What’s your point of view?
Time, frequency, and modal domains offer complementary views, insight.
Kevin C. Craig, PhD, Marquette University College of Engineering -- Test & Measurement World, 2/1/2010 2:00:00 AM
Each of us is a critical-thinking problem solver. We have to be, as society's problems are mounting, getting harder, broader, deeper, and multidisciplinary. As basic engineering skills-analysis, hardware, and software-have become commodities worldwide, America's competitive advantage comes from being immediate, innovative, integrative, and conceptual. Our innovation must be local; you can't import it, you create it! It is a way of thinking, communicating, and doing. It differentiates us from other engineers around the world.
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As multidisciplinary teams are formed to solve these problems, usually with a core group comprising mechanical, electronic, computer, and controls engineers together with problem-specific experts in, for example, combustion, chemistry, structures, materials, anatomy, and physiology, insight and communication are of utmost importance. We have all witnessed how engineers from different backgrounds describe the same concepts using different language and different points of view, which often can lead to confusion and, ultimately, design errors. Being able to describe concepts with clarity and insight in a variety of ways is essential for the mechatronics engineer as the multidisciplinary team leader.
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The two domains, time and frequency, represent different perspectives. They are interchangeable, complementary points of view—that is, no information is lost in changing from one domain to another—and together lead to better understanding and insight.
Most signals and processes involve both fast and slow components happening at the same time. In the time, or temporal, domain, we measure how long something takes, whereas in the frequency, or spectral, domain, we measure how fast or slow it is. No one domain always offers the best answer, so the ability to easily change domains is quite valuable and aids in communicating with other team members.
A third domain, the modal domain, is particularly valuable in analyzing the behavior of mechanical structures. It breaks down complicated structural vibration problems into simple vibration modes. Unique insight into the use of the modal domain in mechatronic system design has been provided in the work of Dr. Adrian Rankers, manager of mechatronics technologies at Philips Applied Technologies.
The time domain is a record of the response of a dynamic system as indicated by some measured parameter, as a function of time. More than 100 years ago, Jean Baptiste Fourier showed that any real-world signal can be broken down into a sum of sine waves, and this combination of sine waves is unique. By picking the amplitudes, frequencies, and phases of these sine waves, one can generate a waveform identical to the desired signal. To show how the time and frequency domains are the same, the figure shows three axes: time, amplitude, and frequency. The time and amplitude axes are familiar from the time domain. The third axis, frequency, allows us to visually separate the sine waves that add to give us the complex waveform. Note that phase information is not represented here.
If we can predict the response of a system to a sine wave input—that is, the frequency response—then we can predict the response of the system to any real-world signal once we know the frequency spectrum of that signal. The system’s frequency-response curves are really a complete description of the system’s dynamic behavior.
Engineers who can bridge gaps among disciplines and articulate complementary points of view clearly and insightfully will certainly have a competitive advantage.
For more mechatronic news, visit: mechatronicszone.com.
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