Signal reflection occurs when a signal bounces off a medium that doesn’t fully absorb it, and can be used in applications such as SONAR and ground penetrating radar. Impedance matching is important for minimal reflection, and digital audio eliminates crosstalk. Optical distance and RADAR also use signal reflection.
Signal reflection is the process of bouncing a signal off a medium that does not fully absorb it. It can occur in copper cables for electrical signals and in optical fibers for laser or optical signals. Signal reflection can also occur in external metal surfaces for electromagnetic (EM) waves. EM waves travel through most open spaces and are not visible.
The study of signal reflection is used in specialized applications. The signal as sound can be reflected off a hard surface and returned to a receiver as a navigation and range audible beacon (SONAR). Ground penetrating radar uses the principle that different radio frequencies and different ground materials will produce different amounts of signal absorption and reflection. In impedance matching, the goal is to make sure that most of the signal reaches the destination or load. Source impedance usually needs to match the destination or load impedance for a given sub-band of radio frequencies.
In analog transmission cables, signal reflection is experienced as an echo when there is a mismatch in the audio. Most problems in audio transmission have been solved by using digitized audio in the form of Internet Protocol data packets. Any signal reflections will be seen as data errors and eliminated with error correction schemes. Crosstalk, which was the unwanted induction of an analog signal from one cable to another, is also eliminated by using digital audio as Voice over Internet Protocol (VoIP) packets in a digital subscriber line.
The Bergeron diagram shows the voltages and currents resulting when reflected electrical energy combines with incident energy. For the best signal integrity, there should be minimal reflection, achieved by impedance matching. In some cases, the addition of resistive components that absorb electrical energy can eliminate reflection entirely, while in other cases complex impedances formed by series-parallel combinations of chokes and capacitors can provide the solution. The presence of frequency-dependent distributed inductance and capacitance makes the design of good impedance-matching circuits very challenging.
Other specialized methods of signal reflection include optical distance in which the timed light beam can reflect back to a distant target. Given the speed of light and the time it takes to receive the reflection, the distance to the target can be calculated. In radio range and detection (RADAR), the target reflects radio signals when radar equipment sends out a radio frequency burst. The equipment waits for any reflected signal and calculates the distance based on the delay between the transmission of the radio frequency burst and the reception of the reflected signal and the speed of the radio waves in the air.
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