Inductor Basics: Structure, Parameters, and Measurement

Catalog

I Inductor Structure

An inductor is generally composed of a skeleton, a winding, a magnetic core, an iron core, a shielding case, and a package. Modern inductors, particularly surface-mount devices (SMD), may integrate these components in ultra-compact designs suitable for high-density circuit boards.

1. Skeleton

Skeleton usually refers to a bracket for coiling. Most of the enameled wires of large fixed inductors or adjustable inductors (such as oscillating coils, choke coils, etc.) are wrapped on the skeleton, and then the magnetic core, copper core, or iron core is installed into the inner cavity of the skeleton to increase the inductance.

Generally, the skeleton is made of plastic, bakelite, or ceramic, and can be made into different shapes according to actual needs. Small inductors (such as color code inductors) do not have a skeleton, and the enameled wires are directly wrapped on the magnetic core. For air-core inductors, there is no magnetic core, skeleton, or shielding case. The wires are first wound around a mold, and then the mold is removed, leaving a certain distance between the coils.

2. Winding

Winding refers to a group of coils with specified functions, which is the basic component of the inductor. The winding is divided into single-layer types and multiple layer types. The single-layer windings can be subdivided into dense winding and space winding, while the multilayer winding can be further divided into flat winding, random winding, and honeycomb winding.

An Inductor

3. Magnetic Core and Magnetic Rod

The magnetic core and magnetic rod are generally made of Ni-Zn ferrite and Mn-Zn ferrite materials, which are usually in the shape of a pillar, cap, or can. Advanced ferrite materials developed in recent years offer improved permeability and lower core losses, making them ideal for high-frequency applications in 5G and IoT devices.

4. Iron Core

The material of the iron core mainly includes silicon steel sheet, permalloy, etc., and its shape is mostly "E" type. Iron cores are particularly important in power inductors used in automotive and industrial applications where high current handling is required.

5. Shielding Case

In order to prevent the magnetic field generated by some inductors from affecting the normal operation of other circuits and components, a metal screen cover (such as the oscillating coil of a semiconductor radio) is added. The use of the shielding case will increase the loss of the coil and reduce the Q value. Modern shielding designs use advanced materials to minimize these losses while providing effective electromagnetic interference (EMI) protection.

6. Package

After the inductors are wound, the coils and magnetic cores are packaged with plastic or epoxy resin. Modern packaging techniques include ultra-compact SMD packages that enable high-density PCB layouts and improved thermal management for power applications.

II Common Types of Inductors

1. Adjustable Inductor

Commonly used adjustable inductors include oscillating coils for semiconductor radios, horizontal oscillating coils for TV sets, horizontal linear coils, intermediate frequency trap coils, frequency compensation coils for acoustics, and choke coils. While these were more common in legacy electronics, modern adjustable inductors are used in tunable RF circuits and impedance matching networks.

(1) Oscillating Coil for Semiconductor Radios

In a semiconductor radio, the oscillating coil is connected with a variable capacitor to generate a local oscillation signal higher than 465 kHz for the input radio signal received by the tuning circuit. The outer part is a metal shield, and the inner part is composed of a nylon lining, an H-shaped magnetic core, a magnetic cap, and a pin outlet. There are windings with high-strength enameled wire on the H-shaped core. The magnetic cap is mounted on the nylon frame inside the shield, which can be rotated up and down. By changing the distance between the cap and the coil, we can also change the inductance.

(2) Horizontal Oscillating Coils for TV

Horizontal oscillating coils were used in early black and white TV sets, which can form self-excited oscillation circuits (three-point oscillator, intermittent oscillator, or multivibrator) with peripheral resistor-capacitor units and horizontal oscillation transistors, to generate a rectangular pulse voltage signal of 15625Hz.

There is a square hole in the center of the magnetic core, and the line synchronization adjustment knob is directly inserted into it. By rotating the adjustment knob, we can change the relative distance between the core and the coil, thereby changing the inductance of the coil and keeping the line oscillation frequency at 15625Hz. In this way, this oscillation frequency with the line synchronization pulse sent by the automatic frequency control circuit (AFC) will generate synchronous oscillation.

Block Diagram of Receiver Showing Automatic Frequency Control

(3) Horizontal Linear Coil

The horizontal linear coil is a nonlinear magnetic saturation inductance coil, whose inductance decreases with the increase of current. It is generally connected in series in the line deflection coil circuit to compensate for linear distortion of the image with its magnetic saturation characteristics.

The horizontal linear coil is wound with enameled wires on an H-shaped high-frequency ferrite core or ferrite bar, and an adjustable permanent magnet is installed beside the coil. By adjusting the relative position of the permanent magnet and the coil, we can change the size of the coil inductance, so as to achieve linear compensation.

2. Choke Inductors

Choke inductors refer to the inductive coils used to block the AC path in the circuit. They are divided into high-frequency choke coils and low-frequency choke coils.

(1) High-Frequency Choke Coil

A high-frequency choke coil is used to prevent high-frequency alternating currents. It works in high-frequency circuits and is mostly with hollow or ferrite cores. The skeleton is made of ceramic materials or plastics, and the coils are wound with honeycomb segment winding or multilayer flat segment winding.

Choke Inductors

(2) Low-Frequency Choke Coil

Low-frequency choke coils are used in the current circuit, audio circuit, or field output circuit. Their function is to prevent low-frequency AC from passing.

Generally, the low-frequency choke coil used in the audio circuit is called the audio choke coil, the low-frequency choke coil used in the field output circuit is called the field choke coil, and that used in the current filter circuit is named the smoothing choke coil.

Low-frequency choke coils generally use "E" shaped silicon-steel sheet iron core, permalloy iron core, or ferrimagnetic core. In order to prevent magnetic saturation caused by large DC current, an appropriate gap should be left in the core during installation.

3. Surface Mount Inductors (SMD)

Surface Mount Device (SMD) inductors have become the dominant form factor in modern electronics. As of 2024, the SMD inductor market was valued at USD 5.59 billion and is projected to grow to USD 7.55 billion by 2032. These compact inductors are essential in smartphones, tablets, wearables, and IoT devices where space is at a premium. Recent developments by manufacturers like TDK Corporation include ultra-compact, high-current power inductors specifically designed for 5G smartphones, offering improved efficiency and thermal performance in miniaturized packages.

III Characteristics and Functions

1. Characteristics

The property of an inductor is just the opposite of that of the capacitor. It can prevent alternating current from passing and allow direct current to pass through smoothly.

When the DC signal passes through the coil, the resistance is the resistance of the wire itself, and the voltage drop is very small. When the AC signal passes through the coil, a self-induced electromotive force will be generated at both ends of the coil. The direction of self-induced electromotive force is opposite to the direction of applied voltage, hindering the passage of AC. The higher the frequency, the greater the coil impedance.

Inductors often work with capacitors in circuits to form LC filters, LC oscillators, etc. In addition, people also use the characteristics of inductors to manufacture choke coils, transformers, relays, and so on.

2. Functions

In the circuit, the inductor mainly plays the role of filtering, oscillation, delay, and notching. Besides, it can also filter signal and noise, stabilize current, and suppress electromagnetic wave interference.

The most common function of the inductor in the circuit is to form an LC filter circuit together with capacitors. If DC with many interference signals is passing through the LC filter circuit, then the AC interference signal will be changed into heat energy by the inductor. The signal with a higher frequency is the easiest to be impeded, thereby the interference signal of higher frequency is inhibited.

Series and Parallel LC Circuit

IV Parameters of Inductors

The main parameters of the inductor are inductance, allowable deviation, quality factor, distributed capacitance, and rated current.

1. Inductance

Inductance is also called the self-inductance coefficient, which is a physical quantity that represents the self-induction ability of the inductor.

The value of the inductance mainly depends on the number of turns of the coil, the winding method, whether there is a magnetic core, and the material of the magnetic core.

Generally, the greater the number of coil turns, the denser the coils, and the greater the inductance. A coil with a magnetic core has a larger inductance than a coil without a magnetic core. A coil with a larger magnetic permeability will have a larger inductance.

The basic unit of inductance is Henry, which is represented by the letter "H". Other commonly used units are millihenry (mH) and microhenry (μH), and the relationship among them is:

2. Allowable Deviation

Allowable deviation refers to the allowable tolerance between the nominal inductance and the actual inductance.

In general, the inductor used in oscillation or filtering circuits requires high precision, so the allowable deviation is ±0.2% - ±0.5%, while the precision of the coils used for coupling and the high-frequency choke is not high, thus the allowable deviation is usually ±10% - 15%.

3. Quality Factor

The quality factor, also known as Q value or optimal value, is the main parameter to measure the quality of the inductor.

It is the ratio of the inductance to its equivalent loss resistance when the inductor is operating at the AC voltage of a certain frequency.

The higher the Q value of the inductor, the smaller the loss and the higher the efficiency.

The quality factor of the inductor is related to the DC resistance of the coil wires, the dielectric loss of the coil frame, and the loss caused by the iron core and the shielding case.

4. Distributed Capacitance

Distributed capacitance refers to the capacitance between the turns of the coil, between the coil and the magnetic core, between the coil and the ground, and between the coil and the metal.

The smaller the distributed capacitance of the inductor, the better its stability. The distributed capacitance can reduce the equivalent loss resistance and decrease the quality factor.

To reduce the distributed capacitance, silk-covered wires or multistrand enameled wires are commonly used, and sometimes the honeycomb winding method is also employed.

Enameled Wires

5. Rated Current

The rated current is the maximum current value that the inductor can withstand under permitted working conditions.

If the working current exceeds the rated current, the performance parameters of the inductor will change due to heat, and the inductor may even be burned out due to overcurrent.

V Calculation Formulas

1. General Formula

L — inductance

μ — permeability of the magnetic core

Ae — the cross-sectional area of the magnetic core

N — the number of turns of the coil

l — the length of the magnetic path of the magnetic core

2. Empirical Formula

L — inductance, in Henry (H)

μ₀ — vacuum permeability. μ₀ = 4π × 10⁻⁷ H/m

μₛ — relative permeability of the magnetic core. For air core coil, μₛ = 1

N — the number of turns of the coil

S — the cross-sectional area of the coil, in square meters (m²)

l — the length of the coil in meters (m)

k — a coefficient that depends on the ratio of the radius (R) to the length (l) of the coil

VI Measurement of Inductance

1. Measurement Procedures

Types of inductance measurement instruments: RLC (resistance, inductance, and capacitance) meter and inductance measurement meter.

Measurement method: measurement with no-load current (theoretical value) and measurement in the actual circuit (actual value).

Here, we discuss the no-load measurement with RLC meter. The specific measurement procedures are:

(1) Get familiar with the instructions and precautions of the instrument.

(2) Turn on the meter and let it warm up for 15-30 minutes.

(3) Select the L gear, and choose inductance measurement.

(4) Clamp the two clips together and reset to zero.

(5) Clamp the two pins of the inductor with the two clips respectively, and read the value displayed on the screen.

(6) If the measured value is not within the range, adjust the range and measure again.

2. Marking Method on Circuit Diagram

The method of marking the inductance value in the circuit diagram is the same as that of the resistance value. The inductance unit is also marked. For example, if the inductance is 0.5 H, it is marked as 0.5 H; if the inductance is 5 mH, it is marked as 5 mH.

3. Judge the Performance

(1) Intuitive Inspection Method

This method is to check whether the magnetic core of the inductor is broken, whether the enameled wire has traces of breakage, and whether the lead contact is good. These conditions can be observed by the naked eye.

(2) Multimeter Detection Method

Use the resistance gear of the multimeter to measure the resistance of the inductor. If the resistance value is 0, it means the inductor is short-circuited. If the resistance value is infinite, it means the inductor is open-circuited. Both cases indicate that the inductor is damaged.

For inductors with iron cores, in addition to measuring the DC resistance, we should also check whether the iron core is in good contact with the skeleton. This can be done by gently pressing the iron core with a screwdriver to see if there is any change in the resistance value.

(3) Inductance Meter Detection Method

Use an inductance meter to directly measure the inductance value. If the measured value is significantly different from the nominal value, it indicates that the inductor has deteriorated or is damaged.

4. Precautions

(1) When measuring inductance, the inductor should be removed from the circuit to avoid interference from other components.

(2) The test frequency of the inductance meter should be close to the actual working frequency of the inductor.

(3) For adjustable inductors, the inductance value should be measured at the middle position of the adjustment range.

(4) When measuring small inductance values (less than 1 μH), the lead length and connection method will significantly affect the measurement results.

VII Inductor VS. Magnetic Bead

Both inductors and magnetic beads are used to suppress electromagnetic interference (EMI), but they work in different ways and are suitable for different applications.

Inductors:

• Store energy in a magnetic field

• Have high Q values (low resistance)

• Reflect high-frequency noise back to the source

• Used in power supply filtering and energy storage applications

Magnetic Beads:

• Dissipate energy as heat

• Have low Q values (high resistance at high frequencies)

• Absorb high-frequency noise and convert it to heat

• Used for EMI suppression in signal lines and data cables

The key difference is that inductors are reactive components that store and release energy, while magnetic beads are resistive components at high frequencies that dissipate energy. In modern high-speed digital circuits, magnetic beads are often preferred for EMI suppression because they don't reflect noise back into the circuit.

VIII Modern Applications and Market Trends (2024-2025)

The inductor industry has experienced significant evolution and growth in recent years, driven by emerging technologies and expanding applications across multiple sectors.

Market Overview

The global inductor market reached a valuation of USD 10.12-11.28 billion in 2024-2025 and is projected to grow at a compound annual growth rate (CAGR) of 4.3-4.45% through 2030-2032, reaching USD 14.02-14.41 billion. This growth reflects the increasing demand for inductors across consumer electronics, automotive, telecommunications, and industrial applications.

Key Application Areas

1. 5G and High-Frequency Communications

By 2025, adoption of high-frequency inductors has accelerated significantly, driven by the global rollout of 5G networks. These inductors must operate efficiently at frequencies exceeding 6 GHz while maintaining low losses and high Q factors. Manufacturers like TDK Corporation have developed ultra-compact, high-current power inductors specifically designed for 5G smartphones, addressing the challenges of miniaturization and thermal management.

2. Automotive and Electric Vehicles

The automotive power inductor market has shown remarkable growth, valued at USD 1.29 billion in 2024 and predicted to reach USD 3.30 billion in the coming years. Electric vehicles (EVs) require high-current inductors for DC-DC converters, battery management systems, and onboard chargers. These inductors must handle high temperatures, vibration, and electromagnetic interference while maintaining efficiency.

3. Internet of Things (IoT) and Wearables

IoT devices and wearable electronics demand ultra-miniature inductors with excellent power efficiency. The surface mount device (SMD) inductor market, valued at USD 5.59 billion in 2024, is projected to grow to USD 7.55 billion by 2032, reflecting the dominance of compact form factors in modern electronics.

4. Autonomous Systems and Robotics

Autonomous vehicles, drones, and robotic systems require sophisticated power management solutions. Inductors play critical roles in motor control, sensor power supplies, and communication modules, driving innovation in high-reliability components.

Technological Advancements

Advanced Materials

Recent developments in ferrite materials have led to improved permeability and lower core losses, enabling better performance at high frequencies. Nanocrystalline and amorphous metal cores are being adopted for applications requiring high saturation flux density and low losses.

Miniaturization

The trend toward smaller, more powerful devices continues to drive inductor miniaturization. Modern SMD inductors achieve package sizes as small as 0201 (0.6mm × 0.3mm) while maintaining adequate current ratings and inductance values for their applications.

Integrated Magnetics

Integrated magnetic components that combine multiple inductors or integrate inductors with transformers are gaining popularity in power supply designs, offering space savings and improved efficiency.

Market Conditions and Outlook

As of 2025, the inductor market is experiencing a cyclical low point, with lead times suggesting a weak market environment for mass-produced beads and chip inductors. However, this presents opportunities for innovation and consolidation within the industry.

Despite short-term challenges, the long-term outlook remains positive, driven by:

• Continued expansion of 5G infrastructure globally

• Accelerating adoption of electric vehicles

• Growth in renewable energy systems requiring power conversion

• Proliferation of IoT devices and edge computing

• Increasing demand for data centers and cloud computing infrastructure

Specialized Inductor Types

TLVR Dual Winding Inductors

The TLVR (Transient Load Voltage Regulator) dual winding inductor market represents a specialized segment, valued at USD 133 million in 2024 and projected to reach USD 235 million by 2032, growing at 8.7% CAGR. These inductors are critical for high-performance computing applications where rapid load transients must be managed effectively.

Future Directions

The inductor industry is expected to focus on several key areas in the coming years:

1. Higher Operating Frequencies: As wireless communication standards evolve beyond 5G, inductors capable of efficient operation at millimeter-wave frequencies (30-300 GHz) will become increasingly important.

2. Improved Thermal Management: With increasing power densities, inductors with better thermal dissipation characteristics and higher temperature ratings will be essential.

3. Smart Inductors: Integration of sensors and monitoring capabilities within inductors for predictive maintenance and real-time performance optimization.

4. Sustainable Manufacturing: Development of environmentally friendly materials and manufacturing processes to meet increasingly stringent environmental regulations.

5. AI-Optimized Designs: Use of artificial intelligence and machine learning to optimize inductor designs for specific applications, reducing development time and improving performance.

Industry Insight: The inductor market's evolution reflects broader trends in electronics miniaturization, energy efficiency, and the convergence of digital and power electronics. As devices become more sophisticated and power-hungry, the role of inductors in enabling efficient power management becomes increasingly critical.

Conclusion

Inductors remain fundamental components in modern electronics, with their importance growing alongside technological advancement. From basic filtering and energy storage to sophisticated power management in cutting-edge applications like 5G communications and electric vehicles, inductors continue to evolve to meet the demands of next-generation systems.

Understanding inductor structure, parameters, and measurement techniques is essential for engineers and technicians working with electronic circuits. As the industry moves toward higher frequencies, greater miniaturization, and improved efficiency, staying informed about the latest developments in inductor technology becomes increasingly important for successful circuit design and implementation.

The market outlook for inductors remains strong, with steady growth projected across multiple application segments. Innovation in materials, manufacturing processes, and design methodologies will continue to drive the industry forward, enabling new applications and improving the performance of existing systems.

Key Takeaways:

• Inductors are essential passive components that store energy in magnetic fields and oppose changes in current

• Key parameters include inductance, quality factor (Q), rated current, and distributed capacitance

• Surface mount inductors dominate modern applications, with the market valued at USD 5.59 billion in 2024

• Major growth drivers include 5G communications, electric vehicles, IoT devices, and autonomous systems

• The global inductor market is projected to reach USD 14+ billion by 2030-2032

• Technological advances focus on miniaturization, higher frequencies, and improved thermal management

• Proper measurement and testing are critical for ensuring inductor performance in circuit applications

References and Citations:

Intel Market Research - TLVR Dual Winding Inductor Market Outlook 2025-2032
TTII Market Eye - Global Market Update for Inductors, Beads and Cores (2025)
Mordor Intelligence - Inductor Market Size, Growth, Trend Analysis & Industry Report
LinkedIn Industry Analysis - How High Frequency Inductors Works (2025)
Precedence Research - Automotive Power Inductor Market Size Report
Intel Market Research - Surface Mount (SMD) Inductor Market Outlook 2025-2032
Market Report Analytics - Unlocking the Future of Power Inductors for Consumer Application
Straits Research - Inductors, Cores, and Beads Market Size, Trends & Growth Report