Through the "pulse" ultrasonic generator, certain benefits can be obtained in ultrasonic cleaning and processing. In fact, different pulse frequencies and duty cycles produce different benefits. This article explores how "pulse" works and how its variants can benefit ultrasonic cleaning in different ways.

　　

　　Pulse simply refers to turning the generator's ultrasonic output on and off. Two parameters define the generator pulse. The first is the number of power on and off in a given time period. This is called the pulse rate.

　　

　　In the above example of displaying the pulse rate, the rate in the diagram on the right is twice that in the diagram on the left. Pulse is from any repetitive point in one cycle to the next

　　

　　Measured at the same repetitive point of each cycle.

　　

　　Another parameter of the pulse is the duty cycle.

　　

　　The duty cycle change rate shown remains unchanged. Generally, pulse rate and duty cycle are two independent variable parameters.

　　

　　Simply put, the duty cycle refers to the percentage of time that the ultrasonic power is turned on during each pulse from 0 to 100%.

　　

　　Historical record-In the past, most ultrasonic generators had at least one basic pulse form, although it was not necessarily intentional.

　　

　　This inadvertent pulse is due to the fact that very few ultrasonic generators have a filtered power source, and this power source can actually provide an immutable voltage source to operate any circuit that generates an ultrasonic frequency output. As the power cord changes (due to alternating current), the amplitude of the ultrasonic power also changes.

　　

　　Although in some cases, the ultrasonic frequency does not completely disappear, but it changes amplitude at least at a frequency of 120 Hz.

　　

　　In the 1980s, a new type of ultrasonic generator was developed, which can intentionally introduce pulses into the ultrasonic output. In basic ultrasonic generators, the pulse rate and duty cycle are usually fixed at the best values ​​that a given ultrasonic manufacturer considers for their specific transducer design.

　　

　　In fact, the pulse effect will vary due to the characteristics of the ultrasonic generator driving the transducer. More advanced ultrasonic generators allow users to change the pulse frequency and duty cycle to achieve maximum performance. Generally speaking, the pulse rate is variable, from several pulses per second to dozens of pulses per second.

　　

　　In some cases, a longer pulse period called "degassing" is provided to speed up the degassing rate of the liquid in preparation for ultrasonic cleaning. The degas cycle usually provides a pulse cycle every few seconds with a duty cycle of 10% to 50%. The closing time of the degassing cycle allows the bubbles formed by ultrasonic cavitation to float to the surface of the liquid, but the bubbles are trapped in the ultrasonic node.

　　

　　A video showing this effect will be part of the next blog.

　　

　　After all, the implosion of cavitation bubbles produced by ultrasonic waves is the main cleaning mechanism of ultrasonic cleaning. The more cavitation bubbles produced and the more implosion, the better the cleaning effect.