According to an embodiment of the disclosure, an apparatus for a flow of fluid includes a first and a second element that form an exponentially changing restriction between them for a flow of a fluid. At least one of the first and second elements is configured to move in response to changing pressures to change the restriction. One of the first and second elements includes a wall with one or more cutouts that have an admittance that changes exponentially with respect to the movement of the first or second element.