Heat retentive food servingware with temperature self-regulating phase change core

A food retaining apparatus comprising:

• food retaining means including a heatable, food-contacting wall;
• a first magnetic induction heating element in thermal contact with said wall for heating said wall to a first predetermined temperature, said first element including ferromagnetic material responsive to a magnetic field generated by a magnetic field source for inducing an electric current in said first element to heat said first element to the first predetermined temperature;
• a second magnetic induction heating element in thermal contact with said wall for heating said wall to a second predetermined temperature, said second element including ferromagnetic material responsive to the magnetic field generated by the magnetic field source for inducing an electric current in said second element to heat said second element to the second predetermined temperature;
• and
• means for selectively disabling one of said first and second elements so that said wall is heated to the predetermined temperature corresponding to the other of said elements.

A method of heating a food retaining device comprising the steps of:

• positioning a food retaining device including a food-contacting wall and a magnetic induction heating element in thermal contact with the wall in a magnetic field generated by a magnetic field generating means for inducing a current and a corresponding impedance in the heating element and for raising the temperature of the element;
• detecting the value of said corresponding impedance of the element with an impedance detection means;
• comparing said detected corresponding impedance value with a predetermined impedance value;
• and
• interrupting the magnetic field when said detected corresponding impedance value of the element is less than said predetermined impedance value.

A method of heating a food retaining device comprising the steps of:

• providing a magnetic induction heater including generating means for generating a magnetic field, for detecting impedance of a body positioned in the magnetic field, and for interrupting the magnetic field when either the detected impedance drops below a first predetermined impedance value or the absolute value of the rate of change in the impedance exceeds a predetermined rate of change;
• providing a device for retaining food including a magnetic induction heating element positioned to be in thermal contact with food retained by the device for heating the wall to a predetermined temperature;
• generating a magnetic field using the generating means;
• positioning the food retaining device in the magnetic field for inducing current and a corresponding impedance in the element for heating the element;
• detecting said corresponding impedance of the element using the detection means;
• comparing the detected corresponding impedance with the first predetermined impedance value;
• determining the absolute value of the rate of change in the corresponding impedance value;
• comparing the absolute value of the rate of change with the predetermined rate of change;
• and
• interrupting the magnetic field when either the detected corresponding impedance value is less than the first predetermined impedance value or the absolute value of the rate of change in the corresponding impedance is greater than the predetermined rate of change.

Warming apparatus comprising:

• a magnetic induction heater including a magnetic field generator for generating a magnetic field, and an impedance detector for sensing a load impedance parameter of a load magnetically coupled in said magnetic field;
• and
• a temperature self-regulating device in position for magnetic coupling with said magnetic field, said device including a ferromagnetic induction heating element,
• said element responsive to said magnetic field for induction heating of said element to a predetermined temperature;
• said impedance detector being operable for periodically sensing said load impedance parameter while said device remains in said position, and in response thereto, altering the magnetic field strength of the magnetic field to a different level when said load impedance parameter is above or below a selected value correlated with said predetermined temperature.

A method of controlling the temperature of a warming device comprising the steps of:

• placing said device in a position for magnetic coupling of said device and a magnetic field generated by a magnetic induction heater, said heater having a magnetic field generator for generating said magnetic field and an impedance detector for sensing a load impedance parameter of a load magnetically coupled in said magnetic field,
• said device including a ferromagnetic induction heating element responsive to said magnetic field for induction heating of said element to a predetermined temperature;
• and
• operating said impedance detector to sense periodically said load impedance parameter while said device remains in said position, and in response thereto, altering the magnetic field strength of the magnetic field to a different level when the load impedance parameter is above or below a selected value correlated with said predetermined temperature.