Antennae (singular antenna), are the paired appendages connecting to the first (and in crustaceans also to the second) segment of the head of the members of all subphyla of the arthropods except Chelicerata. Also the members of the order protura lack them.
antennae of a luna moth
Antennae are jointed, and in crustaceans branching, they generally extend forward of the animal and are known to be sensory organs, although the exact nature of what they sense and how they sense it is often not entirely clear. It appears that their function can include sensing of any or all of touch, air motion, heat, vibration (sound) and olfaction (smell/taste).
In insects olfactory receptors on the antennae express bind to odor molecules and pheromones. The neurons that express these receptors signal this binding by sending action potentials down their axons to the antenna lobe in the insect brain. From there, neurons in the antenna lobe connect to mushroom bodies that identify the odor.
It is physically an array of conductors intended to transmit an electromagnetic field as a response to an applied alternating voltage as well as the alternating electric current associated with it.
On the other hand, antennas can also be situated into an electromagnetic field in order for the field to bring on an alternating current in the antenna and a voltage right between its terminals.
The length of the antenna, as well as the materials from which they are made of really bring a big difference in the quality of reception that the car stereo receives.
Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use.
The (large) loop antenna is similar to a dipole, except that the ends of the dipole are connected to form a circle, triangle (delta loop antenna) or square.
The Phased array antenna is a group of independently fed active elements in which the relative phases of the respective signals feeding the elements are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.
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