Distributed Microsystems Laboratory: Developing Microsystems that Make Sense Integrated, Distributed Sensing Nodes for Hear/Smell Functionality Sponsoring Agency: National Science Foundation Award Number: ECS Period of Award: 9/00-8/03 PI: D. Wilson Research Assistant: Sam McKennoch Co-PI: Paul Hasler, Georgia Tech Collaborators: Jiri Janata, Georgia Tech

Distributed Microsystems Laboratory: Developing Microsystems that Make Sense Goals: To combine the functions of hear and smell (auditory and chemical sensing) into two-chip sensing nodes for distributed (multiple location) sensing. Chip 1: Auditory Processing Chemical Sensor control and preprocessing Chip 2: 8-element ChemFET array Applications for 3-node proof-of-concept system: Consumer: redundant breath alcohol analysis Environmental: pipeline leak monitoring Military: ground vehicle identification Hear enables smell to reduce system power dissipation

Distributed Microsystems Laboratory Integrated, Distributed Sensing Nodes for Hear/Smell Vapor Airflow ChemFETs Distributed, High- Density, Bandpass Filter Bank Auditory Processing Chemical Sensor Signal Processing External Microphone Chip 1 Chip 2 Microprocessor: Sensor Power Control Final Decision Making Signal Recognition

Distributed Microsystems Laboratory Integrated, Distributed Sensing Nodes for Hear/Smell Chip 1: Auditory Processing Distributed, High-Density Bandpass Filter Bank Biologically-inspired by mammalian cochlea Distributes auditory signal into multiple frequency bands using continuous windowing (analog) in time Auditory Signal Processing Extracts cepstral coefficients and other features relevant to distinguishing sounds of interest from each other and from interferents Chemical Sensor Signal Processing Baseline compensation: forces sensor outputs to same value at baseline (no-stimulus state), with minimal distortion Signal Preprocessing: provides communicaton among signals, preprocesses for concentration-independent analyte discrimination and low-noise concentration determination (and alarm generation)

Distributed Microsystems Laboratory Integrated, Distributed Sensing Nodes for Hear/Smell Chip 2: Chemical Sensor Array Eight independent ChemFETs: Polymer-based coatings Coating matrix modified to provide heterogeneous functionality Custom-fabricated at Georgia Tech Chip 3: Microcontroller Turns power-on to Chip 2 when a sound of interest is detected Performs final pattern recognition: Preprocessed auditory signals from Chip 1 Preprocessed chemical signals (when available) from Chip 1 Provides Control Functions: Sampling of ChemFET sensors Extraction of ChemFET signals Controls auto-calibration cycles of auditory and chemical modes

Distributed Microsystems Laboratory Integrated, Distributed Sensing Nodes for Hear/Smell Recent Results: Baseline Compensation AZBLC compensates for an unknown initial sensor state (an artifact of the sensor manufacturing process not correlated with chemical concentration) to produce an output that is representative only of the differential sensor state change. Uncompensated Outputs Compensated Outputs

Distributed Microsystems Laboratory Integrated, Distributed Sensing Nodes for Hear/Smell Recent Results: Baseline Compensation Justification for Baseline Compensation: Uncompensated outputs can cause baseline variations to consume resolution of the subsequent A/D converter, leaving little resolution allocated to signal differentiation Baseline compensation without distortion requires the tailoring of the baseline compensation circuits to the chemical model of the sensor involved. Minimal distortion ensures that sensors can be replaced or adjusted for drift without requiring a new calibration model. Current Status: Discrete baseline compensation circuits are complete and tested for: Carbon black composite polymer films ChemFETs Integrated baseline compensation circuits for processing signals from composite, chemically sensitive, polymer films are in fabrication Integrated baseline compensation circuits for ChemFETs are currently in design

Distributed Microsystems Laboratory Integrated, Distributed Sensing Nodes for Hear/Smell Chemical Sensor Modeling Initial sensor model results are shown for sensors that have different initial volume percentages of the conductor carbon- black. As the ratiometric volume changes (due to swelling caused by a chemical), the sensor resistance also increases. The sharp increases in dr/r at %CB=.34 to.37 are due to the sensor passing through its percolation point, i.e. this is the point (not accounting for electron tunneling) at which there are no longer any conduction paths through the insulating matrix. Similar models are in progress for the ChemFET to facilitate effective signal preprocessing circuits and architectures.