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

Unified Model or Feroics Hysterisis

Unified Theory for Hysterisis Model

Publish at Scribd or explore others: hysterisis ferroelectric

TEORI DOMAIN WALL untuk Material Ferreoelektrik

Teguh Yoga Raksa ( 2008)

Model histerisis dari ferroelektrik material dapat dikelompokan menjadi beberapa kategori, salah satu kategorinya adalah teori mikroskopis material yang mengacu pada proses pembalikan domain, mekanisme pergerakan dinding domain akibat adanya pengaruh medan listrik dari luar. Sifat dielektrik dari material ferroelektrik dapat dijadikan acuan untuk pemodelan dengan menggunakan statistik boltzman untuk menghitung probabilitas dipol yang menempati energi level tertentu. Beberapa pemodelan yang mengacu pada fenomena domain akan diperkenalkan, yaitu pemodelan dengan menggunakan perumusan Langevin, model Ising Spin dan model yang ketiga adalah gabungan dari keduanya .

Pemodelan pada umumnya menggambarkan adanya area padat dimana perputaran dipol berlawanan arah dengan konfigurasi ionik sehingga menyebabkan perubahan yang sangat besar pada polarisasinya, dan hal ini memperlihatkan adanya saturasi pada saat level medan tinggi ketika distribusi muatan tidak diperkenankan untuk perubahan selanjutnya. Sebaliknya pengukuran kurva polarisasi pada saat level yang tinggi anhysterisis memikili nilai tunggal dan reversibel. Medan efektif dengan asumsi ideal dapat diformulasikan seperti persamaan berikut :

Ee =E+alpha*P

Besaran E, P menunjukan medan listrik dan hasil polarisasi sementara nilai aP merupakan menunjukan interdomain kopling. Pendekatan statistik Boltzman digunakan untuk menghitung probabilitas dipol – dipol yang menempati energi keadaan tertentu, dengan asumsi material isotropik , orientasi sel ke segala arah dan dicapainya keseimbangan termal dan elektrostatik maka diperoleh persamaan Langevin untuk polarisasi anhisterisis.

Model yang kedua pada polarisasi anhisterisis adalah model Ising Spin, dimana mengasumsikan bahwa orientasi momen dipol hanya pada arah medan listrik atau berlawanan arah .

Model yang ketiga adalah model gabungan dari model Langevin dan Ising Spin, model ini dibuat dengan asumsi grain pada material terdistribusi secara acak, akan tetapi dipol – dipol setiap sel hanya memiliki dua arah orientasi yang mungkin, ketiga model ini dapat dpergunakan untuk menghitung polarisasi anhysteritic akibat adanya medan listrik luar

referensi :

Ralph C Smith dan Craig L. Hom, A domain Wall Theory for Ferrolectric Material , Jurnal of Intelligent Material Systems and Structures, 1999

The influence of Mg doping on the materials properties of Ba1−xSrxTiO3 thin films for tunable device applications

References and further reading may be available for this article. To view references and further reading you must purchase this article.

M. W. Cole^{, , a}, P. C. Joshi^a, M. H. Ervin^a, M. C. Wood^a and R. L. Pfeffer^b

^a US Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005, USA

^b Department of Physics, Rurgers University, Piscataway, NJ 08854, USA

Received 31 March 2000;

revised 7 June 2000;

accepted 9 June 2000.

Available online 13 October 2000.

Abstract

We have investigated the structural, microstructural, interfacial, and surface morphological properties of Ba_0.60Sr_0.40TiO₃ thin films Mg doped from 0 to 20 mol%. A strong correlation was observed between the films materials properties and the prior determined dielectric and insulating characteristics as a function of Mg doping. Non-textured polycrystalline films with a dense microstructure and abrupt film-Pt electrode interface were obtained after annealing at 750°C for 30 min. Single phase solid solution films were achieved at Mg doping levels up to 5 mol%, while multiphased films were obtained for Mg doping levels of 20 mol%. Decreases in the films dielectric constant, dielectric loss, tunability and leakage current characteristics were paralleled by a reduction in grain size as a function of increasing Mg dopant concentration. Our results suggest that Mg doping serves to limit grain growth and is thereby responsible for lowering the dielectric constant from 450 to 205. It is suggested that Mg behaves as an acceptor-type dopant at the grain boundary and is responsible for the doped films low dielectric loss and good leakage current characteristics. Examination of the performance-property trade-offs advocates the 5-mol% Mg doped BST film to be an excellent choice for tunable microwave device applications.

Author Keywords: Dilectric properties; Deposition process; Film miscrostructure

Preparation and Characterization of BaxSr1-x, TiO3 Thin Films by a Sol-Gel Technique

Danielle M. Tahan 1 , Ahmad Safari, ★ 1 Lisa C. Klein ★ 1
1 Department of Ceramic Science and Engineering, Rutgers University, Piscataway, New Jersey 08855–0909

W. Huebner–contributing editor

Presented at the 97th Annual Meeting of the American Ceramic Society, Cincinnati, OH, May 1,1995 (Thick and Thin Films: Devices and Technology Symposium, Paper No.SXXII-14).


*Member, American Ceramic Society.
Copyright 1996 by The American Ceramic Society, Inc.
ABSTRACT

Barium strontium titanate, (Bax,Sr1-x TiO3, thin films of various compositions were prepared by a sol-gel method. Solutions consisting of acetate powders and titanium IV isopropoxide in a mixture of acetic acid and ethylene glycol were spin-coated onto silicon and platinum-coated silicon substrates. Processing parameters were optimized to develop stable solutions which yielded films with relatively low crystallization temperatures. It was determined that ethylene glycol was a necessary component of the solution to increase stability to precipitation and to decrease the crystallization temperature of the films. The grain size of the films varied with annealing temperature and atmosphere and directly affected the dielectric properties. A dielectric constant of 400 and a dissipation factor of 0.04 were measured at 1 kHz for (Ba0.8,Sr0.2) TiO3 films heated to 700°C for 1 h with a thickness of approximately 400 nm. Films of this composition maintained low leakage current densities for extended time periods when measured at an applied field of 75 kV/cm.

Manuscript No.192430. Received July 24, 1995; approved January 16, 1996.