Specifications

B-field Exposure From Induction Cooking Appliances 27
Table 5: Signal and envelope modulation frequency of appliances 1, 2 and 3 for the heat settings
4 and P or 12.
signal frequency envelope frequency pulse-width modulation
[kHz] [Hz] frequency [Hz]
heat setting 4 P or 12 4 to max. (P or 12) 1 to 4
appliance 1 42 18 100 0.5
appliance 2 52 21 100 0.5
appliance 3 63 22 300 0.5
Table 6: Duty cycle of appliances 1, 2 and 3 for heat settings 1 to 4, where the signal is pulse-
width modulated (no pulse-width modulation for higher settings).
duty cycle [%]
heat setting 1 2 3 4 5
appliance 1 20 35 65 95 100
appliance 2 15 30 55 75 100
appliance 3 40 60 60 100 100
spectrum analyzer (Rohde & Schwarz FSP30). The signals were measured at the front side of
the appliances for each hob with a measuring distance of 1 cm. For each experiment the standard
pot 3 with lid was centered on the hob and filled with 3 liters of tap water.
Dependency of the signal frequency on the heat setting for each hob The signal
frequencies of all hobs were measured for different heat settings (see Figure 20). As shown in
Figures 17, 18 and 19, the frequency decreases when the heat setting increases. The frequency
ranges are 18−45 kHz, 21−52 kHz and 22−63 kHz for appliances 1, 2 and 3, respectively. The
electronic schemes of the appliances were not provided, and the appliances were not opened.
However, in order to explain why the signal frequency decreases for higher heat settings, a
simple circuit comprised of a coil L, a series resistor R and a AC voltage source U is considered.
The B-field increases with the AC current in the coil. The current in the coil is given by
I(ω) = V (ω)/(R + jωL), where I(ω) = Ie
jωt
and V (ω) = V e
jωt+α
are the current and voltage
in the complex domain, and ω = 2πf is the angular velocity. If R, L and V are fixed, the current
in the coil I is proportional to 1/f (for | ωL | R).
Harmonics contribution Figure 21 shows the power spectral distribution of the B-field
emitted by appliances 1, 2 and 3 for frequencies up to 400 kHz. This frequency range corresponds
to the Narda probe bandwidth (30 Hz−400 kHz). The ratio between the fundamental and the
harmonics peaks is calculated using Equation (7):
P
1[mW ]
P
2[mW ]
= 10
P
1[dB]
−P
2[dB]
10
(7)
where P
1[dB]
− P
2[dB]
is the difference in [dB] between the fundamental and harmonic peaks
(power spectrum), and P
1[mW ]
/P
2[mW ]
is the corresponding ratio. The contribution of the