1. B and H – Magnetic Concepts

Magnetic Flux Density (B, in Tesla):

- Refers to the magnetic field generated inside a coil by an external current.

- Also known as the induced magnetic field.

- Can be converted to/from magnetic field strength (H) under specific conditions.

Magnetic Field Strength (H, in A/m):

- Refers to the intensity of the magnetic field in space.

- Measured using a loop antenna and calculated from its characteristics.

2. Relationship Between Electric Field and Magnetic Field

dBuV/m = dBpT + 49.5 dB

3. Relationship Between H and B

dBuA/m = dBpT - 2 dB

Definition of Magnetic Antenna Coefficient:

Factor(H) = H / VR

Where:

- H = Magnetic field strength (A/m)

- VR = Antenna output voltage (V)

Unit Analysis:

(A/V)/m = (1 / Ω)/m = S/m

Logarithmic form (dB scale):

dBA/m = dBS/m + dBV

4. Magnetic Permeability and Field Conversion

B = μ₀ × H, where μ₀ = 4π × 10⁻⁷ = -118 dB

dBT = -118 dB + dBA/m

dBpT - 240 dB = -118 dB + dBuA/m - 120 dB  

dBpT - 2 dB = dBuA/m          As mentioned above 3

dBuA/m = dBpT - 2 dB        dbuV/m – 51.5db = dbuA/m

dBuV/m = dBpT + 49.5 dB       As mentioned above 2

5. IEC 61000-4-8 Loop – Physical Derivation of Magnetic Field

Formula:

B = (4μ₀ × N × I × a²) / (3.14 × (a² +4 z²)(4 z²+ 2a²)^(1/2))

  =μ₀H

Simplified (Z = 0, a = 1):

H = 0.9 × N × I / a

Note: The regulatory text commonly uses coefficient 0.87 instead of 0.9.

6. Designing a Rectangular Loop Antenna

To generate a desired magnetic field:

1. Calculate required current (A), coil size, and number of turns to meet field specifications.

2. Ensure total wire length of the coil is less than 1/20 of the wavelength.

3. Choose an appropriate wire diameter based on expected current.

4. Apply for calibration to validate performance.