in general two types of noise light one caused by unwanted reflections from nearby surfaces of the light emitted from the photo emitter and other ambient light that leaks into the smoke chamber. Both of these lights need to be avoided since there is no way for the photodetector to decide whether light is caused by reflection or from scattering or from the ambient. When such a smoke detector is adopted, one must design the optical and electrical system to avoid false triggering by noise light. The inventors of the present disclosure have recognized how to improve on both fronts while reducing the size, cost, and adding to the aesthetics.

[0022] However, in such a smoke detector, the light trap is disposed in front of the photo emitter and the photo detector. Therefore, light emitted from the photo emitter is reflected in a direction parallel to a virtual plane including an optical axis of the photo emitter and that of the photo detector. Accordingly, since noise light is easily incident to a light detecting region, occurrence of a false alarm remains highly possible.

[0023] Some smoke detectors employ a labyrinth structure for inhibiting light from entering the dark chamber. Since light emitted from the photo emitter is reflected by edge sections of wall members constituting the labyrinth structure, irregular noise light of an amount that cannot be sufficiently attenuated by the light trap is generated. Therefore, the noise light may enter the light detecting region, to thus cause a false alarm.

[0024] In addition, within these type of smoke detectors, a plurality of light traps must be disposed and, a light trap must be disposed inside the labyrinth structure within the dark chamber. Accordingly, either case requires a large space for disposing the light trap, whereby miniaturization of the smoke detector has encountered difficulty. Also, some smoke detectors include another member such as a lens in addition to the light trap, whereby the cost for manufacturing the smoke detector may be increased. Furthermore, the light trap and / or the lens may inhibit smoke from flowing into the dark chamber.

[0025] In addition to larger footprint, relative to ionization alarms, optical detection devices suffer from confirmation during the course of their service. Both optical smoke alarms which use an infra-red emitter LED and ionization type smoke alarms are used in the detection of both types of fires and rely upon a flux of ambient air passing through them. In some devices (as in one or more of the foregoing embodiments), fans are employed to facilitate the passage of air through them. However, dust and particulate matter can collect and contaminate some of their device elements. These surfaces become more reflective in all directions so that any light falling on these surfaces can now be scattered into the photodetector in a manner similar to the smoke.

[0026] Still, optical detection systems are favored over ionization type systems in certain circumstances. For example, optical systems better detect smoldering fires. Additionally, ionization alarms have the disadvantage that, as they contain radioactive isotopes in their sensors, they are subject to regulations concerning their manufacture and disposal. These regulations depend upon the country but can place a considerable burden on the manufacturer.

[0027] Optical smoke detectors tend to be large, expensive devices which degrade with age from, contamination, giving off false positives. The inventor of the present disclosure has recognized the need for a more robust optical smoke detector, which is on the size order with that of the ubiquitous household ionization unit and is relatively insensitive to the threat of dust and other particulate contamination. Furthermore, the optical surfaces within the chamber itself play an important part to this this end.

[0028] Figure 1, not forming part of the claimed invention, shows a side view of exemplary optical smoke detector boundary surfaces. Smoke detector cap 100 comprises lower boundary 110, circular sidewall 130, upper boundary 120, axial center 160, and geometric surfaces 140, 150.

[0029] To note, Figure 1 depicts a side view of smoke detector cap 100 which is round in shape, while viewing from the top down. So, strictly speaking geometric surfaces 140, 150 are the same surface. They are, however, labeled differently for the purposes of elucidation with respect to photons 165, 175. This will be discussed in greater detail later in the disclosure.

[0030] In one or more examples not forming part of the claimed invention, smoke detector cap 100 functions to reflect and / or absorb light such that light in the smoke detector chamber is largely scattered off of particles, e.g., smoke, etc., and back into the smoke detector system. This is also discussed in greater detail later in the disclosure. Lower boundary 110 can represent the printed circuited board (PCB) or wafer die. For the purposes of discussion, light from one or more light emitting devices are emitted from this surface direction.

[0031] Circular sidewall 130 comprises a substantial cylindrical boundary which either keeps ambient light out or prevents light existing in the chamber to not get redirect back down to lower boundary 110. Again, this premised will be described later. Upper boundary 120 represents to the top of the smoke detector cap 100. Given that smoke detector cap is substantially unchanging in the radial direction, axial center 160 is used to denote the center thereof.

[0032] Operationally, in some examples, light rays (photons 165, 175) are emitted from light emitting device which propagate up through the smoke detector chamber. Light rays are incident upon smoke particles (not shown) and, consequently, get scattered. Scattered light rays propagate back down toward lower boundary surface toward one or more photodetectors. Photodetectors receives nominal light from background in addition to scattered light.

[0033] Geometric surfaces 150, 140 serve to, in one or more examples not forming part of the claimed invention, reflect light emitting from lower boundary 110 away from same. That is, light not being scattered by particulate matter should be mitigated in order to maximize signal to noise (SnR) ratio. For example, in the non claimed example, geometric surfaces 150, 140 have a parabolic (strictly speaking, a paraboloid in 3-d) shape. As such, light emitted from lower boundary 110 will largely get reflected in a substantially orthogonal direction, depending on parabolic foci.

[0034] For example, light ray / photon 165 is incident upon geometric shape 150. Due to its direction and angle of incident on geometric shape, 150, light ray photon 165 is reflected away from lower boundary 110 represented by light ray / photon 170. Similar, light ray / photon 175 is incident upon geometric shape 140. Due to its direction and angle of incident on geometric shape, 140, light ray photon 175 is reflected away from lower boundary 110 represented by light ray / photon 180.

[0035] Predetermined thresholds, background subtraction and other operational parameters will be discussed in more detail later in the disclosure, which will be appreciated by one skilled in the art.

[0036] Figure 2, not forming part of the claimed invention, depicts the top-down view of an exemplary optical smoke detector 200 demonstrative of operation, . Optical smoke detector 200 comprises light emitting diode (LED) 230, optical chamber 210, detector cover 220, case molding 280, photodiode / transducer 250 and optical deflection fins 290.

[0037] In one or more non claimed examples, LED 260 is an off-the-shelf green (495nm - 570nm) light emitting diode. However, any suitable, compact light producing device is not beyond the scope of the present disclosure-whether coherent, incandescent, or even thermal black-body radiation, etc.

[0038] Case molding 290 is a substrate in some non claimed examples providing structure to for attaching detector cover 220 and optical chamber 210 thereto. Typically, it is an object of optical smoke detectors to allow the ingress of smoke from the surrounding air / environment while rejecting the ambient light emanating from same. Generally speaking, detector cover 220 and optical chamber 210 attempt to serve these purposes.

[0039] That is, detector cover 220 has two ports (e.g., ingress and egress) for gas / smoke passage, while optical chamber 210 substantially surrounds the detector interior preventing most ambient light to enter. Detector cover 220 and optical chamber 210 are made of an opaque polymer and / or lossy material having a thickness much greater than the average skin depth, according to some non claimed examples. High conductivity (mirrored) or any other suitable material, e.g., metal, semi-metallic, composite, are also not beyond the scope of these non claimed examples.

[0040] Photodetector 250 is a sensor of light or other electromagnetic energy. Photodetector 250 has p-n junctions that converts light photons into current. The absorbed photons make electron-hole pairs in the depletion region, which is used to detect received light intensity. In some non claimed examples, photodetector 250 are photodiodes or phototransistors. However, any light detecting means, e.g., avalanche, photo-multiplier tube, etc. is not beyond the scope of the present disclosure.

[0041] In operation, light 240 is emitted from LED 260. As can be appreciated by on skilled in art, some of light 240 gets scattered off of smoke particles 270. Scattered light 260 can rescatter or is directed to and therefore detected by photodetector 250. Light 240 which is not scattered by smoke particles 270 are either blocked by a blocking member to prevent direct illumination of photodetector 250 or are incident upon and redirected by optical defector fins 290. Optical deflector fins 290 typically have a black, matt finish whose purpose is to redirect light into other optical deflector fins 290.

[0042] Figure 3 depicts the top-down view of elements forming an exemplary optical smoke detection device 300, in accordance with the invention provided herein. In the embodiments, substrate 310 comprises an analog front-end (AFE), photodetector, and light source which will be discussed in greater detail later in the disclosure.

[0043] The opto-isolating structural chamber columns 320 are made from a material that absorbs the light in its bulk. Furthermore, the elements are smooth and have mirror like finish instead of matte finish. A bulk absorption material is such that absorption depth > 10's of wavelengths of light. Thus, the real part of refractive index remains very close to the same as the non-absorbing material.

[0044] According to the invention opto-isolating structural chamber columns 320 comprise a polymer. Most plastics to have index near 1.45-1.6. This can yield a reflectance R ~ 3% from Fresnel equations and smooth surfaces reflect light in a specular fashion, as calculated in the following: where, B 1 COS COS B 1 COS ft + ≫ 2 COS ft ≫ 1 COS ft − ≫ 2 1 − n 1 n 2 sin θ i 2 ≫ 1 COS ft + 1 − n 1 n 2 sin θ i 2 and, 1 − ≫ 2 COS ft n 1 1 − n 1 n 2 sin θ i 2 + n 2 cos θ i Bl COS ft - «a C ®< ft »1 COS ft + «2 COS ft

[0092] Thus, most of the light incident is absorbed inside the material of the optoisolating stnictural chamber columns and even the part that is reflected, very little is back- scattered.

[0045] Figure 4A demonstrates the shortcomings with regard to the state of the art in optical smoke detection devices 400 in operation, in accordance with some embodiments of the disclosure provided herein. Given that smoke detectors are expected to last 10 or more years, it is an object of the present disclosure to present a robust, long-lasting optical smoke detector.

[0046] Given the constant air flux throughout a smoke detector, one of ordinary skill will appreciate the debilitating properties of dust accumulation which will now be discussed in detail with respect to figures 4A and 4B. Dust particle 420 adsorbs to optoisolating structural chamber columns 410. Incident light ray 430 can be from either ambient, background lighting or from a smoke detector's internal light source. For the purposes of illustration, the present depiction represents a simplification for clarity. That is, we assume light ray 430 is entirely transmitted into dust particle 420.

[0047] Incident light ray 430 is transmitted into dust particle 420 becoming light ray 440. When light ray 440 is incident upon opto-isolating structural chamber columns 410, its energy (or vector magnitude) gets decomposed pursuant to Fresnel equations for transmission and reflectance. This is due to an impedance mismatch between the dust and the opto-isolating structural chamber columns 410. Consequently, light ray(s) 450 get reflected and light ray 460 is transmitted into opto-isolating structural chamber columns 410. Additionally, the inventor of the present disclosure notes that light is also scattered if a rough surface, such as matte, is used on opto-isolating structural chamber columns 410, which is also depicted in figure 4A.

[0048] Figure 4B demonstrates the overcoming of aforementioned shortcomings with regard to the state of the art in optical smoke detection devices in operation and elements comprised by an exemplary optical smoke detector 400, in accordance with some embodiments of the disclosure provided herein. Dust particle 420 adsorbs to opto-isolating structural chamber columns 410. Incident light ray 430 can be from either ambient, background lighting or from a smoke detector's internal light source. Again, for the purposes of illustration, the present depiction represents a simplification for clarity. That is, we assume light ray 430 is entirely transmitted into dust particle 420.

[0049] Incident light ray 430 is transmitted into dust particle 420 becoming light ray 440. When light ray 440 is incident upon opto-isolating structural chamber columns 410, its energy (or vector magnitude) normally gets decomposed pursuant to Fresnel equations for transmission and reflectance. However, in one or more embodiment of the present disclosure, the real part of the complex impedance (or refractive index) of opto-isolating structural chamber columns 410 is matched to common dust 420. Therefore, light ray 440 is transmitted into opto-isolating structural chamber columns 410 in almost its entirety. Most dust particles have refractive index between 1.35 and 1.55 while most plastics and glass have indices between 1.45 to 1.55.

[0050] According to the invention, the imaginary part of the complex impedance of opto-isolating structural chamber columns 410 is chosen such that the material is very lossy, such that, the penetration depth is on the order of tens of wavelengths. If the penetration depth were shorter, than the impedance mismatch becomes large and again the substrate begins to reflect the ray 440. If the absorption depth is too large, then thick members are needed to absorb the light and thus increasing the overall size of the chamber. This is exemplified in the decaying light wave 470 in figure 4B. Additionally, the inventor of the present disclosure presents a smooth, specular finish to the surface of opto-isolating structural chamber columns 410 in a preferred embodiment.

[0051] Figure 5 depicts the top-down perspective of an optical detection die comprised by an exemplary optical smoke detection device 500, in accordance with some embodiments of the disclosure provided herein. Optical smoke detection device 500 comprises substrate 590, light emitting diodes (LED) 560, 565, LED cover 520, analog front end (AFE) 540, photodetector (PD1) 550, photodetector (PD2) 530, photodetector cover 570, PD pin-out 575, and AFE pin-out 585.

[0052] Substrate 590 is a die manufactured from Silicon on Chip (SoC) fabrication processes which are known in the art, however any suitable support structure is not beyond the scope of the present disclosure. For example, substrate 590 can be made from any metal, semi-metallic, semiconductor, mixture / compound or polymer, provided caution is taken to ensure the AFE 540 is not shorted.

[0053] Light blocking members run along the perimeter of the upper substrate 590. Their function is to block ambient light from being received by photodetectors 530, 550. As such, ambient light blocking members are made from an opaque polymer and / or lossy material having a thickness much greater than the average skin depth, according to some embodiments of the present invention. High conductivity (mirrored) are also not beyond the scope of the present disclosure.

[0054] Similarly, opto-isolator traverses the entire span between the LEDs 560, 565 side and the photodetectors 530, 550 side of the device, which will be explained in greater detail later in the disclosure. The function of the opto-isolator is to block LEDs 560, 565 light from being directly received by photodetectors 530, 550. As such, opto-isolator is made from an opaque polymer and / or lossy material having a thickness much greater than the average skin depth, according to some embodiments of the present invention. High conductivity (mirrored) are also not beyond the scope of the present disclosure, however, this is not a preferred embodiment as will be clear later in the disclosure.

[0055] Photodetector cover 570 and LED cover 520 are transparent polymer protective encasements of photodetectors 530, 550 and LEDs 560, 565, respectively. In other embodiments, photodetector cover 570 and LED covers are crystalline (glass, Pyrex, etc.), although any suitable can be used.

[0056] In one or more embodiments, LEDs 560, 565 are an off-the-shelf red and near-infrared (450nm~" 1400nm) light emitting diode. However, any suitable, compact light producing device of any color is not beyond the scope of the present disclosure. In some embodiments where LEDs, 560, 565 emit different wavelengths, photodetector (PD1) 550 and photodetector (PD2) 530 can be modified to accommodate the detection thereof. For example, half of photodetector (PD1) 550 and photodetector (PD2) 530 can be covered with different optical filters.

[0057] In particular, photodetector (PD1) 550 and photodetector (PD2) 530 can be covered with dichroic filters, at least in part. A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color(s) of light that they reflect, rather than the color(s) they pass.

[0058] While dichroic filters are used in the present embodiment, other optical filters are not beyond the scope of the present invention, such as, interference, absorption, diffraction, grating, Fabry-Perot, etc. An interference filter consists of multiple thin layers of dielectric material having different refractive indices. There also may be metallic layers. In its broadest meaning, interference filters comprise also etalons that could be implemented as tunable interference filters. Interference filters are wavelength-selective by virtu e of the interference effects that take place between the incident and reflected waves at the thin-film boundaries.

[0059] In other embodiments, a plurality of detectors is implemented, e.g., at least two for wavelength such that each of the pair of the plurality is wavelength specific. For example, there are at least two detectors (PDI, PD2) for every light emitting diode for a particular lambda.

[0060] Analog front-end 540 (AFE) is a set of analog signal conditioning circuitry that uses sensitive analog amplifiers., operational amplifiers, filters, and application-specific integrated circuits as needed to interface with sensors to analog to digital converter and / or microcontroller.

[0061] AFE 540 is in electrical communication with photodetectors 530, 550 through PD pin-outs 575. PD pin-outs 575 electrically communicate with photodetectors 530, 550 through traces. In the present embodiment, photodetectors 530, 550 and AFE 540 are packed as dies with soldered pin-outs. However, in other embodiments, they are integrated at the wafer level communicating through traces and vertical interconnect access (VIA) or through silicon VIA (TSV).

[0062] In some embodiments, AFE pin-out 585 is electrical communication with pulse oximeter 100. In other embodiments, AFE pin-out 585 can be in electrical communication with a microcontroller unit (MCU), field programmable gate array (FPGA), bus, or other computer platform, such as, Arduino or Raspberry Pi, etc.-all of which are not beyond the scope of the present disclosure.

[0063] Figure 6 depicts the side view of an optical detection die 600 comprised by an exemplary optical smoke detection device, in accordance with some embodiments of the disclosure provided herein. Optical detection dies 600 comprises ambient light blocking members 610, opto-isolator 680, substrate 690, light emitting diode (LED) 660, LED cover 620, analog front end (AFE) 640, photodetector (PD1) 650, photodetector (PD2) 630, and photodetector cover 670.

[0064] In one or more embodiments, substrate 690 is a die manufactured from Silicon on Chip (SoC) fabrication processes which are known in the art, however any suitable support structure is not beyond the scope of the present disclosure. For example, substrate 690 can be made from any metal, semi-metallic, semiconductor, mixture / compound or polymer, provided caution is taken to ensure the AFE 640 is not shorted.

[0065] Ambient light blocking members 610 run along the perimeter of the upper substrate 690. Their function is to block ambient light from being received by photodetectors 630, 650. As such, ambient light blocking members 610 are made from an opaque polymer and / or lossy material having a thickness much greater than the average skin depth, according to some embodiments examples of the present invention. High conductivity (mirrored) are also not beyond the scope of the present disclosure.

[0066] Similarly, opto-isolator 680 traverses the entire span between the LED 660 side and the photodetectors 630, 650 side of the device, which will be explained in greater detail later in the disclosure. The function of the opto-isolator 680 is to block LED 660 light from being directly received by photodetectors 630, 650. As such, opto-isolator 680 are made from an opaque polymer and / or lossy material having a thickness much greater than the average skin depth, according to some examples of the present invention. High conductivity (mirrored) are also not beyond the scope of the present disclosure, however, this is not a preferred example as will be clear later in the disclosure.

[0067] LED 660 is an off-the-shelf green (495nm - 570nm) light emitting diode. However, any suitable, compact light producing device is not beyond the scope of the present disclosure-whether coherent, incandescent, or even thermal black-body radiation, etc. LED cover 630 is a transparent polymer protective encasement of LED 260. In other examples, LED cover 630 is crystalline (glass, Pyrex, etc.), although any suitable can be used. While translucent and / or lossy materials may be used within the scope of the present disclosure, these are not preferred examples, which will be made more apparent later in the disclosure.

[0068] Photodetectors 650, 630 (PDI, PD2, respectively) are sensors of light or other electromagnetic energy. Photodetector 630, 650 have p-n junctions that converts light photons into current. The absorbed photons make electron-hole pairs in the depletion region, which is used to detect received light intensity. In some examples, photodetectors 650, 630 are photodiodes or pho to transistors. However, any light detecting means, e.g., avalanche, photo-multiplier tube, etc. is not beyond the scope of the present disclosure.

[0069] Analog front-end 640 (AFE or analog front-end controller AFEC) is a set of analog signal conditioning circuitry that uses sensitive analog amplifiers, often operational amplifiers, filters, and sometimes application-specific integrated circuits for sensors, radio receivers, and other circuits to provide a configurable and flexible electronics functional block, needed to interface a variety of sensors to an, antenna, analog to digital converter or in some cases to a microcontroller. AFE 640 is in electrical communication with photodetectors 650, 630 and optical smoke detector.

[0070] Photodetector cover 670 is a transparent polymer protective encasement of PD1 and PD2. In other examples, photodetector cover 670 is crystalline (glass, Pyrex, etc.), although any suitable can be used. While translucent and / or lossy materials may be used within the scope of the present disclosure.

[0071] Figure 7 graphically illustrates an isometric view of an exemplary optical smoke detection device 700 in operation, in accordance with an embodiment of the claimed invention. The inventors of the present disclosure have built one of the smallest smoke detectors 700 which only needs a very small chamber around the detector to protect it from insects, ambient light, and large particulate matter.

[0072] Heretofore in the art, large housings are used to prevent light scattering from dust build-up over time. Light scattered from the housing elements can prevent detection of small changes in light scattering from the smoke particles hindering the performance of these sensor systems. Thus, housing or chamber design plays acriticai role. It must also allow for easy exchange of smoke from the surroundings and thus have fairly large openings.

[0073] This 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.

[0074] Optical smoke detection device 700 comprises base 750, die substrate 710, side enclosure 730, opto-isolating structural chamber columns 720, and upper reflecting surface 740. In one or more embodiments, base 750 which may consist of PCB or ways to carry all the electronics and provide means of attachment, opto-isolating structural chamber columns 720 and die substrate 710 are in accordance with those described in association with figures 2, 3, 5, and 6. Side enclosure 730 can serve two purposes. That is, side enclosure 730 block the entrance of ambient while directing air through the optical smoke detection device 700 passage.

[0075] Upper reflecting surface 740 is constructed similar to the side structures and uses the same design idea. That the light incident from the photo emitter directly impinging on this surface should be minimally reflected / scatteredback from the surface of this structure. This is achieved using a highly corrugated or curved surface so that no direct reflection from this surface is directed towards the photo detector elements. The light is reflected towards other surfaces in the chamber. As described earlier for Fig 4b, the light incident on the surface is mostly absorbed in the bulk of the material. A small amount of roughly 3% that is reflected is directed towards another surface either on the upper reflecting or any of the side surfaces, where the process repeats. Thus, very small amount of light is returned to the photodetector.

[0076] It is noted that upper reflecting surface may be anti-reflection coated for better absorption in the bulk but in practice it may not be necessary. This is because, the light may be incident from many angles to the surface especially if the top reflecting surface is corrugated or curved in a complex fashion. Also, after collection of dust on the surface, the surface may not act like anti-reflective.

[0077] In operation, light ray from light cone 760 are directed in an upward manner. Rays that do return to the detector have bounced many times from the various members and have lost most of the energy. Ray trace shows how the rays have very low probability of returning to the detector.

[0078] Opto-isolating structural chamber columns 720, 740 comprise absorbing rods of plastic. For example, opto-isolating structural chamber columns 720 comprise acrylic, PMMA, polycarbonate, etc. However, any suitable material can be used, e.g., with a properly match index of refraction and complex impedance.

[0079] The design shown in Fig. 7 allows one to measure the light scattered off the smoke particles back towards the photodetector while the optical structures are designed to reduce noise light to a very low level. Furthermore, these optical structures can be placed very close to each other and to the light generation and detection apparatus making for a very compact structure. This structure reduces (1) noise light from the light emitter, (2) noise light from the ambient, and (3) provides for a compact measurement with a single module such as those shown in Fig 5 and 6.

[0080] Figure 8, not forming part of the claimed invention, depicts the top-down view of another design of elements forming an exemplary optical smoke detection device 800. In one or more non claimed examples, substrate 810 comprises an analog front-end (AFE), photodetector, and light source in accordance with the previous examples. Furthermore, similar upper reflecting structures such as 740 can be used.

[0081] Optical smoke detection device 800 comprises ingress port 850, egress port 860 and ionization smoke detector 840, according to some non claimed examples. Ports 850, 860 allow for an air path to travel through optical smoke detection device 800. In alternate non claimed examples ingress port 850 and egress port 860 comprise small low power fans to facilitate this passing of gas.

[0082] An ionization smoke detector 840 uses a radioisotope, typically americium-241, to ionize air; a difference due to smoke is detected and an alarm is generated. Ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smoldering stage.

[0083] The smoke detector has two ionization chambers 840, 880, one open to the air (840), and a reference chamber (880) which does not allow the entry of particles. The radioactive source emits alpha particles into both chambers, which ionizes some air molecules. There is a potential difference (voltage) between pairs of electrodes in the chambers; the electrical charge on the ions allows an electric current to flow.

[0084] The currents in both chambers should be the same as they are equally affected by air pressure, temperature, and the ageing of the source. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm.

[0085] In some non claimed examples, the opto-isolating structural chamber deflectors 820 are made from a material that absorbs the light in its bulk. Furthermore, the elements are smooth and have mirror like finish instead of matte finish. A bulk absorption material is such that absorption depth > 10's of wavelengths of light. Thus, the real part of refractive index remains very close to the same as the non-absorbing material.

[0086] In some non claimed examples, opto-isolating structural chamber deflectors 820 substantially comprise three-dimensional orthotopes, right rectangular prisms, rectangular cuboids, or rectangular parallelepipeds. In one more example, opto-isolating structural chamber deflectors 820 are substantially rounded on one surface or may have knife edge. Note that this applies to the upper reflecting surface 740 too. The purpose of opto-isolating structural chamber deflectors 820 is to direct reflected light into another opto-isolating structural chamber deflectors 820, which can be appreciated by one of ordinary skill in the art. Thus, most of the light incident is absorbed inside the material and even the part that is reflected, very little is back-scattered.

[0087] Most dust particles have index of glass and are between 1.4-1.7. Opto-isolating structural chamber deflectors 820 are index matched and produce lower scattering compared to the same particle attached to a surface of a very different refractive index. All forward scattering from these particles is also absorbed by their substrate. Again, this leads to very low back-scattering from the dust build-up over time.

[0088] Members of the chamber, i.e., opto-isolating structural chamber deflectors 820, are aligned to reflect light away from the source and towards other members of the chamber. Thus, the light is extinguished extremely rapidly. After n reflections, the reflected light is reduced to R n< and is rapidly removed. This makes for very compact design: less than a 1 cm in radius from the center where the smoke sensor is and < 1 cm in height.

[0089] Figure 9A, not forming part of the claimed invention, illustrates a side view of an exemplary compact smoke detector cap. Smoke detector cap 900 comprises upper boundary 910 and optical deflector fins 920.

[0090] Figure 9B, not forming part of the claimed invention, depicts a top-down view of an exemplary compact smoke detector cap. Smoke detector cap 900 comprises geometric space 940 and optical deflector fins 920. In one or more non claimed examples, geometric shape 940 can be any parabolic or elliptical shape. In other non claimed examples, it can be variegated or even linear.

[0091] Figure 9C, not forming part of the claimed invention, illustrates an isometric view of an exemplary compact smoke detector cap. Smoke detector cap 900 comprises geometric shape 940 and optical deflector fins 920.

[0092] In some non claimed examples, the opto-isolating structural chamber optical deflector fins 920 are made from a material that absorbs the light in its bulk. Furthermore, the elements are smooth and have mirror like finish instead of matte finish. A bulk absorption material is such that absorption depth > 10's of wavelengths of light. Thus, the real part of refractive index remains very close to the same as the non-absorbing material.

[0093] In some non claimed examples, opto-isolating structural chamber optical deflector fins 920 comprise a polymer or glass. Most plastics and glasses to have index near 1.45-1.6. This can yield a reflectance R ~ 3% from Fresnel equations and smooth surfaces reflect light in a specular fashion, as calculated in the following: R^ (R s+ R v ) where, ≫ 1 COS − ≪ 2 COS ≫ 1 COS ft + ≫ 2 cos ft Bi COS ft − ≫ 2 1 − n 1 n 2 sinθ i 2 ≫ ! COS ft + ≫ J 1 − n 1 n 2 sinθ i 2 and, ≫ 1 COS Ot − ≪ 2 cos Rj COS + fig COS 2 = n 1 1 − n 1 n 2 sin θ i 2 − n 2 cos θ i n 1 1 − n 1 n 2 sin θ i 2 + n 2 cos θ i 2 .

[0094] Thus, most of the light incident is absorbed inside the material of the optoisolating structural chamber columns and even the part that is reflected, very little is back- scattered.

[0095] Figure 10A, not forming part of the claimed invention, illustrates a side view of an exemplary compact smoke detector cap. Smoke detector cap 1000 comprises upper boundary 1010, axial center 1060, center packaging pins 1040 and outer packaging pins 1070. Axial center packaging pins 1040 and outer packaging pins 1070 allow for convenient

[0096] Figure 10B, not forming part of the claimed invention, depicts a top-down view of an exemplary compact smoke detector cap. Smoke detector cap 1000 comprises geometric space 1040 and optical deflector fins 1020. In one or more non claimed examples, geometric shape 1040 can be any parabolic or elliptical shape. In other non claimed examples, it can be variegated or even linear. Outer boundary 1030 represent the physical circular cap of the construction.

[0097] Figure 10C, not forming part of the claimed invention, illustrates an isometric view of an exemplary compact smoke detector cap. Smoke detector cap 1000 comprises physical circular cap 1010 of the construction 1080 and optical deflector fins 1020.

[0098] Figure 11, not forming part of the claimed invention, shows a side view of an exemplary optical smoke detector boundary surface. Smoke detector cap 1100 comprises lower boundary 1110, circular sidewall 1130, upper boundary 120, axial center 1160, and geometric surfaces 1140, 1150.

[0099] To note, Figure 11 depicts a side view of smoke detector cap 1100 which is round in shape, while viewing from the top down. So, strictly speaking geometric surfaces 1140, 1150 are the same surface. They are, however, labeled differently for the purposes of elucidation with respect to photons 1165, 1175.

[0100] In one or more non claimed examples, smoke detector cap 1100 functions to reflect and / or absorb light such that light in the smoke detector chamber is largely scattered off of particles, e.g., smoke, etc., and back into the smoke detector system. Lower boundary 1110 can represent the printed circuited board (PCB) or wafer die. For the purposes of discussion, light from one or more light emitting devices are emitted from this surface direction.

[0101] Circular sidewall 1130 comprises a substantial cylindrical boundary which either keeps ambient light out or prevents light existing in the chamber to not get redirect back down to lower boundary 1110. Again, this premised will be described later. Upper boundary 1120 represents to the top of the smoke detector cap 1100. Given that smoke detector cap is substantially unchanging in the radial direction, axial center 1160 is used to denote the center thereof.

[0102] Operationally, in some non claimed examples, light rays (photons 1165, 1175) are emitted from light emitting device which propagate up through the smoke detector chamber. Light rays are incident upon smoke particles (not shown) and, consequently, get scattered. Scattered light rays propagate back down toward lower boundary surface toward one or more photodetectors. Photodetectors receives nominal light from background in addition to scattered light.

[0103] Geometric surfaces 1150, 1140 serve to, in one or more non claimed examples, reflect light emitting from lower boundary 1110 away from same. That is, light not being scattered by particulate matter should be mitigated in order to maximize signal to noise (SnR) ratio. For example, in the present embodiment, geometric surfaces 1150, 1140 have a parabolic (strictly speaking, a paraboloid in 3-d) shape. As such, light emitted from lower boundary 110 will largely get reflected in a substantially orthogonal direction, depending on parabolic foci.

[0104] For example, light ray / photon 1165 is incident upon geometric shape 1150. Due to its direction and angle of incident on geometric shape, 1150, light ray photon 165 is reflected away from lower boundary 1110 represented by light ray / photon 1170. similarly, light ray / photon 1175 is incident upon geometric shape 1140. Due to its direction and angle of incident on geometric shape, 1140, light ray photon 1165 is reflected away from lower boundary 1110 represented by light ray / photon 117.

[0105] In one or more non claimed examples, an additional antireflective coating 1180 is included. An antireflective or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses and other optical elements to reduce reflection. In typical imaging systems, this improves the efficiency since less light is lost due to reflection. This coating is not exclusive to the top cap but can be applied to anti-reflective fins as previously described.

[0106] Many coatings consist of transparent thin film structures with alternating layers of contrasting refractive index. Layer thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams. This makes the structure's performance change with wavelength and incident angle, so that color effects often appear at oblique angles.

[0107] In one more non claimed examples, the geometric shape is that of a parabola. A parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits any of several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. More specifically, as in the present non claimed example depicted in Figure 11, a half parabola is implements. That is, sqrt(r), which is turned about the axial center 1160.

[0108] One description of a parabola involves a point (the focus) and a line (the directrix). The focus does not lie on the directrix. The parabola is the locus of points in that plane that are equidistant from both the directrix and the focus. Another description of a parabola is as a conic section, created from the intersection of a right circular conical surface and a plane which is parallel to another plane that is tangential to the conical surface.

[0109] In other non claimed examples, the geometric shape is an ellipse, at least in part. An ellipse is a curve in a plane surrounding two focal points such that the sum of the distances to the two focal points is constant for every point on the curve. As such, it is a generalization of a circle, which is a special type of an ellipse having both focal points at the same location. The shape of an ellipse (how "elongated" it is) is represented by its eccentricity, which for an ellipse can be any number from 0 (the limiting case of a circle) to arbitrarily close to but less than 1.

[0110] Ellipses are the closed type of conic section: a plane curve resulting from the intersection of a cone by a plane (see figure to the right). Ellipses have many similarities with the other two forms of conic sections: parabolas and hyperbolas, both of which are open and unbounded. The cross section of a cylinder is an ellipse, unless the section is parallel to the axis of the cylinder.

[0111] However, any conic section is not beyond the scope of the non claimed examples.

[0112] The present disclosure gives rise to a total attenuation from the LED to the detector of the order of 10' 6< . This has been achieved by design in simulations and by construction.

[0113] The inventors of the present disclosure also exploit the notion these scattering characteristics can be wavelength dependent. Thus, an analysis and / or comparison of different wavelength, lambdas, and / or ratio of PD1 / PD2 maybe wavelength dependent and useful in detection of numerous particulate matters.

[0114] Other means, systems and devices are not beyond the scope of the present invention. For example, a plurality of 3 or more photodetectors could be used to further interpolate and extrapolate characteristic signals of materials. Additionally, alternate LED / photodetector dispositions and geometries can be used.

[0115] In reference to the scattering theory of light, the inventors' observations and models closely conform, is consistent with and reflect this well-known theory, known to those in the art. As such, the observations that follow stem from an underlying physics and thus more general than any particular device enumerated in several of the embodiments.

[0116] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that the scope of the invention is defined by the appended claims.

[0117] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[0118] The phrase "and / or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and / or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined.

[0119] As used herein, the term "between" is to be inclusive unless indicated otherwise. For example, "between A and B" includes A and B unless indicated otherwise.

[0120] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0121] In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of' and "consisting essentially of' shall be closed or semi-closed transitional phrases, respectively.

[0122] The present invention should therefore not be considered limited to the particular embodiments described above, and is defined by the appended claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable, will be readily apparent to those skilled in the art to which the present invention is directed upon review of the present disclosure.

Claims

1. An apparatus (700) for detecting smoke within a compact footprint detector which mitigates deleterious effects of dust, thereby increasing longevity and efficacy, the apparatus comprising: a substrate (710), the substrate comprising: a first light source (660); a first photodetector (650) disposed substantially proximal to the first light source (660), wherein the first light source (660) and the first photodetector (650) are located on the substrate (750); an analog front-end in electrical communication with the first photodetector (650); non-volatile logic for performing: receiving a first signal from the first photodetector (650); and, determining the presence of smoke at least based on the first received signal; and a plurality of opto-isolating structural chamber columns (720) having a refractive index matched to that of common dust, wherein common dust comprises particles having a refractive index between 1.35 to 1.55, wherein each column of the plurality of opto-isolating structural chamber columns (720) is lossy and causes most of the light incident on the surface of the column (720) to be absorbed in the bulk of the column (720), and wherein each column of the plurality of opto-isolating structural chamber columns (720) has a penetration depth on the order of tens of wavelengths of light, wherein the opto-isolating structural chamber columns (720) are absorbing rods of plastic, and wherein the opto-isolating structural chamber columns (720) are located around the perimeter of the substrate (750) so as to prevent ambient light from outside the apparatus (700) from being received by the first photodetector (650).

2. The apparatus (700) of claim 1, wherein the surface of each column of the plurality of opto-isolating structural chamber columns (720) comprises a smooth, specular finish.

3. The apparatus (700) of any preceding claim, wherein each column of the plurality of opto-isolating structural chamber columns (720) comprises a polymer having a refractive index between 1.45 and 1.55.

4. The apparatus (700) of any preceding claim, wherein the received first signal is based on scattering and is correlated to an amount of particulate matter present in the apparatus (700).

5. The apparatus (700) of claim 4, wherein the plurality of opto-isolating structural chamber columns (720) reduce noise light caused by ambient light and reflections of the light emitted from the first light source (660), by absorbing the noise light in the bulk of the opto-isolating structural chamber columns (720), such that the received first signal is representative of an amount of smoke in the apparatus (700).

6. The apparatus (700) of any preceding claim, further comprising a substantially opaque barrier (680) located on the substrate (710) between the first light source (660) and the first photodetector (650), the substantially opaque barrier (680) arranged to block direct illumination of the first photodetector (650) by the first light source (660).

7. A method for detecting smoke within a compact footprint detector (700) which mitigates deleterious effects of dust, thereby increasing longevity and efficacy, the method comprising: providing light from a first light source (660); detecting the light on a first photodetector (650) disposed proximal to the first light source (660) wherein the first light source (660) and the first photodetector (650) are located on a substrate (750); receiving a first signal from the first photodetector (650); determining the presence of smoke at least based on the first received signal which is based on scattered particulate matter, at least in part; and absorbing ambient light using a plurality of opto-isolating structural chamber columns (720), each column of the plurality of opto-isolating structural chamber columns (720) having a refractive index matched to that of common dust, wherein common dust comprises particles having a refractive index between 1.35 and 1.55, wherein each column of the plurality of opto-isolating structural chamber columns (720) is lossy and causes most of the light incident on the surface of the column to be absorbed in the bulk of the column(720), and wherein each column of the plurality of opto-isolating structural chamber columns (720) has a penetration depth on the order of tens of wavelengths of light, wherein the opto-isolating structural chamber columns (720) are absorbing rods of plastic, and wherein plurality of opto-isolating structural chamber columns (720) are located around the perimeter of the substrate (750) so as to prevent ambient light from outside the apparatus (700) from being received by the first photodetector (650).

8. The method for detecting smoke within a compact footprint detector (700) according to claim 7, wherein the method further comprises: preventing ambient light from outside the compact footprint detector (700) from being received by the first photodetector (650) by positioning the plurality of opto-isolating structural chamber columns (720) relative to the first light source (660) and the first photodetector (650).

9. The method for detecting smoke within a compact footprint detector (700) according to any of claims 7 or 8, wherein the method further comprises correlating the received first signal to an amount of particulate matter present in the compact footprint detector (700), wherein the received first signal is based on scattering.

10. The method for detecting smoke within a compact footprint detector (700) according to any of claims 7-9, wherein the method further comprises blocking direct illumination of the first photodetector (650) between the first light source (660) and the first photodetector (650) by arranging a substantially opaque barrier (680) on the substrate (710) between the first light source (660) and the first photodetector (650).