Shape memory thermal exposure monitor

A cumulative thermal exposure monitor for monitoring heat energy absorbed over time and indicating the degree of deterioration based on a time and temperature thermal deterioration profile of a perishable product that has a known time and temperature thermal deterioration profile and is prescribed to be maintained within a preferred storage temperature range, comprising:

• a thermally-conductive housing having a fluid sealed interior cavity and a transparent window portion, said housing formed of a material having thermal capacity and insulative properties which moderate heat energy conducted therethrough over time;
• a thermally-responsive member movably disposed in said interior cavity formed of a shape memory material selected from the group consisting of shape memory alloys and shape memory polymer composites having a phase transition temperature range encompassing at least the preferred storage temperature range and having a first shape at temperatures below said phase transition temperature range and gradually changing to a second shape at temperatures within or above the preferred storage temperature range;
• and
• indicator means visible through said window portion and associated with said thermally-responsive member to be moved from an initial position thereby as said thermally-responsive member gradually changes from said first shape to said second shape;
• said thermal capacity and insulative properties of said housing material and said shape memory material phase transition temperature range calibrated relative to one another to function in mutual cooperation such that said housing moderates heat energy conducted therethrough over time and said thermally-responsive member absorbs the heat energy and gradually assumes its said second shape upon absorption of heat energy over time to closely match the known time and temperature thermal deterioration profile of the perishable product;
• and
• said indicator means remains substantially in a position at which it was last moved by said thermally-responsive member, regardless of subsequent exposures of said shape memory material to lower temperatures, to indicate the cumulative amount of heat energy absorbed in and above said preferred storage temperature range and whether, at any time, the temperature has been above said preferred storage temperature range for a period of time sufficient to cause any degree of deterioration based on the time and temperature thermal deterioration profile of the perishable product.