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Research Papers

Strain Transfer Analysis of Integrated Surface Acoustic Wave Sensors

[+] Author and Article Information
Jochen Hempel

Laboratory for Electrical Instrumentation,
Department of Microsystems Engineering,
University of Freiburg,
Freiburg, Germany
e-mail: hempel@imtek.de

Sohaib Anees

Laboratory for Electrical Instrumentation,
Department of Microsystems Engineering,
University of Freiburg,
Freiburg, Germany
e-mail: sohaibanees@gmail.com

Elena Zukowski

Laboratory for Assembly
and Packaging Technology,
Department of Microsystems Engineering,
University of Freiburg,
Freiburg, Germany
e-mail: Elena.Zukowski@de.bosch.com

Michael Berndt

Laboratory for Assembly
and Packaging Technology,
Department of Microsystems Engineering,
University of Freiburg,
Freiburg, Germany
e-mail: Michael.Berndt@imtek.uni-freiburg.de

Jürgen Wilde

Laboratory for Assembly
and Packaging Technology,
Department of Microsystems Engineering,
University of Freiburg,
Freiburg, Germany
e-mail: juergen.wilde@imtek.uni-freiburg.de

Leonhard M. Reindl

Laboratory for Electrical Instrumentation,
Department of Microsystems Engineering,
University of Freiburg,
Freiburg, Germany
e-mail: leonhard.reindl@imtek.uni-freiburg.de

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received July 29, 2013; final manuscript received December 30, 2013; published online September 19, 2014. Assoc. Editor: Nils Høivik.

J. Electron. Packag 136(4), 041002 (Sep 19, 2014) (6 pages) Paper No: EP-13-1078; doi: 10.1115/1.4026437 History: Received July 29, 2013; Revised December 30, 2013

This paper presents a strain transfer investigation for Surface Acoustic Wave (SAW) strain sensors. For evaluation, a SAW strain sensor is assembled with a pretested bond material for potentially high strain transfer on a test holder. The setup is stressed with an axially homogeneous strain up to 500 ppm. The strain transfer ratio is computed from the applied load, the reference measurements with foil strain gauge, and the measured SAW strain sensor signal. The strain transfer performance of the bond material is also investigated with respect to the temperature dependency in the range between 22 °C and 85 °C. At these elevated temperatures an average strain transfer ratio of 0.606 ± 0.7% was measured. Mechanical load cycling tests up to 1000 cycles are used for the evaluation of the elastic fatigue of the bond material. The effects of mechanical load cycling and aging of the bond layer are analyzed with the SAW strain sensor response. After 1000 mechanical load cycles, the transferred strain into the SAW strain sensor is 0.582 ± 0.153%. Finally, the experimental results are compared with the results of a 3D FEM simulation which are deviating by less than 10%.

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References

Figures

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Fig. 5

Experimental setup for strain transfer experiments, consisting of a tensile test bench with thermal chamber, network analyzer, source meter, and digital multimeter

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Fig. 6

Test holder made of heat-treatable steel with attached SAW strain sensor on front side and the reference foil strain gauge on backside

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Fig. 7

Test holder with mounted SAW strain sensor in the thermal chamber for temperature dependence investigations up to 85 °C

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Fig. 8

Strain reference measurements of the foil strain gauge and linear fit of the strain values with respect to the applied load

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Fig. 9

Strain response Δf/f0 from the SAW strain sensor from room temperature up to 85 °C in dependence of the measured strain with the foil strain gauge

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Fig. 10

Temperature dependency of the STR into the assembled SAW strain sensor

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Fig. 11

STR into the assembled SAW strain sensor in dependence of the number of load cycles

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Fig. 4

Simulated STR in dependence of the temperature

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Fig. 3

FE model for strain transfer simulations for the temperature range of 22 °C to 85 °C

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Fig. 2

Simulated stress distribution of the test holder, loaded as in the experimental setup

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Fig. 1

Sketch of the experimental setup for the strain transfer investigations

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Fig. 12

Comparison of the simulated and measured strain transfer ratio into the SAW device

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