[Lindsay] has a wonderful writeup about a new toy in the shop, an ultrasonic transducer ... Not missing the meaning of DIY [Lindsay] casts and machines a horn for the transducer with a high ...

Not so, if you use a pair of specialised ultrasonic transducer arrays to move the air instead! (Video, embedded below) Three banks of thrusters provide a 180 degree steerable net force Details are ...