scholarly journals Ferroelectret Ultrasonic Transducers for Pulse-Echo Water Immersion

2020 ◽  
Vol 10 (24) ◽  
pp. 8771
Author(s):  
Julio Quirce ◽  
Linas Svilainis ◽  
Jorge Camacho ◽  
Tomas Gomez Alvarez-Arenas
Keyword(s):  
Short Pulse ◽  
Water Immersion ◽  
Wide Band ◽  
Spot Size ◽  
Ultrasonic Transducers ◽  
Piezoelectric Response ◽  
Radius Of Curvature ◽  
High Porosity ◽  
Technical Problems ◽  
Pulse Echo

Ferroelectrets are thin and porous polymeric films with a cellular microstructure, high porosity, permanent polarization and piezoelectric response. They have been used for different applications, where one of the most interesting ones is for the fabrication of air-coupled ultrasonic transducers. More recently they have been tested as water immersion transducers, showing a promising wide bandwidth but limited sensitivity along with other technical problems. This paper investigates ultrasonic transducers for water immersion and pulse-echo operation based on ferroelectret films. Two different ferroelectret foams with different resonant frequencies, acoustic impedances and cellular structures were tried. Flat and spherically focused prototypes (radius of curvature of 22 and 35 mm) were produced and tested. Finally, different materials and methods were tried to provide a protective surface coating. Acoustic field measurements for the focused transducers confirm the possibility to efficiently focus the ultrasonic beam by the proposed fabrication method, with focal spot size of 1.86 mm at −6 dB. Results show that in spite of the reduced sensitivity (about −115 dB), some of the tried ferroelectret films provide a very wide band response (−6 dB band from 0.29 to 2.7 MHz) and short pulse duration (2–3 us) that can be of interest for different applications.

scholarly journals Modification of Mechanical and Electromechanical Resonances of Cellular Ferroelectret Films Depending on the External Load

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3239
Author(s):  
Julio Quirce Aguilar ◽  
Tomás Gómez Álvarez-Arenas
Keyword(s):  
Film Thickness ◽  
External Load ◽  
Mechanical Load ◽  
Water Immersion ◽  
Polarization Vector ◽  
Ultrasonic Transducers ◽  
Piezoelectric Response ◽  
Active Elements ◽  
Electromechanical Responses ◽  
Electrically Charged

Ferroelectret films are cellular polymers with electrically charged pores that exhibit piezoelectric response. Among other applications, ferroelectret films have been widely used as active elements in air-coupled ultrasonic transducers. More recently, they have also been tested in water immersion. They show a promising wide frequency band response, but a poor sensitivity produced by the disappearance of the electromechanical resonances. This paper studies in detail the modification of FE films response when put into water immersion, both the mechanical and the electromechanical responses (the latter in transmission and reception modes). The lack of electromechanical thickness resonances when the films are put into water is explained as the result of the different profile of the modification of the polarization vector along the film thickness imposed by the large mechanical load produced by the water. This different electromechanical response can also be the reason for the subtle modification of the mechanical thickness resonances that is also observed and analyzed.

scholarly journals Measurement of synchrotron-radiation-excited Kossel patterns

2016 ◽  
Vol 23 (1) ◽  
pp. 214-218 ◽  
Author(s):  
G. Bortel ◽  
G. Faigel ◽  
M. Tegze ◽  
A. Chumakov
Keyword(s):  
High Resolution ◽  
Dynamic Range ◽  
Structural Information ◽  
Photon Counting ◽  
Spot Size ◽  
Low Noise ◽  
X Rays ◽  
Technical Problems ◽  
Pixel Detectors ◽  
Exciting Beam

Kossel line patterns contain information on the crystalline structure, such as the magnitude and the phase of Bragg reflections. For technical reasons, most of these patterns are obtained using electron beam excitation, which leads to surface sensitivity that limits the spatial extent of the structural information. To obtain the atomic structure in bulk volumes, X-rays should be used as the excitation radiation. However, there are technical problems, such as the need for high resolution, low noise, large dynamic range, photon counting, two-dimensional pixel detectors and the small spot size of the exciting beam, which have prevented the widespread use of Kossel pattern analysis. Here, an experimental setup is described, which can be used for the measurement of Kossel patterns in a reasonable time and with high resolution to recover structural information.

Body Area Networks

2011 ◽  
pp. 61-91 ◽  
Author(s):  
Leonardo Betancur Agudelo ◽  
Andres Navarro Cadavid
Keyword(s):  
Wide Band ◽  
Body Area Networks ◽  
Ultra Wide Band ◽  
Future Research ◽  
Area Network ◽  
Body Area ◽  
Daily Lives ◽  
Technical Problems ◽  
Wireless Protocols ◽  
Network Channel

Nowadays, wireless Body Area Networks (wBAN) have gained more relevance, in particular in the areas of health care, emergencies, ranging, location, domotics and entertainment applications. Regulations and several wireless protocols and standards have appeared in recent years. Some of them, like Bluetooth, ZigBee, Ultra Wide Band (UWB), ECMA368, WiFi, GPRS and mobile applications offer different kinds of solutions for personal area communications. In this chapter, body area network channel modelling will be described; also, a brief description of the applications and state-of-the-art of regulation and standardization processes pertaining to these kinds of networks will be presented. For each topic, the chapter shows not only the main technical characteristics, but also the technical problems and challenges in recent and future research. Finally, the chapter provides an analysis of Body Area Networks, opinions about the future and possible scenarios in the short- and medium-term for the development of standards and applications and their impacts on our daily lives.

scholarly journals MFC/NFC-Based Foam/Aerogel for Production of Porous Materials: Preparation, Properties and Applications

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5568
Author(s):  
Chenni Qin ◽  
Mingzhu Yao ◽  
Yang Liu ◽  
Yujie Yang ◽  
Yifeng Zong ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Porous Materials ◽  
Raw Materials ◽  
Sewage Treatment ◽  
Nanofibrillated Cellulose ◽  
High Specific Surface Area ◽  
High Porosity ◽  
Retention Performance ◽  
Plant Fibers ◽  
Technical Problems

Nanofibrillated cellulose and microfibrillated cellulose are potential raw materials separated from plant fibers with a high aspect ratio and excellent mechanical properties, which can be applied in various fields (packaging, medicine, etc.). They have unique advantages in the preparation of aerogels and foams, and have attracted widespread attention in recent years. Cellulose-based porous materials have good biodegradability and biocompatibility, while high porosity and high specific surface area endow them with strong mechanical properties and liquid retention performance, which can be used in wall construction, sewage treatment and other fields. At present, the preparation method of this material has been widely reported, however, due to various process problems, the actual production has not been realized. In this paper, we summarize the existing technical problems and main solutions; in the meantime, two stable systems and several drying processes are described, and the application potential of cellulose-based porous materials in the future is described, which provides a reference for subsequent research.

Effect of Externally-Imposed Radial Strain on the Piezoelectric Response of MOCVD-Grown Gallium Nitride

2000 ◽  
Vol 639 ◽  
Author(s):  
Jennifer A. Himes ◽  
James R. Willis ◽  
Daniel A. Gulino
Keyword(s):  
Gallium Nitride ◽  
Radial Stress ◽  
Contact Point ◽  
Electrical Contact ◽  
Radial Strain ◽  
Wide Band ◽  
Piezoelectric Response ◽  
Mocvd Reactor ◽  
Ionic Systems ◽  
Film Substrate

ABSTRACTThe large piezoelectric constants of GaN suggest possible application of GaN-based materials in piezoelectric sensors, among other areas. GaN's wide band gap implies that these sensors will fare well over a broad temperature range and/or in a harsh environment.In this work, films of gallium nitride approximately 0.75 micron thick and grown by MOCVD were subject to an externally-imposed radial stress condition. Deposition was performed in a commercial MOCVD reactor (CVD, Inc.) at 1323K using trimethylgallium and ammonia as the chemical precursors. The substrate was one-inch diameter silicon (111). After deposition, titanium dots were deposited in various locations, including the wafer center, by evaporation. Stress was applied to the film/substrate system using a modified micrometer head (Mitutoyo) mounted to an Ionic Systems Basic Stressgauge (model 30285). Stress levels were calculated based on the magnitude of the imposed deflection as read from the micrometer head display, and the piezoelectric response at any particular dot with respect to the center dot was measured by measuring the voltage difference using a digital multimeter (Keithley 175). The micrometer head impinged on the center dot and served as one electrical contact point.Effective piezoelectric coefficients were measured as a function of imposed radial stress. Applied stresses in the range of 1 to 5 GPa resulted in effective piezoelectric coefficients ranging from –0.6 to –2.0 × 10-5 C/m2

Comparative study of wide-band ultrasonic transducers

Ultrasonics ◽  
1987 ◽  
Vol 25 (6) ◽  
pp. 315-321 ◽  
Author(s):  
R.J. Dewhurst ◽  
C.E. Edwards ◽  
A.D.W. McKie ◽  
S.B. Palmer
Keyword(s):  
Comparative Study ◽  
Wide Band ◽  
Ultrasonic Transducers
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