NIST Tech - Environment/Climate

Cavity Ringdown Spectroscopy System using Differential Heterodyne Detection

A novel AC technique in cavity ringdown spectroscopy that permits IXIO-IO absorption sensitivity with microwatt level light power has been developed. Two cavity modes, one probing the empty cavity and the other probing intracavity absorption, are excited simultaneously, but their intensities are temporally out of phase, with one mode decaying and the other rising. Heterodyne detection between the two modes reveals the dynamic time constants associated with the empty cavity and the additional intracavity gas absorption. The method offers a quick comparison between the on-resonance and off-resonance information, a prerequisite to reaching the fundamental shot noise limit. This simple and yet important improvement of cavity ringdown spectroscopy should lead to enhanced performance in a wide range of applications.

MICRO-HOTPLATE DEVICES AND METHODS FOR THEIR FABRICATION

A design and fabrication methodology, for silicon micromachined micro-hotplates which are manufactured using commercial CMOS foundries techniques with additional post-fabrication processing. The micro-hotplates are adaptable for a host of applications. The methodology for the fabrication of the micro-hotplates is based on commercial CMOS compatible micromachining techniques. The novel aspects of the micro-hotplates are in the design, choice and layout of the materials layers, and the applications for the devices. The micro-hotplates have advantages over other similar devices in the manufacture by a standard CMOS process which include low-cost and easy integration of VLSI circuits for drive, communication, and control. The micro-hotplates can be easily incorporated into arrays of micro-hotplates each with individualized circuits for control and sensing for independent operation.

Rotary Cam-Driven Free Fall Dropping Chamber Mechanism

An improved gravimeter mechanism includes a mass balanced cam having mutually opposed camming surfaces for controlling the free fall of a measuring mass. The cam is attached to a camshaft which turns at a constant rate, the rate being selected so that the drop time appropriate to achieve lift-off of the dropped object together with the time required to return to the start position equals the cam's rotational period. The mutually opposed camming surfaces cooperate to drive both a cart which supports a measuring mass and a compensating mass which is built into the gravimeter mechanism. The cam drives the cart, the measuring mass, and the compensating mass so that the time varying reduction in weight produced when the measuring mass is in free fall is exactly compensated by the compensating mass which is driven by the opposing camming surface.  The opposing camming surface is displaced from the lift off region of the camming surface which drives the cart and measuring mass by 180 degrees. The measuring mass contains a mirror element of a Michelson interferometer, and the interferometer produces a signal indicative of the rate of free fall, which is directly proportional to the local gravity.

Mixing Liquids & Entrainment Mixing of Vapor into Liquids

Disclosed is a fluid mixer that mixes liquids while simultaneously promoting rapid mixing entrainment of vapor in the liquid. The device includes a vertical rotor mounted centrally on a base assembly. The rotor comprises a tube which is hollow from an open top end to a bottom closed end, having an external screw thread in a right-side configuration relative from top to bottom and one or more holes located in the sidewall of the tube at the bottom of the hollow portion of the tube, preferably located centrally between two flanking surfaces of the screw thread. The base assembly comprises a stirbar and a supporting disk which contains a ceramic magnet. The base rests on the floor of a containment vessel. A magnetic stirring motor is centrally located sufficiently close to and beneath the containment vessel as to achieve magnetic flux coupling with the base magnet. Operation of the mixer develops a liquid vortex in the liquid phase material. As the speed increases, the external screw threads generate turbulence and draw vapor into the liquid from above the tube and urge the vapor into intimate contact with the turbulent, droplet-forming liquid. A circulation develops causing a vortex to develop. As the speed of circulation increases, the surface of the liquid is lowered until it matches the hole in the sidewall of the tube. The liquid enters the holes in the sidewall of the tube along with entrained vapor, and rises through the liquid in the hollow tube, and exits the open top end.

THREE DEGREE-OF-FREEDOM TELESCOPING GEOMETRY SCANNER

The invention relates to a three-dimensional measuring device, comprising a rotating 360 degree sensor head, a laser scanner and an extendable mast system. The sensor head contains a 360 degree rotating multi-faceted mirror, which determines total path distance from the laser scanner to a particular target.  Angular orientations on both the scanner and the faceted mirrors are calculated by a precision encoding system. The measured total path distance, mast system extension, scanner head rotation, mirror rotation angles, and mast deflection are all used to calculate the location of a target point in 3-D space relative to the scanner. The sensing device can be utilized in the construction and nuclear power areas. In the nuclear power area, the mast system can be extended into a contaminated area which the sensor remains outside the contaminated area, thereby avoiding contamination problems.

Versatile, Simple Microfluidics for Field Portable Applications

Fluidic Temperature Gradient Focusing: Docket # 01-029

The present invention concerns a method and device for concentrating and separating ionic species in solution within fluid conduits which include channels, microchannels and capillary tubes. The concentration is achieved by balancing the electrophoretic velocity of an analyte against the bulk flow of solution in the presence of a temperature gradient. Unlike previous methods, such as salt bridges or electrodes, which severely limit the type of analyte that can be concentrated, this invention can be adapted for use with any charged analyte, including fluorescent dyes, amino acids, proteins, DNA, cells and particles. Additionally, the use of a temperature gradient prevents the need for an electric field gradient which tends to be difficult to construct and require a control of voltage on an additional electrode. Finally, this invention can be used to achieve higher degrees of sample concentration, which can provide up to or, in some instances, exceed a 10,000-fold concentration of a dilute analyte.

Mixing Reactions by Temperature Gradient Focusing: Docket # 01-029CIP1

A method is provided for observing mixing interactions and reactions of two materials in a fluid. The method in one form provides for concentrating by balancing electrophoretic velocities of a material against the bulk flow of fluid in the presence of a temperature gradient. Using an appropriate fluid, the temperature gradient can generate a corresponding gradient in the electrophoretic velocity of the material so that the electrophoretic and bulk velocities sum to zero at a unique position and the material will be focused at that position. A second material can then be introduced into the fluid and allowed to move through and interact with the focused band of the first material. Products of the interaction can then be detected as they are focused at a different position along the gradient. The method can be adapted to study the temperature dependence of the molecular interaction.

Chiral Temperature Gradient Focusing: Docket # 01-029CIP2

The present invention combines the high resolution of chiral capillary electrophoresis with the high concentration enhancement and low detection limits of temperature gradient focusing. The temperature gradient focusing allows for higher degrees of sample concentration, such as more than a 10,000 fold concentration of a dilute material, when compared with any prior single sample preconcentration method. Additionally, the electrophoretic velocity gradient is formed in response to the temperature gradient without the need for externally manipulated voltages or complicated and difficult to fabricate semi-permeable structures. Finally, the present invention is able to separate stereoisomers of a material which have different affinities for the additive. Essentially, with the addition of a chiral additive, the present focusing method allows for simultaneous separation and concentration of materials that cannot be separated using temperature gradient focusing based purely upon their electrophoretic mobilities. One benefit of being able to separate chiral stereoisomers is that many drugs and drug candidates are chiral and in most cases, one stereoisomer is more desired for drug use than the other. In some instances, one stereoisomer is a beneficial drug, whereas the other results in adverse side effects.

RECIRCULATING TEMPERATURE WAVE FOCUSING CHROMATOGRAPHY

The invention is a device and method for performing chromatography in an equilibrium gradient focusing mode rather than a transient, migration-based mode. The present invention utilizes temperature gradient focusing (TGF) for a wide array of chromatography applications.  The invention is based upon a discovery that by recirculating a moving temperature wave through a system preferably comprising two or more chromatography columns, analytes accumulate at select locations on the temperature wave.  Thus, analyte peaks become narrower and more intense as the temperature wave is circulated about the system.  The resulting focusing of analyte peaks enables higher resolution and lower detection limits for the system.

ELECTROSTATICALLY-ASSISTED CENTRIFUGATION APPARATUS FOR TRANSFERRING FILTER-BOUND PARTICLES TO A SUBSTRATE FOR MICROSCOPIC ANALYSIS

The invention, a Particle Transfer Apparatus, facilitates the transfer of atmospheric particles for fibrous filter such as quartz fiber to a smooth substrate that is suitable for scanning electron micrscopy (SEM) and x-ray microanalyisis. The invention may also be suitable for transferring particles embedded in clothing textiles for this purpose.

The Microfluidic Palette: Generation of Multiple Chemical Gradients within a Microfluidic Chamber

The invention consists in a microfluidic device that generates multiple chemical gradients simultaneously within a microfluidic chamber. The chemical gradients are generated without convection, only by diffusion, and they can be maintained over long periods of time, or be modified dynamically.

Description of the microfluidic device:

The device consists of a main microfluidic chamber where there is no convection (no flow movement) and where mixing is done by diffusion. The chamber is accessed by "convection-diffusion units". A convection-diffusion unit consists of a microchannel that has matched flow at its inlet and outlet; thus, even if the microchannel has an opening to the microfluidic chamber, all the liquid that is introduced through the inlet has to come out through the outlet (conservation of mass) making it impossible to get into the chamber except by diffusion. If the inlet and outlet of each convection-diffusion unit were not exactly matched, difference in pressure among microchannels would generate convection through the chamber ruining the diffusion-only premise inside the microfluidic chamber.

The convection-diffusion units decouple convection in the microchannels from diffusion in the chamber. Therefore, if a solution of a drug is introduced through inlet 1 and retrieved through outlet 1, the concentration of this drug at the opening 1 to the chamber will be the same as at the channel. If only buffer flows through channels 2 and 3, the concentration of the drug at the openings 2 and 3 necessarily will be zero. Thus, in the microfluidic chamber, opening 1 works as a diffusive source of the drug, while opening 2 and 3 work as sinks, and all the space in between (after some transient time) will have a static gradient in concentration of the drug.

FREQUENCY COMB CAVITY ENHANCED SPECTROSCOPY

We invent and demonstrate a qualitatively new form of cavity ringdown
spectroscopy utilizing a broad bandwidth optical frequency comb coherently
coupled to a high finesse optical cavity inside which molecular samples are located.
125,000 optical comb components, each coupled into a specific longitudinal cavity
mode, undergo ring down decays when the cavity input is shut off This provides
sensitive intracavity absOlption information simultaneously available across 100
nm in the visible and near IR spectral region. By placing various atomic and
molecular species (Ar, C2H2, O2, H20, NH3) inside the cavity, we demonstrate realtime,
quantitative measurements of the trace presence, transition strengths and
linewidths, and population redistributions due to collisions and temperature
changes. This novel capability to sensitively and quantitatively monitor multispecies
molecular spectra over a large optical bandwidth in real-time provides a
new spectroscopic paradigm for studying molecular vibrational dynamics, chemical
reactions, and trace analysis.

AN ATOMIC MAGNETOMETER AND METHOD OF SENSING MAGNETIC FIELDS

A magnetometer and method of use is presently disclosed.  The magnetometer has at least one sensor void of extraneous metallic components, electrical contacts and electrically conducting pathways.  The sensor contains an active material vapor, such as an alkali vapor, that alters at least one measurable parameter of light passing there through, when in a magnetic field.  The sensor may have an absorptive material configured to absorb laser light and thereby activate or heat the active material vapor.   

Integrated Microchip Incorporating Atomic Magnetometers and Microfluidic Channels for Detection of NMR and MRI

A microfluidic chip incorporating an alkali vapor cell and microfluidic channel is described, which can be used to detect the nuclear magnetism of a polarized sample of nuclei in a fluid.  Small magnetic fields in the vicinity of the vapor cell can be measured by optically polarizing and probing the spin precession in said small magnetic field.  This can then be used to detect the magnetic field due to the sample of nuclei in the adjacent microfluidic channel. The nuclear magnetism in the microfluidic channel can be modulated by applying an appropriate series of radio or audio frequency pulses upstream from the microfluidic chip to yield a sensitive means of detecting nuclear magnetic resonance and magnetic resonance imaging.

Photoacoustic Spectrometer With Calculable Cell Constant for Quantitiative Absorption Measurements of Pure Gases, Gaseous Mixtures, and Aerosols

We have invented and modeled an intensity-modulated, laser-driven photoacoustic (PA) spectrometer with a calculable cell constant. The uncertainty in the calculated cell constant has been demonstrated to be about 1% or less. To this end, we combined first-principles models of acoustic wave propagation with high-resolution spectroscopic measurements. We modeled and measured the absolute response of an intensity-modulated photoacoustic spectrometer comprising a 10 cm long resonator and having a Q-factor of approximately 30. We used a detailed theoretical analysis of the system and predicted its response as a function of gas properties, resonance frequency, and sample energy transfer relaxation rates.

Domain Engineered Ferroelectric Optical Radiation Detector with Multiple Domain Regions for Acoustic Dampening (Continuation-in-part Patent)

A pyroelectric detector with significantly reduced microphonic noise sensitivity that includes a pyroelectric detector element constructed from a z-cut LiNbO₃ or LiTaO₃ electret. Selective domain reversal is accomplished in the electret by applying an electric field. Electrodes are attached to either surface of the electret spanning the domain reversed region and a portion of the original domain region to create areas of equal and opposite sensitivity. The detector is mounted in an electrically grounded container or housing. The detector may also be constructed having multiple detector regions to accommodate resonant acoustic frequencies of the electret, to function as a position sensor, or both. In other words, the position sensor has multiple domain regions that also accommodate acoustic frequencies. The detector may also be constructed having domain reversed regions placed on the electret in a periodic pattern having a geometry and spacing that is related to the acoustic impulse response of the electret. Needle domains may also be interspersed in portions or throughout the electret to scatter acoustic waves and thereby reduce acoustic noise. Multiple detectors can be produced in a simple and inexpensive manner using shadow masking techniques.