Spread Spectrum It’s not just for breakfast anymore! Don't blame me, the title is the work of this month's guest columnist, Steve Bible, N7HPR (n7hpr@tapr.org). While cruising the net recently, I noticed a sudden bump in the number of times Spread Spectrum (SS) techniques were mentioned in the amateur digital areas. While QEX has discussed SS in the past, we haven't touched on it in this forum. Steve was a frequent cogent contributor, so I asked him to give us some background. Steve enlisted in the Navy in 1977 and became a Data Systems Technician, a repairman of shipboard computer systems. In 1985 he was accepted into the Navy’s Enlisted Commissioning Program and attended the University of Utah where he studied computer science. Upon graduation in 1988 he was commissioned an Ensign and entered Nuclear Power School. His subsequent assignment was onboard the USS Georgia, a trident submarine stationed in Bangor, Washington. Today Steve is a Lieutenant and he is completing a master’s degree in computer science at the Naval Postgraduate School in Monterey, California. His areas of interest are digital communications, amateur satellites, VHF/UHF contesting, and QRP. His research area closely follows his interest in amateur radio. His thesis topic is Multihop Packet Radio Routing Protocol Using Dynamic Power Control. Steve is also the AMSAT Area Coordinator for the Monterey Bay area. Here's Steve, I'll have some additional comments at the end.

http://ieeexplore.ieee.org/iel5/5/31355/01457623.pdf

Digital communications

Lead has recently been expelled from many commercial applications and materials (for example, from solder, glass and pottery glaze) owing to concerns regarding its toxicity. Lead zirconium titanate (PZT) ceramics are high-performance piezoelectric materials, which are widely used in sensors, actuators and other electronic devices; they contain more than 60 weight per cent lead. Although there has been a concerted effort to develop lead-free piezoelectric ceramics, no effective alternative to PZT has yet been found. Here we report a lead-free piezoelectric ceramic with an electric-field-induced strain comparable to typical actuator-grade PZT. We achieved this through the combination of the discovery of a morphotropic phase boundary in an alkaline niobate-based perovskite solid solution, and the development of a processing route leading to highly textured polycrystals. The ceramic exhibits a piezoelectric constant d33 (the induced charge per unit force applied in the same direction) of above 300 picocoulombs per newton (pC N(-1)), and texturing the material leads to a peak d33 of 416 pC N(-1). The textured material also exhibits temperature-independent field-induced strain characteristics.

Lead-free piezoceramics

This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

The invention concerns a quantum cascade laser comprising in particular a gain region (14) consisting of several layers (20) each including: alternating strata of a first type (28) defining each an AllnAs quantum barrier and strata of a second type (28) defining each an InGaAs quantum barrier, and injection barriers (22), interposed between two of the layers (20). The layers of the gain region (14) form each an active zone extending from one to the other of the injection barriers (22) adjacent thereto. The strata (26, 28) are dimensioned such that: each of the wells comprises, in the presence of an electric field, at least a first upper subband, a second median subband, and a third lower subband, and the probability of an electron being present in the first subband is highest in the proximity of one of the adjacent injection barriers, in the second subband in the median part of the zone and in the third subband in the proximity of the other adjacent barriers. The laser is formed by a succession of active zones and injection barriers, without interposition of a relaxation zone.

https://science.sciencemag.org/content/sci/264/5158/553.full.pdf

Quantum cascade laser

Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Recent progress in relaxor ferroelectrics with perovskite structure

STIMULATED EMISSION OF RADIATION FROM GaAs p‐n JUNCTIONS

We report measurements of the optic index of refraction as a function of temperature, $n (T)$, in the crystalline ferroelectrics having the simple perovskite ($\mathrm{AB}{\mathrm{O}}_{3}$) structure. We show that these crystals possess a local, randomly oriented, nonreversible polarization below a temperature ${T}_{d}$ several hundred degrees above the ferroelectric phase-transition temperature ${T}_{c}$. Using a simple model, we account for this behavior and understand quantitatively the values of ${T}_{d}$. This model, we believe, contains the basic physical understanding of ferroelectrics with a diffuse phase transition.

Crystalline ferroelectrics with glassy polarization behavior

Glassy polarization behavior in ferroelectric compounds Pb(Mg13Nb23)O3 and Pb(Zn13Nb23)O3

A complete study of the lattice-dynamical behavior of the ferroelectric tetragonal perovskite PbTi${\mathrm{O}}_{3}$ has been carried out using Raman spectroscopy. The temperature dependence of all the long-wavelength mode frequencies are determined. We show that a damped-harmonic-oscillator model with a frequency-independent damping coefficient is sufficient to explain the observed shape of the soft $E(1\mathrm{TO})$ mode in the ferroelectric phase at all temperatures below ${T}_{c}=493$ \ifmmode^\circ\else\textdegree\fi{}C. Moreover, by combining our experimental mode-frequency data with pyroelectric measurements of the change in spontaneous polarization ${P}_{s}$ with temperature, we obtain values of ${P}_{s}(25 ^{\ensuremath{\circ}}\mathrm{C})=81$ \ensuremath{\mu}C/${\mathrm{cm}}^{2}$ and ${P}_{s}({T}_{c})=42$ \ensuremath{\mu}C/${\mathrm{cm}}^{2}$. This is in excellent agreement with a recent direct experimental measurement. The temperature dependence of all the mode strengths has also been determined to ${T}_{c}$. These results are used to extract the temperature dependence of the clamped dielectric constants. In PbTi${\mathrm{O}}_{3}$ the dielectric constant along the ferroelectric axis ${\ensuremath{\epsilon}}_{c}$ is determined primarily by the lowest frequency ${A}_{1}(1\mathrm{TO})$ mode at all temperatures to ${T}_{c}$, in contrast to BaTi${\mathrm{O}}_{3}$ where in the ferroelectric phase the lowest mode determines only $\ensuremath{\approx}25%$ of ${\ensuremath{\epsilon}}_{c}$. In PbTi${\mathrm{O}}_{3}$ the dielectric constant perpendicular to the $c$ axis ${\ensuremath{\epsilon}}_{a}$ is also determined by the lowest $E(1\mathrm{TO})$ mode at all temperatures. The possibility of observing critical effects near ${T}_{c}$ in the soft-mode data of PbTi${\mathrm{O}}_{3}$ has been examined. These effects are not observed. Also, it is shown that very careful fitting of the soft-mode temperature dependence to a functional form containing a minimum number of separately determined parameters is required before critical effects can be invoked in first-order phase transitions of the displacive type.

Lattice Modes in Ferroelectric Perovskites: PbTi O 3

It is shown that Raman scattering from polycrystalline piezoelectric solids contains all of the essential features of Raman single-crystal spectra even when the crystal spectrum is quite anisotropic As an illustration of the Raman powder technique, the ceramic ferroelectric-antiferroelectric system PbTi${\mathrm{O}}_{3}$-PbZr${\mathrm{O}}_{3}$ has been investigated and the "soft" $E(\mathrm{TO})$ optical phonon modes measured in the tetragonal ferroelectric region

Gerald Burns

Papers

STIMULATED EMISSION OF RADIATION FROM GaAs p‐n JUNCTIONS

Crystalline ferroelectrics with glassy polarization behavior

Glassy polarization behavior in ferroelectric compounds Pb(Mg13Nb23)O3 and Pb(Zn13Nb23)O3

Lattice Modes in Ferroelectric Perovskites: PbTi O 3

Raman Spectra of Polycrystalline Solids; Application to the Pb Ti 1 − x Zr x O 3 System