Most transducers are not resistive but have some impedance. The inductive or capacitive bit must be tuned out as it only gets in the way of true power which is dissipated in the resistive part. Like wise once this has done, the resistive part must be matched to the optimum resistance for the RF source. So suppose your transducer is 10 ohms and this is matched to the RF source for maximum power transfer. Putting a second one in would give you 5 ohms which is not matched for optimum power transfer and the output amplifier might over heat/blow up as its trying to deliver twice as much current for the same amount of voltage.
Frank