GESAC, Inc Development of Abdomen Compression Measurement Sensors T. Shams, N. Rangarajan, J. Rowe, H. Conner GESAC, Inc

October 28, 2007Thirty-Fifth International Workshop 2 Outline Usefulness of compression as injury measure –some limitations of current methods Exploring alternative measurement methods Hall sensors –packaging, calibration, response Shape sensors Flex sensors –packaging, calibration, response Discussion Current work

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 3 Measuring Abdomen Compression Compression measure important in abdomen injury assessment –Maximum compression, V.C, Vmax.Cmax –(Cavanaugh, Viano, Rouhana, etc) Current measurement methods –Pressure (Mooney) –Stringpots (e.g Thor) –Fluid resistance (Rouhana) Limitations of current methods –relies on measuring deflections at a points may miss location of maximum deflection reliability under oblique loading may not be optimum –no reliable method for measuring in children

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 4 Exploring Alternative Methods Looked at several alternative methods –Hall sensors They can measure relative rotations of a small section up to +/- 40 deg Number of sensors can be used to measure deformation of linear strip –Shape sensor Measure displacement at end of flexible beam due to delay in transmission of light beam –Resistive flex sensors Depends on change of resistivity when a flex sensor is bent Can be used to measure average curvature of small sections

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 5 Hall Sensor-Description Sensor is small - < 0.5 cm Voltage output proportional to relative distance between magnet and sensor –high level signal –function of distance or angle Easily available Can be programmed –Sensitivity –Range –Temperature coefficients

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 6 Hall Sensor-Mounting & Calibration Evaluated sensor response for various geometries –Relative location –Relative angle Decided on hinge mechanism for mounting sensor & magnet Developed calibration fixture for obtaining calibration data

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 7 Hall Sensor-Calibration Fit Shows good linear fit between – 25 deg and +25 deg –Correlation > 0.99 Shows excellent cubic fit between – 40 deg and +40deg –Correlation > Normally, will program best range & sensitivity for individual sensors Excellent repeatability –variation < 0.1%

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 8 Hall Sensor-Packaging for Abdomen Built bands with 3-7 sensors –Used flexible strips with low stretchability –Fit into groove cut into abdomen foam Tested with disk and rod impactors

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 9 Hall Sensor-Quasi-Static Response In quasi-static loading, voltage output from sensors at different locations reflected local curvature Output lagged behind LVDT but reached peaks at same time Calculated deflection using calibration values similar to LVDT

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 10 Hall Sensor-Dynamic Response In dynamic loading, similar situation –Initial and final lag –Computed peak below external measurement –Peak also appears more smoothed out

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 11 Hall Sensor-Limitations Problems –Proper sizing and mounting of hinges Found adhesive that would work with PVC material and Urethane strip –Mounting of strip Strip had lag in following foam deformation Tends to move away from foam after impact Flexibility of strip requires additional tension-interferes with foam stiffness

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 12 Shape Sensor-Description Available from Measurand, Inc (Canada) –Has processing box attached Tested with angular calibration fixture

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 13 Shape Sensor-Calibration & Limitations Shows reasonable linear fit between – 90 deg and +90 deg Limitations –Requires multiple sensor array to cover perimeter of abdomen –Much more expensive –Requires separate processing box, especially for high speed applications –Previous user experience indicated special procedures for using with soft foam substrates

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 14 Flex Sensor-Description Resistive flexible sensor –Resistive layer painted, usually on Mylar backing –Conductive sections painted on one side –Resistance proportional to amount of bending Obtained from electronic stores –Used in data gloves –Inexpensive –Longer strips can be made

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 15 Flex Sensor-Calibration Procedure Calibration –Using various radii wooden templates –Get voltage output as function of curvature (or radius) –End point at location of solder tabs can cause problems

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 16 Flex Sensor-Calibration Fit-1 Calibration graph –Each segment appears fairly linear after initial low slope (~ 0.1 (1/in) curvature) Linearity depends on uniformity of conductive sections –Better fit over longer segments

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 17 Flex Sensor-Calibration Fit-2 Multi-segment strips show some variation between segments Quadratic (with flat as zero) shows best fit –R 2 ~ 0.99

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 18 Flex Sensor-Preliminary Testing Tested using small foam components –Horizontal & vertical orientations of sensors –Quasi-static –Impact speeds = 1 – 3 m/s –Impactor mass = 3 – 5 kg –External displacement measured by LVDT

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 19 Flex Sensor-Preliminary Results Preliminary results show –Peak deflection and peak time predicted within +/- 5% –Unloading occurs more rapidly –With two strips, the peak deflections show similar time histories

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 20 Flex Sensor-Testing with Infant Dummy Testing with Aprica 3.4 kg infant dummy –Disk and cylindrical impactors –Tested in horizontal and vertical configurations –Tested with two or three strips

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 21 Flex Sensor-Results with Infant Dummy Comparison with LVDT –Small initial lag –General agreement in time –Peak underestimated –Faster unloading –Two parallel strips show good agreement

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 22 Flex Sensor-Offset Testing Offset impacts with rod –Expected variation with distance No internal stringpot to measure deflection independently

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 23 Discussion-1 Both Hall sensors and Flex sensors show promise as possible instruments for measuring dynamic compression –end conditions need to be addressed Hall sensors –with proper mounting, show good calibration fit (cubic fit) and repeatability (R 2 > ) –problem with maintaining contact with abdomen surface –still need proper procedure for stringing array of sensors into linear strip

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 24 Discussion-2 Flex sensors –can be obtained as strip- eliminating difficulties in construction –calibration fit not as precise as Hall (quadratic fit) - R 2 ~ 0.99 –good repeatability –problems in securely attaching additional wire contacts along length –ends tend to rebound faster, making unloading appear faster –smaller strips ( 4.5 in – 9 in) are appropriate size for child abdomens can be mounted in horizontal and vertical arrangements

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 25 Current Work Selecting optimum length and number of segments for use in different abdomen sizes including infant dummy Verifying measurements under oblique and offset impacts Improving computation procedure with variable end conditions

GESAC, Inc October 28, 2007Thirty-Fifth International Workshop 26 Acknowledgment We would like to thank Toyota Motor Corporation, Japan for funding this work