Distributed Microsystems Laboratory:Developing Microsystems that Make Sense

Integrated, Distributed Sensing Nodes for Hear/Smell Functionality

Sponsoring Agency: National Science Foundation

Award Number: ECS-9988905

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 LaboratoryIntegrated, 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 LaboratoryIntegrated, 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 LaboratoryIntegrated, 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 LaboratoryIntegrated, 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 LaboratoryIntegrated, 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 LaboratoryIntegrated, 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.