Acoustoelectric Effect in Fluorinated Carbon Nanotube in the Absence of External Electric Field

Acoustoelectric effect (AE) in a non-degenerate Fluorine modified single walled carbon nanotube (FSWCNT) semiconductor is studied theoretically using the Boltzmann’s transport equation. The study is done in the hypersound regime i.e. , where q is the acoustic phonon wavenumber and is the electron mean free path. The results obtained are compared with that of undoped single walled carbon nanotube (SWCNT). The AE current density for FSWCNT is observed to be four orders of magnitude smaller than that of undoped SWCNT with increasing temperature, that is . This is because the electron-phonon interactions in SWCNT are stronger than FSWCNT. Thus, there are more intra-mini-band electrons interacting with the acoustic phonons to generate a higher AE current in SWCNT than in FSWCNT. This has been observed experimentally, where the electrical resistance of FSWCNT is higher than pristine SWCNT i.e. . The study shows the potential for FSWCNT as an ultrasound current source density imaging (UCSDI) and AE hydrophone material. However, FSWCNT offers the potential for room temperature applications of acoustoelectric device but other techniques are needed to reduce the resistance.

Acoustoelectric effect in semiconductor materials and devices

This paper reviews the studies on acoustoelectric effect in extrinsic semiconductor materials used in various scientific and other measurements. A historical review of earlier findings is given with special reference to associated mechanisms. Acoustoelectric studies in solid state devioes require further attention and the work done in this area is also discussed.

Semiconductor Fluorinated Carbon Nanotube as a Low Voltage Current Amplifier Acoustic Device

Acoustoelectric effect (AE) in a non-degenerate fluorinated single walled carbon nanotube (FSWCNT) semiconductor was carried out using a tractable analytical approach in the hypersound regime , where q is the acoustic wavenumber and is the electron mean-free path. In the presence of an external electric field, a strong nonlinear dependence of the normalized AE current density , on (?is the electron drift velocity and is the speed of sound in the medium) was observed and depends on the acoustic wave frequency, , wavenumber q, temperature T and the electron-phonon interactions parameter, . When , decreases to a resonance minimum and increases again, where the FSWCNT is said to be amplifying the current. Conversely, when , rises to a maximum and starts to decrease, similar to the observed behaviour in negative differential conductivity which is a consequence of Bragg’s reflection at the band edges at T=300K. However, FSWCNT will offer the potential for room temperature application as an acoustic switch or transistor and also as a material for ultrasound current source density imaging (UCSDI) and AE hydrophone devices in biomedical engineering. Moreover, our results prove the feasibility of implementing chip-scale non-reciprocal acoustic devices in an FSWCNT platform through acoustoelectric amplification.

Hypersound Absorption of Acoustic Phonons in a Degenerate Carbon Nanotube

Absorption of acoustic phonons was studied in degenerate Carbon Nanotube (i.e. where the electrons are found close to the Fermi level). The calculation of the hypersound absorption coefficient ()?was done in the regime where (q is the acoustic phonon number and l is the electron mean free path). At T = 10K and θ > 0 (θ being scattering angle), the dependence of on acoustic wave number (q), frequency (ωq), and , (Vs and VD being the speed of sound and the drift velocity respectively) were analysed numerically at n = 0,±1,±2 (where n is an integer ) and presented graphically. It was observed that when γ VD = 1.1Vs which occurred at E = 51.7V·cm-1. In the second harmonics, (n = ±2), the absorption obtained was compared to experimental measurement of acoustoelectric current via the Weinreich relation and the results qualitatively agreed with each other.

Thermally drawn multifunctional fibers: Toward the next generation of information technology

As the fundamental building block of optical fiber communication technology,thermally drawn optical fibers have fueled the development and prosperity of modern information society.However,the conventional step-index configured silica optical fibers have scarcely altered since their invention.In recent years,thermally drawn multifunctional fibers have emerged as a new yet promising route to enable unprecedented development in information technology.By adopting the well-developed preform-to-fiber manufacturing technique,a broad range of functional materials can be seamlessly integrated into a single fiber on a kilometer length scale to deliver sophisticated functions.Functions such as photodetection,imaging,acoustoelectric detection,chemical sensing,tactile sensing,biological probing,energy harvesting and storage,data storage,program operation,and information processing on fiber devices.In addition to the original light-guiding function,these flexible fibers can be woven into fab-rics to achieve large-scale personal health monitoring and interpersonal com-munication.Thermally drawn multifunctional fibers have opened up a new stage for the next generation of information technology.This review article summarizes an overview of the basic concepts,fabrication processes,and developments of multifunctional fibers.It also highlights the significant pro-gress and future development in information applications.

Investigation of surface acoustic waves in laser shock peened metals

Laser shock peening is a well-known method for extending the fatigue life of metal components by introducing near-surface compressive residual stress. The surface acoustic waves （SAWs） are dispersive when the near-surface properties of materials are changed. So the near-surface properties （such as the thickness of hardened layers, elastic properties, residual stresses, etc.） can be analyzed by the phase velocity dispersion. To study the propagation of SAWs in metal samples after peening, a more reasonable experimental method of broadband excitation and reception is introduced. The ultrasonic signals are excited by laser and received by polyvinylindene fluoride （PVDF） transducer. The SAW signals in aluminum alloy materials with different impact times by laser shock peening are detected. Signal spectrum and phase velocity dispersion curves of SAWs are analyzed. Moreover, reasons for dispersion are discussed.

Multi-channel surface acoustic wave device and its application on all-fiber acousto-optic modulation

The interaction of multi-channel surface acoustic waves （SAWs） and a guided optical wave in fiber is studied, and the corresponding coupled wave equations are derived. A novel two-channel SAW all-fiber acousto-optic modulator is designed, fabricated, and tested. The theoretical analysis is supported by the experimental results.

Elimination of LWD (Logging While Drilling) Tool Modes Using Seismoelectric Data

Borehole acoustic logging-while-drilling (LWD) for formation evaluationhas become an indispensable part of hydrocarbon reservoir assessment [F. Citt ´a, C. Rus-sell, R. Deady and D. Hinz, The Leading Edge, 23 (2004), pp. 566-573]. However,the detection of acoustic formation arrivals over tool mode contamination has beena challenging problem in acoustic LWD technology. In this paper we propose a newmethod for separating tool waves from formation acoustic waves in acoustic LWD.This method is to measure the seismoelectric signal excited by the LWD acoustic waves.The LWD tool waves which propagate along the rigid tool rim can not excite any elec-tric signal. This is due to the effectively grounding of the drill string during the LWDprocess makes it impossible to accumulate any excess charge at the conductive tool —borehole fluid interface. Therefore, there should be no contribution by the tool modesto the recorded seismoelectric signals. To theoretically understand the seismoelectricconversion in the LWD geometry, we calculate the synthetic waveforms for the multi-pole LWD seismoelectric signals based on Pride’s theory [S. R. Pride, Phys. Rev. B, 50(1994), pp. 15678-15696]. The synthetic waveforms for the electric field induced by theLWD-acoustic-wave along the borehole wall demonstrate the absence of the tool mode.We also designed the laboratory experiments to collect simulated LWD monopole anddipole acoustic and seismoelectric signals in a borehole in sandstone. By analyzing thespectrum of acoustic and electric signals, we can detect and filter out the differencebetween the two signals, which are the mainly tool modes and noise.