IEEE FOOTHILL MEMBERS SUPPORT CLASTECH 2014 MEETING
|December 9, 2014||Posted by COMauthor under CN, COMSOC, CS, EDCAS, MTT/APS||
Notes from CLASTECH meeting on Friday October 24, 2014 at Hacienda Hotel, El Segundo
This is an annual meeting on state-of-the-art technology with distinguished speakers coming to Los Angeles from throughout the world. This meeting, originated and continuously organized by the IEEE Coastal LA Section for several years now ,brings together many technical IEEE professionals with these speakers, representatives from academia, and industry exhibitors for a productive all-day session.
The agenda subjects covered include microwaves and electromagnetics, antenna design and testing, propagation, radiation at RF frequencies, and scattering. Over 160 attendees from IEEE Sections throughout the Los Angeles area were present; the IEEE Foothill sent a small contingent of professionals and student engineers. Many engineering concepts and ideas were exchanged over the luncheon.
Some review notes on a few of the many excellent technical talks follow:
Dr C J Reddy / Altair presented a talk on “Advanced Computational Tools for Antenna Design and Placement Studies”
Consider a generic multifaceted / UAV type aircraft model with stabilizing tails in the rear. There is a need to place multiple antennas on board this UAV: GPS patch antenna, UHF mode antenna, VHF blade antenna and two RF monopole antennas. For typical sizes, this aircraft platform would be 14.2 meters in length. This equates to about 75 wavelengths at 1.575 GHz frequency. This is a large structure to be analyzed by EM computational means. One method developed by Dr Reddy and associates uses the Uniform Theory of Diffraction (UTD). Here ray tracing plus diffraction and creeping current waves on the structure are modeled. The aim is to produce accurate radiation patterns.
Some of the computational problems that need to be considered are:
(1) Interactions with other antenna structures and other parts of the fuselage mean that we must compute near-fields(for mutual coupling effects) as well as far field for the UHF and VHF antenna, Current density plots show current builds up on the tail surfaces, among other places We should expect that these effects show in in far field observer scattering measurements.
(2) What happens if a carbon-fiber light weight composite material is used in place of the aluminum for the outer fuselage skin (perfect electrical conductor PEC model)? A wire mesh model is used, together with FEM (Finite Element Model) with multiple unit cells of varying geometric sizes and shapes to model the diffusion of RF energy through anisotropic panels. It was reported that the GPS antenna performance is unchanged, but the UHF patterns differ between an aluminum skin and a composite carbon fiber skin. Also, polarization changes through the composite fiber airframe must be considered.
(3) Can the radiation from cable pin connectors and the actual interior cables give spurious radiation? To analyze, we need to model interior cable as a discrete lumped L /C transmission line and proceed to compute propagation and scattering from that cable. What effects would be seen in what patterns.
(4) There is a requirement to analyze transient EMP (Electro-Magnetic Pulse) effects, with E field coupling to the UHF antenna, and the H field diffusing through the Carbon Fiber panels. Just how would a high intensity transient E field effect the antennas?
Dr Reddy noted that all these problems show the need for both near-field and far-field computations using different problem solver and commercial analyses packages. The computational problems grow in size and complexity as the need for more accurate solutions evolve. Perhaps our attendees and our readers would like to conjecture when the antenna accuracy performance and needs for more computer CPUs asymptotically converge.
Dr R M Dickinson / OFF Earth –WPT, presented a talk on “Long-Range Wireless Power Transmission Systems”
This presentation was a tour-de-force summary of the past several decades of efforts by many engineers to harness and use microwave power. Dr Dickinson is uniquely qualified to speak on this topic. His resume includes designing and building the RF transmitter for the NASA Voyager spacecraft, and the high power transmitter for NASA Deep Space Network sited at Goldstone, CA.
Many programs in recent history attempting to use RF power from a remote source were discussed:
WC Brown ( 1960-1964 era) demonstrated a small helicopter, powered by an electric drill motor, that sustained in flight above the ground for 25 hours, using a microwave dish on the ground as the transmitting power source to the helicopter.
Other pioneering efforts included: Japan Minix 1983; Marshall Space Flight Center tested an UAH (unmanned aerial helicopter) at Dryden Space Flight Center in 2003; Japan MiLax 1992; USAF and Leik Myrabo 1996 (high altitude transmission between two vehicles); Canadian aircraft 1988 test with a large receiving dish on the aircraft interacting with ground based sources of EF energy; Lockheed Martin Stalker project-laser powered UAV August 2012.
Other engineering programs that were noted included the NASA concept Blended Wing and Electrical Propulsion Transfer with the engines at rear of aircraft; Jody Aviation (San Jose, CA) LEAP technology (Leading Edge Asymmetrical Propeller Technology, asymmetrical due to the need to reduce noise onboard aircraft), and an English proposal to use a high altitude airship as an alternative to building many wireless cell towers in remote parts of their country.
Another ongoing effort is at EADS (European Aeronautical Defense Space Group) Their innovative plan is to develop an new type of aircraft with both Rolls-Royce turbo-jet engines and batteries for propulsion. It is possible that superconductive motors would be developed and used for their efficiency and lighter weight. The general flight profile would be as follows: For takeoff, turbojet and battery power would be used. For cruise, battery power would presumable be adequate. During descent, the batteries would be recharged. Landing power would use both turbojet and battery power.
This was followed by a discussion of issues related to getting microwave power up to an aircraft . Mention was made of Goubau and Schwering calculations for RF beam power transmitter efficiency. These lead to a description of the results of power transmission experiment conducted during a Goldstone test. Dr Dickinson, during experiments with the Goldstone 26 meter dish, was involved in building a receiving tower on a hill relatively near and within an adjusted angular slew position of the 26 meter dish. Dr Dickinson and his team had installed small dipoles, with about 5K such dipoles in the planar array. Power was received and recorded power levels were determined from the dipole array. A small dipole of the type used was circulated around the meeting room. So, sending microwave power to a remote location is feasible.
How much would a high power microwave transmission ground station cost? Dr Dickinson recommended using a coarse cost estimate from the cost of the high power direction transmitter in the PAVE PAWS radar transmitter system, currently in use at Clear AFB in Alaska. The Government of Taiwan purchased a similar unit; this gives us a cost baseline.
Another concept of interest is to make use of microwave transmission in space from a satellite, back through the earth’s atmosphere to a ground station. This could be done at a selected microwave frequency band with low attenuation in our known (nominal) atmosphere. A sketch of such a concept for space based solar power was presented. A large photovoltaic array is built on a low-earth orbit(?) satellite. Think large panels pointing toward the sun. Power from the photovoltaic array is converted to microwave frequency. Single gimbal system would be used if possible to point microwave transmitter/ antenna to the ground receiving antenna. So, there you have “clean” solar power from space.
But you need to temper your enthusiasm for this concept. There are numerous engineering issues with these Wireless Power Transfer (WPT) interfaces issues. There are many, including cost, beam safety, improvements needed in heat exchange material technology and development of diaphanous sails for the satellite. All these require extensive engineering analyses. It would be a marvel of satellite engineering to make such a system operational.
AND there is no existing business WPT application at this time. But there might be when PG&E, under contract to receive solar energy from Ivanpah and other CA desert solar sites in 2016, has to disclose the actual costs.
(What will the good people of San Francisco say then? What will the environmental residents on the PG&E grid say then? What will the residents of San Bernardino County say when seeing all the new transmissions lines through their countryside?)
Will WPT from space be in the future electrical power mix then? Dr Dickinson did mention fracking, so he is aware of the competitive technology to supply energy for a more-energy-demanding world.
Be prepared to keep this WPT concept within your future engineering horizon.
We thank Dr Dickinson for his comprehensive presentation of the WPT efforts to date.
Mahdur S. Gupta “Microwave Engineering: What is it, Where is it headed, and How it serves Mankind”
Dr Gupta is a Professor at San Diego State University, where he teaches the usual spectrum of classes that cover generation, transmission, and reception of electromagnetic energy. His current activities include, in his own informal description, “Recruiting Sergeant for the IEEE Microwave Theory and Techniques Society”. His talk convinced the audience that he is a Master at this “Recruiting Sergeant” task. The IEEE students in attendance were convinced that some knowledge of microwaves would enhance their future careers.
What are the topics that he sees as the most interest to the Microwave community? His list, in no hierarchical order includes phase shifters, reflectors, noise, spectral width, parasite effects, coupling, radiation, packaging, and active devices beyond a cutoff frequence, when they become passive. In other words, about every problem that a microwave engineer could encounter in building a working device.
Why should a student explore and seriously study electromagnetics and microwaves? Many properties of microwaves have been measured and explained, at least in part, such as transparency of the earth’s atmosphere with known transmission “windows” for optical and microwave frequencies; known microwave vibration frequencies in gases and other materials; known propagation in various materials, ability and techniques for wavefront polarization control; and non-ionizing radiation in the microwave band (This fact for microwave bands which should be compared to the frequency bands for Sun’s radiation and X-Ray radiation sources. Hdre there are ionization effects. More stringent handling would be required.). It is readily possibility to generate microwave at a very narrow frequency band, with the source frequency stable to 1 part in (10 raised to the 9th power).
So, it is possible to imagine many new applications for microwave devices. Since almost everyone in the audience had a cell phone, there was no need to discuss the MMICs in these phone devices.
Our presenter asked us to just consider these possible commercial applications:
(1) Directed heating of tomato plants, so that they can grow in a cold winter climate. (Professor Gupta thinks Manhattan Beach in winter would not be a challenge to grow tomato plants under a microwave beam.)
(2)Space based solar power collectors with use of antennas plus rectifiers.
(3) Gas discharge Lamps, with gases under high pressure excited by microwaves, without any use of mercury. Since the compact fluorescent lights in everyday use contain mercury, these have dropping and disposal problems if the bulb cracks. This may indicate a future microwave device R&D effort.
Note: (The US Supreme Court on 11/25/2014 accepted (writ of certiorari) a series of cases(14-46, 14-47, and 14-49), involving mercury emissions, from US states with coal driven power plants, versus the Environmental Protection Agency rules and regulations. The debate question involves costs for the power plant operators versus overall economic benefit. The issue revolves around the amount of mercury released into the atmosphere when coal is burnt in generating electrical power. Will this case, depending on its outcome, mean that the EPA Environmental Protection Agency would have to revisit the current compact fluorescent lights mandate with their inclusive mercury in current use in every home and office?)
Naturally, Professor Gupta would not let his audience leave without answering this riddle. When an amoeba wants to go surfing, what does it do? You are right; it looks for a Micro-Wave.
We thank Professor Gupta for making a strong case that IEEE students should study microwaves. Even the microwave experts present enjoyed his refreshing look at the microwave fiekd.
“Tunable Filters for Wireless Systems”, presented by Professor Raafat R Mansour, Research Chair, Center for Integrated RF Electronics, University of Waterloo, Canada
Special designs are needed for the narrow frequency modulated bandwidth filters that are needed to make wireless communication commercially possible. As cited by Professor Mansour, the general requirements for wireless filters start with multiband capability, reduced size to fit into a small package, compensations built in for temperature drift, and optimization for reduced power loss through the filter. The related power amplifiers (PA) and low noise amplifiers (LNA) are designed for multi channels, whether GSM LTE of WiMAX, etc. This leads to the next iteration of RF filter design requirements, These include developing numerical ranges and numerical bounds for the High Q and average Q of the filter; the required filter tuning range; the bandwidth peak variation over the tuning range, with 3dB widths and out-of-range falloff in amplitude; width of the tuning range; and the linearity over this tuning range.
Professor Mansour’s examples of his laboratory’s work covered a number of piezoelectric and RF MEMS (RF Micro Electro Mechanical Systems) filters. He covered two types of tunable combline Bandpass (BP) filters. The basic configuration is a resonant cavity with a fixed tuning post and an adjustable disk. Adjusting this separation between tuning post and disk will change the resonant frequency of the EM modes in the cavity. The two methods have been attested and analyzed for resonant frequency adjustment are mechanical tuning via piezomotors, and tuning via RF MEMS capacitor banks. Examples were shown of a two-pole (or two cavity configuration), designed for fc =2.5 GHz, which had a tuning range of 110 MHz, a Q ranging from 1300 down to 400. (A lower Q means more energy is dissipated in the filter and the insertion losses increase.) Another design showed a 6-pole (cavity) filter with more involved tuning requirements (e.g., asymmetric tuning of the capacitor bank, and the use of iris between some cavities). The fc was about 2.6 GHz, tuning range of 44 MHz, and the out-of-band roll off was > 25db. Both a piezoelectric motor and an RF capacitor bank were used for this latter tuning. The space requirements for the RF MEMS tuning elements were set to be comparable to the resonator (including heights). Simulated and measured filter (S11, S12) parameter results were presented. Various materials (including NiCo) were mentioned for the RF MEMS unit.
As these RF MEMS devices are, for now, a laboratory R&D effort, Professor Mansour shared some additional technical brain-teasers. Why not use a Josephson junction for a circuit to convert an RF signal directly to ADC output? Why not a superconductor, say using an Nb device operating at temperature of 4 Kelvin, to create an ultra-low-insertion loss UHF BP filter? Professor Mansour gave an excellent description of the outstanding work within his laboratory group at the University of Waterloo.
It seems that an unstated question for our audience today would be, when would these RF MEMS concepts be ready to be incorporated into an update for the current wireless communication RF filters baseline? Our experts need to reexamine the specifications and parameters of microstrip / slotline/ surface acoustic wave/ bulk acoustic wave/ vibration resonant beam devices, and construct a comparative performance matrix.
Our Thanks to Dr Charlie Jackson and his CLASTECH committee for all their efforts in preparing and presenting this excellent IEEE event for the MTT / APS community in the Los Angeles area.