Tim Dallas

Feature Selection and Activity Recognition System Using a Single Triaxial Accelerometer

Activity recognition is required in various applications such as medical monitoring and rehabilitation. Previously developed activity recognition systems utilizing triaxial accelerometers have provided mixed results, with subject-to-subject variability. This paper presents an accurate activity recognition system utilizing a body worn wireless accelerometer, to be used in the real-life application of patient monitoring. The algorithm utilizes data from a single, waist-mounted triaxial accelerometer to classify gait events into six daily living activities and transitional events. The accelerometer can be worn at any location around the circumference of the waist, thereby reducing user training. Feature selection is performed using Relief-F and sequential forward floating search (SFFS) from a range of previously published features, as well as new features introduced in this paper. Relevant and robust features that are insensitive to the positioning of accelerometer around the waist are selected. SFFS selected almost half the number of features in comparison to Relief-F and provided higher accuracy than Relief-F. Activity classification is performed using Naïve Bayes and k-nearest neighbor (k-NN) and the results are compared. Activity recognition results on seven subjects with leave-one-person-out error estimates show an overall accuracy of about 98% for both the classifiers. Accuracy for each of the individual activity is also more than 95%.

Enhanced Signal-to-Background Ratios in Voltammetric Measurements Made at Diamond Thin-Film Electrochemical Interfaces

Large signal-to-background (S/B) ratios for the Fe(CN)(6)(3)(-)(/4)(-) and IrCl(6)(2)(-)(/3)(-) redox couples in KCl have been observed in cyclic voltammetric measurements made at a conductive diamond thin-film electrode without any conventional surface pretreatment. The S/B ratios were a factor of ∼16 and 8 larger at diamond than at freshly polished glassy carbon (GC) for Fe(CN)(6)(3)(-)(/4)(-) and IrCl(6)(2)(-)(/3)(-), respectively. The polycrystalline diamond film, grown on a p-Si(100) substrate, possessed significant cubic {100} faceting, as evidenced by AFM images, and was of high quality, as indicated by Raman spectroscopy. The high degree of electrochemical activity without surface pretreatment, the enhanced S/B ratios, and the excellent response stability demonstrate that diamond might be an attractive new electrode material for electroanalysis.

Microfabrication and characterization of teflon AF-coated liquid core waveguide channels in silicon

The fabrication and testing of Teflon AF-coated channels on silicon and bonding of the same to a similarly coated glass wafer are described. With water or aqueous solutions in such channels, the channels exhibit much better light conduction ability than similar uncoated channels. Although the loss is greater than extruded Teflon AF tubes, light throughput is far superior to channels described in the literature consisting of [110] planes in silicon with 45/spl deg/ sidewalls. Absorbance noise levels under actual flow conditions using an LED source, an inexpensive photodiode and a simple operational amplifier circuitry was 1/spl times/ 10/sup -4/ absorbance units over a 10-mm path length (channel 0.17-mm deep /spl times/0.49-mm wide), comparable to many commercially available macroscale flow-through absorbance detectors. Adherence to Beers law was tested over a 50-fold concentration range of an injected dye, with the linear r/sup 2/ relating the concentration to the observed absorbance being 0.9993. Fluorescence detection was tested with fluorescein as the test solute, a high brightness blue LED as the excitation source and an inexpensive miniature PMT. The concentration detection limit was 3 /spl times/ 10/sup -9/ M and the corresponding mass detection limit was estimated to be 5 /spl times/ 10 /sup -16/ mol.

Light at the end of the tunnel: recent analytical applications of liquid-core waveguides

Abstract Optical chemical analysis systems are the most important tools to analytical chemists in need of sensitive measurement techniques. Liquid-core waveguides (Fig. 1) have proved to be an important innovation that has led to improvements in detection limits when incorporated into many types of optical analysis systems, especially UV–Vis absorbance, fluorescence and Raman measurements.

A two-stage discrete peristaltic micropump

We demonstrate a discrete, two-stage peristaltic micropump for applications in microfluidics. Prototypes are fabricated in polydimethylsiloxane (PDMS) with water as the working fluid. Off-wafer compressed nitrogen gas provides the actuation energy. The device may be operated in three- or two-stage modes for direct comparison. We show that two-stage pumps have comparable flow rates to the three-stage counterparts, and produce ∼2/3 the static head. Our results suggest that two-stage pumps may be a viable choice under low backpressure conditions where available on-chip area or the number of external connections is limited.

Microfabrication and characterization of liquid core waveguide glass channels coated with Teflon AF

We report on the microfabrication and testing of liquid core waveguides (LCW) using Teflon AF for integration in microfabricated microanalysis systems. Teflon AF has an index of refraction less than that of water allowing it to function as a waveguide when used as a cladding layer surrounding an aqueous core. Straight microchannels (400-/spl mu/m width, 60-/spl mu/m depth) etched into Pyrex and soda-lime glass wafers were coated with Teflon AF and sealed with a Teflon AF coated capping wafer. Aqueous fluorescein solutions with varying concentrations were injected into the channels and were illuminated transversely using an ultraviolet light emitting diode. For studying the waveguide attenuation performance, light was focused to a point on the channel. Fluorescence generated in the channel was used to quantify the light collection and waveguide characteristics. The Teflon coating produces a significant enhancement in the amount of light collected in the channel, allowing light to be collected from the 16-mm length tested. This is compared to a control microchannel in glass (no coating), for which the fluorescence drops to the background level in an illumination-detection separation of <4 mm. For sensitivity performance, the entire channel was illuminated. The lower detection limit for spectroscopically resolved fluorescence was /spl sim/10 nMolar.

Cell Detachment Model for an Antibody-Based Microfluidic Cancer Screening System

We consider cells bound to the floor of a microfluidic channel and present a model of their flow‐induced detachment. We approximate hydrodynamic force and cell elastic response using static finite‐element simulation of a single cell. Detachment is assumed to occur when hydrodynamic and adhesive forces are roughly equal. The result is extended to multiple cells at the device level using a sigmoidal curve fit. The model is applied to a microfluidic cancer‐screening device that discriminates between normal epithelial cells and cells infected with human papillomavirus (HPV), on the basis of increased expression of the transmembrane protein α6 integrin in the latter. Here, the cells to be tested are bound to a microchannel floor coated with anti α6 integrin antibodies. In an appropriate flow rate range, normal cells are washed away while HPV‐infected cells remain bound. The model allows interpolation between data points to choose the optimal flow rate and provides insight into interaction of cell mechanical properties and the flow‐induced detachment mechanism. Notably, the results suggest a significant influence of cell elastic response on detachment.

In Situ Characterization of Induced Stiction in a MEMS

Stiction remains a limiting factor in the performance and lifetime of MEMS devices. We have developed experimental tools for inducing and quantifying changes in stiction on a large array of MEMS actuators. Thousands of elements were subjected to aggressive wear in order to produce shearing forces that contributed to the degradation of contacting surfaces. Custom electronics were developed to accomplish nonstandard actuation of the MEMS array. Optical techniques were used to characterize the induction of and progression of stiction. A model incorporating experimental and geometrical values was used to determine stiction force as a function of actuation duration and packaging. For a depackaged array, an increase in stiction force of ~230nN (per element) was induced through three days of high-speed actuation

Rotating Out-of-Plane Micromirror

Out-of-plane micromirrors have been developed for a wide range of applications including optical switching, beam steering, and precise transmission and reception of bio-optical signals. This paper focuses on the design, simulation, and testing of a rotating out-of-plane micromirror. The system consists of a polysilicon micromirror, which is erected to an out-of-plane position using a relatively simple postprocessing procedure. The mirror is mounted on a gear which has a rotational freedom of 360° and can be driven at frequencies ranging from 1 to 1000 Hz using an electrostatically actuated rotational drive. Multiple out-of-plane configurations of the mirror are possible, with each utilizing a serpentine spring that attaches the mirror to the gear and a position specific ?catch block? to allow 30 °, 45° , 60°, 75°, and 90° orientations of the mirror. This paper focuses on the 45° out-of-plane mirror, and it was tested for robustness as well as optical performance. A good correlation was found between experiment and various simulations.

Haptic controlled three-axis MEMS gripper system

In this work, we describe the development and testing of a three degree of freedom meso/micromanipulation system for handling micro-objects, including biological cells and microbeads. Three-axis control is obtained using stepper motors coupled to micromanipulators. The test specimen is placed on a linear X-stage, which is coupled to one stepper motor. The remaining two stepper motors are coupled to the Y and Z axes of a micromanipulator. The stepper motor-micromanipulator arrangement in the Y and Z axes has a minimum step resolution of ∼0.4 μm with a total travel of 12 mm and the stepper motor-X stage arrangement has a minimum resolution of ∼0.3 μm with a total travel of 10 mm. Mechanical backlash error is ∼0.8 μm for ∼750 μm of travel. A MEMS microgripper from Femtotools™ acts as an end-effector in the shaft end of the micromanipulator. The gripping ranges of the grippers used are 0-100 μm (for FT-G100) and 0-60 μm (for FT-G60). As the gripping action is performed, the force sense circuit of FT-G100 measures the handling force. This force feedback is integrated to a commercially available three degree of freedom haptic device (Novint Falcon) allowing the user to receive tactile feedback during the microscale handling. Both mesoscale and microscale controls are important, as mesoscale control is required for the travel motion of the test object whereas microscale control is required for the gripping action. The haptic device is used to control the position of the microgripper, control the actuation of the microgripper, and provide force feedback. A LABVIEW program was developed to interlink communication and control among hardware used in the system. Micro-objects such as SF-9 cells and polystyrene beads (∼45 μm) are handled and handling forces of ∼50 μN were experienced.