Amorphous silicon varactors as rf amplitude modulators and their application to acoustic ink printers

The combination comprising

• an rf voltage source;
• an electrical load;
• at least one voltage controlled capacitive device coupled to said load and to said source, with said capacitive device being vertically integrated with said load;
• and
• control means coupled to said capacitive device for applying a variable polarity bias to it for switching it between an accumulation mode and a depletion mode in response to different binary states of a time varying input signal, whereby the rf voltage applied to said load is amplitude modulated in accordance with said input signal.

In combination with an acoustic ink printer including a supply of liquid ink with a free surface, a printhead having at least one droplet ejector, and an rf source;

• said droplet ejector including a piezoelectric transducer means, with said rf source being coupled across said transducer means for exciting it into oscillation to cause said droplet ejector to launch a converging acoustic beam into said ink such that said beam impinges upon and exerts an acoustic radiation pressure against said free surface;
• the improvement comprising
• at least one aSi capacitor coupled to said rf source and to said transducer means;
• and
• control means coupled to said capacitor for applying a variable polarity bias to it for switching it between a first capacitance level in response to data samples representing black pixels and a second capacitance level in response to data samples representing white pixels, whereby the rf applied to said transducer means is amplitude modulated to vary the radiation pressure said acoustic beam exerts against the free surface of said ink between a level at least equal to an ejection threshold pressure level for the printing of black pixels and a lower, subthreshold level for the printing of white pixels.

In combination with an acoustic ink printer including an supply of liquid ink with a free surface, a printhead having at lease one droplet ejector, and an rf source;

• said droplet ejector including a piezoelectric transducer means, with said rf source being coupled across said transducer means for exciting it into oscillation to cause said droplet ejector to launch a converging acoustic beam into said ink such that said beam impinges upon and exerts an acoustic radiation pressure against said free surface;
• the improvement comprising
• at least one voltage controlled semiconductor varactor vertically integrated with said droplet ejector, said varactor being coupled to said source and to said transducer means;
• and
• control means coupled to said varactor for applying a variable polarity bias to it for switching it between a first capacitance level in response to data samples representing black pixels and a second capacitance level in response to data samples representing white pixels, thereby modulating the radiation pressure said acoustic beam exerts against the free surface of said ink between a level at least equal to an ejection threshold pressure level for the printing of black pixels and a lower, subthreshold level for the printing of white pixels.

In an acoustic ink printer having a plurality of droplet ejectors for ejecting droplets of ink on command from a free surface of a supply of liquid ink, each of said droplet ejectors having a piezoelectric transducer means, and said printer having an rf source which is coupled across said transducer means to excite them into oscillation;

• the improvement comprising
• at least one aSi capacitive varactor associated with each of said droplet ejectors, with each varactor being being coupled to said source and to the transducer means of its associated droplet ejector;
• and
• control means coupled to said varactors for applying variable biases to them in response to data samples representing pixels that are to be printed by their associated droplet ejectors, whereby said varactors amplitude modulate the rf applied to the transducer means of their associated droplet ejectors in accordance with said data samples.