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Lower-frequency electromagnetic radiation, typically microwaves or radar, can be used to discern the location of hidden objects by passing through obstacles such as walls and floors. Existing technologies for detecting objects behind obstacles suffer from a lack of precision. They often have difficulty, for example, in determining whether the target is in front of or behind a particular obstacle. Both passive and active devices have difficulties of this type. Obstacles may also interfere with the signal. This invention uses two active microwave systems to improve the effectiveness of detection.
The invention uses two microwave transmitter modules operating at two different frequencies. One frequency is designed to penetrate the obstacle (e.g. a wall) and the other will not. Return signals are detected by two receivers or by one integrated receiver. Comparing the data from the two signals allows clear differentiation of an object's position relative to the obstacle. Frequencies can be varied depending on the materials that will typically constitute obstacles for the system. A larger range of obstacles implies the need for a larger difference between the two transmitted frequencies.
The invention calls for two microwave transmitters. One module is higher frequency, preferably greater than four times the other, and as a consequence less able to penetrate obstacles. 2GHZ and 20GHZ are cited as workable frequencies. Both frequencies may undergo continuous modulation. The transmitters should be positioned close together. A third frequency may be used to differentiate between different types of obstacles, or to detect different types of objects. The invention also covers a simple computer program that would classify objects on the basis of their responses to the two signals.