A practical guide for engineers working with magnetic materials

Magnetic materials are at the heart of modern power electronics. Transformers, inductors, and EMI filters determine efficiency, switching performance, and thermal behavior in nearly every converter topology. One of the most powerful tools for this purpose is the IWATSU B-H analyzer, featuring frequency domain signal calculation according to the CROSS-POWER method (Compatible to IEC62044-3 standard), providing reference-quality core measurements.

What is a B-H analyzer?

A B-H analyzer is a specialized instrument used to measure the magnetic properties of materials such as ferrites, nanocrystalline alloys, amorphous metals, powdered iron cores, and laminated steels. Engineers use these systems to evaluate hysteresis loops, core loss, magnetic permeability, and phase angle behavior across a wide frequency range. These measurements are critical when designing transformers, inductors, and EMI filters for modern power electronics.

Why Magnetic Characterization Matters

In power electronics, magnetic components often determine:

• efficiency
• switching performance
• thermal behavior
• EMI characteristics
• converter size and weight

For magnetic material RnD, the IWATSU B-H analyzer is considered the reference quality characterization device. It is also used in product development. Designers often rely on datasheet parameters such as permeability, saturation flux density, and core loss. However, actual magnetic behavior depends strongly on frequency, temperature, waveform shape, and DC bias.

Magnetic characterization allows engineers to measure the true dynamic behavior of magnetic materials under realistic operating conditions.

Typical materials analyzed include:

• ferrites
• nanocrystalline alloys
• amorphous metals
• powdered iron cores
• laminated steels

Understanding these materials requires measuring the relationship between magnetic field H and magnetic flux density B.

The B-H Curve: A Window into Magnetic Behavior

The B-H curve, also known as the hysteresis loop, is the most fundamental representation of a magnetic material.

It shows how magnetic flux density B responds to an applied magnetic field H.

Important properties extracted from this curve include:

The area inside the hysteresis loop represents the energy dissipated during each magnetization cycle. This is the primary contributor to magnetic core losses.

For power electronics designers, these losses translate directly into heat generation and efficiency penalties.

B-H Analyzer Measurement Principle

A B-H analyzer measures magnetic properties using two windings around the magnetic sample.

From these signals, the analyzer calculates:

Magnetic field

H = (N₁ × I) / l_e

Where:

• N₁ = primary turns
• I = excitation current
• l_e = magnetic path length

Magnetic flux density

B = (1 / (N₂A_e)) × ∫V₂(t) dt

Where:

• N₂ = secondary turns
• A_e = effective core cross-section
• V₂(t) = induced voltage

Using these relationships, the analyzer reconstructs the complete hysteresis loop.

Key Measurements Provided by IWATSU B-H Analyzers

Systems such as the SY-8218 / SY-8219 / SY-8264 Series (NEW) automatically compute a wide range of magnetic parameters.

Magnetic parameters

• B_m — maximum flux density
• B_r — residual flux density
• H_m — maximum field
• H_c — coercive force

Loss parameters

• P_c — core loss
• P_cv — core loss per volume (W/m³)
• P_cm — core loss per mass (W/kg)

Electrical parameters

• inductance (L)
• impedance (Z)
• resistance (R)
• apparent power (VA)
• phase angle (θ)

These measurements allow engineers to evaluate both magnetic behavior and electrical equivalent properties.

The area enclosed by the hysteresis loop represents the energy dissipated during one magnetization cycle. Multiplying this energy by the excitation frequency f yields the core loss density:

P_cv = f · ∮ H dB

Normal Mode: Classical Hysteresis Analysis

In Normal Mode, the analyzer focuses on the time-domain hysteresis loop.

This mode provides direct insight into:

• saturation behavior
• coercivity
• residual magnetization
• energy loss per cycle

It is commonly used for:

• transformer core evaluation
• switching loss analysis
• magnetic material development

A narrow loop typically indicates low-loss soft magnetic materials, while a wide loop suggests higher hysteresis loss.

μ-Mode: Permeability and Impedance Analysis

Modern B-H analyzers also provide μ-mode, which evaluates magnetic behavior using impedance analysis. In μ-mode the magnetic core is treated as a complex impedance, allowing the analyzer to determine permeability, loss tangent, quality factor, and other parameters as a function of frequency.

Instead of focusing purely on the hysteresis loop, μ-mode analyzes the material as a complex magnetic impedance.

Key outputs include:

Complex permeability is defined as:

μ = μ′ - jμ″

Where:

• μ′ represents stored magnetic energy
• μ″ represents magnetic losses

This mode is particularly valuable for high-frequency magnetic materials such as ferrites used in switching power supplies.

Why Oscilloscopes Are Not Enough for Magnetic Characterization

Engineers sometimes attempt to measure magnetic behavior using a standard oscilloscope, a current probe, and numerical integration. While this approach can approximate a B-H curve, it has several important limitations.

Limited accuracy in flux integration

To calculate magnetic flux density B, the induced voltage must be integrated over time:

B = (1 / (N A_e)) × ∫V(t) dt

Oscilloscopes typically perform this integration digitally. However, even small offset errors or noise in the measured voltage can accumulate during integration and produce significant drift in the calculated B-value.

Dedicated B-H analyzers use specialized integration circuits and calibration routines to minimize these errors.

Difficulty measuring phase angle

Another critical limitation is the phase relationship between magnetic field and magnetic flux density.

In real magnetic materials:

• the magnetic field H is generated by excitation current
• the magnetic flux density B is derived from the induced voltage

Because of magnetic losses, these quantities are not perfectly in phase.

The resulting phase angle is directly related to the energy dissipated inside the material and strongly influences:

• core loss
• complex permeability
• loss tangent (tanδ)

Accurately measuring this phase angle requires precise synchronization between current and voltage signals. Small timing or offset errors can lead to large errors in calculated magnetic losses.

Dedicated B-H analyzers are designed specifically to maintain this phase accuracy across a wide frequency range.

Missing complex permeability information

Oscilloscopes can reconstruct a hysteresis loop, but they typically cannot directly extract frequency-dependent magnetic parameters such as μ′, μ″, tanδ, and Q.

These parameters require impedance-based analysis, which is implemented in modern B-H analyzers through μ-mode measurements.

Lack of automated magnetic parameter extraction

Even when an oscilloscope successfully reconstructs a B-H loop, the engineer must manually calculate many parameters such as:

• coercive force
• residual flux density
• core loss
• permeability

Dedicated analyzers automate these calculations and provide repeatable measurement results, which is essential for:

• material research
• transformer design
• production quality control

Oscilloscopes remain indispensable tools for observing waveforms in power electronics systems. However, when the goal is accurate magnetic characterization, a dedicated B-H analyzer provides the precision, automation, and phase accuracy required for reliable results.

How Core Loss Is Measured in Magnetic Materials

Core losses are among the most important measurements in magnetic characterization.

They can be calculated using:

P_c = (N₁/N₂) × (1/T) × ∫₀^T i₁(t)V₂(t) dt

Where:

• i₁(t) is the excitation current
• V₂(t) is the induced voltage

Losses are typically reported as:

• W/kg (loss per mass)
• W/m³ (loss per volume)

These values allow engineers to compare materials independently of core size.

Advantages of Using a Dedicated B-H Analyzer

While oscilloscopes and current probes can approximate B-H curves, dedicated analyzers provide several advantages.

High measurement accuracy

Specialized integration and digitization circuits reduce error in flux measurements.

Automatic parameter extraction

The analyzer calculates dozens of parameters automatically.

High dynamic range

Magnetic materials can be evaluated across wide frequency and excitation ranges.

Waveform flexibility

Excitation waveforms can include:

• sinusoidal
• rectangular
• DC-biased signals

This allows realistic testing of power electronics operating conditions.

Typical Applications of Magnetic Characterization

Magnetic characterization using B-H analyzers is widely used in:

Power electronics design

Optimizing transformers and inductors for high-efficiency converters.

Magnetic material research

Evaluating new ferrites, nanocrystalline alloys, and amorphous metals.

EMI filter design

Understanding permeability and loss characteristics at high frequency.

Quality control

Verifying consistency of magnetic cores during production.

Interpreting the Hysteresis Loop

The shape of the B-H loop reveals important material properties.

Soft magnetic materials used in power electronics typically exhibit:

• low coercivity
• narrow loops
• high permeability

Conclusion

Magnetic characterization is essential for understanding and optimizing magnetic components in modern electronic systems. Dedicated tools such as IWATSU B-H analyzers provide engineers with deep insight into magnetic materials, enabling precise measurement of hysteresis behavior, permeability, and core losses.

By combining classical B-H analysis with advanced impedance-based μ-mode measurements, these systems offer a comprehensive view of magnetic performance across a wide range of frequencies and operating conditions.

For engineers developing the next generation of power electronics, accurate magnetic characterization is not just helpful—it is indispensable.