Sub-threshold addressing and erasing in a magneto-electrophoretic writing medium
A magneto-electrophoretic medium that can be globally and locally addressed and erased. The medium provides a writeable display with no perceivable lag and the ability to write and erase with only minimal power requirements. In particular, the magneto-electrophoretic medium can be erased by providing a subthreshold electric stimulus and supplementing a second non-electric stimulus that disturbs the written state and allows the magneto-electrophoretic particles to return to their original state.
1. A method for erasing a magneto-electrophoretic medium including magneto-electrophoretic particles, the method comprising a local erase step and a global erase step,
the local erase step comprising applying a magnetic field stimulus to the magneto-electrophoretic medium and simultaneously applying a sub-threshold voltage to the magneto-electrophoretic medium, thereby causing the magneto-electrophoretic medium to switch from a first state to a second state,
the sub-threshold voltage being greater than zero but insufficient alone to cause the magneto-electrophoretic medium to switch from the first state to the second state within five seconds,
the sub-threshold voltage being less than one half of a threshold voltage required to cause the magneto-electrophoretic medium to switch from the first state to the second state over a same period, and
the global erase step comprising applying a first voltage that is sufficient alone to cause the magneto-electrophoretic medium to switch from the first state to the second state over the same period.
2. The method of claim 1 , wherein the magnetic field stimulus is provided by a stylus.
3. The method of claim 2 , wherein the stylus is constructed from a permanent magnet.
4. The method of claim 2 , wherein the stylus comprises a magnet providing a field strength between 10 and 1000 Gauss at a surface of the stylus.
5. The method of claim 2 , wherein the stylus has a body with a first end and a second end, comprising:
a first magnet proximal to the first end and providing a first magnetic field between 500 Gauss and 5000 Gauss at the first end;
a second magnet proximal to the second end and providing a second magnetic field between 10 Gauss and 500 Gauss at the second end;
a wireless transmitter within the body; and
a switch on the body of the stylus operatively connected to the wireless transmitter.
6. The method of claim 1 , wherein the magnetic field stimulus is provided by a striped-pole magnetic material.
7. The method of claim 1 , wherein the magneto-electrophoretic medium comprises electrically-charged ferromagnetic particles.
8. The method of claim 1 , wherein the global erase step comprises a first time-varying waveform.
9. The method of claim 8 , further comprising:
measuring a remnant voltage on the magneto-electrophoretic medium; and
if an absolute value of the remnant voltage is higher than 0.3 V, modifying the first time-varying waveform to diminish the remnant voltage on the magneto-electrophoretic medium.
10. The method of claim 9 , wherein the first time-varying waveform is modified by changing an offset of the first time-varying waveform, or changing a duty cycle of the first time-varying waveform, or changing an amplitude of the first time-varying waveform.
11. The method of claim 1 , wherein the sub-threshold voltage comprises a second time-varying waveform.
12. The method of claim 11 , further comprising:
measuring a remnant voltage on the magneto-electrophoretic medium; and
if an absolute value of the remnant voltage is higher than 0.3 V, modifying the second time-varying waveform to diminish the remnant voltage on the magneto-electrophoretic medium.
13. The method of claim 12 , wherein the second time-varying waveform is modified by changing an offset of the second time-varying waveform, or changing a duty cycle of the second time-varying waveform, or changing an amplitude of the second time-varying waveform.
14. A method for erasing a magneto-electrophoretic medium including magneto-electrophoretic particles, the method comprising a local erase step and a global erase step,
the local erase step comprising applying a magnetic field stimulus to the magneto-electrophoretic medium and simultaneously applying a sub-threshold voltage to the magneto-electrophoretic medium, thereby causing the magneto-electrophoretic medium to switch from a first state to a second state,
the sub-threshold voltage being greater than zero but insufficient alone to cause the magneto-electrophoretic medium to switch from the first state to the second state within five seconds, and
the global erase step comprising
applying a first time-varying waveform, the first time-varying waveform comprising a first voltage that is sufficient alone to cause the magneto-electrophoretic medium to switch from the first state to the second state over a same period,
measuring a remnant voltage on the magneto-electrophoretic medium; and, if an absolute value of the remnant voltage is higher than 0.3 V, modifying the first time-varying waveform to diminish the remnant voltage on the magneto-electrophoretic medium.
15. The method of claim 14 , wherein the first time-varying waveform is modified by changing an offset of the first time-varying waveform, or changing a duty cycle of the first time-varying waveform, or changing an amplitude of the first time-varying waveform.
16. A method for erasing a magneto-electrophoretic medium including magneto-electrophoretic particles, the method comprising a local erase step and a global erase step,
the local erase step comprising
applying a magnetic field stimulus to the magneto-electrophoretic medium and simultaneously applying a second time-varying waveform to the magneto-electrophoretic medium, the second time-varying waveform comprising a sub-threshold voltage being greater than zero but insufficient alone to cause the magneto-electrophoretic medium to switch from the first state to the second state within five seconds, thereby causing the magneto-electrophoretic medium to switch from a first state to a second state,
measuring a remnant voltage on the magneto-electrophoretic medium; and, if an absolute value of the remnant voltage is higher than 0.3 V, modifying the second time-varying waveform to diminish the remnant voltage on the magneto-electrophoretic medium,
the global erase step comprising applying a first voltage that is sufficient alone to cause the magneto-electrophoretic medium to switch from the first state to the second state over the same period.
17. The method of claim 16 , wherein the second time-varying waveform is modified by changing an offset of the second time-varying waveform, or changing a duty cycle of the second time-varying waveform, or changing an amplitude of the second time-varying waveform.