In Memory Of Seviğ Ayter




Ankara Science High School [Ankara Fen Lisesi]: Class of 1969

Turkish Military: 1983-1985

Middle East Technical University: 1969-1976

Middle East Technical University: 1985-1986

      BS - Electrical Engineering

      Electrical Engineering department

      MS - Electrical Engineering

Schlumberger Doll Research: 1986-1988

Stanford University: 1976-1983

      Geoacoustics department

      PhD - Electrical Engineering

Acuson/Siemens: 1988-2003

      Acoustics/transducer development department




There’s no doubt that Seviğ was a major reason for Acuson’s success. Amin made a steal getting him from Schlumberger in 1988. To that point, Amin was heading up the small transducer engineering group. Phased array transducer design was in its infancy and simulation tools were rudimentary. Amin, Worth, Umit or Jack could elaborate on this, but I understand that Seviğ’s first task was to solve a lateral mode coupling problem on the S3194 card probe, which he did successfully.

He spent the next 2 years developing and optimizing the Matlab-based transducer simulation that we still use today (TLM). He made a key modification to the KLM transmission line model in literature to account for frequency-dependent waveguide velocity and relied on 2-port network analysis to handle electrical components. He developed the measurement capabilities and analysis routines for piezoelectrics and for material acoustic properties. He oversaw development of an extensive database of materials. In the mid 1990’s he managed and worked with Sam Howard as he modified the TLM model to allow modeling of bullet or Hanafy lens components by segmenting the element into small staircase elements, calculating the surface particle velocity and receive current for each segment and summing. The type of agreement we have been able to achieve between the model and measurements is remarkable. For years, Acuson’s transducers were regarded as the ones to beat and Seviğ’s contributions are a big reason.

By my count, he was directly responsible for design or managed the design of more than 35 transducers, transducers that are used every day around the world to improve lives.  These include: 

        4C1, 6C2, 8C4 (urethane lens), C3, C5, C7, 15L8 (ran project), 15L8w, 13L5 (first 3ML), L5, L7 (still in high demand), L7T, L538,

        L558, L582, 4V1c (multi-layer), 10V4, 8V3c (head tuning), 7V3c, 5V2c, 3v2c (composite), S7146, S228, S2194 (multi-layer),

        4V1, 4V2c (first bullet), S328, S519, AcuNav (ICE), V5m (TEE), V7b, V510b, V705b, I7505, I7146, ER7B

Over several years in the late 1990’s he led the development team for the premier high frequency linear arrays in the industry, the 15L8w and 15L8 or Saturn.

Seviğ was an inventor on 20 patents while with Acuson, all related to transducers and covering:

·          piezoelectric composites

·          reduced sidelobes

·          rotationally steerable transducer (V5m)

·          coupling of acoustic window and lens (V5m)

·          micromachined spiral arrays

·          CMUTs

·          multi-layer PZT

·          multi-dimensional arrays

·          method for US imaging of the heart

He was active in early investigation of CMUT technology with Siemens CT, single crystal piezoelectrics, new cable technology, 1-3 and 2-2 composites, electrostatic transducers, multi-D transducers using TDM, and he was a key member of the patent committee.  He was well known throughout the ultrasound community.




U.S. PATENTS (Seviğ also has patents in Canada, Germany, & other countries)

       *6994674  Multi-dimensional transducer arrays and method of manufacture
       *6971148  Method of manufacturing a multi-dimensional transducer array
       *6780152  Method and apparatus for ultrasound imaging of the heart
       *6761688  Multi-layered transducer array and method having identical layers
       *6673016  Ultrasound selectable frequency response system and method for multi-layer transducers
       *6664717  Multi-dimensional transducer array and method with air separation
       *6645145  Diagnostic medical ultrasound systems and transducers utilizing micro-mechanical components
       *6558330  Stacked and filled capacitive microelectromechanical ultrasonic transducer for medical diagnostic ultrasound systems
       *6437487  Transducer array using multi-layered elements and a method of manufacture thereof

       *6429574  Transducer array using multi-layered elements having an even number of elements & method for manufacture
       *6359367  Micromachined ultrasonic spiral arrays for medical diagnostic imaging
       *6182341  Method of manufacturing an improved coupling of acoustic window and lens for medical ultrasound transducers
       *5924986  Method and system for coherent ultrasound imaging of induced, distributed source, bulk acoustic emissions
       *5834687  Coupling of acoustic window and lens for medical ultrasound transducers
       *5792058  Broadband phased array transducer with wide bandwidth, high sensitivity, reduced cross-talk & method for
       *5771896  Compact rotationally steerable ultrasound transducer
       *5575288  Compact rotationally steerable ultrasound transducer
       *5465724  Compact rotationally steerable ultrasound transducer
       *5410208  Ultrasound transducers with reduced sidelobes & method for manufacture thereof
       *5297553  Ultrasound transducer with improved rigid backing
       *5239736  Method for making piezoelectric composites
       *5146432  Method for making cement impedance measurements with characterized transducer




SCHOLARLY WORKS (courtesy of Abdullah Atalar)

The following paper is probably Seviğ's most highly-cited work. It appeared in the most prestigious journal of Microwave Theory and describes the frequency behavior of a circulator (a passive microwave component build from ferrite materials). This paper is a result of his Masters Thesis completed at Middle East Technical University.

          · S. Ayter, Y. Ayasli, “The frequency behavior of stripline circulator junctions” IEEE Transactions on  Microwave Theory and

            Techniques,  vol. 26 p. 197-202 (1978)

The following papers are about the scattering of surface acoustic waves due to cracks on the surfaces of materials, typically a metal or a ceramic. This method can be used to detect very small flaws in critical structures such as airplane wings or nuclear reactor parts, before the parts break and cause failure and disaster. Surface waves are like waves on the ocean surface, but they are much smaller in amplitude and they travel on metal surfaces at much higher speed. The papers are as a result of Seviğ's PhD work at Stanford University under the guidance of Prof. Bert Auld, a very well-known professor of acoustics.

          · B.A. Auld, S. Ayter, M. Tan, “Theory of scattering of Rayleigh waves by surface breaking cracks” Proc. IEEE Ultrasonics

            Symposium, pp. 384-390 (1978)

          · S. Ayter, B.A. Auld, “Characterization of surface wave scattering by surface breaking cracks” in Review of Progress in

            Quantitative Nondestructive Evaluation, pp. 498-504 (1979)

          · B.A. Auld, S. Ayter, “Perturbation method for analyzing the effect on ultrasonic echo returns on rough surfaces in material

            cracks and voids” Proc. IEEE Ultrasonics Symposium, pp. 852-856 (1980)

          · S. Ayter, B.A. Auld, “On the resonances of surface breaking cracks” Review of Progress in Quantitative Nondestructive

            Evaluation, L Jolla, vol. pp. 394-402 (1980)

          · S. Ayter, B.A. Auld, “Resonances and crack roughness effects in surface breaking cracks” in Review of Progress in

            Quantitative Nondestructive Evaluation, pp. 348-354 (1981)

          · S. Ayter, B.A. Auld, “Inverse scattering from rough cracks” Proc. IEEE Ultrasonics Symposium pp. 988-993 (1982)

The following two papers are about a new method of detecting surface waves in a very sensitive manner using a laser beam. Laser can detect very small variations if it is reflected off a shiny surface. Since the surface waves move the surface of the material up and down (less than one micron), a laser beam can detect this small motion.

          · B.A. Auld, S. Ayter, M. Tan, D. Hauden, “Filter detection of phase-modulated laser probe signals” Electronics Letters, vol. 17,

            pp. 662-662 (1981)

          · S. Ayter, B.A. Auld, M. Tan, “Optical probing of resonant ultrasonic scattering from machined flaws in plates” in Review of

            Progress in Quantitative Nondestructive Evaluation, pp. 565-568 (1982)

The following papers are on the theory and experiments of eddy currents for the purpose of detecting cracks on the surfaces of materials. Eddy currents are generated when a magnet (or a magnetic field) is moved in close proximity of a conducting surface. Since the eddy currents are confined to surface, they are sensitive to surface properties and hence can be used to detect small cracks on the surfaces before they grow.

          · F. Muennemann, S. Ayter, B.A. Auld, “Computation of eddy current signals and quantitative inversion with realistic probe models”

            in Review of Progress in quantitative nondestructive evaluation. Volume 3A - Proceedings of the Tenth Annual Review,

            Santa Cruz, CA; United States; 7-12 Aug. 1983. pp. 621-631. (1984)

          · B.A. Auld, J.C. Moulder, S. Jefferies, P.J. Shull, S. Ayter, J. Kenney, “Eddy-current reflection probes: Theory and experiment, as

            a chapter in “Research in Nondestructive Evaluation” Springer ISSN: 0934-9847 pp. 1-11 (1989)

          · B.A. Auld, J.C. Moulder, S. Jeffries, P.J. Shull, S. Ayter, “Eddy-current reflection probes: theory and experiment: Research in

            non-destructive evaluation”, Vol. 1, No. 1, pp. 1–11 (1989)  NDT International, Volume 23, Issue 6, , p. 362 (1990)

The paper below describes a novel method of focusing surface waves on the surfaces of materials.

          · S. Ayter, “Focusing surface waves using conical transducers” Proc IEEE Ultrasonics Symposium, pp. 301-304 (1987)

The following papers are as a result of his work in Acuson. He was involved in the design of acoustic transducers for ultrasound imaging. He was an expert of transducer modelling. With an accurate model it is possible to improve the performance of the transducers. A high performance transducer will improve the image quality of an ultrasound scanner.

          · S. Ayter, “Transmission line modelling for array transducer elements” Proc IEEE Ultrasonics Symposium, Honolulu, pp. 791-794


          · G. Wojcik, J. Mould, L. Carcione, B. Fornberg, R. Waag, S. Ayter, “Large-scale modelling of ultrasound transducer pulses in

            lossy, nonlinear tissue” J. Acoustical Society of America, vol. 104, p. 1843 (1998)

          · G. Wojcik, J. Mould, S. Ayter, L. Carcione, “A study of second harmonic generation by focused medical transducer pulses”

            IEEE Ultrasonics Symposium, Sendai, pp. 1583-1588 (1998)