Ultrasonic Transducers: Stacked vs. Crystal Bonded

In the ultrasonic cleaner industry units are typically manufactured in two ways - with stacked transducers or with crystal bonded or flat transducers. The transducers emit high frequency sound waves into a liquid solution that creates cavitation in the ultrasonic bath to clean for numerous applications. Generally speaking flat transducers have lower power parameters than stacked transducers, and as such stacked transducers with their higher power parameters are usually used in heavy duty industrial cleaning applications. However, as will see a little later in this article the term “power” does not translate into “cavitation intensity” and the term “more power” does not reflect on cleaning efficiency. Some manufacturers and importers have created a misnomer in regards to the power of stacked vs. flat transducers in ultrasonic cleaners and as such the intent of this article is to clarify the terminology and context in which it’s used.

Many cleaning applications such as those in health care, jewelry, laboratories, weapons, and recreational industries require the use of standard lab type ultrasonic cleaning units. These units generally make use of strategically placed flat ultrasonic transducers as to provide enough cavitation intensity to effectively clean without damaging parts, or the integrity of the stainless steel tank and the transducer itself. There has been some misleading marketing hype stating that stacked transducers have far more power than crystal bonded transducers - this is true, but only in context.

Stacked transducers are indeed capable of much more power input and output amplitude levels than flat transducers as they are constructed to accommodate the stresses from high energy output amplitudes. The easiest way to think of transducers is like sound system speakers. The speakers in your car are manufactured to provide ample listening pleasure because there are many small speakers strategically placed throughout - this is similar to crystal bonded or flat transducers. In contrast the speakers at a U2 concert are massive and constructed to handle the high power input signals and intense output amplitudes to provide more than ample listening pleasure for stadiums that hold tens of thousands of fans - this would be the stacked transducer.

The context in which these transducers (speakers) are designed, constructed, and used is imperative to understanding so called power levels. It would be accurate to say that stacked transducers are capable of more power; however, it would be inaccurate to say an ultrasonic cleaner is more powerful simply due to the fact that it has stacked transducers bonded to the bottom of the tank. A stacked transducer requires more power simply because of the mass that has to be moved due to its construction, but what about the transducer’s output amplitude and the cavitation intensity within the ultrasonic bath? A well designed stacked transducer bonded to the bottom of a standard off-the-shelf lab type ultrasonic cleaner will have such intense output levels that it would cause problems for the integrity of the ultrasonic tank. Think about our speakers again - put concert style speakers in your car matched with the output amplitude or sound levels they are designed for and you’d destroy your car - not to mention your hearing. The same concept applies to ultrasonic cleaners - we want to match a well designed and constructed transducer with a durable environment that will take the punishment of high level output amplitudes.

Lab type, table top ultrasonic cleaners are limited in regards to their durable environment both in construction and size. Therefore, we want to match a well designed transducer to fit within these confines in order to be capable of generating intense cavitation (cleaning power) throughout the range of varying load conditions that the cleaning application will encounter. We need to also consider that there is a cavitation threshold limit for ultrasonic cleaners - that is a point at which regardless of how much power is introduced into the system the cavitation intensity will not increase. We also need to recognize the fact that if we try to impart too much power and subsequent output amplitude into a lab type ultrasonic it will cause the radiating surface (the tank) to erode and create a hole. So, this misnomer that suggests that an ultrasonic cleaner with a stacked transducer is more powerful than an ultrasonic unit with a crystal bonded transducer has not been put in context thus far, but let’s delve a little deeper.

The design and materials of any transducer are extremely important in regards to efficiency and life - they must be designed to accommodate the frequencies, output amplitude, and stresses incurred during operation, and should be designed for maximum life. Poorly designed and poorly constructed transducers regardless if they are stacked or flat will have a short life expectancy as they will become fatigued during the stresses of operation and deteriorate thus becoming inefficient and/or cracking. A well designed and well constructed transducer will provide long life expectancy and will efficiently accommodate the rigors of the fluctuating power demands and stresses it realizes in maintaining cavitation intensity as load conditions change inside an ultrasonic bath.

The term “power” in itself can be misleading - generally speaking “power” is the amount of energy required to move the mechanical components such as the transducer and radiating surface/tank in order to create cavitation. Cavitation intensity is what determines the effectiveness of an ultrasonic cleaner, and cavitation intensity must be controlled to accommodate varying load demands within the parameters of the ultrasonic cleaner specifications to be effective. Simply stated, a stacked transducer by its design alone is going to require more power than a crystal bonded transducer so as to move its mass in order to create any level of cavitation intensity. Increasing the load conditions in the ultrasonic bath is going to cause the transducer to have an increase in power level to sustain adequate cavitation intensity. Too much power is not going to have any effect on cavitation intensity, and will cause the ultrasonic unit to become cannibalistic.

It seems that most of the hype over stacked transducers versus crystal bonded transducers has come from availability of inexpensive, less than quality constructed transducers that are available from outsourced vendors today. The claim is both true and false depending upon the context in which the expression “stacked transducers are more powerful” is used. Sonix 4 uses stacked transducers on our industrial duty systems, and they are indeed powerful - if we were to use them on our lab type units the units the integrity of the tank would be compromised over a very short period of time.

So now what? Disregard the general claim that just because the ultrasonic unit has a stacked transducer it’s more powerful. Trust a manufacturer that knows how to design, match, and manufacture ultrasonic transducers for the environment that they are intended. It is even better if the manufacturer backs their transducers with a 10 Year Warranty as is the case with Sonix 4.