David Menard

The necessity to develop new technologies for high-sensitivity malaria diagnosis has sparked a global effort in medical and integrative sciences. Most developing procedures rely on research-grade instruments, sophisticated assays, or on expertise. In this work, we propose an alternative optical methodology using a compact and user-friendly apparatus based on a photonic crystal fiber (PCF). Malaria pigment known as hemozoin is an insoluble reddish brown microcrystalline. These crystallites stand out from other blood components in terms of their exceptional magneto-optical features. Consequently, they can function as spinning entities in suspension in response to the external magnetic field. Here synthetic hemozoin (SHz) was obtained in a forthright way with a high yield of 75%. In addition, the prepared sample was characterized morphologically and structurally. The PCF’s nanoholes were filled with the aqueous suspension of SHz with various concentrations and transmitted power recorded in response to the magnetic field. We demonstrate a sensor with a detection threshold of 7.2 parasite/μl well below the level of clinical relevance (50-100 parasite/μl) at a very small liquid sample (less than 0.5 μl). The results of this investigation may provide new light on potential medicinal and sensor applications.

This work presents the design and validation of a vibrating coil magnetometer for the characterization of the field dependence of the critical current density of centimeter-sized bulk superconductors as an alternative to the destructive methods typically used. The magnetometer is also shown to be capable of measuring the magnetic moment in an applied field of up to 5 T for diverse magnetic materials, such as soft and hard ferromagnets and high-temperature superconducting pellets. The vibrating coil magnetometer was first optimized using finite element simulations and calibrated using a commercial vibrating sample magnetometer. The vibrating coil magnetometer was benchmarked with hysteresis measurements of a Nd2Fe14B disk made with a commercial hysteresisgraph, showing good agreement between the different setups. The magnetic hysteresis of a YBa2Cu3O7−x superconducting pellet was measured at 77 K, showing a penetration field of 1 T and an irreversibility field of 4 T. The field dependent critical current density of the superconductor was then inferred from the magnetic hysteresis measurements and extrapolated at low fields. Finally, the resulting critical current density was used to successfully reproduce the measured magnetization curve of the pellet at 2 T with finite element simulations.

The performance of magnetoelastic torquemeters based on the changes in a measurable magnetic field is obtained with a simplified numerical model, assuming isotropic magnetoelastic properties throughout the ferromagnetic shaft and independent magnetic cells. The output gain of two torquemeter designs is obtained as a function of the distance of the magnetometers and of the width of the magnetic bands. Results show that a radial sensor configuration gives a gain 1.76 times larger in average than an axial sensor configuration. It is also shown that the radial configuration is more sensitive to magnetometer position errors, and requires a tighter control over the device parameters to maintain a constant gain. Further computations reveal that fluctuations in the magnetization of the shaft decrease the gain, increases the signal offset and that the shaft radius can alter this dependency due to an enhance magnetoelastic response.

Low-frequency equivalent magnetic noise levels of four different giant magneto-impedance (GMI) samples, exhibiting 1/f spectral behavior, have been experimentally determined, for several excitation conditions (involving both dc current and ac excitation amplitude). Under appropriate conditions, for which the noise level at 1 Hz is minimal, coherence measurements show that the main noise source responsible for this low frequency noise is the intrinsic noise of the GMI sample. The lowest corresponding magnetic noise performances of the four samples were determined. The lowest noise level observed was 17 pT/(Hz)^1/2 at 1 Hz. It has been proposed that the imaginary part of the magnetic susceptibility, χ", a measure of the low frequency magnetization fluctuations, determines the resulting magnetic noise level of the sensor. Its values at 1 Hz have been been evaluated for all four samples. Using these evaluations, expected noise levels at 1 Hz are computed, based on a previously proposed theoretical model, and compared with the measured noise performances. Under conditions for which correlation measurements show that system noise is dominated by sensor noise, the two sets of values are in reasonably good agreement, suggesting that the proposed model for low frequency excess noise of GMI materials is essentially correct.