Alexandra Garraud

Investigation of the Capture of Magnetic Particles From High-Viscosity Fluids Using Permanent Magnets

Goal: This paper investigates the practicality of using a small, permanent magnet to capture magnetic particles out of high-viscosity biological fluids, such as synovial fluid. Methods: Numerical simulations are used to predict the trajectory of magnetic particles toward the permanent magnet. The simulations are used to determine a “collection volume” with a time-dependent size and shape, which determines the number of particles that can be captured from the fluid in a given amount of time. Results: The viscosity of the fluid strongly influences the velocity of the magnetic particles toward the magnet, hence, the collection volume after a given time. In regards to the design of the magnet, the overall size is shown to most strongly influence the collection volume in comparison to the magnet shape or aspect ratio. Conclusion: Numerical results showed good agreement with in vitro experimental magnetic collection results. Significance: In the long term, this paper aims to facilitate optimization of the collection of magnetic particle-biomarker conjugates from high-viscosity biological fluids without the need to remove the fluid from a patient.

Imprinting of fine-scale magnetic patterns in electroplated hard magnetic films using magnetic foil masks

This paper presents a batch-fabrication approach to imprint complex magnetic pole patterns (perpendicular north/south poles) into hard magnetic films using fine-scale, laser-machined iron foil “masks.” In this approach, pulsed magnetic fields varying between 0.1 and 1.0 T are used in conjunction with the field-concentrating effect of the iron foil masks to selectively reverse the magnetization of selected regions of 10-μm-thick Co80Pt20 films (Br = 1 T, Hci = 340 kA/m). Simple stripe array patterns are systematically studied both experimentally and via simulation, achieving patterned feature sizes (poles) down to 30 μm. Double exposures are also explored to create checkerboard patterns from simple stripe-like masks. Finally, masks with more complex patterns are used to demonstrate the viability of the approach to imprint arbitrary features.

Watt-level wireless power transmission to multiple compact receivers

This paper reports an electrodynamic wireless power transmission (EWPT) system using a low-frequency (300 Hz) magnetic field to transmit watt-scale power levels to multiple compact receivers. As compared to inductively or resonantly coupled coils, EWPT facilitates transmission to multiple non-interacting receivers with little restriction on their orientation. A single 3.0 cm3 receiver achieves 1.25 W power transmission with 8% efficiency at a distance of 1 cm (350 mW/cm3 power density) from the transmitter. The same prototype achieves 9 mW at a distance of 9 cm. Moreover, we demonstrate simultaneous recharge of two wearable devices, using two receivers located in arbitrary positions and orientations.

Influence of temperature on the magnetic properties of electroplated L10 CoPt thick films

This paper reports the magnetic properties of 2 μm thick electroplated isotropic L10 CoPt films on silicon at temperatures ranging from 300 K to 790 K, as well as the room-temperature properties of the films after various thermal cycles. Electroplated equiatomic CoPt layers require a post-deposition annealing typically at ∼973 K to induce L10 ordering so that they exhibit hard magnetic properties at room temperature. However, the influence of temperature on these post-deposition annealed films is an important consideration for their utility in end applications. Here, a reversible temperature coefficient of remanence of −0.11% K−1 is measured along with a maximum operating temperature of 400 K (recovery to 95% of the initial remanence). The maximal energy density of the films is reduced by 50% at a temperature of 550 K. However, the original room-temperature magnetic properties are shown to be fully recoverable by remagnetization after various thermal cycles—800 K for 15 min in Ar, 373 K for 168 h in air, ...

Collection of magnetic particles from synovial fluid using Nd-Fe-B micromagnets

In this paper, the collection of magnetic particles from synovial fluid using Nd-Fe-B micromagnets is quantitatively studied to determine the influence of fluid viscosity and magnet geometry on the velocity distribution and collection rate. Magnetic capture is validated in highly viscous fluids, such as bovine synovial fluid (η~ 1 Pa·s). A first-order theoretical model has been developed to predict the particle motion, as well as a numerical multiphysics model. Both models exhibit good agreement with in vitro experimental magnetic collection results. The velocity of the magnetic particles is shown to be inversely proportional to fluid viscosity, and two magnetic structures are compared in term of collection efficiency: a cylindrical Nd-Fe-B permanent magnet and a laser-machined conical Nd-Fe-B permanent magnet.

Electrodynamic Wireless Power Transmission to Rotating Magnet Receivers

This paper presents an approach for electrodynamic wireless power transmission (EWPT) using a synchronously rotating magnet located in a 3.2 cm3 receiver. We demonstrate wireless power transmission up to 99 mW (power density equal to 31 mW/cm3) over a 5-cm distance and 5 mW over a 20-cm distance. The maximum operational frequency, and hence maximal output power, is constrained by the magnetic field amplitude. A quadratic relationship is found between the maximal output power and the magnetic field. We also demonstrate simultaneous, power transmission to multiple receivers positioned at different locations.

Influence of temperature on the magnetic properties of electroplated Co-rich Co–Pt thick films

In this paper, the magnetic properties of 10 µm thick Co-rich Co–Pt films (~80:20 atomic ratio) hard magnetic films electroplated on silicon substrates are characterized at temperatures from 300 to 1000 K. With an increase in temperature up to 500 K, the coercivity and remanence of the films both decrease rapidly, dropping to only 10% of their respective as-deposited values. Above 500 K, the coercivity and remanence continue declining but at a slower rate, reaching nearly zero at 1000 K. Conversely, the saturation magnetization reduces by only 15% at 800 K and 40% at 1000 K from the as-deposited value. In addition to these measurements at elevated temperature measurements, thermal cycling tests are performed to examine the influence of various thermal exposures. Cycles up to 500 K are shown to have little impact on the film morphology but notably reduce the layer adhesion. Most importantly, a thermal cycle to just 400 K is shown to essentially destroy the hard magnetic properties. Because of these temperature sensitivities, Co-rich Co–Pt films may be significantly limited for end applications.

Advancements in electrodynamic wireless power transmission

This article summarizes recent advancements in near-field electrodynamic wireless power transmission (EWPT), which relies on a time-varying magnetic field produced by a transmitter to excite the mechanical motion of permanent magnet in the receiver. The mechanical energy absorbed by the magnet is then converted into electrical energy via one or more transduction mechanisms, most commonly Faraday induction. EWPT is compared against other wireless power strategies, and theoretical upper bounds of power transmission are provided.