A system for determining a temperature of a susceptor element (140; 540) comprising: an induction heating circuit (150; 550); characterized by: at least one processor programmed or configured to: determine a first response phase of the induction heating circuit, wherein the first response phase is based on a magnetic property of the susceptor element at a first driving frequency, and wherein the first response phase is a value of phase difference between a phase of a driving current at the first driving frequency and a phase of a voltage across an electrical component of the induction heating circuit at the first driving frequency; determine a second response phase of the induction heating circuit, wherein the second response phase is based on a magnetic property of the susceptor element at a second driving frequency, and wherein the second response phase is a value of phase difference between a phase of a driving current at the second driving frequency and a phase of a voltage across the electrical component of the induction heating circuit at the second driving frequency; determine a function of phase versus frequency for the induction heating circuit based on the first response phase and the second response phase; determine a frequency value where a phase value of the function is in quadrature based on the function of phase versus frequency; and determine a temperature of the susceptor element based on the frequency value. an induction heating circuit (150; 550); characterized by: at least one processor programmed or configured to: determine a first response phase of the induction heating circuit, wherein the first response phase is based on a magnetic property of the susceptor element at a first driving frequency, and wherein the first response phase is a value of phase difference between a phase of a driving current at the first driving frequency and a phase of a voltage across an electrical component of the induction heating circuit at the first driving frequency; determine a second response phase of the induction heating circuit, wherein the second response phase is based on a magnetic property of the susceptor element at a second driving frequency, and wherein the second response phase is a value of phase difference between a phase of a driving current at the second driving frequency and a phase of a voltage across the electrical component of the induction heating circuit at the second driving frequency; determine a function of phase versus frequency for the induction heating circuit based on the first response phase and the second response phase; determine a frequency value where a phase value of the function is in quadrature based on the function of phase versus frequency; and determine a temperature of the susceptor element based on the frequency value. determine a first response phase of the induction heating circuit, wherein the first response phase is based on a magnetic property of the susceptor element at a first driving frequency, and wherein the first response phase is a value of phase difference between a phase of a driving current at the first driving frequency and a phase of a voltage across an electrical component of the induction heating circuit at the first driving frequency; determine a second response phase of the induction heating circuit, wherein the second response phase is based on a magnetic property of the susceptor element at a second driving frequency, and wherein the second response phase is a value of phase difference between a phase of a driving current at the second driving frequency and a phase of a voltage across the electrical component of the induction heating circuit at the second driving frequency; determine a function of phase versus frequency for the induction heating circuit based on the first response phase and the second response phase; determine a frequency value where a phase value of the function is in quadrature based on the function of phase versus frequency; and determine a temperature of the susceptor element based on the frequency value.