Core Materials Core Materials & Properties The core material of an inductor dramatically affects its performance. Choosing the right core is essential for achieving the desired inductance, Q factor, and frequency response in VIC applications. Why Use a Core? A magnetic core increases inductance by providing a low-reluctance path for magnetic flux: L = μ₀μᵣN²A/l The relative permeability (μᵣ) of the core multiplies the inductance compared to an air core. Core Material Comparison Material μᵣ (typical) Frequency Range Saturation Cost Air 1 Any N/A Free Iron Powder 10-100 1 kHz - 100 MHz High (0.5-1.5T) Low Ferrite (MnZn) 1000-10000 1 kHz - 1 MHz Low (0.3-0.5T) Medium Ferrite (NiZn) 50-1500 100 kHz - 500 MHz Low (0.3-0.4T) Medium Laminated Silicon Steel 2000-6000 50 Hz - 10 kHz High (1.5-2.0T) Low Amorphous Metal 10000-100000 50 Hz - 100 kHz High (1.5T) High Nanocrystalline 15000-100000 1 kHz - 1 MHz High (1.2T) High Core Losses All magnetic cores dissipate energy through two mechanisms: 1. Hysteresis Loss Energy lost each time the core is magnetized and demagnetized. P h ∝ f × B max n (n ≈ 1.6-2.5) Proportional to frequency and flux density. 2. Eddy Current Loss Circulating currents induced in the core material. P e ∝ f² × B max ² Proportional to frequency squared - dominates at high frequencies. Steinmetz Equation P core = k × f α × B β × Volume Where k, α, β are material-specific constants from datasheets. Ferrite Materials for VIC Ferrites are the most common choice for VIC frequencies (1-50 kHz): Material μᵢ Optimal Frequency Application 3C90 (TDK) 2300 25-200 kHz Power transformers N87 (EPCOS) 2200 25-500 kHz General purpose N97 (EPCOS) 2300 25-150 kHz Low loss 3F3 (Ferroxcube) 2000 100-500 kHz Higher frequency 77 Material (Fair-Rite) 2000 Up to 1 MHz EMI/RFI suppression Iron Powder Cores Micrometals and Amidon iron powder cores are popular for their: High saturation flux density Gradual saturation (soft saturation) Good temperature stability Self-gapping (distributed gap) Common Iron Powder Mixes Mix μ Color Frequency Range Mix 26 75 Yellow/White DC - 1 MHz Mix 52 75 Green/Blue DC - 3 MHz Mix 2 10 Red/Clear 1 - 30 MHz Mix 6 8 Yellow 10 - 50 MHz Core Shapes Toroidal Doughnut shape with closed magnetic path. Excellent flux containment, low EMI. Harder to wind but very efficient. E-Core / EI-Core E-shaped halves that mate together. Easy to wind on bobbin. Can add air gap easily. Pot Core Cylindrical with center post. Shields winding from external fields. Good for sensitive applications. Rod Core Simple cylindrical rod. Open magnetic path, lower inductance per turn but no saturation issues. Core Saturation When the magnetic flux density exceeds the saturation limit: Permeability drops dramatically Inductance decreases Current increases rapidly Core heating increases Avoiding Saturation: B peak = (L × I peak ) / (N × A e ) < B sat Always check that peak flux density stays below saturation limit of your core material. Recommendations for VIC Frequency Range Recommended Core Notes 1-10 kHz N97/3C90 ferrite or iron powder Low loss at these frequencies 10-50 kHz N87/3F3 ferrite Good balance of μ and loss 50-200 kHz 3F3/3F4 ferrite or Mix 26 powder Lower permeability, lower loss >200 kHz NiZn ferrite or Mix 2 powder Designed for high frequency VIC Matrix Calculator: The Choke Design module includes a core database with A L values and frequency recommendations. Select your core and it will calculate the required turns for your target inductance. Next: Wire Gauge & Material Selection →