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When liquid is driven in pulses through two small apertures with liquid between them, there is a hydrodynamic pumping phenomena in the liquid flow. The pulsation can be produced by volume variations obtained from a piezoelectric crystal. The device works as an impulse pump, which can be controlled by modulated electric pulses. When the liquid is ink, the device can be used to generate a dot pattern on paper. Using this technique, two types of printing devices have been developed: one for printing alphanumeric characters in a 7 × 5 matrix, where speeds of more than 1000 characters/s are obtained, and another for copying pictures by a scanning method.