Acoustic band-pass filter assemblies, wireless blockage monitors, and related methods
An acoustic band-pass filter assembly includes an inlet, a microphone configured to receive acoustic energy from the inlet, and a plurality of resonator chambers disposed in series between the inlet and the microphone and configured to transmit acoustic energy between the inlet and the microphone. Each of the plurality of resonator chambers has a different cross-sectional area.
1. An acoustic band-pass filter assembly comprising:
an inlet;
a microphone configured to receive acoustic energy from the inlet; and
a plurality of resonator chambers disposed in series between the inlet and the microphone and configured to transmit acoustic energy between the inlet and the microphone, each of the plurality of resonator chambers having a different cross-sectional area; wherein the cross-section of each resonator chamber increases between the inlet and the microphone.
2. The acoustic band-pass filter assembly of claim 1 , wherein each resonator chamber of the plurality of resonator chambers has a first end closer to the inlet than to the microphone, and an opposite second end closer to the microphone than to the inlet, wherein the resonator chamber extends from the first end to the second end along a primary axis extending from the inlet to the microphone, and wherein the plurality of resonator chambers includes:
at least one open resonator chamber, wherein the first end includes a first wall with an opening therethrough and wherein the second end is fully open to a first end of an adjacent resonator chamber of the plurality of resonator chambers; and
a closed resonator chamber disposed adjacent the microphone, wherein the first end has a second wall with an opening therethrough connecting the closed resonator chamber to the second end of the at least one open resonator chamber, and wherein the second end of the closed resonator chamber has a closed wall, wherein the microphone forms at least a portion of the closed wall.
3. The acoustic band-pass filter assembly of claim 2 , wherein the at least one open resonator chamber comprises a plurality of open resonator chambers.
4. The acoustic band-pass filter assembly of claim 3 , wherein each open resonator chamber of the plurality of open resonator chambers has a first length along the primary axis.
5. The acoustic band-pass filter assembly of claim 4 , wherein the closed resonator chamber has a second length along the primary axis, the second length being greater than the first length.
6. The acoustic band-pass filter assembly of claim 5 , wherein the second length is twice the first length.
7. The acoustic band-pass filter assembly of claim 2 , wherein each resonator chamber of the plurality of resonator chambers has a generally cylindrical tapered wall centered about the primary axis.
8. The acoustic band-pass filter assembly of claim 2 , wherein the inlet has a horn shape decreasing in cross-sectional area between an upstream opening of the inlet and the at least one open resonator chamber.
9. The acoustic band-pass filter assembly of claim 7 , wherein the resonator chambers are arranged in series from the inlet to the microphone in order of increasing diameter.
10. A wireless blockage monitor for determining a rate of flow, the wireless blockage monitor comprising:
a sensor membrane configured to be impacted by a flowing material;
a microphone configured to receive acoustic energy created by impact of the sensor membrane;
a tube connecting the sensor membrane to the microphone; and
a band-pass filter disposed between the tube and the microphone, wherein the band-pass filter comprises:
an inlet connected to the tube; and
a plurality of resonator chambers disposed in series between the inlet and the microphone and configured to transmit acoustic energy between the inlet and microphone, plurality of resonator chambers including:
at least one open resonator chamber, wherein the first end includes a first wall with an opening therethrough and wherein the second end is fully open; and
a closed resonator chamber disposed adjacent the microphone, wherein the first end has a second wall with an opening therethrough connecting the closed resonator chamber to the second end of the at least one open resonator chamber, wherein the second end of the closed resonator chamber has a closed wall, and wherein the microphone forms at least a portion of the closed wall;
wherein the cross-section of each resonator chamber increases between the inlet and the microphone.
11. The wireless blockage monitor of claim 10 , wherein the at least one open resonator chamber comprises a plurality of open resonator chambers.
12. The wireless blockage monitor of claim 10 , wherein each resonator chamber of the plurality of resonator chambers extends a length from the first end to the second end along a primary axis extending from the inlet to the microphone, and wherein the length of the closed resonator chamber is at least twice the length of the at least one open resonator chamber.
13. The wireless blockage monitor of claim 10 , wherein each resonator chamber is generally cylindrical.
14. The wireless blockage monitor of claim 10 , wherein the inlet has a horn shape decreasing in cross-sectional area between an upstream opening of the inlet and the at least one open resonator chamber.
15. A method of forming an acoustic band-pass filter assembly, the method comprising:
forming a body defining an inlet, an open end, and a plurality of resonator chambers disposed in series between the inlet and the open end, each of the plurality of resonator chambers having a different cross-sectional area; wherein the cross-section of each resonator chamber increases between the inlet and the open end;
providing an end wall over the open end of the body, the end wall configured to receive a microphone; and
providing a microphone on the end wall.
16. The method of claim 15 , wherein forming a body comprises molding the body.
17. The method of claim 15 , wherein forming a body comprises forming the body to have a horn shape decreasing in cross-sectional area between the inlet and the at least one open resonator chamber.
18. The method of claim 15 , wherein forming a body comprises forming the resonator chambers to each have a generally cylindrical tapered wall.