The present invention provides an iron-type golf club head having a bridge member across a cavity on its rear surface, which member influences the trajectory of a golf ball struck by the club head. The sensor of the subject invention is effective in detecting multiple layers of biomolecular interactions, termed cascade sensing, including sensitive detection of small molecule recognition events that take place relatively far from the semiconductor surface. The first signal and the second signal are of opposite phases. The split input signal is applied through a 90 transformer to the carrier amplifier, and the outputs of the peak amplifiers are applied through 90 transformers to a output load.