Ultrasonic velocity measurement in conductive magnetic fluids

Photoacoustics (PA) is a promising technology for medical imaging due to its superior contrast and resolution. This technique can be implemented either in time domain by powerful nanosecond laser pulses or in frequency domain (FD) by low power intensity-modulated continuous wave (CW) chirped laser irradiation (“the photoacoustic radar”). In our previous work [1,2] FD-PA imaging with linear frequency-swept optical modulation was implemented and the application of various signal processing methods to obtain depth-selective imaging was demonstrated. Later on we compared the FD and the pulsed techniques with respect to the maximum detectable depth using a dual-mode PA system [3]. Comparable depths were found with the FD technique exhibiting significantly superior signal-to-noise ratio (SNR). Very recently [4] we demonstrated that by combining the additional imaging channel that CW method possess due to its phase information with the cross-correlation amplitude results, the contrast and resolution of the image can be improved. In this study the contrast of images produced with both techniques is compared for various depths of a scattering medium. Experiments were implemented using two ultrasonic transducers with different center frequencies of 3.5 and 0.5 MHz. The samples consisted of two black rubber squares of areas 2x2 mm 2 and 4x4 mm 2 located at the same depth. These specifications were devised to enhance the comparison to the limits of the system, in other words, as we are trying to determine how small and how deep we can detect an absorber in a highly scattering medium, by comparing the contrast of the two rival methods. The wavelength of both pulsed and CW lasers utilized was 1064 nm and laser energies were controlled under the safety standard limits [5]. Since the CW method provides the capability to control the waveform shape and its bandwidth (BW), it is essential to examine the optimal BW of the frequency-modulated chirps to maximize the signal-to-noise ratio (SNR). It is demonstrated theoretically and experimentally that the optimal frequency BW does not depend exclusively on the transfer function of the ultrasonic transducer and its -6 dB BW, but also on the acoustic and optical properties of the tissue and lesion. To be specific, other than the transducer’s BW, acoustic attenuation of the medium and optical absorption and speed of sound in the lesion are key factors. Some results are demonstrated in figures 1 and 2 by utilizing the high frequency transducer. Figure 1.a shows the cross-correlation amplitude in the PA radar method generated in the middle of a black rubber square of 4x4 mm 2 in 19 mm depth of a 0.47% intralipid solution. Figure 1.b shows the transient response of the same sample to a pulsed laser. Comparison of these signal traces, demonstrates the higher SNR achieved by the CW method. Figures 2.a and b are the complete images produced at a specific depth corresponding to the surface of the black rubber samples. These images are constructed by complete scanning of a 15x15 mm 2 area using the CW and pulsed methods. It demonstrates that at the ultimate depth for the high frequency transducer, the pulsed laser achieved better detectivity. Nevertheless by employing the additional phase channel it is demonstrated that the contrast and resolution of the CW method is superior for shallower absorbers in the case of high frequency transducer. Next experiment exhibits the results of imaging a sample (absorption coefficient: 2 cm

Influence of a magnetic field on ultrasound propagation in a magnetic fluid

Ultrasonic measurement in variation of a degree of saturation in compacted bentonite

Measurements of ultrasonic velocity and attenuation were made on welded austenitic stainless steel specimens, and data correlated to flaw detectability. Measurements were made at 2.25 MHz for both longitudinal and shear waves as functions of propagation and polarization directions. The results of ultrasonic velocity measurements show that, in stainless steel welds, a high degree of anisotropy exists with respect to ultrasonic wave propagation: for different propagation and polarization directions, shear wave velocities varied from 2.8 to 4.2 mm/..mu..s compared to 3.1 mm ..mu..s for base material, and longitudinal wave velocities varied from 5.5 to 6.0 mm/..mu..s compared to 5.9 mm ..mu..s for base material. Measurements of reflected signals from simulated defects in a welded stainless steel plate indicate that, for 45-degree angle beams, longitudinal waves exhibit larger signal-to-noise ratios than shear waves. Horizontally polarized shear waves exhibit larger signal-to-noise ratios than shear waves. Horizontally polarized shear waves exhibit larger signal-to-noise ratios than commonly used vertically polarized shear waves at 45-degrees. These results have potential significance for practical ultrasonic examination of welded stainless steel structures.

In many fields, such as aerospace and marine environmental monitoring, magnetic field measurement is an important link. In recent years, optical fiber magnetic field sensor has received much attention because of its advantages such as small size, electromagnetic immunity, resistance to erosion and capability of remote sensing. In that case, magnetic fluid as a kind of medium between photons and magnetic field is widely used in optical fiber magnetic field sensors. Moreover, in the process of magnetic field measurement, disturbance introduced by temperature fluctuation always happens and brings uncertainty to the sensor. Temperature is also an important parameter in production process and needs to be measured. Therefore, designing a high-sensitive optical fiber sensor for simultaneously measuring magnetic field and temperature is a valuable work. In this paper, we present a high-sensitive hollow core fiber (HCF) interferometer for simultaneously measuring magnetic field and temperature. A segment of HCF filled with alcohol is inserted into single mode fiber (SMF) with 50 m offset at two splicing joints to guide light into the wall of HCF. And then this SMF-HCF-SMF structure is packaged by a capillary tube with full magnetic fluid (MF) inside it. Since the modal field area is large enough, the silica wall can support a series of guiding modes among which modal interference occurs and the interference spectrum can be recorded by an optical spectrum analyzer. Besides thermo-optic effect and thermal expansion effect of silica itself, the RI variations caused by thermo-optic effect of alcohol and MF as well as the magneto-optic effect of MF can also cause the phase difference of the guiding modes to change, thereby rendering interference dips movable. Thus, the sensitivity of temperature or magnetic field is higher than those given in some other previous studies. In addition, it is calculated that the effective RI sensitivities of guiding modes for inside and outside liquid are different because of the peculiar non-circular symmetry structure of HCF. So there is a possibility to find two dips in interference spectrum, which are formed with different modes and have various sensitivities to the variations of temperature and magnetic field. Finally, a sensitivity matrix can be built to demodulate those two parameters simultaneously. Experimental results show that within 20-58℃, the temperature sensitivities are 112 pm/℃ and 468 pm/℃ for dip1 and dip 2 whose magnetic field sensitivities are 37 pm/Oe and 82 pm/Oe within 0-169 Oe, respectively. The proposed sensor possesses high sensitivity and good mechanical strength, and can effectively eliminate the cross disturbances between temperature and magnetic field.

Modeling concept and numerical simulation of ultrasonic wave propagation in a moving fluid-structure domain based on a monolithic approach

An aqueous magnetic fluid based on iron oxide particles as solid nano-magnetic phase was prepared by applying the chemical precipitation method. Tartaric acid (C4H6O6) was used to functionalize magnetic cores. Physical tests have been performed in order to reveal the microstructural and magnetic features, their optimization being needed for biomedical utilization. The particles’ size was investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM) and magnetization measurements. Fourier transform infrared absorption spectra (FT-IR) have been recorded aiming to get some information on the solid phase structure. 1. Introduction. Recently, the synthesis of magnetic materials on the nano-scale has become a field of increased interest due to the mesoscopic properties shown by nanoparticles of quantum dimensions located in the transition region between atoms and bulk solids. Magnetic fluids (ferrofluids) are two-phase systems, consisting of small ferri- and ferromagnetic nanoparticles dispersed in a liquid [1]. Because the size of the magnetic particles lies in the nanometer range (often around 10 nm in diameter), those suspensions are referred to as magnetic nano-colloids. The colloidal nanoparticles are subject to random displacement due to their bombardment by impulsive forces from the solvent molecules, in which they are dispersed. Colloidal stability is assured by coating the nanoparticles with shells of a nonmagnetic molecular surfactant, which prevents close approach of the magnetic cores, thereby, reduces the possibility of aggregation via Van der Waals or dipolar attractions. When the dipolar interactions are much stronger than the thermal energies, particle chains start growing and forming more complex structures, depending on the particle volume fraction, size distribution, temperature or a magnetic field applied [2]. The colloidal stability of magnetic fluids is a complex issue related to the synthesis procedure followed, including the nature of surfactant(s) and carrier liquids used [3]. The magnetic fluid stability is the main characteristic that determines the possibility to exploit magnetic fluids in different industrial and biomedical applications. Magnetic fluids are said to be superparamagnetic, meaning that they are attracted by a magnetic field but retain no residual magnetism after the field is removed [1]. When the magnetic nanoparticles are dispersed in an ionic solution, the dissociation of ionogenic groups is followed by the differential adsorption on the particle surface generating a particle surface potential. Biophysicists pay more and more attention to the magnetic nanoparticles functionalized with a biocompatible nonmagnetic molecular surfac

The magnetic fluid (MF) viscosity in MF targeting drug delivery system isn’t constant. With the change of magnetic field strength, MF viscosity will change due to MF magnetoviscous effect. The magnetoviscous effect mechanisms in low and high concentration MF are different and qualitatively analyzed respectively. Drop needle movement method under controlled temperature was adopted to measure magnetoviscous effect. Experiment results show the viscosity linearly increases by magnetic filed strength under low magnetic field. The viscosity reaches max value when MF is magnetic saturation. Through curve fitting, the magnetoviscous effect formula is got. Based on this formula, the MF viscosity in changed magnetic field can be obtained. The MF drug movement behave will be controlled by magnetic field and can be transferred accurately to target. This result also can be generalized to other MF viscosity research field.

Magnetic characteristics of magnetic compound fluid (MCF) under DC and AC magnetic fields

An intensity-interrogated fiber magnetic field sensor based on magnetic fluid (MF) and tilted long-period fiber grating (TLPFG) has been proposed. The sensor is constructed by a TLPFG immersed in the MF. The TLPFGs supported the coupling between the LP01 core mode and the forward-propagating cladding modes with different azimuthal order l = 0, 1, 2,…, which shows different spectral response behaviors with normal long-period fiber gratings. The experimental results and theoretical analysis show that resonance wavelengths of TLPFG present different characteristics by tuning the applied magnetic field intensity. The transmission loss of the TLPFG increases for some dips, while they reduce for the others with the increment of the applied magnetic field intensity. Taking advantage of the optical power difference for various wavelength regions, a magnetic field intensity sensitivity of 0.05 dB Oe−1 could be achieved for a magnetic intensity range from 75 Oe to 300 Oe. Due to its low cost and compactness, the proposed sensor is expected to find potential applications in the field of magnetic field measurement and photonic devices.

The ultrasonic wave propagation in composite material and its characteristic evaluation

Although a pulsed-wave (PW) Doppler system can measure blood velocity with range information, measurable velocity is limited by frequency aliasing, and signal-noise-ratio (SNR) is poor. Continuous wave (CW) Doppler system offers a higher SNR in Doppler signal and no measurable velocity limitations but does not provide ranging information. Linear frequency-modulated continuous wave (LFMCW) and sine frequency-modulating continuous wave are able to provide high SNR Doppler signals with ranging information, and low clutter power, but with a certain range ambiguity due to signal periodicity of the Doppler signal spectrum. Various efforts have been made to improve the SNR, range resolution, and velocity limitations with FMCW Doppler system. An ultrasonic doppler blood flow velocity measurement system based on chaotic FMCW is proposed which has a higher SNR with no range ambiguity because of the aperiodicity of the Doppler signal spectrum. Principle analysis and experimental simulation show that the effectiveness of the new system is verified.

This paper presents a vector magnetic field sensor based on magnetic fluid (MF) encapsulation and a cascaded special optical fiber structure. The sensor consists of single-mode fiber (SMF)–three core fiber (TCF)–no core fiber (NCF)–TCF–SMF. The introduction of two short TCF segments effectively excites higher-order modes, generating intermodal interference, and simultaneously imparts favorable circular asymmetry to the sensing structure, enabling the detection of the magnetic field direction around the fiber. Experimental results demonstrate that the sensor performs optimally when the NCF length is 8 mm. The sensor achieves a magnetic field sensitivity of –914 pm/mT and a maximum directional sensitivity of –390 pm/°. Moreover, temperature compensation for magnetic field measurements is realized using a sensitivity demodulation matrix, resulting in a temperature cross-sensitivity of only 160 pm/°C in experiments. The proposed magnetic field sensor features high sensitivity, a simple structure, and low cross-sensitivity, indicating promising potential for future applications.

Heat transfer, thermal management, and acoustics are the important parameters that determine the effectiveness of any miniaturized electronic circuit. As the density of electronic components is increasing, the reliability of such systems is of great concern. The proposed work discusses a novel technique of a magnetic pumping fluid system without conventional cooling components. Here the integrated effect of the conjugate heat transfer and magnetic field is taken into account to study flow phenomena. Two different fluids—water and kerosene—as a base fluid for ferrofluid are evaluated for physical quantities such as pressure, temperature, and heat transfer coefficient to measure the performance of a magnetic cooling system. Flow in the cooling setup is optimized by using numerical analysis and number of experiments on the given setup. It was found that flow depends on the magnetic field gradient, temperature gradient, fluid properties, and material combination. In addition, flow characteristics depend on the influence of magnetic field and temperature of the fluid. Analysis results show that the heat transfer and pressure head in the kerosene-based ferrofluid are more stable compared to the water-based ferrofluid. A better magnetic fluid with both high magnetization and a high pyromagnetic coefficient can enhance the flowability of the ferrofluid to a large extent.

Characterization of intermetallic precipitates in a Nimonic alloy by ultrasonic velocity measurements