This document describes an ultra-thin sensor developed at Lawrence Livermore National Laboratory for measuring contact stress and interface loads. The sensor is more accurate, repeatable, and capable of dynamic measurements compared to existing commercial sensors. It can measure static or dynamic loads with high bandwidth, and can withstand harsh environments for long-term embedded use. Potential applications of the sensor include real-time monitoring of contact forces in rollers, robot grips, tires, medical implants, shoes, beds, gaskets, and bulletproof vests. The sensor technology is production-ready and available for commercialization.

1. An Ultra-Thin Sensor for Measuring Contact Stress
LLNL-PRES-637035
This work was performed under the auspices of the
U.S. Department of Energy by Lawrence Livermore
National Laboratory under contract DE-AC52-07NA27344.
Lawrence Livermore National Security, LLC
Jack Kotovsky, Ph.D.

2.  Automotive
• Brake Pads
• Gaskets
• Impact Studies
• In-situ Tire Monitoring
 Medical
• Cartilage Mechanics
• Podiatry
• Bedding/Prosthetics (Pressure Sores)
• Clinical Tumor Monitoring
 Industrial
• Composite Layups/Lamination
• Molding
• Presses
• Gaskets and Bolted Joints
• Roller Systems
• Robotics
Author-9/12/2014-2
Lawrence Livermore National Laboratory LLNL-PRES-637035

3. Commercial Sensors Are Inadequate
Functions Needed: Fuji Pressensor Film Tekscan Sensor LLNL MEMS Sensor
Repeated Measurements No
Author-9/12/2014-3
Lawrence Livermore National Laboratory LLNL-PRES-637035
Yes
(~100 load cycles)
Yes
Dynamic Measurements No
Yes
(~100 load cycles, limited
bandwidth)
Yes, bandwidth ~200kHz
Accuracy 10%
+/- 3% (immediately
following calibration)
+/- 3%
Hysteresis N.A. 4.5% 2%
Minimum Thickness (limits
accuracy in application)
220 μm (0.009”) 200 μm (0.008”) 100 μm (0.004”)

4.  The sensor measures contact stress (squeezing force) between two
surfaces
 The measurement is:
• Accurate
• Repeatable for long-term (embedded) use
• Static or dynamic (200 kHz+)
 This technology was developed to address a measurement gap
• Measures real-time interface loads accurately and
reproducibly
• Measures dynamic interface loads
• Can be embedded in a product
• Withstands harsh environments (-40 °C to 70 °C, severe
vibration, persistent use)
Lawrence Livermore National Laboratory LLNL-PRES-637035
4
MEMS Sensor
Bond Pad
Diaphragm
Dopant Implant (Piezoresistors)
Contact Windows Metallization
Diaphragm Etch Street Etch

5.  This technology conquers a barrier in silicon fabrication and
packaging
• LLNL IP: thin MEMS design and paper-thin packaging
• The device is similar to successful pressure sensors but is paper
thin
 A full Wheatstone bridge provides thermal compensation
 Sensor measures temperature and/or stress
 Piezoresistive single-crystal silicon (large signal)
 Silicon is perfectly elastic
• No calibration loss
• High bandwidth
 Load sensitivity tuned by diaphragm dimensioning
Lawrence Livermore National Laboratory LLNL-PRES-637035
LLNL Sensor Demonstrates Excellent
5
Load Performance

6. 900 Independent silicon device ‘islands’ on
860 μm centers
220
μm
Lawrence Livermore National Laboratory LLNL-PRES-637035 6

7. Application Description Target Customers Current Practice
#1 Real-time, Embedded, Nip Roller pinch control Roller-system manufacturers manual adjustment of pinch =
Lawrence Livermore National Laboratory LLNL-PRES-637035
production pauses
#2 Robotic manipulator grip force control Robotics companies Total force measurement misses
local interface pressure
#3 Automotive tire molding: Real-time pressure adjustment Tire manufacturers Models and empirical data
#4 Cartilage load sensing for orthopedic implants and procedures Orthopedic companies Laboratory sensors only
#5 Embedded shoe sensor for wear detection and injury
prevention
Shoe companies No sensor for embedded shoe
monitoring
#6 Hospital bed monitoring for the prevention of bed sores Medical device companies No sensor for embedded product use
#7 Gasket/seal stress sensing Industrial and Automotive No sensor for real-time interface
load measurement
#8 Bullet Proof vest/helmet design for the prevention of blast
injury or impact loading in sports
Military and civilian helmet and
armor manufacturers
No dynamic interface load sensor
exists
7

8.  The technology is available for commercialization and is production ready
 The sensor is in production within the Department of Energy and continues
to find new internal applications and customers
 Sensor critical to LLNL programmatic needs
• >10 year investment
 No research is necessary to bring the single sensor to market
Lawrence Livermore National Laboratory LLNL-PRES-637035
8
Wmpoweruser.com

9. Charity Follett
follett2@llnl.gov
Lawrence Livermore National Laboratory LLNL-PRES-637035 9