Standard definition of transducers

Instruments or devices used to achieve the mutual conversion of different forms of energy can be collectively referred to as transducers. For example, an electroacoustic transducer that converts audio electrical signals into audible sound, or converts audible sound into audio electrical signals to achieve mutual conversion of electrical and sound energy, such as speakers (speakers), headphones, microphones, etc;
An electromagnetic transducer that converts electrical and magnetic energy into each other, such as an electromagnet that generates magnetic force by applying current, or a recording head that converts audio electrical signals into magnetic signals and records them on a magnetic tape, or converts magnetic signals on a magnetic tape into audio electrical signals, which are amplified and processed before being converted into audible sound by an electroacoustic transducer.
An electromechanical transducer that converts electrical and mechanical energy into each other. For example, an electric motor generates magnetic field force by inputting current, which then drives the armature to rotate, while a generator generates current due to the rotation of the armature and the action of the magnetic field. Another example is the pickup head of a record player, where the needle moves along the grooves of the record to generate audio mechanical vibration and convert the output audio electrical signal. After amplification, it is converted into audible sound by an electroacoustic transducer.
Photoelectric transducers that realize the mutual conversion of electric energy and light energy, such as incandescent bulbs, solar batteries (photocells), photodiodes and other electroluminescent devices.
In addition, there are devices that can realize the mutual conversion of electric energy and Chemical energy. For example, when the battery is discharged, it converts Chemical energy into electric energy, and when it is charged, it converts electrical energy into Chemical energy. There are more devices to realize the mutual conversion of electric energy and heat energy. For example, electric stoves, ovens, Rice cooker, electric frying pans, electric cups, Electric blanket, electric combs, electric soldering irons, electric irons, etc. are devices that convert electric energy in one direction into heat energy, while thermocouples are devices that convert heat energy into electric energy. The emerging electromagnetic cookers in household appliances are devices that generate Eddy current on metal utensils by the action of magnetic fields excited by electric energy, causing metal utensils to heat up, A microwave oven is a device that excites microwaves (electromagnetic energy) from electrical energy and further heats up food
In summary, there are various types of devices that can convert energy forms and new types will continue to emerge. In a broad sense, they can all be referred to as transducers. However, the transducer mentioned in the detection technology has a specific definition, which is the transducer to be explained in this textbook.
The transducer referred to in engineering inspection technology specifically refers to a device that can receive signals from one system and output signals to another system. The received signal and output signal belong to different energy forms, but the output signal can represent certain characteristics of the input signal. Therefore, as a transducer system, it is usually necessary to include an energy storage element, which stores one form of energy and converts it into another form of energy output during its operation.
In practical applications, it is required that the transducer can convert some energy that is not easy or inconvenient to test and process into another energy that is easy to further process or facilitate testing, thus making it possible to evaluate or analyze the original input energy. For example, a sound level meter used to measure environmental noise can convert a certain level of environmental noise into a certain size of electrical signal, which can further quantitatively display the intensity of environmental noise. For example, the transducer (probe) used in non-destructive testing technology that utilizes magnetic leakage characteristics can convert the magnetic leakage flux at the defect location on the magnetized workpiece into an electrical signal. After processing, the presence of the defect can be displayed and the size of the defect can be evaluated.