Dual-frequency ultrasonic air transducer
Ultrasonic air transducers have been widely used for non-contact level detection, in particular, for liquid, solid and powder level detection, regardless of colors, transparency, hardness, etc. However, the ultrasonic air transducers for non-contact level sensing or object detection currently available on the market are just with single operating frequency, facing the dilemma between sensing range and blind zone. Generally speaking, the ultrasonic transducer with lower operating frequency has longer sensing distance along with a longer blind zone and poorer resolution; on the other hand, the ultrasonic transducer with higher operating frequency has shorter sensing distance along with a shorter blind zone and better resolution.
The blind zone means the minimum detection distance from the face of the ultrasonic transducer. An object inside the blind zone is not detected or can cause an unexpected reading signal. The main factor affecting the blind zone is ringing of an ultrasonic transducer. The key component of an ultrasonic transducer is piezoceramic element. When the ultrasonic transducer is driven by a specific frequency of electronic driving power, the piezoceramics correspondingly generate vibration and emit ultrasonic waves simultaneously, but this vibration does not stop immediately when the driving power is cut off. It fades away gradually to a static state after the remaining vibration is absorbed completely by the back-damping layer of the transducer. The duration between the power cut-off and the static state of an ultrasonic transducer is called ringing. The longer the ringing, the longer the blind zone. If the blind zone overlaps with the echo signal, the actual time of flight (ToF) cannot be calculated so as not to detect the actual distance, as shown in figure 1.
Unictron has developed a novel type of dual-frequency ultrasonic air transducer, which can operate at both lower operating frequency and higher operating frequency in one transducer. For example 50 & 200 kHz for non-contact dual-frequency ultrasonic level transducer. This innovation provides the advantage of maximizing detection distance and minimizing the blind zone in one compact transducer, making the application of the transducer more versatile, and its sensing range can cover most of non-contact ultrasonic transducers for level detection on the market, as shown in figure 2.