This article discusses crime fighting sensors that are being designed to identify ceramic weapons, plastic explosives, chemical weapons, and organic materials. They are also being developed to help protect citizens from terrorism and aid police in solving crimes. One organization leading the development of innovative antiterrorism sensing technologies is Sandia National Laboratories in Albuquerque, N.M. Among Sandia’s projects is an explosives-detection portal, designed for the Federal Aviation Administration (FAA). The portal is intended to help prevent airliner hijackings and bombings by identifying passengers, airport visitors, and employees who have been recently working with any of a wide variety of explosive chemicals. Upcoming tests with the Albuquerque Police Department’s crime lab are designed to help work out any bugs in the technique, define what kinds of evidence it can help find, and determine whether the system will be practical as a tool for law enforcement. Its most promising features are its portability and the fact that it does not contaminate evidence.
Not too long ago, terrorism was something that Americans only heard about on the news. But events in this decade like the bombings of New York's World Trade Center, the Alfred P. Murrah Federal Building in Oklahoma City, and Atlanta's Olympic Park have brought terrorism to American soil and have shown the need to develop new technologies to detect potential terrorist acts before they occur. This can require identifying a wide array of explosives and chemical weapons. Meanwhile, the challenges raised by more ordinary criminal activity also have been inspiring novel engineering approaches.
One organization leading the development of innovative antiterrorism sensing technologies is Sandia National Laboratories in Albuquerque, N.M. Among Sandia 's projects is an explosives-detection portal, designed for the Federal Aviation Administration (FAA). The portal is intended to help prevent airliner hijackings and bombings by identifying passengers, airport visitors, and employees who have been recently working with any of a wide variety of explosive chemicals. These people do not necessarily have to be actually carrying these substances with them at the time of detection.
Barring the Airport Gates
Airports, of course, have long relied on metal detectors to identify possible explosive devices, but the proliferation of plastic explosives and ceramic weapons has made metal detectors increasingly unreliable. Another device had to be developed to pick up on these nonmetallic weapons. Not only does such a detector need to be effective in finding a wide array of substances but it also has to do so quickly to avoid creating backups in passenger traffic that could make travelers late for their flights.
The technological basis of the device is that the chemicals of concern are released into the air in minute concentrations. Typically, such concentrations would be far too low to be detectable by any device. The advance that makes the portal possible is what Sandia has dubbed its preconcentrator technology, which the organization originally developed as part of its Department of Energy mission to protect critical nuclear-weapons facilities. The portal itself has been in laboratory development for three years. Breakthroughs in the preconcentrator's development have resulted in 1,000 times better sensitivity, 200 times smaller size, 13 times lower cost, and four times greater speed, so the portal exceeds the FAA's explosives- detection goals.
One of the first field tests of the device was last fall at Albuquerque International Airport. As usual, passengers and visitors to the airport's terminals had to pass through metal detectors and the usual carry-on baggage- check regimen. A uniformed security officer then asked some passengers to volunteer to help researchers test the portal.
The portal looks like an airport metal detector, but it has vents and nozzles on its inside walls and ceiling. Passengers who agreed to participate in the tests were asked to stand inside the portal for a few seconds as the detector passed a puff of air over them. The air sample was then collected and passed through a commercially available ion-mobility spectrometer, which recognizes the chemical signatures of a variety of explosives. The portal is fully automated: A computer-genera ted voice even instructs participants to enter the portal, turn left, and exit.
If any passenger had even a minute concentration of explosive residue on his or her skin or clothing, the quantity and type of chemical were di splayed on an adjacent computer screen. If a participant tested positive for explosives during the tests and suspicions remained after further screening, airport security would be notified. "We cannot disclose specific information about the portal's capabilities- such as the types and quantities of explosives it can detect- for security reasons ," said Kevin Linker, Sandia's lead researcher for the project. "However, it is capable of detecting very small concentrations of all substances of interest to the FAA."
During the four weeks that the portal was in operation, Sandia researchers tested more than 2,000 passengers, who had a wide range of body sizes and shapes. The purposes of the FAA-required tests were to gauge passenger acceptance of the technology, identify any reliability issues that needed to be addressed, and optimize the detector's performance, with the ultimate goal of its widespread adoption at airports across the country.
Once tests were complete, Sandia submitted its findings to the FAA, which is using the data to determine the feasibility of licensing and manufacturing the system for airports across the country. "Ultimately, the technology probably would be incorporated into airport metal detectors as a single walk- through unit," Linker said. Although tests so far have verified that the device is effective and works as intended, its use on a widespread basis remains unclear. One major barrier is its cost, which neither the individual airports n or the FAA want to bear.
Besides airports, such portals could be useful at security checkpoints in public building entrances. The basic technology could also be adapted to detect drugs, chemical and biological agents, and land mines.
Another approach is being taken by researchers at Rensselaer Polytechnic Institute (RPI) in Troy, N.Y., who are developing an imaging system that is showing promise in detecting items such as plastic explosives hidden in suitcases. This system, called real- time electro-optic terahertz sensing, is similar to X-ray and radar technologies. However, the frequency of the electromagnetic radiation used is more than 1 trillion cycles per second. "Until recently, there was no technology that could use electromagnetic radiation in this frequency range to create images rapidly," said Xi-Cheng Zhang, an RPl associate professor who oversaw the development of the technology. " Imaging work done by other organizations can create images, but not in real time." RPI's detector can create instantaneous images of 250,000 pixels.
The detector features a zinc telluride crystal onto which the terahertz radiation is focused after flowing through the target material. Simultaneously, a laser read-out beam is directed into the system. This is use d to convert the spatial and temp oral distributions into visible images that can be capture d by a video camera linked to a computer. The technology has been licensed by Molecular Opto-Electronics Corp. in Watervliet, N.Y., which is working on developing it into a commercial imaging system.
Detecting Chemical Weapons
Brookhaven National Laboratory in Upton, N.Y., has designed a sensor to help curb possible terrorist attacks on the ground that involve chemical weapons. The Brookhaven- designed minisensor, which is about the size of a 2- foot cube, works at distances up to tens of fee t. The device combines the latest laser and detector technology with a phenomen on known as Raman scattering, which is the ability of laser light aimed at a target to scatter off its molecules. A spectrometer analyzes the scattered light, revealing a chemical fingerprint. That signature fingerprint is then compared with a computerized library of fingerprints of potentially dangerous substances.
The minisensor is an offshoot of a large chemical sensor system developed at Brookhaven a 33-foot-long mobile detection van that can identify chemicals in the atmosphere from several miles away. While the larger sensor system is best used for atmospheric applications, the minisensor is most efficient in determining ground or surface contamination. According to Brookhaven, a big advantage of both sensors is that they can identify chemicals from a safe distance.
New York City's Office of Emergency Management staged a drill late last year to test the city's response to a possible terrorist attack using chemical weapons, and Brookhaven's device played a major role in the exercise. The sensor successfully detected the chemical used in the drill (acetone, the active ingredient in nail-polish remover) from a distance of about 15 feet. "The sensor performed well in just 8 minutes, under difficult conditions--specifically, at night in a driving rain," said Brookhaven scientist Arthur Sedlacek, who played a key role in designing the sensor system. "We are excited about its potential as an invaluable tool for assessing unknown chemicals in the field." Besides using the sensor in response to terrorist attacks, potential applications include identifying chemical- weapons production, monitoring industrial emissions, investigating environmental crimes, determining the effectiveness of environmental cleanups, and assessing the hazards of chemical fires.
Sensors at the Crime Scene
Terrorist acts involving the loss of many lives may receive the most media attention, but they are rare compared with smaller-scale crimes such as murder, theft, and rap e. To help bring those who have committed such acts to justice, the National Institute of Justice-the Department of Justice 's research and development branch in Washington, D.C. asked Sandia to develop what it refers to as a portable evidence finder.
At a crin1e scene, some evidence can be hard to find, particularly the kinds of evidence that can help police place the perpetrator at the scene of the crime: fingerprints, semen, and urine. To locate organic evidence, police usually rely on optical aids such as powders, lamps that give off various wavelengths of light, and yellow-tinted goggles that increase the evidence's visibility. However, investigators often must conduct their investigations at night or in a darkened room, and even with these aids it can take hours to scour every inch of a crime scene.
Most fingerprints that the police discover are lifted from smooth surfaces such as glass windows or polished furniture. Fingerprints on walls and other textured surfaces are more difficult to find, and some kinds of organic evidence-such as semen or urine-don't show themselves even with optical aids. Sometimes fluorescent dyes are used when there is no danger that they could contaminate other evidence, but this is done rarely and only as a last resort. Using chemicals also requires that the entire room be sprayed down, which is expensive.
As a result of these difficulties, potential evidence can go unnoticed. Sandia's evidence-detection technique relies on the fact that all types of organic substances give off weak fluorescent emissions, which are normally invisible to the naked eye because other, much brighter sources of light interfere. The proposed system takes advantage of the periodic dissonance between two signals at lightly different frequencies-an effect called heterodyning and the human eye's natural attraction toward anything that moves or blinks.
The system's lamp is modulated at a specific frequency, approximately 100 times per second, which is too fast for the human eye to detect. The glasses, modified from a three-dimensional video game, shutter open and closed at a slightly different frequency, 102 times per second, which essentially turns the user's eyes on and off at a rate that is also too fast to be detected by the human eye. To the wearer, the lenses appear transparent. About twice a second, the glasses shutter open at the exact moment the lamp is on. For a split second, this drowns out most background light with wavelengths different from that of the lamp. With the background light masked, the net effect is that the fluorescing materials appear to flash brightly at a rate that is distinctly noticeable to the human eye.
From behind the shuttered glasses, the crime-scene investigator would see the room lit normally, but any organic substances would flash a few times per second when illuminated by the system's lamp. Researchers may also test the system using a low- light video camcorder that is more sensitive to the fluorescence than the human eye.
Upcoming tests with the Albuquerque Police Department's crime lab are designed to help work out any bugs in the technique, define what kinds of evidence it can help find, and determine whether the system will be practical as a tool for law enforcement. Its most promising features are its portability and the fact that it does not contaminate evidence. Sandia believes that when a manufacturer licenses the technology, it will be able to produce the device at a cost low enough to make owning one feasible for a significant number of police departments.
One concern is that the technique might work too well, identifying thousands of fingerprints and making it impractical to discern the actual evidence. The amount that a fingerprint fluoresces may change over time, however, which will help differentiate new prints from older ones. The researchers hope to begin testing the prototype this year and have it available for licensing and manufacture by early 1999.