Andrew J. Provenza and Carlos R. Morrison

Glenn Research Center, Cleveland, Ohio

Control of Fan Blade Vibrations Using

Piezoelectrics and Bi-Directional Telemetry

NASA/TM—2011-217093

June 2011

GT2011–46714
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Andrew J. Provenza and Carlos R. Morrison

Glenn Research Center, Cleveland, Ohio

Control of Fan Blade Vibrations Using

Piezoelectrics and Bi-Directional Telemetry

NASA/TM—2011-217093

June 2011

GT2011–46714

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Turbo Expo 2011

sponsored by the American Society of Mechanical Engineers (ASME)

Vancouver, British Columbia, Canada, June 6–10, 2011
Acknowledgments

The authors would like to thank Efrain Patino for his assistance in manufacturing hardware for damping tests described herein.

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-217093 1

Control of Fan Blade Vibrations Using Piezoelectrics

and Bi-Directional Telemetry

Andrew J. Provenza and Carlos R. Morrison

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

A novel wireless device which transfers supply power 

through induction to rotating operational amplifiers and 

transmits low voltage AC signals to and from a rotating body 

by way of radio telemetry has been successfully demonstrated 

in the NASA Glenn Research Center (GRC) Dynamic Spin 

Test Facility. 

In the demonstration described herein, a rotating 

operational amplifier provides controllable AC power to a 

piezoelectric patch epoxied to the surface of a rotating Ti 

plate. The amplitude and phase of the sinusoidal voltage 

command signal, transmitted wirelessly to the amplifier, was 

tuned to completely suppress the third bending resonant 

vibration of the plate.

The plate’s third bending resonance was excited using 

rotating magnetic bearing excitation while it spun at slow 

speed in a vacuum chamber. A second patch on the opposite 

side of the plate was used as a sensor.

This paper discusses the characteristics of this novel device, 

the details of a spin test, results from a preliminary 

demonstration, and future plans.

Introduction

NASA’s Fundamental Aeronautics Program is interested in 

pursuing research in technology areas which facilitate the 

development of lighter, quieter and more efficient fans for 

propulsion applications. One such application is commercial fixed 

wing, powered flight. High performance fan blades designed to 

achieve such goals will be subjected to higher levels of 

aerodynamic excitations which will undoubtedly lead to more 

serious and complex vibration problems (Ref. 1). There is 

concern over the levels of vibratory stresses, the reduction of high 

cycle fatigue (HCF), and aeroelastic instabilities. Furthermore, 

blade material and mechanical damping become issues of concern 

when material is removed from the blade design and when 

advanced stage design increases the number of vibration modes 

within the engine operating speed range (Ref. 1). 

Historically, NASA Glenn Research Center has used the 

Dynamic Spin Rig (DSR) to characterize the vibrations of fan 

blades and bladed structures and to study damping. In the past 

several years, this facility has been used to assess the effects of 

advanced blade damping concepts on flat plates and subscale 

fan blades. Damping concepts, such as viscoelastic material 

patches (Refs. 2 and 3), impact dampers (Refs. 4 and 5),

plasma-sprayed damping coatings (Ref. 6), and high-damping 

high-temperature shape memory alloy materials (Ref. 7) are 

typically investigated in this facility. Recent experiments 

explore the possibility of using piezoelectric materials in the 

form of patches to dampen problematic blade vibration modes 

(Refs. 8 to 10).

To facilitate the effective testing of damping concepts, an 

active magnetic bearing (AMB) support system was designed 

for the DSR with the intent of using it to excite blade 

vibrations (Refs. 11 to 13). A description of the AMB system 

for use as an exciter in DSR experiments can be found in 

Reference 14.

Slip rings are typically used in rotating machinery 

experiments to extract instrumentation signals from sensor 

devices on or in the rotating body. Electrical signals from the 

sensors travel though rotating brush contacts within the slip 

ring and out to external instrumentation. Since there is 

physical contact between the brushes and the stationary 

contacts within the slip ring, there is friction. Coolant is 

required to remove the resulting heat to mitigate rising 

temperature. Often, oil is mixed with the coolant to lubricate 

the contacts. The potential for brush degradation due to wear 

is possible. 

Slip rings, although not usually designed for it, can also 

move signals from the stationary to the rotating system. 

Channel contacts are not typically designed to carry much 

power—usually a signal with a voltage up to 200 V, but with 

little current—on the order of milliamps. When more than 

tenths of a watt are required to be sent into the rotating frame, 

multiple channels can be used and the transfer duty shared. 

Sending power in through a slip ring, while using it for 

obtaining measurements, can degrade signal quality and even 

create erroneous quantities, especially if the signals out are of 

low voltage. To avoid this problem in using a slip ring bidirectionally, Fulton and Ormiston (Ref. 15) used two slip 

rings—one for powering piezoceramic bimorph actuators in 

model helicopter rotor blades and a second slip ring for 

instrumentation. Baz and Ro (Ref. 16) used a single slip ring 

for sending and receiving information, however their 10 

channel set-up was bulky and rated only to 500 rpm. Channels 

were so far apart, that cross-talk between channels was 

probably less of an issue. 

As mentioned, signal noise is an issue with slip rings. The 

noise is a result of the nature of the transmission. The 

brush/contact environment is a noisy place. Channel isolation 

is difficult as the channels usually are packed closely together 

at the rotating contact point.
NASA/TM—2011-217093 2

GRC’s DSR slip ring was not designed for bi-directional 

use. There is a limit of 0.2 W per channel affecting its 

potential for commanding the rotating operational amplifiers. 

Signal noise was also a concern when considering extractinglow power sensor signals and sending higher-power actuation

signals though the same device. As a result, the authors and 

their team sought to find a different mechanism to provide 

these functions. 

Slip rings have been used in the DSR in the past, with 

limited success. Despite aforementioned concerns, upcoming 

piezoelectric damping experiments will be performed using a 

slip ring. In these tests, a 100 channel unit will be used to send 

signal into the rotor and also extract sensor information. Input 

signals will power fan blade specimen piezoelectric actuators. 

The true capability of the slip ring to facilitate active feedback 

control of rotating blade vibration will be assessed.

Telemetry is a non-contacting method of signal transfer and 

was selected as a signal transfer alternative and upgrade for 

the DSR. Commercially available telemetry devices are 

designed to only extract signals from the rotating components. 

Bi-directional communication was required to meet the 

requirements of DSR experiments. In order to control 

vibrations from the stationary frame, controllable power 

sources would be needed on the rotating side. A device with 

such requirements was not commercially available, so a new 

device was conceived of at GRC and a prototype constructed. 

Device Description

The wireless inductive power and telemetry device 

(WIPTD) was designed by the authors and the Mesa Systems 

Company as an alternative to slip rings for providing active

feedback control of blade vibrations and damping techniques.

There are two primary components of this device—a 

rotating component and a stationary one (see Fig. 1). The 

rotating component is attached to the end of the DSR AMB

rotor. The stationary structure is fixed to the rig’s lower 

bearing housing (Fig. 2). There is a gap of 0.5 mm between 

these two components during testing. The rotating part is

10 cm in diameter and 20 cm long. It weighs about 13 N. The 

stationary apparatus is made up of three circuit boards and 

weighs about 4.5 N. 

This device allows for bi-directional communication via 

capacitive coupling with the rotating system. The WIPTD 

contains rotating operational amplifiers which can provide 

commanded AC power to rotating actuators. Rotating 

electronics receive their power from a wireless inductive 

apparatus. This element is essentially a transformer with an 

input stage/primary coil composed of a pulse width modulator 

located in the stationary unit, and two secondary coils, located 

in the rotating unit. The primary coil is located flush with the 

top surface of the stationary unit directly in line with the 

secondary coils. The primary coil is powered by a 24 V

supply, which is then transformed in one secondary coil to
NASA/TM—2011-217093 3

provide 200 V dc, after conditioning, to drive rotating

operational amplifiers. The other secondary coil provides 5 V

dc to power other onboard electronics.

The device mode of operation is as follows; a vibration 

voltage signal from the piezoelectric sensor is transmitted 

through wires to the rotating unit which houses, among other 

supporting electronics, a driver or conditioning circuit and an 

A/D converter circuit. The signal from the A/D converter then 

passes to conducting strips, which are fashioned in the shape of 

concentric rings on the underside of the rotating unit. The 

stationary base unit also has concentric rings which are mirror 

images of the concentric rings positioned on the rotating unit. 

The concentric rings on both units, including the air gap, 

constitute a capacitive plate coupler. The conductive rings on 

each unit serve as sides of an air core capacitor. The sensor 

signal from the rotating unit is transmitted capacitively to the 

stationary base unit. Subsequently, this signal is converted from 

a digital to an analog signal by a D/A converter, which is 

located in the base unit. The signal is then passed to a microchip 

or, as in our case, a rapid-prototyping controller where it is 

processed into a vibration suppression signal. This suppression 

signal is then retransmitted, in a sequence inversed to that 

described above, through to an operational amplifier which 

actuates the piezoelectric patch on the test blade.

The block diagram in Figure 3 shows details of the WIPTD 

and vibration suppression system constructed for the 

demonstration described herein. The WIPTD has the capacity 

to control eight actuators and transmit eight sensor signals. 

However, only one actuator channel and one sensor channel 

are shown for simplicity.

Device Characterization

Figure 4 shows a plot of the transfer function between 

commanded voltage input pre-telemetry and power amplifier 

voltage output post-telemetry versus frequency on the rotating 

side. This figure shows that the magnitude of the output to a 

command input stays constant out to at least 2 kHz. The 

measured gain is 48.75, which is very close to the design goal 

of 50. An amplifier with a gain of 50 on the rotor allows for a 

voltage maximum of 250 V to be applied to an actuator patch.

Figure 5 shows the phase angle for this transfer function in 

a linear graph format. A linear curve fit provides an equation 

for the phase lag as a function of input signal frequency. Using 

this equation, the time delay due to signal transfer through 

telemetry and signal processing can be computed. The time 

delay is simply the ratio of the phase angle in radians to the 

frequency of the command signal in radians/sec. The time 

delay is consistent across the frequency range shown at

0.0015 sec, or 1.5 msec.

Figures 6 and 7 show similar results for the transfer 

function between a simulated sensor signal on the rotating side 

and a measured signal post-telemetry on the stationary side. 

Note that the gain is 1 and that there is no degradation in 

signal amplitude until 20 kHz. 20 kHz is a sufficient sensor 

signal bandwidth. Also note that the linear curve fit to the 

phase angle delay in Figure 7 is almost identical to that in 

Figure 5 for the amplified signal. The time delay for this 

signal is also 1.5 msec.
NASA/TM—2011-217093 4

When considering closed-loop control of fan blade 

vibrations, where the controller is physically located off the 

rotor, the combined time delay is 3 msec. This amount of 

delay would cause vibration control instability at the blade 

frequencies of interest—typically in the kHz range. If, 

however, the controller was resident in a DSP chip located on 

the rotor, this signal transfer delay would not be problematic.

Figure 8 shows the signal output received on the stationary 

side of the unit when a simulated 5 V sensor signal is input on 

the rotating side. Notice that the magnitude out is preserved; 

however, the signal shape is mildly augmented. In Figure 9, 

the sensor signal is 10 V. The output is saturating at about 7 V 

and the signal is severely affected by this saturation. This test 

shows that the hardware voltage limit from a sensor signal is 

±5 V. Voltages from piezoelectric patches used as sensors like

the one shown in Figure 10 can reach at least 50 V under
NASA/TM—2011-217093 5

typical test conditions. The prototype WIPTD cannot

accommodate this. A future model of this device would 

include circuitry to impose a voltage reduction so that the 

output voltage is in the 5 or 10 V range.

Experiment

The Dynamic Spin Test Facility at NASA Glenn Research 

Center was used to demonstrate the capability of the WIPTD.

The experimental setup is described in (Refs. 13 and 14). A 

vertical rotor suspended magnetically in a vacuum 

environment was used. The rotor has two clamped flat 

titanium plates bolted to the rotor hub. One of the plates has 

two piezoelectric patches both located in a high third bending 

strain region on either side of the plate (Fig. 10). The other 

plate is primarily for balance. The telemetry unit’s rotating 

system is attached at the bottom of the rotor. The stationary 

system is mounted to a cage structure which is mounted to the 

DSR’s lower bearing housing (see Figs. 1 and 2). The axial 

gap was 0.5 mm during operation. One patch was used as a 

sensor and the other as an actuator. The sensor patch was 

connected to a telemetry-out circuit. The actuator was attached 

to the amplifier circuit.

The rotor system was spun up to 565 rpm. This speed was 

the maximum out-of-tank speed achieved and was selected as 

the speed for the vacuum spin test. Since this was a prototype 

unit, speed was limited to circumvent potential damage. The 

WIPTD prototype was rated to 1500 rpm and at the time of 

writing had been spun to 1000 rpm. At speed, the radial 

AMB’s were used to prescribe a rotating sinusoidal excitation 

to the plates. The frequency and phase of this excitation with 

respect to the rotor’s once per rev signal were tuned to 

maximize the plate’s third bending vibration amplitude. The 

third bending frequency was determined and optimized by 

tuning the excitation in the region of the experimental value 

determined from a static test and the out-of-tank test.

Oscilloscope visual feedback was used in this manual tuning 

procedure. The phase of the excitation force, which is really 

the angle between the blade row and the rotating AMB 

excitation force (Ref. 14), was then tuned to maximize the 

response. Amplitude then was tuned to produce a clean 

sinusoidal plate response. 

The actuator patch was used to reduce the plate’s third

bending response. An open loop control scheme was used. A 

sinusoidal voltage with the same frequency of the AMB 

excitation was sent from the control computer through 

telemetry to the rotating power operational amplifier attached 

to the actuator. The amplitude and phase of this command 

were also tuned using the sensor patch signal as visual 

feedback to eliminate the vibration. The successful results of 

this test are shown in the next section. This test proved that the 

bi-directional telemetry unit worked. This was a 

demonstration of active fan blade vibration control under 

rotating conditions without using slip rings and without 

contact with the rotor.

Results

Results for the experiment described in the previous section 

are presented here. Figure 11 shows the power spectral density 

(PSD) of the voltage signal from the sensor patch signal while 

the rotor was spinning freely without excitation or control. 

Recall that both the sensor and actuator patches are located on 

opposite sides of the plate in a region of high strain (Fig. 10). 

A small 80 mV signal component is evident at the plates third

bending frequency of 669 Hz. The feedback control of the 

AMB system induces noise into the rotor system which can 

excite rotor and rotor hardware resonances on its own. Often, 

notch filters in the AMB controller are used to reduce or 

eliminate these responses (Ref. 14). The third bending 

resonance at 565 rpm is close to the first harmonic of the 

rotor’s first bending resonance. A notch for this rotor mode 

was not used. As a result, a small plate response occurred. 

Figures 12 and 13 show the sensor response when a 669 Hz

AMB excitation is applied to the rotor causing the 

instrumented plate to vibrate. The constant excitation 

amplitude evident in Figure 12 proves that the AMB excitation 

is indeed rotating with the rotor. The response frequency 

matches the excitation frequency. The PSD in Figure 13 

shows the increase in third bending signal component 

amplitude.
NASA/TM—2011-217093 6

Figures 14 and 15 show the plate response once the actuator 

control signal is manually tuned to suppress the plate response 

to AMB excitation. The frequency of the command was 

identical to the excitation frequency and the amplitude and 

phase were tuned to optimize (reduce) the response. Figure 14 

shows a small signal amplitude—virtually identical to the 

excitation-free data. A comparison between the PSDs in 

Figures 11 and 15 shows how effective this open loop 

technique was at suppressing the blade response.

Summary

A wireless bi-directional telemetry device which includes 

rotating amplifiers for powering rotating actuators was 

demonstrated in the DSR at NASA Glenn Research Center. 

Although this wireless concept in not entirely new (Ref. 17), it 

is possible that this is the first embodiment of the idea and the 

first demonstration thereof. A patent application was filed for 

the WIPTD and its potential use in suppressing 

turbomachinery blade vibrations. Some details and 

characteristics of the device were provided in this paper.

In the demonstration explained herein, a third bending plate 

vibration was suppressed using open loop control of a 

piezoelectric actuator patch glued to the surface of the plate 

while the plate was rotating at 565 rpm. A second 

piezoelectric patch was used as a sensor to help set the 

excitation and the actuation. Results show that the plate 

resonance was completely suppressed.

Concluding Remarks

Slip rings are used successfully in experiments. Telemetry has 

become popular and test rigs, especially at GRC, are being 

upgraded to include telemetry systems. Signals transmitted via 

radio telemetry are less noisy and these systems require less 

maintenance.
NASA/TM—2011-217093 7

The development of the WIPTD was not done solely to 

create a device which could replace a slip ring. It was 

developed keeping in mind the eventual application of active 

blade vibration suppression or damping using piezoelectric 

elements. A wireless device, which doesn’t require cooling, 

reduces the potential maintenance requirement of a contacting 

signal transfer component, is inherently less noisy and could

facilitate eventual application to ground-based and aeroderivative turbomachines. DeAnna discussed what it might 

take to implement telemetry in gas turbine engines in 

Reference 18. 

When considering the use of piezoelectrics for damping fan 

blade vibrations in aero-derivative engines, is it more feasible 

to consider adding slip rings or telemetry to a turbine rotor? 

Perhaps in the final adaptation of this damping technique, 

communication with the rotor would not be required—

eliminating the need for either. Each piezoelectric patch used 

for a blade would be connected to circuitry which rotated with 

the rotor. This circuitry would be designed to dissipate 

vibratory energy. The power for this system (if needed) could

be extracted via energy harvesting or received from a small 

induction ring. Perhaps an autonomous controller can be 

developed which can be downloaded to a DSP chip directly on 

the rotor. For health monitoring, communication with the rotor 

would be needed.

Future experiments in the DSR will include the testing of 

improved WIPTDs where the signal time delay is minimized. 

This will facilitate the testing of closed-loop feedback control 

systems. Metal and composite subscale blades that represent 

those from real aircraft engines will be modified. Piezoelectric 

elements will be incorporated in unique ways into their design 

and their ability to dampen or suppress vibrations will be 

determined.

References

1. El Aini, Y., deLaneuville, A., Stoner, A., and Capece, V., 

“High Cycle Fatigue of Turbomachinery Components—

Industry Perspective,” AIAA–1997–3365, 1997.

2. Kosmatka, J., “Experimental Spin Testing of Integrally 

Damped Composite Plates,” NASA/CR—1998-207058, 

1998.

3. Kosmatka, J.B., Appuhn, G., “Design and Fabrication of 

Integrally Damped Composite Fan Blades,” SPIE 

Conference on Passive Damping and Isolation, Newport 

Beach, CA, SPIE vol. 3672, March 1999.

4. Duffy, K., Bagley, R., Mehmed, O., “On a Self-Tuning 

Impact Vibration Damper for Rotating Turbomachinery,”

36th Joint Propulsion Conference, Huntsville, AL., AIAA 

200-3100, July 17–19, 2000.

5. Duffy, K. Brown, G., Bagley, R., “Self-Tuning Impact 

Damper for Rotating Blades,” U.S. Patent 6,827,551, 

December, 2004.

6. Duffy, K., Miller, R., Nguyen, Q., Fox, D., “Damping 

Coatings Research at NASA Glenn Research Center,”

Propulsion—Safety and Affordable Readiness (P-SAR) 

Conference, San Diego, CA, March 13–15, 2007.

7. Duffy, K.P., Padula, S.A., Scheiman, D.A., “Damping of 

High-Temperature Shape Memory Alloys,” Proceedings 

of SPIE Smart Structures and Materials and 

Nondestructive Evaluation and Health Monitoring, San 

Diego, CA, March 10–13 2008, vol. 6929-48, 2008.

8. Choi, B., Morrison, C., Duffy, K., “An Active Damping at 

Blade Resonances Using Piezoelectric Transducers,”

Proceedings of the Propulsion—Safety and Affordable 

Readiness (P-SAR) Conference, Myrtle Beach, SC, 

March 18–20, 2008.

9. Choi, B., Morrison, C., Min, J., “A Multi-Mode Blade 

Damping Control Using Shunted Piezoelectric 

Transducers With Active Feedback Structure,”

Proceedings of the Propulsion-Safety and Affordable 

Readiness (P-SAR) Conference, Jacksonville, FL, March 

24–26, 2009.

10. Duffy, K., Provenza, A., Trudell, J., Min, J., “Passively 

Shunted Piezoelectric Damping of Centrifugally Loaded 

Plates,” Proceeding of the 17th AIAA Adaptive Structures 

Conference, Palm Springs, CA, May 4–7, 2009. AIAA–

2009–2524.

11. Johnson, D., Mehmed, O., Brown, G.V., “Magnetic 

Excitation for Spin Vibration Testing,” Physics and 

Process Modeling (PPM) and Other Propulsion R&T, 

Volume 2; NASA-CP-10193, April, 1997.

12. Johnson, D., Brown, G.V., Mehmed, O., “A Magnetic 

Suspension and Excitation System for Spin Vibration 

Testing of Turbomachinery Blades,” 39th AIAA 

Structures, Structural Dynamics and Materials 

Conference, Long Beach, CA, April 20–23, 1998.

13. Morrison, C.R., Provenza, A.J., et al., “Fully Suspended, 

Five-axis, Three-magnetic-bearing Dynamic Spin Rig 

With Forced Excitation,” Experimental Mechanics,

vol. 45, no. 3, June 2005, pp. 226–237.

14. Provenza, A.J., Duffy, K.P., “Experimental Methodology 

for Determining Turbomachinery Blade Damping Using 

Magnetic Bearing Excitation and Non-Contacting Optical 

Measurements,” Proceeding of ASME Turbo Expo: 

Power for Land, Sea, and Air, June 14–18, 2010.

15. Fulton, M.V., Ormiston, R.A., “Hover Testing of a SmailScale Rotor with On-Blade Elevons,” Journal of the 

American Helicopter Society, April 2001, pp. 90–106.

16. Baz, A., Ro, J., “Vibration Control Of Rotating Beams 

with Active Constrained Layer Damping,” Smart 

Materials and Structures, vol. 10, 2001, pp. 112–120.

17. Khorrami, F., Das, K., “Integrated Micro-Strip Antenna 

Apparatus and a System Utilizing the Same for Wireless 

Communications for Sensing and Actuation Purposes,”

U.S. Patent #5,970,393 Oct. 19, 1999.

18. DeAnna, R.G., “Wireless Telemetry for Gas-Turbine 

Applications,” NASA/TM—2000-209815, ARL-MR-474, 

Mar, 2000.
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14. ABSTRACT

A novel wireless device which transfers supply power through induction to rotating operational amplifiers and transmits low voltage AC 

signals to and from a rotating body by way of radio telemetry has been successfully demonstrated in the NASA Glenn Research Center 

(GRC) Dynamic Spin Test Facility. In the demonstration described herein, a rotating operational amplifier provides controllable AC power 

to a piezoelectric patch epoxied to the surface of a rotating Ti plate. The amplitude and phase of the sinusoidal voltage command signal, 

transmitted wirelessly to the amplifier, was tuned to completely suppress the 3rd bending resonant vibration of the plate. The plate’s 3rd 

bending resonance was excited using rotating magnetic bearing excitation while it spun at slow speed in a vacuum chamber. A second patch 

on the opposite side of the plate was used as a sensor. This paper discusses the characteristics of this novel device, the details of a spin test, 

results from a preliminary demonstration, and future plans.

15. SUBJECT TERMS

Turbomachinery; Vibration; Piezoelectricity; Magnetic bearings; Excitation; Damping; Control 

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