How to Improve the Quality Factor of the Solenoid Coil?

Pictures showing a solenoid with coil in operation

Figure 1: A solenoid with coil in operation.

The quality factor Q is an important parameter reflecting the quality of the Solenoid coil, and improving the Q factor of the coil can be said to be one of the key points of winding the coil. Then, how to improve the Q factor of the wound coil? The specific methods are described below:

1. Select the Wire of the Coil According to the Operating Frequency

Inductance coils that work in low frequency bands are generally wound with insulated wires such as enameled wires. The operating frequency is higher than tens of thousands of hertz, and in the circuit below 2MHz, the coil is wound with multiple insulated wires. In this way, the surface area of the conductor can be effectively increased, so that the influence of the skin effect can be overcome, and the Q factor is 30%-50% higher than that of the coil wound by a single wire of the same cross-sectional area. In circuits with frequencies higher than 2MHz, the inductance coil should be wound with a single thick wire, with the diameter of 0.3mm-1.5mm.

2. Choose High-Quality Coil Bobbins to Reduce Dielectric Loss

In higher operating frequency occasions, such as short wave band, the use of ordinary coils will lead to a significant increase in the dielectric loss of the bobbin. Therefore, high-operating-frequency dielectric materials, such as high-frequency porcelain, polytetrafluoroethylene, polystyrene, etc., should be selected as the skeleton, and the winding method should be adopted.

3. Choose a Proper Coil Size

This can reduce the wear of a single-layer coil with a certain outer diameter (φ20mm-30mm). When the ratio of the winding length L to the outer diameter D is L/D=0.7, the wear is the smallest. The multi-layer coil with a certain outer diameter has L/D=0.2-0.5, and when t/D=0.25-0.1, the wear is the smallest. When the winding thickness t, the winding length L and the outer diameter D meet 3t+2L=D, the wear is also the smallest. For coils with shielding covers, L/D=0.8-1.2 functions the best.

Solenoid Valve Coil: 120V AC, 16 mm Valve Coil Size, DIN 43650C

Figure 2: Solenoid valve coil with 16 mm coil size.

4. Choose a Shielding Cover with Proper Diameter

Using a shield will increase the wear of the coil and reduce the Q factor. Therefore, the size of the shield should not be too small. However, if the size of the shielding cover is too large, the volume will be increased. Thus, it is suggested to balance these two factors and choose a proper diameter.
For you information, when the ratio of the shield diameter Ds to the coil diameter D satisfies the following values: Ds/D=1.6-2.5, the Q factor decreases by no more than 10%.

5. Use a Magnetic Core to Reduce the Coil Turns

The use of a magnetic core reduces the number of turns, resistance value and volume of the coil, and help to improve the Q factor.

Pictures showing the components of a solenoid coil including its iron coil

Figure 3: The iron core of the solenoid coil.

6. Choose the Coil with a Relatively Larger Diameter

The coil with a relatively larger diameter can increase the volume and reduce the wear of the coil. For general receivers, the diameter of the single-layer coil is 12mm-30mm; the multi-layer coil is 6mm-13mm, but considering the volume, it should not exceed 25mm.