Types of Ultrasonic Transducers
All ultrasonic cleaning systems utilize 1 of 2 available types of ultrasonic
transducers; piezoelectric transducers and magnetostrictive transducers.
There are many differences between these transducer designs, including the way
in which they are bonded to the "radiating surface" or ultrasonic diaphragm, the
frequencies which can be generated, and the electrical efficiency of the system.
We will discuss each difference in detail.
How Each Transducer Design Functions
Both transducer designs produce ultrasonic activity by rapidly oscillating
the ultrasonic diaphragm to which they are mounted. However, each design
performs this action differently. Magnetostrictive transducers are
essentially electromagnets made of a heavy nickel or alloy core which is wound
with wire. As electrical current is pulsed through the wires, the core
vibrates at a frequency which matches the output frequency of the ultrasonic
generator, thereby producing the ultrasonic cleaning effect in the tank.
This is the oldest ultrasonic transducer technology known, and was used prior to
the development of efficient and powerful piezoelectric transducers which
offered 95% + electrical efficiency when compared to the 50-60% electrical
efficiency of magnetostrictive transducers. This efficiency difference
still exists today, and is the one of the reasons why 98% of ultrasonic
equipment manufacturers use piezoelectric transducers.
Piezoelectric transducers are manufactured of lead zirconate titanate, a
common piezoelectric material which expands and contracts when provided with the
appropriate electrical frequency and voltage. As the transducer expands
and contracts rapidly, the ultrasonic diaphragm vibrates to introduce ultrasonic
activity into the cleaning tank. This design represents the most efficient
design currently available.
Most manufacturers of piezoelectric ultrasonic systems use high-temperature
epoxy to attach the transducers to its radiating surface. Zenith bonds its
transducers using a metallurgical stud, and uses epoxy to prevent the ROTATION
of the transducer off of this stud, leading a significantly greater bond
strength than when using epoxy alone. In fact, if you used a hammer and
attempted to break one of our transducers off of the tank, you would rip a hole
in the tank rather than detaching the transducer!
Magnetostrictive transducers are bonded
using vacuum brazing of the transducer base to the ultrasonic diaphragm.
Manufacturers of magnetostrictive ultrasonic designs are quick to point out that
a vacuum-brazed transducer bond is superior to an epoxy-bonded transducer.
This may be the case when dealing with Zenith competitors, but it is NOT the
case when comparing to Zenith's transducer bonding system. Epoxy-bonded transducers
without the metallurgic stud cannot withstand highly
abusive environments, such as environments in which objects may be dropped onto the diaphragm which may
cause damage to the epoxy bond. However, these environments do not exist
in 99% of ultrasonic cleaning operations. Additionally, transducers can
easily be protected against such damage.
Ultrasonic cleaning systems operate by converting electrical energy into
mechanical vibration to produce ultrasonic cavitation in the cleaning fluid.
When an ultrasonic system is highly-efficient, most of the incoming electrical
power is converted to mechanical vibration. For example, piezoelectric
ultrasonic cleaning systems manufactured at Zenith are 95-98% electrically
efficient. Most of the in-coming power is being converted into mechanical
vibration. This efficiency is common to most piezoelectric ultrasonic
systems, and is one of the primary reasons why over 95% of all ultrasonic
equipment manufacturers utilize piezoelectric transducers.
Magnetostrictive transducers are highly in-efficient in design. More electrical power will be
required to generate the same amount of ultrasonic cleaning action as a
comparable piezoelectric system. Not only do these systems require more
electrical current, but the generators are also very large, and may require
air-conditioning or other special cooling methods to keep components within
acceptable operating temperatures. As mentioned earlier, this is a very
old technology that is being marketed as something new. Electromagnets are
not new technology.
The lack of electrical efficiency is one of the main reasons why
magnetostrictive systems are rated for such high wattages, but purchasers must
know that these ratings represent INPUT wattage, not OUTPUT wattage in the tank.
For example, if a magnetostrictive transducer system is rated for 1000 watts,
the power in the tank will be only 500-600 watts due to electrical inefficiency.
Ultrasonic Frequency Choices
Ultrasonic operating frequency is perhaps the single most important
consideration when choosing an ultrasonic cleaning system. Each frequency
has its own unique characteristics. Low frequencies are used for large,
un-detailed parts with heavy contamination and produce un-even cleaning action
in the fluid, while higher frequencies produce more evenly-distributed cleaning
action, and have the ability to penetrate small blind holes, threaded areas, and
other detail. More information is available under the "Technical Info"
drop-down menu above, under "Frequency
Choosing an ultrasonic frequency for a magnetostrictive system is easy, since
there really is no choice at all. Magnetostrictive system designs
typically operate at frequencies below 30kHz, making these systems unsuitable
for most ultrasonic cleaning applications. Most parts being cleaned
ultrasonically require the removal of lightly-bonded contaminants on the surface
of precision parts, applications which are addressed with 40kHz, 80kHz or
CROSSFIRE Multiple Frequency Ultrasonics
operating in this range. Low frequencies would produce inconsistent
cleaning results on such parts, and parts may be damaged by
To get an idea of the type of scrubbing action produced by low-frequency
systems, take a look at the top photo at the right. This screen was
cleaned in a 25kHz ultrasonic system. Note the spotty cleaning results
created by the large areas of lower ultrasonic power produced in a low frequency
system. There are areas of high lower, and areas of lower power, and the
contaminant in this example could not be removed in the lower power areas of the
ultrasonic cleaning tank. Parts being cleaned in lower frequency systems
will obtain different levels of ultrasonic power depending upon where they
happen to rest in the ultrasonic cleaning tank.
The lower photo depicts an identical sample cleaned in the same cleaning
fluid with Zenith's CROSSFIRE 40/80kHz ultrasonic system. The even energy
distribution created by the combination of 40kHz and 80kHz ultrasonics produces
a much more evenly distributed cleaning effect, and results in consistent and
even cleaning regardless of part position in the tank.
Although Zenith manufactures
systems, they are rarely recommended for any ultrasonic cleaning
applications, unless they are combined with
CROSSFIRE system. This is the
direct result of the thousands of sample parts which have been test-cleaned
ultrasonically at Zenith. Our
Testing Service is used to develop complete processes for our potential
customers. Parts are submitted and tested in various ultrasonic
frequencies and cleaning agents to determine the best process to use for a given
application. Low frequency ultrasonic cleaning systems in the 25kHz-30kHz
range never produce a better cleaning result than higher frequency systems do.
In fact, it is exactly the opposite. Parts are cleaned more effectively in
systems operating at 40kHz and above. Since these systems are less
damaging to components, quieter in operation, and better at cleaning in fine
detailed areas, these systems are usually recommended for any cleaning
Generation of Audible Noise
The lower the operating frequency of the ultrasonic system, the more audible
noise generated since the frequency of the ultrasonic system is closer to the
human hearing range. 25kHz and 30kHz ultrasonic systems are so loud that
they commonly require expensive acoustic insulation to reduce decibel levels.
In some cases, it may be impossible to reduce the decibel level to within OSHA
guidelines for un-protected hearing in such systems, another reason why higher
ultrasonic frequencies are typically recommended. Since magnetostrictive
ultrasonic systems operate at these low frequencies, the decibel level which is
produced is very high, which must be considered when purchasing an ultrasonic
system where operators will be located.
Magnetostrictive ultrasonic generators operate at such high temperatures that
it is common for these systems to require extensive additional cooling, such as
air conditioning equipment dedicated to cooling the generators. This
excessive heat may cause premature failure of certain components in the system.
To overcome these issues, most manufacturers of magnetostrictive systems utilize
more expensive, large electronic components which are able to withstand these
high operating temperatures, and generator enclosures are significantly larger
as a result.
Piezoelectric cleaning systems are highly-reliable electronic devices when
properly engineered. If they weren't, no one would buy them, and 98% of
ultrasonic cleaner manufacturers would not use them. Generators are manufactured using surface mounted
devices, transistors, and common MOSFET components, and run cool when compared
to a magnetostrictive design. Generators are relatively small,
lightweight, and do not require air conditioning or excessive cooling.
With regards to transducer reliability, piezoelectric transducers are in use
for decades, and contrary to the claims of the 2% of the manufacturers that
utilize these transducers, they are highly reliable. This is why
manufacturers of piezoelectric systems such as Zenith Ultrasonics include a 10
year transducer bond warrantee. We could not offer such a warrantee unless
we were very sure of the bond reliability.
Long-term operational reliability and power of piezoelectric transducers has
been questioned by manufacturers of magnetostrictive ultrasonic systems, which
claim that transducers lose power over time, and continuously deteriorate
internally. Zenith has not found this to be the case, and has over 79
years of experience proving otherwise. Zenith performs repairs on
piezoelectric systems which have been in operation for 20-30 years. These
systems have perfect transducer bonds that have not deteriorated, and the
cleaning power is just as good or better than when originally installed, leading
one to conclude that piezoelectric transducer systems, when properly engineered,
can last for decades depending upon the application.
Erosion of the Diaphragm
Since magnetostrictive ultrasonic systems operate at very low ultrasonic
created by such systems is much greater than that of higher ultrasonic
frequencies. Cavitational erosion is the deterioration of the transducer
diaphragm, and is normal for all ultrasonic cleaning systems. Over time,
the ultrasonic diaphragm will slowly erode, and will eventually deteriorate to
the point where replacement is required. The lower the operational
frequency of the system, the faster erosion will occur, and since magnetostrictive transducers operate at low frequencies, one can expect
significant erosion of the ultrasonic diaphragm.
To overcome this limitation, magnetostrictive system manufacturers construct
their radiating diaphragms from very thick materials which extends the life of
these systems. However, by increasing the thickness of the diaphragm, it
also becomes less flexible as well, and reduces the effective cleaning power in
the ultrasonic tank. The radiating diaphragm must be flexible enough to
produce compression/expansion cycles in the cleaning fluid, a task which
requires enormous power with diaphragms which are 3/8" thick.
Piezoelectric ultrasonic systems utilize thinner radiating diaphragms to
maximize the ultrasonic power and energy distribution in the cleaning tank.
To overcome excessive
cavitational erosion, Zenith applies hard-chrome plating
to the radiating surface to decrease the rate of erosion.
erosion is a direct indicator of ultrasonic power being generated. If your
diaphragm is not eroding, there is not enough power on the diaphragm to damage
Since magnetostrictive systems operate at lower frequencies, the distribution
of the cleaning action in the fluid is poor. Every ultrasonic
system produces a cleaning action which is distributed in the fluid as a series
of equidistant bands of cleaning action, with very little cleaning action
produced between these bands. At 30kHz, the active cleaning bands, or
standing waves, are approximately 1" apart from one-another. If the
parts being cleaned have small blind holes, and these holes happen to rest
between standing waves, they may not be cleaned.
Since piezoelectric systems typically operate at higher ultrasonic
frequencies, the cleaning action produced in the tank is more evenly-distributed
when a higher frequency is chosen. For example, at
80kHz, the standing waves produced are less than
1/4" apart. Even the smallest blind holes or detailed part areas are
effectively and evenly cleaned in such a system. For more information
about ultrasonic energy distribution, and its relationship to frequency, select
the Technical Info drop down menu and select "Frequency
After reading the above, one can see why most ultrasonic equipment
manufacturers choose piezoelectric transducers. While magnetostrictive
designs are not damaged by shock, this is easily overcome by the use of
protection devices mounted in the tank. Piezoelectric systems are superior
in every other regard, including frequency selection, energy distribution in the
tank, decibel levels generated, reliability, equipment size, and efficiency.
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