Detection of blockage in a porous member

1. A method of detecting a state of blockage in a porous member separating an inner chamber of a device comprising a gas sensor responsive to an analyte gas positioned within the inner chamber and an ambient environment from which the analyte gas transports through the porous member to reach the gas sensor responsive to the analyte gas, comprising:

emitting pressure waves within the inner chamber via a source of pressure waves positioned within the inner chamber and spaced from the porous member so that any pressure waves emitted from the source of pressure waves that are transmitted out of the inner chamber are transmitted through the porous member, measuring a response to the pressure waves via a sensor responsive to pressure waves, different from the gas sensor, positioned within the inner chamber; and relating a response of the sensor responsive to pressure waves to the state of blockage in the porous member, wherein a blockage of the porous member inhibits transport of analyte gas therethrough.

2. The method of claim 1 wherein emitting pressure waves within the inner chamber comprises activating a speaker positioned within the inner chamber, and measuring the response via the sensor responsive to pressure waves comprises measuring the response via a microphone positioned within the inner chamber.

3. The method of claim 2 wherein pressure waves are emitted at a plurality of frequencies within the chamber and a response is measured at more than one of the plurality of frequencies.

4. The method of claim 2 wherein measuring the response comprises measuring at least pressure waves reflected off the porous member.

5. The method of claim 1 wherein at least one of a change in amplitude and a change in phase is measured.

6. The method of claim 1 wherein a change in phase is measured.

7. The method of claim 6 wherein a change in amplitude is also measured.

8. The method of claim 7 wherein a lock-in algorithm is used to measure each of the change in amplitude and the change in phase.

9. The method of claim 3 wherein at least one of the plurality of frequencies is a self-resonant frequency of the porous member and a response measured at the at least one of the plurality of frequencies is associable with the state of blockage.

10. The method of claim 2 further comprising using the measured response to discriminate between at least a partial blockage associated with an outside surface of the porous member and at least a partial blockage infiltrating pores of the porous member.

11. The method of claim 10 wherein pressure waves are emitted at a self-resonant frequency of the porous member and a response measured at the self-resonant frequency is associated with a determination of the at least a partial blockage infiltrating pores of the porous membrane.