US 4,895,017 A · Apparatus and method for early detection and identification of dilute chemical vapors

Abstract

A detector and method for identifying a chemical vapor and determining its concentration in the ambient atmosphere. The chemical detector apparatus (120) preferably includes a plurality of surface acoustic wave (SAW) devices (10), each including a piezoelectric substrate (20), one-half (32) of which is coated with a selected polymer. The polymer characteristically absorbs one or more of a group of chemical vapors. Diffusion of a chemical vapor into the polymer increases its mass and proportionately changes the resonant frequency of the SAW device. A microcomputer control (186) is operative to determine a predicted time constant (or rate) for diffusion and a predicted equilibrium concentration of the chemical vapor within the polymer coating of the SAW device and to identify the chemical vapor and its relative concentration in the ambient atmosphere using the predicted values for these parameters long before the SAW device has reached equilibrium with the chemical vapor.

Claims30

Dependent claims

Apparatus for rapidly detecting and identifying a chemical substance, comprising:

(a) a sensor having a surface exposed to the chemical substance and comprising a material selectively absorptive of a group of chemical substances of which said chemical substance is a member, a physical parameter associated with that surface changing as the quality of the chemical substance absorbed by diffusion into the material changes;
(b) monitoring means, coupled to the sensor, for monitoring the change in the physical parameter associated with said surface due to absorption of the chemical substance, producing an electrical signal indicative of said charge;
(c) analysis means, connected to the monitoring means, for determining a predicted time constant for diffusion of the chemical substance into the material and a predicted equilibrium concentration of the chemical substance in the material as a function of the electrical signal, well before the concentration of the chemical substance in the material asymptotically approaches equilibrium;
and
(d) identification means for identifying the chemical substance from said group of chemical substances based on both its predicted time constant for diffusion and predicted equilibrium concentration, which are generally characteristic of the chemical substance and different than those of other chemical substances of the group.

2 more elements

A method for detecting and identifying a particular chemical substance from a group of chemical substances, comprising the steps of:

(a) exposing a surface to the chemical substance, said surface comprising a material selectively absorptive of said group of chemical substances;
(b) sensing a physical parameter associated with the surface, which changes due to absorption of the chemical substance by the material comprising said surface;
(c) producing an electrical signal indicative of the change in the physical parameter associated with said surface due to absorption of the chemical substance;
(d) determining a predicted time constant for diffusion of the chemical substance into the surface and a predicted equilibrium concentration of the chemical substance within the material as a function of the electrical signal, well before the concentration asymptotically reaches equilibrium;
and
(e) identifying the chemical substance from said group of chemical substances, based on both its predicted time constant for diffusion and predicted equilibrium concentration, which are generally characteristic of the chemical substance and different than those of other chemical substances of the group.

3 more elements

A method for rapidly identifying an unknown chemical substance that is one of a group of chemical substances, comprising the steps of:

(a) exposing the chemical substance to a surface of a sensor that includes a material selected for its affinity to absorb a chemical substance from said group of chemical substances, said sensor effecting an electrical signal that changes as the chemical substance diffuses into the material as a function of the quantity of the chemical substance absorbed therein;
(b) monitoring the sensor for changes in the electrical signal indicative of the diffusion of the chemical substance into the material;
(c) predicting the time constant for diffusion of said chemical substance into the material of the sensor and its equilibrium concentration in the material, at a time substantially prior to chemical substance reaching its equilibrium concentration in the material;
and
(d) identifying the chemical substance as a function of both its predicted time constant for diffusion and its predicted equilibrium concentration in the material of the sensor.

2 more elements

Dependencies are inferred from the claim text.

Apparatus and method for early detection and identification of dilute chemical vapors

Life of this patent

Apparatus and method for early detection and identification of dilute chemical vapors

Life of this patent

Abstract

Claims30