Erik P. Anderson

Coordinated target assignment and intercept for unmanned air vehicles

Presents an end-to-end solution to the cooperative control problem represented by the scenario where M unmanned air vehicles (UAVs) are assigned to transition through N known target locations in the presence of dynamic threats. The problem is decomposed into the subproblems of: 1) cooperative target assignment; 2) coordinated UAV intercept; 3) path planning; 4) feasible trajectory generation; and 5) asymptotic trajectory following. The design technique is based on a hierarchical approach to coordinated control. Simulation results are presented to demonstrate the effectiveness of the approach.

In vivo brain imaging using a portable 3.9 gram two-photon fluorescence microendoscope

We introduce a compact two-photon fluorescence microendoscope based on a compound gradient refractive index endoscope probe, a DC micromotor for remote adjustment of the image plane, and a flexible photonic bandgap fiber for near distortion-free delivery of ultrashort excitation pulses. The imaging head has a mass of only 3.9 g and provides micrometer-scale resolution. We used portable two-photon microendoscopy to visualize hippocampal blood vessels in the brains of live mice.

Real-time dynamic trajectory smoothing for unmanned air vehicles

This brief presents a real-time, feasible trajectory generation algorithm for unmanned air vehicles (UAVs) flying through a sequence of waypoints. The algorithm produces extremal trajectories that transition between straight-line path segments in a time-optimal fashion. In addition, the algorithm can be configured so that the dynamically feasible trajectory has the same path length as the straight-line waypoint path. Implementation issues associated with the algorithm are described in detail. Simulation studies show the effectiveness of the proposed method.

Simultaneous measurement of nonlinearity and electrochemical impedance for protein sensing using two-tone excitation

Impedance biosensors detect the binding of a target to an immobilized probe by quantifying changes in the impedance of the electrode-electrolyte interface. The interfaces I–V relationship is inherently nonlinear, varying with DC bias, and target binding can alter the degree of nonlinearity. We propose and demonstrate a method to simultaneously measure the nonlinearity and conventional small-signal impedance using intermodulation products from a two-tone input. Intermodulation amplitudes accurately reflect the impedances manually-measured voltage dependence. We demonstrate that changes in nonlinearity can discriminate protein binding. Our measurements suggest that target binding can alter nonlinearity via the voltage dependence of the ionic double layer.

A Label-free CMOS DNA Microarray based on Charge Sensing

The first label-free CMOS DNA polymerization sensor is reported. The 5-by-5 sensor array measures the charge induced on an electrode from a DNA fragment undergoing polymerization. Importantly, no post-processing is required as passivated top-metal electrodes are used. The measured limit of detection (with enzymatic buffer) is 25 fA for a one second integration time, or equivalently 25 fC of charge, although the limit set by the electronic noise is 3.5 times smaller. Using our chip, we demonstrate the detection of DNA polymerization. The sensor can be used to sequence short DNA segments in addition to detect DNA hybridization in microarrays.

Crosstalk in Integrated Microarrays With Current Sensing

Various investigators have developed DNA microarrays with electronic readout; however, crosstalk between microarray pixels has received little attention. Electronic crosstalk can occur through the solution between electrodes, giving false results. Here we analyze crosstalk when an integrating readout scheme is used to measure the electrode current for multiplexed single electrode systems (e.g., charge sensing). Crosstalk between channels can easily exceed 10% and thus can be the dominant factor in the microarray limit-of-detection. The crosstalk depends on amplifier design (gain and integrating capacitance), electrode-solution impedance, integration time, and the profile of the measured current. Proper selection of the integration time, integration capacitance, amplifier pole frequency, and dc amplifier gain can reduce crosstalk considerably. The area required for an integrated circuit implementation trades off with crosstalk.

CMOS impedance biosensor array with active tone cancellation for simultaneous impedance and nonlinearity measurement

We present a 6×6 array of impedance biosensor circuits implemented in 0.18 µm CMOS. Each pixel contains impedance-measuring circuitry plus tone cancellation circuitry to enable simultaneous measurement of the impedances dependence on DC bias point. Changes in both impedance and nonlinearity of the electrode-solution interface can indicate binding of the biomolecule of interest. Our measurement scheme uses a large-amplitude low-frequency tone superimposed on the traditional small-signal excitation. The weakly nonlinear nature of the electrode-solution interface generates intermodulation tones which can be used to quantify the amount of nonlinearity. To avoid the large-amplitude signal saturating the amplifier output, a digital feedback loop actively cancels the low-frequency component by injecting an antiphase current at the summing node of the transimpedance amplifier, so that only the small-signal tone and intermodulation tones remain. Impedance changes of 0.2% can be detected. Each measurement pixel occupies 0.14 mm2 and consumes 1.9 mW.

Fiber optic two-photon fluorescence microendoscopy: towards brain imaging in freely moving mice

We introduce a compact and lightweight (3.7 g) two-photon fluorescence microendoscope, which is based on a flexible photonic bandgap fiber and a DC micromotor, and which is designed for brain imaging in freely moving mice.