Dynamic Focusing High-Voltage Control for Electron-Beam 3D Printing

Electrospinning of uniform nanofiber mats at industrial scale requires 30–120 simultaneously driven needles operating at 18–45 kV with individual current monitoring and voltage synchronization better than ±60 V to prevent jet instability and fiber diameter variation greater than 12 % across the web.

The distribution system uses a single high-power resonant charging supply feeding a 60 kV intermediate bus, followed by individual needle modules containing compact 8-stage Cockcroft-Walton multipliers driven in parallel from a common 45 kHz sinusoidal source. Phase-locked digital control of each module’s input amplitude via primary-side pulse-width modulation allows independent voltage setting while maintaining identical drive phase, ensuring that Taylor cone formation and jet initiation occur within a 180 ns window across the entire array.

Current sharing and corona onset uniformity are achieved by active impedance matching. Each needle module includes a programmable air-core inductor in series with the multiplier input that is automatically tuned every 30 seconds via a varactor-switched capacitor bank to null reflected power differences caused by needle length tolerance or solution conductivity drift. Resulting voltage droop under full load remains under 1.1 % from center to edge needles.

Real-time individual needle current is measured via 1:1000 capacitive pick-off rings around each high-voltage feed line, digitized at 120 kS/s, and used for closed-loop voltage correction. When a needle begins clogging (current drops >18 %), the controller momentarily increases its voltage by 2–4 kV for 80 ms to clear the obstruction before returning to setpoint, maintaining fiber production continuity without operator intervention.

Safety and process uptime are enhanced by a hierarchical arc detection scheme: local per-needle detection collapses only the affected module in <9 µs, while global bus monitoring initiates full system shutdown only for catastrophic events. Recovery is staggered in 40 ms intervals to prevent simultaneous re-ignition of multiple needles.

Solution-level multiplexing supports rapid flavor or polymer switching in medical textile production: all needles are simultaneously ramped to 4 kV cleaning potential with reversed polarity for 400 ms between batches, burning off residual polymer without mechanical cleaning.

These synchronous multi-needle systems routinely produce 1.2 m wide nonwoven mats with fiber diameter variation below 9 % at deposition rates exceeding 450 g/m²/h, enabling continuous roll-to-roll manufacturing of filtration media and tissue engineering scaffolds previously limited to laboratory scale.