Ali Moazenzadeh

Micro-fabricated Helmholtz coil featuring disposable microfluidic sample inserts for applications in nuclear magnetic resonance

In this study, we report on a novel, multi-use, high-resolution NMR/MRI micro-detection probe for the screening of flat samples. It is based on a Helmholtz coil pair in the centre of the probe, built out of two 1.5?mm diameter wirebonded copper coils, resulting in a homogeneous distribution of the magnetic field. For liquids and suspensions, custom fabricated, disposable sample inserts are placed inside the pair and aligned automatically, preventing the sensor and the samples from contamination. The sensor was successfully tested in a 500?MHz (11.7 T) spectrometer where we achieved a linewidth of 1.79?Hz (3.58?ppb) of a water phantom. Nutation experiments revealed an overall B1-field uniformity of 92% (ratio in signal intensity at flip angles of 810?/90?), leading to a homogeneous excitation of concentration limited samples. To demonstrate the imaging capabilities of the detector, we acquired images of a solid and a liquid sample?of a piece of leaf, directly inserted into the probe and of a sample insert, filled with a suspension of 50 ?m diameter polymer beads and deionized water, with in-plane resolutions of 20 ? 20 ??m2 and 10 ? 10 ??m2, respectively.

Heteronuclear Micro-Helmholtz Coil Facilitates µm-Range Spatial and Sub-Hz Spectral Resolution NMR of nL-Volume Samples on Customisable Microfluidic Chips.

We present a completely revised generation of a modular micro-NMR detector, featuring an active sample volume of ∼ 100 nL, and an improvement of 87% in probe efficiency. The detector is capable of rapidly screening different samples using exchangeable, application-specific, MEMS-fabricated, microfluidic sample containers. In contrast to our previous design, the sample holder chips can be simply sealed with adhesive tape, with excellent adhesion due to the smooth surfaces surrounding the fluidic ports, and so withstand pressures of ∼2.5 bar, while simultaneously enabling high spectral resolution up to 0.62 Hz for H2O, due to its optimised geometry. We have additionally reworked the coil design and fabrication processes, replacing liquid photoresists by dry film stock, whose final thickness does not depend on accurate volume dispensing or precise levelling during curing. We further introduced mechanical alignment structures to avoid time-intensive optical alignment of the chip stacks during assembly, while we exchanged the laser-cut, PMMA spacers by diced glass spacers, which are not susceptible to melting during cutting. Doing so led to an overall simplification of the entire fabrication chain, while simultaneously increasing the yield, due to an improved uniformity of thickness of the individual layers, and in addition, due to more accurate vertical positioning of the wirebonded coils, now delimited by a post base plateau. We demonstrate the capability of the design by acquiring a 1H spectrum of ∼ 11 nmol sucrose dissolved in D2O, where we achieved a linewidth of 1.25 Hz for the TSP reference peak. Chemical shift imaging experiments were further recorded from voxel volumes of only ∼ 1.5nL, which corresponded to amounts of just 1.5 nmol per voxel for a 1 M concentration. To extend the micro-detector to other nuclei of interest, we have implemented a trap circuit, enabling heteronuclear spectroscopy, demonstrated by two 1H/13C 2D HSQC experiments.

High-performance, 3D-microtransformers on multilayered magnetic cores

We present the fabrication of 3D-microtransformers combining a new type of multilayered magnetic core and coil winding with an automatic wirebonder. For the magnetic cores we stapled up to 30 layers of 20 μm thick amorphous metal layers with an industrial laminator. Intermediate layers of 10 μm thick double-sided sticky tape provided adhesion and electrical insulation. Electrical discharge machining was used to precisely cut these magnetic stacks to sub-millimeter cubes. To flip the cubes by 90° and assemble them onto a wafer for coil winding, we produced a receptor wafer providing magnetic landing sites. Subsequently, to wind a primary and secondary coil, one on top of the other, an automatic wirebonder was employed with 25 μm thick insulated Gold wire. A fabricated transformer with a core size of 0.9*0.8*1 mm3 yielded an inductance of 1412 nH and a coupling factor of 97%. The maximum transformer efficiency of 73% was measured at a load of 50 Ω.

3-D Microtransformers for DC–DC On-Chip Power Conversion

We address the miniaturization of power converters by introducing novel 3-D microtransformers with magnetic core for low-megahertz frequency applications. The core is fabricated by lamination and microstructuring of Metglas 2714A magnetic alloy. The solenoids of the microtransformers are wound around the core using a ball-wedge wirebonder. The wirebonding process is fast, allowing the fabrication of solenoids with up to 40 turns in 10 s. The fabricated devices yield the high inductance per unit volume of 2.95 μH/mm3 and energy per unit volume of 133 nJ/mm3 at the frequency of 1 MHz. The power efficiency of 64-76% is measured for different turns ratio with coupling factors as high as 98%. To demonstrate the applicability of our passive components, two PWM controllers were selected to implement an isolated and a nonisolated switch-mode power supply. The isolated converter operates with overall efficiency of 55% and maximum output power of 136 mW; then, we experimentally demonstrate how we increased this efficiency to 71% and output power to 408 mW. The nonisolated converter can deliver an overall efficiency of 81% with a maximum output power of 515 mW. Finally, we benchmarked the results to underline the potential of the technology for power on-chip applications.

Polymer Magnetic Composite Core Based Microcoils and Microtransformers for Very High Frequency Power Applications

We present a rapid prototyping and a cost effective fabrication process on batch fabricated wafer-level micro inductive components with polymer magnetic composite (PMC) cores. The new PMC cores provide a possibility to bridge the gap between the non-magnetic and magnetic core inductive devices in terms of both the operating frequency and electrical performance. An optimized fabrication process of molding, casting, and demolding which uses teflon for the molding tool is presented. High permeability NiFeZn powder was mixed with Araldite epoxy to form high resistive PMC cores. Cylindrical PMC cores having a footprint of 0.79 mm2 were fabricated with varying percentage of the magnetic powder on FR4 substrates. The core influence on the electrical performance of the inductive elements is discussed. Inductor chips having a solenoidal coil as well as transformer chips with primary and secondary coils wound around each other have been fabricated and evaluated. A core with 65% powder equipped with a solenoid made out of 25 µm thick insulated Au wire having 30 turns, yielded a constant inductance value of 2 µH up to the frequency of 50 MHz and a peak quality factor of 13. A 1:1 transformer with similar PMC core and solenoidal coils having 10 turns yielded a maximum efficiency of 84% and a coupling factor of 96%. In order to protect the solenoids and to increase the mechanical robustness and handling of the chips, a novel process was developed to encapsulate the components with an epoxy based magnetic composite. The effect on the electrical performance through the magnetic composite encapsulation is reported as well.

Polymer Magnetic Composite Core Boosts Performance of Three-Dimensional Micromachined Inductive Contactless Suspension

We introduce a newly developed polymer magnetic composite for use as a high resistivity, high permeability magnetic core to significantly improve the energy consumption of micromachined inductive suspensions. Compared to a similar inductive suspension structure without a core, the electrical current required to obtain a levitation height of 110 μm is 65 mA versus 120 mA. The use of the core brings the operating temperature in ambient air at 27 °C down from 120 °C to 60 °C, the lowest value among all previously reported micromachined inductive suspensions. Beyond this performance improvement, the present contribution demonstrates the feasibility of three-dimensional micromachined inductive suspensions as integrated elements of levitated micromachined systems.

Hollow microcoils made possible with external support structures manufactured with a two-solvent process

We present a process to manufacture solenoidal microcoils with external support structures, which leaves the space within the coil windings free. The manufacturing procedure is based on a two solvent approach (water and acetone), for selectively etching polyvinyl alcohol and polymethyl methacrylate. Two sets of microcoils were manufactured with an inner diameter of 1.5 mm, an interwinding pitch of 100 μm and five or eight coil windings respectively. The coils were designed for application in magnetic resonance imaging and spectroscopy, and characterised in a 9.4 T MR scanner. An NMR spectrum of water and MR images in receive only and transceive mode were acquired as proof of concept.

Wire bonded MEMS-scale on-chip transformers

We present a novel, wafer-level fabrication method of 3D solenoidal microtransformers using an automatic wire bonder. Automatic wire bonders allow to precisely shape 25 μm diameter wire around prefabricated yokes or magnetic cores within seconds. Former reports of wire bonded microcoils treated individual solenoids showing low mutual inductances, whereas in this study transformers with strongly coupled microsolenoids are presented. The process is fully compatible with standard microelectronic manufacturing, therefore, enables the direct integration of transformers into a given electronic circuit. Two different prototypes are presented here. A non-magnetic core transformer with a footprint of 1 mm2 and 20 windings in both the primary and the secondary coil, yields a power efficiency of 67% and a coupling factor of 94%. A magnetic core transformer with a footprint of 0.64 mm2 and 18 windings in both the primary and the secondary coil, yields more than 1 μH inductance and 74% power efficiency with a coupling factor of 98%. The feasibility of both prototypes with respect to the power conversion in miniaturized circuits is evaluated. Finally, the microtransformers are benchmarked to underline the potential of the wire bonded microtransformers compared to other state-of-the-art publications.

Double-spiral coils and live impedance modulation for efficient wireless power transfer via magnetoinductive waves

We present the design and fabrication of a double-spiral coil used as the inductive element of a two-layer coupled resonator array for wireless power transfer applications. The waveguide presents an in-plane coupling coefficient of 0.92 and LC resonators with Q-factors of 97 at 13.56 MHz. Wireless monitoring of the power supply voltage enabled live modulation of the terminating impedance in the array. With load modulation and the low attenuation of our device we demonstrate how to power-up a receiver device with a system efficiency of nearly 60% anywhere over the 30 cm length of our resonating array.

Energy-aware 3D micro-machined inductive suspensions with polymer magnetic composite core

This paper addresses the issue of Joule heating in micromachined inductive suspensions (MIS) and reports a significant decrease of the operating temperature by using a polymer magnetic composite (PMC) core. The PMC material has a high resistivity, thus inhibiting the formation of eddy currents, and a high permeability, thus guiding the magnetic field more efficiently within the MIS structure. We experimentally study the distribution of the PMC material inside the MIS structure and evaluate the effect of the core from the dependence of the levitation height on the excitation current. The experiments carried on in ambient room temperature demonstrate that the temperature inside the micromachined inductive suspension is reduced to 58°C, which is a record-low temperature compared to other MIS structures reported before.