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Recent efforts in single-cell research call for precise liquid level detection (LLD) for end-effectors to manipulate small volume of liquid samples such as nano- to pico-liter droplets. Existing LLD methods, however, are yet satisfactory for such delicate micromanipulation tasks. This article presents a vision-based contact type LLD method, which adopts the hardware settings normally used in typical micromanipulation scenarios. The detection principle is based on the generation of patterned ripples when the end-effector (e.g., glass micropipette), that is being vibrated, moves to get contact with the liquid surface. Through the microscopic imaging system in micromanipulation, the image frames of patterned ripples such as concentric circles are recorded, from which the wavelength is extracted to determine the contact moment. The vision-based LLD method was cross-validated by the electrical impedance-based method. Experiments revealed that the best detection accuracy was 40 nm, only limited by the micromanipulator's positioning resolution. Moreover, the method was robust to various micromanipulation settings, such as illumination intensity, microscopy magnification, exposure time, and focal plane. As a demonstration, this method was successful in detecting the surface of droplets with a volume as low as 450 pL for different liquids. Given its generality, this method is expected to suit many scenarios involving liquid handling tasks in micromanipulation and industry. [ABSTRACT FROM AUTHOR]

Magnetic fluid seals are widely used. However, during the filling process of the magnetic fluid, a large part of the magnetic fluid is attracted to the magnet, causing the loss of the magnetic fluid, and the magnetic fluid sealing device can easily cause damage to the pole teeth due to the problem of disassembly and installation. To solve the above problems, this article designs a pole piece integrated magnetic-fluid sealing structure and a new type of disassembly and installation method. The finite element method is used to calculate the magnetic field distribution of the pole piece integrated magnetic fluid seal structure, and the theoretical withstand pressure value is obtained according to the withstand pressure calculation formula. Three kinds of magnetic fluids were used to conduct comparative experiments on the magnetic fluid sealing device at different temperatures and different filling amounts. The results showed that the pressure resistance of the magnetic fluid sealing increased with the increase of the filling amount, and the increase of the saturation magnetization, consistent with theory. It is also found that the thickness of the pole piece is very thin. During the processing, Compared with the ordinary pole piece, the integrated pole piece has the advantage of large length, the coaxial is easily ensured, and the processing difficulty is reduced; second, during the filling process, all the magnetic fluid is sucked to the pole teeth, there is no loss of the magnetic fluid, and the pole teeth are intact after more than a hundred times of disassembly and installation, which further improves the life of the magnetic fluid sealing device. [ABSTRACT FROM AUTHOR]

Fe3O4 nanoparticles have been a research focus area for many years and have been applied in fields like medical treatment, catalysis and sensors. Particularly, they can be coated and dispersed in a solvent to prepare magnetic fluids. Magnetic fluid sealing is a high-performance sealing method, but it is still not capable to work in extreme conditions such as elevated temperatures. Here we present a new sealing method with nano-micro magnetic powders as the sealing medium. Fe3O4 particles with average sizes of 20 nm, 200 nm, and 25 $\mu \text{m}$ are prepared by the chemical co-precipitation method. The fluid permeability of magnetic powders is estimated by Darcy’s law. Finally, a static sealing prototype is designed and optimized based on magnetic field distribution analysis. Sealing experiments show a strong relevance between particle sizes and leakage rate. The mixture of nano and micrometer-sized Fe3O4 particles leads to a significant decrease in leakage rate, making magnetic powder sealing a promising novel sealing method. [ABSTRACT FROM AUTHOR]

The optical properties of magnetic emulsions with microdroplets of a magnetic fluid in hydraulic oil under the influence of a magnetic field are investigated. It is shown that the optical transmittance of a magnetic emulsion can be controlled by changing the strength and direction of the magnetic field. With prolonged exposure to a magnetic field, diffraction of light occurs in a magnetic emulsion, the intensity and shape of the diffraction pattern are determined by the field parameters. It is shown that magnetic emulsions can be a promising medium for controlled neutral optical filters and magneto-optical sensors. [ABSTRACT FROM AUTHOR]

Core–shell particles of the poly-2-methylaniline (PMAN)/carbonyl iron (CI) composite material were prepared by dispersion polymerization. Dopamine was used as a chemical grafting agent to modify the surface of CI particles to enhance the affinity between PMAN particles and pure CI particles. The morphology and crystalline structure of the prepared core–shell PMAN/CI microspheres were tested by TEM and X-ray diffraction, respectively. Their magnetic behaviors were analyzed using a vibrating-sample magnetometer. The sedimentation stability of the particles was further analyzed using a Turbiscan analyzer. The analysis results revealed that the dispersion stability of the particles was better than that of the pure CI particles. The characteristics of the PMAN/CI particle-based magnetorheological fluid with a yield stress of 4800 Pa at 342 kA/m were measured using a rheometer. [ABSTRACT FROM AUTHOR]

A novel magnetic liquid silicone rubber composite core design applicable to wireless power transfer (WPT) for medical applications is presented. As a case study, the integration of WPT, including the proposed cores for the coils, with ventricular-assist devices (VADs) was investigated. This facilitates transferring 4.6 W of power wirelessly through the skin layer, which, thus, allows to disposal of the transcutaneous cable that connects the extracorporal batteries to the implanted blood pump. To enhance the coupling coefficient and consequently increase the WPT efficiency, the geometry of the cores was optimized. This reduces the temperature increase in the implant area. The field and thermal simulations were carried out with CST software. The electrical properties of the proposed design as obtained by simulation were validated by measurements. The simulation results perfectly coincide with the measured results. Finally, a new optimized design with additional high permeability core inserts is introduced to further increase the coupling coefficient. The results indicate that the coupling coefficient is increased from 0.31 to 0.52 with the optimized design compared to the case without cores. Moreover, by fixing the initial temperature as 37 °C, the maximum temperature is decreased from 38.19 °C to 37.27 °C while keeping the transferred power fixed. Its high magnetic conductivity, biocompatibility, low-loss property, flexibility, and Qi-standard compatibility make the proposed WPT design an excellent candidate for the wireless powering of heart-assist devices, such as VADs. [ABSTRACT FROM AUTHOR]

The rheological behavior of magnetorheological fluids (MRFs) is greatly influenced by many key parameters such as concentration, composition, temperature, and magnetic field. As magnetic particles are dispersed in a non-magnetic liquid, MRFs exhibit an increase in viscosity with increasing magnetic fields due to the formation of chain-like structures. However, this viscosity change has often been studied as a function of any one or two of the key parameters. Herein, we studied the simultaneous effect of temperature, magnetic field, concentration of dispersed phase, and MRF composition on the viscosity of MRFs. Understanding the simultaneous effect of tunable parameters such as temperature and magnetic field allows for optimization of MRF performance and enhanced viscosity in commercial applications. Rheological experiments were performed on MRFs over a wide range of temperatures (15–65 °C) under magnetic fields between 0.1 and 1 T. The thermo-magnetorheological response was also studied with varying magnetic particle concentration (1 vol%–25 vol%) and MRF composition (both dispersed phase and carrier liquid). The results demonstrated a strong influence of magnetic particle composition and concentration on the MRF viscosity along with temperature while the carrier liquid composition had relatively negligible influence. [ABSTRACT FROM AUTHOR]

A low-loss all-straight optical fiber vector magnetic field sensor (OFVMS) based on magnetic fluid (MF) is designed and proposed. The sensing structure is composed of a Section of the C-type optical fiber (CTF) embedded in a pair of multi-mode optical fibers (MMF) and wrapped in a capillary with MF. The asymmetry of the CTF provides support for the vector magnetic field measurement whose direction is perpendicular to the optical transmission direction. According to the results of experiments, it can be obtained that the refractive index (RI) sensitivity of the sensing structure is as high as −15716.6072 nm/RIU. In addition, the intensity sensitivity of the OFVMS in the calibrated 90° direction can reach 202.23 pm/G between 0 and 123 G. At the same time, the transmission loss of the proposed sensor structure is not increased by the filling of MF. The sensor demonstrated has dominance in low cost, easy manufacture, and lower loss compared with the same type of sensor device, which has application prospects in vector magnetic field sensing. [ABSTRACT FROM AUTHOR]

In this work, we propose and analyze a plasmonic sensor with a three-layer waveguide structure. We consider the transverse spin-dependent shift (SDS) of the horizontal photonic spin Hall effect (PSHE) in the waveguide at a given wavelength (1557 nm) for a TM (transverse magnetic or p-polarized) mode. The sensor structure is analyzed in two ways. First, under the normal methods, that is, angular and intensity interrogation methods, for which the results indicate that the maximum figure of merit (FOM) of 4007.0 RIU−1 is attained for an optimum thickness ($d_{2}=51$ nm) of the gold layer and this FOM is significantly greater than the corresponding FOM (413.7 RIU−1) reported earlier (for a 50 nm thick gold layer). Also, the average sensitivity increases from 0.0005 to 0.002°/Oe when the volume fraction of Fe3O4 particles ($c$) in the magnetic fluid is increased from 1.48% to 1.93%. Correspondingly, a considerably finer value of the resolution (0.046 Oe) is obtained when the volume fraction is increased to 1.93% (compared to 0.199 Oe at 1.48%). Second way is the proposed method of PSHE, for which the analysis indicates that transverse SDS of the horizontal PSHE is the maximum for $d_{2} = 51$ nm leads to the maximum sensitivity $6.25 \times 10^{7}~\mu$ m/RIU for an amplified angle $\Delta = 0.1^{\circ}$ and $1.09 \times 10^{6}~\mu$ m/RIU for $\Delta = 0.1$ rad in the conventional weak measurements. The corresponding finest possible resolution of magnetic field detection at 1.93% is $1.5 \times 10^{-6}$ Oe in the conventional weak measurements for $\Delta = 0.1^{\circ}$ and $7.8 \times 10^{-8}$ Oe in the modified weak measurements for $\Delta = 0.5$ rad, which are significantly finer than those existing in the related state of the art. The above resolution is also superior to those found under normal methods mentioned earlier. Furthermore, the effect of temperature (24.3 °C–60 °C) on PSHE-based magnetic field sensor’s performance is also analyzed which indicates that the proposed PSHE-based magnetic field sensor should be operated in a thermally controlled milieu. [ABSTRACT FROM AUTHOR]

Magnetorheological fluid seal and brush seal are successful sealing forms. To address problems such as pole pieces colliding with spindles, precise sealing clearance in magnetic fluid seals, and inevitable leakage in brush seals, this article combines the advantages of magnetic fluid seal and brush seal and proposes a magnetorheological fluid seal with flexible pole pieces. The magnetic field of the seal was estimated using the finite-element method and the seal capacity was studied in theory. Single structural parameters of the seal that affect sealing capacity such as the relative permeability and thickness were discussed. The combined effects of various structural parameters were analyzed. The results show that an increase in the relative permeability and length of the flexible pole pieces leads to the enhancement of the seal capacity. The thickness of the flexible magnetic pole piece and the magnetic part of the flap and coating are inversely proportional to the sealing pressure value. The experimentally obtained seal capacity agrees with the value calculated through the simulation. This article presents a structure of the magnetorheological fluid seal and comparative results of the seal capacity obtained from both experimental studies and numerical simulation calculations. [ABSTRACT FROM AUTHOR]

The advantages of magnetic fluid seals, such as low friction moment, high tightness, and high durability, have been known for many years. However, they are used particularly in air or vacuum environments and the application of this type of seal in water still remains a problem. This is mainly due to the friction occurring between the two fluids and interfacial instability. This publication focuses on investigating the influence of magnetic fluid properties on the mechanism of pressure transfer between sealing stages. The main aim was to better understand the leak mechanism in this type of seal and to be able to select ferrofluids (FFs) resistant to water for long-term operation after short-term testing. The tested seals rotated over 4.3 million times without failure. The results of the research carried out are recommendations for the selection of magnetic fluid, sealing stage width, and FF volume. [ABSTRACT FROM AUTHOR]

A compact vector magnetometer based on balloon-like fiber structure functionalized by magnetic fluid (MF) was proposed. To fabricate the sensor, the single mode fiber (SMF) was bent into a balloon-like structure, and then the shape was fixed by using the alcohol lamp flame. Because of the bending, the fiber core mode leaks into the cladding, thereby forming higher order cladding modes that are sensitive to the variations of external refractive index. When the structure is encapsulated in MF, due to the anisotropic distribution of ferromagnetic nanoparticles under magnetic field, the refractive index around the fiber structure also presents anisotropy. By measuring the refractive index of the MF under different magnetic-field directions and intensities, both the measurement of the magnetic field intensity and direction can be achieved. The experimental results show that a high magnetic field intensity sensitivity of 0.78 nm/mT and a high magnetic-field direction sensitivity of 0.094°/mT were obtained. Due to the simple fabricating method, low cost, and highly sensitivity, the proposed fiber vector magnetometer has potential applications in the navigation, aviation, and electric power industry. [ABSTRACT FROM AUTHOR]

A novel magnetic field measurement method based on the magneto-volume effect is proposed. The magnetic field sensing structure fabricated by the proposed measurement method is made by the magnetic fluid (MF) partially filled into the hollow core fiber (HCF). The presence of air provides conditions for the change of MF volume with the magnetic field in the proposed sensing structure. Therefore, the magneto-volume effect is introduced into the magnetic field sensing mechanism. From 109.6 to 125.8 Gs, the peak wavelength shift is −65480 pm and the sensitivity is −4219.15 pm/Gs, which is 28.16 times higher than that of the fabricated contrast sensing structure. The sensitivity of the magnetic field sensing structure is greatly improved by introducing the magneto-volume effect compared with the contrast sensing structure. The response time and recovery time of the sensing structure are equally 0.2 s. Therefore, the sensing structure has high sensitivity, good linearity, and short response time, which has potential application prospects in magnetic field sensing. [ABSTRACT FROM AUTHOR]

A magnetic field measurement method based on the magneto-volume effect of magnetic fluid (MF) and Fabry–Perot (FP) interferometer (FPI) is proposed, which has higher magnetic field sensitivity and shorter response time than the traditional optical fiber methods. The MF is partially injected into the fabricated FP cavity composed of two sections of SMFs and a capillary glass tube (CGT), where the FPI is made up of optical fiber end face and MF end face. When the external magnetic field is applied to the sensor, the volume change of MF will cause the change of air cavity length. Therefore, the reflection spectrum changes with external magnetic field due to the magneto-volume effect of MF. Experimental results show that the magnetic field sensor shows a sensitivity of 268.81 pm/Gs from 15.5 to 139.7 Gs even with a small amount of MF. The response time is 0.2 s at a step magnetic field of 7.7, 31.0, 46.5, and 139.7 Gs. In this work, the magnetic field sensor boasts high sensitivity, good repeatability, short response time, and low cost, which shows a great potential in applications. [ABSTRACT FROM AUTHOR]

In this article, a novel methodology to tune parameters of a resonant accelerometer realized by a flexible structure is presented. A model describing the behavior of the tuning mechanism has been proposed and experimentally validated as well as a suitable design flow is presented through case studies. The device under test, whose dimensions are in the mesoscale, adopts a resistive sensing readout strategy implemented through strain gauges, directly inkjet printed on the flexures (springs) supporting the central membrane. The tuning mechanism, which exploits the interaction between an external magnetic field and a magnetic fluid (ferrofluid) embedded in the device’s springs, has been experimentally investigated by using a lab-scale prototype. The procedure for the optimal design of the sensor has also been addressed. The prototype shows a responsivity of 721.0 $\mu $ strain/m/s2 at the resonance frequency of 30.5 Hz and a noise floor of 7.5e $- 5 { \text {m/}}\text {s}^{{2}} {/}\sqrt {\text {Hz}} $ estimated in a bandwidth of 500 Hz. Responsivities of $657.0~\mu $ strain/m/s2 and $580.0~\mu $ strain/m/s2 as well as noise floor of 8.7e $- 5 { \text {m/}}\text {s}^{{2}} {/}\sqrt {\text {Hz}} $ and 10.9e $- 5 { \text {m/}}\text {s}^{{2}} {/}\sqrt {\text {Hz}} $ have been estimated in case of the tuning magnetic fields of $H =6.8\text{e}-3$ T and $H =11.4\text{e}-3$ T, respectively, showing resonance frequencies of 31.0 and 32.5 Hz. The main novelty of the proposed approach arises from the tuning strategy that is important for many real applications requiring a fine-tuning of the sensor parameters while the use of a cheap inkjet printing technology for the device realization represents a substantial advantage in terms of costs and to enable the rapid prototyping of customizable devices on flexible substrates. [ABSTRACT FROM AUTHOR]

The permanent magnet sodium flowmeter (PMSF) without the bluff body installed on the large-diameter pipe in the fast reactors to measure the sodium coolant flow rate has to be calibrated in situ owing to the degradation of the magnetic field. Since the length of the magnetic field of the PMSF is limited in practical engineering applications, the characteristic between the cross correlation flow rate (CCFR) and the standard flow rate is nonlinear in in situ calibration based on the cross correlation method. Moreover, the nonlinear characteristic has a large repeatability error, which is difficult to apply to in situ calibration. In order to realize the in situ calibration, an “M-type” mean velocity profile in the pipe is obtained by analyzing the influence of the magnetic field on the fluid field. The distribution of the CCFR of the signal at each frequency is analyzed by using the phase-frequency characteristic of the cross-power spectral density (CPSD) of the two signals, and a physical model of the turbulence distribution in the pipe cross section is obtained combining with the “M-type” mean velocity profile. A nonlinearity correction method based on signal frequency band selection is proposed according to the physical model. The in situ calibration experiments of DN150 PMSF without the bluff body are carried out at the sodium temperatures of 400 °C. The signals within 11–20 and 18–35 Hz are used to calculate the CCFR for correcting the nonlinear characteristic, and sodium flow rate measurement accuracy is ±3.0%. [ABSTRACT FROM AUTHOR]

We present a novel methodology for magnetic field sensing by exploiting surface plasmon resonance (SPR) sensors based on D-shaped plastic optical fiber (POF) and magnetic fluids (MFs). The proposed methodology adopts a multimode POF patch covered with ferrofluid placed between the light source and the SPR-POF platform. The working principle exploits the changing of the SPR spectra due to variations of the SPR resonance conditions generated by the changing in the input light in the SPR-POF sensor due to the attractive force exerted by the target magnetic field on the POF covered with ferrofluid. A model showing a good fitting between the simulated and measured values of the magnetic field is also presented. A proof of concept for this novel sensing approach has been obtained exploiting a prototype of a sensor that has been characterized in the range of values between 0.15 and 1.2 mT. Particularly, we have estimated, in the linear range of the sensor response, sensitivity equal to about 6800 pm/mT and resolution equal to about 0.029 mT. Moreover, the comparison between the expected and the experimental behavior has shown a very good match with a mean squared error of about 5%. [ABSTRACT FROM AUTHOR]

A highly sensitive reflective Fabry–Perot (FP) magnetic field sensor using magnetic fluid (MF) based on the Vernier effect is presented and experimentally verified. Capillary action acts as an injection of MF into an FP cavity, which is composed of a single-mode fiber (SMF), capillary glass tube, and a short section of SMF coated with gold film. Vernier effect is formed by the MF cavity and air cavity in the FP magnetic field sensor, where the surface of MF is concave. The refractive index (RI) of MF depends on the magnetic field, and therefore, the wavelength of the reflection spectrum of the fabricated sensor can be sensitive to the magnetic field. The magnetic field sensor’s sensitivity is up to 1.02602 nm/Gs from 118.768 to 166.261 Gs, and the resolution is 0.0078 Gs. The sensor shows good linearity within the range of 71.317–231.751 Gs, and the linearity is larger than 0.999. In this article, a new type FP cavity fabricated by splicing SMF inside the capillary glass tube is proposed, and MF can be injected into the FP cavity, which can also be applied to other liquids to generate Vernier effect. The concave surface of MF is creatively applied to the sensors, and the experimental verification is carried out in a capillary glass tube, which provides a basis on the capillary action of other fluids in fiber sensing. [ABSTRACT FROM AUTHOR]

The benefit of transformer oil seeded with magnetic nanoparticles (forming a transformer oil-based ferrofluid) is numerically studied in an axisymmetric model of 40 kVA transformer. The maximum temperature in the system is decreased by 2.2 °C when using ferrofluid instead of transformer oil. This effect is mainly due to the magnetic body force, which modifies the convective flow in the system and enhances heat transfer. The leakage magnetic field is highly localized and limits the effect of thermomagnetic convection. Varying the geometry of the primary coil assembly allows to increase this effect and to decrease the maximum temperature. [ABSTRACT FROM AUTHOR]

In this article, the experimental investigation and analysis of the effect of rheological properties on the starting torque of the magnetic fluid seal are reported. The change of the starting torque with a standing time for perfluoropolyether-based magnetic fluid seal and diester-based magnetic fluid seal, as well as the viscosity of magnetic fluids under the relevant magnetic field and shear rate, were measured. It was observed that the magnetic fluid with higher viscosity correspondingly exhibited higher starting torque. The starting torque of seals with two different magnetic fluids exhibited the same variation tendency. The starting torque was exponentially increased with the standing time and then tended to be a stable state with small scale fluctuation. The average maximum starting torque of PFPE-based ferrofluid seal after standing five days was ten times as large as the value of the initial standing, whereas that of diester-based ferrofluid seal was 3.5 times as large the value of the initial standing. The rheological behavior was the key factor influencing the starting torque of the magnetic fluid seal. Particle agglomeration and shear thinning were the main microscopic mechanisms leading to the change of starting torque with a standing time. The correlation between macroscopic rheological properties and starting torque was established based on the microstructure variation. [ABSTRACT FROM AUTHOR]

The magnetic fluid seal is widely used in the high-speed mechanical devices. Also, the temperature of the seal increases with the viscous heating under the high shearing rate in the magnetic fluid. However, the influence of the temperature on the sealing performance has not been studied quantitatively in the available research. In this article, the change rule of magnetic fluid temperature and the influence on the sealing performance are researched through the simulation and experiment methods. The thermal field simulation is conducted with the heat generation in the fluid. To calculate the decrease of the magnetic properties quantitatively, the magnetization curves under different temperatures are measured to carry out the relationship between the saturation magnetization and temperature. Based on the magnetization curve result, the two-phase flow between air and magnetic fluid is solved under different shaft rotation speeds with the influence of temperature change. Besides, the sealing experiment is conducted with the highest rotation speed of 8000 rpm. The results of the simulation and experiment show good consistency, and the sealing capacity decreases with the rise of rotation speed. [ABSTRACT FROM AUTHOR]

We report magnetic field-driven dynamic morphological change of a liquid metal droplet: deformation and recovery; separation and merge. Low melting, non-toxic gallium-based liquid metal has been widely investigated due to its material properties and thus utilized to various applications. Morphological change of the liquid metal in required to tune characteristics of application. In order to enable the liquid metal to be non-wettable and magnetically controllable, we coated the surface with ferromagnetic iron (Fe) particles using hydrochloric acid (HCl) solution resulting in a magnetic liquid metal marble. With and without magnetic field, Fe particles-coated magnetic liquid metal marble was deformed and recovered readily. Against $\sim 8~\mu \text{L}$ magnetic liquid metal marble, depending on the coated Fe particles mass, the shape deformation under magnetic field was changed: conventional (Fe < 4mg) and arbitrary (Fe $\geqq ~4$ mg) wetting shape. Accordingly, the deformability and recovery time of the magnetic liquid metal marble were varied. With an applied magnetic field, one marble was readily separated into 2, 3, and 4 marbles. Due to re-oxidation of the magnetic liquid metal marble surface, we treated the marble with HCl solution and vapor. Split and merge occurred depending on treatment time of HCl solution or vapor. Finally, we demonstrated magnetic field-based dynamic behavior which is reversible. [2020-0218] [ABSTRACT FROM AUTHOR]

A new, linear, nonintrusive, and cost-effective inductive liquid level sensor is designed and developed. The sensor consists of a simple coil that floats on the liquid surface. A couple of printed planar coils partially surround the liquid column and sense the position of the floating coil and hence the liquid level. The planar coils are arranged with overlap such that the floating coil is always in proximity to both the coils. The coils are excited, and their response is processed, such that the final output is proportional to the liquid level. The input–output characteristics of the proposed liquid level measurement are linear, with a worst case percentage nonlinearity < 1%. A prototype sensor built for a range of 180 mm, had a resolution of 0.73 mm. The output of the prototype has very low sensitivity to the position of the floating coil in the xy plane, indicating that the movement of the floating coil on the surface of the liquid column does not affect the liquid level measurement. Since the sensing part is just made of passive elements, the lifetime of the sensor can be made very high. [ABSTRACT FROM AUTHOR]

A novel design of a magnetorheological (MR) damper is developed, fabricated, modeled, and tested. The design includes some features that enhance the magnetic characteristics of the damper. The iron–cobalt–vanadium “Vacoflux-50” alloy and the “AMT-Smartec+” MR fluid, whose magnetic characteristics have been predicted to enhance the performance of the damper, are used in the new design. Moreover, the location of the MR fluid region in the piston construction has been chosen so that the magnetic field maximizes. To evaluate the impact of the proposed design improvements, an approach to modeling the performance of a previously tested MR damper of a different design, different magnetic material, and different MR fluid has been developed. The approach combines a finite element analysis (FEA) of the magnetic circuit and a nonlinear analytical model of fluid flow. The results of the FE/analytical approach have been validated using the available published results of the same damper. Hence, the approach has been used to predict the performance of the same damper due to the use of the proposed design improvements. The FE/analytical approach accounts for the nonlinear characteristics caused by the magnetic saturation of materials and the effects of fluid compressibility and aeration in the damper. It has been found that the implementation of the proposed design features leads to a remarkable increase in the magnetic field and the fluid yield stress. Also, the inclusion of the nonlinear magnetic and fluid flow characteristics have been found to affect the magnetic field distribution and the fluid yield stress greatly. [ABSTRACT FROM AUTHOR]

In this article, a novel inclinometer exploiting a magnetic fluid as the inertial mass and an optical readout strategy is addressed. In particular, the device behavior has been modeled and experimentally observed by means of a dedicated set-up. The proposed inclinometer uses a 5-mm diameter glass pipe filled with water and a drop of ferrofluid (FF), a retaining mechanism based on a permanent magnet and an infrared (IR) readout strategy. The latter is used to measure the position of the inertial mass inside the pipe, which strictly correlated with the sensor inclination. The main outcomes of the proposed sensing solution consist of the use of a passive restoring mechanism and an IR sensing strategy, which are convenient in terms of power budget with respect to sensors exploiting an electromagnetic readout strategy and a powered restoring mechanism acting on the inertial mass. The developed lab-scale prototype exhibits an operating range of ±15°, a responsivity of 0.56 V/°, and a resolution of 0.25°, as well as a span-to-threshold value of 120. [ABSTRACT FROM AUTHOR]

Electroactive-Polymers (EAPs) are one of the best soft $\mu $ -actuators with great biomedical applications. Ionic ones (i-EAPs) have more promising features and have adequate potential for using in the active microfluidic devices. Here, as a case study, we have designed and fabricated a microfluidic micromixer using an i-EAP named Ionic Polymer-Metal Composite (IPMC). In microfluidics, active devices have more functionality but due to their required facilities are less effective for Point of Care Tests (POCTs). In the direction of solving this paradox, we should use some active components that they need minimum facilities. IPMC can be one of these components, hence by integrating the IPMC actuator into a microfluidic channel; a micromixer chip was designed and put to the simulation and experimental tests. The result showed that the proposed micromixer can mix the micro fluids properly and the IPMC actuator has adequate potential to be an active component for POCT-based microfluidic chips. [2020-0013] [ABSTRACT FROM AUTHOR]

Synchronized motion and pattern formation of magnetic particle aggregates in variable magnetic field is of growing interest from the point of view of both fundamental science and its applications. In this article, the role of size differences in synchronized motion of magnetic particles under external rotating magnetic field at low Reynolds number flow regimes is considered. Several different motion regimes are observed in simulations as a function of particle size differences and field rotation rate. Simulation indicates phase-like transitions between different motion regimes when particle size differences become significant. It is also shown that particle size differences permit the possibility of locomotion for particle aggregates which cannot be observed for uniform particle sizes. [ABSTRACT FROM AUTHOR]

There has been no study for measuring the comprehensive flow field of magnetic fluids. A pumpless transport system has been envisaged based on the temperature dependence of the magnetization of magnetic fluid; however, the knowledge regarding the internal flow is still limited. It is difficult to optimize the design and realize the practical use of the transport system using magnetic fluid. Therefore, in this study, for the first time, a two-dimensional flow field was visualized by encapsulating a magnetic material in a microcapsule and labeling it with fluorescence. The flow field was measured with high accuracy using a fluorescent capsule, and the effectiveness of this method was demonstrated. When a magnetic field was applied, the location of the velocity peak shifted toward the magnetic field. Chain clusters were generated and gathered on a wall. The clusters maintained their shape and slid on the wall owing to the fluid shear force. At high temperatures, the capsules did not form clusters, and there was no change in peak velocity. In a previous study, it was shown that the heat transfer efficiency of magnetic fluids increases when a magnetic field is applied. In this study, it was suggested for the first time that the clusters generated on the wall promoted heat transfer on the wall, and the wall velocity could induce a change in the temperature boundary condition. The results of this study can help elucidate the flow characteristics of magnetic fluids and optimize the device design of the transport system using magnetic fluid. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the size induced on the viscoelasticity of CoFe2O4 magnetic nanofluids (MNFs). The focus of this work is to provide an insight into the effect of varying particle size on viscoelastic properties of CoFe2O4 MNFs with varying CoFe2O4 nanoparticle sizes. Kerosene-based MNFs containing surfactant coated CoFe2O4 were synthesized using standard optimized coprecipitation method, and variations in average mean size ~ 9–30 nm have been synthesized. The physical properties, such as structural and morphology, have been investigated to confirm the purity, and variation in size. Steady-state and oscillatory mode measurements were performed using a magneto-rheometer to investigate the field-induced magneto-rheology. The steady-state rheograms (viscosity vs. shear rate curve) has been well fitted with power-law $\eta =c\dot {\gamma }^{n}+\eta _{\infty }$ , confirming the shear thinning behavior with $n\le 1$. Furthermore, magneto-sweep rheograms (viscosity vs. magnetic field) has been used to investigate the steady increase in viscosity, which is due to the formation of a chain-like structure in the field direction causing an interruption in the smooth streamline flow of the MNFs. Furthermore, dynamic oscillatory measurement shows the transition between G’ and G” with applied dynamic strain confirming solid-liquid phase transition behavior. Field-induced viscoelastic behavior in static and dynamic mode provides significant information for optimization of MNFs for various applications. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles of nickel ferrite were synthesized by using the high-temperature thermal decomposition method. The crystal structure and the size of the nanoparticles were determined. The magnetic properties of the nanoparticles were studied in detail, as well as the heating power of a magnetic fluid prepared with the synthesized nanoparticles. X-ray diffraction revealed that the nanoparticles crystallized in the cubic spinel structure. Transmission electron microscopy showed two populations of dispersed nanoparticles. The mean particle size of the most abundant population is approximately 13 nm. Magnetization measurements showed that the nanocompound is in the superparamagnetic regime at room temperature. It was found that nanoparticles have giant magnetic moments of more than 16 $\text{k}\mu _{\mathrm {B}}$. Self-heating experiments carried out in ac magnetic fields indicate that the nanoparticles have high efficiency as heating agents. Specific power absorption (SPA) and intrinsic loss power (ILP) values as large as 997 W/g and 3.6 nH $\cdot \text{m}^{2}$ /kg, respectively, were obtained. [ABSTRACT FROM AUTHOR]

The minimum point determination method of the magnetic energy surface has been proposed on the basis of magnetic dipole theory in our study. This method can effectively explain the behaviors that the polydisperse magnetorheological fluids (MRFs) can form more complex chain-like structures and the magnetic energy of the particle system will decrease with the formation of the aggregations. The minimum points on the magnetic energy surface of two-particle and three-particle system are observed, and several kinds of stable microstructures are obtained by analyzing these points. Finally, both the stability and evolution mechanism of these microstructures have been explored based on the concept of the magnetic energy barrier. The results demonstrate that a minimum point on the magnetic energy surface of the particle system corresponds to a type of stable microstructure, and the migrations between the minimum points in the systematic magnetic energy phase space can be accounted for the mutual evolutions of these stable microstructures. The microstructural stability depends on the magnetic energy barrier height. For this reason, the microstructural evolution is more likely to appear when the barrier height is relatively low. In the case of sufficient perturbation, the particle system always evolves into the state with lower magnetic energy. [ABSTRACT FROM AUTHOR]

We have showed that surface layer can determine cardiac effects of the magnetic nanoparticles (MNPs). Considering the high binding capacity of albumin and low side-effects, the aim of this study was to evaluate the influence of albumin coating on the cardiovascular effects of two manganese ferrite-based MNPs: citrate-coated and bare MNPs. Isolated rat hearts were perfused with citrate-coated magnetic nanoparticles (CiMNPs), citrate albumin-coated magnetic nanoparticles (CiAlbMNPs), bare magnetic nanoparticles (BaMNPs), and albumin-coated magnetic nanoparticles (AlbMNPs). CiMNPs induce a transient decrease in the left ventricular end-systolic pressure, +dP/dt and −dP/dt. These effects were not worsened by albumin coating. BaMNPs significantly increased the left ventricular end-diastolic pressure and perfusion pressure and decreased the +dP/dt and −dP/dt. These effects were completely absent in hearts perfused with AlbMNPs. None of the MNPs changed heart rate or arterial blood pressure in conscious rats. Magnetic signals in isolated hearts perfused with BaMNPs were significantly higher than AlbMNPs perfused hearts. However, the magnetic signal in heart tissue was similar when the MNPs were infused in conscious rats. These data indicate that albumin-coated can reduce cardiovascular effects of MNPs. These findings suggest a protective effect of albumin surface in MNPs, favoring its future therapeutic applications. [ABSTRACT FROM AUTHOR]

A magnetic fluid ring, which can be compared to a liquid O-ring, held at a given place by a magnetic field is used for various applications, such as seals, compressors, dampers, or sensors. The work of this type of system is the result of a number of factors, such as the distribution and magnitude of the magnetic field in the gap, rheological and magnetic properties, physical properties of the surrounding environment (interfacial phenomena) and operating conditions (differential pressure and relative velocity). The research area of this publication is related to the recognition and assessment of how the magnetic fluid properties influence the mechanism of the local loss of continuity for a single liquid ring. This applies to the case when the differential pressure on two sides of the magnetic fluid-free surface exceeds a critical value and a leak channel is formed. Previous studies have shown that the process of equalizing the pressure difference in this type of system is related to pressure jumps. This phenomenon has not been linked to such properties as saturation magnetization, dynamic viscosity or surface tension. This paper takes these factors into account. In addition, the shape of the stage (trapezoid and rectangle) on which the fluid is held and the magnetic field value are considered. The loss of continuity is an important issue and the obtained results allow this problem to be better understood and the magnetic fluid to be chosen for appropriate working conditions, e.g., in the case of multistage seals. The studied phenomenon may also contribute to the development of new types of pressure regulators or sensors. [ABSTRACT FROM AUTHOR]

An advanced plasmonic sensor for high sensitivity measurement of magnetic field is presented. It is based on the combination of a SPR refractometer (doubly-deposited tapered optical fiber) with magnetic fluids used as transducers. The device is compact and robust and has been theoretically analyzed and completely characterized, showing a very good experimental performance. We have studied the dependence of the response of the device with the direction of the field, confirming that, as expected, the sense of the variation of the refractive index is opposite for parallel and perpendicular fields, which is an interesting feature for practical applications. We have also evaluated the dependence on the concentration of the employed magnetic fluid and the influence of the chosen type of ferrofluid. In all these measurements the sensitivity experimentally obtained is amongst the highest reported in the literature for this kind of devices and we have extended the dynamic range. Finally, we have applied a novel, auto-referential, signal processing algorithm to the measurements, showing its possibilities. The obtained experimental results demonstrate the feasibility and the advantages of the application of SPR fiber-optic sensors to magnetic field measurements. [ABSTRACT FROM AUTHOR]

The liquid conducting film flowing along a diverging gap between rail and armature in a railgun is considered. This paper attempts to investigate whether the liquid film flowing along a diverging gap can achieve purely hydrodynamic lubrication preventing direct contact between rail and armature. Specific cases of linearly diverging gaps are assumed with a minimum thickness at leading edge. Analytical solution of pressure distribution is obtained with the lubrication approximation. The carrying capability of film is estimated by integrating the pressure distribution numerically. Conditions for stable liquid film are proposed through analyzing positive pressure distribution and carrying capability of the film. If the film can generate positive pressure distribution and its carrying capability is able to support the contact force between rail and armature, stable film appears which can prevent direct contact between the rail and armature surfaces achieving purely hydrodynamic lubrication. In the end, hydrodynamic lubrication stability of a liquid conducting film under different film thickness and launching mass are analyzed and discussed. It is found that the film’s stability can be improved with the increase of film thickness and launching mass. A thicker film and heavier load are well expected in order to realize hydrodynamic lubrication at high speed. [ABSTRACT FROM AUTHOR]

This paper describes the deformation control of a ferrofluid-based robotic sheet for object handling. The ferrofluid sheet consists of ferrofluid wrapped in thin polyethylene sheets and allows us to handle the transport of objects by controlling its deformation due to the characteristics of a ferrofluid. To control sheet deformation, we need to develop the sheet’s mechanical model. Although the mechanical model of the ferrofluid has already been researched, the effect of the polyethylene sheet on the ferrofluid has not been considered. In this paper, we first verify the relationship between the fluid shape in the ferrofluid sheet and the thickness of the sheet on the fluid. Next, we verify the transportation method by making the ferrofluid sheet to move two balls simultaneously and a thin circular plate on its surface. We also confirm the deformation control of this robotic sheet in an alternative configuration. The achievement contributes to the technology for soft robotics and advanced control, opening new aspects for fluid-based 3-D manipulations. Note to Practitioners—This paper is motivated by the problem of manipulation of flexible objects. It is difficult for conventional manipulators to handle flexible objects, such as droplets, because their shapes dynamically deform while being handled. We considered that a flexible system should be able to conform to the object shape. Therefore, we investigate the possible use of a ferrofluid as an actuating component because of its fluidity and peculiar characteristics. A ferrofluid has the characteristics of a fluid and magnetic material; therefore, the fluid gathers around the source of a magnetic field and applies force to an object on it. In this paper, we verify the characteristics of the proposed system as well as the object manipulation. Through characteristic verification, the behavior of our system can be modeled, and the method of object transportation can be systematized. [ABSTRACT FROM AUTHOR]

An all-fiber magnetic-field sensor combining a multicore fiber taper and magnetic fluid is proposed and experimentally demonstrated. The magnetic-field sensing mechanism is investigated theoretically and experimentally. Experimental results demonstrate that the dip-wavelength of the proposed sensor regularly varies with the changes of the applied magnetic field. The measuring sensitivity is achieved to be ~34 pm/Gs in the magnetic induction intensity range of 50–300 Gs. Moreover, the sensor responding to the 50-Hz alternating magnetic field is also experimentally investigated, and a minimal detectable magnetic induction intensity of ~23.7 Gs is successfully achieved. The proposed magnetic field sensor is attractive due to its compact size, low cost, and immunity to electromagnetic interference. [ABSTRACT FROM AUTHOR]

In this paper, techniques to improve the collector’s dissipated power density threshold are discussed first. Then, theories of electron collection are presented, aiming at improving the effective electron-collecting area and collecting uniformity. Specifically, the layered electron beam collection in linear-taper collector, respectively, with constant and gradually varying magnetic field is modeled and discussed. Results indicate that a quasi-rectangular shape collection can be realized as the tangential collection dominates. Finally, the using of a compensation coil is analyzed and the corresponding collector is designed. [ABSTRACT FROM AUTHOR]

To improve the pressure capability of ordinary ferrofluid seals with a large gap, a novel type of converging stepped ferrofluid seals was proposed. The leakage positions and the magnetic field distributions in the sealing gaps of the new device are studied computationally by means of the finite-element method. The theoretical pressure capabilities of the seal are calculated based on a new expression introduced for the particular new seal geometry and for different sealing gaps. Computational results for effects of the radial and axial sealing gaps on the pressure capabilities of the seal are compared to the experimental results obtained from measurements employing a prototype of the proposed new seal. A good agreement between theoretical and experimental results is obtained. It is found that the pressure capabilities of the new seal depend on the height of the radial sealing gap and on the width of the axial sealing gap. [ABSTRACT FROM AUTHOR]

With the development of science technology, ferrofluid seal has been intensively applied in mechanical industry, but more and more larger sealing stages are needed. At present, the literature mostly concentrated on numerical analysis with few pole pieces ferrofluid seals and focused on the critical pressure value in one-stage magnetic fluid seal, lacking of numerical simulation and experimental validation on the static pressure of multi-stage ferrofluid seals. On this basis, the analysis of larger number of sealing stages is presented. And numerical simulation along with experiment investigation was used to study the seal capacity of ferrofluids in different seal gaps and different seal stages in this paper. The results show that the theoretical value is well coincident with experimental value when the sealing gap is less than 0.2 mm. Increase the number of the pole tooth can significantly improve the seal capacity of ferrofluid seal, but the sealing pressure of ferrofluids does not increase linearly with the addition of the number of pole teeth. For the new structure, the pressure of one-stage pole tooth has more than doubled as the sealing clearance is 0.2 mm and 3.5 times increase when the sealing gap is 0.3 mm. [ABSTRACT FROM AUTHOR]

The magnetic fluid seal is one of the best known and widely used technical applications of magnetic fluid. However, the boundary and the flow regime with the rotation shaft cannot be observed by the experiment method. This paper presents a novel numerical simulation method to obtain the boundary and the velocity of the fluid in seals. The magnetic field of the seal is solved by the finite-element method, and the Navier–Stokes equations of the magnetic fluid based on the influence of magnetic force are solved by the finite-volume method. The two-phase flow is solved by the volume of fluid method. The seal capacities of the rectangle tooth and the trapezoid tooth with different rotation velocities are obtained. The result shows that the seal capacity decreases with the increase in the rotation velocity. [ABSTRACT FROM AUTHOR]

The relationship between integrated media noise power and linear density in heat-assisted magnetic recording (HAMR) is discussed. A noise plateau for intermediate recording density has been observed in HAMR, similar to that found in perpendicular magnetic recording (PMR). Here, we show, by changing the temperature profile of the heat spot in HAMR, that we can tune the noise plateau regions to different recording densities. The heat spot with sharp temperature gradient favors a plateau at high recording density, while the heat spot with gradual temperature gradient favors a plateau at low recording density. This effect is argued to be a consequence of the competition between transition noise and remanence noise in HAMR. [ABSTRACT FROM AUTHOR]

A tunable polarization beam splitter (PBS) is proposed based on a dual-core photonic crystal fiber (DCPCF). The DCPCF is filled with magnetic fluids in the air holes, whose refractive index varies with the magnetic field strength. The two polarized modes are separated into the two cores at the output ports in a magnetic-free condition. When magnetic field is applied, the output intensities of the two polarized modes would fluctuate. The polarized modes can be ported out with arbitrary proportion by adjusting the magnetic field intensity. Moreover, the polarized mode would be completely converted at some magnetic field strength. The properties of the DCPCF are investigated by the finite element method (FEM), including mode-conversion magnetic field strength, extinction ratio, fabrication tolerance of the PBS, and the performance of PBS at various temperatures. The numerical results show that at 1550-nm wavelength, the length of the tunable PBS is 8.13 mm. The polarized mode converts at a magnetic intensity of 25 mT with a high extinction ratio greater than -100 dB. In addition, the tunable PBS sustains a fabrication tolerance of at least 0.5% and works well at temperatures in the range of 0-55 °C by adjusting the magnetic field strength.

Magnetic fluid is a new type of functional materials. The seal of reciprocating shaft is a typical application of the magnetic fluid. However, there is little research on the magnetic fluid reciprocating seals, thus improving the sealing life and seal capacity is the key problem of studying the reciprocating seals. This paper presents a structure of the seal to test the sealing life and other characteristics. The magnetic field of the seal is estimated using the finite-element method. The thickness of the magnetic fluid on the surface of reciprocating shaft and the flow rate of magnetic fluid are obtained theoretically. The experimental result shows that the static seal capacity is related to the fluid volume. The static seal capacity obtained by experiment is approximately equal to the value through the simulation with sufficient magnetic fluid. The relationship between sealing life and the motion of the reciprocating shaft is obtained experimentally. The sealing life decreases rapidly with the increase of the stroke and velocity. [ABSTRACT FROM AUTHOR]

The noise generated by rotating machines and electrical transformers is harmful and its reduction has been the subject of several studies. Such systems are likely to come into resonance and become noisier. This resonance may come from mechanical or magnetic forces. The phenomenon of resonance is usually studied only if the frequency and the known spatial distribution of the excitation force are consistent with the natural frequency and the shape of the corresponding mode of the structure. We demonstrate in this paper that magnetostriction can induce resonance without, however, knowing its spatial distribution. A ferromagnetic frame made of a stack of non-oriented electrical steel (e.g., low-power transformers for railway applications) is used to confirm that mechanical resonance can be induced by magnetostrictive strain at a very low magnitude in in-plane and out-of-plane directions. Finite-element calculations are performed with laminated model and vibratory measurements are presented. A numerical model based on homogenization technique is also detailed. Then, experimental and computation results are analyzed and compared. Finally, results of resonance under magnetization when double the magnetizing frequency matches the resonance frequency of the ferromagnetic frame are described as well as the corresponding spectrum. [ABSTRACT FROM AUTHOR]

Compared with a ferrofluid (FF) seal used as a sealing material, magnetorheological (MR) fluid has higher sealing pressure at the same condition. This is because MR fluid not only has magnetic property but also shows obviously elasto-plastic performance, which differs from FFs, under the magnetic field. On this basis, this paper analyzed, respectively, the static seal performance of MR fluids and FFs based on their magnetic properties through experimental and numerical studies. The results showed that an obvious pressure drop happened when the pressure is about 400 kPa in seal cavity for MR fluid seal, but the pressure was quickly down to around 390 kPa; nevertheless, the maximum pressure of the FF seal is 200 kPa, and the seal time with leak-free is about 2.5 min, and then the value quickly goes down to zero. The maximum pressure of every pole tooth of FF seal is about 11.11 kPa. The pressure of MR fluid seal is 21.67 kPa when there is a significant decrease during pressuring, and the maximum pressure of every pole tooth of MR fluid seal is 41.37 kPa. At last, the relationship of the sealing pressure of MR fluid seal with the time was derived. [ABSTRACT FROM AUTHOR]

Triangular-shaped single-crystalline Fe3O4 nanoparticles were synthesized using 1,3-propanediamine via a hydrothermal process and their magnetorheological (MR) characteristics were examined. Their crystallinity, magnetic property, and morphology were examined by X-ray diffraction, vibrating sample magnetometer, and transmission electron microscopy, respectively. The MR properties of triangular-shaped Fe3O4 nanoparticles dispersed in silicone oil were investigated using a rotational rheometer under external magnetic field strengths applied. Typical MR behavior of a phase change from liquid-like to solid-like was observed along with significant changes of rheological properties such as shear stress, viscosity, and yield stress. [ABSTRACT FROM AUTHOR]

Fault current limitation is an urgent but challenging technology for medium-voltage dc (MVDC) power systems. For a liquid metal current limiter (LMCL), the arc discharge characteristics often determine its current-limiting properties. The evolving arc in liquid metal is measured by contacting voltage probes, and the properties of the formed dumbbell-like arc column are studied and discussed in detail. It indicates that the total arc voltage almost behaves as a linear function of arc current for an LMCL. Besides, a simplified numerical arc model based on magnetohydrodynamics theory is built and solved by the software FLUENT. It is concluded that the temperature rather than the slightly fluctuant pressure dominates the arc properties, which coincides well with test results to some extent. Finally, a fault current limiter topology including serial LMCLs and parallel resistors is put forward, whose feasibility for MVDC application is discussed on the basis of its current-limiting behaviors. [ABSTRACT FROM AUTHOR]

One of the main engineering applications of ferrofluids is in magnetic fluid seals, working in rotary motion. An area, which has so far been insufficiently examined, is the mechanism of leaks between seal stages in this type of seal. This is an important issue in order to understand the principle of the seal operation and to properly design this type of seal. This paper presents the results of research into the mechanism of leaks between stages in multi-stage magnetic fluid seals. The tests were conducted when the pressure of the sealing air increased and reached its maximum value. The influence of the magnetic fluid properties, such as saturation magnetization or dynamic viscosity, was taken into account. Studies were performed for different seal temperatures. Experiments allowed models for determining the maximum pressure of the multi-stage seal to be proposed, based on the information about this pressure for a one-stage seal. This paper presents the comparative results of the critical pressure value obtained from experimental studies and calculations based on numerical simulations. [ABSTRACT FROM PUBLISHER]

Microwave-assisted (MWA) technique has been used in the syntheses area as it has many advantages over the conventional routes. Optimization of one-pot synthesis of ferrofluid was conducted using domestic 2.45 GHz microwave (MW). The nanoparticles were synthesized in an aqueous solution of FeCl3.6H2O as precursor and NH3 as nucleating agent. Although there are a number of reports on the MWA iron oxide nanoparticle synthesis, a quantitative optimization study on the process is still lacking. Here, MW parameters were manipulated in order to optimize the synthesis. The optimization was designed and statistically analyzed using face-centered central composite design software. The optimized conditions for MWA synthesis of ferrofluid were 80 °C reaction temperature, 14 min reaction time at 300 W producing 0.338 g of magnetic nanoparticles. Based on the characteristic studies done on synthesized ferrofluid by using X-ray diffraction, field emission scanning electron microscope, antitransmit receive (ATR) Fourier-transform infrared spectroscopy, and vibrating sample magnetometer, the nanoparticles possessed the same structure as the standard maghemite with good magnetic properties. The process produces ferrofluid of high purity with an average crystallite size of ~15 nm. [ABSTRACT FROM PUBLISHER]