Ultrasonics – Ultrasonic Generators – Introduction

In an ultrasonic cleaning system, the device that provides the electrical energy to power the ultrasonic transducers is known as the ultrasonic “generator.”  Basically, the ultrasonic generator converts electrical energy received from the power line into electrical energy with the proper frequency, voltage and amperage to power or “drive” the ultrasonic transducers.  In most cases, the power line provides “Alternating Current” or AC at a voltage of 100 to 250 Volts and at a frequency of 50 or 60 Hz depending on location.  The power requirements for driving ultrasonic transducers vary but, in general, the ultrasonic generator needs to provide the transducer with a signal at the frequency of intended operation and (usually) at a voltage significantly higher than that delivered from the power line.

The earliest ultrasonic generators consisted simply of a frequency generator which, in turn, excited a power amplifier capable of operating at the ultrasonic frequency to power the ultrasonic transducers.  This is not unlike typical high fidelity sound reproduction systems but with a fixed frequency signal generator replacing the music source.  Since characteristics of ultrasonic transducers vary depending several factors including temperature, tank depth and parts loading, this method of driving ultrasonic transducers was dependant on an operator to select the proper frequency and driving power.  Although there were (and are) devices that are able to detect the efficiency of energy delivery from an electrical circuit, “tuning,” as it was called then, was often based on nothing more sophisticated than listening to the sound (consisting of subharmonics of the ultrasonic frequency) produced by the cleaning system.

Today’s ultrasonic generators are a world apart from that described above.  Part of the change was due to the advent of solid-state technology but there have also been many changes driven by the state-of-the-art of ultrasonic cleaning.  In fact, new generator technology has contributed more significantly to the growth of ultrasonic cleaning technology development over the last 15 or so years than have any developments in ultrasonic transducer technology.  Many advances have been a result of new generator technology being used to power the same transducers used by the previous technology but in different ways.

Ultrasonic generators today are “smart.”  They are often able to obtain feedback from the transducers which allows them to adjust frequency and power output to maintain maximum ultrasonic cleaning effect.  Ultrasonic generators also have the ability to provide customized variations in waveform to maximize the ultrasonic cleaning effect while minimizing the possibility of damage to the parts being cleaned.  The following is a “short list” of enhanced generator features and waveform options which will be subjects for detailed discussions in upcoming blogs –

• Pulse – Turning the ultrasonic energy on and off in a controlled way to speed degassing and improve ultrasonic cavitation.
• Sweep – Varying the ultrasonic frequency over a variable or fixed bandwidth to maximize transducer utilization and help provide uniform ultrasonic intensity throughout a cleaning tank.
• Dual Sweep – The ability to vary the rate of sweep in a random way to limit possible part damage due to resonances at the sweep frequency.
• Phase Locked Loop – Improved, automatic frequency control based on impedance feedback from the transducer to assure maximum transducer efficiency.
• UP Sweep – Technology that uses wave fronts in the tank to improve removal of bubbles and contaminants from the cleaning system.
• Multi-Frequency Generators – Generator technology that when combined with advancements in transducer technology allow ultrasonic operation at a number of frequencies using the same hardware in a single cleaning tank.

For those who can’t wait, the above topics and more are covered in a paper available at Designer Waveforms.

–  FJF  –