Thermally pulsed chemielectric point sensing
Inventors
Ancona, Mario • Perkins, F. Keith • Snow, Arthur W.
Assignees
Publication Number
US-10466190-B1
Publication Date
2019-11-05
Expiration Date
2038-09-24
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Abstract
An apparatus and method for producing chemielectric point-sensor systems with increased sensitivity and increased selectivity. The chemielectric sensor system includes a sensor/heater assembly, where the sensor is a chemielectric sensor whose resistance or capacitance changes upon exposure to chemical analytes. The heater functionality applies a programmed sequence of one or more thermal pulses to the sensor to quickly raise its temperature. After each thermal pulse ends the change in resistivity of the sensor is measured. Such data as a function of the pulse time and temperature are recorded and analyzed to determine the chemical composition (selectivity) and concentrations in the ambient vapor by comparison to a library dataset. The sensor operation with fast thermal pulses also allows operation at higher frequencies where the noise is lower and hence sensitivity is improved.
Core Innovation
The invention concerns chemielectric sensor systems that combine a chemielectric sensor and a heater element to apply thermal pulses, rapidly raising the sensor temperature. The sensor's resistivity changes both due to exposure to chemical analytes and temperature variations. After each thermal pulse, the change in resistivity is measured, capturing thermokinetic information about analyte sorption and desorption from the sensor surface. By analyzing these resistance transients as a function of pulse time and temperature, the chemical composition and concentrations in ambient vapor can be inferred, yielding increased sensitivity and selectivity in chemical vapor detection.
Conventional chemielectric vapor point-sensor systems face challenges in selectivity and sensitivity due to noise floors dominated by low-frequency 1/f electrical noise and slow sorption-desorption kinetics that impose quasi-dc operation. Existing systems often require complex additions such as scrubbed air supplies, preconcentrators, micro-gas-chromatographs, and pumps to improve performance, resulting in increased size, power consumption, and cost. Furthermore, typical methods rely on time-separated measurements before and during vapor exposure, which further limits response speed and sensitivity.
The present invention addresses these issues by enabling chemielectric sensors to operate with fast thermal pulses at frequencies between 10-1000 Hz or higher, reducing noise by shifting measurements away from the 1/f noise dominant region. The use of thermal pulses causes rapid, temperature-controlled desorption of analytes, with measurements taken immediately before and after each pulse. This approach captures dynamic thermokinetic data, improving the discrimination of analytes by their desorption characteristics and enabling higher sensor bandwidth. Architecturally, the invention includes several embodiments of sensor/heater assemblies with thermal isolation features such as micro air bridges or multilayer structures, or designs where the sensor element self-heats via Joule heating.
Claims Coverage
The patent includes one independent apparatus claim detailing a chemielectric sensor apparatus and one independent method claim describing a process for detecting analytes. The claims define features relating to sensor construction, thermal pulse application, measurement timing and frequencies, and data analysis for analyte detection.
Thermally pulsed chemielectric sensor apparatus with high-frequency operation
A chemielectric sensor assembly disposed on a substrate comprising a sensor element that sorbs analytes, and a heater applying multiple thermal pulses of 0.1 sec or less duration at frequencies of 10-1000 Hz or higher. The pulses heat the sensor element to predetermined temperatures, with timing constraints ensuring the sensor reaches, holds, and returns from each temperature. The thermal pulses cause analyte desorption from the sensor surface.
High-frequency electrical property measurement
Measurement means configured to determine an electrical property of the sensor element immediately before and after each thermal pulse at frequencies exceeding the 1/f noise corner frequency, producing a spectrum of differences. This spectrum is indicative of specified analytes and provides enhanced sensitivity.
Thermal isolation and sensor/heater assembly configurations
Various structural embodiments include a sensor on a thermally isolated air bridge with a resistive heater wire; a multilayer solid assembly with the sensor on an electrically insulating, thermally conducting material over a substrate having a resistive heater wire; and a design where the sensor element itself conducts Joule heating for self-heating. The sensor element can comprise materials such as functionalized gold nanoparticles, carbon nanotube networks, graphene films, or transition metal dichalcogenides.
Multiple sensors on a single substrate
Provision for a plurality of sensor/heater assemblies situated on a single substrate to improve redundancy or selectivity through sensor diversity.
Method for detecting analytes by thermally pulsed sensing
A method involving exposure of a chemielectric sensor to an ambient, application of controlled thermal pulses that desorb analytes, and high-frequency electrical property measurements before and after pulses. Variations in these measurements forming a spectrum serve to identify and quantify analytes based on characteristic thermal desorption signatures.
The claims collectively cover a chemielectric sensor system employing high-frequency thermally pulsed heating for rapid analyte desorption, paired with electrical property measurements taken above the 1/f noise frequency to enhance sensitivity and selectivity. Structural embodiments provide thermal isolation or integrated self-heating designs, while methods describe pulsed operation and spectral analysis for chemical detection.
Stated Advantages
Increased sensitivity by operating at higher frequencies to reduce 1/f noise, improving the signal-to-noise ratio.
Enhanced selectivity through analysis of thermokinetic desorption spectra from temperature-controlled thermal pulses.
Smaller size, lighter weight, greater power efficiency, and lower cost due to elimination of system components like scrubbed air supplies, preconcentrators, and gas chromatographs.
Broader range of applications enabled by simplified, compact, and fast chemical detection.
Versatility allowing real-time adjustment of thermal pulse parameters to optimize for sensitivity, speed, or specific analyte detection.
Capability for autonomous and networked operation suitable for monitoring urban or crowded environments.
Documented Applications
Hand-held and autonomous chemical vapor detection systems requiring small size, low power, and low cost.
Unobtrusive monitoring devices such as garment, badge, and small vehicle attachments.
Networked sensor arrays for environmental mapping or chemical source locating using high-speed sensing mimicking canine olfaction.
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