If you are looking to build an at-home power ultrasonics system, there are a lot of options available to you, and deciding what you need can be confusing.Power ultrasonics are heavy industrial tools with heavy industrial price tags, especially if you look to do anything with high power greater than about 50 watts. Here is a quick breakdown of what you need, and what’s available.
A power ultrasonic system has 3 main components. These often come bundled together as either completed or partial systems. The components are:
- Power supply
- Ultrasonic transducer
- Output horn or mechanical coupling
These three components generate electrical power, convert electrical power to mechanical vibrations, and direct the vibrations into your target.
A power supply needs to provide high voltage, high power AC at the resonant or anti-resonant frequency of the transducer system. The main things to consider are: drive frequency, drive power, user friendliness, and safety of the design. Your transducer must match the resonant frequency of the transducer for best results and longest tool life. High quality industrial systems will provide features that automatically detect the resonant frequency and adjust their output accordingly. This will control for drift due to tool wear, cleanliness, loosening of fasteners, temperature shifts, component aging, and the like. This can also provide a warning to the operator if the system has gone out of tune and needs maintenance, repair, or replacement. High quality systems also permit reliable adjustment and measurement of output power to permit process control, especially for sonochemical or cell disruption processes. Safety consists of fuses, grounding, isolation, and other common high power safety systems. When I get my hands on some physical units, I will determine how safe these various options are.
You have three main options for power supplies:
- Chinese ultrasonic cleaner power supplies. These cost around $30, output a fixed frequency of 28kHz or 40Khz, and have have no frequency adjustment, power adjustment, or any other “nice” features built in. They are by far the easiest and cheapest option available. I have purchased one and will be experimenting with it soon. Sources: ebay, alibaba, and ilk.
- Real industrial systems. These are the high end “cadillac” option. Common brands include Dukane and Branson, but others are available. You can pick whatever features, frequency, and power output you want, but they will cost you. I have not done an exhaustive search of actual sale price, but they typically list for around $1000 used, often more. These may be a viable option for a small company, but they are solidly out of my price range as a hobbyist.
- DIY. I’m still investigating the price point you can expect out of this, but this is what I perceive to be the only viable option for >100W supplies at sub $1k prices.
The transducer is a large piezoelectric element. They come as “raw” ceramic components, or completed assemblies that stack several ceramic elements, electrodes, and possibly mechanical preload screws, mounting enclosures, cooling elements, and mounting fasteners.
Power systems require mechanical preload. Almost all piezo elements are made from a ceramic material called lead zirconate titanate, or PZT. Like other ceramics, it is brittle, and does not handle large changes in shape without cracking. Preload means clamping the ceramic to allow large forces to be created without large changes in physical size, thus decreasing the tendency to crack or break. The most common design is the Langevin, which uses annular ring ceramics clamped between two pieces of steel with a bolt. Here is a cross section image sourced from http://techblog.ctgclean.com/2012/01/ultrasonics-transducers-piezoelectric-hardware/:
- Flat, raw element ultrasonic bath disk transducers. ~$3, 35W, 40Khz. No housing, cooling, or even wiring. This is just a chunk of PZT with some metallic contacts. I have purchased a couple of these, and haven’t done to much with them yet. Buy from ebay, alibaba, et. al.
- Ultrasonic bath Langevin transducer. ~$15, 50W-100W, 28kHz or 40kHz.These are the most common transducer you will find, and the basis of most hobbyist projects you’ll find. They consist of a piezoelectric stack, typically 2 elements, as well as steel mounting that provides heat sink, output coupling, and mechanical preload. These can be purchased with a cheapo supply in a kit and have you up and running in no time. Purchase from ebay, alibaba, et. al.
- Industrial transducers. Price is highly variable, typically >$50, >500W, 28kHz or 40kHz. These tend to be “full featured” systems. The main brands you’ll find are Branson and Dukane, and are designed for industrial use in industrial environments. These are often referred to as “converters” or “RF converters”. They have a housing that you can mount to, cooling ports to force air flow, and are typically capable of 500W - 2kW, and have preload built in. As a hobbyist you will only find these used. They often come with output boosters and horns. Pro tip: at time of writing most sellers are re-listing these repeatedly. These vary rarely sell on ebay for list price. You can lowball sellers with counteroffers and they will accept offers 20% below list price. Do your homework on the output horns and extras before bidding as you can get a good deal on packaged extras. Usual haggling algorithm of “you want 100%, I’ll bid 60%. How about 90%? How about 70%? How about 80%? Sold!” applies.
- “Specialty” items. I’m not going to go into a lot of detail here, but there is a huge variety of specialty piezo transducers available. These aren’t really available on common marketplaces like ebay, and you really have to go to specialty suppliers. These may come as raw piezo elements or packaged systems. Here’s a quick, non-exhaustive list of some available components:
- hemi-spherical transducers
- conical transducers
- shear element plates
- piezo benders disks, and bars
- piezo fans
- spherical resonators
- tubular elements
- multi-axis positioners stacks.
See: https://www.steminc.com/PZT/en/ for examples.
Output Coupling; Horns, Boosters, Tips, and Others
This is where you will find the most variety for power systems, and what you need will greatly depend on your intended application. These are passive mechanical elements that direct the ultrasound energy from your transducer into your workpiece/sample. There is a specialty variant of this for every possible use, and industrial customers often make custom tooling for their specific application. If you go that route, you will really have spend some time with finite elements methods and some textbooks. There is free software available, but I have not used it: http://www.sonoanalyzer.com/Downloads. Fortunately many applications don’t need that level of detail. For another writeup on this topic see: http://usblog.dukane.com/2010/03/how-does-your-ultrasonic-probestack.html
These are the workhorse design for most power applications hobbyist would look to do. Again, the main brands are Branson, Dukane, and Emerson. Applications for variations on this design include: emulsification / cell disruption, welding, drilling, and cutting. These often come with a threaded tip so that the tip can be replaced as it wears down, or changed to permit multiple applications.
Considerations for purchasing: resonant frequency, probe size, horn material, and gain. These must match the resonant frequency of the transducer to work well. The probe size will be determined by your application, and basically boils down to “will it fit”. If you are looking to sonicate small liquids or components, double check that your tip will match your size. Brand name horns are typically made from steel or titanium. This affects what they react with chemically, how fast they wear out, and their physical size. Gain is the amount that horn increases the output amplitude. Piezo transducer stacks typically expand and contract by about 20um. These horns can increase the amplitude by as much as a factor of 3 depending on their output profile. In general, the more abruptly the diameter of the horn decreases, the higher the gain.
You can buy these on ebay, alone or bundled with industrial transducers for less than $100. Wear will vary greatly, and only you can decide if the wear is acceptable for your project and budget. Key phrases to search for include “ultrasonic horn”, “catenoidal horn”.
Caveat emptor on horn tips
Many power ultrasonic applications involve pushing >100W of ultrasonic energy through the fairly small tip of the output horn. This causes wear on the tip much faster than any other part of the system. In industrial applications, the tip is considered a wear item. Be careful when buying used horns without replaceable tips as these may be worn or broken unacceptably. These may also deposit small amounts of tip material into your workpiece or mixture.
Boosters attach between the transducer and an output horn. These serve two main purposes: increased gain and adding an additional mounting point. Many boosters are designed with a ring at a nodal point, where the vibrations are 0 amplitude, that permits them to be mounted to other machinery. Like horns, they can also amplify the vibrational amplitude. Combining a booster and a horn multiplies the amplitude several times. For instance, you might have a 1:1.5 booster and a 1:2 horn. For 20um of piezo amplitude the booster increases this to 30um at the horn input, and the horn to 60um at the output.
Other types of horns
You can find a wide variety of horns for specialty applications. Some common examples include:
- Slitting horns, which are shaped like knives for ultrasonic cutting
- Large “blocks” for welding large components.
- “Feed through” horns. Which have pipes to mix or sonicate liquids.
- Some have specialty couplings to attach them to various industrial equipment, such as a pipe to help move or settle granular material.
- You may occasionally find discarded horns that have entire product outlines that may designed to assemble a completed item from time to time.
Go forth and have fun! Post in the comments if you make anything cool so I can watch! Post if you have questions and I can be just as confused as you!