Abstract: A flow sensor for determining the velocity and direction of a fluid flow including a substrate, a heat source located on the substrate, and a first and a second heat sensor located on the substrate to detect at least a portion of heat generated by the heat source. The first and second heat sensors and the heat source are arranged in a non-linear orientation.

Abstract: A flow sensor for determining the velocity and direction of a fluid flow including a substrate, a heat source located on the substrate, and a first and a second heat sensor located on the substrate to detect at least a portion of heat generated by the heat source. The first and second heat sensors and the heat source are arranged in a non-linear orientation.

Abstract: A portable apparatus for measuring the thoracic lung volume of a patient without enclosing the patient in a sealed chamber, comprising first and second impedance belts, a flow meter, shutter and a microprocessor-based controller. The flow meter includes pressure transducers for measuring the change in volume and pressure as the patient respires therethrough. The change in thoracic cage volume of the patient's lungs is directly correlated with the change of impedance in the belts. The thoracic lung volume is then determined from a measured barometric pressure, the measured change in pressure and the measured volume change in the thoracic cage volume utilizing a correction factor to determine the thoracic cage volume.

Abstract: A method and apparatus is described for preventing contamination of a gas analyzer of respiratory gas exchange analyzing equipment due to a patient's saliva. The method involves determining a resistance value of the inspired respiratory gas flow in a sample line leading to the gas analyzer. This is determined by calculating the absolute pressure in the line at the gas analyzer. The pressure difference from atmospheric pressure is then divided by the sample flow rate to obtain a resistance value. A microprocessor in the equipment compares the calculated resistance of the flow with a previously stored reference threshold resistance. If the calculated resistance exceeds the predetermined threshold, the microprocessor sends a signal to a vacuum pump used to draw the respiratory gases through the gas analyzer. The vacuum pump is immediately shut down when the calculated resistance exceeds the predetermined resistance threshold and, hence, any saliva in the sample line is not drawn into the gas analyzer.

Abstract: The specific gravity, l, of a fluid of interest is determined based on thermal conductivity, k, and specific heat, c.sub.p, of the fluid of interest. An embodiment uses proximately positioned resistive heater and thermal sensor elements coupled by the fluid of interest. Pulses of electrical energy are applied to the heater of a level and duration such that both a transient change and a substantially steady-state temperature occur in the sensor. The k of the fluid of interest is determined based upon sensor output at steady-state elevated temperature, c.sub.p of the fluid of interest is determined based upon the rate of change of sensor output during a time interval of transient temperature change in the sensor, and l is determined from k and c.sub.p.

Abstract: A microbridge air flow sensor which has a sealed etched cavity beneath the silicon nitride diaphragm so that the cavity is not susceptible to contamination from residual films or other material accumulating within the cavity. The cavity thermally isolates the heater and detectors which are encapsulated in the diaphragm. The cavity is fabricated by front side etching of the silicon wafer. Narrow slots are made through the silicon nitride diaphragm to expose a thin film (400 angstrom) rectangle of aluminum. A first etch removes the aluminum leaving a 400 angstrom very shallow cavity under the diaphragm. Anisotropic etch is then introduced into the shallow cavity to etch the silicon pit.

Abstract: A microbridge air flow sensor which has a sealed etched cavity beneath the silicon nitride diaphragm so that the cavity is not susceptible to contamination from residual films or other material accumulating within the cavity. The cavity thermally isolates the heater and detectors which are encapsulated in the diaphragm. The cavity is fabricated by front side etching of the silicon wafer. Narrow slots are made through the silicon nitride diaphragm to expose a thin film (400 angstrom) rectangle of aluminum. A first etch removes the aluminum leaving a 400 angstrom very shallow cavity under the diaphragm. Anisotropic etch is then introduced into the shallow cavity to etch the silicon pit.

Abstract: A microbridge air flow sensor having a silicon nitride diaphragm formed on the surface of a single crystal silicon wafer. A rectangular 500 angstrom thick sacrificial layer was deposited on the silicon surface before the silicon nitride to define the exact position of the diaphragm. A series of etches from the backside of the wafer is performed to fabricate the device. A first silicon anisotropic etch from the backside is stopped at the sacrificial layer. A sacrificial layer selective etch is applied from the backside first pit to the sacrificial layer to remove all of the rectangular sacrificial layer. Anisotropic etch is again applied into the space created by the removed sacrificial layer whereby the second etch attacks the silicon exposed by the removal of the sacrificial layer and etches downward forming a second anisotropic etch pit. Thus all the etches are from the backside of the silicon wafer.

Abstract: A microscopic size absolute pressure sensor for air or gas of the thermal conductivity type, a silicon nitride covered silicon microchip has an elongated V-groove anisotropically etched in the silicon with a heated silicon nitride bridge element extending over the surface of the V-groove.