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I found a video demonstration of small particles levitating in air held and manipulated by ultrasonic field.

My first thought was: this could be used in 3d printing!

Particles could be manipulated and held in shape by this ultrasound technology and then melted together by laser or ultrasound energy itself. I know it is far fetched theory ... but somehow I think it could be done ...

Ultrasonic technology is already used in high-end metal 3d printing by Fabrisonic:

http://diy3dprinting.blogspot.com/2013/07/ultrasonic-metal-3d-printing.html

And similar technology is also used to weld plastic:

http://diy3dprinting.blogspot.com/2012/12/diy-ultrasonic-plastic-welding.html

So, all these technologies could be merged together, why not?

Video of ultrasonic particle levitation:


Video description:

The essence of levitation technology is the countervailing of gravity. It is known that an ultrasound standing wave is capable of suspending small particles at its sound pressure nodes and, so far, this method has been used to levitate lightweight particles, small creatures, and water droplets.
The acoustic axis of the ultrasound beam in these previous studies was parallel to the gravitational force, and the levitated objects were manipulated along the fixed axis (i.e. one-dimensionally) by controlling the phases or frequencies of bolted Langevin-type transducers. In the present study, we considered extended acoustic manipulation whereby millimetre-sized particles were levitated and moved three-dimensionally by localised ultrasonic standing waves, which were generated by ultrasonic phased arrays. Our manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its centre is also utilised. The other is the manipulation principle by which a localised standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays. We experimentally confirmed that various materials could be manipulated by our proposed method.

Source:

http://96ochiai.ws/3DOFacoustic

Experiment was done and domnstrated by Yoichi Ochiai, Takayuki Hoshi and Jun Rekimoto ( University of Tokyo, Nagoya Institute of Technology, University of Tokyo and Sony CSL ).

PLA and BAS are most used materials in 3d printing. If we used PLA as support meterial, how can it be removed from ABS without damage to ABS? PLA can be dissolved with caustic soda  in ultrasonic tank.

Bertho Boman experimented with various concentrations and presented results on his blog:

This time I tested several different plastic types and varying strength Sodium Hydroxide.
1.0 Molar: 40g per liter water
1.8 Molar: 72g per liter water (same as the video)
3 Molar: 120g per liter water
6 Molar: 240g per liter water

Test Result:
After 5 hours in the ultrasonic tank @ 60°C there was no visual effect or surface hardness change evaluating the samples under a microscope of the different plastic types except the PLA.

http://www.vinland.com/blog/?p=162




































Extensive details and experiments with other methods and how to dissolve PLA fast when no other material is involved:

http://www.vinland.com/blog/?p=68#more-68


Here is video showing the process with professional ultrasonic tank and caustic soda (sodium hydroxide) that takes 3 hours to remove PLA support material from ABS part. 217 grams is added to 3 liters of water heated at 60C.
Ultrasonic tank used in the video is priced around 1300 USD, but it can be found much cheaper at some 300 USD.




They talk about dissolving PLA in .stl podcast (great podcast btw):



RepRap forums discussion:

http://forums.reprap.org/read.php?1,153508,199753

SOLIDICA (Ultrasonic consolidation of metal sheets with integrated wiring)





POM (Direct Metal Depostioning - metal powder spray laser sintering and coating)






ARCAM (Electron Beam Melting)




Via:

http://www.youtube.com/user/manufactureornl/videos