Non-invasive electromagnetic fluid level sensor

Abstract

A disposable sensor is disclosed for non-invasively detecting and characterizing a container's contents. By generating microwave frequency signals, electromagnetic fields are produced by a sensor and penetrate a container. The EM fields are analyzed in regards to how they are perturbed by the container contents. Analysis of the perturbed EM fields enables determination of content level, content purity, content density, content temperature, container pressure, content conductivity, etc.

What is claimed is:  
     
         1 . A sensor system for use in characterizing contents of a container, wherein said sensor system analyzes microwave frequency electromagnetic signals generated therefrom to thereby determine characteristics of the container contents, said system comprising: 
 an electromagnetic sensor which is disposable on a container, and which is capable of transmitting the microwave frequency electromagnetic signals;    a processing device which is electrically coupled to the electromagnetic sensor, wherein the processing device develops the microwave frequency electromagnetic signals to be transmitted, analyzes the transmitted microwave frequency electromagnetic signals to thereby detect perturbations therein, and provide a human perceptible alarm when the detected perturbations indicate that an alarm condition is met; and    a power supply for supplying electrical current to the sensor system.    
     
     
         2 . The sensor system as defined in    claim 1    wherein the processing device is further comprised of: 
 an oscillator which is electrically coupled to the electromagnetic sensor, and which develops the microwave frequency electromagnetic signals for transmission therefrom;  
 a detector circuit which is electrically coupled to the electromagnetic sensor to thereby detect the perturbations in the microwave frequency electromagnetic signals; and  
 a controller for activating the oscillator and the detector circuit when the electromagnetic sensor is in a sensing mode, and for deactivating the oscillator and the detector circuit when the sensor system is in a sleep mode, and wherein a duration of the sensing and the sleep modes is programmable.  
 
     
     
         3 . The sensor system as defined in    claim 2    wherein the processing device is further comprised of: 
 a digital signal processor (DSP) which is electrically coupled to the detector circuit, wherein the DSP filters data received therefrom so as to determine whether at least one alarm condition is met, and which transmits a signal if it is determined that the at least one alarm condition is met; and  
 a human perceptible alarm which is electrically coupled to the DSP for receiving the signal indicating that the at least one alarm condition is met, and which activates the human perceptible alarm.  
 
     
     
         4 . The sensor system as defined in    claim 2    wherein the processing device further comprises an analog driven human perceptible alarm which is electrically coupled to the detector circuit, and which receives a signal indicating that the at least one alarm condition is met, and which activates the analog driven human perceptible alarm in response to receiving the signal.  
     
     
         5 . The sensor system as defined in    claim 3    wherein the processing device is further comprised of a data output port so that the signal indicating that the at least one alarm condition is met can be transmitted to a remote location.  
     
     
         6 . The sensor system as defined in    claim 1    wherein the perturbations are manifested as a compression of electromagnetic fields generated by the microwave frequency electromagnetic sensor.  
     
     
         7 . The sensor system as defined in    claim 1    wherein the electromagnetic sensor is coupled to the container by an adhesive which binds a sensing surface of the electromagnetic sensor generally flush against the container.  
     
     
         8 . The sensor system as defined in    claim 2    wherein the electromagnetic sensor is further comprised of a microwave frequency multi-port coupler which includes: 
 an input port for receiving from the processing device the microwave frequency electromagnetic signals to be transmitted; and  
 at least one output port for detecting the perturbations in an electromagnetic field generated by the transmitted microwave frequency signals and for transmitting an output signal to the processing device.  
 
     
     
         9 . The sensor system as defined in    claim 8    wherein the input port is interchangeable with at least one of the at least one output ports.  
     
     
         10 . The sensor system as defined in    claim 8    wherein the microwave frequency multi-port coupler is selected from the group of microwave frequency multi-port couplers including 2-port, 3-port and 4-port microwave frequency couplers.  
     
     
         11 . The sensor system as defined in    claim 10    wherein the microwave frequency multi-port couplers which are suitable as the microwave frequency electromagnetic sensor are formed on generally planar surfaces as stripline traces.  
     
     
         12 . The sensor system as defined in    claim 11    wherein the microwave frequency multi-port couplers are configured in a direct coupling or parallel coupling arrangement.  
     
     
         13 . The sensor system as defined in    claim 2    wherein the oscillator further comprises an oscillating transistor having a common-base bipolar configuration, and which utilizes feedback to tune the oscillator to a desired microwave frequency.  
     
     
         14 . The sensor system as defined in    claim 13    wherein the system further comprises the oscillator having an output impedance which generally matches an input impedance of the microwave frequency electromagnetic sensor to thereby obtain maximum power transfer therebetween.  
     
     
         15 . The sensor system as defined in    claim 13    wherein the oscillating transistor is biased via a direct current (DC) voltage through a current limiting resistor and a microwave frequency blocking inductor.  
     
     
         16 . The sensor system as defined in    claim 13    wherein the controller controls the sensing mode and the sleeping mode through a power supply transistor which is caused to provide bias current to the oscillating transistor when in sensing mode, and which is caused to terminate the bias current to the oscillating transistor when in sleeping mode.  
     
     
         17 . The sensor system as defined in    claim 8    wherein the detector circuit is comprised of: 
 a rectifying circuit which is electrically coupled to the at least one output port to thereby receive and rectify the output signal; and  
 an integrating circuit which is electrically coupled to an output of the rectifying circuit and which integrates the rectified output signal to thereby develop an output voltage which is proportional to an integral of the output signal, and which is a measure of a degree of coupling in the microwave frequency electromagnetic sensor.  
 
     
     
         18 . The sensor system as defined in    claim 17    wherein the rectifying circuit is comprised of: 
 a diode which when forward biased enables the output signal to be rectified to thereby create a time-varying DC current, and which is capable of operating at microwave frequencies; and  
 a biasing network which is electrically coupled to an input of the diode and which causes the diode to be forward biased when the sensor system is in the sensing mode.  
 
     
     
         19 . The sensor system as defined in    claim 18    wherein the detector circuit further comprises: 
 the integrator which is comprised of a capacitor for generating a steady-state DC output voltage; and  
 a length of conductor between an output of the diode and the capacitor, wherein the length of the conductor is a quarter wavelength of the microwave frequency electromagnetic signals, so that a zero impedance of the capacitor to microwave frequencies is transformed to an infinite impedance as seen by the diode.  
 
     
     
         20 . The sensor system as defined in    claim 19    wherein the detector circuit further comprises a resistor coupled to the diode output and ground which bleeds off a charge on the capacitor so that a voltage across the capacitor can be reduced as strength of the output signal from the microwave frequency electromagnetic sensor decreases.  
     
     
         21 . The sensor system as defined in    claim 20    wherein the detector circuit further comprises the resistor having a value that when combined with an impedance of the diode, a combined diode and resistor impedance is generally equal to an output impedance of the microwave frequency electromagnetic sensor.  
     
     
         22 . The sensor system as defined in    claim 21    wherein the detector circuit further comprises a differential amplifier which is electrically coupled to the integrator and a reference voltage, and which receives as inputs the voltage across the capacitor of the integrator, and a reference voltage.  
     
     
         23 . The sensor system as defined in    claim 22    wherein the detector system further comprises an analog-to-digital (A/D) converter which is electrically coupled to the differential amplifier and which receives as input an output signal therefrom.  
     
     
         24 . The sensor system as defined in    claim 23    wherein the detector system further comprises the DSP which is electrically coupled to the A/D convertor and which receives as an input signal an output signal therefrom.  
     
     
         25 . The sensor system as defined in    claim 24    wherein the DSP is a programmable device for executing at least one algorithm to accomplish error correction, noise filtering, signal enhancement, pattern recognition and internal calibration.  
     
     
         26 . The sensor system as defined in    claim 24    wherein the DSP further comprises filters for executing low-pass filtering, high-pass filtering, non-linear filtering and combinations thereof to enable reduction of environmental effects, microwave frequency electromagnetic sensor sensitivity, liquid level detection, noise reduction, edge enhancement, and increased sensitivity to anticipated electromagnetic sensor output.  
     
     
         27 . The sensor system as defined in    claim 24    wherein the DSP is electrically coupled to a human perceptible alarm system capable of generating different alarms for different alarm conditions, wherein the human perceptible alarm system receives input signals from the DSP which indicate when an alarm condition exists, and what type of alarm condition exists.  
     
     
         28 . The sensor system as defined in    claim 8    wherein the system further comprises: 
 a plurality of output ports on the microwave frequency electromagnetic sensor; and  
 a plurality of detector circuits, wherein each of the plurality of detector circuits is coupled to a corresponding one of the plurality of output ports to thereby enable the sensor system to simultaneously detect different alarm conditions.  
 
     
     
         29 . The sensor system as defined in    claim 10    wherein the sensor system further comprises a sensor circuit having a high common mode rejection ratio to thereby reduce sensor system sensitivity, said sensor system comprising: 
 the 3-port coupler used as the microwave frequency electromagnetic sensor which has a first output port and a second output port; and  
 the detector circuit which processes each signal from the first and the second output ports of the 3-port coupler by rectifying, integrating, and then comparing the rectified and integrated signals from the first and the second output ports using a differential amplifier circuit which amplifies any difference between each signal, wherein the detector circuit will minimize an influence of external factors so that it can then be determined whether an alarm condition exists.  
 
     
     
         30 . The sensor system as defined in    claim 29    wherein the differential amplifier circuit includes: 
 a first operational amplifier which has coupled at a first positive terminal a first voltage divider which divides a first signal from the first output port, and which is also coupled to a first resistor which modifies hysteresis, said operational amplifier also being coupled at an output port to an opposite side of the first resistor, and to a second resistor which modifies a gain of the first operational amplifier, said operational amplifier also being coupled at a negative terminal to an opposite side of the second resistor, and to a third resistor which attenuates a second signal from the second output port;  
 a second operational amplifier which has coupled at a second positive terminal a second voltage divider which divides the second signal from the second output port, and which is also coupled to a fourth resistor which modifies hysteresis, said operational amplifier also being coupled at an output port to an opposite side of the fourth resistor, and to a fifth resistor which modifies a gain of the second operational amplifier, said operational amplifier also being coupled at a negative terminal to an opposite side of the fifth resistor, and to a sixth resistor which attenuates the first signal from the first output port; and  
 wherein the output ports of the first and the second operational amplifiers are compared to determine if they are approximately equal.  
 
     
     
         31 . A method for characterizing contents of a container using a sensor system, wherein said method includes analyzing microwave frequency electromagnetic signals which are generated by an electromagnetic sensor to thereby determine characteristics of the container contents, said method comprising the steps of: 
 (1) disposing the electromagnetic sensor, which is capable of transmitting the microwave frequency electromagnetic signals, on a container;    (2) developing the microwave frequency electromagnetic signals in a processing device which is electrically coupled to the electromagnetic sensor, and transmitting said signals from the electromagnetic sensor;    (3) analyzing the transmitted microwave frequency electromagnetic signals to thereby detect perturbations therein; and    (4) providing a human perceptible alarm when the detected perturbations indicate that an alarm condition is met.    
     
     
         32 . The method as defined in    claim 31    wherein the method further comprises the steps of: 
 (1) generating a microwave frequency utilizing an oscillator which is electrically coupled to the electromagnetic sensor, and which develops the microwave frequency electromagnetic signals for transmission therefrom;  
 (2) utilizing a detector circuit which is electrically coupled to the electromagnetic sensor to thereby detect the perturbations in the microwave frequency electromagnetic signals;  
 (3) activating the oscillator and the detector circuit when the electromagnetic sensor is in a sensing mode; and  
 (4) deactivating the oscillator and the detector circuit when the sensor system is in a sleep mode.  
 
     
     
         33 . The method as defined in    claim 32    wherein the method further comprises the step of programming a duration of the sensing modes and the sleep modes to thereby limit energy consumption when the sensor is used as a stand-alone device.  
     
     
         34 . The method as defined in    claim 32    wherein the method further comprises the steps of: 
 (1) filtering data from the detector circuit through a digital signal processor (DSP) so as to determine whether at least one alarm condition is met;  
 (2) transmitting a signal from the DSP if it is determined that the at least one alarm condition is met; and  
 (3) generating a human perceptible alarm in response to the signal from the DSP, thereby indicating that the at least one alarm condition is met.  
 
     
     
         35 . The method as defined in    claim 32    wherein the method further comprises the step of activating an analog driven human perceptible alarm directly from the detector circuit when the detector circuit determines that at least one alarm condition is met.  
     
     
         36 . The method as defined in    claim 34    wherein the method further comprises the step of transmitting the signal indicating that the at least one alarm condition is met to a remote location.  
     
     
         37 . The method as defined in    claim 31    wherein the step of detecting perturbations more specifically comprises the step of detecting a compression of electromagnetic fields generated by the microwave frequency electromagnetic sensor, wherein a degree of compression indicates properties of the contents.  
     
     
         38 . The method as defined in    claim 31    wherein the method further comprises the step of coupling the electromagnetic sensor to the container by an adhesive which binds a sensing surface of the electromagnetic sensor generally flush against the container.  
     
     
         39 . The method as defined in    claim 32    wherein the method further comprises the step of utilizing a multi-port coupler as the microwave frequency electromagnetic sensor, wherein the multi-port coupler includes an input port for receiving from the processing device the microwave frequency electromagnetic signals to be transmitted, and at least one output port for detecting the perturbations in an electromagnetic field generated by the transmitted microwave frequency signals and for transmitting an output signal to the processing device.  
     
     
         40 . The method as defined in    claim 39    wherein the method further comprises the step of interchanging the input port with the at least one output port when desired.  
     
     
         41 . The method as defined in    claim 39    wherein the method further comprises the step of selecting the microwave frequency multi-port coupler from the group of microwave frequency multi-port couplers including 2-port, 3-port and 4-port microwave frequency couplers.  
     
     
         42 . The method as defined in    claim 41    wherein the method further comprises the step of configuring the microwave frequency multi-port couplers in a direct coupling or parallel coupling arrangement.  
     
     
         43 . The method as defined in    claim 32    wherein the method further comprises the step of generating microwave frequencies utilizing a transistor having adjustable feedback to modify the microwave frequency being generated.  
     
     
         44 . The method as defined in    claim 43    wherein the method further comprises the step of biasing the transistor via a direct current (DC) voltage through a current limiting resistor and a microwave frequency blocking inductor.  
     
     
         45 . The method as defined in    claim 43    wherein the method further comprises the step of controlling the sensing mode and the sleeping mode through a power supply transistor which is caused to provide bias current to the transistor when in sensing mode, and which is caused to terminate the bias current to the transistor when in sleeping mode.  
     
     
         46 . The method as defined in    claim 39    wherein the method further comprises the steps of: 
 (1) rectifying a signal from the at least one output port to thereby create a signal having a time-varying DC current; and  
 (2) integrating the signal having the time-varying DC current to thereby develop an output voltage which is proportional to an integral of the output signal, and which is a measure of a degree of coupling in the microwave frequency electromagnetic sensor.  
 
     
     
         47 . The method as defined in    claim 46    wherein the method further comprises the steps of: 
 (1) rectifying the signal from the at least one output port through a diode which is forward biased and operates at microwave frequencies; and  
 (2) forward biasing the diode when the sensor system is in the sensing mode.  
 
     
     
         48 . The method as defined in    claim 47    wherein the method further comprises the steps of: 
 (1) integrating the time-varying DC signal using a capacitor to thereby generate a steady-state DC output voltage; and  
 (2) preventing excessive loading on the sensor system by inserting a length of conductor between an output of the diode and the capacitor which is a quarter wavelength of the microwave frequency electromagnetic signals, so that a zero impedance of the capacitor to microwave frequencies is transformed to an infinite impedance as seen by the diode  
 
     
     
         49 . The method as defined in    claim 48    wherein the method further comprises the step of bleeding off a charge on the capacitor so that a voltage across the capacitor can be reduced as strength of the output signal from the microwave frequency electromagnetic sensor decreases.  
     
     
         50 . The method as defined in    claim 49    wherein the method further comprises the step of matching an output impedance of the electromagnetic sensor with an input impedance of the detector circuit by selecting the resistor to have a value which when combined with an impedance of the diode results in the input impedance being generally equal to the output impedance of the microwave frequency electromagnetic sensor.  
     
     
         51 . The method as defined in    claim 50    wherein the method further comprises the step of obtaining a signal which is generally proportional to a coupling coefficient of the electromagnetic sensor by electrically coupling a differential amplifier to the integrator and a reference voltage so that the differential amplifier receives as inputs the voltage across the capacitor of the integrator, and a reference voltage.  
     
     
         52 . The method as defined in    claim 51    wherein the method further comprises the step of generating a digital output signal representative of the coupling coefficient by electrically coupling an analog-to-digital (A/D) converter to the differential amplifier.  
     
     
         53 . The method as defined in    claim 52    wherein the method further comprises the step of digitally processing the digital output signal from the A/D converter using a digital signal processor to thereby accomplish error correction, noise filtering, signal enhancement, pattern recognition and internal calibration.  
     
     
         54 . The method as defined in    claim 53    wherein the method further comprises the steps of: 
 (1) filtering the digital output signal from the A/D converter utilizing low-pass filtering to reduce environmental effects and to modify electromagnetic sensor sensitivity;  
 (2) filtering the digital output signal from the A/D converter utilizing high-pass filtering to increase sensitivity to rapidly occurring events; and  
 (3) filtering the digital output signal from the A/D converter utilizing non-linear filtering and combinations of low-pass, high-pass and non-linear filtering to enable liquid level detection, edge enhancement, and increased sensitivity to anticipated electromagnetic sensor output.  
 
     
     
         55 . The method as defined in    claim 53    wherein the method further comprises the step of generating a selectable human perceptible alarm depending upon which alarm condition is indicated as being received from the digital signal processor.  
     
     
         56 . The method as defined in    claim 55    wherein the method further comprises the step of simultaneously checking for a plurality of different alarm conditions, all of which can trigger an alarm event, by providing a plurality of output ports on the electromagnetic sensor.  
     
     
         57 . The method as defined in    claim 56    wherein the method further comprises the step of generating a plurality of different human perceptible alarms, each of which is indicative of a different alarm condition.  
     
     
         58 . The method as defined in    claim 39    wherein the method further comprises the step of providing a sensor system having a high common mode rejection ratio to thereby reduce sensor system sensitivity, wherein the sensor system includes the 3-port coupler used as the microwave frequency electromagnetic sensor which has a first output port and a second output port, and wherein the detector circuit processes each signal from the first and the second output ports of the 3-port coupler by rectifying, integrating, and then comparing the rectified and integrated signals from the first and the second output ports using a differential amplifier circuit which amplifies any difference between each signal, wherein the detector circuit will minimize an influence of external factors so that the detector circuit can determine whether an alarm condition exists.  
     
     
         59 . The method as defined in    claim 51    wherein the method further comprises the step of quantifying the coupling coefficient using the following equation:  
         c   =     10                 log               p        (   in   )         p        (   out   )                  ,       φ        (   out   )       -     φ        (   in   )                       

 where p(in) is a magnitude and Ø(in) is a phase of input power, and p(out) and Ø(out) are a measurable output power and phase, respectively.  
 
     
     
         60 . A method for characterizing contents within a container, wherein said method includes analyzing microwave frequency electromagnetic signals which are generated by an electromagnetic sensor element to thereby determine characteristics of the container contents, said method comprising the steps of: 
 (1) selecting a multi-port coupler as the electromagnetic sensor element which generates the microwave frequency electromagnetic signals;    (2) disposing the multi-port coupler on the container;    (3) developing the microwave frequency electromagnetic signals in a processing device which is electrically coupled to the multi-port coupler, and transmitting said signals therefrom as electromagnetic fields; and    (4) analyzing a degree of compression of the electromagnetic fields to thereby characterize the container contents.    
     
     
         61 . The method as defined in    claim 60    wherein the method further comprises the step of generating a human perceptible alarm when the degree of compression of the electromagnetic fields passes a predetermined threshold of compression which is indicative of a predetermined alarm condition.