# How Piezoelectric Inkjet Printing Works > A 1970 patent describing how to print images by using electrical pulses to bend a tiny crystal plate, squeezing individual ink drops out of a nozzle on demand. - **Patent:** US 3946398 - **Original title:** Method and apparatus for recording with writing fluids and drop projection means therefor - **Owner:** SILONICS Inc - **Granted:** 1976 - **Status:** Public domain (expired) - **Times cited:** 448 - **Field:** consumer_electronics, mechanical, materials ## What it does This patent describes a drop-on-demand inkjet printing mechanism. Instead of spraying a continuous stream of ink, it ejects individual droplets only when needed. The system features a fluid chamber connected to a constant ink supply and a nozzle orifice. One wall of the chamber contains a piezoelectric actuator made of two plates bonded together. When an electrical pulse is applied, these plates expand in opposite directions, causing the actuator to bend inward. This sudden volume reduction squeezes exactly one droplet of ink out of the nozzle at a rate of 100 to 3,000 drops per second. ## What it does NOT cover - Does not cover continuous inkjet printing where a constant stream of droplets is electrostatically deflected. - Does not cover thermal inkjet printing, which uses heat resistors to vaporize ink and create a bubble to eject drops. - Does not cover printing rates outside the claimed range of 100 to 3,000 droplets per second. - Does not cover single-layer piezoelectric actuators that do not use two transversely expanding plates secured together to bend. ## The clever bit Using a bimorph piezoelectric actuator—two plates that expand in opposite directions when electrified—to act as a tiny, solid-state pump. This bending motion creates a highly controllable, rapid physical displacement without moving parts like gears or pistons. ## Real-world examples 1. Epson Micro Piezo printheads 2. Brother desktop inkjet printers 3. Industrial wide-format UV flatbed printers 4. Piezoelectric 3D bioprinters ## Why it matters This patent is a foundational document for drop-on-demand piezoelectric inkjet printing. This technology eventually enabled high-resolution color home printing, industrial textile printing, and modern 3D bioprinting. It avoided the messy ink-recirculation systems required by earlier continuous inkjet printers. ## Frequently asked questions ### What does How Piezoelectric Inkjet Printing Works cover? A 1970 patent describing how to print images by using electrical pulses to bend a tiny crystal plate, squeezing individual ink drops out of a nozzle on demand. ### Who owns patent US 3946398? SILONICS Inc owns this patent, granted in 1976. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 3946398 cited by? This patent has been cited by 448 later patents that build on its ideas. ### What problem does this patent solve? This patent is a foundational document for drop-on-demand piezoelectric inkjet printing. This technology eventually enabled high-resolution color home printing, industrial textile printing, and modern 3D bioprinting. It avoided the messy ink-recirculation systems required by earlier continuous inkjet printers. ### What does this patent NOT cover? Does not cover continuous inkjet printing where a constant stream of droplets is electrostatically deflected. **Full plain-English explainer:** https://patentbrief.org/patent/us/3946398/drop-on-demand-inkjet **Original patent:** https://patents.google.com/patent/US3946398 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Canon's Bubble Jet Printers Make Ink Droplets](https://patentbrief.org/patent/us/4723129/inkjet-bubble-jet-printing) — Canon's 1988 patent on bubble jet printing uses a tiny heater to instantly vaporize ink, creating a bubble that pushes out a droplet of ink from the printer head. - [How Thermal Inkjet Printers Use Two-Step Heating to Shoot Ink](https://patentbrief.org/patent/us/4490728/thermal-inkjet-printing) — Hewlett-Packard's 1982 patent on a two-stage electrical pulse method that preheats ink before vaporizing it, allowing thermal inkjet printers to reliably eject precise droplets without clogging. - [How 3D Printers Build Objects Layer by Layer from Liquid](https://patentbrief.org/patent/us/4575330/stereolithography-3d-printing) — This patent describes the foundational method for 3D printing, where a machine builds a three-dimensional object layer by layer by hardening a liquid material with light or other energy. - [How Laser Printers Use Rotating Mirrors to Write Information](https://patentbrief.org/patent/us/3867571/laser-printer-starkweather) — A 1972 Xerox patent describing how to use a spinning mirror to scan a laser beam across a page, adjusting the speed of the data to keep the image sharp. - [Tiny Capsules for Electronic Paper Displays](https://patentbrief.org/patent/us/5961804/e-ink-electronic-paper-display) — MIT's 1999 patent on a special ink made of tiny capsules that can change color when an electric field is applied, forming the basis for early e-readers.