The Earth's magnetic field is one of those natural phenomena that, although often overlooked in our daily lives, has been essential to the evolution of our planet and to scientific and technological development from ancient times to the present day. Today, their study and measurement, as well as the understanding of their properties and applications in various fields, constitute a fundamental basis for branches such as geophysics, industry, medicine, and engineering.
Many of us wonder how it is measured, what magnitudes describe it, what instruments are used (such as the gaussmeter), and why it is so relevant in our modern lives. In this article, we will thoroughly and thoroughly break down the nature, characteristics, and methods of measuring the Earth's magnetic field, reviewing well-known concepts such as the tesla and the gauss, as well as the historical and conceptual evolution of this physical field, its technological implications, and the role of scientists such as Gauss, Faraday, Ampère, and Maxwell in the understanding of magnetism. There will be no shortage of explanations about magnetic materials, measuring devices, units of measurement, technical applications, and recent advances. Prepare for an in-depth and accessible tour of the fascinating world of Earth's magnetism and its measurement, guided by science and technology.
What is a magnetic field? A physical approach
El magnetic field It is a vector-type physical quantity. This means that it is described by a magnitude (intensity), a direction, and a sense. A magnetic field can be generated by moving electric charges (for example, an electric current in a wire), by magnets, or even by subatomic particles. In mathematical terms, a magnetic field is usually represented by the letter B.
The intensity of the magnetic field is measured in the International System of Units (SI) using the tesla (T), while in the cgs system the gauss (G) is used. To give you an idea, one tesla is equal to 10.000 gauss, meaning the tesla is a much larger unit; the gauss is more practical for everyday applications or for describing less intense magnetic fields, such as the Earth's. For example, the Earth's magnetic field at sea level is around 0,5 gauss.
How is Tesla defined?
Un tesla is the magnetic field that exerts a force of 1 newton (N) on a charge of 1 coulomb (C) moving at a speed of 1 meter per second (m/s) perpendicular to the field. Mathematically, it is the magnitude of B in the expression for the Lorentz force: F = q · (v × B), where the force exerted depends on the charge, its speed and the angle with respect to the field.
And the gauss?
El gauss It is the centigram unit for measuring magnetic flux density or magnetic field intensity. Although it does not belong to the SI, it is still widely used in physics, engineering, geophysics, and technical disciplines. 1 Tesla = 10.000 gaussIf you work in laboratories, industry, or education, you'll encounter both units depending on the context.
History and evolution of the study of magnetism
Magnetism has been known and used by humanity since ancient times. magnetite, a mineral capable of attracting iron, was already mentioned by the Chinese and Greeks thousands of years ago. The compass, used for maritime navigation, appeared in China around the 11th century and revolutionized navigation methods worldwide.
The great scientific leap comes with william gilbert In 1600, in his work "De Magnete," he proposed that the Earth is itself a gigantic spherical magnet. He not only observed the behavior of compasses, but also proposed that the magnetic field surrounding the planet originates within the Earth itself.
Later, the science of magnetism advanced thanks to discoveries and research by scientists such as Hans Christian Orsted (discovered the relationship between electricity and magnetism in 1820), Andre-Marie Ampere (formulated the law that bears his name on the interaction of electric currents), Michael Faraday (developed electromagnetic induction) and Carl Friedrich Gauss (German mathematician and physicist who, together with Wilhelm Weber, contributed to the modern formulation of magnetism and the measurement of the Earth's field).
In 1838, Gauss publishes his "General Theory of Magnetism", demonstrating that the main origin of the Earth's magnetic field is within the planet, a fundamental idea for modern geophysics that complements the current dynamo theory (explains the generation of the field by the movement of molten metals in the Earth's outer core).
The Earth's magnetic field: origin and variability
The Earth behaves like a gigantic magnet, with their corresponding magnetic poles. Although for centuries it was thought that its origin was in the crust, today we know that the The Earth's magnetic field is generated by electric currents originating from the movement of liquid metals and ions in the planet's outer core. (at depths of between 2.900 and 5.100 km below the surface). This is the well-known dynamo theory.
How is the Earth's magnetic field measured?
Since the magnetic field is a vector magnitude, is characterized by three parameters: modulus (intensity), direction and sense. It is also often broken down into Cartesian components: X (north-south component), Y (east-west) and Z (vertical). The composition of X and Y gives the horizontal component (H). In addition, two key angles are measured:
- Declination (D): angle between magnetic north and geographic north.
- Tilt (I): angle formed by the horizontal component with respect to the Z axis (vertical).
The total module of the field (also called F) results from the combination of the three components. It is generally expressed in Tesla or, being more manageable submultiples, in nanoteslas (nT): 1 nT = 10-9 TTo give you a reference, the magnetic field at the Earth's equator is around 30.000 nT and at the poles it reaches 60.000 nT, with a more horizontal direction at the equator and almost vertical at the poles.
Temporal and geographical variability
The Earth's magnetic field is not static. It can change both in intensity and direction over the years (secular variation). In addition, there are diurnal variations caused by solar radiation, and phenomena such as magnetic storms (caused by the interaction of the solar wind with the Earth's magnetosphere) that can significantly alter the field, especially at high latitudes.
The magnetic poles do not coincide exactly with the geographic poles and shift over time.For this reason, magnetic declination must be taken into account in navigation and when creating nautical charts, in order to correct compass headings.
Historical and practical importance
Since ancient times, knowledge of the Earth's magnetic field has been essential for navigation. In ancient times, sailors steered by the stars, but they could only do so at night and if weather conditions permitted. The magnetic compass It allowed orientation during the day and under any weather conditions, increasing navigation safety, as long as updated magnetic declination charts were available.
Units of measurement of the magnetic field: from tesla to gauss
Magnetic field measurements use various historical and modern units. Currently, the most relevant are:
- Tesla (T): International System unit for magnetic flux density (B).
- Gauss (G): cg/g unit also used to measure magnetic flux density; 1 tesla = 10.000 gauss.
- Oersted (Oe): cgs unit for measuring magnetic field strength (H), related but not equivalent to B.
- Weber (Wb): SI unit for measuring the total magnetic flux (φ), resulting from multiplying the magnetic flux density (B) by the area crossed by the field lines.
- Maxwell (Mx): cgs unit of magnetic flux, with the ratio 1 Wb = 108 Max.
Using different units can sometimes be confusing, especially when converting values between systems. It is important to always remember that 1 tesla is equivalent to 10.000 gauss and that 1 ampere per meter (SI unit for H) is equal to 4π × 10-3 oersted in the cegesimal system.
Magnetic materials and magnetic field response
When an external magnetic field acts on a substance or material, the response depends on its atomic structure and intrinsic magnetic properties. Therefore, materials are classified as:
- Diamagnetic: They oppose resistance to the external field, magnetizing in the opposite direction. They are repelled by the magnetic field. Examples: water, bismuth, gold, silver, noble gases.
- Paramagnetic: They are attracted to the magnetic field and become magnetized in the same direction. Without an external field, they do not remain magnetized. Examples: aluminum, platinum, oxygen.
- ferromagnetic: They can spontaneously magnetize and maintain magnetism even without an external field. They are the basis of permanent magnets. Examples: iron, nickel, cobalt, gadolinium, and some alloys.
La magnetic permeability measures the ability of a material to conduct magnetic flux lines. In the SI, a distinction is made between absolute permeability (in H/m) and relative permeability (ratio with respect to that of the vacuum, whose value is 4π·10-7 H/m). Diamagnetics have a permeability slightly less than one, paramagnetics slightly higher, and ferromagnetic ones are much higher and non-linear.
A notable phenomenon is the magnetic hysteresis In ferromagnetic materials: once magnetized, they can maintain the field even if the external field disappears, and they require a field in the opposite direction to demagnetize them.
Magnetic field measurement: gaussmeter and other devices
Various instruments are used to measure the intensity and orientation of magnetic fields, both in the laboratory and in industrial or geophysical applications. The most widely used is the gaussmeter.
What is a gaussmeter?
El gaussmeter It is an electronic instrument designed to measure magnetic flux density, expressed in gauss or tesla, and sometimes with submultiples such as microtesla. It allows for the analysis of both the intensity (modulus) and direction of the field, and can detect static (permanent magnets, Earth's field) or dynamic (electric currents, alternating fields) magnetic fields.
Types of gaussmeters according to the operating principle
- Hall effect sensors: Based on the hall effect (generation of a perpendicular voltage in a conductive material by the action of a magnetic field). They are precise and suitable for most applications, both in the laboratory and in industry.
- Magnetoresistive sensorsThey exploit the variation in the electrical resistance of certain materials under the influence of a magnetic field. They are compact, efficient, and used to detect low or fluctuating fields.
- induction coils: They detect variations in the magnetic field through electromagnetic induction (Faraday's law), mainly useful for alternating fields.
The choice of gaussmeter type will depend on the application, the measurement range, and the nature of the magnetic field.
Parts of a modern gaussmeter
- Esophageal Temperature : This is the sensitive part of the device, where the sensor is located. There are flat probes (for measuring the transverse field) and cylindrical or axial probes (for measuring the parallel field, such as inside solenoids).
- Processor: Interprets the sensor signal and performs the necessary calculations.
- Screen: Displays the detected magnetic field values in real time.
Many gaussmeters incorporate data storage, maximum/minimum recording, and the ability to transfer results to computers or geographic information systems (GIS) for advanced analysis.
How do you use a gaussmeter?
- Calibration and preparation: It is essential to ensure that the device is calibrated (following the manufacturer's guidelines) and prepared with the appropriate scale for the expected field range.
- probe placement: The probe must be positioned correctly, usually using the lettered side to ensure the measurement direction. Orientation depends on the field type (transverse or axial).
- Reading and recordingOnce the probe is positioned, wait for the reading to stabilize and then document the result. Advanced devices can store multiple readings for comparison or to analyze time trends.
La gaussmeter accuracy It depends on the quality of the sensor, its calibration, the probe used, and the absence of interference. Typical resolution for advanced models can reach 0,1%–2% of the maximum measurement range. Factors such as temperature and the presence of external magnetic fields can affect accuracy, so it is advisable to repeat measurements and, if necessary, recalibrate.
What fields can a gaussmeter measure?
Gaussmeters can measure both direct current (DC) and alternating current (AC) magnetic fieldsIn the case of alternating fields, the instrument typically displays the effective (RMS) value of the field. Some advanced models can distinguish between the two types, which is especially useful in industrial or scientific applications where the nature of the field is important.
Also exist teslameters, equivalent devices but which display the results directly in teslas, more suitable for very intense magnetic fields (such as those generated in magnetic resonance imaging or in materials physics laboratories).
Applications of the gaussmeter and magnetic field measurement
Magnetic field monitoring and analysis has enormous practical applications in a variety of fields, from fundamental research to everyday life.
Industry and manufacturing
Magnetic quality control: Ensure that the magnets produced meet specifications and that the electric motors and generators operate under optimal conditions.
Electrical equipment testing: Evaluation of motors, transformers, solenoids and other components to prevent failures or low efficiency.
Detection of hidden metal objects or security systems: Used in access controls, alarm systems and location of ferromagnetic elements.
Scientific and geophysical research
Study of the Earth's magnetic field: Analysis of field variations allows for investigation of the planet's internal structure, the dynamics of the Earth's core, and its interaction with the solar wind.
Materials Physics: Research into the magnetic properties of new materials and compounds in physics and chemistry laboratories.
Geology and mining prospecting: Used to detect variations in the magnetic field associated with the presence of minerals.
Medicine and health
Calibration of medical equipment: Such as magnetic resonance imaging (MRI) machines, where the accuracy of the magnetic field is essential for image safety and quality.
Environmental studies: Evaluation of magnetic fields in domestic, industrial or urban environments to analyze possible health effects.
Everyday practical applications
Technical diagnosis: Troubleshooting motors and domestic or industrial electrical equipment.
Construction and installation checks: Verification of the integrity of magnetic shields, electromagnetic protection, etc.
Automotive, renewable energy and electronics
Automotive: Optimization of electric motors in hybrid and electric vehicles, testing of magnetic sensors and actuators.
Renewable energy: Measuring the efficiency of magnetic generators in wind turbines and controls in sustainable power generation systems.
Electronics devices: Calibration of magnetic sensors in mobile phones, tablets, digital cameras and other gadgets.
Recent innovations and emerging applications
Advances in the development of miniaturized sensors, portable devices, and automated data acquisition systems They have expanded the use of the gaussmeter and its applications into new fields: from robotics, artificial intelligence and the Internet of Things (IoT), to space exploration and biomedicine.
Converting and comparing units: from the laboratory to everyday life
The combination of tesla and gauss is common in technical, educational, and everyday settings. Here are some important equivalences to remember:
- 1 tesla (T) = 10.000 gauss (G)
- 1 gauss = 0,0001 tesla (T)
- 1 weber = 108 Maxwell (Mx)
In advanced measuring instruments, the results are usually presented in microtesla (μT) or nanoteslas (nT), especially in geophysical and environmental applications. Thus, the Earth's magnetic field typically ranges between 30.000 nT and 60.000 nT, depending on latitude and other conditions.
The physics of the magnetic field: flux density and force on particles
The physical analysis of the magnetic field is based on the magnetic flux density (B), which describes the action of the field on moving electric charges. The force exerted by a magnetic field on a charge is expressed by the Lorentz force: F = q · (v × B)Where q is the load, v speed and B the magnetic flux density.
Depending on the angle between the velocity and the field, the force can vary between zero (if they are parallel) and maximum (if they are perpendicular). The direction of this force is determined by the well-known right hand rule.
Magnetic properties and behaviors of materials
Diamagnetism
Characteristic of substances that slightly oppose the external magnetic field, generating an induced field in the opposite direction. Diamagnetism is universal, but is only noticeable in materials where other types of magnetism (such as ferromagnetism or paramagnetism) are very weak or nonexistent. Notable examples are bismuth, copper, gold, silver, water, and noble gases. Diamagnets are repelled from areas of strong magnetic fields, and this phenomenon is the basis of the diamagnetic levitation.
Paramagnetism
In paramagnetic materials, atoms or molecules have individual magnetic moments that align with the external field, attracting each other to the areas of greatest intensity. However, they do not retain significant magnetization when the field is turned off. Examples include aluminum, platinum, oxygen, certain metal oxides, and other chemicals.
Ferromagnetism
It is the property that allows some materials (such as iron, nickel, cobalt, or gadolinium) to spontaneously magnetize and maintain that state once the field is removed. Their atomic magnetic moments align spontaneously. Ferromagnetism is essential in the manufacture of permanent magnets, transformer cores, and magnetic memories. When the Curie temperature, ferromagnetic materials become paramagnetic, losing their spontaneous magnetism.
Magnetic permeability
La permeability It defines the ease with which a material allows the passage of magnetic field lines. In superconductors, the permeability is practically zero, causing them to completely expel the magnetic field (Meissner effect).
The practical measurement of the Earth's magnetic field
Measuring the Earth's magnetic field, its components and variations is essential in numerous experiments, studies and technical applications. One of the most common experiments is the determination of the horizontal component of the Earth's field (H) using, for example, the Biot-Savart law and Ampère's law. These laws allow the calculation of the contribution of electric currents to the generation of the local magnetic field.
To perform these measurements it is important:
- Use calibrated equipment (gaussmeters, Hall probes, precision magnetometers).
- Pay attention to environmental conditions (absence of nearby sources of electromagnetic interference, thermal stability).
- Take a series of repeated measurements to obtain an average value and reduce errors due to temporary fluctuations.
The values obtained are usually expressed in teslas, gauss, or, more commonly, nanoteslas. The results allow for analysis of the vectorial nature of the field and its possible local variations due to geological structures, solar activity, or anthropogenic factors.
Technological and scientific applications of magnetism and its measurement
Electronics and appliances
The principle of action of the magnetic field is the base of the vast majority of motors, electric generators and transformers present in modern life. These devices convert mechanical energy into electrical energy (and vice versa) and operate thanks to the magnetic forces acting on moving conductors within a field.
The electromagnetic relays, for example, enable automatic circuit switching in a multitude of applications, from doorbells to large industrial systems, based on the properties of magnetism and induction.
Communications and information storage
Magnetism is also the basis of the functioning of magnetic memories (hard drives, tapes, cards), speakers, dynamic microphones and numerous sensors used in electronic devices and automatic control systems.
In laboratories and scientific experiments, accurately recording magnetic fields with advanced gaussmeters is essential for developing new technologies, studying innovative materials, and discovering new applications in the era of artificial intelligence and the Internet of Things.
Space exploration, drones and automotive
The development of efficient and lightweight electric motors has enabled the emergence of robots, drones, and autonomous vehicles, both on land and in space. Many of these systems use high-precision magnetic sensors for navigation, positioning, and trajectory correction. Next-generation delivery drones, space rovers, and electric vehicles feature multiple integrated magnetic field sensors.
Health and radiation protection
In medicine, magnetic resonance imaging relies on precise control of the magnetic field to obtain reliable and safe diagnostic images. Quality control, calibration, and monitoring of these fields are performed using high-resolution gaussmeters.
Challenges in the measurement and control of current magnetic fields
Accurate measurement of magnetic fields poses technical and scientific challenges, both in maintaining long-term accuracy and in reducing errors caused by interference, changes in sensor properties, or environmental variations. Therefore, the development of Robust sensors, automatic calibration systems and wireless technologies constitutes one of the most dynamic trends in the sector.
Furthermore, the expansion of artificial magnetic fields generated by modern technology (power lines, antennas, transformers, electronic devices) has opened up new lines of study on potential effects on the environment and human health, as well as the need to establish appropriate regulations and control procedures.
Future and trends in magnetic field measurement
The integration of magnetic sensor systems in industry 4.0, the miniaturization of portable devices, the emergence of systems for recording and processing massive data (big data) and the digitalization of measurements allow us to imagine a future with smart magnetic sensors, capable of being integrated into textiles, autonomous vehicles, satellites and personal devices.
In geophysics, real-time monitoring of the Earth's field, the development of automated observatories, the creation of global models of magnetic variation, and the application of artificial intelligence to predict solar storms or geodynamic trends represent a research and development frontier of great social and scientific impact.
The magnetic field surrounds us, influences life and technology, and continues to offer challenges and opportunities for scientific exploration, technical innovation, and the protection of our planet from external and internal threats. Its precise measurement, understanding of its properties, and the ability to manipulate it with increasingly sophisticated tools will continue to drive key advances in the coming decades. Today, understanding how to measure, interpret, and harness it is as relevant today as it was for 11th-century Chinese navigators or 19th-century physicists: we continue to navigate, but now in the seas of technology and knowledge.