A combined Smith-Carter chart shows the impedance of ideal electric and magnetic dipole fields normalized to free-space impedance.

This week, I’ll be presenting my paper on “A simple procedure for measuring gain of very electrically small antennas” at the 2014 Loughborough Antenna and Propagation Conference.

Gain measurements of very electrically small antennas (VESAs) present special challenges. These antennas radiate with poor efficiency, and great care is needed to make a suitable gain measurement using radiative techniques. This paper presents a novel gain measurement technique based upon the observation that the gain of well-matched VESAs is proportional to electrical volume and antenna quality factor (Q) for antennas of similar shape factor. Thus, antenna gain may be determined by a measurement of antenna quality factor and antenna size. This paper presents three distinct derivations for the antenna gain relation. Finally this paper validates the theoretical prediction using a NEC model and demonstrates that a “Brooks Coil” with a diameter three times the length yields optimal results.

I originally derived and presented the gain result in my 2013 Allerton Antenna Applications Symposium paper, “Simple formulas for near-field transmission gain and fields.” The novelty of this paper lies in using Schelkunoff’s dipole impedance formulas to understand power flow of electrically small antennas. We can define a power factor based on the impedance phase. Just as the phase difference between current and voltage defines the power factor for an AC circuit, the ratio of electric to magnetic field phase defines the power factor for energy flow in fields. The Smith chart to the right plots the dipole impedance normalized to free-space impedance. The blue arcs are lines of constant phase – an enhancement suggested by Phillip S. Carter. The larger the size of the ideal dipole, expressed here in terms of wave number and boundary sphere radius, the smaller the phase difference and the larger the power factor.

This analysis ties together lots of fascinating small antenna physics because the power factor is the inverse of the quality factor – a parameter of considerable interest in the study of electrically small antennas.

Here are my slides:

Here is a video of my presentation:

My full paper, “A simple procedure for measuring gain of very electrically small antennas,” is available through ResearchGate.

Oct 022014
 

The Allerton Park and Retreat Center in Monticello, IL was the site of the 2014 Antenna Applications Symposium.

Last week, I traveled to the Allerton Park and Retreat Center to present a new paper on fundamental electromagnetic physics at the 2014 Antenna Applications Symposium. My paper, “On Energy Flow in Standing Waves,” analyzes and explains the propagation of energy in a variety of standing waves. The conventional point of view in electromagnetics holds that near fields only matter close to sources, sinks, or scatterers of electromagnetic energy. I argue that near-fields arise whenever multiple electromagnetic waves interact. Although fields pass through each other, in so doing, the individual waves exchange energy with each other. These insights have helped Q-Track create better precision location systems, and may be helpful in making antennas work better in multipath environments. The standing wave perspective also has fascinating implications. The propagation of electromagnetic energy from source to destination follows, not ideal optical rays, but rather a complicated meander or drift as particular fields perturb the energy of the collective electromagnetic superposition one way or another. Also, it appears that although electromagnetic signals and fields propagate at the speed of light, electromagnetic energy only rarely propagates so quickly and instead ebbs and flows at a drift velocity less than the speed of light. The full text of my paper, “On Energy Flow in Standing Waves,” is available if you sign up on ResearchGate.net.

A video of my talk is also available.

 

The Heaviside Memorial Project recently completed the restoration of the memorial to Oliver Heaviside and his family in the Paignton Cemetary near Torquay, Devon.

The Heaviside Memorial Project successfully raised funds and completed the restoration of the memorial to Oliver Heaviside and his family in the Paignton Cemetary near Torquay, Devon. Details and additional photos of the unveiling ceremony are available at their web site.

The group, organized by the Newcastle Electromagnetics Interest Group and spearheaded by Christopher Spargo, is on to their next challenge. Their goal is to republish Searle’s 1950 biography of Heaviside. G.F.C. Searle (1864-1950) was a friend and professional colleague of Heaviside and shared many fascinating insights to Heaviside’s character and thinking in his posthumously published biography. The Heaviside Memorial Project is accepting donations to aid in the publication.

Update: A $50 donation now entitles you to a signed copy when available.

Jul 202014
 

Heaviside's barely legible monument tilts atop the family plot where he lies with his parents in Paignton Cemetary, Torquay, Devon, UK.

He developed the theory of transmission lines, coined such terms as inductance, impedance, and admittance, and rewrote James Clerk Maxwell’s awkwardly expressed equations into the vector form familiar to any student of electromagnetics. Today, Oliver Heaviside’s neglected tombstone is barely legible and is beginning to lean.

Chris Spargo and Professor Alex Yakolev aim to restore the monument, and they could use our help.

Founders of The Heaviside Memorial Project, the two have set up a website aiming to collect £800 in donations for the £660 repair and £140 for any unexpected costs. The restoration will relevel, clean, and repair the monument. Their campaign has already raised nearly half of the required funds. Please go to their website and donate what you can to this worthy cause.

Jul 162014
 

Yesterday, UWB pioneer Time Domain announced their acquisition by a private equity group led by Bonaventure Capital and Fidelis Capital. Time Domain did not disclose the terms of the transaction. Additional details are available in a statement from the company and in coverage from the Huntsville Times.

Jul 032014
 

I’ll be presenting my short course on UWB antennas at the IEEE Antennas and Propagation Symposium (APS) in Memphis, TN on Sunday July 6. This is the first time I’ve been back to IEEE APS since 2007, and my short course includes some interesting revisions from the second edition of my book, underway. Here’s a summary.

The wide scale commercial deployment of ultra-wideband (UWB) systems has led to increased interest in UWB antenna designs. In many cases, though, investigators have unknowingly resurrected already known designs rather than developing new ones. Also, the subtleties of UWB antenna physics and design are not always obvious to those more familiar with narrowband antennas. For instance, the spectral and impedance matching properties of a UWB antenna exert a profound influence on an overall UWB system design.

This workshop will enable attendees to:

  • Understand basic antenna physics as applied to UWB antennas
  • Quickly and correctly apply UWB antennas to current projects
  • Design and analyze UWB antennas
  • Integrate these antennas in an RF system
 

Near-field wireless technology is an emerging area of great importance in Radio Frequency Identification (RFID). Specific applications include low frequency (LF) and high frequency (HF) RFID, Near-Field Communications (NFC), Near-Field Electromagnetic Ranging (NFER), and wireless power transfer. This talk discusses the origins of near-field wireless, surveys applications, presents near-field links laws, and reviews the properties and performance of electrically-small antennas. This March 31, 2014 presentation to the Huntsville, AL section of the IEEE previews the full three hour workshop presented April 8, 2014 at the 8th Annual IEEE International Conference on RFID held in conjunction with 2014 RFID Journal Live.

 A couple of misstatements I caught in reviewing this: first, Preece transmitted near field wireless signals across the Bristol Channel not the “British” Channel; and second, “unlike” links go as 40dB/decade, not 20dB/decade in the near-field. Prezi slides are available here: http://bit.ly/1x0FY7W if you’d like to take a closer look. In some of the views, you can’t see all the details.

 

 

James Clerk Maxwell (1831-1879) formalized a set of equations that describe the behavior and interaction of electricity and magnetism.

From Scientific Papers of James Clerk Maxwell, vol 2, LIV, p.311 (Proceedings of the Royal Institution of Great Britain, vol. VII, 1876). Emphasis added inn bold.

I HAVE no new discovery to bring before you this evening. I must ask you to go over very old ground, and to turn your attention to a question which has been raised again and again ever since men began to think. The question is that of the transmission of force. We see that two bodies at a distance from each other exert a mutual influence on each others’ motion. Does this mutual action depend on the existence of some third thing, some medium of communication, occupying the space between the bodies, or do the bodies act on each other immediately, without the intervention of anything else?The mode in which Faraday was accustomed to look at phenomena of this kind differs from that adopted by many other modem inquirers, and my special aim will be to enable you to place yourselves at Faraday’s point of view, and to point out the scientific value of that conception of lines of forcewhich, in his hands, became the key to the science of electricity.When we observe one body acting on another at a distance, before we assume that this action is direct and immediate, we generally inquire whether there is any material connection between the two bodies; and if we find strings, or rods, or mechanism of any kind, capable of accounting for the observed action between the bodies, we prefer to explain the action by means of these intermediate connections, rather than to admit the notion of direct action at a distance.Thus, when we ring a bell by means of a wire, the successive parts of the wire are first tightened and then moved, till at last the bell is rung at a distance by a process in which all the intermediate particles of the wire have taken part one after the other. We may ring a bell at a distance in other ways, as by forcing air into a long tube, at the other end of which is a cylinder with a piston which is made to fly out and strike the bell. We may also use a wire; but instead of pulling it, we may connect it at one end with a voltaic battery, and at the other with an electro-magnet, and thus ring the bell by electricity.

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Roger Bowley of the University of Nottingham demonstrates a dramatic increase in the range of your car’s ~315MHz key-fob merely by holding it to his head (H/T Glenn Wolenec).

 

Q-Track Corporation won the RFID Journal Live "Coolest Demo" Award for our indoor location system which tracked the real-time location of an AR parrot drone flying around the Exhibit Hall floor.

The last couple of weeks were action packed. Two weeks ago, I spoke at the Texas Wireless and Microwave Circuits and System Symposium at Baylor University in Waco (see my post “Demystifying Electromagnetic Superposition“). Last week, I joined the Q-Track team in Orlando for RFID Journal Live, our industry’s leading trade show. Q-Track came home from the show with the “Coolest Demo” award enabled by our remarkably precise NFER® indoor location system. In this post, I’ll share some of the story behind what we did and how and why it worked.

I arrived the night of Monday April 7, because I was scheduled to deliver a tutorial on Near-Field Wireless Technology to the folks at the co-located 2014 IEEE International Symposium on RFID Tuesday afternoon. That night, I got the word that the rest of the Q-Track team, our CEO Steve Werner, and our new Marketing Director, Chad Ludwig, would be delayed due to weather-related flight disruptions. They would not be able to arrive until an hour or so after the show’s opening reception, so the burden was entirely on me.

I spent Tuesday morning getting our booth set-up and our demonstration system deployed. It took me about an hour to unpack all our boxes and set up the pop-up booth backdrop. In another hour, I was able to get three receivers deployed in and around our booth and connected to the laptop computer that would be our tracking server. It took me a little more than an hour to walk around the tracking area taking calibration points to characterize the signal perturbations caused by the tracking environment – principally the building structure and the wiring. Then I confirmed that the system was working properly by walking around the tracking area with several NFER® Tag Transmitters deployed around my belt and the “history trails” function enabled to leave a trail on the screen. When one of our indoor location systems is working properly, you can see the difference in location of the “left” and “right” tags by observing the slightly offset paths in the tracking display. Everything checked out perfectly. Although the job would have been faster and easier with help, it wasn’t beyond the ability of a single person to get the Q-Track NFER® RTLS system up and running in relatively short order.

Q-Track CEO Steve Werner drives an AR Parrot Drone around the RFID Live Exhibit Hall floor while an NFER® RTLS tracks the drone's position to 40cm rms accuracy or better.

I ran off to get changed – the organizers do not turn on the AC in the Exhibit Hall until just before the show starts – I had lunch, and I presented my tutorial. Finishing a bit early, I returned to our booth in the Exhibit Hall to fire up the demonstration.

This has always been a moment of some trepidation. At the first show Q-Track attended way back in 2006, we had a beautiful demo set up and calibrated with some of our earliest prototype equipment. We shut everything down, and then turned it all back on right when the trade show opened up. The tracking showed embarrassingly large errors. I had to hurriedly recalibrate the system while my colleagues distracted our potential customers. Finally everything worked again, and we could show it off. But then a while later, tracking would deteriorate again, requiring another panicked round of recalibration. We spent half our time at the show tracking, and the other half recalibrating the system. In retrospect, we were being bit by thermal drift. Our system relies on very precise phase and amplitude measurements. Electronic circuits behave a bit differently when first turned on, i.e. cold, than they do after they’ve been running for a while, i.e. hot. Between the variations in tags and receivers, it was tough to get consistent performance for more than an hour or two at a time.

But with several generations of hardware improvements and years of additional experience under Q-Track’s collective belts, those days are behind us. When I fired up the demonstration system for the opening reception of RFID Journal Live, everything worked perfectly – exactly the same as when I’d last checked it that morning.  We advertise 40cm rms accurate tracking. Our demonstration was probably delivering even better than that, although I was too busy to perform a detailed accuracy check.

Q-Track's QT-701 Tag Transmitter weighs in at only 50 grams (~1.6 oz), yet delivers that same 40cm rms accurate indoor location capability of Q-Track's ruggedized industrial-strength NFER® RTLS tags. This photo shows one of the first prototypes.

Not long after the Opening Reception began, Steve and Chad arrived to help me handle the crush of opening night visitors interested in our demonstration and curious about our products. In fact, we were so busy that Steve didn’t get a chance to try out the drone until the next morning. The Parrot AR.Drone Quadricopter survived shipping and worked well. The control datalink for the drone requires a 2.4GHz wireless connection. With so many vendors trying out their wireless products, it was difficult getting a reliable connection. Steve’s demonstration worked best at the beginning and end of each day’s session when interference was at a minimum.

The technology that enables the The Parrot AR.Drone Quadricopter is remarkable in and of itself, but what made our demonstration really fly was Q-Track’s new, lightweight QT-701 Tag Transmitter. Weighing in at only 50 grams, the QT-701 Active Tag enables the same 40cm rms accurate tracking as our larger, more ruggedized industrial tracking tags, but in a compact form-factor suitable for everyday office use.

The other remarkable feature of our demonstration was its robustness. We were up and tracking for the entire duration of the show with no more than a momentary interruption. Naturally, that’s what you’d expect from a commercial indoor location system. But obtaining that kind of reliability is extremely difficult in the hostile RF environment of a trade show. With so many vendors operating so many devices, reliable wireless links are challenge to maintain, if they can be established at all. In fact a couple of our much larger competitors had much larger footprints and much fancier displays on the trade show floor. But neither was able or willing to try to demonstrate a working location system at the show. I think that fact was influential in the decision making behind the “Coolest Demo” Award.

Q-Track’s “Near-Field Electromagnetic Ranging” (NFER®) indoor location systems offer an effective, if unconventional, solution to many indoor location problems. My Q-Track colleague and co-founder, Bob DePierre, and I came from an ultra-wideband (UWB) RF background. We saw first-hand how UWB location systems could be quite accurate with a line-of-sight between a tag and a receiver, but as soon as the direct path was blocked, accuracy began to degrade. Try to go through a wall or two, and it becomes very difficult for a UWB system to get a good fix on your location. Short-wavelength and high-frequency microwave systems work great if you need to send lots of data, but location systems just require getting a signal through a complicated and cluttered environment with minimal distortion or degradation.

Bob and I left our then employer to pursue a different path. We reasoned that low frequencies were the way to go. Low-frequency, long-wavelength signals bend around or penetrate through obstructions much better than comparable high frequency signals. And when the wavelength is much longer than the distance of the link, you don’t get the kind of cancellation and fading you see in high frequency short wavelength signals. I discovered a variety of techniques for using “near-field” physics in localization, and Bob reduced them to practice by building the hardware to prove that my ideas would work. In a matter of a few months, we had a prototype that could track a little red wagon up and down Bob’s driveway to an accuracy of a few inches.

Today, our NFER systems operate at around 1MHz under FCC Part 15 rules for unlicensed low-power transmitters. With a wavelength of 300m, they deliver 40cm rms accurate tracking. Typical ranges are around 15-20m (45-60ft). In a particularly noisy environment (like the Exhibit Hall) range may be as short as 10m (30ft). In really quiet settings (like many retail or warehouse environments) range may be up to 30m (100ft).

The Orange County Convention Center in Orlando housed the 2014 RFID Journal Live trade show.

Below is a great screenshot of our NFER® indoor location system in action. We deployed three QT-555 Locator-Receivers and we were tracking about a 40ft x 60ft area around our 10ft x 10ft booth with the 40cm rms accuracy typical of NFER® real-time location systems. The system can accommodate up to 84 tags simultaneously at a 1Hz update rate, but we were never using more than four or five at a time. You can see solid, repeatable tracking on the inside loop of me (blue trail), Chad Ludwig (orange trail), and Steve Werner (green trail). Note the head shot “avatars.” I looped the outside edge of the tracking area – you can tell the system was having some difficulty because the update rate slowed down a bit (i.e. the space between the blue dots showing the location fixes got bigger). Finally, I walked the perimeter of three 10ft x 10ft squares and their diagonals to highlight the precision of our tracking. Ultimately, our system ran for the duration of the show with no tweaking or adjustment needed.

Screenshot of Q-Track's NFER RTLS indoor location system GUI. The colored lines show history trails as we tested the system the morning of April 10.

 In the final hours of the show, we heard an announcement that the Awards Ceremony was beginning. While we were excited about how well our location system was performing, the broader world of RFID encompasses many other interesting and useful applications. And no one from RFID Journal had been by to hint that we needed to attend. Chad and I were surprised when someone came by to tell us we’d won. By the time Chad could get to the stage, Steve, who had been walking back to us after meeting with a potential customer, arrived to collect the award. Chad captured this shot of Steve holding the award and me holding the drone.

Steve Werner (left) displays the 2014 RFID Journal Live "Coolest Demo" award. Dr. Hans Schantz (right) holds the Parrot AR.Drone Quadricopter. The QT-701 tag is mounted on top of the drone.

 The show ended at 3pm on Thursday. We broke down the tracking demonstration and the booth and flew home that night. I made it home around midnight.
Now we’re looking forward to the challenge of an even cooler demo at 2015 RFID Journal Live in San Diego. What would you propose we do with a robust accurate tracking system on the Exhibit Floor of a trade show? Leave your ideas and suggestions in the comments.
© 2010-14 Hans Schantz except as noted. Suffusion theme by Sayontan Sinha

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