Bradley Davis

Optical fiber sensor for breathing diagnostics

We report improvements of an optical fiber-based humidity sensor to the problem of breathing diagnostics. The sensor is fabricated by molecularly self-assembling selected polymers and functionalized inorganic nanoclusters into multilayered optical thin films on the cleaved and polished flat end of a singlemode optical fiber. Recent work has studied the synthesis process and the fundamental mechanisms responsible for the change in optical reflection from such a multicomponent film that occurs as a function of humidity and various chemicals. We briefly review that prior work as a way to introduce more recent developments. The paper then discusses the application of these humidity sensors to the analysis of air flow associated with breathing [1]. We have designed the sensor thin film materials to enable the detection of relative humidity over a wide range, from approximately 5 to 95%, and for response times as short as several microseconds. This fast response time allows the near real-time analysis of air flow and water vapor transport during a single breath, with the advantage of very small size. The use of multiple sensors spaced a known distance apart allows the measurement of flow velocity, and recent work indicates a variation in sensor response versus coating thickness.

Commercial applications of metal rubber

This paper describes the commercial applications of Metal Rubber, the first material of its kind, a self-assembled free-standing electrically conductive elastomer in biomedical, aerospace and microelectronic areas. Metal Rubber is a novel nanocomposite formed via the self-assembly processing of metal nanoparticles and elastomeric polyectrolytes. This type of processing allows for control over bulk mechanical and electrical properties and requires only ppm quantities of metal to achieve percolation. The use of nanostructured precursors also results in transparent, electrically conductive nanocomposites. Metal Rubber elastomers are being developed as electrodes, for biomedical applications; flexible interconnects for microelectronics, and sensors to detect fatigue, impact and large strain for aerospace applications. This novel material may be formed as a conformal coating on nearly any substrate or as free standing films.

Metal Rubber electrodes for active polymer devices

This paper describes the use of Metal Rubber, which is an electrically conductive, low modulus, and optically transparent free-standing nanocomposite, as an electrode for active polymer devices. With its controllable and tailorable properties [such as modulus (from ~ 1 MPa to 100 MPa), electrical conductivity, sensitivity to flex and strain, thickness, transmission, glass transition, and more], Metal Rubber exhibits massive improvements over traditional stiff electrodes that physically constrain the actuator device motion and thus limit productivity. Metal Rubber shows exceptional potential for use as flexible electrodes for many active polymer applications.

Self-assembled nanostructured conducting elastomeric electrodes

We report the development of low modulus, highly conducting thin film electrodes formed by molecular-level self-assembly processing methods. The electrodes may be used on sensor or actuator materials requiring large strain.

Metal Rubber sensors

We report recent improvements of Metal RubberTM strain sensors formed by electrostatic self-assembly (ESA) processing. The sensors may be used to measure strains from approximately 1 microstrain to several hundred percent strain, over gauge lengths ranging from approximately 1 millimeter to several tens of centimeters.

Shape Memory-Metal Rubber™ Morphing Aircraft Skins

This paper discusses electrically conductive, shape changing, elastomeric nanocomposites capable of surviving repeated mechanical strains while remaining highly electrically conductive. Morphing nanocomposites were formed in-situ by chemically reacting monolayers of well defined, electrically conductive, nanostructured constituents with high performance shape memory copolymers. In this study, electrical conductivity was investigated as a function of volume fraction of nanoparticles and processing conditions. It was found that self-assembly processing results in percolation and surface resistivity of <1 Ohm/square with <0.01 volume % of metal nanoparticles. Waveguide measurements verified electrical stability of the thermoresponsive nanocomposites. The conclusion is that ultra-low mass density <0.99 g/cc skins formed via layer-by-layer processing exhibit electromagnetic integrity before, during and after shape change; when simulating disparate configurations that may be required on future morphing unmanned aerial vehicles.Copyright

Self-assembled nanostructured optical fiber sensors (Invited Paper)

This paper summarizes nanostructured optical fiber sensors fabricated by molecular self-assembly chemistry. Strain, pressure, vibration and chemical sensors are described which are based on selfassembled fiber cores, claddings, distal endface coatings and free-standing membranes.

Nanostructured Flexible Materials: Metal Rubber™ Strain Sensors

Strain sensors are fundamental building blocks in measurement of materials and structures. Conventional foil strain gages are based on macroscopic principles of bulk material deformation due to stress, and changes in the electrical resistance of deformed bulk metal geometries. Nanostructured strain sensors that operate based on very different physical principles may be envisioned. This chapter discusses such nanostructured strain sensor devices based on self-assembled Metal Rubber™ materials. The first part of the chapter reviews the background on self-assembly processing. The second part of the chapter discusses Metal Rubber™ manufacturing and Metal Rubber™ strain sensor operation.

Improvements in self-assembled optical fiber-based biosensors

This paper describes improvements that have been made in optical fiber biosensors based on thin films deposited onto the ends of optical fiber waveguides using molecular-level self-assembly processes. The properties of the sensor films may be varied by controlling both the chemistry and the morphology and ordering of the films during their fabrication. For example, multilayer segments of films having different indices of refraction may be deposited to form quarter wavelength stack filters whose reflection properties change as a function of concentration of target chemical that modifies the index of the outermost layer or layers. Prior work has shown that by using different chemicals in the self-assembled layers, correspondingly different target chemicals may be detected. These have included water vapor, ammonia, dichloromethane and others. Improvements have been made in the range of index of refraction that may be achieved in the individual layer segments, specifically over the range of 1.2 to 1.8 at visible and near-infrared wavelengths. This paper shows how such an improvement in index difference influences the minimum detectable chemical concentration difference detectable using this approach.

Self-assembled nanostructured sensors

We report the development of nanostructured strain sensors formed by electrostatic self-assembly (ESA) processing. The sensors may be used to measure strains from 1 microstrain to more than 100% strain, over gauge lengths ranging from approximately 1 millimeter to tens of centimeters.