Analytical Instrumentation : Sensors

Analytical Instrumentation Portfolios


Field Portable Smartphone Device for Water Quality Monitoring

A University of Wisconsin-Green Bay professor of chemistry has developed a portable, accurate, low cost, smartphone-based analytical device for the field-measurement and geographical mapping of environmentally relevant water quality parameters. In its current embodiment, the device is a colorimeter for measuring absorbance that includes a visible light source with onboard power, imaging filters, a sample cuvette, and a mounting mechanism for attachment to a smartphone or tablet. An accompanying app is used to record camera images of samples and convert them to numerical absorbance data for analysis. The app will be further developed to allow integration with an online ArcGIS platform for uploading and mapping the data.

Optical Phase Shift Solution: Compact and Easy to Install

UW–Madison researchers have developed an innovative OPS that delivers tunable optical phase shifting with a wide aperture. Unlike many electro-optic modulators, its liquid-based design makes it a versatile candidate for many imaging devices.

The shifter consists of two immiscible liquid layers with different refractive indices. Between the two liquids is a rigid membrane that moves freely along the optical axis. When pressure alters the thicknesses of the liquid layers, it induces an optical path difference, resulting in a phase shift.

High Accuracy Angle Measuring Device for Industrial, Medical, Scientific or Recreational Use

A UW-Stout researcher has developed a high-accuracy angle measurement system that addresses the problems inherent to commercially available systems. In this novel device, a high accuracy rotary optical encoder is controlled by a microprocessor. The encoder consists of rotating optical disks and sensors that are precisely formed and placed to read angles with 0.001 arc second sensitivity (average) and better than ±0.1 arc second accuracy (single readings), which is comparable to the accuracy of the high-end commercial encoders currently on the market. This accuracy is maintained with strategies that combat the mechanical sources of error that are known disadvantages of other devices. The system can also be adjusted to compensate for any asymmetrical shifts that may occur. Mechanical sources of error and noise are further minimized by precision placement of disks and sensors, as well as low-friction reference points that keep components centered and level during rotation. In addition, multiple sensor heads eliminate major readout errors and remove the need for recalibration. All of these features and benefits are contained within a design that is both compact and portable. Beyond high accuracy and portability, the cost of this new angle measurement system is substantially lower than a high-end commercial system because it is easily constructed from readily available industrial grade components, bringing the production cost to roughly $2,000. Strikingly, this cost is comparable to the advertised price of other rotary position encoders that are less than one tenth as accurate. Its high accuracy, low cost, and portability make this new angle measurement system a strong option for use in virtually any of the current applications for absolute rotary encoders.

New Discoveries in Biological Safety: Liquid Crystal Detection of Hazardous Environmental Products

UW–Madison researchers have developed a novel LC-based method and device for accurately detecting low concentrations of volatile organic compounds.

When exposed to a VOC or other target analyte, blue phase-forming compositions consisting of nematic liquid crystals and chiral dopants undergo a response that can be observed with the naked eye, eliminating the need for additional steps. The VOCs can be detected in gaseous and liquid forms, and the sensitivity of the composition can be adjusted by changing the level of dopant concentration as well as adding non-volatile organics as sensitizing agents.

To address the problems of stability and dewetting, the inventors have developed a device that uses LC-phobic surfaces to isolate LC films within the microwells of an array. The LC films have uniform dimensions and are stabilized by capillary forces protecting against shock, gravity, heat and solvent exposure. They can be deposited via high throughput methods such as spin coating.

Bioreversible Protein Esterification

UW–Madison researchers have developed an efficient new method for esterifying proteins using certain diazo compounds. The compounds convert protein carboxyl groups into esters in buffered water. The modification is removed by enzymes that reside in all human cells, making the method bioreversible.

Diazo compounds have the general formula R2C=N2, but not all are effective. They must have a basicity within a certain range.

Strain-Tunable Light Emitting Diodes Using Germanium

UW–Madison researchers have developed new tunable LEDs with germanium PIN heterojunctions. The diodes are made of an undoped (intrinsic) Ge layer between p-type and n-type doped Ge layers. The nano-thin structure can be epitaxially grown and then transferred to a flexible substrate.

Once bonded to the flexible substrate, the whole structure is stretched, causing biaxial tensile strain. Given sufficient strain, the Ge is transformed into a direct-bandgap semiconductor. When voltage is applied, radiation is emitted via electroluminescence. The wavelengths of the emitted radiation can be tuned by adjusting the amount of stretch (i.e., the amount of tensile strain) that is applied.

Electrodes with Low-Cost Replaceable Tips

UW–Madison researchers have developed a new electrode design incorporating disposable tips. The tips can have a snapping mechanism or embedded magnet that attaches to the main shaft of the electrode. An insulating material seals the connection against any liquid. The tips may be modified with other entities such as nanoparticles, enzymes and antibodies.

Ultra-Efficient Continuous Monitoring of Sensors

UW–Madison researchers have developed reconfigurable event-driven hardware that enables low-power continuous monitoring by offloading tasks from the primary processor.

The hardware interfaces with sensors and invokes the processor only when a trigger signature is detected. It can be implemented as a separate integrated chip or as a low-power compute resource within the primary processor.

Ultrasonic Welding with Real-Time Quality Control

UW–Madison researchers and others have developed an ultrasonic welding system that uses thin-film sensors to measure control values, like temperature and heat flux, at the working surface.

The system includes an anvil, welding horn and process controller. The process controller receives measurements taken by the sensors. It then can determine weld quality as the joint is being formed or record the results to help evaluate tool wear.

The thin-film sensors can be commercially available microelectromechanical systems (MEMS) sensors. They may be inserted into slots or attached in the welding device adjacent to the working surface.

Short-Pulsed Alkali Magnetometer for Precision in Ambient Fields

UW–Madison researchers have developed a method of spin polarization using an AC-coupled short pulse, permitting ultrasensitive magnetometry in the presence of Earth-level magnetic fields. By suppressing the spin-relaxation due to interactions between the instrument’s alkali atoms, the short pulses attain high transverse spin polarization free of dephasing collisions.

With increased sensitivity, the new design permits detection of minute fluctuations on par with other alkali-based magnetometers that require a near zero magnetic field environment.

The magnetometer includes a gas chamber exposable to an external magnetic field. An electromagnet is positioned to apply a local magnetic field to the chamber. By modulating the rotational change of the alkali atoms with a controllable time-dependent magnetic field, the atoms can be retained in a state in which collisions do not dephase their magnetic orientation.

Monolithic Fiber Optic Sensor Assembly for High-Temperature or Corrosive Environments

A UW–Madison researcher has developed a high-temperature U-bench sensor constructed from monolithic optical ceramic material. The supporting structure of the sensor and elements such as two opposed lenses or an opposed lens and mirror are constructed of compatible materials and fused together. The material provides a system robust against high temperatures and temperature changes that might affect precision optical alignment or cause mechanical failure in more traditional sensors.

Precision Magnetometer for More Accurate Magnetic Field Readings

UW–Madison researchers have developed a method and apparatus for measuring the magnetic resonance of noble gas nuclei in a magnetic field. Their discovery reduces the effects of the magnetic field produced by the alkali atoms.

The system comprises a chamber holding an intermixed noble gas and an alkali gas exposed to a magnetic field external to those generated by the gases. A spin aligner acts on the alkali gas to promote a precession of a magnetic moment of the alkali gas so that a time-averaged angular difference is essentially zero. Precise measurements are obtained by constraining the time-averaged direction of the spins of a stimulating alkaline gas to lie in a plane perpendicular to the magnetic field. Additionally, a monitor outputs a signal indicating the precession frequency of the noble gas.

Devices and Methods for Immobilizing Liquid Crystal Droplets onto a Chemically Functionalized Substrate Surface

UW–Madison researchers have developed devices and methods for immobilizing micrometer-sized liquid domains such as liquid crystal or isotropic oil droplets on a variety of chemically-functionalized surfaces. A multifunctional polymer, which may be a polyamine, is adsorbed at the surface interface of the liquid crystal droplets. Then the droplets are immobilized by covalent bonding, electrostatic interactions or other interactions between the adsorbed polymer and the functionalized substrate surface. The immobilized droplets can be used, for example, in liquid crystal droplet-based sensing devices or devices engineered to possess optical band gaps.

Night Vision System, Device and Method for Enhanced Signal-to-Noise Ratio

UW-Madison researchers have developed a method for displaying images using motion adaptive frame integration with real time digital processing and display. The method for filtering a series of image frames of a moving subject improves the signal-to-noise ratio of each image frame. The method combined with an optical apparatus configured to receive light from the scene comprises a lightweight, non-intensified imaging system for night vision.

A filtered image is formed by combining pixel values in a current image frame with weighted pixel values in previous and subsequent processed frames. Motion of the imaging system is compensated for so that the corresponding pixels in each image frame are registered to the same pixel locations before filtering. In effect, this registers the series of image frames with each other, providing an enhanced signal-to-noise ratio.

Robust, Moldable Colloidal Liquid Crystal Gels Provide User-Friendly, Portable Sensors

UW-Madison researchers have developed self-supporting and mechanically robust gels that can be molded, easily handled and processed yet retain their responsiveness to chemical and biological species.  These colloidal liquid crystal gels can be used to produce improved liquid crystal-based devices, including wearable, personalized sensors.

The gels are produced by dispersing liquid crystals into colloids, which spontaneously form a network.  The combination of colloids and liquid crystals yields a visco-elastic gel that has high mechanical strength because of the network of colloids.  The high strength allows the gels to be molded into any desired shape, making the detection of chemicals and biochemicals much easier than previous methods using liquid crystals.

Varied Monodisperse Oil or Liquid Crystal Emulsion Droplets for Improved Nanoviewing, Sensing and Biosensors

UW-Madison researchers have developed a versatile, scalable and highly parallel method of producing monodisperse emulsion droplets in a range of predetermined sizes.  The oil emulsion droplets, in which the oils can be liquid crystal molecules, can be prepared with or without polymeric shells or capsules.

This method is based on templating polyelectrolyte multilayer (PEM) capsules formed by the layer-by-layer adsorption of polyelectrolytes on sacrificial particles.  A polymeric shell is formed around a sacrificial particle, such as silica.  Then the silica is etched away and the shell is infiltrated with an oil.  The shell then can be removed to reveal monodisperse oil or liquid crystal emulsion droplets of a uniform, predetermined size.  These droplets could be used as biosensors to detect enzymatic activity or target analytes, such as bacteria or viruses, in a sample.

An Enhanced Method of Embedding Thin Film Sensors

A UW-Madison researcher has developed an improved method to embed microsensors into a wide array of metallic and ceramic materials of various dimensions through a unique combination of standard microfabrication and diffusion bonding techniques.

The thin film sensor is produced using photolithography, lift-off etching and other microfabrication techniques. Then the microsensor is positioned between a base part and a cover piece that can be joined together by diffusion bonding. This process takes place in a protective atmosphere or vacuum. The surface of the cover piece is polished before bonding to avoid damaging the thin films and to reduce local pressures during bonding. The bonding surfaces may contain an interlayer to improve bond quality and/or reduce required bonding temperature, particularly when bonding ceramic to ceramic and ceramic to metal.

After bonding, the finished structure acts as a single functional component with the ability for the bonded area to possess a mechanical strength equal or close to the base material. Subsequently, sensors consisting of a stack of thin films are fabricated on the bonded material, layer by layer, in a clean-room environment by standard thin film deposition and patterning techniques. This approach is capable of joining both small and large components composed of similar or dissimilar material combinations of various alloys and ceramics, thus expanding the applications for embedding sensors.

Dielectric Sensor for Stress and Strain Detection

UW–Madison researchers have developed capacitive strain sensors that measure stress and strain based only on dielectric properties. The two parallel plates are affixed to a substrate so that variance in capacitance occurs only due to change in dielectric properties rather than mechanical displacement. The dielectric change is then translated into an indication of stress and strain.

The sensors consist of interlocked electrodes that can be deposited on a rigid or flexible substrate. They can be implemented as single sensing elements or arranged in rosettes of up to eight capacitors to measure dielectric properties along multiple axes at once. The planar geometry of the electrodes makes the sensors compatible with standard complementary metal-oxide semiconductors (CMOS) fabrication processes, so their characteristics may be tailored easily to particular applications. Signal conditioning circuits also may be incorporated on the same substrate to reduce the need for additional external components and simplify the construction process.

Because rosettes are capable of detecting the dielectric response without direct physical contact, they are suspended slightly away from the measured object to eliminate mechanical contact that could disrupt the measurement. The sensors may be interfaced to the material through a thin layer of mineral oil, which reduces mechanical constraints by lubricating the surface. In addition, the oil eliminates moisture effects and minimizes sensitivity loss.

Smart Leaf Technology - Floating Semiconductor Membranes for Wireless Sensing

UW-Madison researchers have developed wireless sensors made from nanoscale membranes for use in detecting the presence or absence of analytes, systems incorporating the sensors and methods for using the sensors. The “smart leaf” sensors are made of two thin films with opposing front and back surfaces. The surfaces are coated with molecules that react with the target analyte. Upon exposure to the analyte, the molecules alter the geometry of the leaf and change its dielectric response in a manner that depends on the concentration of the target chemical. An electromagnetic source continually exposes an array of sensors to an electromagnetic signal, while a detector regularly scans the sensor array to observe any change in the reflected and/or transmitted radiation. In this way, the presence or even the concentration of a particular analyte may be easily detected without requiring the sensors to be directly wired to a power supply.

Simple Biological Method and Device for Detecting a Toxin or Other Chemical

UW-Madison researchers have developed a simple biological sensing method that can be used to detect toxins or other chemical compounds. The technology uses the elastic instability of swelling hydrogels to act as a trigger when contacted by a designated stimulus, such as a particular chemical.

Two different types of hydrogels are bonded together by a sensitive material, such as a degradable adhesive material specific to a certain enzyme or chemical. The hydrogels swell at different rates, causing them to bend. Because the adhesive restricts the motion of the hydrogels, an elastic force is generated. When the adhesive material contacts the target chemical, the adhesive degrades, releasing the elastic instability and causing the two hydrogels to separate with an explosive motion that is detectable by the naked eye.

Embedded Photonic Sensors for Sensing Workpiece Properties

UW–Madison researchers have developed a system and method for sensing properties of a workpiece that are less susceptible to harsh operating conditions. The photonic device of the system may be embedded in a metal layer of the workpiece, allowing the system to be incorporated into a mechanical device without interfering with normal operation of the piece.

The complete system includes an optical input, a photonic device, an optical detector and a digital processing device. The photonic device is coupled to the workpiece and to the output of the optical input, and generates an output signal in response to the optical signal. The intensity and/or wavelength of the output signal depend on the thermal and/or mechanical characteristics of the workpiece. The optical detector receives the output signal and generates a corresponding electronic signal. The digital processing device is coupled to the optical detector and determines the thermal and/or mechanical characteristics of the workpiece.

The system may act as a complete feedback loop that allows parameters of the process to be modified in response to the thermomechanical characteristics of the system. By implementing integrated microphotonic devices, the system allows for sensing and monitoring of thermomechanical variables even in conditions of strong electromagnetic or thermal interference.

PIN Diodes for Fast Photodetection, and High-Speed, High-Resolution Imaging and Sensing

By employing improved methods for integrating Si and Ge in thin multilayer structures, or “nanomembranes” (see WARF reference number P04286US), UW-Madison researchers have created PIN diodes in which the intrinsic layer is Ge or SiGe and the p-type and n-type layers are silicon. In some applications, these nanomembrane PIN diodes are fabricated on a solid silicon-on-insulator support. In others, the nanomembranes are released from the support and transferred to flexible substrates, such as plastic films.

Temperature Estimation Based on a Signal Oscillation

UW-Madison researchers have developed a novel method of obtaining temperature information without adding new sensors or communications channels. In a switched-mode power converter module, a semiconductor device is rapidly switched off and on. This switching introduces a ringing or oscillating signal that is a function of the temperature and the duty ratio of the module, although the two effects can be decoupled. Because loads are interleaved between modules to reduce ripple currents, operations occur in sequence rather than simultaneously across all modules. The interleaving introduces a time separation between the signals from each module, so that the ringing signal from each module can be detected and sent to a processor that estimates the temperature of that module.

Microelectronics Grade Metal Substrate and Related Metal-Embedded Devices

UW-Madison researchers have developed a novel method of creating a microelectronics-grade metal substrate with embedded sensors or other microelectronic devices. The metal substrate is formed on a sacrificial silicon substrate. An adhesion layer is deposited on the sacrificial substrate, followed by a seed layer of the metal. The metal material is then deposited on the seed layer via a low-temperature, low-stress process, such as electroplating, to form a microelectronics-grade substrate. Thin film sensors and/or other microelectronic devices, followed by the appropriate insulating layer(s), may be fabricated on the sacrificial substrate before the metal substrate is formed. The sacrificial silicon substrate is then etched away, leaving the microelectronics-grade metal substrate and possibly the microelectronics device. Finally, an insulating layer(s), followed by an adhesion layer, a seed layer, and additional amounts of the metal substrate, are deposited over the now exposed microelectronics device to encapsulate it within a metal shell. The encapsulated sensor and microelectronics-grade metal substrate are then ready to be embedded in high-melting temperature bulk material.

Solid-State Strain Sensor That Can Sense Shear and Normal Deformation in Almost Any Dielectric Material

A UW-Madison engineer has now developed a novel class of strain sensors that can sense shear and normal deformation in nearly any dielectric material, without the need for mechanical contact. These new strain sensors are based on electrostriction, a phenomenon in which a material's dielectric properties change with deformation.

The sensor is a solid-state, single-plate device in which pairs of electrodes are positioned in close proximity to the material being measured. As the material deforms and its electrostrictive properties change, this alteration registers as a change in capacitance between paired electrodes. The strain force in the material is then determined by calculating the material’s change in electrostrictive parameters from the change in capacitance.

Micromachined Scanning Thermal Probe

UW-Madison researchers have developed a micromachined scanning thermal probe with polyimide as its structural material and an embedded thin-film thermocouple as its temperature-sensing element. Probes are micromachined using a low-temperature, multimask process that can be easily integrated into a CMOS fabrication sequence, and contain a built-in scanning tip that is exposed by a unique flip-over assembly step at the end of processing.

Micromachined Shock Sensor

UW–Madison researchers have developed a micromachined shock sensor that has an array of acceleration sensing units formed to make contact at different levels of acceleration. This allows the shock sensor to measure a wide range of accelerations from 10g to 150g. The system also contains a built-in redundancy that circumvents challenges with the closing and opening of electrical contacts.