Yasemin Vardar

Postdoctoral Researcher

Haptic Intelligence

Office: 5N14
70569 Stuttgart
Germany

+49 711 689-2002

yasemin._._.vardar

https://yaseminvardar.com/

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I am a post-doctoral researcher in the Haptic Intelligence Department at the MPI for Intelligent Systems. I earned my Ph.D. in Mechanical Engineering from Koç University (Istanbul, Turkey) in January of 2018. Before my Ph.D., I worked as a control engineer at TNO Additive Manufacturing Department in Eindhoven, the Netherlands. I received my M.Sc. degree in Systems and Control at the Eindhoven University of Technology in 2012, and my B.Sc degree in Mechatronics Engineering from Sabanci University (Istanbul, Turkey) in 2010.

My research focuses on designing haptic devices and applications by considering the capabilities of human haptic perception. My long-term goal is to build an intelligent system that enables delivering a wide variety of realistic and controllable haptic experiences on today’s electronic devices such as computers, smartphones, or tablet computers.

For detailed information, please see my personal website https://yaseminvardar.com/

Understanding Fingerpad Moisture and Friction

The interaction between a human finger-pad and a physical surface generates not only the tangential friction needed for gripping objects but also a wide variety of perceptual experiences. Finger-surface contact behavior is known to depend on the ...

Saekwang Nam Katherine J. Kuchenbecker David Gueorguiev Yasemin Vardar

Understanding the Physics Behind Electroadhesion

Researchers worldwide want to discover how to generate compelling tactile sensations on touchscreens to increase the usability of mobile devices and other interactive computer systems. One approach for generating such sensations is to control the friction force between the screen and the finger-pad of the ...

Yasemin Vardar Katherine J. Kuchenbecker Shao-Wen Wu Luzia Knoedler Saekwang Nam

Visual and Haptic Perception of Real Surfaces

Both vision and touch play important roles in human perception of real surfaces. Judging material properties based on only one modality may not give reliable results. For example, many of us have had the experience th...

Yasemin Vardar Elisa Loeffler Katherine J. Kuchenbecker Ben Richardson

15 results (View BibTeX file of all listed publications)

2020

Physical Variables Underlying Tactile Stickiness during Fingerpad Detachment

Nam, S., Vardar, Y., Gueorguiev, D., Kuchenbecker, K. J.

Frontiers in Neuroscience, 14(235):1-14, April 2020 (article)

Abstract

One may notice a relatively wide range of tactile sensations even when touching the same hard, flat surface in similar ways. Little is known about the reasons for this variability, so we decided to investigate how the perceptual intensity of light stickiness relates to the physical interaction between the skin and the surface. We conducted a psychophysical experiment in which nine participants actively pressed their finger on a flat glass plate with a normal force close to 1.5 N and detached it after a few seconds. A custom-designed apparatus recorded the contact force vector and the finger contact area during each interaction as well as pre- and post-trial finger moisture. After detaching their finger, participants judged the stickiness of the glass using a nine-point scale. We explored how sixteen physical variables derived from the recorded data correlate with each other and with the stickiness judgments of each participant. These analyses indicate that stickiness perception mainly depends on the pre-detachment pressing duration, the time taken for the finger to detach, and the impulse in the normal direction after the normal force changes sign; finger-surface adhesion seems to build with pressing time, causing a larger normal impulse during detachment and thus a more intense stickiness sensation. We additionally found a strong between-subjects correlation between maximum real contact area and peak pull-off force, as well as between finger moisture and impulse.

link (url) DOI Project Page [BibTex]

2020

hi Nam, S., Vardar, Y., Gueorguiev, D., Kuchenbecker, K. J. Physical Variables Underlying Tactile Stickiness during Fingerpad Detachment Frontiers in Neuroscience, 14(235):1-14, April 2020 (article)

link (url) DOI Project Page [BibTex]

Do Touch Gestures Affect How Electrovibration Feels?

Vardar, Y., Kuchenbecker, K. J.

Hands-on demonstration (1 page) presented at the IEEE Haptics Symposium, Washington, DC, USA, March 2020 (misc)

[BibTex]

hi Vardar, Y., Kuchenbecker, K. J. Do Touch Gestures Affect How Electrovibration Feels? Hands-on demonstration (1 page) presented at the IEEE Haptics Symposium, Washington, DC, USA, March 2020 (misc)

[BibTex]

2019

Effect of Remote Masking on Detection of Electrovibration

Jamalzadeh, M., Güçlü, B., Vardar, Y., Basdogan, C.

In Proceedings of the IEEE World Haptics Conference (WHC), pages: 229-234, Tokyo, Japan, July 2019 (inproceedings)

Abstract

Masking has been used to study human perception of tactile stimuli, including those created on haptic touch screens. Earlier studies have investigated the effect of in-site masking on tactile perception of electrovibration. In this study, we investigated whether it is possible to change detection threshold of electrovibration at fingertip of index finger via remote masking, i.e. by applying a (mechanical) vibrotactile stimulus on the proximal phalanx of the same finger. The masking stimuli were generated by a voice coil (Haptuator). For eight participants, we first measured the detection thresholds for electrovibration at the fingertip and for vibrotactile stimuli at the proximal phalanx. Then, the vibrations on the skin were measured at four different locations on the index finger of subjects to investigate how the mechanical masking stimulus propagated as the masking level was varied. Finally, electrovibration thresholds measured in the presence of vibrotactile masking stimuli. Our results show that vibrotactile masking stimuli generated sub-threshold vibrations around fingertip, and hence did not mechanically interfere with the electrovibration stimulus. However, there was a clear psychophysical masking effect due to central neural processes. Electrovibration absolute threshold increased approximately 0.19 dB for each dB increase in the masking level.

DOI [BibTex]

2019

hi Jamalzadeh, M., Güçlü, B., Vardar, Y., Basdogan, C. Effect of Remote Masking on Detection of Electrovibration In Proceedings of the IEEE World Haptics Conference (WHC), pages: 229-234, Tokyo, Japan, July 2019 (inproceedings)

DOI [BibTex]

Fingertip Interaction Metrics Correlate with Visual and Haptic Perception of Real Surfaces

Vardar, Y., Wallraven, C., Kuchenbecker, K. J.

In Proceedings of the IEEE World Haptics Conference (WHC), pages: 395-400, Tokyo, Japan, July 2019 (inproceedings)

Abstract

Both vision and touch contribute to the perception of real surfaces. Although there have been many studies on the individual contributions of each sense, it is still unclear how each modality’s information is processed and integrated. To fill this gap, we investigated the similarity of visual and haptic perceptual spaces, as well as how well they each correlate with fingertip interaction metrics. Twenty participants interacted with ten different surfaces from the Penn Haptic Texture Toolkit by either looking at or touching them and judged their similarity in pairs. By analyzing the resulting similarity ratings using multi-dimensional scaling (MDS), we found that surfaces are similarly organized within the three-dimensional perceptual spaces of both modalities. Also, between-participant correlations were significantly higher in the haptic condition. In a separate experiment, we obtained the contact forces and accelerations acting on one finger interacting with each surface in a controlled way. We analyzed the collected fingertip interaction data in both the time and frequency domains. Our results suggest that the three perceptual dimensions for each modality can be represented by roughness/smoothness, hardness/softness, and friction, and that these dimensions can be estimated by surface vibration power, tap spectral centroid, and kinetic friction coefficient, respectively.

DOI Project Page [BibTex]

hi Vardar, Y., Wallraven, C., Kuchenbecker, K. J. Fingertip Interaction Metrics Correlate with Visual and Haptic Perception of Real Surfaces In Proceedings of the IEEE World Haptics Conference (WHC), pages: 395-400, Tokyo, Japan, July 2019 (inproceedings)

DOI Project Page [BibTex]

A Novel Texture Rendering Approach for Electrostatic Displays

Fiedler, T., Vardar, Y.

In Proceedings of International Workshop on Haptic and Audio Interaction Design (HAID), Lille, France, March 2019 (inproceedings)

Abstract

Generating realistic texture feelings on tactile displays using data-driven methods has attracted a lot of interest in the last decade. However, the need for large data storages and transmission rates complicates the use of these methods for the future commercial displays. In this paper, we propose a new texture rendering approach which can compress the texture data signicantly for electrostatic displays. Using three sample surfaces, we first explain how to record, analyze and compress the texture data, and render them on a touchscreen. Then, through psychophysical experiments conducted with nineteen participants, we show that the textures can be reproduced by a signicantly less number of frequency components than the ones in the original signal without inducing perceptual degradation. Moreover, our results indicate that the possible degree of compression is affected by the surface properties.

Fiedler19-HAID-Electrostatic [BibTex]

hi Fiedler, T., Vardar, Y. A Novel Texture Rendering Approach for Electrostatic Displays In Proceedings of International Workshop on Haptic and Audio Interaction Design (HAID), Lille, France, March 2019 (inproceedings)

Fiedler19-HAID-Electrostatic [BibTex]

Tactile Roughness Perception of Virtual Gratings by Electrovibration

Isleyen, A., Vardar, Y., Basdogan, C.

IEEE Transactions on Haptics, 2019 (article) Accepted

[BibTex]

hi Isleyen, A., Vardar, Y., Basdogan, C. Tactile Roughness Perception of Virtual Gratings by Electrovibration IEEE Transactions on Haptics, 2019 (article) Accepted

[BibTex]

2018

Tactile perception by electrovibration

Vardar, Y.

Koc University, 2018 (phdthesis)

Abstract

One approach to generating realistic haptic feedback on touch screens is electrovibration. In this technique, the friction force is altered via electrostatic forces, which are generated by applying an alternating voltage signal to the conductive layer of a capacitive touchscreen. Although the technology for rendering haptic effects on touch surfaces using electrovibration is already in place, our knowledge of the perception mechanisms behind these effects is limited. This thesis aims to explore the mechanisms underlying haptic perception of electrovibration in two parts. In the first part, the effect of input signal properties on electrovibration perception is investigated. Our findings indicate that the perception of electrovibration stimuli depends on frequency-dependent electrical properties of human skin and human tactile sensitivity. When a voltage signal is applied to a touchscreen, it is filtered electrically by human finger and it generates electrostatic forces in the skin and mechanoreceptors. Depending on the spectral energy content of this electrostatic force signal, different psychophysical channels may be activated. The channel which mediates the detection is determined by the frequency component which has a higher energy than the sensory threshold at that frequency. In the second part, effect of masking on the electrovibration perception is investigated. We show that the detection thresholds are elevated as linear functions of masking levels for simultaneous and pedestal masking. The masking effectiveness is larger for pedestal masking compared to simultaneous masking. Moreover, our results suggest that sharpness perception depends on the local contrast between background and foreground stimuli, which varies as a function of masking amplitude and activation levels of frequency-dependent psychophysical channels.

Tactile perception by electrovibration [BibTex]

2018

hi Vardar, Y. Tactile perception by electrovibration Koc University, 2018 (phdthesis)

Tactile perception by electrovibration [BibTex]

Tactile Masking by Electrovibration

Vardar, Y., Güçlü, B., Basdogan, C.

IEEE Transactions on Haptics, 11(4):623-635, 2018 (article)

Abstract

Future touch screen applications will include multiple tactile stimuli displayed simultaneously or consecutively to single finger or multiple fingers. These applications should be designed by considering human tactile masking mechanism since it is known that presenting one stimulus may interfere with the perception of the other. In this study, we investigate the effect of masking on tactile perception of electrovibration displayed on touch screens. Through conducting psychophysical experiments with nine subjects, we measured the masked thresholds of sinusoidal electrovibration bursts (125 Hz) under two masking conditions: simultaneous and pedestal. The masking stimuli were noise bursts, applied at five different sensation levels varying from 2 to 22 dB SL, also presented by electrovibration. For each subject, the detection thresholds were elevated as linear functions of masking levels for both masking types. We observed that the masking effectiveness was larger with pedestal masking than simultaneous masking. Moreover, in order to investigate the effect of tactile masking on our haptic perception of edge sharpness, we compared the perceived sharpness of edges separating two textured regions displayed with and without various masking stimuli. Our results suggest that sharpness perception depends on the local contrast between background and foreground stimuli, which varies as a function of masking amplitude and activation levels of frequency-dependent psychophysical channels.

vardar_toh2018 DOI [BibTex]

hi Vardar, Y., Güçlü, B., Basdogan, C. Tactile Masking by Electrovibration IEEE Transactions on Haptics, 11(4):623-635, 2018 (article)

vardar_toh2018 DOI [BibTex]

2017

Enhancing Human-Computer Interaction via Electrovibration

Emgin, S. E., Sadia, B., Vardar, Y., Basdogan, C.

Demo in IEEE World Haptics, 2017 (misc)

Abstract

We present a compact tablet that displays electrostatic haptic feedback to the user. We track user?s finger position via an infrared frame and then display haptic feedback through a capacitive touch screen based on her/his position. In order to demonstrate practical utility of the proposed system, the following applications have been developed: (1) Online Shopping application allows users to be able to feel the cord density of two different fabrics. (2) Education application asks user to add two numbers by dragging one number onto another in order to match the sum. After selecting the first number, haptic feedback assists user to select the right pair. (3) Gaming/Entertainment application presents users a bike riding experience on three different road textures -smooth, bumpy, and sandy. (4) User Interface application in which users are asked to drag two visually identical folders. While dragging, users are able to differentiate the amount of data in each folder based on haptic resistance.

[BibTex]

2017

hi Emgin, S. E., Sadia, B., Vardar, Y., Basdogan, C. Enhancing Human-Computer Interaction via Electrovibration Demo in IEEE World Haptics, 2017 (misc)

[BibTex]

Roughness perception of virtual textures displayed by electrovibration on touch screens

Vardar, Y., Isleyen, A., Saleem, M. K., Basdogan, C.

In 2017 IEEE World Haptics Conference (WHC), pages: 263-268, 2017 (inproceedings)

Abstract

In this study, we have investigated the human roughness perception of periodical textures on an electrostatic display by conducting psychophysical experiments with 10 subjects. To generate virtual textures, we used low frequency unipolar pulse waves in different waveform (sinusoidal, square, saw-tooth, triangle), and spacing. We modulated these waves with a 3kHz high frequency sinusoidal carrier signal to minimize perceptional differences due to the electrical filtering of human finger and eliminate low-frequency distortions. The subjects were asked to rate 40 different macro textures on a Likert scale of 1-7. We also collected the normal and tangential forces acting on the fingers of subjects during the experiment. The results of our user study showed that subjects perceived the square wave as the roughest while they perceived the other waveforms equally rough. The perceived roughness followed an inverted U-shaped curve as a function of groove width, but the peak point shifted to the left compared to the results of the earlier studies. Moreover, we found that the roughness perception of subjects is best correlated with the rate of change of the contact forces rather than themselves.

vardar_whc2017 DOI [BibTex]

hi Vardar, Y., Isleyen, A., Saleem, M. K., Basdogan, C. Roughness perception of virtual textures displayed by electrovibration on touch screens In 2017 IEEE World Haptics Conference (WHC), pages: 263-268, 2017 (inproceedings)

vardar_whc2017 DOI [BibTex]

Reproduction of textures based on electrovibration

Fiedler, T., Vardar, Y., Strese, M., Steinbach, E., Basdogan, C.

Demo in IEEE World Haptics, 2017 (misc)

Abstract

This demonstration presents an approach to represent textures based on electovibration. We collect acceleration data which occurs while sliding a tool tip over a real texture surface. The prerecorded data was collected by a ADXL335 accelerometer, which is mounted on a FALCON device moving on the x-axis with a regulated velocity. In order to replicate the same acceleration with electrovibration, we found two problems. The frequency of one sine wave shifts to the double frequency. This effect originates from the electrostatic force between the finger pad and the tactile display as proposed by Kactmarek et Al. [1]. Taking the square root of the input signal corrects the effect. This was also earlier proposed by [1, 2, 3] However, if not only one but multiple sine waves are displayed interference occur and acceleration signals from real textures may not feel perceptually realistic. We propose to display only the dominant frequencies from a real texture signal. Peak frequencies are determined within the respect of the JND of 11 percent found by earlier literature. A new sine wave signal with the dominant frequencies is created. In the demo, we will let the attendees feel the differences between prerecorded and artificially created textures.

[BibTex]

hi Fiedler, T., Vardar, Y., Strese, M., Steinbach, E., Basdogan, C. Reproduction of textures based on electrovibration Demo in IEEE World Haptics, 2017 (misc)

[BibTex]

Effect of Waveform on Tactile Perception by Electrovibration Displayed on Touch Screens

Vardar, Y., Güçlü, B., Basdogan, C.

IEEE Transactions on Haptics, 10(4):488-499, 2017 (article)

Abstract

In this study, we investigated the effect of input voltage waveform on our haptic perception of electrovibration on touch screens. Through psychophysical experiments performed with eight subjects, we first measured the detection thresholds of electrovibration stimuli generated by sinusoidal and square voltages at various fundamental frequencies. We observed that the subjects were more sensitive to stimuli generated by square wave voltage than sinusoidal one for frequencies lower than 60 Hz. Using Matlab simulations, we showed that the sensation difference of waveforms in low fundamental frequencies occurred due to the frequency-dependent electrical properties of human skin and human tactile sensitivity. To validate our simulations, we conducted a second experiment with another group of eight subjects. We first actuated the touch screen at the threshold voltages estimated in the first experiment and then measured the contact force and acceleration acting on the index fingers of the subjects moving on the screen with a constant speed. We analyzed the collected data in the frequency domain using the human vibrotactile sensitivity curve. The results suggested that Pacinian channel was the primary psychophysical channel in the detection of the electrovibration stimuli caused by all the square-wave inputs tested in this study. We also observed that the measured force and acceleration data were affected by finger speed in a complex manner suggesting that it may also affect our haptic perception accordingly.

vardar_toh2017 DOI [BibTex]

hi Vardar, Y., Güçlü, B., Basdogan, C. Effect of Waveform on Tactile Perception by Electrovibration Displayed on Touch Screens IEEE Transactions on Haptics, 10(4):488-499, 2017 (article)

vardar_toh2017 DOI [BibTex]

2016

Effect of Waveform in Haptic Perception of Electrovibration on Touchscreens

Vardar, Y., Güçlü, B., Basdogan, C.

In Haptics: Perception, Devices, Control, and Applications, pages: 190-203, Springer International Publishing, Cham, 2016 (inproceedings)

Abstract

The perceived intensity of electrovibration can be altered by modulating the amplitude, frequency, and waveform of the input voltage signal applied to the conductive layer of a touchscreen. Even though the effect of the first two has been already investigated for sinusoidal signals, we are not aware of any detailed study investigating the effect of the waveform on our haptic perception in the domain of electrovibration. This paper investigates how input voltage waveform affects our haptic perception of electrovibration on touchscreens. We conducted absolute detection experiments using square wave and sinusoidal input signals at seven fundamental frequencies (15, 30, 60, 120, 240, 480 and 1920 Hz). Experimental results depicted the well-known U-shaped tactile sensitivity across frequencies. However, the sensory thresholds were lower for the square wave than the sinusoidal wave at fundamental frequencies less than 60 Hz while they were similar at higher frequencies. Using an equivalent circuit model of a finger-touchscreen system, we show that the sensation difference between the waveforms at low fundamental frequencies can be explained by frequency-dependent electrical properties of human skin and the differential sensitivity of mechanoreceptor channels to individual frequency components in the electrostatic force. As a matter of fact, when the electrostatic force waveforms are analyzed in the frequency domain based on human vibrotactile sensitivity data from the literature [15], the electrovibration stimuli caused by square-wave input signals at all the tested frequencies in this study are found to be detected by the Pacinian psychophysical channel.

vardar_eurohaptics_2016 [BibTex]

2016

hi Vardar, Y., Güçlü, B., Basdogan, C. Effect of Waveform in Haptic Perception of Electrovibration on Touchscreens In Haptics: Perception, Devices, Control, and Applications, pages: 190-203, Springer International Publishing, Cham, 2016 (inproceedings)

vardar_eurohaptics_2016 [BibTex]

2013

Self-tuning in Sliding Mode Control of High-Precision Motion Systems

Heertjes, M. F., Vardar, Y.

In IFAC Proceedings Volumes, 46(5):13 - 19, 2013, 6th IFAC Symposium on Mechatronic Systems (inproceedings)

Abstract

In high-precision motion systems, set-point tracking often comes with the problem of overshoot, hence poor settling behavior. To avoid overshoot, PD control (thus without using an integrator) is preferred over PID control. However, PD control gives rise to steady-state error in view of the constant disturbances acting on the system. To deal with both overshoot and steady-state error, a sliding mode controller with saturated integrator is studied. For large servo signals the controller is switched to PD mode as to constrain the integrator buffer and therefore the overshoot. For small servo signals the controller switches to PID mode as to avoid steady-state error. The tuning of the switching parameters will be done automatically with the aim to optimize the settling behavior. The sliding mode controller will be tested on a high-precision motion system.

heertjes_ifac2013 link (url) DOI [BibTex]

2013

hi Heertjes, M. F., Vardar, Y. Self-tuning in Sliding Mode Control of High-Precision Motion Systems In IFAC Proceedings Volumes, 46(5):13 - 19, 2013, 6th IFAC Symposium on Mechatronic Systems (inproceedings)

heertjes_ifac2013 link (url) DOI [BibTex]

2012

Estimation of MIMO Closed-Loop Poles using Transfer Function Data

Vardar, Y.

Eindhoven University of Technology, the Netherlands, 2012 (mastersthesis)

Abstract

For the development of high-tech systems such as lithographic positioning systems, throughput and accuracy are the main requirements. Nowadays, the trend to reach demanded accuracy and throughput levels is designing lightweight and consequently more flexible systems. To control these systems with a more effective and less conservative way, control design should go beyond the traditional rigid control and cope with the flexibilities that limit achievable bandwidth and performance. Therefore, conventional loop shaping methods are not sufficient to reach the performance criterions. Since obtaining an accurate parametric model is very complex and time-consuming for these high-tech systems, using well-developed model-based controller synthesis methods is also not a superior option. To achieve desired performance criterions, one solution can be implemented is reducing the gap between model-based and data-based control synthesis methods. In previous research, a method was developed to define the dynamic behavior of the system without a need for a parametric model. By this method transfer function data (TFD), which provides the information on the whole s-plane can be obtained from frequency response data (FRD) of the system. This innovation was a very important step to use data-based techniques for model-based controller synthesis methods. In this thesis firstly the standard technique to obtain TFD defined in [2] is extended. This standard technique to obtain TFD is not compatible with systems with pure integrators. To extend the methodology also for those systems, two techniques, which are altering the contour and filtering the system, are proposed. Then, the accuracy of TFD is investigated in detail. It is shown that the accuracy of TFD depends on the quality of FRD obtained and the computation techniques used to calculate TFD. Then, a technique which enables to determine the closed-loop poles of a MIMO system using TFD is discussed. The validity of the technique is proven with the help of complex function theory and calculus. Also, the factors that prevent determination of the closed-loop poles are discussed. In addition, it is observed that the accuracy of the closed-loop determination method depends on the quality of obtained TFD and the computation techniques. The proposed theory to obtain TFD and determination of closed-loop poles is validated with experiments conducted to a prototype lightweight system. Also, using experimental frequency response data of NXT-A7 test rig, the success of the proposed methodology is validated also for complex systems. Through these experimental results, it can be concluded that this new technique could be very advantageous in terms of ease of use and accuracy to determine the closed-loop poles of a MIMO lightly damped system.

[BibTex]

2012

hi Vardar, Y. Estimation of MIMO Closed-Loop Poles using Transfer Function Data Eindhoven University of Technology, the Netherlands, 2012 (mastersthesis)

[BibTex]

Yasemin Vardar

Understanding Fingerpad Moisture and Friction

Understanding the Physics Behind Electroadhesion

Visual and Haptic Perception of Real Surfaces

2020

Physical Variables Underlying Tactile Stickiness during Fingerpad Detachment

2020

Do Touch Gestures Affect How Electrovibration Feels?

2019

Effect of Remote Masking on Detection of Electrovibration

2019

Fingertip Interaction Metrics Correlate with Visual and Haptic Perception of Real Surfaces

A Novel Texture Rendering Approach for Electrostatic Displays

Tactile Roughness Perception of Virtual Gratings by Electrovibration

2018

Tactile perception by electrovibration

2018

Tactile Masking by Electrovibration

2017

Enhancing Human-Computer Interaction via Electrovibration

2017

Roughness perception of virtual textures displayed by electrovibration on touch screens

Reproduction of textures based on electrovibration

Effect of Waveform on Tactile Perception by Electrovibration Displayed on Touch Screens

2016

Effect of Waveform in Haptic Perception of Electrovibration on Touchscreens

2016

2013

Self-tuning in Sliding Mode Control of High-Precision Motion Systems

2013

2012

Estimation of MIMO Closed-Loop Poles using Transfer Function Data

2012

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