1. Radiation Pressure Sensor
NIST & University of Colorado at Boulder
Anfal Abdulrahman - Kyle Christianssen - Mitchell Klein - Dylan Klomhaus - Brendan Moon - Matt Smith
Background
• Lasers are gaining importance in manufacturing processes
• Knowing the power output of the laser is essential
• Current process for calibrating a laser is time intensive
• Shine laser in thermopile - measure the rate at which it
heats up
• NIST has been developing a process to measure the force of a
laser in real time while using it in the manufacturing process
• A precision scale with an attached mirror can measure the
radiation force of light and correlate this to laser power output.
Objectives
1) Design a scale with sensitivity suitable to measure
- radiation pressure of manufacturing lasers
• Force Sensitivity Range: 10 mg – 10 mg (100 mN – 100 nN)
2) The Null Approach – Does not depend on spring constant
• Detect change in capacitance with AC signal, apply compensating force
with large DC voltage
3) Demonstrate Double Bounce Concept to Reduce Noise
Design Results
Conclusions
• Capacitance approach was verified
• Capacitance approach might not be suitable for the whole
range of the project obectives
• Steel and silicon springs proved rather fragile and should
be reconsidered for manufacturing environment
Acknowledgements
Paul Williams, Oyvind Nilsen, Ivan Ryger, Joel Rutkowski, John
Maushammer
Laser Power Application Equivalent
Mass
Object
10 W Marking 6.7 microgram Eyelash
1 kW Welding/Cutting 670 microgram Grain of Sand
100 kW Research / Defense 67 milligrams Two Staples
V1=Radiation pressure +
Gravity + Vibration noise
V2=Radiation pressure –
Gravity – Vibration noise
V1+V2 = 2 x Radiation pressure
Results
Spiral Flexure
• In the final version,
surface would be
highly reflective
• Low Stiffness
• Single Axis linear
displacement
• Top plate of
capacitor
Spiral
Flexure
Air Cover
Bottom plate
Capacitor Housing
Spring-Loaded
Pin Contact
Top Plate
Connection
Bottom Plate
Connection
Capacitor Bottom
Plate Adjustment
Screw
Sensor Housing
Capacitor
Housing
Digital Display
PCB
Aluminum
Casing
Electrical
Connections
Spiral
Flexure
Microcontroller
.002” Plate
Spacing
• Spiral flexure capacitor demonstrated 6-19 pF capacitance
• Open loop testing demonstrated change in voltage when
pressure is applied
• Closed-loop testing demonstrated high sensitivity