Новини світу мікро- та наноелектроніки

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How the fuck would this even work lmao🤣. submitted by /u/ThomasTTEe2 [link] [comments]

Perceptra of Oakland, CA, USA — which was spun off from Massachusetts Institute of Technology (MIT) in 2021 to pioneer photonic chip-based AI-enabled Raman sensors for chemical monitoring — has secured a €1.2m investment from photonic chip industry accelerator PhotonDelta of Eindhoven, the Netherlands (which connects and collaborates with an ecosystem of photonic chip technology organizations worldwide)...

Experienced network designers know that the performance achievable of a data link depends on many factors, including the quality and consistency of the inherently analog medium between the two endpoints. Whether it’s air, copper, fiber, or even vacuum, that link sets a basic operating constraint on the speed and bit error rate (BER) of the link.

Any short- or longer-term perturbation in the link—including external and internal noise, distortion, phase shifts, media shifts, and other imperfections—will result in a lower effective data rate, need for more data encoding, error detection, correction, and re-transmissions.

A critical element in high-speed, low-BER data recovery is the advanced clock recovery and re-clocking for synchronization accomplished using phase-locked loops (analog or digital) and other arrangements. The unspoken assumption is that the fundamental measurement of “time” is the same at both ends of the link. This can be established by use of atomic and laser-optical clocks of outstanding precision and performance, if crystal or resonator-based won’t suffice.

But that endpoint equivalence is not necessarily the case. If we want to establish a long-term robotic or even human presence on our neighbor Mars, and set up a robust high-speed data link, we need to know the answer to a basic question: What time is it on Mars?

It turns out that it’s not a trivial question to answer. As Einstein showed in his classic 1905 paper on special relativity “On the Electrodynamics of Moving Bodies,” and subsequent work on general relativity, clocks don’t tick at the same rate across the universe. They will run slightly faster or slower depending on the strength of gravity in their environment, as well as their relative velocity with respect to other clocks.

This time dilation is not a fanciful theory, as it has been measured and verified in many experiments. It even points to a correction factor that must be applied to satellites orbiting the Earth. Without those adjustments, GPS signal timing would be “off” and its accuracy seriously degraded. It’s a phenomenon that is often, and quite correctly, summarized simply as “moving clocks run slow.”

The general problem of time-dilation, objects in motion, and gravity’s effects have been known for many years, and it can be a problem for non-orbiting space vehicles as well. To manage the problem, Barycentric Coordinate Time—known as TCB, from the French name—is a coordinate time standard defined in 1991 by the International Astronomical Union.

TCB is intended to be used as the independent variable of time for all calculations related to orbits of planets, asteroids, comets, and interplanetary spacecraft in the solar system, and defines time as experienced by a clock at rest in a coordinate frame co-moving with the barycenter (center of mass) of the solar system.

What does this have to do with Mars and data links? As shown in Figure 1, the magnitude of the dilation-induced time “slippage” between Earth and Mars is one factor that affects maintaining a high-speed link between these two planets.

Figure 1 In addition to “hard” data from landed rover and orbiting science packages, Mars—also known as “the red planet”—presents a complicated time-dilation scenario. Source: NIST

Now, a team of physicists at the National Institute of Standards and Technology (NIST) has calculated a fairly precise answer for the first time. The problem is complicated as there are four primary “players” to consider: Mars, Earth, Sun, and even our Moon (and the two small moons of Mars also have an effect, though much smaller).

Why the complication? It’s been known since the 1800s that the three-body problem has no general closed-form solution, and the four-body problem is worse. That means there is no explicit formula that can resolve the positions of the bodies in the dilation analysis. Consequently, number-crunching numerical calculations must be used, and it’s even more challenging with four and more bodies.

The researchers’ work is based not only on theory but also measurements from the various “rovers” that have landed on Mars as well as Mars orbiters. The team chose a point on the Martian surface as a reference, somewhat like sea level at the equator on Earth, and used years of data collected from Mars missions to estimate gravity on the surface of the planet, which is five times weaker than Earth’s.

I won’t even try to explain the mathematics of the analysis; all I will say it’s the most “intense” set of equations I have even seen, even compared to solid-state physics.

They determined that on average, clocks on Mars will tick 477 microseconds faster than those on Earth per day (Figure 2). However, Mars’ eccentric orbit and the gravity from its celestial neighbors can increase or decrease this amount by as much as 226 microseconds a day over the course of the Martian year.

Figure 2 Plots of the clock-rate offsets between a clock on Mars compared to clocks on the Earth and the Moon for ∼40 years starting from modified Julian date (MJD) 52275 (January 1, 2003), using DE440 data. DE440 is a highly accurate planetary and lunar ephemeris (a table of positions) from NASA’s Jet Propulsion Laboratory, representing precise orbital data for the Sun, Moon, planets, and Pluto. Source: NIST

The clock is not only “squeezed” with respect to Earth, but the amount of squeeze varies in a non-periodic way. In contrast, they note that the Earth and Moon orbits are relatively constant; time on the Moon is consistently 56 microseconds faster than time on Earth.

If you want the details, check out their open-access paper “A Comparative Study of Time on Mars with Lunar and Terrestrial Clocks” published in The Astronomical Journal of the American Astronomical Society. Don’t worry: a readable summary and overview is also posted at the NIST site, “What Time Is It on Mars? NIST Physicists Have the Answer.”

How engineers will deal with these results is another story, but timing is an important piece of the data link signal chain. Perhaps they will have to build an equivalent of the tide-predicting machine designed by William Thomson (later known as Lord Kelvin) shown in Figure 3.

Figure 3 This analog all-mechanical computer design by William Thomson was designed to predict tides, which are determined by cyclic motion of the Earth, Moon, and many other factors. Source: Science Museum London via IEEE Spectrum

This analog mechanical computer on display at the Science Museum in London was designed for one purpose only: combining 10 cyclic oscillations linked to the periodic motions of the Earth, Sun, and Moon and other bodies to trace the tidal curve for a given location.

Have you ever had to synchronize a data link with a nominally accurate clock on each end, but with clocks that actually had significant differences as well as cyclic and unknown shifting of their frequencies?

Bill Schweber is a degreed senior EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features. Prior to becoming an author and editor, he spent his entire hands-on career on the analog side by working on power supplies, sensors, signal conditioning, and wired and wireless communication links. His work experience includes many years at Analog Devices in applications and marketing.

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