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Magnetic Fields

Magnetic Fields

A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...

Magnetic Field of a Solenoid

Magnetic Field of a Solenoid

A solenoid is a conducting wire coated with an insulating material, wound tightly in the form of a helical coil. The magnetic field due to a solenoid is the vector sum of the magnetic fields due to its individual turns. Therefore, for an ideal solenoid, the magnetic field within the solenoid is directly proportional to the number of turns per unit length and the current. Conversely, the magnetic field outside the solenoid is zero.
Consider a solenoid with 100 turns wrapped around a cylinder of...

Magnetic Field Lines

Magnetic Field Lines

The representation of magnetic fields by magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. Each of the magnetic field lines forms a closed loop. The field lines emerge from the north pole (N), loop around to the south pole (S), and continue through the bar magnet back to the north pole.
Magnetic field lines follow several hard-and-fast rules:

Energy In A Magnetic Field

Energy In A Magnetic Field

If a magnetic field is sustained, there must be a current in a closed circuit or loop, implying some energy has been spent in creating the field. If this energy is not dissipated via the circuit's resistance, it is stored in the field.
Take an ideal inductor with zero resistance. Although it's practically impossible, assume that the coil's resistance is so small that it is practically negligible. The loss of the field's energy to dissipate thermal energy (or heat) is thus...

Magnetic Field Of A Current Loop

Magnetic Field Of A Current Loop

Consider a circular loop with a radius a, that carries a current I. The magnetic field due to the current at an arbitrary point P along the axis of the loop can be calculated using the Biot-Savart law.

Magnetic Field due to Moving Charges

Magnetic Field due to Moving Charges

A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...

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Related Experiment Video

Updated: Jan 23, 2026

Smartphone Fundus Photography

Smartphone Fundus Photography

Published on: July 6, 2017

Floor Identification Using Magnetic Field Data With Smartphone Sensors.

Imran Ashraf¹, Soojung Hur², Muhammad Shafiq³

¹Department of Information and Communication Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 38541, South Korea. ashrafimran@live.com.

Sensors (Basel, Switzerland)

|June 6, 2019

Summary

This study introduces a novel magnetic field-based floor identification system using smartphone sensors. This infrastructure-free approach significantly improves indoor positioning accuracy compared to Wi-Fi and barometric methods.

Keywords:

fingerprinting floor identification geomagnetism indoor localization machine learning smartphone sensors

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Area of Science:

Utilizes geomagnetism for indoor positioning and localization applications.

Background:

Existing floor identification systems using Wi-Fi and barometric pressure have limitations.
Wi-Fi systems are susceptible to environmental interference and signal degradation.
Barometric systems necessitate dedicated, additional sensor installations.

Purpose of the Study:

To develop an infrastructure-free and cost-effective floor identification system.
To leverage pervasive magnetic fields and smartphone sensors for enhanced indoor localization.
To improve the accuracy of floor identification in multi-story buildings.

Main Methods:

Employs smartphone magnetic sensors for floor detection.
Utilizes user activities like walking, call listening, and phone swinging.
Applies various machine learning techniques for activity recognition and floor identification.
Investigates the effect of device heterogeneity on system performance.

Main Results:

Magnetic floor identification demonstrates superior accuracy over barometric and Wi-Fi methods.
The proposed scheme is infrastructure-free and cost-effective.
Incorporation of a floor change module further boosts identification accuracy.
Performance is validated across different smartphone models (Samsung Galaxy S8, LG G6, LG G7).

Conclusions:

Magnetic field-based floor identification offers a robust and accurate alternative for indoor positioning.
Smartphone sensors are effective for implementing an infrastructure-free localization solution.
The system shows promise for widespread adoption in multi-story indoor environments.