A large portion of energy consumption (50%) in buildings arises from heat transfer to buildings, specifically through windows due to solar illumination. Energy-efficient thermochromic smart windows, which are composed of special materials that enable them to adjust light transmission dynamically based on the ambient temperature, can allow energy demand for building cooling to be reduced. Hybrid halide perovskites are promising candidates for thermochromic smart windows owing to their capability to undergo reversible color and phase transitions between low and high temperatures. Furthermore, a new concept for smart photovoltaic windows has been realized based on inorganic perovskite CsPbI3-xBrx thin films, which possess both photovoltaic and thermochromic features. However, the perovskite-based thermochromic smart windows require relatively high transition temperatures (>50°C), and this hinders their practical application in buildings since in most places the window temperatures do not reach 50°C in direct sunlight. Therefore, a configuration based on a thermochromic perovskite layer integrated with an external heating source is needed for the activation of thermochromism. Transparent heaters are a key component in thermochromic smart window devices that employ transparent conductive electrodes (TCEs) to provide electric heating. Low resistance and high optical transparency of TCEs are two essential prerequisites for the fabrication of thermochromic smart windows. Among various TCEs, indium tin oxide (ITO) is most commonly used; but the brittle nature limits its application in flexible optoelectronics, and the scarcity of indium results in high material cost. Transparent and conductive metal nanomesh (NM) films, which are composed of periodic nanostructured metal networks, have gained considerable attention as high-performance TCEs offering several advantages, including excellent mechanical flexibility, high conductivity, tunable transmittance, and low fabrication cost. In this study, we introduce a new class of dielectric/metal/dielectric nanomesh films based on ZnO/Au/Al2O3 with periodicities of 200 nm and 370 nm which are fabricated using nanosphere lithography. For the metal mesh film design, an Au (15nm) thin film is chosen as the electrode material due to its malleability and high electrical conductivity. Thin layers of Al2O3 film (20 nm) and ZnO film (20 nm) are used as high refractive index dielectric layers to induce antireflective effect and suppress surface plasmons. We use relatively smaller metal mesh periodicities of 200 nm and 370 nm as compared to previously reported nanomesh films to create a potential pathway to optoelectronic applications, such as smart windows. As a result, the ZnO/Au/Al2O3 NM film with a 370-nm periodicity exhibits a transmittance over 90% at 550 nm and sheet resistance lower than 20 Ω/sq. Based on a standard figure of merit, this structure outperforms current state-of-the-art nanomesh films. Moreover, we integrate the ZnO/Au/Al2O3 NM film into thermochromic perovskite smart windows that operate by inducing a thermochromic transition from transparent to opaque state via electric heating of ZnO/Au/Al2O3 NM film at 50°C, which can be then maintained solely by 1-sun AM 1.5G solar illumination. This climate-adaptive, low power-activated, and fast-switching smart window structure opens new pathways toward its practical application in the real world.

Climate-Adaptive Thermochromic Perovskite Smart Window Structures

Blue and green InGaN/GaN light-emitting diodes (LEDs) are crucial for solid-state lighting and display applications. Violet–blue LEDs have achieved a high EQE of ~80%. However, InGaN/GaN LEDs still suffer from strong efficiency loss in the green region, which is usually referred to as the “green gap.” The green gap issue has been related to Auger recombination, the quantum-confined Stark effect (QCSE), carrier leakage, random alloy fluctuations, and defects and carrier localization, among other causes. To achieve longer emission wavelengths, the indium composition must be increased, leading to several problems. First, high indium content increases lattice mismatch and introduces additional point defects during metalorganic chemical vapor deposition (MOCVD). High indium content also leads to strong polarization-related electric fields in the quantum wells (QWs), lowering the wave function overlap and decreasing the radiative and non-radiative recombination rates (i.e., from the QCSE). An important question is how much of the change in efficiency reduction from blue to green is due to intrinsic effects (i.e., wave-function overlap and phase-space filling (PSF)) vs. extrinsic effects (i.e., material degradation). In this work, we use small-signal electroluminescence (SSEL) to study the carrier dynamics in commercial c-plane LEDs with various emission wavelengths ranging from blue (~470 nm), to cyan (~500 nm), to green (~530 nm). The LED series consists of three wafers grown by Lumileds with identical active region designs (3X, 3 nm QWs) but different indium compositions. LEDs with mesa diameters of 100 µm and ground-signal-ground electrodes were fabricated. SSEL was then used to study the carrier dynamics of the LEDs. Each element in an equivalent circuit model was acquired via simultaneous fitting of the impedance and modulation responses, leading to the injection efficiency and total carrier recombination lifetime. Combining the total carrier lifetime with internal quantum efficiency (IQE) enables the separation of the radiative and non-radiative recombination lifetimes and rates as a function of carrier density (n) and current density (J). The results reveal that efficiency loss at longer wavelength is related to reductions in injection efficiency and radiative recombination, and an increase in Auger recombination. The interplay between the QCSE and carrier-current density relationship is shown to determine the relative importance of the radiative (B(n)*n2) and non-radiative recombination rates (A(n) and C(n)*n3) as the indium content is increased. Both the SSEL experiment and Schrödinger-Poisson calculations showed C(n)/B(n) is similar for the three wafers at high n, indicating that intrinsic material degradation is not significant. In addition, compared with QCSE, PSF, and material degradation, the increase of the carrier density at a given J for longer wavelengths is the dominant reason for the green gap. Thus, methods to decrease the carrier density in each QW are suggested to increase the EQE of green LEDs.

Carrier Dynamics in Blue, Cyan and Green Commercial InGaN/GaN LEDs Measured by Small-Signal Electroluminescence

GaN-based light emitting diodes (LEDs) for white light illumination are one of the biggest technological achievements in energy efficiency. However, challenges remain with GaN-based LEDs such as efficiency droop and low efficiency for longer wavelengths. Auger-Meitner recombination, a three-carrier process, has been identified as the dominant mechanism for efficiency droop via electron emission spectroscopy (EES). In EES, LEDs were activated to negative electron affinity (NEA) to allow for the emission of hot electrons from the surface which were quantitatively correlated to Auger-Meitner recombination processes. In recent years, V-defects have been proposed as the solution to the excess driving voltage of long wavelength nitride-based LEDs, one of the sources of their diminished efficiency. One way to image the effects of V-defects is using electron emission microscopy (EEM). EEM is a newly developed technique analogous to EES that allows for spatially resolved microscopy of hot electrons. EEM uses a low energy electron microscope with its illumination column turned off, such that only internally generated electrons escaping out the surface during electrical driving of the device are observed. Commercial blue (λ ≈ 460 nm) and green (λ ≈ 525 nm) LED wafers from Seoul Viosys were acquired and processed into LEDs. The diodes were formed by Pd/Au (20/30 nm) p-contacts with open circular and hexagonal apertures lithographically defined with known dimensions. A C-shaped n-contact partially surrounding the p-contact was formed by reactive ion etching into the n-region and contacted with Ti/Au (30/300 nm). EEM was performed in an ELMITEC LEEM III system modified to allow for electrical biasing of devices from the sample stage, where Cs was deposited onto the sample using a SAES Getters Cs source to activate the sample to NEA. For LEDs, EEM images the non-radiatively-recombined electrons that cross the diode junction and diffuse through the p-GaN and escape out the surface, which can include overflow, Auger-Meitner, and trap-assisted Auger-Meitner electrons. EEM images of blue and green LEDs show non-electron emitting regions (dark spots) with densities of ~2 × 107 cm-2 and ~3 × 108 cm-2, respectively, which we identify as V-defects. This is confirmed through the corresponding dark spots of panchromatic CL measurements of the same samples, as well as SEM and plan-view TEM for V-defect densities. Since the density and dimensions of the non-electro-emitting and non-illuminating regions are identical, we attribute our measured lack of electron emission directly from the V-defect areas to electrons fast traveling through the sidewalls of the V-defects and being injected laterally and efficiently into planar quantum wells without any Auger-Meitner recombination or overflow within the sidewalls. This is supported by the stronger electron emission observed at the ridge of the V-defects due to larger carrier densities there and thus increased hot electrons generation. Our results agree with simulations that electrons travel up the sidewalls of V-defects that have been nucleated prior to the active region and directly inject themselves into the quantum wells in the active region, so the carrier density in these sidewalls is negligible [1]. Support at UCSB was provided by U.S. Department of Energy under the Office of Energy Efficiency & Renewable Energy (EERE) Award No. DE-EE0009691. [1] C.-H. Ho, J. S. Speck, C. Weisbuch, and Y.-R. Wu. Phys. Rev. Appl. 17, 014033 (2022).

Electron Emission Microscopy of an Electrically Driven III-Nitride-Based LED: Evidence of Lateral Electron Injection at V-Defect Sidewalls

Ferrite-based junction circulators [1,2] are microwave devices made of at least three ports that have been widely used in emission/reception applications ensuring an
isolation between the incoming and outgoing signals. They are especially useful in single antenna applications where signals are being transmitted and received simultaneously.
Conventional circulators are based on a ferrite disk, magnetized to saturation, placed under the central conductor ensuring electromagnetic waves to propagate in a non-reciprocal manner.
The external magnetic field allowing this saturation is provided by a permanent magnet positioned right above of the central conductor.
Due to the size, weight, cost of these systems and the fact that high frequency applications are recently the main concern, the miniaturization of the circulator is inevitable. This can be
achieved using self-biased hexagonal ferrite materials [3,4] which eliminates the use of a permanent magnet. These self-polarized materials, suitable for high frequency applications, are
pellets made out of hexaferrite powder pressed and sintered. During pressing, the orientation of the particles should be achieved in the remanence state using an external magnetic field. In
order to avoid the application of a magnetic field during pressing, and thus to minimize the cost of manufacturing circulators, we propose to design and manufacture circulators based on
hexaferrite particles in the form of platelets. It has been shown that this platelet shape, as shown in Fig. 1, induces a self-alignment of the crystals with the particles orienting themselves
spontaneously, therefore dropping the application of an external magnetic field in any way. This material will be then characterized using a coaxial cell capable of determining its dielectric
and magnetic properties such as the permittivity and the permeability [5]. The values obtained will then be used in the simulation of a coplanar circulator [6,7], that operates in the 5G band
especially around 28 GHz, using HFSS simulator. 

**References ** 
1. H. Bosma, IEEE Transactions on Microwave Theory and Techniques, Vol 12(1), p. 61-72 (1964). 
2. Y. S. Wu and F. J. Rosenbaum. IEEE Transactions on Microwave Theory and Techniques Vol 22(10), p. 849-856 (1974). 
3. N. Zeina, H. How, C. Vittoria, In 1992 IEEE International Magnetics Conference (INTERMAG), pp. 458-458 (1992). 
4. N. Noutehou, C. Patris, D. Névo, Circulateur planaire ultra-compact en bande Q." In JNM (2019). 
5. F. Costa, M. Borgese, M. Degiorgi, In Electronics, Vol 6(4), p. 95 (2017). 
6. O. Zahwe,H. Harb and H. Nasrallah, Int. Arab J. Inf. Technol., Vol 16(3A), p.600-608 (2019). 
7. R. El Bouslemti,F. Salah-Belkhodja and Y. H. A. Fekhar, Revue Méditerranéenne des Télécommunications, Vol 4(1) (2014). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/a9382678fd6176ba6e400762d0ad1e12.png)

Development of an Auto Oriented Circulator Based on Hexaferrite Materials in the 5G Frequency Band

One of the most important parts of a fluxgate sensor is the magnetic core. This work is dedicated to the study of fluxgate sensors based on the nanocrystalline wire as a core
and comparing them to the performance of amorphous wire with chemical composition (Co94Fe6)75Si15B10 [1]. Both wires were manufactured by the Institute of Technical Physics, Iasi,
Romania. Compared to the previous studies on nanocrystalline materials, we demonstrate that proper processing of nanocrystalline alloys can bring sensors with properties comparable to
the traditionally used amorphous alloys, but with better stability at elevated temperatures.
The amorphous Fe73,5Si13,5B9Cu1Nb3 master alloy wires 0.5m in length, and 0.12 mm in diameter were annealed by DC pulse to achieve the nanocrystalline structure. Contrary to other
researchers we found problems with surface oxidation in air, so our annealing was performed in Argon. During the annealing and cooling, we applied mechanical stress to achieve
transverse anisotropy. The character of changing Hc varies depending on tension as shown in Fig.1. Higher tension increases anisotropy and reduces the longitudinal permeability (Fig. 2).
Best results were shown by wires annealed under tension 9 g and 13 g with the current in the range 485 mA up to 510 mA. In these cases, coercivity was in the range of 7 A/m up to 17
A/m at 1 kHz. Annealed wires were used as a core for fluxgate sensors of the Förster and Vacquier types and with ring core.
As an example, Förster type sensor with amorphous (Hc = 20 A/m) wire as a core had max. sensitivity of 0.88 V/mT and min. the noise of 164pT/√Hz at 1 Hz.
By using nanocrystalline wire with Hc = 17A/m we achieved lower sensitivity (0.7 V/mT) but lower noise (111 pT/√Hz). The nanocrystalline core with lower Hc (9 A/m) had higher
sensitivity (1.1 V/mT) but higher noise (204 pT/√Hz) compared to the amorphous core. And the core with Hc = 13A/m had almost the same results as the amorphous wire.
This study was supported by the Grant Agency of the Czech Republic within the Nanofluxgate project (GACR GA20-27150S). 

**References:** 

[1] P. Ripka, D. Hrakova, “Multiwire Parallel Fluxgate Sensors”, IEEE Transactions on Magnetics. 2022, 58(2), 1-5. ISSN 0018-9464. DOI 10.1109/TMAG.2021.3093017 
[2] Y.-F. Li, M. Vazquez, D.-X. Chen, “Circular magnetization process of nanocrystalline wires as deduced from impedance measurements”, Journal of Applied Physics 97, 124311 (2005) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/dc0c8aa0034b27a0fcea032449a5d896.png)

Creep induced Magnetic Anisotropy of Nanocrystalline Wire as a Core of Fluxgate Sensor

Susceptibility measurement of magnetic nanoparticles (MNPs) in radio frequency (RF) has been widely studied. However, most of the studies only examined frequencies
up to 20 GHz [1]. In addtion, applying two axial DC fields to increase resonance in specific frequency range and magnetic susceptibility has hardly been done before, since applying a
single static DC field is more common [2-3]. The MNPs can be used for magnetic hyperthermia and biological substances detection [4-6]. In this study, we proposed a novel method for
measuring magnetic susceptibility by a broadband microstrip line type probe up to 67 GHz [7]. Fig. 1 shows the basic principle of the experimental setup. The microtube with MNPs
(SVM-025-5H, 200 nmf, about 300 ml) was put on the microstrip line type probe, which is connected with a network analyzer (N5227A) to generate a magnetic field in a range of 10 MHz
to 67 GHz. The MNPs were put between two electromagnets connected with power supplies to generate a changeable DC field up to 1000 Oe and another orthogonal about 35 Oe DC field.
When the two orthogonal DC fields are around equal, the magnetic susceptibility of MNPs should maximize because of the magnetic switching theory [8], which results in enhancing the
signal to noise ratio. By applying the bias magnetic field, we measured the transmission coefficient, S21, of the microstrip line type probe and obtained magnetic susceptibility [7]. Fig. 2
shows the magnetic susceptibility when the DC field ranges from 0 Oe to 1000 Oe. In the DC field around 0 Oe, the magnetic susceptibility was very low because the MNPs were relaxed.
However, in the DC field of 25 Oe-75 Oe, we observed clear magnetic resonances in 20 - 40 GHz. The resonance frequency increased as the DC field increased. In this case, both fixed and
changeable DC fields are around 35 Oe, which means the magnetic susceptibility is biggest at this condition and the orthogonal DC field enhance the signal to noise ratio to detect magnetic
nanoparticle. The clear magnetic resonance of MNPs has hardly been observed in this broad bandwidth up to 67 GHz before. 


**References:** 

[1] B. K. Kuanr, V. Veerakumar and K. Lingam, Journal of Applied Physics, Vol. 105 (2009). 
[2] M. Jadav, S. P. Bhatnagar, IEEE Transactions on Magnetics, Vol. 56, p. 1-8 (2020). 
[3] P. C. Fannin, I. Malaescu and C. N. Marin, The European Physical Journal E, Vol. 27, p. 145-148 (2008). 
[4] A. Shikano, L. Tonthat, Transaction of the Magnetics Society of Japan Special Issues, Vol. 6, p. 100-104 (2022). 
[5] S. Yabukami, T. Murayama and S. Takahashi, IEEE Transactions on Magnetics, Vol. 58, 6100305 (2022, in press). 
[6] T. Yoneyama, A. Kuwahata and T. Murayama, IEEE Transactions on Magnetics, Vol. 58 (2022, in press). 
[7] S. Yabukami, C. Iwasaki and K. Nozawa, IEEE Transactions on Magnetics, Vol. 58, No. 2, p. 1-5 (2022) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/715b881ce9b3e0d6f065037d7f9ab76f.png)

Method for Measuring Magnetic Susceptibility of Magnetic Nanoparticles up to Millimeter Wave Frequency Range

The usage of antibody selective biding for the detection of biomolecules provides a fast and low-cost testing platform. The most common type of antibody selective biding
bio-detection tags the bio-molecule of interest with a visual marker. An example of this type of bio-detection is the lateral flow immunoassays like the pregnancy or rapid COVID tests [1].
These visual nanotags are a valid solution for binary detection in high concentrated samples. To have a quantifiable and high sensitivity bio-sensing we use magnetic nanoparticles. The
measurements of this type of magnetic nanotags require expensive laboratory equipment. A novel method using the self-resonant frequency (SRF) of inductors allows high sensitivity with
low-cost and portable systems.
Using the equivalent impedance calculation [2] and the Lichtenecker’s mixing formulas [3] we extracted an analytic simplification to describe the relation between masses of nanomaterial
in the sensing area to variations of the SRF of the inductor. The model correlates variations of the refraction index of the nanotag making the technique able to quantify not only magnetic
nanotags but other types of nanomaterials like gold or latex.
The mathematical model and its simplifications are tested against electromagnetic simulations and experimental measurements. These verifications demonstrate the validity of the model,
the value of magnetic nanoparticles as nanotags for precise quantification, and the advantages of the SRF measuring method for low-cost, high-sensitivity systems. 

**References:** 

1] Moyano, A. et al., 2020. Magnetic Lateral Flow Immunoassays. Diagnostics. 
[2] Qin Yu. et al., 2002. RF Equivalent Circuit Modeling of Ferrite-Core Inductors and Characterization of Core Materials. 
[3] A.V. Goncharenko. et al., 1999. Lichtenecker’s equation: applicability and limitations. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/f53b5fd75dba2f666b231ac46824d773.png)

Self resonant frequency of inductors for quantification of magnetic nanoparticles

Permanents magnets, or hard ferromagnets, provide a “free” source of magnetic field, with no need of external power. Considering the integration with microsystems,
permanent micromagnets are critical components for the fabrication of microscale motors, generators, switches, pumps, acoustic speakers and energy harvester. Even though the
understanding of magnetism and magnetic materials has led to advancements in their magnetic properties [1], the application of permanent magnets in microsystems is still limited. The
reasons for that are: i) the methods for magnet fabrication at the macroscale (casting and powder processing) are fundamentally different to thin-film microfabrication approaches (physical
vapor deposition, chemical vapor deposition, electrochemical deposition); ii) even if microfabrication approaches are exploited, difficulties remain in depositing thick magnetic films (> 1
μm) and issues due to process compatibility [2].
In this work, we present a process to integrate MEMS (MicroElectroMechanical Systems) and thick permanent magnets. We have designed test structures (Fig. 1) and optimized a process
to fabricate the devices. The optimizations concern: i) deposition of a micron-thick layer of a magnetic material; ii) thermal treatment to enhance the magnetic characteristics of the
material; iii) patterning technique employed to obtain micromagnets; iv) introduction of a passivation layer to protect the material from the subsequent process steps. An image of the final
fabricated device is shown in Fig.2. Examples of application of said process to devices for energy harvesting and magnetic sensing will be discussed. 

**References:** 

M. Sagawa, S. Fujimura, N. Togawa, Journal of Applied Physics, Vol. 55, p. 2083 (1984) 
D. P. Arnold, N. Wang, Journal of microelectromechanical systems, Vol. 18, p.1255 (2009) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/2e8453b58011aaaa96750f6eb42a03f7.png)

Integration of hard magnetic layer in MEMS process

The use of time-varying magnetic field sources is indispensable in numerous applications, such as magnetic resonance imaging, sensors, motors, actuators, magnetometers or magnetic
refrigerators. Halbach cylinders have been used as an alternative to electromagnets, since they have no losses by the Joule effect. However, rod mangle systems are cheap and promising
alternatives to the currently used Halbach cylinders [1-3]. The use of rotation patterns has potential for application in several innovative áreas [4].
In this work, we modeled rod mangle structures with different number of rods, aiming to control the magnitude, direction and homogeneity of the magnetic field. Figure 1 (a) shows the
modeled system for 3 rods. After determining the configuration with the maximum magnetic flux density at the center of each system, it was possible to generate a homogeneous magnetic
field. The homogeneity increases with the number of rods and for a large number of rods, the rod mangle structure begins to resemble an ideal Halbach. We also analyzed two different
rotation patterns to generate a decreasing magnetic field over time. For the first pattern only the direction of the magnetic field of the odd configurations remained constant. For the second
rotation pattern, after the magnetic field is reduced to zero, it starts to increase in the opposite direction and then decreases to zero again. If we rotate all rods counterclockwise, the
magnetic field will rotate clockwise, keeping the magnitude fairly constant. Finally, we validated the results experimentally with structures of 3 and 4 rods (Fig 1 (b)). 

**References:** 

[1] J. M. D. Coey, Permanent magnet applications, Journal of Magnetism and Magnetic Materials 248 (3) (2002) 441–456. 
[2] O. Cugat, P. Hansson, J. M. D.Coey, Permanent magnet variable flux sources, IEEE Transactions on Magnetics 30 (6) (1994) 4602–4604. 
[3] F. Hiptmair, Z. Major, R. Haßlacher, S. Hild, Design and application of permanent magnet flux sources for mechanical testing of magnetoactive elastomers at variable field directions,
Review of Scientific Instruments 86 (8) (2015) 085107. 
[4] H. Sakuma, T. Nakagawara, Optimization of rotation patterns of a mangle-type magnetic field source using covariance matrix adaptation evolution strategy, Journal of Magnetism and
Magnetic Materials 527 (2021) 167752. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/38aef6bfcfd0e0a9d8729e58145a10d4.png)

Rod mangle rotation patterns for magnetic field generation

Magnetorheological fluids (MRFs) can change their viscosity in response to applied magnetic field. Magnetorheological energy absorbers (MREAs) are being investigated for adaptive shock isolation because MREAs can adjust their stroking load to severity of impact when magnetic field is used to control MRF viscosity. Employing MRFs in MREAs requires a highly stable suspension to maintain a uniform concentration, because MREAs would be used only in the event of an impact or crash event, that is, rarely. Suspension stability of MRFs can be studied using an automated vertical axis inductance monitoring system (AVAIMS), where an inductance sensor is translated vertically along a column of MRF to measure particle concentration as a function of column height and time [1,2]. The AVAIMS allows for tracking discontinuities in density or shocks including: the mud-line (boundary between the topmost supernatant (clear fluid) zone and the original concentration zone), the gel-line (boundary between the original concentration zone below mud-line and variable concentration zone), and the cake-line (boundary between the variable concentration zone and the sediment zone at the bottom of the column). MRF sedimentation can be evaluated comprehensively analyzing these boundaries. The AVAIMS developed here (Fig. 1) seeks to improve sedimentation zone boundary localization using an optimized inductance sensor to measure concentration gradient as a function of time. The inductance sensor design, material selection, and geometry were optimized and permalloy and plastic were used advantageously to improve sensor sensitivity. The calibration curve of the sensor was obtained by measuring samples with different particle volume fractions. The sensor design was validated by examining a uniformly mixed MRF column for seven consecutive days after preparation of an MRF with an Fe solids loading of 20 vol%. These tests show that the AVAIMS developed here was able to better localize sedimentation zone boundaries using concentration gradient profile method (Fig. 2).

Sedimentation of Magnetorheological Fluids Measured Using a Automated Vertical Axis Inductance Monitoring System

Magnetorheological fluids (MRFs) consist of micron-sized magnetic particles dispersed in a carrier fluid for which rheological properties can be tuned reversibly with
magnetic field.1 If an MRF is contained in a cellular elastomeric encapsulant (CEE), its mechanical properties, such as stiffness and damping, can be controlled via magnetic field. Such
tunability can be exploited for adaptive vibration control or energy absorption systems. A magnetorheological damper often uses an accumulator to modulate pressure injected by external
forces applied to the damper.2 An accumulator is implemented into the cellular encapsulant to enable essentially incompressible fluid to enter the accumulator and to allow compression of
the cellular material to take place, and also enables a mechanical bulge stiffness to the design.
Here, MRF was prepared with silicon oil (40% vol. fraction). Thermoplastic polyurethane (TPU) was 3-D printed as the CEE system. (Fig. 1 a). The MRF was injected into the TPU-CEE,
followed by the printing of a sealing layer. The wall adjacent to the sealing layer had a circular opening and a TPU membrane was bonded to its perimeter so that the pressurized MRF
could flow through the opening and be accumulated in the resulting pocket.
An external magnetic field (0 and 7 kG) was applied along the sample longitudinal axis at the time of uniaxial dynamic testing with 5% pre-strain. The TPU-CEE samples were
characterized via force-displacement tests at 1 Hz under strain amplitudes. The MR effect on the dynamic stiffness is defined as the ratio of the dynamic stiffness under the maximum
magnetic field to the dynamic stiffness in the absence of a magnetic field. Dynamic stiffness in the presence as opposed to the absence of magnetic field was 264%. (Fig.2a) The area of the
force-displacement curve of the system with an accumulator is about 41% greater than one without an accumulator. The accumulator enhanced the increase in damping (Fig. 2b). The
increase in damping capacity generally increased as strain amplitude increased. 

**References:** 

1. Ashtiani M, Hashemabadi SH, Ghaffari A. A review on the magnetorheological fluid preparation and stabilization. Journal of Magnetism and Magnetic Materials. 374, 716.
(2015) 
2. Yu, Jianqiang & Dong, Xiaomin & Wang, Xuhong & Pan, Chengwang & Zhou, Yaqin. Asymmetric Dynamic Model of Temperature-Dependent Magnetorheological Damper and
Application for Semi-active System. Frontiers in Materials. 6. 227. (2019) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9e96476131d9b4e1a0c5d4b36a289cf6.png)

Development of Magnetorheological Fluids within 3D Printed Elastomeric Cellular Structures with an Accumulator

Most research on remotely driven magnetic micro-robots focuses on their manipulation within fluids [1]. Actuating their motion in soft media and living tissue raises
challenges along with new opportunities for minimally invasive medicine. In contrast to fluids, moving solids in soft media irreversibly rearranges the material, leading to highly non-linear
and history dependent reaction forces. The present work demonstrates that this behavior enables solutions of certain long-standing problems. One problem stems from using magnetic field
gradients to generate forces which limits their range particularly for sub-millimeter size magnetic robots. Locomotion by the transfer of energy via a time varying uniform magnetic field
provides an alternative. In fluids where locomotion effectively occurs through swimming at low Reynolds numbers, this strategy can be costly, requiring more complex shapes (e.g. a screw
[2]) and control over a non-reciprocal motion gait [3]. In tissues, such complex shapes have difficulties in changing their trajectory direction over short distances. The novel finding in this
work is that soft media enables locomotion of simple solids, such as a pair of spheres (see Fig. 1), without requiring them to execute a complex motion gait. Using an external uniform
magnetic field to change the relative orientations of the magnetic moments, the disconnected spherical solids of slightly different diameters can locomote as one in a soft medium via
ratchet-like movements that are completely reciprocal. Such a configuration also allows the pair to change the direction of locomotion quickly. A demonstration is carried out in this work
via development of a theoretical model and its numerical simulation, although some experimental observations support these findings. 

**References:** 

[1] J. J. Abbott et al., "How should microrobots swim?," The international journal of Robotics Research, vol. 28, no. 11-12, pp. 1434-1447, 2009. 
[2] T. W. Fountain, P. V. Kailat, and J. J. Abbott, "Wireless control of magnetic helical microrobots using a rotating-permanent-magnet manipulator," in 2010 IEEE International
Conference on Robotics and Automation, 2010: IEEE, pp. 576-581. 
[3] E. Lauga, "Life around the scallop theorem," Soft Matter, vol. 7, no. 7, pp. 3060-3065, 2011. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9995c10406482e83eef181eaa6b200c6.png)

Underline digital video library

Climate-Adaptive Thermochromic Perovskite Smart Window Structures

Carrier Dynamics in Blue, Cyan and Green Commercial InGaN/GaN LEDs Measured by Small-Signal Electroluminescence

Electron Emission Microscopy of an Electrically Driven III-Nitride-Based LED: Evidence of Lateral Electron Injection at V-Defect Sidewalls

Development of an Auto Oriented Circulator Based on Hexaferrite Materials in the 5G Frequency Band

Creep induced Magnetic Anisotropy of Nanocrystalline Wire as a Core of Fluxgate Sensor

Method for Measuring Magnetic Susceptibility of Magnetic Nanoparticles up to Millimeter Wave Frequency Range

Self resonant frequency of inductors for quantification of magnetic nanoparticles

Integration of hard magnetic layer in MEMS process

Rod mangle rotation patterns for magnetic field generation

Sedimentation of Magnetorheological Fluids Measured Using a Automated Vertical Axis Inductance Monitoring System

Development of Magnetorheological Fluids within 3D Printed Elastomeric Cellular Structures with an Accumulator

On Locomotion of Magnetized Spherical Solids in Soft Media

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES