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A millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing using a form of electromagnetic radiation. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security checkpoints. Several countries employ the scanners for security screening.
It is one of the common technologies of full body scanner used for body imaging; a competing technology is backscatter X-ray. Millimeter wave scanners themselves come in two varieties: active and passive. Active scanners direct millimeter wave energy at the subject and then interpret the reflected energy. Passive systems create images using only ambient radiation and radiation emitted from the human body or objects.
Clothing and many other materials are translucent in some EHF (millimeter wave) radio frequency bands. This frequency range is just below the (related) sub-millimeter terahertz radiation (or "T-ray") range.
With active scanners, the millimeter wave is transmitted from two antennas simultaneously as they rotate around the body. The wave energy reflected back from the body or other objects on the body is used to construct a three-dimensional image, which is displayed on a remote monitor for analysis.[dead link][non-primary source needed]
Privacy advocates are concerned about the use of active millimeter wave technology because it effectively implements routine and, in many cases, mandatory virtual strip searches. It allows screeners to see the surface of the skin under clothing, prosthetics including breast prostheses, and other medical equipment normally hidden, such as colostomy bags. Passive millimeter wave devices do not have the same privacy concerns because the images produced with passive screening technology expose no anatomical details.[dead link][non-primary source needed]
While the radiation itself cannot distinguish between private and non-private areas, software imaging technology can mask specific body parts. Proposed remedies for privacy concerns include scanning only people who are independently detected to be carrying contraband, or developing technology to mask genitals and other private parts. In some locations, travelers have the choice between the body scan or a traditional "patdown". In locations such as the UK and Australia, the scans are mandatory.
In the United States, the Transportation Security Administration (TSA) claimed to have taken steps to address privacy objections. TSA claimed that the images captured by the machines were not stored. On the other hand, the U.S. Marshals Service admitted that it had saved thousands of images captured from a Florida checkpoint. The officer sitting at the machine does not see the image; rather that screen shows only whether the viewing officer has confirmed that the passenger has cleared. Conversely, the officer who views the image does not see the person being scanned by the device. In some locations, updated software has removed the necessity of a separate officer in a remote location. These units now generate a generic image of a person, with specific areas of suspicion highlighted by boxes. If no suspicious items are detected by the machine, a green screen instead appears indicating the passenger is cleared.
Concerns remain about alternative ways to capture and disseminate the image. Additionally, the protective steps often do not entirely address the underlying privacy concerns. Subjects may object to anyone viewing them in a state of effective undress, even if it is not the agent next to the machine, or even if the image is not retrievable.
Claims that images are immediately destroyed were questioned after Indian film star Shahrukh Khan said that his image was circulated by airport staff at Heathrow in London. This comment appears to be a joke according to one UK media outlet, but reports of full-body scanner images being improperly and perhaps illegally saved and disseminated continue to emerge.
The evidence regarding health concerns is mixed. Some research has dismissed the fears based on the fact that active scanners emit millimeter wavelength radiation which is non-ionizing—i.e., it does not have enough energy to directly damage DNA—and is not known to be genotoxic.
A team led by Los Alamos National Labs found that although the forces that terahertz waves exert on double-stranded DNA are tiny, in certain circumstances resonant effects can unzip the DNA strands, tearing them apart. This creates bubbles in the strands that can significantly interfere with processes such as gene expression and DNA replication. 
While the majority of animal cancer studies show no response to chronic exposure to microwave radiation, some show an increased rate of tumor growth. The same increase also occurs in chronically-stressed animals not exposed to radiation. Other studies have found that exposure to millimeter wave radiation reduced metastasis of tumor cells.
The efficacy of millimeter wave scanners in detecting threatening objects has been questioned. Formal studies demonstrated the relative inability of these scanners in detecting objects—dangerous or not—on the person being scanned. Additionally, some studies suggested that the cost–benefit ratios of these scanners is poor. As of January 2011, there had been no report of a terrorist capture as a result of a body scanner. In a series of repeated tests, the body scanners were unable to detect a handgun hidden in an undercover agent's undergarments.
Millimeter wave scanner also has problems reading through sweat. After being required to stop due for an additional back pat down, I observed 10 people in a row who had been wearing backpacks before going through the scanner also get stopped for additional pat downs.
While airport security may be the most visible and public use of body scanners, companies have opted to deploy passive employee screening to help reduce inventory shrink from key distribution centers.
As of April 2009, the U.S. Transportation Security Administration began deploying scanners at airports, e.g., at the Los Angeles International Airport (LAX). These machines have also been deployed in the Jersey City PATH train system. They have also been deployed at San Francisco International airport (SFO), as well as Salt Lake International Airport (SLC), Indianapolis International Airport (IND), Detroit-Wayne County Metropolitan Airport (DTW), Minneapolis-St. Paul International Airport (MSP), and Las Vegas International Airport (LAS).
Three security scanners using millimeter waves were put into use at Schiphol Airport in Amsterdam on 15 May 2007, with more expected to be installed later. The passenger's head is masked from the view of the security personnel.
The federal courthouse in Orlando, Florida employs passive screening devices capable of recording and storing images.
Kelowna International Airport in Kelowna, British Columbia hosted the first such device in a Canadian airport. It was pulled from service in 2008 for undisclosed reasons, but may have simply been a test unit on loan.
Scanners are currently in use at Pearson Airport in Toronto, Ontario (YYZ), Montréal – Pierre Elliott Trudeau International Airport, Quebec (YUL), Calgary International Airport, Alberta (YYC), Vancouver International Airport, British Columbia (YVR), Halifax Stanfield International Airport, Nova Scotia (YHZ), and the Winnipeg James Armstrong Richardson International Airport (YWG).
The Canadian Air Transport Security Authority held a trial of the scanners at Kelowna International Airport in 2008. Before the trial, the Office of the Privacy Commissioner of Canada (OPCC) reviewed a preliminary Privacy Impact Assessment and CATSA accepted recommendations from the OPCC. In October 2009, an Assistant Privacy Commissioner, Chantal Bernier, announced that the OPCC had tested the scanning procedure, and the privacy safeguards that CATSA had agreed to would “meet the test for the proper reconciliation of public safety and privacy”. In January 2010, Transport Canada confirmed that 44 scanners had been ordered, to be used in secondary screening at eight Canadian airports. The announcement resulted in controversies over privacy, effectiveness and whether the exemption for those under 18 would be too large a loophole.
Scanners can be used for 3D physical measurement of body shape for applications such as apparel design, prosthetic devices design, ergonomics, entertainment and gaming.
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