How William Coolidge Invented the Modern X-Ray Tube
A 1916 patent by William Coolidge for a high-vacuum X-ray tube that used a heated tungsten filament to control electron flow, replacing older, unreliable gas-filled tubes.
Original patent title: “Vacuum-tube.”
A 1916 patent by William Coolidge for a high-vacuum X-ray tube that used a heated tungsten filament to control electron flow, replacing older, unreliable gas-filled tubes. Granted to General Electric Co in 1916 with 32 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
The patent describes a vacuum tube designed for generating X-rays by heating a tungsten filament to emit electrons. Unlike previous designs that relied on residual gas to conduct electricity, this tube maintains a high vacuum, allowing the user to precisely control the electron beam's intensity and energy. By adjusting the filament temperature, the operator can independently regulate the number of electrons hitting the target, which directly controls the X-ray output.
The gap
What does this patent NOT cover?
- Does not cover X-ray tubes that rely on gas discharge for electron production.
- Does not cover non-vacuum electronic tubes or cold-cathode discharge devices.
- Does not cover the medical imaging software or digital sensors used to process X-ray data.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
Coolidge realized that by using a high vacuum and a separate heating source for the filament, he could decouple the electron emission from the tube's internal gas pressure, giving engineers total control over the beam.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Early 20th-century medical X-ray machines
Industrial radiography equipment
High-voltage vacuum rectifiers
Why it matters
The bigger picture
This technology transformed medical diagnostics by making X-ray machines stable, predictable, and safe enough for routine clinical use. It effectively ended the era of 'gas tubes' that were notoriously difficult to calibrate and prone to failure, establishing the foundation for modern radiology.
Filed
May 9, 1913
Granted
October 31, 1916
Market context
Who's building on this
Companies in this space
General Electric continued to dominate the medical imaging market for decades, evolving this technology into the sophisticated CT scanners and diagnostic systems produced by GE HealthCare today.
Market impact
This patent solidified GE's position as a leader in medical technology and set the technical standard for X-ray generation that remains in use for stationary X-ray tubes to this day.
Claim 1 — Plain English
What this patent covers
The patent describes a vacuum tube designed for generating X-rays by heating a tungsten filament to emit electrons. Unlike previous designs that relied on residual gas to conduct electricity, this tube maintains a high vacuum, allowing the user to precisely control the electron beam's intensity and energy. By adjusting the filament temperature, the operator can independently regulate the number of electrons hitting the target, which directly controls the X-ray output.
The clever bit
Coolidge realized that by using a high vacuum and a separate heating source for the filament, he could decouple the electron emission from the tube's internal gas pressure, giving engineers total control over the beam.
What it does not cover
- Does not cover X-ray tubes that rely on gas discharge for electron production.
- Does not cover non-vacuum electronic tubes or cold-cathode discharge devices.
- Does not cover the medical imaging software or digital sensors used to process X-ray data.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
30/40
Moderately cited
Claim breadth
0/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$13K – $40K
Midpoint $25K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
Concepts involved
Citations
Patent lineage
Cite this patent
Coolidge, W. D. (1916). How William Coolidge Invented the Modern X-Ray Tube (U.S. Patent No. 1,203,495). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/1203495/coolidge-x-ray-tube
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How William Coolidge Invented the Modern X-Ray Tube cover?
A 1916 patent by William Coolidge for a high-vacuum X-ray tube that used a heated tungsten filament to control electron flow, replacing older, unreliable gas-filled tubes.
Who owns patent US 1203495?
General Electric Co owns this patent, granted in 1916.
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 1203495 cited by?
This patent has been cited by 32 later patents that build on its ideas.
What problem does this patent solve?
This technology transformed medical diagnostics by making X-ray machines stable, predictable, and safe enough for routine clinical use. It effectively ended the era of 'gas tubes' that were notoriously difficult to calibrate and prone to failure, establishing the foundation for modern radiology.
What does this patent NOT cover?
Does not cover X-ray tubes that rely on gas discharge for electron production.
Same assignee
More from General Electric Co
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