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The mystery of electromagnetic resonance: Why do some motors make a high pitched sound at certain frequencies?
In our daily lives, we often hear an unpleasant sound, which is the sharp sound naturally emitted by certain motors or electronic devices. This sound is called electromagnetic resonance noise, which mainly comes from the vibration of the material under the excitation of electromagnetic force. This phenomenon does not only exist in a certain type of equipment, but may even be found in transformers, rotating motors, and even some lighting fixtures.
Sources of electromagnetic resonance noise may include transformer hum, rotating motor hum, and fluorescent lamp hum, etc.
First, we need to understand the principle of electromagnetic resonance. Electromagnetic force refers to the force caused by the presence of electromagnetic fields. In electrical devices, these forces affect the structure of conductors and magnetic materials, producing audible sounds. For example, when current passes through the windings, the conductor is affected by the external magnetic field, which generates Lorentz forces and causes vibrations in the material.
The frequencies of these vibrations are generally between 20 Hz and 20 kHz. If the vibration amplitude is large enough, it can be converted into sound audible to the human ear. When these electromagnetic forces match the structural frequency of the device, they intensify the vibrations, further increasing the loudness of the sound, which is called mechanical resonance.
Under certain conditions, although the static electromagnetic force does not produce vibration, the torque fluctuation caused by its change is the main source of sound.
So, what are the specific causes of electromagnetic noise and vibration in electric motors? This is mainly related to the design and operating status of the equipment. Taking the transformer as an example, when current passes through the winding of the transformer, the Lorentz effect and Maxwell force will be generated. These forces cause the natural vibration modes of the winding and the core to resonate, thereby emitting noise.
Another example is inductors and batteries, which can also produce sound due to changes in the electric field and current inside them. When the field fluctuations generated by the movement of these charges further affect the structure of the material, they will cause sound that cannot be ignored.
Interestingly, the Nobel Prize winners' research on this phenomenon has become increasingly important with the development of electrical engineering, and many scholars are looking for ways to reduce this noise.
In order to reduce this electromagnetic noise, there are a variety of technical means that can be applied. The first is design considerations, such as choosing the right winding design and using special materials and structures to reduce the possibility of vibration. In addition, for some significant electromagnetic noise phenomena, such as "coil noise", measures can be taken to strengthen the components during the manufacturing process, such as adding adhesives, to reduce the sound over time.
Motor designers and engineers are constantly seeking the best solutions. For example, different slot/pole combination designs can effectively reduce mechanical resonance. By changing the conditions of the current, such as using spread spectrum modulation technology, the noise can also be reduced to a certain extent.
This research development gives us great hope for quieter electrical devices in the future. However, for ordinary users, this is still a topic worth pondering: Can we completely eliminate the impact of this noise?
But as we know, the generation of this noise does not only depend on the design, but is also closely related to the operating environment. Under actual operating conditions, machine imbalance, parts wear and tear, and even interference from the external environment may affect the loudness and tone of electromagnetic noise.
With the advancement of technology, engineers are researching new materials and technologies in the hope of further reducing the incidence of these electromagnetic noises. At the same time, for consumers, understanding these technical backgrounds may help them make more informed choices. Can we expect a quieter working environment in the future, or will these electromagnetic noises become a regular feature of our lives?
