 | This article needs additional citations for verification .(July 2007) |
Near-field electromagnetic ranging (NFER) refers to any radio technology employing the near-field properties of radio waves as a Real Time Location System (RTLS).
| | This article needs additional citations for verification .(July 2007) |
Near-field electromagnetic ranging (NFER) refers to any radio technology employing the near-field properties of radio waves as a Real Time Location System (RTLS).
Near-field electromagnetic ranging is an emerging RTLS technology that employs transmitter tags and one or more receiving units. Operating within a half-wavelength of a receiver, transmitter tags must use relatively low frequencies (less than 30 M Hz) to achieve significant ranging. Depending on the choice of frequency, NFER has the potential for range resolution of 30 cm (12 in) and ranges up to 300 m (980 ft). [1]
The phase relations between the EH components of an electro-magnetic field ((E and H are the components E=electric and H=magnetic)) vary with distance around small antennas. This was first discovered by Heinrich Hertz and is formulated with Maxwell's field theory.
Close to a small antenna, the electric and magnetic field components of a radio wave are 90 degrees out of phase. As the distance from the antenna increases, the EH phase difference decreases. Far from a small antenna in the far-field, the EH phase difference goes to zero. [2] Thus a receiver that can separately measure the electric and magnetic field components of a near-field signal and compare their phases can measure the range to the transmitter. [3]
NFER technology is a different approach for locating systems. It has several inherent advantages over other RTLS systems.
For instance, a radio wave at 1 MHz has a period of 1 μs, and the EH phase difference changes about 45 degrees between 30 m (98 ft) to 60 m (200 ft). Thus, a 1 degree EH phase difference in a 1 MHz signal corresponds to a range difference of about 67 cm (26 in) and 1/360 of the period or 27.78 ns difference in time between the electric and magnetic signals. Down-converted to a 1 kHz audio signal, the period becomes 1 ms, and the time difference required to measure becomes 27.78 μs. A comparable time-of-flight (TOF) or Time difference of arrival (TDOA) system would require 2 ns to 4 ns to make the same measurement.[ citation needed ]
Using relatively low frequencies also conveys additional advantages. First, low frequencies are generally more penetrating than higher frequencies.[ citation needed ] For instance, at 2.4 GHz a reinforced concrete wall might attenuate signals as much as 20 dB. [4] Second, the long wavelengths associated with low frequencies are far less vulnerable to multipath. In dense metallic structures, multipath obscures or destroys the ability of microwave or UHF signals to be used for reliable positioning. Low frequencies are less affected by this problem.[ citation needed ]
Operation at low frequencies faces challenges as well. In general, antennas are most efficient at frequencies whose wavelengths are comparable to the antennas' dimensions (e.g., a quarter-wavelength monopole antenna).[ citation needed ] Therefore, since higher frequencies have smaller wavelengths, high frequency antennas are typically smaller than low frequency antennas. The larger size of practically efficient low frequency antennas is a significant hurdle that near-field electromagnetic ranging systems cannot overcome without decreasing gain. Applying fractal antennae to NFC requires complex adaptive controls [5]
The low-frequency, multipath-resistant characteristics of NFER make it well suited for tracking in dense metallic locations, such as typical office and industrial environments.[ citation needed ] Low frequencies also readily diffract around the human body, which makes tracking people possible without the body blockage experienced by microwave systems like Ultra-wideband (UWB).[ citation needed ] Systems deployed in complicated indoor propagation environments reportedly achieve 60 cm (24 in) accuracy or better at ranges of 46 m (151 ft) or more. [6] There is also an indication that multiple frequency implementations may yield increased accuracy. [7]
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. Types of EMR include radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays, all of which are part of the electromagnetic spectrum.
The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high frequency these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications.
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and 300 GHz, broadly construed. A more common definition in radio-frequency engineering is the range between 1 and 100 GHz, or between 1 and 3000 GHz . The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range; rather, it indicates that microwaves are small, compared to the radio waves used in prior radio technology.
In electrical engineering, electrical length is a dimensionless parameter equal to the physical length of an electrical conductor such as a cable or wire, divided by the wavelength of alternating current at a given frequency traveling through the conductor. In other words, it is the length of the conductor measured in wavelengths. It can alternately be expressed as an angle, in radians or degrees, equal to the phase shift the alternating current experiences traveling through the conductor.
Radio waves are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths greater than 1 millimeter, about the diameter of a grain of rice. Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a slightly slower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters. Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves. In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment.
The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative near-field behaviors dominate close to the antenna or scatterer, while electromagnetic radiation far-field behaviors predominate at greater distances.
This is an index of articles relating to electronics and electricity or natural electricity and things that run on electricity and things that use or conduct electricity.
Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower-frequency electromagnetic oscillations are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands.
Wireless power transfer (WPT), wireless power transmission, wireless energy transmission (WET), or electromagnetic power transfer is the transmission of electrical energy without wires as a physical link. In a wireless power transmission system, an electrically powered transmitter device generates a time-varying electromagnetic field that transmits power across space to a receiver device; the receiver device extracts power from the field and supplies it to an electrical load. The technology of wireless power transmission can eliminate the use of the wires and batteries, thereby increasing the mobility, convenience, and safety of an electronic device for all users. Wireless power transfer is useful to power electrical devices where interconnecting wires are inconvenient, hazardous, or are not possible.
Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data. Both human-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras. EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.
A spark-gap transmitter is an obsolete type of radio transmitter which generates radio waves by means of an electric spark. Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the wireless telegraphy or "spark" era, the first three decades of radio, from 1887 to the end of World War I. German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties.
Radiolocation, also known as radiolocating or radiopositioning, is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar—as well as detecting buried cables, water mains, and other public utilities. It is similar to radionavigation, but radiolocation usually refers to passively seeking a distant object rather than actively finding one's own position; both are types of radiodetermination. Radiolocation is also used in real-time locating systems (RTLS) for tracking valuable assets.
A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing, or other electrical conductor, that for transmitting is usually fed by a balanced power source or for receiving feeds a balanced load. Within this physical description there are two distinct types:
Non-line-of-sight (NLOS) radio propagation occurs outside of the typical line-of-sight (LOS) between the transmitter and receiver, such as in ground reflections. Near-line-of-sight conditions refer to partial obstruction by a physical object present in the innermost Fresnel zone.
The Earth–ionosphere waveguide is the phenomenon in which certain radio waves can propagate in the space between the ground and the boundary of the ionosphere. Because the ionosphere contains charged particles, it can behave as a conductor. The earth operates as a ground plane, and the resulting cavity behaves as a large waveguide.
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.
A magnetoquasistatic field is a class of electromagnetic field in which a slowly oscillating magnetic field is dominant. A magnetoquasistatic field is typically generated by low-frequency induction from a magnetic dipole or a current loop. The magnetic near-field of such an emitter behaves differently from the more commonly used far-field electromagnetic radiation. At low frequencies the rate of change of the instantaneous field strength with each cycle is relatively slow, giving rise to the name "magneto-quasistatic". The near field or quasistatic region typically extends no more than a wavelength from the antenna, and within this region the electric and magnetic fields are approximately decoupled.
A lens antenna is a directional antenna that uses a shaped piece of microwave-transparent material to bend and focus microwaves by refraction, as an optical lens does for light. Typically it consists of a small feed antenna such as a patch antenna or horn antenna which radiates radio waves, with a piece of dielectric or composite material in front which functions as a converging lens to collimate the radio waves into a beam. Conversely, in a receiving antenna the lens focuses the incoming radio waves onto the feed antenna, which converts them to electric currents which are delivered to a radio receiver. They can also be fed by an array of feed antennas, called a focal plane array (FPA), to create more complicated radiation patterns.