Method and apparatus for intelligent flow sensors

Abstract

A single sensor capable of detecting both airflow in spirometry and the full range of sound frequencies needed to track clinically relevant breath sounds is provided. The airflow sensor includes a movable flap with one or more integrated strain gauges for measuring displacement and vibration. The airflow sensor is inherently bidirectional. The sensor is an elastic flap airflow sensor that is capable of detecting data needed for both spirometry and auscultation measurements. The sensor is sterilizable and designed for the measurement of human respiratory airflow. The sterilizable sensor is also suitable for non-medical fluid flow metering applications. Additional devices such as sensors for the ambient level of various chemicals, sensors for temperature, sensors for humidity and microphones, may be affixed to the flap. When the strain gauge is placed in a conventional Wheatstone bridge configuration, the sensor can provide the airflow measurements needed for medical spirometry.

What is claimed is: 
     
         1 . A fluid flow sensing system comprising:
 a housing having a chamber that is sized and dimensioned to allow fluid to pass therethrough;   a flap provided within the chamber, wherein the fluid causes the flap to move when the fluid passes thereover;   a sensor coupled to the flap for generating an output signal when the flap moves, wherein:
 the sensor is configured to sense a displacement of the movable flap and a vibration of the movable flap, 
 the displacement of the movable flap is representative of a flow rate associated with the fluid and the vibration of said movable flap is representative of a frequency associated with the fluid; and 
   a determining unit that is configured to receive the output signal of the sensor and in response thereto, determine flow rate data associated with the fluid and determine frequency data associated with the fluid.   
     
     
         2 . The system of  claim 1  wherein the fluid comprises air, the flow rate is an air flow rate and the frequency is a sound. 
     
     
         3 . The system of  claim 1  wherein the sensor is a piezoresistive sensor. 
     
     
         4 . The system of  claim 3  wherein the piezoresistive sensor comprises first and second piezoresistive circuits and the first and second piezoresistive circuits are substantially perpendicular to each other. 
     
     
         5 . The system of  claim 4  wherein the first and second piezoresistive circuits have a resistance of about 120 ohms. 
     
     
         6 . The system of  claim 1  wherein the sensor is a strain gauge. 
     
     
         7 . The system of  claim 1  wherein the determining unit further comprises:
 a voltage conversion unit for receiving the output signal of the sensor and converting said the output signal into a voltage output signal; and 
 an amplification unit for receiving the voltage output signal and generating an amplified voltage output signal. 
 
     
     
         8 . The system of  claim 2  wherein the determining unit further comprises:
 a voltage conversion unit for receiving the output signal of the sensor and converting the output signal into a voltage output signal; 
 an amplification unit for receiving the voltage output signal and generating an amplified voltage output signal; 
 an air flow rate determining unit for receiving the amplified voltage output signal and determining in response thereto the air flow rate data based at least in part upon the output signal of said sensor; and 
 a sound determining unit for receiving the amplified voltage output signal and generating in response thereto the sound data signal representative of the sound. 
 
     
     
         9 . The system of  claim 8  wherein the air flow rate determining unit further comprises:
 a converter for converting the amplified voltage output signal into a digital output signal; and 
 a calculation unit for determining the air flow rate of the air based upon the digital output signal. 
 
     
     
         10 . The system of  claim 9  wherein the calculation unit includes a calibration curve that correlates the digital output signal to an air flow rate. 
     
     
         11 . The system of  claim 8  wherein the sound determining unit comprises:
 a sound processing unit for generating the sound data signal in response to the amplified voltage output signal, and 
 a frequency conversion unit for receiving the sound data signal and in response thereto converting the signal into a frequency signal. 
 
     
     
         12 . The system of  claim 11  wherein the sound processing unit includes a sound card. 
     
     
         13 . The system of  claim 11  wherein the frequency conversion unit includes a fast fourier transform module. 
     
     
         14 . The system of  claim 1  wherein the output signal of the sensor has a direct current electrical component that represents the flow rate associated with the fluid and a high frequency alternating current component that represents the frequency associated with the fluid. 
     
     
         15 . A method for determining a flow rate and a frequency of a fluid, the method comprising:
 providing a sensor coupled to a flap, wherein the sensor is configured to generate an output signal in response to detecting movement of the flap moves;   providing a flow of fluid across the sensor;   sensing a displacement of the flap with the sensor, said displacement being representative of a flow rate associated with the fluid flow;   sensing a vibration of the flap with the sensor, the vibration being representative of a frequency associated with the fluid flow;   generating the output signal from the sensor; and   determining from the output signal the flow rate and frequency associated with the fluid flow from the sensed displacements and the sensed vibrations respectively.   
     
     
         16 . The method of  claim 15  wherein the steps of sensing both a displacement and a vibration of said flap occur simultaneously using the sensor. 
     
     
         17 . The method of  claim 15  wherein:
 the fluid comprises air; 
 the flow rate is an air flow rate; 
 the frequency is a sound; and 
 the determining step further comprises:
 determining the air flow rate based at least in part upon said output signal of the sensor, and 
 generating the sound representative of the sound associated with the air based at least in part upon said output signal of the sensor. 
 
 
     
     
         18 . The method of  claim 17  wherein the determining step further comprises:
 converting the output signal into a voltage output signal; 
 generating an amplified voltage output signal from the voltage output signal; 
 determining the flow rate based on the amplified voltage output signal; and 
 determining the frequency based on the amplified voltage output signal. 
 
     
     
         19 . The method of  claim 18  wherein:
 determining the flow rate further comprises
 converting the amplified voltage output signal into a digital output signal, and 
 determining the airflow rate based upon the digital output signal; and 
 
 determining the frequency further comprises:
 generating a frequency data signal based on the amplified voltage signal; and 
 converting the frequency data signal into a frequency waveform.