(Link updated Oct 2013)
John Perkins has vast experience in power ultrasonics. Here he starts with the basics, covering the design and construction of piezo sandwich transducers and sonotrodes, before giving a detailed description of sonochemistry principles - cavitation, energy-density, monitoring power and amplitude.
(Now updated with a new link to NASA Telerobotics Program Plan, since the old page has been removed.)
An interesting page about research at MIT to develop a high torque-density solid-state actuator for use in the NASA/JPL Mars Micro Lander manipulator arm. It includes a general explanation of the principles of ultrasonic motors, and some cool animations! Note the use of dynamic and time-averaged ESPI (electronic speckle pattern interferometry) to evaluate the vibration modes.
(Link updated Oct 2013)
Canon's brief description of their development of ultrasonic motors for use in camera auto-focus lenses. Their explanation of the arrangement of piezoelectric elements is particularly good. There are two sets of elements, offset by a quarter-wavelength, each generating a standing wave. Superimposing the offset standing waves creates a traveling wave that drives the rotor.
(Link updated March 2008)
The AEA Technology Sonocrystallizer (TM) is a new reactor which produces better crystals for the pharmaceutical and bio-tech industries. For more details see the July 2000 newsletter.
(Link updated August 2004)
Ultrasound in liquids creates cavitation bubbles, which as they collapse can generate immense temperatures and pressures, and brief faint flashes of light - called sonoluminescence. It's a strange phenomenon, not yet fully understood but very reproducible. This article gives a clear account of the equipment required to generate and study sonoluminescence - a surprisingly simple set up suitable for a high-school laboratory.
(Link updated Jan 2007)
The subject of metal welding seems to attract high-quality articles from equipment suppliers. While not as comprehensive as Stapla's book, this article from AmTech gives a good introduction to the theory and practice of welding metals, aimed particularly at wire-joining applications.
Using liquid carbon dioxide as a cleaning solvent offers some great environmental advantages. Compared to conventional chlorinated solvents and detergents it is very clean, with no harmful emissions. Separating the liquid from the dissolved contaminants is easy - just reduce the pressure and allow the CO2 to boil off (after which it can be trapped and recycled). However the pressure required to maintain CO2 in liquid form (>60 bar) does present some challenges for ultrasonic tank design...
And in order to maintain a strict sense of balance... this is an excellent tutorial on the piezo-electric effect, provided by Piezo Systems, Inc..
Not an article as such, but hopefully of interest to readers...
Since the early 1980's, piezo-electric transducers have dominated the power ultrasonics industry. After some early reliability problems (cured largely by improvements to the electronic control systems used to drive them) they have now almost completely replaced the old inefficient laminated nickel alloy transducers wrapped in coils of PTFE insulated wire (the heat generated would melt conventional plastic insulation!).
ETREMA plans to change all that, with their new ultrasonic transducers based on Terfenol D®.
This is a special magneto-strictive iron alloy which tolerates high strains. It has been available for many years but only from laboratory-scale production. Now full production brings larger sizes and much better pricing, plus laminated blocks to reduce eddy-current losses in high frequency systems. Their new 20 kHz, 6kW transducer handles more power than any other ultrasonic transducer I know, and they are promising something much bigger in the near future...
Watch this space!
The CCFRA is a food-industry funded research organisation in the UK. This is the March 1999 newsletter (I found it rather late but I still think it's worth a look!) in which they describe results of early trials using ultrasonics to speed up food processing. Most of their results are available only to subscribers.