Benjamin B. Choi

Glenn Research Center, Cleveland, Ohio

Kirsten Duffy

The University of Toledo, Toledo, Ohio 

Jeffrey L. Kauffman

The Pennsylvania State University, University Park, Pennsylvania 

Nicholas Kray

GE Aviation, Cincinnati, Ohio

Optimal Topology and Experimental Evaluation of 

Piezoelectric Materials for Actively Shunted General 

Electric Polymer Matrix Fiber Composite Blades

NASA/TM—2012-217631

December 2012

SPIE83452G
NASA STI Program . . . in Profile

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientific and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Officer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major significant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of significant 

scientific and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientific and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientific, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 443–757–5803

• Phone the NASA STI Information Desk at

443–757–5802

• Write to:

 STI Information Desk

 NASA Center for AeroSpace Information

 7115 Standard Drive

 Hanover, MD 21076–1320
Benjamin B. Choi

Glenn Research Center, Cleveland, Ohio

Kirsten Duffy

The University of Toledo, Toledo, Ohio 

Jeffrey L. Kauffman

The Pennsylvania State University, University Park, Pennsylvania 

Nicholas Kray

GE Aviation, Cincinnati, Ohio

Optimal Topology and Experimental Evaluation of 

Piezoelectric Materials for Actively Shunted General 

Electric Polymer Matrix Fiber Composite Blades

NASA/TM—2012-217631

December 2012

SPIE83452G

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Smart Structures and Materials and Nondestructive Evaluation and Health Monitoring 2012

sponsored by the International Society for Optical Engineering (SPIE)

San Diego, California, March 11–15, 2012
Acknowledgments

This work was in support of a Space Act Agreement with GE Aviation and part of NASA’s Subsonic Fixed Wing (SFW) project. 

It was funded by the Fundamental Aeronautics Program. Test articles were provided by GE Aviation, and testing was performed 

at NASA Glenn. The authors extend their thanks to Mr. Andrew Provenza at NASA Glenn for his great efforts in operating the 

Dynamic Spin Rig during testing. 

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217631 1

Optimal Topology and Experimental Evaluation of Piezoelectric

Materials for Actively Shunted General Electric

Polymer Matrix Fiber Composite Blades

Benjamin B. Choi

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Kirsten Duffy

The University of Toledo

Toledo, Ohio 43606

Jeffrey L. Kauffman

The Pennsylvania State University

University Park, Pennsylvania 16802

Nicholas Kray

GE Aviation

Cincinnati, Ohio 45215

Summary

NASA Glenn Research Center, in collaboration with GE Aviation, has begun the development of a 

smart adaptive structure system with piezoelectric (PE) transducers to improve composite fan blade 

damping at resonances. Traditional resonant damping approaches may not be realistic for rotating frame 

applications such as engine blades. The limited space in which the blades reside in the engine makes it 

impossible to accommodate the circuit size required to implement passive resonant damping. Thus, a 

novel digital shunt scheme has been developed to replace the conventional electric passive shunt circuits. 

The digital shunt dissipates strain energy through the load resistor on a power amplifier. General Electric 

(GE) designed and fabricated a variety of polymer matrix fiber composite (PMFC) test specimens. 

Investigating the optimal topology of PE sensors and actuators for each test specimen has revealed the 

best PE transducer location for each target mode. Also a variety of flexible patches, which can conform to 

the blade surface, have been tested to identify the best performing PE patch. The active damping control 

achieved significant performance at target modes. This work has been highlighted by successful spin 

testing up to 5000 rpm of subscale GEnx composite blades in Glenn’s Dynamic Spin Rig.

Introduction 

Previously, NASA Glenn Research Center developed several damping technologies to reduce 

excessive vibratory stresses that led to high-cycle fatigue (HCF) failures in aircraft engine 

turbomachinery. These activities included viscoelastic damping by Mehmed and Kosmatka (Ref. 1), 

passive impact damping by Duffy (Ref. 2), plasma sprayed damping coating, and high-temperature shape 

memory alloy (Ref. 3).

Recently, in support of a Space Act Agreement with GE Aviation and as part of NASA’s Subsonic 

Fixed Wing (SFW) Project, Glenn’s researchers have been investigating a new damping technology for 

composite fan blades for future aircraft designed to achieve a higher level of aerodynamic performance.

As a means of reducing engine blade vibration, piezoelectric (PE) blade damping has been proposed to 

support part of the project’s goals such as lighter, quieter, and fuel-efficient composite fans for 
NASA/TM—2012-217631 2

turbomachinery applications. GE has designed and instrumented a variety of polymer matrix fiber 

composite (PMFC) test specimens, including subscale GEnx fan blades. For PMFC blades, the 

piezoelectric (PE) elements could be embedded within the blade material, protecting the brittle PE

material from the airflow and minimizing aerodynamic performance degradation.

In the past few decades, it has become evident that PE shunt damping is a promising technology for 

suppressing significant mechanical vibration at structural modes. The principle of PE shunt damping is 

that PE materials can convert mechanical energy into electrical energy, and the electrical energy can be 

dissipated through a connected load resistor of a power amplifier. Hagood and von Flotow (Ref. 4) first 

presented an analytical model for resistive and inductive-resistive shunt dampened systems, showing that 

the resonant shunt behaves like a mechanical vibration absorber. Since then, many researchers have begun 

to further develop PE damping with tests and analyses. Lesieutre (Ref. 5) described the different types of 

shunt circuits and how they affect vibration behavior.

In recent advances in the turbomachinery applications, Cross and Fleeter (Ref. 6) developed a passive 

control for turbomachine blading flow-induced vibrations, and employed a synthetic inductor that 

replaced a large size inductor to control the first bending mode of the PE blade. Livet (Ref. 7)tested a 

virtual inductor for compressor disk blade damping control. Numerous papers for passive shunt 

development in turbomachinery applications have been published, and most of them have dealt with 

analog semipassive circuits that consist of operational amplifiers (op-amps), resistors, gyrators, and an 

external power supply.

Some researchers have used an active control approach for the PE actuators for turbomachinery blade 

vibration control. Remington (Ref. 8) reduced low-speed fan noise control using actively controlled PE

actuators mounted on stator vanes. Watanabe (Ref. 9) used a traditional feedback control scheme to 

oscillate the PE patches for cascade flutter control in subsonic flow. In 2009, NASA Ames and Boeing

(Ref. 10) developed and successfully demonstrated a civilian, full-scale MD 900 Explorer helicopter rotor

(SMART rotor) with on-blade PE actuators that have a conventional controller driving the trailing edge 

flaps. This wind-tunnel testing obviated a controversial issue concerning the use of PE materials to 

generate enough force to excite the rotating blades. This experiment motivated us to continue the PE

damping of high-speed turbomachinery fan blades. 

However, the aforementioned semipassive damping approaches may not be viable for rotating frame 

applications such as engine blades. The limited space in which the blades reside in the engine makes it 

impossible to accommodate the circuit size required to implement damping. Additionally, there is the risk 

of rotor imbalance with operation at high-centrifugal loads. Further, the active control approach using 

proportional-integral-derivative (PID) controller law, used by most researchers, is not effective for

resonant vibration suppression. 

In this report, therefore, a novel digital shunt scheme to replace the conventional electric passive 

shunt circuits is presented. The digital shunt dissipates strain energy through the load resistor on a power 

amplifier. The feasibility and effectiveness of using PE materials to suppress the resonant vibrations of 

composite test specimens is then investigated by testing several off-the-shelf PE patches with different 

material properties to identify the best performing PE actuators and sensors for actively controlled test 

specimens. In this work, GE designed and fabricated a variety of PMFC test specimens: wide and narrow 

beams for surface-mounted PE transducers as well as small subscale GEnx composite fan blades for spin 

testing.

After selecting the best PE patches, the Glenn team continued to investigate the optimal topology of 

PE sensors and actuators for the subscale GEnx composite fan blades. Finally, Glenn’s Dynamic Spin Rig 

(DSR) test results of subscale GEnx blades with PE patches at 0 to 5000 rpm in vacuum is presented here.

Symbols

A controller transfer function 

C capacitance

d distance from blade base to position where external force is applied
NASA/TM—2012-217631 3

F external force

G transfer function 

L inductance

Q quality factor

R resistance

r distance where displacement is measured 

TF transfer function

V voltage

Y displacement

Z impedance

η loss factor

ζ critical damping ratio

ω circular frequency

Subscripts:

a actuator

ac active control

b baseline

fv actuator voltage with respect to external force

fy displacement with respect to external force

in input

out output

PEB_base patch PE B to base excitation

p PE patch

s sensor

tip_base blade tip to base excitation

vv sensor voltage with respect to actuator voltage

vy displacement with respect to sensor voltage

Shunt Damping and Digital Control Design

PE materials, because of their lightness and easy integration into the host structure, have been 

extensively employed in vibration-control schemes used in aeronautics and aerospace structures. 

Strategies for vibration control include passive and active concepts.

Passive Resistive-Inductive (RL) Shunt

Passive vibration damping is intrinsically stable and cheap and is easily implemented by using PE

actuators. In general, the actuators are bonded to the mechanical structure and shunted to suitable external 

circuits, containing resistive and inductive components that dissipate electric energy. That is, the PE patch,

shunted through a RL circuit, acts as a vibration absorber, which is tuned to the same frequency of the 

motion to be damped. The RL series circuit is generally accepted as one the best passive shunts for 

vibration damping of a single mode or multimodes (Refs. 4, 5, 11, and 12).

However, a major problem with using this approach arises from the large inductor size and mass for 

the low-frequency-tuned resonant circuit that is needed when the mechanical frequency of interest is low. 

Consequently, many researchers have proposed the use of synthetic inductors (Refs. 6 and 7)to reduce the 

weight and volume of the circuits. It required a constant power supply, and its size was still considerably 

large. Nevertheless, the RL shunt or synthetic inductor is suitable for stationary frame applications. For 

turbomachinery applications, however, an implementation issue can arise when applied to the limited 

space in which the blades reside in the engine. Further, there is the risk of rotor imbalance during

operation at high-centrifugal loads.
NASA/TM—2012-217631 4

Digital Control Design

As an alternative to the passive RL shunt, Choi (Refs. 13 and 14) developed a new active control 

approach that replaces equivalent passive-shunt analog circuits with a digital code. His controller 

demonstrated significant resonance damping performance when used on titanium-alloy flat plates

(Ref. 13) and titanium-alloy fan blades (Ref. 14). For dynamic spin testing, the blade’s natural 

frequencies will vary as a function of the shaft’s rotation speed. Thus, a real-time adaptive feature to 

follow changes in the blade’s natural frequencies must be developed to generate adaptive controller 

tuning in real time to the changing condition.

Figure 1(a) shows a general feedback control of analog RLC (resistive-inductive-capacitive) network. 

Its transfer function (Ref. 15) can be described as

Z = R + iωL − i (ωC) in (1)

Zout = R + iωL (2)

( )

( )

1 2

in

out

in

out

+ +

+ = + ω − ω+ ω = = LCs CRsCs R Ls

R i L i C

R i L

Z

Z

V

V

(3)

where Zin and Zout are the impedance input and output, respectively; ω is the circular frequency; Vout and 

Vin are the voltage output and input, respectively; and s represents the complex frequency domain.

As shown in Equation (3), the transfer function of the feedback controller is expressed in terms of 

passive circuit components (RLC) regardless of modal shape. Figure 1(b) shows a block diagram of active 

feedback controller. The sensor voltage signal Vs(s) is fed back to the transfer function and the actuator 

control signal; hence,

V (s) A (s)V (s) V (s) a = − i s + in (4)

where Ai is the ith controller transfer function,

( ) ( ) ( 1) 2 Ai s = Cs Ri + Lis Li

Cs + CRis + (5)

Also, Vs is the sensor voltage and Vin is the voltage input. This control law is completely different from

PID control law, which has been used for the active PE damping control done by many researchers

(Refs. 7 to 10). It is of interest to note that multimode control, using only one actuator patch, might be 

possible if the single patch can excite the target multimodes sufficiently. A set of control laws for each 

target mode shown in Equation (5) are mathematically summed and can be applied as a single control 

command to the single actuator patch.
NASA/TM—2012-217631 5

In Figure 1(b), the closed-loop system performance of sensor voltage and displacement, respectively,

are

1 ( ) ( )

( ) ( )

1 ( ) ( )

( ) ( , ) ( ) A s G s

G s V s

A s G s

G s F d s

V s

vv

vv i

vv

fv

s +

+

+ =

(6)

1 ( ) ( )

( , ) ( )

1 ( ) ( )

( , ) ( , ) ( , ) A s G s

G r s V s

A s G s

G r s F d s

Y r s

vv

vy i

vv

fy

+

+

+ =

(7)

where 

( )

( ) , ( ) ( , )( ) ( ) V sV s G s

F d s

V s G s

a

s vv a fv = =

(8)

( )

( , ) , ( ) ( , )( , ) ( , ) V sY r s G s

F d s

Y r s G r s

a

fy = vy =

(9)

Note 

Gfv transfer function of the actuator voltage with respect to external force

Gfy transfer function of displacement with respect to external force, Gvv is the transfer function of sensor 

voltage with respect to actuator voltage

Gfy transfer function of displacement with respect to external force

Gvy transfer function of displacement with respect to sensor voltage 

F external force

d distance from the blade base to the position where the external force is applied

Y displacement

r distance from the blade base to where displacement is measured

The transfer functions in Equations (8) and (9) can be obtained by using MATLAB (The MathWorks, 

Inc.) software based on the experimental system frequency response. A spectrum analyzer was used to 

obtain experimental measurement of the test specimen’s modal frequency response. The MATLAB

Frequency Domain System software identifies the linear dynamic transfer function of a singleinput/single-output (SISO) system. Finally, by using the Symbolic Math Toolbox, a complete 

mathematical model of the closed-loop system in Equations (6) and (7) can be derived, where the control 

law is described in Equation (5).

The inductor value Li is chosen for the particular (target) frequency ωi as

i pi

i LC

1

ω = (10)

where the value of Cpi is the capacitance of the PE patch in farads. The resistor value R is chosen to 

optimize the damping over a frequency bandwidth. In general, increasing the R value means good 

damping, but high control power consumption. Thus, the optimized R value must be selected by taking 

into account the test equipment specifications. 

Simulation Results

To assess the merit of the active damping control, a number of simulations of open- and closed-loop 

transfer functions were performed on a simply supported beam with bonded PE transducers. For this 

simulation study, a six-mode truncated mathematical model was constructed (Fig. 2), assuming the values 
NASA/TM—2012-217631 6

of the resonant frequencies and damping ratios of the PE beam. It was also assumed that six pairs of 

collocated PE actuator and sensor patches were needed; these were placed on the optimal locations to 

control the six target modes. The digital shunt control technique (described in the upcoming section, 

“Optimal Patch Selection”) was then employed to determine the feedback control laws for the optimal 

parallel and series shunt circuits for the target resonances. Damping performance was evaluated by 

measuring the open- and closed-loop frequency responses (Fig. 3(a)) and time history (Fig. 3(b)) of the 

PE beam.

The simulation results showed that the active controller significantly reduced the vibrations of the 

beam, pushing the resonant peaks down. Notice that unlike PID control law, this feedback is effective at 

targeted blade frequencies only. It was concluded that a transfer function of the RLC shunt circuit can be 

expressed in S-domain as in Equation (4), so that it can be programmed in a digital code. Further, a realtime adaptive control for change in blade frequencies for spin testing can be implemented, as opposed to 

the analog shunt circuit approach.
NASA/TM—2012-217631 7

Bench Test Setup

Figure 4 shows the experimental bench test setup. For baseline (open-loop) testing, the test specimen 

was excited with a frequency sweep through target resonance using a spectrum analyzer. The base 

excitation level and the tip response were measured using accelerometers. The resonance frequency and 

damping are then calculated from the experimental transfer function of the tip response to the base 

excitation.

For the active control (closed-loop) testing, Simulink and the Real Time Workshop for MATLAB are 

used to generate C code for the digital shunt control laws, and the executable control code is downloaded 

into the dSPACE control system to implement the digital shunt. The accelerometer signal of the tip 

displacement is fed back to the dSPACE control system that generates the control command signal. The 

power amplifier magnifies the signal and delivers power to energize the PE patches on the test specimen.

The closed-loop transfer function of the tip response to that of the base acceleration is measured to

calculate the active damping performance. Here, the value for L is chosen to target a particular frequency, 

and the value for R is chosen to optimize the damping over the target frequency band. The closed-loop 

gain is carefully selected to meet the damping requirement within the feedback stability margin. In 

practice, the entire control system can be implemented on a powered chip on the rotating frame if DC 

power can be supplied to energize the power electronics.

Experimental Evaluation of PE Materials

The goal of this section is to investigate the ability and effectiveness of using PE materials to damp 

resonant vibrations of GE-made graphite/epoxy composite coupons. It is then determined which type of 

PE patch generates the best performance in terms of damping and required control power consumption. A 

variety of commercially available PE materials were tested to identify the optimally performing sensor 

and actuator for nonrotating vibration reduction.

Tested PE Materials

All tests were performed on PMFC test specimens with surface-mounted PE elements. Table I

describes the material properties of the different patch types that were used in the test. Evaluated PE

patches are Midé nonflexible, Smart Material (S‒M) flexible d31 and d33 types, and Advanced Cerametrics

flexible d33-type patches. The PE patches all incorporate Navy Type-II lead zirconium titanate (PZT-5A, 

Annon Piezo Technology Co., Ltd.) material. 
NASA/TM—2012-217631 8

TABLE I.—MATERIAL PROPERTIES OF PIEZOELECTRIC PATCHES

Patch Type Dimensions,

in3

Capacitance,

C,

μF

Maximum voltage,

Vmax,

V

Maximum force,

Fmax,

lbf

Midé QP10w Flat, d31 1.81 by 1.310 by 0.010 105 ±200 15

Smart Material (S‒M)

M2814–P1 Flexible, d33 1.10 by 0.600 by 0.012 0.61 –500 to 1500 195

S–M M2814–P2 Flexible, d31 1.10 by 0.600 by 0.012 25.7 –60 to 360 85

S–M M0714–P2 Flexible, d31 0.275 by 0.30 by 0.012 6.5 –60 to 360 85

Advanced Cerametrics Flexible, d33 0.275 by 0.27 by N/A 0.95 –60 to 360 N/A

Optimal Patch Selection

PE patches were tested on the two composite coupons: narrow and wide cantilever composite beams. 

The dimension of the narrow beam is 9.5 by 1.30 by 0.25 in.; the wide beam is 9.5 by 2.0 by 0.25 in. Each 

beam length of 2.0 in. at one end was inserted into the shaker armature clamp so that 7.5 in. extended 

from the clamp. PE patches were surface mounted with Duralco 4537N epoxy (Cotronics Corp.) near the 

base of the test specimens. This location was optimal for the actuator patch at the first bending site, which 

was of interest in this work.

We began bench testing the Advanced Cerametrics d33 type versus S‒M’s M2814-P1d33 type on the 

narrow beam. As shown in Figure 5, each patch was placed 2.0 in. (clamp area) from one end of the 

narrow beam, and one accelerometer was mounted at the blade tip for the displacement measurement. The 

target resonance of this test was the first bending mode, around 162.5 Hz. The HP analyzer generated a 

swept sine signal that was used to excite the beam through the target mode as well as experimental openand closed-loop transfer functions of the tip response relative to the base excitation. Damping was 

calculated from this data.
NASA/TM—2012-217631 9

We first measured baseline damping without the control system ζb and then damping with active 

vibration control ζac so that the added damping can be calculated as ∆ζ = ζac – ζb. Figure 5 shows the 

Bode plot of the open- and closed-loop transfer functions of using the two different patches. With the 

same controller setup, the Advanced Cerametrics d33-type patch produced ∆ζ = 0.0185, and the S‒M d33

type produced ∆ζ = 0.009. In general, the assumed target damping is ζac > 0.005 (i.e., loss factor η > 0.01

and quality factor Q < 100). However, the problem with this type of bench testing configuration is that the 

first bending mode had already high damping of ζac ≅ 0.02. Nevertheless, both actuator patches achieved, 

surprisingly, significant damping capabilities at the target mode of 162.5 Hz. This kind of low-frequency 

damping has been considered to be a significant challenge because of difficult implementation.

Another factor in determining the best performing patch candidate is the required control power 

consumption for the added damping performance. Figure 6 shows that the required control effort in using 

the Advanced Cerametrics d33-type patch, consumed 0.185 W to perform ∆ζ = 0.0185, and the S‒M

M2814-P1d33-type patch consumed 0.93 W to perform ∆ζ = 0.009. In comparing the two experimental 

results, one can conclude that the Advance Cerametrics d33 actuator capability outperformed the S‒M d33-

type patch in terms of the damping and associated power efficiency.
NASA/TM—2012-217631 10

Similarly, all other type patches were tested on the same narrow and/or other wide beams. All test 

results are summarized in Table II. The best performing patch was the Advanced Cerametrics d33 type. 

However, the second best candidate, the S‒M M2814-P2 d31-type patch, was selected for the subscale 

GEnx blade damping work because of the availability of the correct size of off-the-shelf patches. 

TABLE II.—ACTIVE DAMPING INCREASE RESULTS USING

DIFFERENT TYPE PIEZOELECTRIC PATCHES

Beam Patch type Piezoelectric actuator Damping increase,

∆ξ

Wide Nonflexible Midé QP10n d31 0.005

Wide Nonflexible Midé QP10w d31 (wide) 0.001

Wide Flexible Smart Material (S‒M) d31 0.012

Wide Flexible S‒M d33 0.007

Narrow Flexible S‒M d31 0.012

Narrow Flexible S‒M d33 0.009

Narrow Flexible Advanced Cerametrics d33 0.019

Here, a Midé QPA200 amplifier (±200 V) for all the bench tests. However, since the S‒M d33 patch 

can be excited with –500 to +1500 V to generate higher blocking force as shown in Table I, it is expected

the d33 type would work very well with the higher voltage amplifier. Thus, material selection in this study 

was constrained by the current QPA200 amplifier.

Nonrotating Testing of Subscale GEnx Blade

The goal of this section is to determine the actuation, sensing, and vibration damping capabilities of 

the S–M d31-type patches. They were surface mounted to the small-scale GEnx composite fan blade, since 

the subscale blade thickness was too small to contain the patches. However, the full-size blades will have 

enough thickness for embedded PE patches. Figure 7 shows the modal stress of the target first bending 

mode at 0 rpm as determined by ANSYS finite element (FE) code. The star shows the optimum patch 

locations on the concave and convex sides, respectively.

Now it must be decided on which side of the blade the PE actuator patch must be placed for better 

damping. A comprehensive FE model of the GEnx blade with surface-mounted PE patches was not 

developed at the time of this test. Thus, several experimental tests were carried out to identify the optimal 

actuator and sensor patch configuration. Two identical S–M d31-type patches were placed in an area of 

high modal stress (Fig. 7) on each side. One patch on the concave side acts as an actuator, and the other 

on the convex side senses the strain, or vice versa. In the tests, additional accelerometer feedback signal 

was used to confirm the accuracy and validity of the sensor patch functionality. Notice that an 

accelerometer is not able to be used in an actual engine. A tiny PE sensor is necessary, which can be 

easily embedded into the real composite blade.

Test 1 began with a S–M d31-type actuator (PE A) placed on the convex side and another S–M

d31-type sensor patch (PE B) placed on the concave side. In this test setup (shown in Fig. 8), a sensing 

signal of the strain of PE B was fed back to the dSPACE control system, and the control force went to the

S–M d31 actuator patch (PE A) on the convex side. The transfer function of the strain on the concave side 

to the base excitation TFPEB_base was measured, and ∆ζ = 0.009 was calculated as shown in Figure 9(a). 

For comparison purposes, the accelerometer signal was also measured to investigate the blade tip 

vibration damping when the PE B feedback sensor was used. The transfer function of the accelerometer 

signal of the tip response on the concave side to the base excitation TFtip_base was measured, and ∆ζ =

0.009 was calculated as shown in Figure 9(b). This test results show that by using a feedback sensor 

signal of the 

PE B, the active damping achievement on PE B is the same as that on the tip displacement.
NASA/TM—2012-217631 11
NASA/TM—2012-217631 12

Similarly, all other configurations were tested and evaluated by the blade tip damping and the PE 

sensor strain reduction. All experimental testing results are summarized in Table III. Test 4 produced the 

best damping performance of ∆ζ = 0.021 from the TFtip_base, and 0.019 from the TFPEB_base. Thus, the 

actuator patch on the concave side of the blade and a small sensing patch on the convex side was the 

arrangement used for the dynamic spinning test.

TABLE III.—EXPERIMENTAL RESULTS OF INCREASE IN DAMPING RATIO 

USING DIFFERENT PATCH CONFIGURATIONS

Test Feedback sensor Actuator Transfer function 

of tip to base, 

TFtip_base

Transfer function of sensor 

piezoelectric (PE) to base, 

TFPE_base

1 PE, concave PE, convex ∆ξ = 0.009 ∆ξ = 0.009

2 Accelerometer, concave PE, convex ∆ξ = 0.011 ∆ξ = 0.011

3 Accelerometer, convex PE, concave ∆ξ = 0.011 ∆ξ = 0.009

4 PE, convex PE, concave ∆ξ = 0.021 ∆ξ = 0.019

Optimal Topology for Spin Test

Two different patch configurations were tested and evaluated to determine which configuration

generated the best performance in terms of vibration damping.

Single-Patch Configuration

Recent FE analysis shows that the strain level on the suction (convex) side of the GEnx blade exceeds

the PE patch’s durable strain limit for high rotor speed. However, up to 5000 rpm, the FE analysis 

predicts the safe operation of the patches mounted on the pressure (concave) side, where the strain 

spreads out at high rotor speed. Thus, the previous optimal configuration as shown in Test 4, where the 

sensing patch is placed on the suction side, is no longer viable for the spin test. All PE patches must be 

located in the vicinity of the target placement on the pressure side.

As shown in Figure 10(a), a large actuator (S–M M2814-P2) was glued on the highly strained area, 

and a small sensing patch (S–M M0714-P2) was lined up along the blade length above the exciter

(actuator) patch. In this test setup, ∆ζ = 0.011 was achieved as shown in Figure 10(b). 
NASA/TM—2012-217631 13

Double-Patch Configuration

In this section, a unique double-patch configuration was proposed as one of the optimal topologies. 

This resulted in substantial improvement over the single-patch configuration. As shown in Figure 11(a), 

two large actuator patches and one small sensor patch (S–M M0714–P2) are placed around the high 

modal strain location on the concave (pressure) side. The two large patches can be energized 

simultaneously to increase the actuating power, or only one actuator can be used at a time, while the other

can function as a backup in the event of actuation patch failure.

Two dissimilar S–M d31- (S–M M2814–P2) and d33-type (S–M M2814–P1) materials for Actuator 1 

and Actuator 2 (Fig. 11(a)), respectively, were secured on the blade in order to determine which type of 

patch works better as an actuation patch. Figure 11(b) shows that the S–M d31-type patch achieved ∆ζ = 

0.014, while the S–M d33-type patch achieved ∆ζ = 0.008. As mentioned earlier, another factor in 

evaluating the optimal patch selection is the required power consumption for the added damping. As 

shown in Figure 11(c), the S–M d31-type patch consumed peak-to-peak power of 0.82 V-A to achieve ∆ζ

= 0.035, and the S–M d33-type patch consumed peak-to-peak power of 1.34 V-A to achieve ∆ζ = 0.029. 

Evidently, the S–M d31-type patch (S–M M2814–P2) outperformed the d33-type patch (S–M M2814–P1) 

in terms of damping improvement and associated control power efficiency. This test results reconfirmed 

the previous experimental results in Table II.

Therefore, we have concluded that the optimal topology of the spin test for the subscale GEnx blade 

is the double-patch configuration with two S–M d31-type (S–M M2814–P2) actuators and one small S–M

d31-type patch (S–M M0714–P2), all bonded on the concave (pressure) side.
NASA/TM—2012-217631 14

Spin Test Results

GE Aviation instrumented two test blades with the double-patch configuration described in the 

previous section, and they were installed in the Dynamic Spin Rig (DSR) (Refs. 16 and 17) facility at 

NASA Glenn to perform the spin test. The two blades were fixed to a vertical rotor and placed opposite 

each other (Fig. 12). The rotor was placed in a vacuum tank during operation to reduce the effects of 

aerodynamic loads. Excitation was provided to the blades through the magnetic bearings that levitated the 

rotor and blades in five axes. This excitation rotated with the rotor, while maintaining a 90° angle to the

blade faces to maximize the excitation force. The magnetic bearings have a bandwidth of 1000 Hz, which 

is well above the maximum vibration frequency tested. The signals to and from the sensors and actuators 

traveled through a slip ring, which is located at the bottom of the rotor. The control system and power 

supplies were all located outside of the spin rig in the control room for safety.

As the shaft rotational speed changes, the blade’s natural frequencies will vary due to centrifugal 

loads so that the tuned controller at 0 rpm is no longer effective. Thus, prior to spinning the blades, a 

control code modification was needed to address those changing conditions. An adaptive control feature 

using a lookup table method was added to the closed-loop control system with scheduling variables of 

inductance and capacitance, which vary as a function of the rotor speed. 

It was found that the blades have slightly different resonance frequencies, and coupling exists 

between the blades through the rotor. This resulted in each blade exhibiting two peaks for each mode as 

shown in Figure 13(a). The system is inherently a mistuned two-bladed rotor. The test was done using 

Blade 2 that has the higher response. No accelerometer was installed at the blade base at the time of this 

test, so the excitation command signal was alternatively used to replace the base acceleration signal for 

the calculation of the damping ratio.

Finally, the spin test yielded the transfer functions of the PE sensor signal relative to the excitation 

command signal from 0 to 5000 rpm, in increments of 1000 rpm. Figure 13(b) shows the damping ratio 

for the baseline open circuit and actively controlled blades using only one actuator (Actuator 2 

malfunctioned).

Significant blade damping at 0 rpm was achieved, but the ability to damp decreased as the rotor speed 

increased. This experimental result agreed with the FE analysis, and is caused by the blade’s centrifugal 

stiffening and by the peak modal strain location changing with the rotor speed. Thus, in practice, the 

actuator patch location must be decided based on the rotor speed of interest. A more detailed discussion, 

using additional experimental data is found in Reference 18.
NASA/TM—2012-217631 15

Conclusion

An active feedback control technique that emulated the tuned RLC circuit was developed. This 

technique is an alternative to traditional semipassive circuits, which could be problematic in integration of

the piezoelectric (PE) damping technology into the rotating fan blades. This active controller enabled our 

team to demonstrate blade damping in a spin test.

The technique was successfully demonstrated on a variety of GE composite test specimens, resulting 

in significant resonance damping at the target modes. For the optimal PE patch selection for the test 

specimens, several commercially available off-the-shelf PE materials were tested through a series of 

bench-top tests. They were evaluated in terms of damping capability and associated control power 

requirement, and the Smart Material (S‒M) d31 type (M2814-P2) was finally selected.

As a result of the experimental comparison study, we finalized the optimal patch topology of the 

GEnx fan blade with the double-patch configuration, where two identical S–M d31-type actuator patches

and one small S–M d31-type sensor patch were placed around the high-modal-strain location on the 

concave (pressure) side. Finally, successful spin testing up to 5000 rpm was done in Glenn’s Dynamic 

Spin Rig. As anticipated, the damping was reduced as the rotor speed increased because of blade 

centrifugal stiffening and movement of the area of high modal strain. If damping is required over a 

particular speed range, the actuator location(s) should be chosen based on high modal strain for that speed 

range of interest.

However, one question remains unanswered: The actuation patch on the concave (pressure) side of 

the GEnx achieved more damping than that on the convex (suction) side of the GEnx, which was not 

expected. This open question must be answered through complete system analysis of an FE model with 

PE materials.

Future work to improve the PE blade damping must address the following technical challenges:

1. A sophisticated FE model with embedded or surface-mounted PE materials must be developed as a 

complete analytical tool to simulate and predict the system performance.

2. A higher excitation level must be used to evaluate the PE damping for full-scale fan blades. Possible 

approaches would be to employ customized patch geometry, a stack of d33-type PE patches, with a 

high-voltage amplifier and to develop a material with a higher value of electromechanical coupling 

constant.

3. Implementation of the active control system using mainly operational amplifiers, a digital signal 

processor (DSP) chip, and a noncontact direct-current (DC) power transmitter from the stationary 
NASA/TM—2012-217631 16

frame to the electronic components in the moving frame. An associated system trade study of blade 

weights reduction versus added electronics weights must be done to justify our efforts to meet the 

project’s ultimate goal.

In addition, there are more challenging technical aspects that must be considered, and more research must 

be accomplished before implementing the active control system. However, this paper is an attempt at the 

initial task of proving the feasibility of blade damping.

References

1. Mehmed, Oral; and Kosmatka, John B.: Damping Experiment of Spinning Composite Plates With 

Embedded Viscoelastic Material. Physics & Process Modeling (PPM) and Other Propulsion R&T, 

NASA CP–10193, Vol. II, 1997, p. 28.

2. Duffy, Kirsten P.; and Mehmed, Oral: Self-Tuning Impact Dampers for Turbine Blades. Proceedings 

of the 7th National Turbine Engine High Cycle Fatigue Conference, Palm Beach Gardens, FL, 2002.

3. Duffy, Kirsten P.; Padula II, Santo A.; and Scheiman, Daniel A.: Damping of High-Temperature

Shape Memory Alloys. Proc. SPIE, vol. 6929, 2008, p. 69291C.

4. Hagood, N.W.; and von Flotow, A.: Damping of Structural Vibrations With Piezoelectric Materials 

and Passive Electrical Networks. J. Sound Vib., vol. 146, no. 2, 1991, pp. 243–268.

5. Lesieutre, G.A.: Vibration Damping and Control Using Shunted Piezoelectric Materials. Shock Vib. 

Dig., vol. 30, no. 3, 1998, pp. 187–195.

6. Cross, Charles J.; and Fleeter, Sanford: Shunted Piezoelectrics for Passive Control of Turbomachine 

Blading Flow-Induced Vibrations. Smart Mater. Struct., vol. 11, 2002, pp. 239–248. 

7. Livet, S., et al.: Numerical and Experimental Optimized Shunted Piezoelectric Circuit. 12th

IFToMM World Congress, Besancon, France, 2007.

8. Remington, Paul; Sutliff, Daniel; and Sommerfeldt, Scott: Active Control of Low-Speed Fan Tonal 

Noise Using Actuators Mounted in Stator Vanes: Part 1 Control System Design and Implementation. 

AIAA 2003–3190, 2003.

9. Watanabe, Toshinori, et al.: Numerical and Experimental Study of Active Flutter Suppression With 

Piezoelectric Device for Transonic Cascade. GT2008–51467, 2008.

10. Straub, Friedrich, et al.: SMART Rotor Development and Wind-Tunnel Test. 35th European 

Rotorcraft Forum, Hamburg, Germany, 2009.

11. Moheimani, S.O. Reza; Halim, Dunant; and Fleming, Andrew J.: Spatial Control of Vibration: 

Theory and Experiments. Series A, Vol. 10, World Scientific, Singapore, 2003.

12. Moheimani, S.O. Reza; and Fleming, Andrew J.: Piezoelectric Transducers for Vibration Control 

and Damping. Springer, London, UK, 2006.

13. Choi, Benjamin; Morrison, Carlos; and Duffy, Kirsten: An Active Damping at Blade Resonances 

Using Piezoelectric Transducers. NASA/TM—2008-215212, 2008.

14. Choi, Benjamin, et al.: Active Vibration Reduction of Titanium Alloy Fan Blades (FAN1) Using 

Piezoelectric Materials. NASA/TM—2010-216335, 2010.

15. Choi, Benjamin; Morrison, Carlos; and Min, James: A Multi-Mode Blade Damping Control Using 

Shunted Piezoelectric Transducers With Active Feedback Structure. Presented at the Propulsion, 

Safety and Affordable Readiness (P‒SAR) Conference, Myrtle Beach, SC, 2009.

16. Johnson, Dexter; Brown, Gerald V.; and Mehmed, Oral: A Magnetic Suspension and Excitation 

System for Spin Vibration Testing of Turbomachinery Blades. NASA/TM—1998-206976, 1998.

17. Choi, Benjamin, et al.: Control Study for Five-Axis Dynamic Spin Rig Using Magnetic Bearings. 

NASA/TM—2003-212295 (GT2003‒38912), 2003.

18. Duffy, Kirsten P., et al.: Active Piezoelectric Vibration Control of Subscale Composite Fan Blades. 

GT2012‒68639, 2012. 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-12-2012 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Optimal Topology and Experimental Evaluation of Piezoelectric Materials for Actively 

Shunted General Electric Polymer Matrix Fiber Composite Blades 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Choi, Benjamin, B.; Duffy, Kirsten; Kauffman, Jeffrey, L.; Kray, Nicholas 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 561581.02.08.03.43.04.04 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-18220 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2012-217631 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Categories: 05 and 07 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

NASA Glenn Research Center, in collaboration with GE Aviation, has begun the development of a smart adaptive structure system with 

piezoelectric (PE) transducers to improve composite fan blade damping at resonances. Traditional resonant damping approaches may not be 

realistic for rotating frame applications such as engine blades. The limited space in which the blades reside in the engine makes it impossible 

to accommodate the circuit size required to implement passive resonant damping. Thus, a novel digital shunt scheme has been developed to 

replace the conventional electric passive shunt circuits. The digital shunt dissipates strain energy through the load resistor on a power 

amplifier. General Electric (GE) designed and fabricated a variety of polymer matrix fiber composite (PMFC) test specimens. Investigating 

the optimal topology of PE sensors and actuators for each test specimen has revealed the best PE transducer location for each target mode. 

Also a variety of flexible patches, which can conform to the blade surface, have been tested to identify the best performing PE patch. The 

active damping control achieved significant performance at target modes. This work has been highlighted by successful spin testing up to 

5000 rpm of subscale GEnx composite blades in Glenn’s Dynamic Spin Rig.

15. SUBJECT TERMS

Piezoelectric transducer; Active damping; Digital shunt; Digital resonant control; Blade damping; Digital passive damping 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

24 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18