**3. Measurements and analysis of polypropylene capacitor radiation**

Measurements are performed in the time domain using a high-bandwidth oscilloscope. We have measured the vertical component Hz of the magnetic near-field

#### *Development of Generic Radiating Model for Rectangular Capacitors: Magnetic Near Fields… DOI: http://dx.doi.org/10.5772/intechopen.98894*

radiated above a plastic polypropylene capacitor of a 2.2 uF capacitance and a maximum voltage of 100 V (the capacitor size is 15 mm 6 mm 26.5 mm). To avoid the interferences caused by the capacitor legs, we have folded the legs of the latter. The probe is located at a distance of 2 mm above the capacitor in a plane whose dimensions are 4 cm x 2 cm. The displacements are done with a measuring step of 2 mm on the X-axis and 1 mm on the Y-axis. Thus, we have 400 measurement points. **Figure 8** shows the measurement plane and the component under test. It gives a particular point (3, 5) position in the measurement plane.

**Figure 9** shows the temporal voltage measured at the terminals of the magnetic probe once it is situated at the point (3, 5): the third position along the X-axis and the fifth position along the Y-axis. When analyzing the measured magnetic field signal, the existence of switching transients is noticed during turning on and off the power component utilized in the chopper.

We present in **Figure 10** the spectrum of radiated magnetic field Hz above the capacitor in the point (3,5). **Figure 10** shows the spectrum analysis of the whole temporal signal with both switching phases (closing and opening of the MOSFET in the excitation circuit where our studied component is characterized). That measured above the capacitor at the point of the coordinates (3,5) presented in **Figure 9**. By analyzing the measured temporal signal spectrum, four principal harmonics are observed, which have the following frequencies: 3 MHz, 11 MHz, 20 MHz, and 40 MHz. The resonances that appear above the capacitor are principally due to the

**Figure 8.**

*Measurement plane over component under test.*

**Figure 9.** *Measured voltage at the terminals of the probe above capacitor under test.*

**Figure 10.** *Spectrum of radiated magnetic field Hz at the terminals of the probe above the studied capacitor at point (3.5).*

**Figure 11.** *Cartographies of the near field for 3 MHz, 11 MHz, 20 MHz, and 40 MHz frequencies.*

operating current flowing into the chopper circuit. **Figure 11** presents the cartographies of the field above the capacitor at these different frequencies.

According to the previous cartographies, the distribution of the radiated magnetic field above the capacitor is over the entire component surface, as illustrated in **Figure 12**.
