About Winding RF Coils
What are RF coils and how are they made?
How is an RF coil manufactured? In this article we will explore the nature of RF coils and the technology required for winding RF coils in an industrial setting.
Description of an RF Coil
An RF coil has the following features:
- An insulated wire wound around a core. The wire itself generates a magnetic field. However, the coil intensifies the magnetic field considerably.
- The magnetic field around the coil is in the shape of a bar magnet with a north and south pole. Coils can be shaped differently, as well.
- When additional layers are wound about the coil, the strength of the magnetic field is increased.
Uses of RF Coils
RF coils have many uses in a variety of industries and applications, including medicine and electronics. RF coils are used extensively in MRI (Magnetic Resonance Imaging) machines, where they function as transmitters and receivers.
The manufacturing process for winding RF coils is described in the following procedure:
- Modeling and simulation tools are used for the initial design of the coil, especially for coils used in MRI. One such tool is COMSOL Multiphysics from Sweden. Orthocyclic winding needs space that is achieved using an iterative approach. Thus, the calculation requires as input the required number of windings, the wire cross section, and the maximum space available for an insulated core.
- The type of core is determined. The material for the core depends on the operating frequency of the device. There are many factors to consider when deciding which kind of core to use. For example, materials such as ferrite or powdered-iron cores may be used.
- A conductor, for example insulated copper wire, is wound around the core. The number of turns must be decided upon and is a function of the inductance and the properties of the core material. The larger the inductance, the more turns are required. In today's industrial manufacturing, the winding of coils is done by automated machinery. Orthocyclic winding machines are the best method for producing RF coils. The wire of an upper level is placed in the grooves of wires wound in lower levels.
This kind of winding provides an excellent fill factor for round wires. In other words, you pack the most wire for a given volume.
However, the unevenness and bends in a wire on a delivery roll mean that wires never reach the optimal number of windings in a coil nor the highest volume of wire. Other factors that influence the winding of RF coils include the quality of the copper and its coating. Counteractions can be taken, including placing the wire in predefined grooves on the coil body.
The finished product is submitted for testing and validation.