David R. Novotny

Manipulating particle trajectories with phase-control in surface acoustic wave microfluidics

We present a 91 MHz surface acoustic wave resonator with integrated microfluidics that includes a flow focus, an expansion region, and a binning region in order to manipulate particle trajectories. We demonstrate the ability to change the position of the acoustic nodes by varying the electronic phase of one of the transducers relative to the other in a pseudo-static manner. The measurements were performed at room temperature with 3 μm diameter latex beads dispersed in a water-based solution. We demonstrate the dependence of nodal position on pseudo-static phase and show simultaneous control of 9 bead streams with spatial control of -0.058 μm/deg ± 0.001 μm/deg. As a consequence of changing the position of bead streams perpendicular to their flow direction, we also show that the integrated acoustic-microfluidic device can be used to change the trajectory of a bead stream towards a selected bin with an angular control of 0.008 deg/deg ± 0.000(2) deg/deg.

Waveguides Composed of Metafilms/Metasurfaces: The Two-Dimensional Equivalent of Metamaterials

In this letter, we illustrate how metafilms (the two-dimensional equivalents of metamaterials, also referred to as metasurfaces) can be used to design novel waveguiding structures. Metafilm waveguides can be flexible with low material and radiation losses. They are attractive alternatives to traditional core-cladding types of surface waveguides and, as such, could have potential applications at terahertz frequencies. We show comparisons to full-wave numerical results in order to validate first the proposed waveguiding structure and, second, the technique used in the analysis of the waveguide.

Efficient and accurate testing of an EMC compliance chamber using an ultrawideband measurement system

This paper summarizes a joint NIST-Industry measurement effort. The purpose of this effort was to use a NIST-developed ultrawideband measurement system to assess the performance improvement of a ferrite tile anechoic chamber after a partial retrofit. Measurements were performed in the 30-1200 MHz frequency range before and after treatments were applied and excellent results were obtained. The system exhibited good sensitivity and the results highlight the effects of various retrofitting treatments. The effort also demonstrates that the NIST ultra wideband system is an efficient tool for the evaluation for both current and proposed anechoic EMC compliance test chambers.

Dielectric Characterization by Microwave Cavity Perturbation Corrected for Nonuniform Fields

Nonuniform fields decrease the accuracy of dielectric characterization by microwave cavity perturbation. These fields are due to the slot in the cavity through which the sample is inserted and the boundary between the sample and the metallic walls inside of the cavity. To address this problem, we measured the natural frequency and damping ratio of a resonant cavity as a sample is inserted into the rectangular cavity. We found that for a range of cavity filling fractions, a linear regression on the natural frequency and damping ratio versus the effective volume fraction of the sample in the cavity could be used to extract the complex permittivity of the sample. We verified our technique by measuring a known quartz substrate and comparing the results to finite-element simulations. When compared to the conventional technique, we found a significant improvement in the accuracy for our samples and measurement setup. We confirmed our technique on two lossy samples: a neat stoichiometric mixture bisphenol A epoxy resin and one containing a mass fraction of 3.5% multi-walled carbon nanotubes (MWCNTs). At the TE103 mode (7.31 GHz), the permittivity and loss tangent of the epoxy were measured to be εr=2.93±0.11 and tanδ = 0.028±0.002, respectively. The epoxy with a mass fraction of 3.5% MWCNTs had a permittivity of εr=8.01±0.48 and loss tangent of tanδ = 0.137±0.010.

Complex Permittivity of Planar Building Materials Measured With an Ultra-Wideband Free-Field Antenna Measurement System

Building materials are often incorporated into complex, multilayer macrostructures that are simply not amenable to measurements using coax or waveguide sample holders. In response to this, we developed an ultra-wideband (UWB) free-field measurement system. This measurement system uses a ground-plane-based system and two TEM half-horn antennas to transmit and receive the RF signal. The material samples are placed between the antennas, and reflection and transmission measurements made. Digital signal processing techniques are then applied to minimize environmental and systematic effects. The processed data are compared to a plane-wave model to extract the material properties with optimization software based on genetic algorithms.

Across-the-road photo traffic radars: new calibration techniques

We discuss simulator units for calibrating across-the-road Doppler traffic radar transceivers used in enforcement of highway speed limits. Two units of very similar design were developed, one operating at K-band (24 GHz) and the other at Ka-band (35 GHz). The signal received from the radar transmitter is frequency-modulated at rates that correspond to the expected Doppler shift for approaching and receding vehicles travelling at speeds of 25 to 200 km/h. The modulated signal is subsequently retransmitted back to the radar receiver, which demodulates it and then displays the simulated speed. The required calibration accuracy is 1.6 km/h at 90 km/h.

HF RFID electromagnetic emissions and performance

We examined the emissions of commercial HF (high-frequency) proximity RFID (radio frequency identification) systems and the performance of a typical RFID system in the presence of electromagnetic (EM) interference. Some initial investigations into security and reliability were also performed. These investigations highlight detectability and readability of an RFID transaction at a distance. We performed measurements to determine the power radiated by some commercial systems and monitored the RFID transaction in adverse EM environments.

An optically linked three-loop antenna system for determining the radiation characteristics of an electrically small source

Experimental results on an antenna system for determining the radiation characteristics of an electrically small source are presented. Three orthogonal loop antennas, each terminated at diametrically opposite points with identical loads, encircle the source and characterize its equivalent electric and magnetic dipole moments. The total radiated power can be determined from this near-field measurement of the device under test. The test system operates from 3 kHz to over 100 MHz with up to 90 dB of dynamic range. Test results are presented for a system constructed from three 1-m-diameter loops.<<ETX>>

Millimeter-Wave Near-Field Measurements Using Coordinated Robotics

The National Institute of Standards and Technology (NIST) recently developed a new robotic scanning system for performing near-field measurements at millimeter-wave (mm-wave) frequencies above 100 GHz, the configurable robotic millimeterwave antenna (CROMMA) facility. This cost-effective system is designed for high-frequency applications, is capable of scanning in multiple configurations, and is able to track measurement geometry at every point in a scan. The CROMMA combines realtime six-degree-of-freedom optical spatial metrology and robotic motion to achieve antenna positioning to within 25 μm rms. A unified coordinated metrology approach is used to track all positional aspects of scanning. A vector network analyzer is used to capture amplitude and phase. We present spherical near-field measurements of the forward hemisphere of a 24-dBi standard gain horn at 183 GHz. Using the configurable scanning ability, two different scanning radii were used. Near-field data were taken at a 100-mm radius. Direct far-field measurements were also taken at 1000-mm radius. The E- and H-plane patterns are determined from the measurements and compared to theoretical patterns. We describe the system components of the CROMMA and the coordinated metrology approach used. An analysis of the positional repeatability and accuracy achievable is also presented.

Simple Test and Modeling of RFID Tag Backscatter

We consider here worst-case analysis of backscatter from passive radio frequency identification (RFID) tags. The basis is a figure of merit “B” to relate link power at reader ports to tag circuit parameters. A minimum bound for received monostatic backscatter can be determined by inspection from measured B. The bound is general for narrowband signals in any causal linear propagation. For an assembled tag, this minimum varies only with reader transmit power, tag antenna tuning, and chip power sensitivity of different commands. To validate this model, we propose a backscatter calibration device to enable measurements with estimated 0.5 dB uncertainty. We then demonstrate how the minimum bound can inform reader sensitivity specification to help ensure reliable inventory performance.