Guodong Hong

Axial-flux permanent magnet machines for micropower generation

This paper reports on the design, fabrication, and testing of an axial-flux permanent magnet electromagnetic generator. The generator comprises a polymer rotor with embedded permanent magnets sandwiched between two silicon stators with electroplated planar coils. Finite element simulations have been carried out using ANSYS to determine the effects on performance of design parameters such as the number of layers in the stator coils, and the rotor-stator gap. The effect of including soft magnetic pole pieces on the stators has also been studied. A prototype device with a diameter of 7.5 mm has been tested, and shown to deliver an output power of 1.1 mW per stator at a rotation speed of 30 000 rpm. The generator has been integrated with a microfabricated axial-flow microturbine to produce a compact power conversion device for power generation and flow sensing applications.

SU8 resist plasma etching and its optimisation

The thick photoresist SU8, by virtue of its good mechanical durability, water impermeability and dielectric properties on polymerisation, is widely used as a resin for making high aspect ratio, functional MEMS device structures and packaging parts. However, the difficulty associated with removal, stripping or re-patterning of the polymerised SU8 remains a serious issue. This paper presents a novel process, based on O2/SF6 plasma etching, for patterning or removal of fully cross-linked SU8. The Taguchi methodology is used to optimise the O2/SF6 mix for a high etch rate and low under cut.

A miniature mass spectrometer for liquid chromatography applications

A miniature mass spectrometer capable of detecting analytes eluting from a high-performance liquid chromatography (HPLC) system is described and demonstrated for the first time. The entire instrument, including all pumps and the computer, is contained within a single enclosure that may be conveniently accommodated at the base of the HPLC stack. The microspray ion source, vacuum interface, ion guide, and quadrupole ion filter are all microengineered. These components are fabricated in batches using microelectromechanical systems (MEMS) techniques and considered to be consumables. When coupled to a standard HPLC system using an integrated passive split, the limit of detection for reserpine while scanning the full mass range is 5 ng on-column (1 pg of which is passed to the microspray). The mass range is m/z 100-800, and each spectrum is typically acquired at a rate of 1 scan per second.

Microfabricated Quadrupole Mass Spectrometer With a Brubaker Prefilter

Microfabricated quadrupole mass spectrometers with Brubaker prefilters are demonstrated for the first time. Complete filters are assembled from two dies, each carrying two pairs of rods providing the prefilter and main filter sections. The rods are held in precision silicon mounts that are fabricated using wafer-scale deep reactive-ion etching and anodic bonding to glass substrates. Improvements to ion transmission are obtained by tuning the bias potential applied to the prefilter. The effect is explained in terms of a simple analytic theory for ion motion in the prefilter. Mass filtering with a range of m/z = 0-1200 and a resolution of m/¿m ¿ 150 at 10% of peak height is demonstrated using 2-4-mm-long prefilter electrodes, 30-mm-long main electrodes (both of 650 ¿m diameter), and a radio-frequency drive at ¿6.5 MHz.

MEMS-Based Nanospray-Ionization Mass Spectrometer

An electrospray-ionization mass spectrometer (ESI-MS) whose main components are all fabricated using silicon microelectromechanical systems (MEMS) techniques is demonstrated for the first time. The ion source consists of a microengineered alignment bench containing a V-groove mounting for a nanospray capillary, an ion-extraction electrode, and a pneumatic nebulizer. The vacuum interface consists of two plates, each carrying a 50-μm-diameter capillary, that are selectively etched and bonded together to provide a differentially pumped internal cavity. The quadrupole filter consists of a microfabricated frame that provides mountings for stainless-steel rods measuring 650 μm in diameter and 30 mm in length. Two different quadrupoles are compared: a first-generation bonded silicon device and a second-generation silicon-on-glass device with a Brubaker prefilter. Differential pumping of a MEMS component is demonstrated for the first time, atmospheric pressure ionization and ion transfer into vacuum are characterized, ESI-MS operation is demonstrated, and spectra are presented for a variety of compounds.

Design, fabrication and characterization of an axial-flow turbine for flow sensing

This paper presents a novel micro-power conversion device that combines an axial flow turbine with an axial-flux electromagnetic generator. The device has a sandwich structure, consisting of a top silicon stator, a polymer rotor and a bottom silicon stator. Axial gas flow through the device causes rotation, while permanent magnets embedded in the rotor induce output voltage in planar coils on the stators. Compared to radial flow devices the axial-flow design is more compact and can operate at lower pressure ratios. Details of the device design and fabrication process are given, and preliminary results are presented for the variation of output voltage, rotation speed, and pressure ratio with flow rate for nitrogen gas. The test results show operation over a wide dynamic range.

Comparison of ion coupling strategies for a microengineered quadrupole mass filter

The limitations of conventional machining and assembly techniques require that designs for quadrupole mass analyzers with rod diameters less than a millimeter are not merely scale versions of larger instruments. We show how silicon planar processing techniques and microelectromechanical systems (MEMS) design concepts can be used to incorporate complex features into the construction of a miniature quadrupole mass filter chip that could not easily be achieved using other microengineering approaches. Three designs for the entrance and exit to the filter consistent with the chosen materials and techniques have been evaluated. The differences between these seemingly similar structures have a significant effect on the performance. Although one of the designs results in severe attenuation of transmission with increasing mass, the other two can be scanned to m/z=400 without any corruption of the mass spectrum. At m/z=219, the variation in the transmission of the three designs was found to be approximately four orders of magnitude. A maximum resolution of M/ΔM=87 at 10% peak height has been achieved at m/z=219 with a filter operated at 6 MHz and constructed using rods measuring (508±5) µm in diameter.

Rotary RF MEMS Switch Based on the Wobble Motor Principle

A novel, truly rotary, single-pole eight-throw (SP8T) RF MEMS switch is reported. The concept is an adaptation of the axial-gap electrostatic wobble motor. Details of the switch design and fabrication process are presented, together with initial test results for prototype devices. DC contact resistance measurements have been made over half a million rotations, yielding an average contact resistance of 2.5 Ω. The switch shows promising RF performance, with insertion loss varying smoothly from 0.6 dB at 2 GHz to 4 dB at 20 GHz, and isolation better than 31 dB across the frequency range 0.5 to 20 GHz.

Laser profiling of 3D microturbine blades

We have used KrF excimer laser ablation in the fabrication of a novel MEMS power conversion device based on an axial-flow turbine with an integral axial-flux electromagnetic generator. The device has a sandwich structure, comprising a pair of silicon stators either side of an SU8 polymer rotor. The curved turbine rotor blades were fabricated by projection ablation of SU8 parts performed by conventional UV lithography. A variable aperture mask, implemented by stepping a moving aperture in front of a fixed one, was used to achieve the desired spatial variation in the ablated depth. An automatic process was set up on a commercial laser workstation, with the laser firing and mask motion being controlled by computer. High quality SU8 rotor parts with diameters of 13 mm and depths of 1 mm were produced at a fluence of 0.7 J/cm2, corresponding to a material removal rate of approximately 0.3 μm per pulse. A similar approach was used to form SU8 guide vane inserts for the stators.

Design, manufacture and testing of a low-cost micro-channel cooling device

The modelling, simulation, fabrication and testing of a microchannel cooling plate are described in this article. The device is to be used in microelectronic packaging cooling applications. The nickel-based micro-channel cooling plate is fabricated on a glass substrate using a two-layer electroforming process borrowed from the UV-LIGA (UV-lithography, electroforming, replication) process. Forced convection of air or liquid is scheduled for this microchannel plate. The cooling plate has been tested using a custom-made rig to measure the flow pressure head as a function of mass flow rate. Hydraulic performance of the cooling plate is presented