Physics of Ferroelectric

Physics of Ferroelectric

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Nanotube loudspeakers

Physics Today , 2008

In typical loudspeakers, a coil surrounds the apex of a flexible cone; when a varying current flows through the coil, the cone moves toward and away from a fixed permanent magnet and produces pressure waves we hear as sound. But researchers from Tsinghua University and Beijing Normal University have demonstrated a radically simpler loudspeaker design based on nanotubes: They showed that a thin film of nanotubes can reproduce sounds over a wide frequency range--including the full human audible range--with high sound pressure level, low total harmonic distortion, and no magnets. The team created the film by drawing nanotubes from a so-called superaligned array grown on a wafer, a technique the group introduced six years ago (see also PHYSICS TODAY, October 2005, page 23). The resulting film, only tens of nanometers thick but up to 10 cm wide, is transparent and has a nearly purely resistive impedance. When electrodes are placed along its ends and an alternating current is applied, the film produces clear tones that can be as loud as a conventional speaker. Moreover, since the film is flexible, the nanotube speaker can be configured into arbitrary shapes or mounted onto curved substrates; the figure shows an omnidirectional cylindrical loudspeaker 9 cm in diameter and 8.5 cm high. The film can even be stretched with essentially no degradation of the sound reproduction. The researchers attribute the sound generation not to vibration but to a thermoacoustic effect first proposed nearly a century ago: Thanks to the nanotube film's extremely low heat capacity per unit area, changes in the current flowing through the film are reflected in the film's temperature, and those temperature changes excite pressure waves in the surrounding air. The mechanism is independent of the sign of the current, which leads to a frequency doubling of the input signal, but that drawback can be overcome by applying a constant current bias. The movie shows a nanotube loudspeaker being periodically stretched with almost no noticeable effect on the sound intensity. (L. Xiao et al., Nano Lett., in press, doi:10.1021/nl802750z.) -- Richard J. Fitzgerald

2009 IEEE International Ultrasonics Symposium

Short Courses & Tutorials

September 20-23, 2009

Ergife Palace Hotel, Roma, Italy

Sponsored by the IEEE Ultrasonics, Ferroelectrics, & Frequency Control Society

In the section Symposium/Announcements, we have published the Second Call for Papers of 2009 IUS - Roma. Please, download and print the pdf-file with Adobe Acrobat and show it in your Institution
Second Call for Papers
Abstract Deadline: May 3, 2009

We are pleased to welcome you to the 2009 IEEE International Ultrasonics Symposium, which
will be held in Roma, Italy, from September 20 to 23 at the Ergife Palace Hotel.
We are sure that you will enjoy your visit to Roma, which is rightly known as one of the most
beautiful and interesting cities in the world. It is the city of the Caesars with majestic
monuments from the golden days of the ancient Roman Empire. But it is also the center of
the catholic world, with an endless number of grand, beautiful cathedrals and churches. But
Roma is so much more than an open-air museum; everywhere you find great restaurants with
superb food and wine, lovely bars and cafés, excellent shopping, and vibrant night life.
We look forward to meeting you in Roma.
Papers are solicited for this conference describing original work in the field of ultrasonics.
Poster and oral presentation formats will be used at the symposium. Prospective authors
should note that poster sessions provide an alternative format which allows for greater
flexibility and expanded audience interaction. The deadline for submission of abstracts is May
3, 2009. The abstracts should be submitted in electronic form according to the specific
information posted on the conference web page. Additional conference information can be
found at the Symposium web site: http://ewh.ieee.org/conf/ius_2009/. Each abstract will
receive careful review and evaluation by the Symposium Technical Program Committee.
Evaluation criteria will include originality of the work, contribution to the state-of-the-art, and
overall interest to the ultrasonics community. Papers are solicited from the following subject
classifications:

Group 1 : Medical Ultrasonics
MBB Medical Beamforming and Beam Steering
MBE Biological Effects & Dosimetry
MBF Blood Flow Measurement
MCA Contrast Agents
MEL Elastography
MIM Medical Imaging
MPA Medical Photoacoustics
MSD System & Device Design
MSP Medical Signal Processing
MTC Medical Tissue Characterization
MTH Therapeutics, Hyperthermia, and Surgery
Group 3: Physical Acoustics
PBW Bulk Wave Effects & Devices
PGP General Physical Acoustics
PLP Physical Acoustics Laser Interactions
PMI Magnetic/Electromagnetic Interactions
POI Optical Interactions
PPN Phononic Crystals & Devices
PUM Ultrasonic Motors & Actuators
PTF Thin Films
Group 5: Transducers & Transducer Materials
TMC Materials Characterization and Fabrication
TPF Ultrasonic Applications of Piezoelectrics &
Ferroelectrics
TMI Medical Imaging Transducers
TMO Modeling (Analytical & Numerical)
TMU Micromachined Ultrasound Transducers
TTT Medical Therapeutic Transducers
TFT Thick Film Piezo-Technology
Group 2: Sensors, NDE & Industrial Applications
NAM Acoustic Microscopy
NAI Acoustic Imaging
NAS Acoustic Sensors
NDE General NDE Methods
NFM Flow Measurement
NMC Material & Defect Characterization
NSP Signal Processing
NTD Transducers: NDE and Industrial
NWP Wave Propagation
Student Travel Support: Limited funds are available to support IEEE UFFC student member attendees at the 2009 symposium. Awards will be given on a competitive basis. Please see the conference website for details.
Student Paper Competition: Students submitting abstracts are invited to participate in a student paper competition. To participate, the student must be the lead author and present his/her paper. Further information will be posted on the conference website (http://ewh.ieee.org/conf/ius_2009/)
All roads lead to Rome ...

http://ewh.ieee.org/conf/ius_2009