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.
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.
Piezoelectric transducers are bonded to the ultrasonic diaphragm with a
combination of high-temperature epoxy, and a metallurgic bond usually composed
of a welded and threaded stud. 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, which is
true to some extent. Epoxy-bonded transducers 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, and this protection is included when
required on Zenith ultrasonic cleaning systems.
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. In some
cases, systems are only 50-60% efficient. 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.
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 in-consistent
cleaning results on such parts, and parts may be damaged by
cavitational erosion. The photo on the
left depicts a 1/4" thick glass plate that has been damaged by 40kHz ultrasonic
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. 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, one cannot argue that
magnetostrictive transducers are more reliable. The only way a
magnetostrictive transducer can fail is if the wire winding on the transducer is
broken. Piezoelectric transducers are bonded with epoxy and mechanical
means, and is manufactured using a more sensitive material, making them more
sensitive to shock damage caused by heavy objects dropped on the transducer
diaphragm. However, as mentioned earlier, protection to prevent this from
occurring is included in systems manufactured by Zenith for abusive
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 73
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 lower 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.
For additional information,
Zenith Mfg. & Chemical Corp.
85 Oak St.
Norwood, NJ 07648-0412