Abstract: A fuel tank includes a body, a partition, and an opening in the partition. The body has an interior configured to receive and store liquid fuel. The partition substantially divides the interior of the body into upper and lower volumes. The opening in the partition provides fluid communication between the upper and lower volumes, and is located proximate to one of the walls of the body. The fuel tank further includes a fill port and a vent that is coupled to the upper volume away from the opening.

Abstract: Detection of higher order mode transverse modal energy is suppressed for an acoustic wave propagating longitudinally through a duct. First and second microphones are placed in respective first and second nodal planes of the second higher order mode, and the outputs of the microphones are summed. For the first higher order mode, the output of the first microphone is equal in amplitude and opposite in phase to the output of the second microphone, and the resultant sum is zero. For the second higher order mode, the output of each of the first and second microphones is zero, and the resultant sum is zero.