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Surprising sound sources: Do you know how inductors and transformers make noise?
In our daily lives, we often hear humming or hissing noises coming from electrical appliances. The main sources of these sounds are often inductors and transformers that we don't pay much attention to. This phenomenon is called electromagnetically induced noise, which is caused by the vibration of materials under the stimulation of electromagnetic forces. In this article, we'll explore why these devices make noises and how to explain these confusing sounds.
Electromagnetic induced noise is a significant vibration sound caused by materials under the stimulation of electromagnetic force.
Electromagnetic induced noise, often referred to as coil noise, originates from the electromagnetic fields created when electrical appliances operate. These fields cause subtle vibrations in the materials within the device. When the frequency of these vibrations is between 20Hz and 20kHz, they form audible sound. Equipment such as inductors, transformers and certain rotating motors are the main producers of this sound. This acoustic phenomenon can be seen as a counterpart to microphonics, which describes how mechanical vibrations or sounds can cause unwanted electronic disturbances.
Basic Concepts of Electromagnetic Noise
The source of electromagnetic forces lies in the existence of electromagnetic fields, which include forces caused by Maxwell stress tensor, magnetostriction and Lorentz force. When these forces are transferred between different media, they cause deformation of the materials and produce different vibrations and noises. When the natural frequencies of the structural modes coincide with the frequencies of external electromagnetic forces, these vibrations are amplified, resulting in louder sounds. Simply put, this sound is the resonance of the material caused by changes in electric and magnetic fields.
Electromagnetic noise in motors
In an electric motor, electromagnetic forces cause changes in torque, which in turn cause torsional vibrations in the rotor and stator. Especially in permanent magnet synchronous machines, the "cogging torque" is a significant change that leads to structure-borne noise. The size and severity of this noise often depends on the design of the device, its working conditions and the properties of the materials.
Structure-borne noise originates from the diffusion of rotor axis vibrations. When these vibrations affect the frame and axis, additional noise is generated.
Acoustic Characteristics of Inductors and Transformers
In an inductor, electromagnetic energy is stored in the air gap of the magnetic circuit, and the noise caused is closely related to the material of the air gap and the geometry of the magnetic circuit. The same is true for transformers, where magnetostriction in the windings and laminated core can cause vibration and noise when the load changes. Capacitors can store voltage and also produce electroacoustic effects when the voltage is unstable. This is called the "singing capacitor" effect, and everything it brings is surprising.
Methods to reduce electromagnetic noise
Techniques to reduce electromagnetic noise and vibration specifically include design improvements, such as selecting appropriate slot/pole combinations and winding designs, avoiding resonance, and increasing the damping properties of materials. In addition, changes to specific devices, such as adding a layer of glue to a TV, can effectively reduce "coil noise". These simple solutions can often significantly improve the user experience.
Improvements in acoustic design have focused on reducing the intensity of electromagnetic excitation and the intensity of structural response to reduce noise.
Experimental Examples and Digital Simulations
To understand how electromagnetic noise works, it is useful to perform experiments or numerical simulations. Examples of different acoustic effects observed by moving a DC magnetic field or applying variable frequency current not only enhance our understanding of noise generation, but also how these phenomena occur when the correct physical theory is applied.
Whether it is static equipment or rotating equipment, the existence of electromagnetic noise is a huge and complex topic. Studying and understanding the sounds produced by these devices can help us not only improve efficiency in motor design, but also improve the experience of using various products in daily life. However, how will these phenomena affect future appliance design and its use?
