Self-assembled 3D silicon microscanners with self-assembled electrostatic drives

Published versio

Dynamic response modelling of MEMS micromirror corner cube reflectors with angular vertical combdrives

Published versio

Magneto-inductive HF RFID system

Efforts to increase read range in passive HF RFID systems are hampered by the poor range scaling law of inductive coupling. An alternative approach to enlarging capture volume—increasing the lateral extent of the antenna—is proposed, using a magneto-inductive (MI) travelling wave arrangement to allow larger antenna sizes. A theory of load modulation in MI systems is first presented, together with field simulations in the capture volume. A 2.3 metre-long MI antenna is then constructed, and an active tag emulator is used to demonstrate load modulation. RFID is then demonstrated, with the antenna in both reflection and transmission modes, using a custom reader constructed from laboratory equipment. A transverse read range of 0.5 m is obtained using commercial off-the-shelf RFID cards with 12 W RF power, with high uniformity along the length of the antenna

Waveguide antenna topologies for distributed high-frequency near-field communication and localization

High-frequency near-field communication is an inherently short-range technology. However, the total capture volume can be increased with traveling-wave antennas. Here, we report on analysis, design, and measurements of flexible waveguide antennas and discuss their performance for near-field communication and localization. The antennas comprise sections of coaxial transmission lines loaded periodically with field-generating inductive networks. Several topologies were compared to each other theoretically and the best-performing candidate was selected to fabricate antennas between 5 and 48 meters long, each containing 15 read nodes. Waveguiding properties of the antennas were measured and agreement with theory was demonstrated. Afterwards, each antenna was integrated with a custom NFC reader and shown to be capable of near-field communication with and localization of commercial off-the-shelf transponders compliant with ISO 14443 Type A protocol. The transverse detection range was 10 cm with 1 W input RF power. Both one-dimensional and quasi two-dimensional configurations were tested. The proposed antennas are flexible, scalable, have low loss, and could be used for near-field communication, identification, and tracking of distributed and mobile tags

Magnetoinductive breathers in magnetic metamaterials

The existence and stability of discrete breathers (DBs) in one-dimensional and two-dimensional magnetic metamaterials (MMs), which consist of periodic arrangem ents (arrays) of split-ring resonators (SRRs), is investigated numerically. We consider different configurations of the SRR arrays, which are related to the relative orientation of the SRRs in the MM, both in one and two spatial dimensions. In the latter case we also consider anisotropic MMs. Using standard numerical methods we construct several types of linearly stable breather excitations both in Hamiltonian and dissipative MMs (dissipative breathers). The study of stability in both cases is performed using standard Floquet analysi s. In both cases we found that the increase of dimensionality from one to two spatial dimensions does not destroy the DBs, which may also exist in the case of moderate anisotropy (in two dimensions). In dissipative MMs, the dynamics is governed by a power balance between the mainly Ohmic dissipation and driving by an alternating magnetic field. In that case it is demonstrated that DB excitation locally alters the magnetic response of MMs from paramagnetic to diamagnetic. Moreover, when the frequency of the applied field approaches the SRR resonance frequency, the magnetic response of the MM in the region of the DB excitation may even become negative (extreme diamagnetic).Comment: 12 pages 15 figure

Near-field Image Transfer by Magneto-Inductive Arrays: a Modal Perspective

A simple model of near-field pixel-to-pixel image transfer using magneto-inductive arrays is presented. The response of N-dimensional rectangular arrays is first found as an excitation of eigenmodes. This analytical method involves approximating the effect of sources and detectors, and replaces the problem of solving large numbers of simultaneous equations with that of evaluating a sum. Expressions are given for the modal expansion coefficients, and in the low-loss case it is shown that the coefficient values depend only on the difference in reciprocal frequency space of the operating frequency from the resonant frequency of each mode. Analytic expressions are then derived for quasi-optical quantities such as the spatial frequency response, point-spread function and resolving power, and their implications for imaging fidelity and resolution are examined for arrays of different dimension. The results show clearly that there can be no useful image transfer for in-band excitation. Out-of-band excitation allows image transfer. Provided the array is larger than the expected image by at least the size of the point spread function, the effect of the array boundaries may be ignored and imaging is determined purely by the properties of the medium. However, there is a tradeoff between fidelity and throughput, and good imaging performance using thick slabs depends on careful choice of the operating frequency. The approximate analytic method is verified by comparison of exact numerical solution

Shock-free ion transmission in a skimmer-based MEMS mass spectrometer vacuum interface

Shock-free ion transmission from atmospheric pressure to a MEMS-based mass spectrometer has been achieved using micro-engineered nickel skimmers. The signal level has increased 70-fold compared with a previous configuration in which the skimmer did not sample the supersonic flow. The skimmers are formed by electroplating internal surfaces of anisotropically etched, pyramidal holes in (100) silicon. Etching from the reverse of the wafer exposes free- standing, open-ended skimmers supported by remaining silicon. High-resolution schlieren imaging has been used to visualise gas flow within the interface. Signal enhancement and increased gas throughput are observed when the skimmer attaches to the supersonic gas expansion via oblique shocks. The silicon back wall interacts with the flow field, causing the free jet Mach disc to evolve into a bowl-shaped surface shock whose position asymptotically approaches a stand-off separation as the interface pressure decreases. Ideally, the skimmer entrance should be located approximately midway between the inlet and the back wall. This development should allow a sensitivity increase in MEMS mass spectrometers using pumps of moderate capacity

Noise performance of magneto-inductive cables

Magneto-inductive (MI) waveguides are metamaterial structures based on periodic arrangements of inductively coupled resonant magnetic elements. They are of interest for power transfer, communications and sensing, and can be realised in a flexible cable format. Signal-to-noise ratio is extremely important in applications involving signals. Here, we present the first experimental measurements of the noise performance of metamaterial cables. We focus on an application involving radiofrequency signal transmission in internal magnetic resonance imaging (MRI), where the subdivision of the metamaterial cable provides intrinsic patient safety. We consider MI cables suitable for use at 300 MHz during 1H MRI at 7 T, and find noise figures of 2.3–2.8 dB/m, together with losses of 3.0–3.9 dB/m, in good agreement with model calculations. These values are high compared to conventional cables, but become acceptable when (as here) the environment precludes the use of continuous conductors. To understand this behaviour, we present arguments for the fundamental performance limitations of these cables