- Air Core Transformer Definition: An air core transformer is defined as a transformer that uses air instead of a ferromagnetic core to link the magnetic flux between its windings.
- Principle of Operation: It operates on electromagnetic induction, where an alternating current in the primary coil induces an emf in the secondary coil.
- Construction Types: Air core transformers can be cylindrical, with wires wound on a non-metallic cylinder, or toroidal, with wires wound around a plastic ring.
- High-Frequency Suitability: They are suitable for high-frequency applications due to their noise-free operation and avoidance of electromagnetic distortion.
- Advantages: These transformers are lightweight and avoid losses and saturation problems associated with ferromagnetic cores, making them ideal for portable electronic devices.
When an alternating current flows through a coil, it creates an alternating magnetic field around it. If a second coil is placed within this magnetic field, it induces an alternating emf in the second coil due to Faraday’s law of electromagnetic induction. This emf can be used to power a load. In this setup, the magnetic flux links both coils through the air, making it an air core transformer. The first coil is the primary winding, and the second coil is the secondary winding. Electrical transformers are used to change voltage levels in power networks.
Transformers provide electrical isolation between circuits. For lowering current and voltage to measurable levels, we use current transformers and potential transformers. Transformers have various applications, including smaller ones in electronics. Examples include air core transformers and audio frequency transformers.
These are referred as special purpose transformers and simply called special transformer. Construction wise they are different from general power transformer but basic working principle is same as all other transformers. That means in this case, the working principle of transformer is also based on mutual induction between two magnetically linked windings. Here we will discuss about air core transformers.
In an transformer primary winding and secondary windings are coupled with a low reluctance ferromagnetic core. The core is used in an electrical transforme for confining magnetic flux and facilitating maximum flux linkage between primary and secondary winding. Laminated steel sheets are used to construct the core of transformer. But, ferromagnetic materials like steel as core of transformer, suffers from hysteresis loss, eddy current losses. Also it faces problem of getting saturated after certain level of magnetization. But these can be avoided in air core transformer as ferromagnetic core is absent in this transformer.
In high-frequency applications, avoiding electromagnetic distortion is crucial to maintain signal quality. Ferromagnetic materials can cause noise and distortion, so they are unsuitable for high-frequency signal transmission. Air core transformers, used in high-frequency radio transmission, solve this problem. They have no iron core, linking the flux through air, resulting in noise-free operation and a lightweight design. This makes them ideal for portable electronic devices and high-frequency equipment, such as radio transmitters and communication devices.
Construction of Air Core Transformer
The coils of insulated copper wire, are wound on a plastic tube or cardboard etc. There are mainly two forms of air core transformer. One is cylindrical form and other is toroidal form. In cylindrical form of air transformer, insulated copper wires are wound on a non metallic cylindrical structure. This non metallic hollow structure gives the winding necessary mechanical support. The copper winding wounded around the non metallic cylinder is tapped at different points as necessary. The secondary supply is taken across these taps. Sometimes capacitor is connected to the winding to maintain the constant resonance of the tuning circuit. The flux flows through the air surrounding the winding and air inside hollow cylinder. For proper impedance matching, sometime a guard winding is wound surrounding the main copper winding. This guard winding is further connected with antenna receivers or grounded properly.
On the other hand in toroidal form of air core transformer, insulated copper wires are wound around a ring of hard plastic or other non metallic substance. Actually, the wire is wound in circular way around the periphery of the ring. This type of transformers are only used in very high frequency applications. In this case the winding is not tapped, here two separate windings are used for primary and secondary purpose. Therefore, the effect of stray coupling is minimized in toroidal air core transformer. The primary is to secondary ratio of windings varies and it depends upon the frequency range and the type of operation.
