A burner(100, 400), comprising: - a fuel source (112, 227); - an oxidant source (114, 228); - a plenum wall defining an air plenum (111, 411), the air plenum configured to receive fuel and oxidant respectively from the fuel source (112, 227) and the oxidant source (114, 228), the air plenum (111, 411) further configured to convey the fuel and oxidant to facilitate mixture of the fuel and oxidant into a fuel-oxidant mixture; - an ignition source disposed at a distal portion of the air plenum (111. 411) and oriented to ignite the fuel-oxidant mixture to produce a flame in a flame region; and - at least a first electrode (122, 422) and a second electrode (124, 424) arranged adjacent to a flame region and configured to produce a time-varying electromagnetic field across the flame region; wherein a change in electrical permittivity or electrical capacitance in the flame region is determined from the time-varying electromagnetic field, wherein at least the first electrode (122, 422) and the second electrode (124, 424) are disposed opposite each other across the flame region, the first electrode (122, 422) configured to broadcast an excitation signal to produce the time-varying electromagnetic field between the first and second electrodes, the second electrode (124, 424) being configured to receive a detection signal, the detection signal including the broadcast excitation signal as affected by the change in electrical permittivity between the first and second electrodes, wherein the burner (100, 400) further comprises a control circuit configured to generate the excitation signal and provide the excitation signal to the first electrode (122, 422), characterized in that the control circuit is further configured to receive the detection signal from the second electrode (124, 424) and to determine a magnitude of the electrical permittivity of the flame region by measuring or calculating a signal characteristic from the detection signal, and in that the control circuit is further configured to identify a flame characteristic by comparing the determined magnitude of the electrical permittivity against an index of flame characteristics corresponding to respective electrical permittivity magnitudes. - a fuel source (112, 227); - an oxidant source (114, 228); - a plenum wall defining an air plenum (111, 411), the air plenum configured to receive fuel and oxidant respectively from the fuel source (112, 227) and the oxidant source (114, 228), the air plenum (111, 411) further configured to convey the fuel and oxidant to facilitate mixture of the fuel and oxidant into a fuel-oxidant mixture; - an ignition source disposed at a distal portion of the air plenum (111. 411) and oriented to ignite the fuel-oxidant mixture to produce a flame in a flame region; and - at least a first electrode (122, 422) and a second electrode (124, 424) arranged adjacent to a flame region and configured to produce a time-varying electromagnetic field across the flame region; wherein a change in electrical permittivity or electrical capacitance in the flame region is determined from the time-varying electromagnetic field, wherein at least the first electrode (122, 422) and the second electrode (124, 424) are disposed opposite each other across the flame region, the first electrode (122, 422) configured to broadcast an excitation signal to produce the time-varying electromagnetic field between the first and second electrodes, the second electrode (124, 424) being configured to receive a detection signal, the detection signal including the broadcast excitation signal as affected by the change in electrical permittivity between the first and second electrodes, wherein the burner (100, 400) further comprises a control circuit configured to generate the excitation signal and provide the excitation signal to the first electrode (122, 422), characterized in that the control circuit is further configured to receive the detection signal from the second electrode (124, 424) and to determine a magnitude of the electrical permittivity of the flame region by measuring or calculating a signal characteristic from the detection signal, and in that the control circuit is further configured to identify a flame characteristic by comparing the determined magnitude of the electrical permittivity against an index of flame characteristics corresponding to respective electrical permittivity magnitudes.