Method and device for detecting smoke

1. A smoke detector, comprising:

a chamber provided with apertures configured to allow the smoke to enter a detection area in the chamber;

a light source configured to emit a beam of light rays towards the detection area;

a light receiver sensitive to at least one portion of the wavelengths of the light rays emitted by the light source and configured to transform the reception of light into an electric reception signal;

concentration means configured to create a non-uniform electromagnetic field in at least one portion of the detection area, that, in the presence of smoke, can polarize smoke particles entering the detection area, the non-uniform electromagnetic field having a spatial electromagnetic field gradient configured to exert a dielectrophoretic force on the smoke particles configured to drive the polarized smoke particles into a concentration area in the detection area.

2. The smoke detector according to claim 1 , wherein the spatial electric field gradient is configured to exert a dielectrophoretic force on the smoke particles between 0.01 μm and 10 μm in size.

3. The smoke detector according to claim 1 , wherein the concentration means comprise two electrodes configured to create a non-uniform electric field in at least one portion of the detection area, the electrodes being configured to create a spatial electric field gradient in the detection area when a potential difference V, below a ionization threshold of the gas in the chamber, is applied to these electrodes.

4. The smoke detector according to claim 3 , wherein a portion of the chamber itself constitutes one of the electrodes, the chamber being formed from a conductive polymer.

5. The smoke detector according to claim 3 , further comprising means of applying the voltage V to the terminals of the electrodes, configured to apply voltage pulses with amplitude ΔV between 2 and 300V and duration ΔTv to the electrodes.

6. The smoke detector according to claim 3 , wherein one of the electrodes is formed from a conductive tip, a segment of a cylindrical conductive wire or a conductive edge and the other electrode is formed from a flat conductive surface or a portion of an arc of a cylindrical surface.

7. The smoke detector according to claim 3 , wherein a portion of the chamber itself constitutes one of the electrodes, and the other electrode is located between the light source and the receiver and prevents the receiver from having a direct view of the light source.

8. The smoke detector according to claim 3 , wherein one of the electrodes is a conductive wire placed parallel to a propagation axis of the light emitted by the light source.

9. The smoke detector according to claim 8 , wherein the radius of the conductive wire is between 10 μm and 1 mm.

10. The smoke detector according to claim 3 , wherein one of the electrodes is formed by an edge of a prism, said edge being placed parallel to a propagation axis of the light emitted by the light source.

11. The smoke detector according to claim 1 , wherein the concentration means comprise a focusing means configured to focus light rays in the detection area, to generate electromagnetic field gradients in the detection area.

12. The smoke detector according to claim 1 , wherein the light source is configured to emit a beam of light rays with a wavelength between 800 nm and 1000 nm.

13. The smoke detector according to claim 1 , further comprising means of powering the light source configured to supply current pulses to the light source with amplitude AI and duration ΔTi between 100 ns and 1 ms.

14. The smoke detector according to claim 13 , wherein voltage pulses are applied with a delay ΔT1 after the current pulses are emitted, the delay ΔT1 being between 0 and 60 μs.

15. The smoke detector according to claim 1 , further comprising means of processing the electric reception signal configured to analyze the temporal variation in the amplitude of the electric reception signal.

16. The smoke detector according to claim 14 , wherein the processing means are configured to compare the amplitude of the signal to a reference level determined by reference means, the reference means being configured to modify the reference level according to values of a previously measured electric signal and/or according to the nature of the fire risk to be monitored.

17. The smoke detector according to claim 1 , wherein the non-uniform electromagnetic field is configured to aggregate the smoke particles in the concentration area to form larger smoke particles.

18. The smoke detector according to claim 1 , wherein:

the light receiver is configured to receive, in the presence of smoke particles or aggregates of smoke particles in the detection area, diffused light coming from the detection area, and

the chamber is configured to minimize the penetration of exterior light into the detection area and the source and the receiver being placed relative to each other to configured to prevent the light emitted by the source reaching the receiver directly.

19. A method for detecting smoke, comprising:

emitting a beam of light rays P from a light source towards a detection area in a chamber provided with apertures configured to allow the smoke to enter a detection area;

receiving, with a receiver, in the presence of smoke particles or aggregates of smoke particles in the detection area, of light coming from the detection area; and providing an electric reception signal representative of the received light; and

generating a non-uniform electromagnetic field in at least one portion of the detection area, so that, in the presence of smoke, smoke particles entering the sub-area of the detection area are polarized by the electromagnetic field, the electromagnetic field applying a dielectrophoretic force on the smoke particles in order to drive the polarized smoke particles into a concentration area in the detection area.

20. The method according to claim 19 , further comprising aggregating smoke particles to each other in the concentration area to form larger smoke particles.