IntroductionA lightweight film known as Kapton with 12 piezoelectric transducers attached was subjected to a frequency range of 1 kHz to 15 MHz of current at 10 volts. The resulting sinusoidal waves produced and sensed by an actuator-sensor pair will be compared to the waves produced and sensed by a different actuator-sensor pair or more than one actuator-sensor pair. A transducer can act as an actuator or a sensor. An actuator makes waves and a sensor senses them. Eventually an identical film with a cut in it will be used. The purpose of this research is to see if a pattern can be recognized and used in order to locate, acknowledge or repair a crack in the membrane. The tests that will be run will be in the d31 mode. Periodic excitation in this mode will produce longitudinal (along the length) waves.

 

 

          

A transducer is a device that can be used as an actuator or a sensor contingent upon the circuit and connections made. A transducer is made up of a piece of piezo film pinched between 2 electrodes. The piezo film is a material that will respond to electrical forces and convert it to a mechanical force or convert a mechanical force to an electrical force.

Kapton is a polyimide film that is being tested. Eventually a membrane impregnated with heat sensitive epoxy like material will be used. Below is an example of a 3 part membrane that could be used. An epoxy makes up the larger portion. Packets or bubbles of glue are used as the healing material. A catalyst known as Grubbs’ catalyst is used to help polymerize the healing material.

1. Prepare a 100mm by 200mm piece of Kapton by attaching 4 transducers on each of the 200mm sides and 2 to each of the 100mm

sides.2. Mount the membrane on a rectangular frame.3. Set up the experiment with a voltage waveform generator and oscilloscope.4. Test single-input--multiple-output transfer functions.5. Test multiple-input—multiple-output functions.6. Plot all transfer functions.7. Continue tests on the specimen with a transducer in the center as an obstruction.8. Continue tests on the specimen with a crack.9. Plot all transfers and compare with the original specimen.

Materials

Layout of Piezo Transducers on the Kapton Membrane

Research Objective & Set Up

Kapton Membrane & Transducers

Waveform Generator* Oscilloscope**

TRANSFER FUNCTION TESTS ON SELF HEALING BIOMIMETIC TRANSFER FUNCTION TESTS ON SELF HEALING BIOMIMETIC STRUCTURESSTRUCTURES

D. Daugaard, E. Petersen and U.KordeD. Daugaard, E. Petersen and U.Korde South Dakota School of Mines and Technology, Rapid City, SD 57701South Dakota School of Mines and Technology, Rapid City, SD 57701

Voltage Between Sensors 1 & 2

0

0.00002

0.00004

0.00006

0.00008

0.0001

0.00012

0.00014

0.00016

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Log(Hertz)

Vo

ut/V

in :

Exp

erim

enta

l

Comparison of 1 & 7

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Log(Hertz)

Vou

t/Vin

1 & 7 with center 1 & 7 with center with power 1 & 7 alone

1.Connect the waveform generator and oscilloscope to 2 of the transducers.2.Set the oscilloscope to 10 volts and test for frequencies of 1 kHz to 15 MHz based on a sinusoidal waveform.3.Measure and record the decibel voltages going in the first transducer and out the second transducer.4.Test all the possible combinations of 2 transducers. 5.Record the data on a chart and plot the voltage out divided by the voltage in, against the Log of the frequency.6.Voltage out divided by voltage in was calculated by taking 10 to the power of the negative of dB voltage in minus dB voltage out divided by 20.7.Repeat tests for other variables.8.The results below are for transducers 1 & 2. 9.These results were typical other the pairs tested.

{Voltage out /voltage in =(10^-(dbVin-dbVout)/20)}

Data for Transducers 1 & 2

*A waveform generator is an instrument that converts a wave function, a pattern of electricity, to a waveform with crests, troughs and amplitudes. **An oscilloscope is an instrument that displays and/or records the changes of voltage in an electric circuit.

This graph compares the results of a 1-7 actuation-sensor pair by itself, with an extra transducer placed in the center without power and with the extra transducer with power.

Tension Comparison for Transducers 1 & 2

0

0.0001

0.0002

0.0003

0.0004

0.0005

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Log(Hertz)

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Normal Tension Inner Tension Outer Tension Both outer

This graph shows the results of transducers 1 & 2 with a variety of changes in the tension of the Kapton on the sides and edges.

Procedure

Equipment

Initial Results (Control) Comparison of 2,3,4,5 with 8,9,10,11

0

0.00005

0.0001

0.00015

0.0002

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Log(Hertz)

Vo

ut/

Vin

with center no power with center with power no center

This graph compares the results of 4 powered actuators and 4 sensors by themselves, with an extra transducer placed in the center without power and with the extra transducer with power.

Tested Variable Results

Comparison of 1 & 4 with 1 & 7 with a center sensor with power

0

0.0001

0.0002

0.0003

0.0004

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

Log(Hertz)

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Sensors 1 & 7 with one in the center with power

Sensors 1 & 4 with one in the center with power

This graph compares one pair of transducers with another transducer in the center with power to another pair under the same conditions.

ConclusionsThe tests performed with the individual pairs and with different variables produced similar results of a higher ratio of voltage out to voltage in at a frequency in the range of 3 MHz to 10 MHz. The different transfer functions performed provides insight towards algorithms that will be useful in the repair process. Qualitatively the results are similar. The small particles on top of the membrane did not respond, supporting the fact that the energy movement is longitudinal.

Future WorkFuture tests will include time reversal signal processing, cracked membrane testing with different combinations of the 12 transducers and verification of results with analytical modeling.

Thanks to Dr. Umesh Korde of the School of Mines, Eric Petersen of the University of Nebraska at Lincoln, Brant Miller of the School of Mines, Dr. Rob Winter of the School of Mines, the National Science Foundation RET program and the Air Force Research Laboratory, Kirkland, AFB, New Mexico.

Acknowledgements

A test was done to see if the wave motion was vertical or horizontal. Silver dust particles sprinkled on top to see if nodes and antinodes would form produced negative results as did chalk dust. This supported the fact that the excitation of thewaves were longitudinal.

dBVin dBVout Vout/Vin Hertz Log(Hertz)

36.98333 -49.3767 4.81E-05 1000 3

36.77333 -51.25 3.97E-05 3000 3.477121

37.19 -52.5 3.28E-05 5000 3.69897

36.25 -52.8133 3.52E-05 7000 3.845098

36.04333 -53.23 3.44E-05 9000 3.954243

35.10667 -52.9167 3.97E-05 10000 4

34.37667 -52.8133 4.37E-05 30000 4.477121

36.25 -52.19 3.78E-05 50000 4.69897

35.83667 -51.3533 4.37E-05 70000 4.845098

35.94 -51.7733 4.11E-05 90000 4.954243

35.41667 -50.8333 4.87E-05 100000 5

35.94 -50.62 4.70E-05 300000 5.477121

36.66667 -50.8333 4.22E-05 500000 5.69897

35.31 -51.5633 4.53E-05 700000 5.845098

35 -51.9767 4.48E-05 900000 5.954243

37.08667 -50.1033 4.37E-05 1000000 6

33.74667 -52.1867 5.05E-05 3000000 6.477121

32.70667 -52.2933 5.62E-05 5000000 6.69897

28.13 -56.1467 6.11E-05 7000000 6.845098

23.44 -58.7533 7.77E-05 9000000 6.954243

23.23333 -53.1233 0.000152 10000000 7

36.14667 -55.1033 2.74E-05 15000000 7.176091