A toroid is a coil of insulated or enameled wire (surface of revolution) with a hole in the middle, like a doughnut, forming a solid body. The axis of revolution passes through the hole and so it does not intersect the surface. A toroid is used as an inductor in electric circuits, especially at low frequencies where comparatively large inductances are important.

Discovery of toroid:

The first toroid were created in the early 1830s. A physicist named Michael Faraday invented it. This man was able to watch that a change in magnetic fields can induce voltage in a wire that is close in proximity. Faraday called this phenomenon Faraday’s Law of Induction. Since the early 1830s, people have made improvements and innovations in the field. Today there are so much more options for coils.

A Solenoid and a toroid:

A toroid has more inductance, for a present number of turns, than a solenoid with a core of the same material and similar size. This makes it possible to make high-inductance coils of reasonable mass and physical size. Toroidal coils of a given inductance can carry more current comparatively solenoidal coils of similar size, because larger-diameter wires can be used, and the total amount of wire is less, reducing the resistance.

In a toroid, all the magnetic flux is confined in the core material. This is because the core has no ends from which flux might leak off. The confinement of the flux prevents external magnetic fields from affecting the behavior of the toroid, and also prevents the magnetic field in the toroid from affecting other components in a circuit.

Differences between solenoid and toroid:

Solenoid Toroid
Cylindrical in shape Circular in shape
Magnetic field is created outside Magnetic field is created within
Has uniform magnetic field inside it. It does not have a uniform magnetic field inside it.
Magnetic field due to solenoid is (B) = Magnetic field outside:- magnetic field (B) = 0
Magnetic field inside:- magnetic field (B) = 0
Magnetic field within the toroid:- magnetic field (B) =

Similarities between solenoid and toroid:

  1. Both works on the principle of electromagnetism.
  2. When current is passed through them, they both act like an electromagnet.
  3. Magnetic field due to the solenoid and within the toroid is the same. B =

Toroidal field

A magnetic field with no radial components, e.g. where the magnetic lines of force lie on an electrically conducting spherical surface such as the surface of the Earth’s core. Such a field is not detectable at the Earth’s surface, in contrast to a poloidal field.

Difference between toroid and torus?

Toroid is a derived term of torus.
The difference between toroid and torus, according to mathematics is that toroid is (mathematics) a surface generated by a closed curve (especially a circle) rotating about, but not intersecting or containing, an axis in its own plane while torus is (mathematics) the standard representation of such a space in 3-dimensional euclidean space: a shape consisting of a ring with a circular cross-section: the shape of an inner tube or hollow doughnut.

As nouns the difference between toroid and torus
is that toroid is (mathematics) a surface generated by a closed curve (especially a circle) rotating about, but not intersecting or containing, an axis in its own plane while torus is (topology) a topological space which is a product of two circles.

Toroidal inductors and transformers

Toroidal inductors and transformers are inductors and transformers which use magnetic cores with a toroidal (ring or donut) shape. They are passive electronic components, consisting of a circular ring or donut shaped magnetic core of ferromagnetic material such as laminated iron, iron powder, or ferrite, around which wire is wound.

Although in the past, closed-core inductors and transformers often used cores with a square shape, the use of toroidal-shaped cores has increased greatly because of their superior electrical performance. The advantage of the toroidal shape is that, because to its symmetry, the amount of magnetic flux that escapes outside the core (leakage flux) is quite low, therefore it is more reliable and thus radiates less electromagnetic interference (EMI).

Toroidal inductors and transformers are used in a huge range of electronic circuits: power supplies, amplifiers, and inverters which in turn are used in the big majority of electrical equipment: TVs, radios, computers, and audio systems.

Advantages of toroidal windings

In general, a toroidal inductor/transformer is more compact than other shaped cores because they are made of fewer materials and include a centering washer, nuts, and bolts resulting in up to a 50% lighter weight design. This is especially the case for power devices.

Because the toroid is a closed-loop core it will have a higher magnetic field and thus higher inductance and Q factor than an inductor of the same mass with a straight core (solenoid coils). This is because most of the magnetic field is contained within the core. By comparison, with an inductor with a straight core, the magnetic field emerging from one end of the core has a long path through air to enter the other end.

In addition, because the windings are relatively short and wound in a closed magnetic field, a toroidal transformer will have a lower secondary impedance which will increase efficiency, electrical performance and reduce effects such as distortion and fringing.

Due to the symmetry of a toroid, little magnetic flux escapes from the core (leakage flux). Thus a toroidal inductor/transformer, radiates less electromagnetic interference (EMI) to adjacent circuits and is an ideal choice for highly concentrated environments. Manufacturers have adopted toroidal coils in recent years to comply with increasingly strict international standards limiting the amount of electromagnetic field consumer electronics can produce.

Toroidal Transformers

Transformers are made from a pair of solenoids wrapped around a metal core that is usually a ferrite. Toroidal transformers are two coils wrapped around a metal, such as a ferrite or silicon steel that is doughnut shaped. The coils are either wrapped in different areas or placed one over the other. They are preferred for RF or Radio frequency identification (RFID)radio frequency transformers, where they are used to increase or decrease voltages from power sources, and to isolate different parts in a circuit. RF transformers are also used for impedance matching, which means they help connect input and output parts of different circuits.

Disadvantages and Advantages

Toroid have some disadvantages over regular solenoids. They are harder to wind and also to tune. However, they are more efficient at producing needed inductances. For the same inductance as a regular solenoid, a toroid requires fewer turns, and can be made smaller in size. Another advantage is that since the magnetic field is confined to the inside, toroid and toroidal transformers can be placed near other electronic components without concern about unwanted inductive interactions.

Applications of toroid:

Toroid are used in telecommunications, medical devices, musical instruments, amplifiers, ballasts and more. A tokamak is a nuclear fusion device that uses a magnetic field to confine plasma. A plasma is a gas that contains free electrons and ions, and only appears at high temperatures. The confinement of the plasma in a tokamak is done with the use of a toroid.

All of the loops of wire which make up a toroid contribute magnetic field in the same direction inside the toroid. The sense of the magnetic field is that given by the right hand rule, and a more detailed visualization of the field of each loop can be obtained by examining the field of a single current loop.

A toroid has a magnetic field inside of itself that forms a series of concentric circles. Outside of it, the field is zero. The strength of this magnetic field depends on the number of coils the toroid has on its body.

Toroid are used by:

  • Telecommunication
  • Medical field (at home and hospital)
  • Music instruments
  • Ballasts
  • EMI filter
    So much more.

In each of the above industries the coil will help to direct and restrict magnetic fields RC planes, just like medical gears, needs a constant and regulated flow of energy in order to work properly. An RC plane needs electricity to do so much of its basic functions, like communicating with the control and power feed to ESC and motor. Having noise with electricity will only cause problems between the plane and your controls. A ferrite coil can be added to the RC plane, which is supposed to greatly reduce noise or spikes in voltage. An electric motor has the potentiality to create the spikes that could cause problems when flying planes. When you add a ferrite toroid to the motor it will make your flying better because there will be less noise you have to fight against.

Frequently Asked Questions

1- What is a toroid used for?

A toroid is a coil of insulated or enameled wire wound on a donut-shaped form made of powdered iron. A toroid is used as an inductor in electronic circuits, especially at low frequencies where comparatively large inductances are necessary.

2- What is meant by toroid in physics?

Toroid is a hollow circular ring on which a large number of turns of a wire are closely wound. It can be viewed as a solenoid which has been bent into a circular shape to close on itself.

3- Is a donut a torus?

A torus should not be confused with a solid torus, which is formed by rotating a disk, rather than a circle, around an axis. In the field of topology, a torus is any topological space that is homeomorphic to a torus. A coffee cup and a doughnut are both topological tori.

4- Are humans a torus?

Topologically speaking, a human is a torus. Your digestive system is the hole in the doughnut. Interestingly, this means in a two-dimensional world, an organism couldn’t have a similar structure, since the digestive system would completely separate the animal into two halves

5- What does toroid mean?

1: a surface generated by a closed plane curve rotated about a line that lies in the same plane as the curve but does not intersect it. 2: a body whose surface has the form of a toroid.

6- How many holes does a person have topologically?

For a normal human male, discounting pores, we have 9 holes. So our skin homeomorphic to a disk with 8 holes and has fundamental group the free group on 8 generators.

##$ 7- What is toroid formula for toroid?

The formula for the magnitude of magnetic field inside a toroid is: B=μoNI2πr.

8- What shape is a toroid?

A toroid is a geometric shape that resembles a torus. A toroid is constructed by rotating a geometrical shape around an axis which is outside the shape. If this is done to a circle, a torus results. This short article about mathematics can be made longer.

9- What is an ideal toroid?

The ideal toroid is one in which coils are circular.

10- How do you count turns in a toroid?

You can calculate the number of turns by giving the external diameter of the conductor and asuming that the number of turns is given by the amount of turns that you can have due to the internal circumference of the toroid or, you can simply state the number of turns of the toroid in the respective section.

11- How do you find the magnetic field of a toroid?

The direction of the magnetic B-field can be determined by using the right-hand rule. If your right hand grabs the toroid with the fingers in the direction of the current in the turns of the coils then the raised thumb of the right hand directs in the direction of the magnetic B-field inside the toroid.

12- What is a toroidal surface?

A toroidal surface is a special case of an aspheric surface. It features two different curvatures perpendicular to each other. A lens or a mirror with such a shape therefore has two focal points, separated by an amount dependent on the difference of the two curvatures


Toroid work on the principle of electromagnetism and behave like an electromagnet when current is passed. The magnetic field produces by It is B = Even after having so many similarities solenoid and toroid differs in property such as shape.

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