Electronics engineer Myron L. Crawford (left) hands a piece of electronic equipment to technician John L. Workman, who is inside the Bureau's Transverse Electromagnetic Cell. The specially-developed cell tests equipment for susceptibility to electromagnetic interference, a phenomenon of growing concern. The Electromagnetic Last year, an American electronics firm that was having trouble selling its products in West Germany came to the National Bureau of Standards for help. NBS does not offer marketing services, but the Bureau does offer a range of expertise in the measurement of electromagnetic radiation and interference and that is precisely what the electronics manufacturer needed. Electromagnetic interference, or EMI, occurs when electromagnetic radiation interferes with the operation of electrical or electronic equipment. The major difficulty is caused not by ionizing radiation like x-rays-which present their own benefits and hazards-but by non-ionizing radiation. This sort of radiation is emitted by a multitude of consumer, industrial, and communication products. CB radios, microwave ovens, high voltage transmission lines, and radio and TV transmitters are just a few of the many sources of electromagnetic radiation in the United States today. While we do not yet have a full picture of the EMI situation, the effect of such radiation on electrical and electronic products is of growing concern. A CB radio transmission from a passing car might conceivably trigger blasting charges at a roadside construction site. Interference to radio and television reception can be caused by CB, amateur, and other radio operations. Consumer products have been known to malfunction as a result of EMI. Some electrical and electronic disorders stemming from EMI can Dean G. Melquist, an electronics technician with the NBS/Boulder laboratories, checks the electromagnetic radiation pattern of a waveguide horn in a newly constructed anechoic chamber. indicated that the product met the applicable standards. The firm approached NBS for assistance in resolving the apparent measurement discrepancy. The Bureau has extensive facilities for measuring electromagnetic radiation, including the only U.S. facilities similar to those used by the Germans. It also has a technical staff known for its experience in closely related measurement areas. The manufacturer entered into an agreement with NBS and initiated a Research Associate Program at the Bureau. (The NBS Research Associate Program enables technical specialists in U.S. firms and professional organizations to work at NBS temporarily in order to carry out projects of mutual interest. More information about the program can be found on page 68.) The program brought company engineers to the Center for Electronics and Electrical Engineering at the NBS Boulder, Colorado, laboratories. The probe shown here is being used to measure the radio frequency level around a CB antenna mounted on a vehicle. NBS is working to resolve the measurement uncertainties associated with electromagnetic radiation emitted by and affecting CB radios and a multitude of other consumer, industrial, and communication products. Through this joint effort, NBS and the electronics firm have been trying to pinpoint and explain the measurement discrepancies. The results of their investigations will be published and distributed by NBS. The likely end product? The company may yet be able to sell its products in West Germany, and other U.S. manufacturers will have ready-made measurement procedures for similar situations. This will help not only individual companies, but it will also mean a stronger American export position at a time when our trade balance is of utmost importance. It also may mean that American consumers will be able to purchase products that have less potential for exacerbating the EMI problem in this country. NBS also aided another U.S. firm last year with a specific EMI measurement problem. A major communications and electronics company needed to test electronic telephone equipment for its susceptibility to EMI. Once again, the Center for Electronics and Electrical Engineering was called upon, this time to construct a transverse electromagnetic (TEM) cell for the company. A TEM cell is basically a large enclosure where electronic equipment can be tested to see how it is affected by known sources of EMI or to check its own electromagnetic radiation output. NBS constructed the first such testing tool several years ago, just one of a variety of instruments the Bureau has developed to measure EMI radiation and its effects. The Bureau does not normally build laboratory equipment for a private company. But in this case, NBS decided that the demand for TEM cells would be growing as a result of the increased awareness of EMI and that the Bureau's guidance on building the cells would become more important. Six months after they started on the project, NBS engineers and craftsmen had built and shipped the custom-made cell to the company. Records documenting cell design and construction were maintained as work proceeded. Those step-by-step guidelines will now be made available to any firm or laboratory that wishes to build its own TEM cell. As the premiere government agency for electromagnetic radiation measurement, NBS also provides considerable assistance to other Federal agencies that are concerned with EMI. Last year, NBS developed four devices to help guard sensitive military electronics equipment from EMI which can jeopardize control systems. Under certain conditions of interference, it is conceivable that a weapon might not be deployed or detonated when expected. The devices NBS invented after several years of work for the U.S. Army Communications Command will sound an alarm when high levels of electromagnetic radiation are detected. Sensitive components of the sophisticated military hardware can then be shielded or the radiation source can be tracked and eliminated. The National Highway Traffic Safety Administration has been aware of the possibility that EMI could cause failures in the electronic controls of anti-skid braking systems used in trucks. In fact, a regulation which led to the installation of such electronic anti Bolstering State Weights and Measures The responsibility for ensuring the accuracy of weighing and measuring equipment used in the U.S. marketplace falls to individual states and territories, making their weights and measures offices the first line of defense against chaos in the marketplaces and exchanges of this country. In the early 1960's, NBS officials surveyed various State weights and measures offices and laboratories and found serious weak points in that measurement system. They discovered that many of the State standards were in disarray. Certain sets of standards could not even be physically located. That was not too surprising, since the last official sets of standards had been distributed to the States during the middle of the 19th century. As custodian of the national standards of measurement and as the organization which sponsors and assists the National Conference on Weights and Measures, NBS in 1965 began a program to distribute a complete set of replacement standards to the States and territories. Under the replacement program, weights and measures offices received 67 different mass standards (weights), 4 steel rules for length standards, 17 standards for volume, and 5 precision balances. NBS also trained weights and measures personnel in the operation and maintenance of a modern standards laboratory. Last year, NBS moved into the final phase of its 13-year program when it presented sets of standards to Washington and Mississippi. (The Virgin Islands and Puerto Rico have since received their standards also, completing the weights and measures program for 53 States and territories.) NBS instrument maker Jeffrey Kelley skid systems was withdrawn when the seriousness of the EMI problem was raised as an issue. In recent tests for that agency in which trucks with electronically-controlled brakes were exposed to an electromagnetic radiation field, NBS engineers confirmed that EMI affected the operation of the brakes. Additional research is continuing to determine the extent of the problem. Also last year, NBS completed work for the Federal Aviation Administration on specialized measurement instrumentation and techniques to assess electromagnetic radiation levels around antenna sites at airports and in airplanes. Bureau researchers also supplied NBS-developed instrumentation to assist the Environmental Protection Agency in developing a data base characterizing electromagnetic radiation in 12 major U.S. cities. The aim was to provide a benchmark which will help judge the state of the electromagnetic environment over a number of years. Considering the rapidly mushrooming reliance on electronically controlled products emitting and simultaneously standing to be affected by electromagnetic radiation, the Bureau's EMI measurement research and information is certain to become more important. Progress in Basic Research A number of measurement studies at NBS fall into the realm of basic science. In this category is a whole range of investigations aimed at studying the fundamentals of physics by applying accurate measurements. These experiments strengthen the foundations of our measurement system, but they are first and foremost designed to improve our knowledge of physics by testing basic principles and theories. They are part of the mandate in the NBS Organic Act to undertake "the determination of physical constants and properties of materials when such data are of great importance to scientific ог manufacturing interests and are not to be obtained of sufficient accuracy elsewhere." This type of basic research is exemplified by the work of physicists in the Center for Absolute Physical Quantities who have been characterizing the electromagnetic spectrum to a greater degree of accuracy than has been achieved previously. Using a combination of x-ray and optical interferometry followed by accurate determination of gamma-ray diffraction angles, these NBS physicists have established new wavelength standards in the gamma-ray region that are more closely tied to basic atomic standards in the visible region. Their achievement represents a hundred fold improvement in the overall accuracy of electromagnetic wavelength standards. The new scale has already had several important applications. For instance, it Recent Bureau research in measurement science has improved upon the 1887 "Michelson-Morley" experiment which aided Einstein and others in developing the special theory of relativity. Physicist John L. Hall is shown here with some of the laser equipment which helped to achieve this increased accuracy. has aided other scientists in resolving persistent conflict between experiment and theory involving certain exotic atoms containing mu mesons. This discrepancy had led to a questioning of one of the most basic theories of modern physics, quantum electrody namics (QED). At the root of this experiment-theory discrepancy was the inconsistency of the wavelength standards in this part of the electromagnetic spectrum. Using NBS research results, scientists have been able to bring about greater agreement between experiment and theory, thereby supporting QED. In a second application of the NBS work, other scientists have compared the radiation emitted by atoms containing a pi meson to the new NBS wavelength standards, enabling them to calculate the pi meson mass more accurately. Another test of QED theory also was made possible last year as a result of an improved measurement method for determining the proton gyromagnetic ratio to the unprecedented accuracy of two parts in ten million. When combined with the measured values of other fundamental constants, this new result yields an extraordinarily precise value for the fine structure constant, a critical parameter in QED. This has helped permit the unequivocal comparison of QED theory with experimental observation and will allow testing of theory and experiment for several basic quantities at heretofore unattainable accuracies. Like much of the research NBS performs in measuring fundamental physical constants, this work by the Center for Absolute Physical Quantities required unique capabilities. In this case, a first-class nonmagnetic laboratory and expertise in ultraprecise dimensional metrology were prerequisites. Both are unique to NBS in this country. In fact, this is clearly an experiment which no one else in the United States could have undertaken. At least four other countries have had programs dating back 10 to 20 years to determine the proton gyromagnetic ratio. The NBS results improved by a factor of 20 the previous level of accuracy achieved elsewhere. A new version of this experiment which should yield an additional factor of 10 increase in accuracy is now underway and several measurement spinoffs should result. For example, methods for measuring the physical dimensions of objects at cryogenic temperatures, techniques for determining the load coefficients of precision resistors to high accuracy, and a means to generate, measure, and control magnetic fields to unprecedented |