Microfluidic printing with controlled density

A microfluidic printing system for delivering ink having conductor material to a receiver comprising:

• a) at least one ink reservoir;
• b) a structure defining a plurality chambers arranged so that the chambers form an array with each chamber being arranged to form a conductive ink pixel for delivery to the receiver;
• c) a plurality of microchannels connecting said at least one ink reservoir to the chambers;
• d) a plurality of microfluidic pumps each being associated with a single microchannel of said plurality of microchannels for supplying conductive ink from said at least one ink reservoir through a microchannel of said plurality of microchannels for delivery to a particular chamber of said plurality of chambers, each pump including at least two spaced apart electrodes which produce an electric field in response to an input voltage that act upon the conductive ink to control or prevent an ink flow;
• e) means for providing a high frequency flow measuring signal to the electrodes and means responsive to variations in the signal applied across the electrodes for measuring the flow of the conductive ink through the chambers to determine a correct amount of conductive ink being, delivered to the receiver through the chambers;
• and
• f) flow control means including a source of DC voltage and means f or applying the DC voltage applied across the electrodes of each microfluidic pump of plurality of microfluidic pumps in a first direction for causing the ink to flow through the chambers to the receiver and, in a second direction, for preventing the ink flow to the receiver;
• such flow control means being coupled to the ink flow responsive means for causing the DC voltage to be applied in the second direction to prevent a further flow of ink to the receiver when the correct amount of ink is delivered to the receiver.