Introduction to the Special Issue on Micromachined Ultrasonic

							2162               ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 52, no. 12, december 2005




            Introduction to the Special Issue on
           Micromachined Ultrasonic Transducers

     ltrasonic transducers have traditionally been imple-       realize the full potential of the micromachined ultrasonic
U    mented with crystals such as quartz, lithium niobate,
lead zirconium titanate combinations, and others; or with
                                                                transducers.

capacitors but mostly in airborne ultrasound applications.                Prof. B. (Pierre) T. Khuri-Yakub, Guest Editor
With the advent and maturation of silicon micromachin-                                 E. L. Ginzton Laboratory, room 11
ing, new possibilities for making ultrasonic transducers                                              Stanford University
have emerged, both for piezoelectric based and capacitor                                         Stanford, CA 94305-4088
based devices, and for both airborne and immersion appli-
cations.                                                                                         Butrus T. Khuri-Yakub
   Thin vibrating membranes of silicon, silicon nitride, alu-                                    (S’70–S’73–M’76–SM’87–
mina, diamond, and other materials can be easily made                                            F’95) was born in Beirut,
and vibrated with piezoelectric, capacitive, magnetic, ther-                                     Lebanon. He received the
mal, and other types of driving mechanisms. More at-                                             B.S. degree in 1970 from
tention has been given to capacitive ultrasonic transduc-                                        the American University of
ers because with the use of integrated circuit manufac-                                          Beirut, the M.S. degree in
turing techniques it is possible to make capacitors with                                         1972 from Dartmouth Col-
sub-micron gaps where electric fields of over 108 V/m can                                         lege, Hanover, NH, and the
be sustained. The merit of such a high electric field is                                          Ph.D. degree in 1975 from
that it results in transducers where the electromechani-                                         Stanford University, Stan-
cal coupling coefficient can get close to unity, and thus                                          ford, CA, all in electrical
be very competitive with the best piezoelectric materials.                                       engineering.
Added to this advantage is the broad bandwidth resulting           He joined the research staff at the E. L. Ginzton Lab-
from using over-damped membranes in immersion applica-          oratory of Stanford University in 1976 as a research asso-
tions, the control afforded by integrated circuit manufac-       ciate. He was promoted to a senior research associate in
turing techniques in making single element, 1-dimension,        1978 and to a professor of electrical engineering (research)
1.5-dimension, and 2-dimension arrays, and the ease of in-      in 1982. He has served on many university committees in
tegration of the transducers with electronic circuits.          the School of Engineering and the Department of Electri-
   The last ten years have seen a tremendous rise in the        cal Engineering at Stanford University. Presently, he is the
research and development of the micromachined ultrasonic        Deputy Director of the E. L. Ginzton Laboratory.
transducers as evidenced by the number of papers on the            Dr. Khuri-Yakub has been teaching at both the gradu-
topic in conferences and scientific journals. Another ev-        ate and undergraduate levels for over 15 years. His current
idence of the growth in the field is the development of          research interests include in situ acoustic sensors (temper-
research activities in the topic in most countries around       ature, film thickness, resist cure, etc.) for monitoring and
the world. In Europe for instance, European community           control of integrated circuits manufacturing processes, mi-
funding has enabled research and collaboration between          cromachining silicon to make acoustic materials and de-
groups in various countries. Such activities seem to be         vices such as airborne and water immersion ultrasonic
on a course of continuing growth towards adoption of the        transducers and arrays, and fluid ejectors, and in the field
technology, at least for some niche applications. Presently,    of ultrasonic nondestructive evaluation and acoustic imag-
there is commitment from major medical ultrasound imag-         ing and microscopy.
ing companies to provide commercial products with these            Dr. Khuri-Yakub is a fellow of the IEEE, a senior mem-
transducers, in the very near future.                           ber of the Acoustical Society of America, and a member of
   This special issue attempts to offer a number of publi-       Tau Beta Pi. He is associate editor of Research in Nonde-
cations that span a comprehensive list of topics of interest    structive Evaluation, a Journal of the American Society for
in the development of the micromachined transducer. A           Nondestructive Testing. He has authored over 300 publi-
lot of good development in modeling and implementation          cations and has been principal inventor or coinventor of 52
has taken place in 10 years, but more, much more needs          issued patents. He received the Stanford University School
to be done to bring about a complete understanding of           of Engineering Distinguished Advisor Award, June 1987,
these devices. It is hoped that this issue will help encour-    and the Medal of the City of Bordeaux for contributions
age more research and development in this field to help          to NDE, 1983.

                                               0885–3010/$20.00 c 2005 IEEE