Coupling materials facilitate the transmission of sound waves between a transducer and a sound sample. They can be water-based or oil-based and are used in microphones, sound test equipment, and ultrasonic testing. The main properties sought in a good coupling material are its acoustic properties, corrosion inhibition, and surface wetting. Specialty couplings are designed for use in electrical components, nuclear and medical equipment, and fiber optic cable splicing.
A coupling is a material that serves as a medium for the transmission of sound waves. Usually, mating gel is a form of water-based substance or a paste made up of oils or fat-like chemicals. It is placed in physical contact with a transducer which receives audio signals in the air and then converts them into electrical impulses for transmission. Microphones and sound test equipment use coupling gels or dry couplants to facilitate this.
Ultrasonic testing of materials can also employ complete immersion of the transducer in a couplant-like water, or just a thin film of glycerin or oil between the transducer and the test medium. Acoustic coupling is important for ultrasonic testing because air is a rather poor medium for sound wave transmission in general compared to solids. The level of energy carried by ultrasonic frequencies drops dramatically as it is transmitted through the air, so these materials are intended to minimize this loss.
Many conventional substances can be used as couplants, including motor oil or even hair gel. This is because even a very thin layer of air between a transducer and a sound sample will have a strong damping effect, and nearly any solid place between them will reduce it. However, electrical components can generate a lot of heat, so specially formulated couplings are designed to accommodate for this.
Ultrasonic couplants in the nuclear and medical equipment industries go one step further by requiring low halogen or sulfur compound materials at less than 50 parts per million (ppm). Propylene glycol, the same material used in automotive antifreeze, is another specialty compound used. It is chemically unreactive and can withstand temperatures of 200° Fahrenheit (90° Celsius) before suffering thermal breakdown. Optical coupling fills another unique need. Often referred to as index match gel, it is used in the splicing of fiber optic cable to minimize refractive index changes that occur where fibers meet, which can degrade signal transmission.
The main properties sought in a good coupling material are its acoustic properties, corrosion inhibition and surface wetting so that it bonds well. Also important is the residence time of the moisture, known as the drying time, as well as the temperature levels it can withstand and its uniformity. A unique aspect of some coupling gels is that they contain a fluorescent tracing dye that glows in the ultraviolet band, which is used to monitor coverage levels.
Protect your devices with Threat Protection by NordVPN
