a microwave thawing system for thawing bags of frozen blood products features non - invasively monitoring the internal temperature of the blood product during thawing , and controlling the level of warming energy applied to the blood product based on the monitored temperature . the non - invasive monitoring is performed with one or more antennas which receive electromagnetic energy from the frozen blood product during thawing . because the applied energy level is controlled based on the temperature of the blood , the blood can be thawed rapidly with little risk of damage from overheating . pressure is applied to the bag to maintain a uniform distribution of blood within the bag and to separate the thawed blood from the still - frozen blood during thawing ; for example , the pressure moves the liquid blood to the periphery of the bag and retains the frozen blood in the center of the bag . as a result , the continued application of thawing energy to the frozen blood poses little risk of overheating the liquid blood . the warming energy and the electromagnetic energy are transmitted and received , respectively , through transmit / receive waveguides configured to provide high isolation between its transmit and receive ports .