The transducers alternate between sending and receiving ultrasonic signals. Corrosion-detecting pigs use either magnetic or ultrasonic sensors. Acoustic resonance wind sensors are a variant of the ultrasonic sensor. Mineralization of the ultrasonic transducers requires maintenance and potential for component failure. Ultrasonic, laser, or friction heating are other methods. The inverse piezoelectric effect is used in the production of ultrasonic sound waves. These additives are typically thin film coatings applied using an ultrasonic nozzle. Many technologies have been used including optical, capacitive, RF, thermal, piezoresistive, ultrasonic, piezoelectric, and MEMS. There are various ways to measure distance, including ultrasonic sound waves and infrared light. There are two types of ultrasonic scalers; piezoelectric and magnetostrictive. It can be done using either ultrasonic or optical methods . DSD uses noise shaping techniques to push quantization noise up to inaudible ultrasonic frequencies. Welds are possible by means of heating element, friction or ultrasonic welding. Their origin is seen in a physical phenomenon of ultrasonic cavitation. Packaging is an application where ultrasonic welding is often used.