A method for monitoring a FCC catalyst injection system is provided. The passive mixer receives a low frequency signal as an input. The receiver detects the signals by allocating the modulation scheme of the lowest order to the upper tree level. Next, the copper film is patterned to form a connecting pattern and a die pad. A third cladding is disposed on the second cladding and the second core and an electrode is disposed on top of the third cladding. A plurality of slots in each side rail are configured to receive opposing ends of the rungs and to hold the same in place when the side rails are secured together by the connecting member.