What is Magnetic reluctance?
Magnetic reluctance is a measure of the resistance of a material to the flow of a magnetic field. Just as electrical resistance is a measure of the resistance of a material to the flow of an electric current, magnetic reluctance measures the resistance of a material to the flow of a magnetic field.
In an electric circuit, the electric field provides the path of least resistance for the electric current. This means that the electric current will tend to flow through the path that offers the least resistance to its flow. Similarly, in a magnetic circuit, the magnetic field provides the path of least reluctance for the magnetic flux. The magnetic flux will tend to flow through the path that offers the least reluctance to its flow.
The unit of measurement for magnetic reluctance is the ampere-turn per weber (At/Wb). This unit measures the amount of magnetomotive force (mmf) required to produce a certain flux in a given material. The higher the reluctance of a material, the more mmf is required to produce a given flux in that material.
Magnetic reluctance is an important concept in the field of electrical engineering and is used to design and analyze magnetic circuits, such as transformers and electric motors. Understanding magnetic reluctance can help engineers design more efficient and effective magnetic devices.
It's also important to note that reluctance is a scalar quantity, which means that it is fully described by a magnitude (or numerical value) only. It does not have a direction associated with it. This is in contrast to a vector quantity, which has both a magnitude and a direction.
Reluctance(S)
= l/μo μrA
Where, l – the length of the conductor
μo – permeability of vacuum which is equal to 4Ï€ Χ107 Henry/metre.
μr – relative permeability of the material.
A – cross-section area of the conductor.
It is directly proportional to the length of the magnetic circuit and inversely proportional to the cross-sectional area of the magnetic path. This means that as the length of the magnetic circuit increases, the reluctance will also increase. Conversely, as the cross-sectional area of the magnetic path increases, the reluctance will decrease.
What is Magnetic Permeance?
Magnetic permeance is a measure of the ease with which a magnetic field can pass through a material. It is the reciprocal of the magnetic reluctance, which is a measure of the resistance of a material to the flow of a magnetic field.
The formula for calculating magnetic permeance is:
Permeance (P) = 1 / Reluctance (S)
This formula shows that the permeance of a material is inversely proportional to its reluctance. As the reluctance of a material increases, the permeance decreases, and as the reluctance decreases, the permeance increases.
The unit of measurement for magnetic permeance is the weber per ampere-turn (Wb/At). This unit measures the amount of flux produced by a given mmf in a given material. The higher the permeance of a material, the more flux will be produced by a given mmf in that material.
What is magnetic Reluctance in DC field?
In a DC (direct current) field, the reluctance of a magnetic circuit is defined as the ratio of the magnetomotive force (mmf) to the magnetic flux of the same circuit. This means that the reluctance of a magnetic circuit in a DC field is a measure of the resistance of the circuit to the flow of the magnetic field.
The magnetomotive force (mmf) is a measure of the strength of a magnetic field and is typically expressed in ampere-turns (At). It is the force that drives the magnetic field through a magnetic circuit.
The magnetic flux is the measure of the amount of magnetic field passing through a given area and is typically expressed in webers (Wb). It is a measure of the strength of the magnetic field and is used to calculate the reluctance of a magnetic circuit.
The formula for calculating the reluctance of a magnetic circuit in a DC field is:
Reluctance (S) = Magnetomotive force (F) / Magnetic flux (Φ)
This formula shows that the reluctance of a magnetic circuit in a DC field is directly proportional to the mmf and inversely proportional to the magnetic flux. As the mmf increases, the reluctance increases, and as the magnetic flux increases, the reluctance decreases.
The unit of measurement for reluctance in a DC field is the ampere-turn per weber (At/Wb). This unit measures the amount of mmf required to produce a certain flux in a given material. The higher the reluctance of a material, the more mmf is required to produce a given flux in that material.
What is Permeability?
Permeability is a measure of the ability of a material to support the formation of a magnetic field within itself. It is a measure of how easily a material can be magnetized and is expressed in terms of the magnetic flux density (B) produced within the material by a given magnetomotive force (mmf).
The formula for calculating permeability is:
Permeability (μ) = Magnetic flux density (B) / Magnetomotive force (F)
This formula shows that the permeability of a material is directly proportional to the magnetic flux density produced within the material and inversely proportional to the magnetomotive force. As the magnetic flux density increases, the permeability increases, and as the magnetomotive force increases, the permeability decreases.
The unit of measurement for permeability is the henry per meter (H/m). This unit measures the amount of mmf required to produce a certain flux density in a given material. The higher the permeability of a material, the more flux density will be produced by a given mmf in that material.
What is Relative Permeability?
Relative permeability is a measure of how easily a material can be magnetized compared to free space. It is defined as the ratio of the permeability of the material to the permeability of free space.
The formula for calculating relative permeability is:
Relative permeability (μr) = Permeability of material (μ) / Permeability of free space (μo)
This formula shows that the relative permeability of a material is a measure of the material's ability to support the formation of a magnetic field compared to free space. The permeability of free space, "μo", is a constant value that represents the permeability of a vacuum. It is equal to 4π x 10^-7 henries/meter (H/m).
The unit of measurement for relative permeability is dimensionless, as it is a ratio of two quantities with the same units. A material with a relative permeability of 1 has the same permeability as free space and is considered to be a non-magnetic material. Materials with a relative permeability greater than 1 are considered to be magnetic materials and are more easily magnetized than free space.
What is Reluctivity?
Reluctivity, also known as specific reluctance, is a measure of the resistance of a material to the flow of a magnetic field. It is defined as the reluctance of a magnetic circuit of unit length and unit cross-sectional area.
The formula for calculating reluctivity is:
Reluctivity (r) = Reluctance (S) / Length of magnetic circuit (l) * Cross-sectional area of magnetic path (A)
This formula shows that reluctivity is a measure of the resistance of a material to the flow of a magnetic field per unit length and unit cross-sectional area. As the reluctivity of a material increases, the resistance to the flow of the magnetic field also increases.
The unit of measurement for reluctivity is the ampere-turn per weber per meter (At/Wb/m). This unit measures the amount of magnetomotive force (mmf) required to produce a certain flux in a given material per unit length and unit cross-sectional area. The higher the reluctivity of a material, the more mmf is required to produce a given flux in that material per unit length and unit cross-sectional area.
Difference between Permeance and Reluctance:
| Property | Permeance | Reluctance |
|---|---|---|
| Definition | The measure of ease in the flow of magnetic flux offered by a magnetic material | The measure of opposition in the flow of magnetic flux offered by the magnetic material |
| Denotation | P | S |
| Alternate name | Magnetic conductance | Magnetic resistance |
| Physical meaning | Helps the magnetic flux in flowing through a magnetic material | Restricts the flow of magnetic flux through the material |
| Formula | P = μAl | S = lμA |
| Relation with magnetic flux | P α ϕ (direct proportion) | S α 1/ϕ (inverse proportion) |
| Unit of measurement | Weber per Ampere-Turn (Wb/AT) or Henry | Ampere-Turn per Weber (AT/Wb) or 1/Henry or H-1 |
| Addition | Additive in case of parallel magnetic circuits | Additive in case of series magnetic circuits |
| Analogy to electric circuit | Analogue to conductance in electric circuit | Analogue to resistance in electric circuit |
Magneto Motive Force (M.M.F):
The magneto motive force (M.M.F) is a measure of the strength of the driving force that sets up the magnetic flux in a magnetic circuit. It is defined as the force that tends to establish the flux through a magnetic circuit.
In a magnetic circuit, the M.M.F is created by the current flowing through a coil of wire, which creates a magnetic field. The strength of the M.M.F is directly proportional to the current flowing through the coil and the number of turns of the coil.
The M.M.F can be expressed mathematically as:
M.M.F = I * N
where I is the current flowing through the coil in amperes (A) and N is the number of turns of the coil.
The unit of M.M.F is ampere-turns (AT), which is the product of the current in amperes and the number of turns in the coil.
In a magnetic circuit, the M.M.F drives the magnetic flux through the circuit. The flux is resisted by the reluctance of the magnetic circuit, and the resulting force is known as the magnetic field intensity (H). The relationship between the M.M.F and the magnetic field intensity can be described by the following equation:
M.M.F = H * l
where l is the length of the magnetic circuit in meters.
Applications of Reluctance:
- In transformers: Reluctance is used to reduce the effect of magnetic saturation in transformers. A transformer works by using the changing magnetic field in a coil of wire to induce a voltage in another coil. However, if the magnetic field becomes too strong, the transformer will become saturated and will no longer be able to efficiently transfer the voltage. By introducing a material with a high reluctance into the circuit, such as an air gap, the transformer can store more magnetic energy before reaching saturation.
- In reluctance motors: A reluctance motor is a type of electric motor that uses the principle of variable reluctance to produce rotation. It works by using a rotor with teeth of varying lengths, and a stator with coils of wire arranged in a pattern that creates a varying magnetic field. The rotor will align itself with the strongest part of the field, causing it to rotate. Reluctance motors are used in a varietyconstant-speedpeed applications, such as electric clocks, signaling devices, and recording instruments.
- In permanent magnets: Some materials, such as tungsten steel, cobalt steel, and chromium steel, have a strong magnetic reluctance and are used to create permanent magnets. These materials are magnetically hard, meaning they retain their magnetic properties over long periods of time.
- In speakers: The magnets used in speakers are often covered with a soft magnetic material, such as soft iron, to minimize the effect of the stray magnetic field. This helps to reduce interference with other electronic devices, such as TVs and CRTs (cathode ray tubes).
- In multimedia loudspeakers: Multimedia loudspeakers are often magnetically shielded to reduce magnetic interference with TVs and CRTs. This helps to ensure that the speaker's magnetic field does not interfere with the operation of these devices.