Dosages of inhaled insulin are controlled within a narrow range by controlling the total volume of air inhaled by a patient. A channel protection structure may be disposed on the gate insulation layer to expose a portion of the gate insulation layer. The hook material, and felt pad may be trimmed with a conventional cutting device to conform to the shape and size of the lower end of the furniture. The impedance compensation circuit may generate a negative input impedance that is imposed across the two nodes that is substantially the same as the positive input impedance. Selected ones of the plurality of fins are at least partially removed to form isolation regions and an insulating material is deposited to fill the trenches and to cover the at least partially removed selected ones of the plurality of fins.