The industrial, scientific and medical (ISM) radio bands are radio bands (portions of the radio spectrum) reserved internationally for the use of radio frequency (RF) energy for industrial, scientific and medical purposes other than telecommunications. Examples of applications in these bands include radio-frequency process heating, microwave ovens, and medical diathermy machines. The powerful emissions of these devices can create electromagnetic interference and disrupt radio communication using the same frequency, so these devices were limited to certain bands of frequencies. In general, communications equipment operating in these bands must tolerate any interference generated by ISM equipment, and users have no regulatory protection from ISM device operation.
Despite the intent of the original allocations, and because there are multiple allocations, in recent years the fastest-growing uses of these bands have been for short-range, low power communications systems. Cordless phones, Bluetooth devices, near field communication (NFC) devices, and wireless computer networks all use frequencies allocated to low power communications as well as ISM, although these low power emitters are not considered ISM.
ISM bands
The ISM bands are defined by the ITU-R in 5.138, 5.150, and 5.280 of the Radio Regulations. Individual countries' use of the bands designated in these sections may differ due to variations in national radio regulations. Because communication devices using the ISM bands must tolerate any interference from ISM equipment, unlicensed operations are typically permitted to use these bands, since unlicensed operation typically needs to be tolerant of interference from other devices anyway. The ISM bands share allocations with unlicensed and licensed operations; however, due to the high likelihood of harmful interference, licensed use of the bands is typically low. In the United States, uses of the ISM bands are governed by Part 18 of the Federal Communications Commission (FCC) rules, while Part 15 contains the rules for unlicensed communication devices, even those that share ISM frequencies. In Europe, the ETSI is responsible for governing ISM bands.
The ISM bands defined by the ITU-R are:
| Frequency range | Bandwidth | Center frequency | Availability | Licensed users | |
|---|---|---|---|---|---|
| 6.765 MHz | 6.795 MHz | 30 kHz | 6.780 MHz | Subject to local acceptance | Fixed & Mobile services |
| 13.553 MHz | 13.567 MHz | 14 kHz | 13.560 MHz | Worldwide | Fixed & Mobile services |
| 26.957 MHz | 27.283 MHz | 326 kHz | 27.120 MHz | Worldwide | Citizens band radio |
| 40.660 MHz | 40.700 MHz | 40 kHz | 40.680 MHz | Worldwide | Fixed & Mobile services |
| 433.050 MHz | 434.790 MHz | 1.74 MHz | 433.920 MHz | Region 1 only and subject to local acceptance | Amateur Radio (70 cm band) & Radar |
| 902.000 MHz | 928.000 MHz | 26 MHz | 915.000 MHz | Region 2 only (with some exceptions) | Amateur Radio (33 cm band), Mobile services & Radar |
| 2.400 GHz | 2.500 GHz | 100 MHz | 2.450 GHz | Worldwide | Amateur Radio (13 cm band), Microwave links & Radar |
| 5.725 GHz | 5.875 GHz | 150 MHz | 5.800 GHz | Worldwide | Amateur Radio (5 cm band), Earth stations, Microwave links & Radar |
| 24.000 GHz | 24.250 GHz | 250 MHz | 24.125 GHz | Worldwide | Amateur Radio (1.2 cm band) & Radar (K band Radar guns) |
| 61.000 GHz | 61.500 GHz | 500 MHz | 61.250 GHz | Subject to local acceptance | Microwave links & Radar |
| 122.000 GHz | 123.000 GHz | 1 GHz | 122.500 GHz | Subject to local acceptance | Amateur Radio (2.5 mm band) & Microwave links |
| 244.000 GHz | 246.000 GHz | 2 GHz | 245.000 GHz | Subject to local acceptance | Amateur Radio (1 mm band), Radar & Radio Astronomy |
Regulatory authorities may allocate parts of the radio spectrum for unlicensed communications that may or may not also be allocated as ISM bands.
History
The ISM bands were first established at the International Telecommunications Conference of the ITU in Atlantic City, 1947. The American delegation specifically proposed several bands, including the now commonplace 2.4 GHz band, to accommodate the then nascent process of microwave heating; however, FCC annual reports of that time suggest that much preparation was done ahead of these presentations.
From the proceedings: "The delegate of the United States, referring to his request that the frequency 2450 Mc/s be allocated for I.S.M., indicated that there was in existence in the United States, and working on this frequency a diathermy machine and an electronic cooker, and that the latter might eventually be installed in transatlantic ships and airplanes. There was therefore some point in attempting to reach world agreement on this subject."
Radio frequencies in the ISM bands have been used for communication purposes, although such devices may experience interference from non-communication sources. In the United States, as early as 1958 Class D Citizens Band, a Part 95 service, was allocated to frequencies that are also allocated to ISM.
In the U.S., the FCC first made unlicensed spread spectrum available in the ISM bands in rules adopted on May 9, 1985.
Many other countries later developed similar regulations, enabling use of this technology. The FCC action was proposed by Michael Marcus of the FCC staff in 1980 and the subsequent regulatory action took five more years. It was part of a broader proposal to allow civil use of spread spectrum technology and was opposed at the time by mainstream equipment manufacturers and many radio system operators.
ISM uses
For many people, the most commonly encountered ISM device is the home microwave oven operating at 2.45 GHz; however, many different kinds of ISM devices exist, which are predominantly found outside dwellings. Many industrial settings may use ISM devices in plastic welding processes. In medical settings, shortwave and microwave diathermy machines are ISM devices mostly commonly used for muscle relaxation. Microwave ablation, a type of interventional radiology, is an ISM application which treats solid tumors through the use of RF heating.
Some electrodeless lamp designs are ISM devices, which use RF emissions to excite fluorescent tubes. Sulfur lamps are commercially available plasma lamps, which use a 2.45 GHz magnetron to heat sulfur into a brightly glowing plasma.
Long-distance wireless power systems have been proposed and experimented with which would use high-power transmitters and rectennas, in lieu of overhead transmission lines and underground cables, to send power to remote locations. NASA has studied using microwave power transmission on 2.45 GHz to send energy collected by solar power satellites back to the ground.
Also in space applications, a Helicon Double Layer ion thruster is a prototype spacecraft propulsion engine which uses a 13.56 MHz transmission to break down and heat gas into plasma.
Non-ISM uses
In recent years ISM bands have also been shared with (non-ISM) license-free error-tolerant communications applications such as wireless sensor networks in the 915 MHz and 2.450 GHz bands, as well as wireless LANs and cordless phones in the 915 MHz, 2.450 GHz, and 5.800 GHz bands. Because unlicensed devices are required to be tolerant of ISM emissions in these bands, unlicensed low power users are generally able to operate in these bands without causing problems for ISM users. ISM equipment does not necessarily include a radio receiver in the ISM band (e.g. a microwave oven does not have a receiver).
In the United States, according to 47 CFR Part 15.5, low power communication devices must accept interference from licensed users of that frequency band, and the Part 15 device must not cause interference to licensed users. Note that the 915 MHz band should not be used in countries outside Region 2, except those that specifically allow it, such as Australia and Israel, especially those that use the GSM-900 band for cellphones. The ISM bands are also widely used for Radio-frequency identification (RFID) applications with the most commonly used band being the 13.56 MHz band used by systems compliant with ISO/IEC 14443 including those used by biometric passports and contactless smart cards.
In Europe, the use of the ISM band is covered by Short Range Device regulations issued by European Commission, based on technical recommendations by CEPT and standards by ETSI. In most of Europe, LPD433 band is allowed for license-free voice communication in addition to PMR446.
Wireless LAN devices use wavebands as follows:
- Bluetooth 2450 MHz band falls under WPAN
- HIPERLAN 5800 MHz band
- IEEE 802.11/Wi-Fi 2450 MHz and 5800 MHz bands
IEEE 802.15.4, ZigBee and other personal area networks may use the 915 MHz and 2450 MHz ISM bands because of frequency sharing between different allocations.
Wireless LANs and cordless phones can also use bands other than those shared with ISM, but such uses require approval on a country by country basis. DECT phones use allocated spectrum outside the ISM bands that differs in Europe and North America. Ultra-wideband LANs require more spectrum than the ISM bands can provide, so the relevant standards such as IEEE 802.15.4a are designed to make use of spectrum outside the ISM bands. Despite the fact that these additional bands are outside the official ITU-R ISM bands, because they are used for the same types of low power personal communications, they are sometimes incorrectly referred to as ISM bands as well.
Also note that several brands of radio control equipment use the 2.4 GHz band range for low power remote control of toys, from gas powered cars to miniature aircraft.
Worldwide Digital Cordless Telecommunications or WDCT is a technology that uses the 2.4 GHz radio spectrum.
Google's Project Loon uses ISM bands (specifically 2.4 and 5.8 GHz bands) for balloon-to-balloon and balloon-to-ground communications.
Pursuant to 47 CFR Part 97 some ISM bands are used by licensed amateur radio operators for communication - including amateur television.
