The Ultrasonic and Radar level sensors are generally both 1 wave or pulsed from the sensor head to the surface of the material. Waves, pulses reflect back at a certain delay time, take that time x speed = distance.
Types of Radar + Ultrasonic Level Sensors
Ultrasonic type level sensor: Use ultrasonic waves about >20,000Hz.
Funnel Radar level sensor: Uses waves with a frequency higher than 10~16GHz, carries greater energy, transmits farther and penetrates more.
Guided Radar level sensor: Use microwave fulse transmitted by conductor or conductor, less interference by objects inside tanks, tanks, tanks.