Testing of Piezoresistive Polyurethane-Fe₃O₄ Composites

The piezoresistance of Fe ₃ O ₄ particles encapsulated in polyurethane forming a composite material were studied for hydrostatic and uniaxial response. Electrical and mechanical properties were examined in composite disks with volume percents of Fe ₃ O ₄ loading between 35 and 54%. Uniaxial and hydrostatic loading tests were conducted for electrical resistance under mechanical stress. Data obtained for the uniaxially loaded samples indicate that resistance changes of 5 to 6 orders of magnitude can be tailored in polyurethane composites. Under hydrostatic loading testing indicates that resistance changes of 2 orders of magnitude can be obtained. Mounting the piezoresistors in a rigid epoxy improves the hydrostatic response of the samples allowing resistance change of up to 3 orders of magnitude. Further tests indicate a change of almost 5 orders of magnitude are possible when highly compliant lateral air gaps are incorporated into the sample.

Keywords:

• Piezoresistance
• composite hydrophones
• loaded polymer sensors

Acknowledgments

We gratefully acknowledge the support of the Department of Defense under contract #N00014-96-1-0961.