Ultrasonic transducer type: comparison of magnetostrictive and piezoelectric transducer
There are two types of transducers to generate the sound waves required for the process: piezoelectric and magnetostrictive. Although their functions are sufficient to make it a place in the market, each type of ultrasonic transducer has its own characteristics, making it more suitable for specific tasks. In order to compare them, it is necessary to study how they work and their respective characteristics.
1. Working principle
Piezoelectric technology uses a crystal with special electrical properties made of lead zirconate titanate. In the transducer, this crystal material has two wires attached to opposite faces. Then the crystal and wiring are assembled in the housing between the two metal plates. When current flows through the wiring and enters the crystal, the crystal quickly changes shape and expands. When the current is terminated, the crystal returns to its original shape. The ultrasonic transducer using this technology rapidly circulates the current through the crystal at a set frequency, thereby generating a resonance effect.
The working principle of a magnetostrictive ultrasonic transducer is that iron-rich metals expand and contract when subjected to a magnetic field. To take advantage of this behavior, iron-rich metal cores are wrapped in copper wires. The component is then contained in a tank. When current passes through the copper wire, the metal core expands and lengthens. Like a piezoelectric transducer, a current at a set frequency produces a resonance effect.
2. A fixed way
An adhesive is used to bond the piezoelectric ultrasonic transducer to the housing of the ultrasonic cleaner. When piezoelectric technology was first introduced, this created problems because the adhesive would weaken and eventually fail. Due to the development of engineering technology that can be used in the aircraft industry, this limitation no longer exists. Despite repeated use, modern adhesives still do not allow the transducer to be attached.
The housing of the magnetostrictive transducer is directly welded to the tank of the ultrasonic cleaner, providing a firm, hardly breakable bond.
3. Ultrasonic transducer frequency
The ideal state of ultrasonic cleaning is to operate at a frequency of 40kHz-70kHz, but the process can still be carried out in a wide range of 25kHz-170kHz.
Magnetostrictive ultrasonic transducers can only work at frequencies up to 30kHz, which means that their applicable uses are greatly restricted. In this case, the best use of the magnetostrictive transducer ultrasonic cleaning system is for large machines that have contaminants that are difficult to remove. The process must also not require a thorough cleaning of the machinery. An example of this application can be used on the electroplating processing line.
On the other hand, the piezoelectric ultrasonic transducer can work in the entire range of 25kHz to 170kHz, making its use extremely diverse.
4. Energy consumption
Magnetostrictive ultrasonic transducers must convert electrical energy into magnetic energy, and then use it to generate mechanical energy. The whole process will generate a lot of wasted energy, which is usually wasted in the form of heat energy.
The piezoelectric ultrasonic transducer can convert low-voltage current into mechanical energy in one step, making it highly efficient. Therefore, the piezoelectric transducer can perform more work while consuming the same amount of electrical energy.
5. Inherent ultrasonic transducer noise level
When harmonic frequencies are generated, sub-harmonic frequencies are usually produced as natural products. The operating frequency of most piezoelectric transducers is 40kHz or higher, which means that the first sub-harmonic generated is 20kHz, which is beyond the range of normal human hearing.
Magnetostrictive ultrasonic transducers usually operate at a frequency of 30kHz or lower, producing audible sub-harmonic frequencies. These frequencies sound the same as the hum of high-voltage electrical or transformers heard up close. When multiple magnetostrictive transducers are installed in the same ultrasonic cleaning tank, the noise level requires the use of protective hearing aids.
6. Expected life of ultrasonic transducer
Piezoelectric transducers first use quartz crystals, and over time, the quartz crystals will eventually lose strength. Since then, engineers have created semiconductor ceramic materials that can be pre-aged through a special process, thereby reducing the amount of wear after assembly of the components.
Combined with new crystalline compounds, their service life is as long as that of magnetostrictive transducers, and magnetostrictive transducers have always enjoyed a long service life.
