Glossary of Magnet Terms
A
The air gap, in the context of magnets and magnetic materials, refers to the non-magnetic space or distance that separates two magnetic materials or components. This space is typically filled with air or another non-magnetic material, which is why it’s called an “air gap.” The presence of an air gap affects the magnetic circuit’s overall performance by introducing magnetic resistance, also known as reluctance.
Imagine a bridge made of magnetic material, and the air gap is like a break in the bridge. The magnetic force has to “jump” across the gap to continue its path. The larger the air gap, the more difficult it is for the magnetic field to bridge the gap, resulting in a weaker magnetic field on the other side.
Air gaps are essential in various applications, such as electric motors, transformers, and magnetic sensors, to control the magnetic field’s strength and behavior. In these devices, the air gap allows for precise control over the magnetic field, helping optimize their performance and efficiency.
Anisotropic refers to a property of materials in which their characteristics vary depending on the direction they are measured. In the context of magnetic materials, anisotropic means that the material exhibits different magnetic properties in different directions.
Anisotropic magnetic materials are engineered to have a preferred direction of magnetization, called the “easy axis.” This easy axis is the direction in which the material’s magnetic domains align most efficiently, leading to a stronger magnetic field. When magnetized along the easy axis, anisotropic materials produce a much higher magnetic output than when magnetized in other directions.
An example of anisotropic magnetic material is a Neodymium Iron Boron (NdFeB) magnet, which is specifically designed to have a preferred direction of magnetization. This property allows the magnet to produce a stronger magnetic field when magnetized along the easy axis, making it suitable for applications requiring high magnetic performance, such as electric motors, hard disk drives, and magnetic separators.
B
The B/H curve, also known as the magnetization curve or hysteresis loop, is a graphical representation of the relationship between the magnetic flux density (B) and the magnetic field strength (H) in a magnetic material. This curve provides valuable insights into a material’s magnetic properties, behavior, and performance.
BHmax, or Maximum Energy Product, is a crucial parameter used to describe the performance of a permanent magnet. It represents the maximum amount of magnetic energy that can be stored in the magnet and is typically measured in units of Mega-Gauss-Oersteds (MGOe) or Kilojoules per cubic meter (kJ/m³).
Brmax, or Residual Induction, is a key parameter that describes the magnetic properties of a permanent magnet. It represents the maximum magnetic flux density (B) that a magnetized material can retain after the external magnetic field (H) is removed. In other words, it’s a measure of the magnet’s ability to hold onto its magnetism once it has been magnetized.
C
Coercive force (Hc) is an important parameter that describes the magnetic properties of a permanent magnet. It represents the strength of the external magnetic field (H) required to reduce the magnetic flux density (B) of a magnetized material to zero. In simpler terms, coercive force is a measure of a magnet’s resistance to demagnetization.
Curie Temperature (Tc) is a critical parameter that describes the thermal properties of magnetic materials. It is the temperature at which a magnetic material loses its ferromagnetic properties and transitions into a paramagnetic state. In other words, it’s the temperature at which a magnetic material loses its ability to maintain a stable magnetic field.
When a magnetic material is heated to its Curie Temperature, the thermal energy disrupts the alignment of its magnetic domains, causing them to become randomly oriented. As a result, the material loses its magnetization and is no longer able to generate a strong magnetic field.
Different types of magnetic materials have different Curie Temperatures. For example, Neodymium Iron Boron (NdFeB) magnets have a lower Curie Temperature compared to Samarium Cobalt (SmCo) magnets, making SmCo magnets more suitable for high-temperature applications.
D
The demagnetization curve is a portion of the B/H curve (magnetization curve) that illustrates the behavior of a magnetic material as it loses its magnetization when exposed to a reverse external magnetic field (H). The demagnetization curve is crucial for understanding the stability and performance of permanent magnets under various operating conditions.
Demagnetization force, also known as demagnetizing field or demagnetizing factor, is a term used to describe the internal magnetic field within a magnetic material that opposes its magnetization. This internal magnetic field is generated due to the shape and geometry of the magnet and has the effect of reducing the overall magnetic field strength.
When a magnetic material is magnetized, the magnetic domains within the material align, producing a magnetic field. However, due to the shape of the magnet, the magnetic field lines are not perfectly uniform, and some of them loop back inside the magnet, creating a demagnetizing field that opposes the magnetization. The demagnetization force can weaken the effective magnetic field produced by the magnet and can even lead to demagnetization if the external magnetic field is reversed or if the magnet is exposed to high temperatures.
The demagnetization force is strongly influenced by the shape and geometry of the magnet. Magnets with a high length-to-width ratio, such as long and thin bar magnets, have a lower demagnetization force than those with a low length-to-width ratio, such as flat, wide magnets. By optimizing the shape and geometry of a magnet, engineers can minimize the demagnetization force, improving the stability and performance of the magnetic field in various applications, such as motors, generators, and sensors.
Dimensions refer to the physical measurements of a magnet or magnetic component, such as length, width, height, or diameter.
Our range of product dimensions typically spans from as small as 1/32” to as large as 4”. However, we have the capabilities to produce magnets of dimensions outside this range as well, whether smaller or larger. Should you require such specifications, please don’t hesitate to contact us at sales@epimagnets.com with your specific requirements or technical drawings. We are committed to meeting your magnetic needs!
Dimensional tolerance is a term used to describe the allowable variation in the physical dimensions of a magnet or magnetic component during manufacturing. It indicates the range within which the actual measurements of the magnet can deviate from the specified dimensions without affecting its performance or suitability for its intended application.
Generally, the tolerance of EPI magnets is +/– .004” for all dimensions. Tighter tolerance is also available.
Magnetic dipole moment (m) is a vector quantity that represents the strength and orientation of a magnetic dipole, such as a small bar magnet or a magnetic particle within a material. It is used to describe the magnetic behavior of objects and helps in understanding how they interact with external magnetic fields.
A magnetic dipole can be thought of as a tiny magnet with a north and south pole. The magnetic dipole moment points from the south pole to the north pole and is proportional to the strength of the magnetic field produced by the dipole. The unit of magnetic dipole moment is Ampere square meters (A·m²) or sometimes given in terms of the Bohr magneton or nuclear magneton for atomic and subatomic particles.
E
An electromagnet is a type of magnet that generates a magnetic field through the flow of electric current. Unlike permanent magnets, which maintain their magnetism constantly, electromagnets can be turned on and off by controlling the electric current passing through them.
F
Ferromagnetic materials are a special class of magnetic materials that exhibit strong and spontaneous magnetization due to the alignment of their atomic magnetic dipoles. These materials have the unique ability to become magnetized when exposed to an external magnetic field and can retain their magnetization even after the field is removed, making them suitable for the fabrication of permanent magnets.
G
Gauss (symbol: G) is a unit of measurement used to express magnetic flux density, also known as magnetic induction. It is named in honor of the German mathematician and physicist Carl Friedrich Gauss, who made significant contributions to the field of magnetism.
A gauss meter, also known as a magnetometer or a teslameter, is a device used to measure the magnetic flux density (the strength of a magnetic field) in gauss or tesla.
Various types of magnets exist, such as Neodymium, Samarium Cobalt, Ceramic, and Alnico, to name a few.
Each magnet type is produced in an assortment of grades. The term ‘grade’ refers to the material’s chemical composition and associated magnetic attributes. Depending on its fundamental components and manufacturing process, each material grade will exhibit distinct magnetic characteristics.
Click the following links to explore EPI comprehensive list of Neodymium magnet grades, SmCo magnet grades and Alnico magnet grades.
H
A hysteresis loop, also known as a magnetization curve or B-H curve, is a graphical representation of the relationship between the magnetic flux density (B) and the applied magnetic field strength (H) in a magnetic material. It illustrates the magnetic behavior of the material when it is subjected to cyclic changes in the external magnetic field and provides essential information about its magnetic properties and performance.
I
Induction, represented by the symbol B, refers to the magnetic flux density in a material or a region of space. It is a measure of the strength of a magnetic field and is an important parameter in characterizing magnetic materials and devices. Magnetic flux density is often simply referred to as the magnetic field, although technically, it represents the response of a medium to an applied magnetic field.
The unit of magnetic flux density in the International System of Units (SI) is the tesla (T), while in the CGS system, it is expressed in gauss (G), where 1 tesla equals 10,000 gauss (1 T = 10,000 G).
Intrinsic Coercive Force (Hci) is a magnetic property that represents a material’s inherent resistance to demagnetization. It is an important parameter in characterizing magnetic materials, especially permanent magnets, as it provides insight into their ability to maintain magnetization when subjected to external magnetic fields or changes in temperature.
The intrinsic coercive force is measured in units of oersted (Oe) or ampere per meter (A/m) and is typically determined from the hysteresis loop (B-H curve) of a magnetic material. It is the reverse magnetic field strength required to bring the internal magnetization of the material to zero, removing any remaining influence of the external magnetic field.
Irreversible losses refer to the partial or complete demagnetization of a permanent magnet due to exposure to external factors, such as high temperatures, external magnetic fields, or mechanical stress. These losses can degrade the performance and efficiency of magnetic devices and systems, making it essential to consider them during the design and operation of such devices.
Some common causes of irreversible losses include:
High temperatures: When a magnet is exposed to temperatures beyond its maximum operating temperature or close to its Curie temperature, its magnetic domains can become misaligned, resulting in a reduction of the magnet’s overall magnetic strength.
External magnetic fields: Exposure to strong external magnetic fields can cause the magnetic domains in a magnet to realign or become randomized, reducing the magnet’s magnetic strength.
Mechanical stress: Physical impacts, vibrations, or mechanical stress can cause microstructural changes or damage to a magnet, which can result in a decrease in its magnetic strength.
Isotropic Material
K
A keeper, also known as a shunt or a shorting bar, is a piece of magnetic material that is used to connect the poles of a permanent magnet, creating a closed magnetic circuit. Keepers help to protect the magnet from demagnetization, reduce the external magnetic field, and minimize the risk of attracting ferromagnetic objects unintentionally.
When a keeper is placed across the poles of a magnet, it provides a low reluctance path for the magnetic flux, which means the magnetic field lines prefer to travel through the keeper instead of the surrounding air.
Keepers are typically made of soft magnetic materials, such as iron or low-carbon steel, which have high magnetic permeability and low coercivity. These materials provide an easy path for the magnetic flux while not retaining any significant magnetism when the keeper is removed.
It is important to note that keepers are not necessary for all types of permanent magnets or applications. In some cases, the magnetic circuit may be inherently closed due to the design of the magnetic device or system, making the use of a keeper unnecessary. However, for certain applications, such as storing or handling strong permanent magnets, keepers can provide valuable protection and safety benefits.
Kilogauss (kG) is a unit of measurement used to express magnetic flux density or magnetic induction, which represents the strength of a magnetic field. The term “kilogauss” is derived from “gauss,” a unit named after the German mathematician and physicist Carl Friedrich Gauss, who made significant contributions to the field of magnetism. One kilogauss is equivalent to 1,000 gauss (1 kG = 1,000 G).
In the International System of Units (SI), the standard unit for magnetic flux density is the tesla (symbol: T). To convert from kilogauss to tesla, you can use the following relation:
1 kilogauss = 0.1 tesla (1 kG = 0.1 T)
M
A magnetic circuit is a closed path through which magnetic flux travels, similar to how an electric circuit provides a path for electric current. Magnetic circuits are essential components in many magnetic devices and systems, such as transformers, motors, generators, and solenoids, where they help to control and direct the flow of magnetic flux to achieve the desired performance.
The magnetic field, represented by the symbol B, is a vector quantity that describes the magnetic influence exerted by electric currents, permanent magnets, or changing electric fields. The magnetic field represents the force experienced by charged particles, such as electrons and protons, when they move through the field. Magnetic fields play a crucial role in many physical phenomena, technologies, and applications, such as electromagnetism, magnetism, and solid-state physics.
Magnetic field strength is commonly referred to as magnetic flux density, which measures the density of magnetic field lines in a region of space or a material. The unit of magnetic flux density in the International System of Units (SI) is the tesla (T), while in the CGS system, it is expressed in gauss (G), where 1 tesla equals 10,000 gauss (1 T = 10,000 G).
Magnetic Field Strength (H) is a vector quantity that represents the intensity of an applied magnetic field in a material or a region of space. It is an important parameter in characterizing the magnetic behavior of materials and is used in various applications and fields of study, such as electromagnetism, magnetism, and solid-state physics.
Magnetic field strength is measured in units of ampere per meter (A/m) in the International System of Units (SI) or oersted (Oe) in the CGS system, where 1 Oe is approximately equal to 79.58 A/m.
The relationship between magnetic field strength (H), magnetic flux density (B), and magnetic permeability (µ) of the medium can be described by the following equation:
B = µ * H
In this equation, µ is the product of the permeability of free space (µ₀) and the relative permeability (µr) of the material, which is a dimensionless quantity that indicates how easily the material can be magnetized.
Magnetic field strength plays a crucial role in determining the behavior and performance of magnetic materials and devices. For example, it is used to define the coercive force of a magnetic material, which is the magnetic field strength required to reduce the magnetic flux density to zero. Understanding and controlling the magnetic field strength is essential for optimizing the design and performance of various magnetic devices and systems, such as electric motors, generators, transformers, sensors, and magnetic storage systems.
Magnetic flux, represented by the symbol Φ (phi), is a scalar quantity that measures the total magnetic field that passes through a given surface, taking into account both the strength of the magnetic field (B) and the angle between the field lines and the surface’s normal vector. It is an important parameter in electromagnetism, magnetism, and the analysis of magnetic circuits.
The magnetic flux is calculated using the following equation:
Φ = ∫B ⋅ dA
In this equation, B is the magnetic flux density (or magnetic field), dA is a differential area vector on the surface, and the integral sign (∫) indicates that the magnetic flux is calculated by summing the contributions of magnetic field lines passing through infinitesimal areas (dA) across the entire surface.
The unit of magnetic flux in the International System of Units (SI) is the weber (Wb), while in the CGS system, it is expressed in maxwells, where 1 weber equals 10^8 maxwells (1 Wb = 10^8 Mx).
Magnetic flux is a fundamental concept in the study of electromagnetism and is central to several key principles and phenomena, such as:
Faraday’s law of electromagnetic induction: According to Faraday’s law, a change in magnetic flux through a conducting loop induces an electromotive force (EMF) in the loop, which can drive an electric current. This principle underlies the operation of devices like transformers, generators, and induction motors.
Ampere’s law: Ampere’s law relates the magnetic field around a closed loop to the electric current passing through the loop, which is essential for understanding the behavior of magnetic materials and designing magnetic circuits.
Magnetic circuits: In magnetic circuits, the magnetic flux can be used to describe the flow of magnetic field lines through different components, such as cores, windings, and air gaps, allowing engineers to optimize the design and performance of magnetic devices and systems.
By understanding and controlling magnetic flux, scientists and engineers can develop and optimize various technologies and applications that rely on the interaction between magnetic fields and electric currents, such as electric motors, generators, transformers, sensors, and magnetic storage systems.
Magnetic flux density, represented by the symbol B, is a vector quantity that describes the strength and direction of a magnetic field in a material or a region of space. It is also referred to as the magnetic field and represents the force experienced by charged particles, such as electrons and protons, when they move through the field. Magnetic flux density is an essential parameter in various fields of study and applications, including electromagnetism, magnetism, and solid-state physics.
The unit of magnetic flux density in the International System of Units (SI) is the tesla (T). In the CGS system, it is expressed in gauss (G), where 1 tesla equals 10,000 gauss (1 T = 10,000 G).
Magnetic flux density is related to the magnetic field strength (H) and the magnetic permeability (µ) of the medium through the following equation:
B = µ * H
In this equation, µ is the product of the permeability of free space (µ₀) and the relative permeability (µr) of the material, which is a dimensionless quantity that indicates how easily the material can be magnetized.
Magnetic induction, represented by the symbol B, is another term for magnetic flux density, which describes the strength and direction of a magnetic field in a material or a region of space. Magnetic induction is a key parameter in various fields of study and applications, including electromagnetism, magnetism, and solid-state physics.
The unit of magnetic induction in the International System of Units (SI) is the tesla (T). In the CGS system, it is expressed in gauss (G), where 1 tesla equals 10,000 gauss (1 T = 10,000 G).
Magnetic induction is related to the magnetic field strength (H) and the magnetic permeability (µ) of the medium through the following equation:
B = µ * H
In this equation, µ is the product of the permeability of free space (µ₀) and the relative permeability (µr) of the material, which is a dimensionless quantity that indicates how easily the material can be magnetized.
Magnetic lines of force, also known as magnetic field lines or magnetic flux lines, are imaginary lines that represent the direction and distribution of a magnetic field in a material or a region of space. They help visualize and describe the behavior of magnetic fields, providing a convenient way to understand the magnetic influence exerted by electric currents, permanent magnets, or changing electric fields.
Magnetic lines of force have the following properties:
- Tangential direction: Magnetic lines of force are always tangent to the magnetic field vector at any point in space. This means that the direction of the magnetic field at any point is given by the direction of the magnetic line of force passing through that point.
- Continuous loops: Magnetic lines of force form continuous closed loops, originating from the north pole of a magnet and returning to the south pole. In the case of electric currents, the lines form closed loops around the current-carrying conductors.
- Non-intersecting: Magnetic lines of force never intersect each other. If two lines were to intersect, it would imply that the magnetic field has two different directions at the point of intersection, which is not possible.
- Density: The density of magnetic lines of force (i.e., the number of lines per unit area) is proportional to the strength of the magnetic field. A higher density of lines indicates a stronger magnetic field, while a lower density indicates a weaker field.
By studying the pattern and distribution of magnetic lines of force, scientists and engineers can gain insights into the behavior and properties of magnetic fields. This understanding is crucial for designing and optimizing various magnetic devices and systems, such as electric motors, generators, transformers, sensors, and magnetic storage systems.
A magnetic pole refers to one of the two regions of a magnet where the magnetic field is the strongest and most concentrated. These regions are called the north pole and the south pole, and they are responsible for the attractive and repulsive forces that magnets exert on each other and on certain materials.
In a bar magnet, the north pole is typically marked by an “N” and the south pole by an “S.” The magnetic field lines emerge from the north pole and loop around to enter the south pole, forming continuous closed loops.
Magnetic poles exhibit the following characteristics:
- Opposite poles attract: The north pole of one magnet attracts the south pole of another magnet, while like poles (north-north or south-south) repel each other. This principle is known as the “law of magnetic poles.”
- Inseparability: If a magnet is cut in half, each half becomes a new magnet with its own north and south poles. This is because the magnetic properties of the material are intrinsic and cannot be isolated or removed from a specific region of the magnet.
Magnetomotive Force (MMF), represented by the symbol F or mmf, is a quantity that describes the force that drives a magnetic field through a magnetic circuit, analogous to the electromotive force (EMF) that drives an electric current through an electrical circuit. MMF is a crucial concept in the study of magnetic circuits and the design and optimization of various magnetic devices and systems, such as transformers, inductors, and motors.
MMF is typically expressed in ampere-turns (At), where one ampere-turn is the MMF generated by a current of one ampere flowing through a single turn of a coil or solenoid. The relationship between MMF, the number of turns (N), and the current (I) in the coil can be described by the following equation:
F = N * I
In a magnetic circuit, MMF is responsible for establishing a magnetic field (H) that flows through different components, such as magnetic cores, air gaps, and windings. The magnetic field strength (H) can be related to MMF and the length of the magnetic path (l) as follows:
H = F / l
MMF plays a key role in determining the behavior and performance of magnetic devices and systems. By controlling the MMF in a magnetic circuit, engineers can manipulate the magnetic field strength, the magnetic flux, and the overall efficiency of the system. Understanding and optimizing MMF is essential for the design and operation of various technologies, such as electric motors, generators, transformers, sensors, and magnetic storage systems.
The Maximum Energy Product (BHmax) is an important parameter used to describe the performance of a permanent magnet. It represents the maximum amount of magnetic energy that can be stored in a magnet, which is essential for understanding its potential to perform work in a magnetic circuit or device.
BHmax is obtained from the demagnetization curve of a magnet, also known as the B-H curve, which shows the relationship between the magnetic flux density (B) and the magnetic field strength (H) for a given magnetic material. The Maximum Energy Product is the highest value of the product of B and H on this curve, usually found at the point where the magnet is operating in its most energy-efficient state.
The Maximum Energy Product is expressed in units of energy per unit volume, such as Mega-Gauss-Oersteds (MGOe) or Joules per cubic meter (J/m³). A higher BHmax value indicates that a magnet can store more magnetic energy and thus provide stronger magnetic performance in a given application.
Maximum Operating Temperature (Tmax) is an important parameter used to describe the thermal stability and performance of a magnetic material under elevated temperatures. It refers to the highest temperature at which a magnet can operate without experiencing significant loss in its magnetic properties. Exceeding the maximum operating temperature may result in irreversible demagnetization and a decrease in the magnet’s performance.
Different types of magnetic materials have varying maximum operating temperatures, depending on their composition and intrinsic properties. When selecting a magnet for a specific application, it is crucial to consider the maximum operating temperature, especially if the magnet will be exposed to high temperatures or fluctuating thermal conditions.
O
Orientation, in the context of magnetic materials, refers to the alignment of magnetic domains within a material during its manufacturing process. This alignment is important because it significantly affects the magnetic properties and performance of the final product.
When magnetic materials are manufactured, their tiny magnetic domains are usually randomly oriented, resulting in a low net magnetization. To improve the material’s magnetic performance, the manufacturing process often includes an orientation step that aligns these domains in a preferred direction. This alignment maximizes the magnetic properties of the material, such as its magnetic strength, energy product (BHmax), and coercivity.
There are different methods to orient magnetic materials, depending on the type of material and its intended application. Some common orientation techniques include:
Pressing and sintering: In this method, the magnetic material is pressed into a desired shape under a strong magnetic field, which aligns the magnetic domains. The material is then sintered at high temperatures to lock the aligned domains in place.
Melt spinning: This process involves rapidly solidifying a molten magnetic material in the presence of a strong magnetic field. The rapid cooling and magnetic field help to align the magnetic domains in the material, resulting in an oriented product.
Magnetic annealing: This technique involves heating a magnetic material to a specific temperature range while applying a strong magnetic field. The heat allows the magnetic domains to rearrange and align with the external magnetic field, and the material is then cooled to lock in the orientation.
Extrusion and calendering: For flexible magnetic materials, such as magnetic rubber, the material is extruded or calendered under a magnetic field to align the magnetic domains in the desired direction.
The choice of orientation method depends on the type of magnetic material, its intended application, and the desired magnetic properties. Proper orientation is crucial for optimizing the performance, efficiency, and reliability of magnetic devices and systems in various applications, such as motors, generators, sensors, and data storage devices.
P
Paramagnetic materials are a class of materials that exhibit weak magnetic properties in the presence of an external magnetic field. Unlike ferromagnetic materials, which have a strong, permanent magnetic response, paramagnetic materials have a much weaker response, and they do not retain any significant magnetization once the external magnetic field is removed.
The magnetic behavior of paramagnetic materials is due to the presence of unpaired electrons in their atomic or molecular structure. These unpaired electrons have magnetic moments, which can align with an applied external magnetic field. However, the magnetic moments are typically randomly oriented in the absence of a magnetic field, resulting in no net magnetization.
When a paramagnetic material is exposed to an external magnetic field, the magnetic moments of the unpaired electrons tend to align with the field, creating a weak net magnetization in the same direction as the applied field. This alignment is temporary, and the magnetization disappears as soon as the magnetic field is removed.
Permeance (P) is a term used in the study of magnetism to describe the ease with which magnetic flux can pass through a material or a magnetic circuit. It is essentially a measure of how well a material allows the flow of magnetic lines of force or magnetic flux. The concept of permeance is analogous to electrical conductance in the context of electric circuits.
Permeance Coefficient (Pc), also known as the load line or operating point, is a parameter used to describe the behavior of a permanent magnet in a magnetic circuit. It is a dimensionless number that represents the relationship between the magnet’s magnetic field strength (H) and the magnetic flux density (B) when it is operating at its maximum energy product (BHmax).
Permeability (μ) is a property of a material that describes its ability to support the formation of a magnetic field within itself. In other words, permeability is a measure of how easily a material can be magnetized or how well it can conduct magnetic flux. It is a crucial parameter in the study of magnetism and the design of magnetic circuits and devices.
Plating or coating refers to the process of applying a thin layer of protective material onto the surface of a magnet. plating or coating is typically used to protect the magnet from corrosion, wear, and other environmental factors that could degrade its performance over time. Additionally, some coatings can enhance the magnet’s appearance or provide other functional properties, such as improved electrical conductivity or reduced friction.
Click here to know more information about the plating/coating.
In terms of magnetism, polarity refers to the two ends of a magnet which exhibit different magnetic properties, commonly known as the North Pole and the South Pole. This concept stems from the Earth’s magnetic field, where the magnetic field lines emerge from the South Pole and converge at the North Pole.
Here are some key things to understand about magnetic polarity:
Opposite Poles Attract: The fundamental rule of magnetism is that opposite poles attract each other. So, a North Pole will attract a South Pole, and vice versa.
Like Poles Repel: Similarly, like poles repel each other. A North Pole will repel another North Pole, and a South Pole will repel another South Pole.
Magnetic Field Direction: By convention, the magnetic field direction is always from the North Pole to the South Pole outside of the magnet, and from the South Pole to the North Pole within the magnet.
Monopoles Do Not Exist: In nature, magnetic poles always come in pairs. If you cut a magnet in half, you don’t get a separate North Pole and South Pole. Instead, you get two smaller magnets, each with its own North Pole and South Pole. This is known as the principle of magnetic monopole non-existence.
Understanding magnetic polarity is crucial in various applications, ranging from simple fridge magnets to complex devices like electric motors, generators, magnetic levitation systems, and data storage devices. The correct arrangement of magnetic poles can greatly affect the performance, efficiency, and functionality of these devices.
Pull force refers to the force required to pull a magnet directly away from a ferromagnetic material, such as iron or steel, when the magnet is in full contact with it. It’s an important property to understand when working with magnets, as it helps determine how strong a magnet is, or in other words, how hard it is to separate the magnet from the ferromagnetic material it’s attracted to.
The pull force of a magnet depends on several factors:
- Magnet Size and Shape: Larger and thicker magnets generally have a greater pull force because they contain more magnetic material.
- Magnet Material: Different magnetic materials have different maximum energy products (BHmax), which directly influence their pull force. For example, neodymium magnets, which have a high BHmax, tend to have a stronger pull force than other types of magnets, such as ceramic or alnico magnets.
- Distance: The pull force decreases rapidly as the distance between the magnet and the ferromagnetic material increases. This is due to the nature of the magnetic field, which weakens significantly with distance.
- Surface Condition: The pull force is greatest when the magnet and the ferromagnetic material are in full direct contact with each other, with no air gaps or intervening materials. Surface roughness, dust, or other contaminants can reduce the effective contact area and thus decrease the pull force.
- Thickness of the Ferromagnetic Material: The thickness of the ferromagnetic material should be sufficient enough to fully “absorb” the magnetic field of the magnet. If the material is too thin, it may become magnetically saturated, and the pull force won’t increase even if the material’s thickness increases.
Knowing the pull force of a magnet is crucial in various applications to ensure that the magnet will function correctly and safely. For example, in magnetic holding or lifting devices, the pull force must be strong enough to securely hold or lift the object without risk of it accidentally being detached.
R
Relative permeability (μr) is a dimensionless quantity that compares the ability of a specific material to conduct or transmit a magnetic field (its permeability) to the ability of a vacuum to do the same.
To understand this better, let’s first remind ourselves of what permeability is. Permeability (μ) is a property of a material that describes how well it can carry a magnetic field. Different materials have different absolute permeabilities, depending on their atomic structure and magnetic properties.
Now, when we talk about relative permeability, we’re comparing this property of a material to that of a vacuum. The permeability of a vacuum, often denoted as μ₀, is the base permeability in nature, and it’s equal to approximately 4π x 10⁻⁷ H/m (henries per meter).
So, to get the relative permeability of a material, we use this formula:
μr = μ / μ₀, where:
μr is the relative permeability,
μ is the absolute permeability of the material, and
μ₀ is the permeability of free space (a vacuum).
As a result, relative permeability helps us understand how much “better” or “worse” a material is at conducting a magnetic field compared to a vacuum. For example, if a material has a relative permeability of 1, it means it transmits magnetic fields just as well as a vacuum. If the relative permeability is less than 1, it conducts magnetic fields less effectively than a vacuum (which is the case for diamagnetic materials). If it’s greater than 1, it conducts magnetic fields better than a vacuum (which is the case for paramagnetic and ferromagnetic materials).
Understanding relative permeability is essential in various applications involving magnetic fields, such as designing electrical transformers, inductors, and magnetic shielding, among others.
Reluctance (R), in the context of magnetism, is a measure of how much a material opposes the flow of a magnetic field through it. It’s a concept similar to electrical resistance, which measures how much a material opposes the flow of electric current. Just as an electrical circuit has resistance, a magnetic circuit has reluctance.
The reluctance of a magnetic circuit depends on the geometry and composition of the circuit, and it’s calculated using the following formula:
R = l / (μA), where:
R is the reluctance,
l is the length of the material through which the magnetic field is flowing,
μ is the permeability of the material (which measures how well the material can conduct a magnetic field),
and A is the cross-sectional area of the material perpendicular to the magnetic field.
From the formula, you can see that the reluctance is directly proportional to the length of the material and inversely proportional to its permeability and cross-sectional area. This means that a material will have high reluctance if it’s long, thin, or made of a substance with low permeability (like air or plastic). Conversely, it will have low reluctance if it’s short, wide, or made of a substance with high permeability (like iron or steel).
In a magnetic circuit, the magnetic flux (Φ), which is the total “amount” of magnetic field flowing through the circuit, is determined by the magnetomotive force (F, which is analogous to voltage in an electrical circuit) and the reluctance (R) according to the formula:
Φ = F / R
This is known as Hopkinson’s Law, or the magnetic Ohm’s law, and it’s fundamental to the design and analysis of magnetic circuits, such as those in transformers, electric motors, and magnetic storage devices. It helps engineers understand how changes in the material or geometry of the circuit will affect the magnetic field and the performance of the device.
Remanence, also known as residual induction or residual flux density and denoted by Bd or Br, refers to the magnetic induction that remains in a magnetic material after an external magnetic field is removed.
Imagine you have a bar magnet, and you bring it close to a piece of iron. The iron becomes magnetized due to the magnetic field of the bar magnet. Now, if you take the bar magnet away, the iron doesn’t immediately lose all its magnetism. It retains some amount of magnetism. This leftover magnetism is what we call remanence.
The level of remanence a material has depends on the type of magnetic material. Some materials, like soft magnetic materials (for example, soft iron), have low remanence, meaning they lose most of their magnetism when the external field is removed. On the other hand, hard magnetic materials (for example, neodymium magnets) have high remanence and can retain a substantial portion of their magnetism.
Remanence is a critical property for permanent magnets used in various applications, such as motors, generators, loudspeakers, and magnetic storage devices. It’s one of the factors that determines how strong the magnet will be in its working environment.
The unit of remanence is the tesla (T) in the International System of Units (SI) and the gauss (G) in the centimetre-gram-second system of units (CGS). 1 T equals 10,000 G.
A return path, in the context of magnetism, is the path that the magnetic field or magnetic flux follows to return to its source, completing the magnetic circuit.
Consider a bar magnet. It has a North Pole and a South Pole. The magnetic field lines emerge from the North Pole, travel through the surrounding space, and then return to the South Pole. This complete path—from the North Pole, through space, and back to the South Pole—is the return path of the magnetic field.
In many practical applications, especially in electromagnetics, we often try to create a convenient return path for the magnetic flux. For instance, in a transformer, the iron core serves as the return path for the magnetic field created by the current in the coils. The core guides the magnetic field from one coil to the other, greatly enhancing the transformer’s efficiency by minimizing the magnetic field’s leakage into surrounding space.
Similarly, in a magnetic circuit, the return path is often designed to be through a material with high magnetic permeability (such as iron or steel), because these materials can carry a magnetic field much more effectively than air or vacuum.
Designing an efficient return path is crucial for maximizing the performance and efficiency of devices that work based on magnetic principles, such as electric motors, generators, inductors, transformers, and magnetic storage devices. The goal is to ensure that as much of the magnetic field as possible is confined to the desired path, with minimal leakage or loss.
The Reversible Temperature Coefficient is a term used to describe how the magnetic properties of a material change with temperature, in a reversible manner.
What does that mean? Let’s break it down:
“Temperature Coefficient”: This part refers to the rate at which a specific property changes with temperature. A positive temperature coefficient means that the property increases as temperature increases, while a negative temperature coefficient means that the property decreases as temperature increases.
“Reversible”: This part means that the changes are not permanent – if the temperature returns to its original value, so does the property in question.
In the context of magnetic materials, we often talk about the reversible temperature coefficients of magnetic flux density (Br) and coercive force (Hc). These coefficients tell us how much the material’s magnetization and resistance to demagnetization, respectively, change with temperature.
For example, a neodymium-iron-boron (NdFeB) magnet typically has a negative reversible temperature coefficient of Br, meaning its magnetization decreases as temperature increases. If the magnet is cooled down again, its magnetization will increase back to the original value.
These coefficients are important for engineers and designers to consider when choosing a magnetic material for a particular application, especially for devices that will operate in a wide range of temperatures. Understanding how the magnetic properties will change with temperature allows them to ensure that the device will perform reliably under the expected operating conditions.
S
Saturation, in the context of magnetism, is a state where a magnetic material has been magnetized to its maximum capacity. It’s like a sponge that has soaked up as much water as it possibly can – any additional water just drips off without being absorbed.
Just as the sponge has a limit to how much water it can hold, a magnetic material has a limit to how much magnetic field it can conduct or “hold”. When this limit is reached, the material is said to be “saturated”.
In a saturated magnetic material, nearly all of its magnetic domains (tiny regions within the material that act like tiny magnets) are aligned in the same direction. This means that applying a stronger external magnetic field won’t increase the material’s magnetic flux density (B) any further. The B-H curve of the material, which plots magnetic flux density (B) versus applied magnetic field strength (H), flattens out at saturation, indicating that B no longer increases with H.
Saturation is an important concept in many applications involving magnetic materials. For example, in transformers and inductors, the core material is often operated close to its saturation point to maximize efficiency, but care is taken to avoid actually reaching saturation, as this can cause a sharp increase in current and potentially damage the device.
One important thing to note is that different materials have different saturation points. Soft magnetic materials, such as iron, reach saturation relatively easily, while hard magnetic materials, such as neodymium magnets, have much higher saturation points. This is one of the factors that engineers consider when choosing a magnetic material for a particular application.
A shunt, in the context of magnetism and magnetic circuits, is a path that allows a magnetic field to bypass a certain area or component. The term “shunt” is derived from a term meaning to “turn aside” or “deviate,” and in electrical engineering, it refers to a device that allows electrical current to pass around another point in the circuit.
In a magnetic circuit, a shunt could be a piece of magnetic material that provides a path of lower reluctance (or higher magnetic permeability) for the magnetic field lines. This could effectively “divert” some or all of the magnetic flux away from another path or component.
For instance, imagine a horseshoe magnet with a small air gap. If you place a piece of iron across the gap, this iron piece acts as a shunt, providing a path of much lower reluctance than the air gap. The magnetic field lines prefer to go through the iron rather than the air, so they get “shunted” away from the gap.
In some applications, shunts can be useful for controlling the distribution of the magnetic field, protecting sensitive components from strong magnetic fields, or regulating the magnetic flux in a circuit. However, in other cases, they might be undesirable because they can reduce the magnetic field in certain parts of the circuit. Understanding and managing shunts is an important aspect of designing and optimizing magnetic circuits.
S.I., short for “Système International d’Unités”, is the modern form of the metric system and is the world’s most widely used system of measurement for science and commerce. It’s often referred to as the International System of Units in English.
In the world of magnetism, the South Pole is one of the two ends of a magnet where the magnetic field lines emerge or enter. This is based on the convention that magnetic field lines run from the North Pole to the South Pole.
Now, here comes a bit of a fun, mind-bending fact: the Earth’s geographic North Pole is actually a magnetic South Pole! That’s right. If you think about a compass, the north end of the compass needle is attracted to the Earth’s North Pole. But we know that like magnetic poles repel each other and unlike poles attract. So, for the north end of the compass needle (which is a magnetic North Pole) to be attracted to the Earth’s North Pole, that means the Earth’s North Pole must actually be a magnetic South Pole!
Stabilization, in the context of magnetism and magnetic materials, is the process of preparing a magnet to function reliably under specific conditions or within a certain range of parameters. This is done to ensure that the magnet’s performance will not change unexpectedly during its intended use.
Magnetic materials can change their properties in response to various factors, such as temperature changes, exposure to external magnetic fields, mechanical stress, and more. These changes can be temporary or permanent, and they can affect the magnet’s strength, direction of magnetization, magnetic stability, and other properties.
One common method of stabilization is to expose the magnet to conditions that are similar to, or even more extreme than, those it will experience during its use. For example, a magnet might be heated to a certain temperature, exposed to a strong external magnetic field, or mechanically stressed in some way. This can cause some of the magnetic domains in the material to reorient or change in size, which can reduce the magnet’s overall strength or change other properties. However, once this process is complete, the magnet will be more stable and less likely to change when it is later exposed to similar conditions.
Another method of stabilization is to use various treatments or coatings that can protect the magnet from environmental factors that could affect its properties. For example, a magnet might be coated with a protective layer that can resist corrosion, which can help maintain the magnet’s strength and stability over time.
Stabilization is a crucial step in the manufacture and use of many types of magnetic materials, especially those used in devices like electric motors, generators, magnetic sensors, and data storage devices. Proper stabilization can help ensure that these devices perform reliably and consistently, even under challenging conditions.
The Surface Field, also referred to as Surface Gauss, is a measure of the magnetic field strength right at the surface of a magnet. It’s like standing at the beach and measuring the strength of the wind – except in this case, it’s the invisible magnetic “wind”.
This measurement is usually given in Gauss (G) or Tesla (T), with 1 Tesla equaling 10,000 Gauss. These units are like the miles per hour or kilometers per hour we use to measure wind speed.
The Surface Field gives us a good idea of the magnet’s strength. A magnet with a high Surface Field can exert a strong force on other magnetic materials, or on charged particles that are near its surface. But just like the wind is less strong as you move away from the beach, the strength of the magnetic field decreases rapidly as you move away from the magnet’s surface.
Measuring the Surface Field can be important in many applications, such as in the design of electric motors or generators, in magnetic therapy devices, or in magnetic levitation systems. To measure the Surface Field, we use a device called a Gaussmeter, which can sense the strength of the magnetic field at a specific location. It’s like our weather instrument to measure the magnetic “wind speed”.
T
The Temperature Coefficient is a measure of how much a specific property of a material changes with temperature. It’s typically given as a percentage per degree Celsius (%/°C).
In the world of magnetism, we often talk about the temperature coefficients of a magnet’s key properties – its residual induction (Br) and its coercive force (Hc). These coefficients tell us how much the magnet’s strength and resistance to demagnetization, respectively, change with temperature.
For example, a neodymium-iron-boron (NdFeB) magnet typically has a negative temperature coefficient of Br, meaning that its magnetic strength decreases as the temperature increases. If the temperature coefficient of Br for a particular NdFeB magnet is -0.12%/°C, this means that for every degree Celsius increase in temperature, the magnet’s strength will decrease by 0.12%.
The temperature coefficient is a critical parameter to consider in applications where the magnet will be exposed to a wide range of temperatures. It allows engineers and designers to predict how a magnet’s performance will change with temperature, and to choose a magnet that will perform optimally under the expected operating conditions. For instance, a magnet with a lower (less negative) temperature coefficient of Br would be a better choice for an application where the magnet will be exposed to high temperatures, as it will retain more of its strength under these conditions.
The Tesla (symbol: T) is the unit of measurement for magnetic flux density in the International System of Units (S.I.). Named after the Serbian-American inventor and electrical engineer Nikola Tesla, this unit helps us quantify the strength of a magnetic field.
If you imagine a magnet, it’s surrounded by an invisible magnetic field. This field is represented by lines that exit from the North Pole of the magnet, curve around, and enter back into the South Pole. The density of these lines in a particular area represents the strength of the magnetic field in that area. When we measure this strength in Teslas, we’re measuring how many of these invisible lines are present in a square meter.
To give you an idea of what a Tesla represents, the Earth’s magnetic field is about 25 to 65 microteslas (that’s 0.000025 to 0.000065 Teslas!). A small refrigerator magnet might have a magnetic field of around 0.001 Tesla at its surface. On the other hand, the magnets used in a Magnetic Resonance Imaging (MRI) machine can produce a field of 1.5 to 3 Teslas, or even more! That’s tens of thousands of times stronger than the Earth’s magnetic field.
In short, the Tesla is a key unit of measurement in the world of magnetism, essential in many areas of science and technology, from geophysics to medical imaging to electrical engineering.
W
The Weber (symbol: Wb) is the unit of measurement for magnetic flux in the International System of Units (S.I.). It’s named after the German physicist Wilhelm Eduard Weber, a significant contributor to the field of electrodynamics.
But what exactly is magnetic flux? Well, imagine a magnet. It’s surrounded by an invisible magnetic field, represented by lines that exit from the North Pole of the magnet, curve around, and enter back into the South Pole. Now, if you could count all those lines passing through a certain area, you’d be measuring the magnetic flux through that area.
The Weber is defined as the amount of magnetic flux that, linking a circuit of one turn (a loop of wire), would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.
In practice, a Weber is a fairly large unit of magnetic flux. For instance, the total magnetic flux coming out of a typical refrigerator magnet is on the order of a few millionths (micro) of a Weber.
The concept of magnetic flux is fundamental in the study of electromagnetism and is particularly important in the design and operation of electrical machines like motors, generators, and transformers, where changes in magnetic flux can be used to generate electrical voltage and vice versa.