Smart ice detection systems based on resonant piezoelectric transducers

ss,SgRs ACTUATORS

A ELS EVI ER Sensors and Actuators A 69 (1998) 243-250 PI-IYSlCAt.

Smart ice detection systems based on resonant piezoelectric transducers

Shuvo Roy *, Alain Izad, Russell G. DeAnna t, Mehran Mehregany Microfabrication Laboratory, Department of Electrical Engineering and Applied Physics, Case Western Reserve University, Cleveland, OH 44106, USA

Received 11 November 1997; received in revised form 13 February 1998; accepted t6 February 1998

Abstract

An ice detection system consisting of a resonant piezoelectric sensing-element and microprocessor control has been developed to automatically and distinctly sense ice and water films up to 0.5 mm thick. Accretion of ice and/or water on the sensor surface modifies the effective mass and/or stiffness of the vibrating transducer; these variations are sensed by measuring the changes in transducer resonant frequency. In case of ice films, resonant frequency of the transducer increases steadily from 14 kHz for a 0.06-mm-thick layer to 28 kHz when the ice film is 0.45 mm thick. In contrast, transducer resonant frequency decreases slightly from 10 kHz for a 0.06-ram-thick layer of water to 9.5 kHz for a 0.45-rnm-thick film. Repeatability experiments revealed test-to-test variations of 3.8 and 0.7% for ice and water films, respectively. Thermal cycling and stability tests showed that the dry transducer resonant frequency was 10.5 + 0.1 kHz at 25°C, over a 220 h period. A portable, low-power, microprocessor-controlled electronic circuit has been designed and implemented to automate the resonant frequency measurement and determine the thickness of ice/water present on the transducer surface. © 1998 Elsevier Science S.A. All rights reserved.

Ke>~,ords: Ice sensor; Ice detection; Piezoelectric resonator; Smart system; Resonant sensor

1. Introduct ion

Aircraft ice detection systems have received a great deal of attention because of their importance in flight safety. In- flight icing is caused by metastable, super-cooled water droplets in clouds, which are in a metastable condition [ 1 ]. Although the temperatures normally associated with icing range from - 4 0 to 0°C, aircraft icing most often occurs between - 10 and 0°C [2,3]. When the aircraft encounters these droplets, they may either suddenly change phase from liquid to solid upon impact, or they may impact and flow back as a thin film of water, collect into droplets due to surface tension, and then freeze [4]. The buildup of ice on the leading edges of fixed wings causes an increase in drag and a decrease in lift of the aircraft [ 5 ]. Ice formation can also result in the inability to deploy and retract moveable surfaces, such as slats and flaps. Furthermore, dislodged ice can damage the aircraft skin, antennas or other instrumentation, and cause catastrophic engine failure if ingested. All of these potentially severe problems have led to the need for reliable and robust sensors for the detection of the onset of icing.

Mechanically resonant structures are attractive as transducing elements in sensor systems due to their inherently

* Corresponding author. Tel.: + 1-216-368-3051; fax: + 1-216-368-2668. Visiting Scholar, Army Research Laboratories, NASA Lewis Research

Center, Cleveland, OH 44135, USA.

high sensitivities to small variations in applied loads. Fur- thermore, spurious drifts in the resonant frequency can be canceled by monitoring differences in measured resonant frequencies of matched structures. Ice detection systems based on resonant sensors have been implemented previously [4,6]. In the commercially available Rosemount Aerospace Ice Detection System, accretion of ice on a cylindrical probe leads to a decrease in the measured resonant frequency due to the increase in effective mass of the resonator [ 6]. In such mass-loaded resonant ice detection sensors, variations in probe design and placement are usually restricted in order to favor ice accretion and minimize resonant frequency shifts due to accumulation of water and other fluids. Furthermore, the acceptable probe geometries and orientations may adversely affect the local airflow during aircraft operation. In contrast, a miniature flush-mounted sensor system would be particularly attractive for ice detection.

This paper reports on smart ice detection systems using thin, disc-type, resonant piezoelectric transducers as the sensing elements which are operated by microprocessor-controlled electronic circuitry. A typical ice detection system is operated with the transducer in its stiffness-dominant mode so that resonant frequency varies with effective stiffness, and therefore, enables distinction between the presence of ice and water films. The microprocessor is programmed to measure transducer resonant frequency and automatically determine

0924-4247/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved. PIIS0924-4247(98)00101-0

244 S. Roy et at./Sensors and Actuators A 69 (1998) 243-250

presence and thickness of any ice accretion. The relatively small transducer geometry and portable implementation of the controlling electronic circuitry suggest potential appli- cation as a flush-mounted or airfoil-embedded ice detection sensing system for aircraft.

This paper discusses design and testing issues in the development of smart ice detection systems. First, a possible resonator configuration is selected and quantitatively analyzed to determine operating behavior. Based on these results, a suitable piezoelectric component is experimentally calibrated for ice detection. Experiments are also performed to investigate the effects of thermal cycling and age on transducer operation. Next, a portable, low-power, microprocessor- based, electronic system for the automatic determination of ice accretion is designed and implemented on a printed circuit board. Finally, the smart ice detection system is tested under icing conditions to verify accurate operation.

D T I

I

. ,.0.cP,.,o. t 1

Transducer Lead - - ~ ,

(a) Co) Fig. 1. Schematic view of a piezoelectric transducer consisting of a piezoceramic disc bonded to a tin-plated iron plate: (a) bottom-view; and (b) lateral view. The sensing surface is the right-facing side of the iron plate.

2. Theoret ical considerat ions

A suitable piezoelectric transducer for a potential flush- mounted or embedded ice detection system in aircraft should be relatively small, lightweight, and the transducer geometry and orientation should only minimally affect the local airflow. However, the sensing surface should be large enough for ice accretion to mechanically load the transducer and modify its resonance characteristics.

A possible transducing element configuration consists of a thin metallic plate, of diameter D and total thickness T, bonded to a piezoceramic disc as shown in Fig. 1. When a voltage, V, is applied across electrodes, the piezoceramic distorts inducing lateral forces at the overlying plate/piezoceramic interface. Consequently, the metallic plate deforms through curvature. The transducer can be forced into resonance, characterized by maximum vibration amplitude, by applying a sinusoidal signal at the natural frequency of the transducer. A typical piezoelectric resonator can be modeled using the equivalent lumped electrical network shown in Fig. 2 [7]. In this equivalent network, the circuit elements Lr, C~, and R~ represent parameters associated with the piezoelectric transducer, whereas Co represents the parasitic shunt capacitance of the resonator due to packaging. The inductance Lr is associated with the mass of the transducer, and the capacitance C~ is associated with the stiffness of the transducer. Finally, the resistance Rr is determined by the loss processes associated with transducer vibration,

If the driving electrical signal is not near the natural frequency of the transducer, the piezoelectric component behaves as a parallel plate capacitor with capacitance given by:

k~oA Co = ( I )

d

where A is the electrode area, d is the component thickness, eo is the permittivity of free space, and k is the relative di-

Co

Lr Cr Rr Fig. 2. Equivalent lumped electrical network of a piezoelectric resona[er. The capacitance Co represents the parasitic shunt capacitance due to packaging.

electric constant of the piezoelectric material. The impedance of the nonresonating transducer is then described by:

Zo= j (2) o)Co

where ~o is the angular frequency of the driving signal. When the driving electrical signal is near the resonant

frequency of the transducer, the characteristic series combination impedance may be expressed as:

[ 11 Zr=R~+j wL~- (3) wC~

The equivalent transducer impedance of the total parallel network is determined by calculating the parallel combination of Zo and Z~, which may be called Zp. At resonance, Zp is purely resistive, and this condition is satisfied for:

w=2~-f (4)

= ~Cr+2LrC-~o 2LrCo 2LZJ

with:

>> R r

2L7Co L3rCr (5 )

The resonant frequency,fr, of maximum vibration amplitude

S. Roy et al. /Sensors and Actuators A 59 (1998) 243-250 245

is given by the series resonance condition (obtained using the minus sign above):

Using equivalent mechanical analogues [ 8], this resonant frequency, fr, can be expressed as a function of the mass, m, and stiffness, k, of the transducer system according to the relation:

l ~ n f~= ~--£~ (7)

Consequently, the resonant frequency will tend to increase with greater net stiffness, while an increase in the resonating mass will tend to decrease the resonant frequency of the transducer. In case of water films and/or other fluids on the transducer surface, the effective stiffness increase is negligible and, accordingly, the transducer resonant frequency should decrease due to mass loading.

Now, consider an ice film of thickness t, formed on the transducer surface exposed to the ambient. Assuming cylindrical geometry, the effective transducer mass, m, and stiffness, k, can be expressed as [9]:

m = m p + m i = m p + C l t (8)

k = k p + k i = k p + C 2 t n (9)

where mp and kp represent the transducer plate mass and stiffness, respectively, m~ and ki represent the ice film mass and stiffness, respectively, and CI, C2, and n (typically greater than 2) are constants defined by the geometry of the system. The rate of change of resonant frequency with increasing ice film thickness, given by:

= ok aA am - - - - + - - - - (10) dt Ok at am Ot

can be obtained by substituting Eqs. (8) and (9) in Eq. (10) to give:

df~dt qrfr[ nC2tn-12 k ~-~1 (11)

This equation has a frequency minimum,frmin, for an ice film thickness to, expressed by:

1 1/nC2tn-I

Between no ice and an ice film of thickness to, the resonant frequency will decrease; above to, the resonant frequency increases.

The above analysis suggests that the piezoelectric transducer could be used to distinctly sense ice and water films. As mentioned previously, accumulation of water on the transducer surface should lead to a decrease in resonant frequency from its nominal value, fo. In case of ice films greater than tc, the transducer becomes stiffness-dominant and the reso-

nant frequency increases from frmin with growing film thickness.

3. Transducer characterization

A commercially available ceramic element buzzer (Pan- ansonic EFB-SlOD42A16) was chosen as the piezoelectric resonator for the ice detection system. This 2-terminal, exter- nal drive type transducer is approximately 0.4 mm thick (T) and consists of a 15-mm-diameter (D) tin-plated iron disc bonded to a piezoelectric ceramic plate;

Prior to testing, the accretion surface of the transducer was cleaned with detergent to remove any residual oils and con- taminants. Fig. 3 presents the experimental setup used to characterize the piezoelectric transducer. First, the transducer is placed in a thermally isolated, temperature-controlledcool- ing chamber. Using a micropipette, a fixed volume of deion- ized (DI) water is carefully deposited on the metallic plate of the transducer at 25°C. For icing experiments, the freezer is switched on to cool and freeze the water droplet down to - 10°C. All characterization tests for the dry and water-covered transducers are carried out at 25°C. Also, thickness of the ice and/or water films are estimated from a knowledge of the droplet volume and transducer accretion surface area, assuming cylindrical geometry. Next, a function generator is connected to the input lead of the transducer, while the output lead is connected to electrical ground through a 47 [1 resistor, R. The frequency output of the function generator is adjusted to deliver a 5 Vpp sinusoidal signal. Finally, a multiple channel digital oscilloscope is used to monitor both transducer input signal and the voltage drop across R.

Fig. 4 shows the voltage drop, Vout, across the resistor R as a function of the driving frequency for the dry transducer at 25°C. The series resonance condition, satisfied at the transducer natural frequency as described by Eq. (4), occurs at 10.5 kHz. Consequently, the impedance of the transducer is a minimum and, correspondingly, Vout is a local maximum with a value of 516 inV. The 2nd harmonic response is also observed at 21.0 kHz. The transition from resonator to capacitor behavior is clearly evident for driving frequencies greater than 25.0 kHz. At these frequencies, the impedance of the

Function Generator

I I I

Transducer

®

Cooling Chamber 2 R

Oscilloscope ] r -~ i F O ]

©@ r ~ / D D E l ~ r - - ~ D r l D

CH 1 CH 2

Fig. 3. Experimental setup used to characterize the piezoelectric transducer for the ice detection system.

246 S. Roy et at. /Sensors and Actuators A 69 (1998) 243-250

7 0 0

600

500

{ 4oo

3oo

2 0 0

lOO

0

5 . 0 15 ,0 2 5 . 0 3 5 , 0 4 5 . 0 5 5 . 0 6 5 . 0

F r e q u e n c y ( k H z )

Fig. 4. Graph of voltage drop across R as a function of driving frequency for the dry transducer at 25°C.

nonresonant transducer decreases with increasing driving signal frequency according to Eq. (2), leading to increasing current through R. Accordingly, the value of Vou~ reaches 519 mV at a driving signal frequency of 52.5 kHz, and continues to increase even further with greater drive signal frequency.

Fig. 5 shows resonator-behavior graphs of normalized Vo~ vs. driving frequency under different conditions, including: the dry transducer at 25°C; the ice/water-free transducer at - IO°C; the transducer covered with a 0.50-mm-thick water film at 25°C; and finally, the transducer covered with a 0.50- mm-thick ice film at -10°C. For all these conditions, the transducer exhibits similarly sharp responses to changes in the driving signal frequency; therefore, the determination of transducer resonant frequency based on local maxima is always possible. The resonant frequency of the ice/water- free transducer varies slightly with decreasing temperature, increasing to 10.7 kHz at - 10°C. By linear interpolation, the

temperature coefficient (TC) value of transducer resonant frequency is determined to be approximately 0.006 kHz/°C. Consequently, the temperature-induced shift in transducer resonant frequency from 25 to -40°C should be less than 0.4 kHz. The presence of a 0.50-ram-thick water film on the accretion surface decreases the resonant frequency to 9.4 kHz due to the mass-loading effect. In contrast, with an ice film, 0.50 mm thick, the transducer operates in the stiffness-dQm- inant mode, resonating at 27.8 kHz.

The transducer was calibrated by depositing ice and/or water films of varying thickness and determining the resulting transducer resonant frequency. In order to investigate experimental reproducibility, measurements were repeated at least six times for a given ice/water film thickness. The test data are statistically fitted to a linear equation as shown in Fig. 6, suggesting that the thickness for minimum resonant frequency, to, is certainly tess than 0.06 mm. The mean resonant frequency increases linearly from 14.1 to 27.7 kHz for ice films ranging from 0.06 to 0.45 mm in thickness, respectively. In contrast, the average transducer resonant frequency decreases linearly from 10.1 kHz for a 0.06-mm-thick layer of water to 9.5 kHz for a 0.45-mm-thick film. The data reveals test-to-test variations of 3.8 and 0.7% for ice and water films, respectively. Although the expected ice thickness in actual flight situations can be significantly greater, the performance of the transducer demonstrates its suitability for detection of the onset of icing.

The stability of the piezoelectric ceramic was investigated by subjecting the transducer to a series of random temperature cycling tests between 25 and - 10°C. Resonant frequency measurements were performed periodically over a 220 h period and included more than 30 million resonating cycles. As shown in Fig. 7, the nominal resonant frequency of the ice/water-free transducer remained 10.5 + 0.1 kHz at 25°C.

I00

90

80

7O

6 0

50

40

Z 3O

20

10

0 5.0 I0.0

i * Dry ~ ' [ - ~ - - Cold I---A- Water

II

I x

/ 4 f

J I

]

; x

t i i t r T t i i i t i v 1 T

15.0 20.0 25.0 30.0

Frequency (kHz)

Fig. 5. Normalized voltage drop as a function of driving frequency under different conditions: the dry transducer at 25°C; the ice/water-free transducer at - 10°C; the transducer covered with a 0.50-ram-thick water film at 25°C; and finally, the transducer covered with a 0.50-mm-thick ice f i lm at - 10°C, .

S. Roy et al. / Sensors and Actuawrs A 69 (1998) 243-250 247

~ a

30.0

25.0

20.0

15.0

10.0

~ Ice

J [ , W a t e r

J - - - Ice Fit [ . . . . . . Water Fit

y = -1.3075x + 10.079

5.0 0.00 0.05 0.I0 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Film Thickness (ram)

Fig. 6. Calibration graph of resonant frequency vs. ice/water film thickness.

i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i i i r i i r i r i i i i t i i i 1

0.50

I I .0

10.9

10.8

10.7

lO.6

io.5

'~ 10.4

~a 10.3

10.2

I0.1

1 0 0 . t t t i t t r f i ~ t t t i i i i t i i i r i r

0 50 ?tO0 150 200 250

Time (hrs)

Fig. 7. Variation of dry-transducer resonant frequency during a series of random temperature cycling tests ranging between 25°C and - 10°C.

4. Electronic circuit implementation

The determination of transducer resonant frequency should be made accurately and quickly for applicability in aerospace ice detection systems. Fig. 8 presents the block diagram of an electronic circuit to automatically determine the transducer resonant frequency and compute the thickness of any overlying ice/water film. The potential of this 'smart' circuit in an ice detection system is based on its microprocessor- controlled operation which is described next.

Through a digital-to-analog converter (DAC), the microprocessor directs a voltage-controlled oscillator (VCO) to drive the piezoelectric transducer across a frequency range from 31.1 kHz down to 6.5 kHz in 0.1 kHz steps. At each

frequency step, the impedance of the transducer is indirectly measured by sensing the voltage drop, Vout, across R. This voltage drop is transmitted to the microprocessor after con- version to a relative digital value using an analog-to-digital converter (ADC). The microprocessor is programmed to track transducer driving frequencies for which Vout is a maximum and, at each of these frequencies, the slope, dVout /df ,

is computed. At the resonant frequency, transducer impedance is a minimum and, consequently, Vout is a maximum and I dVo~t/dfI is numerically a minimum. If the determined resonant frequency is less than 10.5 kHz or greater than 14.0 kHz, the microprocessor algorithm computes the water and ice film thickness from the respective linear-regression-fit line equations shown in Fig. 6. A RS232 serial interface is

248 S. Roy et al. / Sensors and Actuators A 69 (1998) 243-250

To P C

t

}

Fig. 8. Block diagram of smart circuit to automatically determine the transducer resonant frequency and compute the thickness of any overlying ice/ water film.

also incorporated into the system to facilitate connection to a personal computer (PC) for visual display and/or comple- mentary data analysis.

In order to enhance portability of the ice detection system, the electronic circuit is implemented as a double-sided printed circuit board using commercially available, low-power components, and is shown in Fig. 9. The system operates on a 9 V battery with a nominal power consumption of less than 200 mW.

Finally, the smart electronic circuit is tested on the same transducer used in the characterization experiments. The transducer is placed inside the cooling chamber and connected to the microprocessor-controlled electronic circuit which is located outside. A graph of actual ice/water film thickness vs. microprocessor-determined film thickness,

shown in Fig. 10, indeed verifies the feasibility of the smart ice detection system.

5. Conclusions

A portable, low-power, smart ice detection system based on resonant piezoelectric transducers has been developed using commercially available components. The piezoelectric transducers have been suitably characterized for calibration of ice film thickness with transducer resonant frequencies. A microprocessor-controlled electronic circuit was designed and implemented to automate the resonant frequency measurement, and distinctly determine the presence and thickness of the ice / water film on the transducer surface. The formation of ice leads to an increase, while the presence of water leads to a decrease, in the measured transducer resonant frequency from its nominal ice/water-free value. The effect of the temperature change during ice formation on the measured transducer resonant frequency is negligible. For ice films, 0.06- 0.45 mm thick, the resonant frequency increases steadily from 14.1 to 27.7 kHz, respectively. In contrast, the transducer resonant frequency decreases slightly from 10.1 kHz for a 0.06-mm-thick layer of water to 9.4 kHz for a 0.50-ram-thick film. Although the expected ice thickness in actual flight situations can be significantly greater, the performance of the transducer demonstrates its suitability for detection of the onset of icing.

Acknowledgements

The authors would like to thank Dr. Wen H. Ko of Case Western Reserve University for valuable technical discus- sions. This work was supported by the Army Research Office

~ , . , • o l I

Fig. 9. Photograph of portable ice detection system.

S. Roy et al. / Sensors and Actuators A 69 (1998) 243-250 249

0.50

0.45

0.40

0.35

~ 0.30

t~ 0.25

0.20

0.15

0.I0

0.05

0.00 . . . . ' . . . . , , , , , t , , , , T r , . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.00 0.05 0.I0 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Actual Film Thickness (ram)

Fig. 10. Verification graph showing actual ice film thickness vs. microprocessor-determined film thickness.

under a Multi-Disciplinary University Research Initiative, Contract No. DAAH04-95-10097.

References

[ I] B. Stankov, A. Bedard, Jr., Remote sensing observations of winter aircraft icing conditions: a case study, J. Aircraft 31, 79-89.

[2] R.G. DeAnna, M. Mehregany, S. Roy, Microfabricated ice-detection sensor, Proceedings of the Conf. Smart Struct. and MEMS, SPIE Syrup. on Smart Struct. and Mater., San Diego, CA, USA, March 1997.

[3] D.J. Moore, D.P. Jensen, An ice detection and control system for fixed and rotary wing aircraft, Proceedings of National Annual Conference on Environmental Effects on Aircraft and Propulsion Systems, Bor- dentown, NJ, USA, October 1968.

[4] A. Heinrich et al., Aircraft Icing Handbook, FAA Technical Center Publication, Atlantic City, NJ.

[5] R. Ranaudo, J. Batterson, A. Reehorst, T. Bond, T. O'Mara, Effects of horizontal tail ice on longitudinal aerodynamic derivatives, J. Air- craft 28, I93-199.

[6] R. Freely, Enhancing aircraft flight safety with primary ice detection sensor, Sensors (June) (1994) 28-30.

[7] J. Whitaker, Electronic Engineers Handbook, Technical Press, Bea- verton, OR.

[8] H.F. Olson, Elements of Acoustical Engineering, D. Van Nostrand, New York, NY.

[9] J.M. Gere, S.P. Timoshenko, Mechanics of Materials, PWS-Kent, Boston, MA.

microelectromechanical systems (MEMS) for harsh appli- cation environments. He received his BS in Physics, Mathe- matics, and Computer Science from Mount Union College in 1992, and his MS in Electrical Engineering from Case West- ern Reserve University in 1995. Mr. Roy has been listed in Who's Who Among Students in American Universities and Colleges and the National Dean's List. He is a member of Sigma Pi Sigma, Pi Mu Epsilon, and Blue Key National Honor fraternities.

Alain Izad has been a Principal Researcher in MEMS group of the Department of Electrical Engineering and Applied Physics at Case Western Reserve University (CWRU). His research interests include sensor/actuator interfacing and their applications in system design. He is currently develop- ing electronic interfaces for miniature sensor systems at Advanced MicroMachines (Cleveland, OH, USA). Before joining CWRU, he worked in technical management on pro- jects relating to IC design for radio-frequency transponders, telemetry for geological applications, and sensor interfacing/ instrumentation for various European companies. He received his PhD in Electrical Engineering from Orsay Uni- versity in 1982, his MS from Ecole Sup~rieure d'Electricit~ in 1980, both in Pads, France, and his BS in E.E. from Shiraz University in 1978.

Biographies

Shuvo Roy is a Research Assistant in the Department of Elec- trical Engineering and Applied Physics at Case Western Reserve University. His research interests include the design, fabrication, packaging, and performance characterization of

Russell G. DeAnna received a BS degree in Mechanical Engi- neering from Ohio State University in 1982, a MS degree in 1985 from the University of California, Berkeley, and a PhD in Mechanical and Aerospace Engineering in 1993 from Case Western Reserve University. He worked at General Electric Nuclear Energy Business (San Jose, CA) in reactor safety analysis before joining NASA Lewis in 1985. Since his arri-

250 S, Roy et al. t Sensors and Actuators A 69 (1998) 243-250

val at NASA Lewis, he has been employed by the Vehicle Technology Center of the Army Research Laboratory (ARL). Dr. DeAnna is a recognized expert in turbomachinery components and has done both empirical testing and analytical modeling of turbomachinery components. He is also an expert on research sensors and instrumentation for the high temperature, harsh environment of the gas-turbine engines. Specifically, he has been active in the development of microfabricated ice-detection, heat flux, pressure, and strain sensors. Since 1995, he has been a Senior Research Associate with the MEMS group in the Electrical Engineering and Applied Physics department of Case Western Reserve University.

M e h r a n M e h r e g a n y received his B S in Electrical Engineering from the University of Missouri in 1984, and his MS and PhD in Electrical Engineering from Massachusetts Institute of Technology in 1986 and 1990, respectively. From 1986 to 1990, he was a consultant to the Robotic Systems Research Department at AT&T Belt Laboratories, where he was a key contributor to groundbreaking research in microelectromechanical systems (MEMS). In 1990, he joined the Depart-

ment of Electrical Engineering and Applied Physics at Case Western Reserve University as an Assistant Professor. Fie was awarded the Nord Assistant Professorship in 1991, was promoted to Associate Professor with tenure in July 1994, and was promoted to Full Professor in July 1997. He was awarded the George S. Dively Professor of Engineering Endowed Chair in January 1998. He has been serving as the Director of the Microfabrication Laboratory at CWRU since July 1995. Prof. Mehregany is "known nationally and inter- nationally for his research in the area of MEMS, and his work has been widely covered by domestic and foreign media. He has over 130 publications describing his work, holds a number of U.S. patents, and is recipient of a number of awards/ honors. He served as the Editor-in-Chief of the Journal of Micromechanics and Microengineering from January 1996 to December 1997, and is Assistant-to-the-President of the Transducers Research Foundation. His research interests include silicon and silicon carbide MEMS and integrated circuit (IC) technologies, micromachining and microfabrication technologies, materials and modeling issues related to MEMS and IC technologies, and MEMS packaging.

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Smart ice detection systems based on resonant piezoelectric transducers