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By A. Gakwaya, P. Vachon-Joannette, P. Gagnon, J. Lévesque

"Predictive numerical methods are essential tools for reduced development cost and improved high performance designs of modern aircrafts. Their use leads to savings in terms of design cycle time and experimental trials. Composite materials subjected to impact loadings demonstrate various damage modes such as matrix cracking, fiber breakage, delamination and, ultimately, fabric fracture. Composite laminates are extensively used in the aerospace industry, and their damage modeling is complex due to their inhomogeneity and anisotropic behavior. Damage evolution affects both in-service properties and performance of these composites. In this work, the drop-weight impact test has been simulated. Using a material model that accounts for both delamination and intralaminar damage, laminates response is analysed using numerical simulations based on 3-D finite-element models of the commercial code Abaqus/Explicit. Experimental and simulation results are compared, in terms of energy absorption and contact force. The obtained numerical results show good agreement with experimental data.INTRODUCTIONAs primary aircraft structures are increasingly being made from advanced fiber-reinforced polymer matrix composites and are in general exposed to a variety of impact scenarios (bird, hail, debris etc.), an understanding of the impact event and the performance of composite materials during impact is important in the development of new structures. This work is focussed on low velocity impacts that typically occur when foreign objects hit the aircraft during maintenance or other on-the-ground operations. These impacts can cause non visible damage that affect the structural integrity of the composite components. While for metallic structures, damaging impact events typically leave noticeable dents due to plastic deformation, in contrast, for high strength carbon fiber reinforced composites, they can deform elastically to strain levels exceeding 1% and the internal damage can often occur without the formation of a visible dent. The identification and effect of impact damage on the performance of the structure is thus of great concern to the aircraft industry as the durability and damage tolerance of these composite structures are strongly influenced by the size of detectable internal damage."

Jan 1, 2016

By Y. Mitani, H. Ikemi, K. Kitamura, H. Honda

"Instead of carbon capture and geological storage (CCS) that does not rely on structural aquifers, injecting carbon dioxide into sedimentary rock deep underground has been considered. For advection velocity of the fluid is slow, the permeability of sedimentary rock deep underground is low. In order to perform the CCS on the low permeable sedimentary rock, it is necessary to clarify the behavior of long term storage properties of carbon dioxide (CO2).In this study, the permeability and storativity of CO2 injected into low permeable rock has been evaluated. The injection of supercritical CO2 has been conducted on the specimen of Ainoura sandstone (unit weight: 2.39 g/cm3, porosity: 11.9 %) saturated with water by using flow pump method. The experiment has been set up to reproduce the similar condition of deep underground reservoir under 20 MPa confining pressure, 10 MPa pore pressure, 35°C temperature and 3 µl/min CO2 injection rate. In order to prevent an increase in pore pressure, the boundary condition on the outlet side of specimen has been kept a constant pressure.As a result, it has been possible to observe step by step the change of the differential pressure between both ends of specimen. Furthermore, the relative permeability and specific storage of rock under supercritical CO2 injection has been examined by the theoretical analysis of flow pump permeability test incorporating Darcy’s law for two-phase flow. It is observed that CO2 has been transmitted gradually while CO2 stored in the rock. It is also clarified that residual water has existed in specimen after showing the constant differential pressure in the end of the experiment. Using the results of the experiment, 3D core-scale flow-simulation by using TOUGH2 has been conducted due to confirm the flow of fluid and CO2 distribution in the specimen. From the experimental results and analytical solution to them, permeability and storativity are identified, and simulation results support the validity of the experimental results."

Jan 1, 2015

By Jin Li

The tensile properties and microstructure of AZ91 Mg alloy before and after equal channel angular extrusion (ECAE), and the fracture behavior during tensile testing for as-extrusion and ECAE AZ91 were investigated. The alloy was performed ECAE from one to eight passes at 498K. The elongation decreased with the pass number increasing after ECAE. Grains were refined, partial coarse ß-Mg17Al12 phase fell to pieces, fine ß-Mg17Al12 precipitated in the AZ91 Mg alloy after ECAE. During tensile test the a-Mg/ ß-Mg17Al12, a-Mg/Al8Mn5 interface and the grain boundaries in a-Mg matrix acted as the crack initiation sources. The frequency of micro-cracks at the a-Mg/ß-Mg17Al12 interfaces and grain boundaries increased after ECAE, which accelerated the growth and coalescence of the micro-cracks during tensile test and resulted in the decrease of elongation of AZ91 Mg alloy by ECAE.

Jan 1, 2006

By J. W. Coetzee, H. E. Deist

Carbon-in-pulp (CIP) and Carbon-in-leach (CIL) processes are used extensively in the gold mining sector to recover aurocyanide from solution. This paper discusses the modelling of these operations, using various simplifying assumptions, in order to simulate the effect of changing operating conditions on the dynamics of the system. It is assumed that the adsorption and leaching rates are a function of concentration difference between the source phase and recipient phase. The simulation was set up using Matlab's Simulink interface. Plant variables are solved using a medium scale Newtonian search algorithm in Matlab, where the differences between the actual and predicted plant outputs are minimized on a continuous time-line.

Jan 1, 2005

By E. Yan, M. Mankosa, E. B. Wasmund

Mechanical cells are the dominant unit operation in base metal rougher flotation applications worldwide. As economic demand for metals increase, and as the feasible ore grades decrease, the installed capacity of mechanical flotation units worldwide has greatly increased, adding significant capital and operating cost. One opportunity to improve this situation is to use fundamental knowledge to make the industrial flotation process more efficient. A key insight is that the flotation process can be optimized by dividing the processing of the pulp into two distinct fluidic environments; a collection cell where air and pulp mix in a highly energetic compartment, and a low energy gravity separation cell. This is the basis of the “2-stage flotation device” that has been patented by Eriez and marketed under the tradename StackCell™. Two industrial case studies will be presented to highlight the potential metallurgical and commercial advantages of the StackCell. In the first, a train consisting of three pilot scale StackCells (each 0.6 metre diameter) was run in parallel with a train of conventional mechanical cells in a major copper concentrator and benchmarked against a batch Denver test. In the second, the performance of a 3 metre diameter StackCell in a nickel sulfide cleaning application was benchmarked against a batch Denver test. The flotation kinetics observed in the StackCells were 2.4 to 2.9 times faster when compared with the lab Denver test. In the first case study, the kinetics of the StackCell was about six times faster than conventional mechanical cells. It is hypothesized that the efficiency improvement in kinetics is because of reduced “drop-back” during the froth recovery phase, which is reduced because of the reduction in the shear that is present in a conventional mechanical tank cell. This result suggests that a 2-stage flotation system can be used to reduce the working volume of flotation units by five to six times. This would allow operators to significantly reduce the size of their flotation lines for a comparable flotation objective. Some discussion will follow about the scale-up criteria, maintenance and operability issues, comparisons of layout, and possible cost savings. INTRODUCTION The solution that most equipment suppliers have offered to reduce the cost of mechanical flotation equipment over the last 30 years has been to increase the size of the flotation unit cell (Mankosa, 2017). For example, three 100 m3 machines with three smaller motors, mechanisms and control valves could be replaced with a geometrically similar 300 m3 with a larger version of each ancillary component. While there are some efficiencies and cost improvements to be gained by this approach, it does not take advantage of fundamental insights into the flotation process, and it does not represent a step-change in terms of process design or economic benefit for the customer. The advantage of the “bigger is better” approach is that there is past experience of incremental improvements by making cells larger and there is a well-established scale-up method, which allows practitioners to estimate equipment capital costs based on very simple laboratory test- work. A different paradigm, which is gaining interest rapidly is to use a unit operation in which it is easier to optimize the flotation process, which will be described in this paper. This approach is often referred to “2- stage flotation”. Because this approach is new, it is important to benchmark it against existing conventional technology and to demonstrate a robust methodology for sizing equipment and flowsheets. This paper aims to address these issues with two case studies.

Jan 1, 2019

By Michael Bowker

Au/TiO2 catalysts were prepared by incipient wetness impregnation and tested for the room temperature photocatalytic reforming of methanol in aqueous solution. These catalysts proved to be more active, on a molar basis, than Pd/TiO2. The dependence on loading of gold was different from that of palladium, showing a double maximum in yield at 0.1 and 2 wt. % with low rate below 0.01% and above 10%. A model is proposed for the reaction involving band gap excitation of titania electrons which are used to oxidise the methanol via adsorbed CO. With palladium, photoreforming of CO and water can be achieved, but this is much less effective on gold, presumably due to the much weaker bonding of CO on Au.

Oct 1, 2003

By J. M. R. Carvalho, M. T. A. Reis, M. R. C. Ismael, M. J. N. Correia, S. M. C. Santos, J. M. Carvajal

A sulphide zinc concentrate (Zn-40%) has been leached in sulphuric and chloride media to optimize the conditions for the recovery of zinc and copper. Previous results showed that extractions of 95% zinc and 20% copper can be achieved in just one stage, after two hours of leaching at 80°C with a solution 0.5M in Fe2(SO4)3 and H2SO4 and a solid/liquid ratio of 5%. This work presents the results obtained in the leaching experiments carried out in sulphuric and chloride media using two and three crosscurrent stages and a countercurrent process simulation for a solid/liquid ratio of 10%.

Jan 1, 2008

By J. A. Eisele, D. L. Pool

"The Bureau of Mines has developed a particle agglomeration technique to improve the flow of leaching solution through heaps of low-grade gold-silver ores which contain clays. Benchscale experiments and industrial practice have shown that the percolation rate of cyanide leaching solution is greatly enhanced by mixing the ore with Portland cement as a binder, moistening the mixture, mechanically tumbling to form agglomerates, and aging before heap building and leaching. A slight modification ofthe technique allows its application to precious-metal-bearing tailings, which cannot normally be treated by heap leaching because they are too fine. IntroductionMany low-grade gold and silver deposits and tailing materials from former mining operations in the western United States are potential sources for precious metals. These sources are too low grade or too small to support the capital cost of a conventional cyanidation plant but have stimulated the development of lowcost procedures, such as extraction of the precious metals by heap leaching with cyanide. The Bureau of Mines has investigated methods to improve the recovery ofgold and silver by heap leaching these low-grade materials.For heap leaching to be successful, the crushed and stacked ore must have good permeability so that uniform distribution of the cyanide leaching solution through the heaps can be achieved. Some of the most difficult gold and silver ores to treat by heap leaching are those containing excessive amounts of clays, or fines generated during crushing. Excessive amounts of slimes, generally minus 50-micrometre or 270-mesh Tyler sieve size particles, in the heap feed will slow the percolation of the leaching solution, cause channelling, or produce dormant or unleached areas within the heap, resulting in long leaching periods and low extractions. In extreme cases, the clays or slimes can seal the heap and cause the leaching solution to run off the sides of the heap rather than through it."

Jan 1, 1987

By R. A. Triglavcanin

Delivering dilution water and mixing this water with incoming feed slurry, addition of flocculant, maximising flocculant-slurry interaction to build aggregate size, unabsorbed flocculant percentage, volume average of solids volume fraction, momentum dissipation ratio, dilution recycle ratio, volume average shear, maximum shear rate at exit, aggregate size on exit, uniform discharge profile and more ? all of these need to occur in the right order and in the right proportions within the thickener feedwell, the secret to thickener performance.

May 1, 2009

By T. P. Riordon

"Major swings in the silver price since 1979, along with the ever constant fight to maintain ore reserves has forced United Keno Hill Mines Limited through several unique series of events in order to survive in the 80s.This paper is specifically meant to be a description of safety and productivity improvements achieved to ensure the survival of a silver mining community ill the Yukon. There are, however, other events and conditions that must be described to complete the story and this paper attempts to do that as well IntroductionUnited Keno Hill Mines Limited, a subsidiary of Falconbridge Limited, is the only silver producer in the Yukon. Operations are located in north central Yukon, in and around the small town of Elsa, latitude 62.5 °, about 275 road miles from Whitehorse. The Arctic Circle is about 185 miles due north of the town.Temperatures in 1986 ranged from a high of 28.5°C in July to a low of -37.0°C in November, however, much lower temperatures have been recorded in previous years. Due to the mountainous terrain the town of Elsa is completely in the shade from mid-November until early February, a period of about 12 weeks.The Elsa area, as is most of the north, is considered semiarid with an average precipitation level of about 15 inches. Vegetation, however, is quite abundant though slightly dwarfed at the townsite elevation of 3200 feet above sea level: Many of our operating and exploration portals as well as our open pits are above the tree line. Permafrost in the area has been recorded up to 400 feet below the surface."

Jan 1, 1988

By Ken McClure, Alex Day

Located North of Williams Lake British Columbia, Gibraltar Mine is the fourth largest open pit Copper mine in North America. Gibraltar commenced Copper concentrate production in 1972 with a mill throughput rate of 30,000 tons per day. A series of expansion projects, including installation of a second SAG mill with variable speed drives in 2013, has increased mill throughput to 85,000 tons per day. Over the past 24 months, Gibraltar Mine in partnership with Spartan Controls has executed several advanced process control programming projects culminating in the implementation of a Continuous Speed Controller (CSC) for the most recently installed SAG mill. This paper covers development and results for the SAG mill speed controller. INTRODUCTION In January 2016, the price of Copper fell below $2.00 USD per pound, the lowest price in 7 years. Gibraltar Mine faced a significant challenge; how to maximize profit in an environment where capital spending was not an option. An opportunity was quickly identified to improve performance through increased automation and advanced control of the grinding processes. Beginning in March 2016, Gibraltar Mine partnered with Spartan Controls to introduce Advanced Process Control (APC) to the grinding circuits. The collaboration between metallurgical and process control engineering disciplines proved to be effective for achieving gains in throughput, reliability and productivity for the mill process. The Gibraltar milling facilities include 2 grinding-flotation plants for concentration of chalcopyrite ore with throughput rates of 58,000 tons per day (Concentrator 1) and 38,000 tons per day (Concentrator 2). Each of the two concentrators has a 34’ diameter SAG mill powered by 2 GE 4800 kW synchronous electric motors. For SAG 1 (in concentrator 1), power is transmitted through 2 Eaton Airflex clutches. For SAG 2 (in concentrator 2), the motors are driven by 2 TMEIC Variable Frequency Drives (VFDs). All programming is done using DeltaV, which Gibraltar uses as its Distributed Control System (DCS) and Human Machine Interface (HMI).

Jan 1, 2019

By C. Poon

For slope stability, knowledge of major and minor discontinuity sets that form the rock mass fabric is paramount for pit slope designs. Due to the increased awareness of health and safety in mining projects, efforts have been made to limit structural mapping in order to minimize the risk to personnel associated with approaching potentially unstable areas. Recognizing the importance of such safety precautions, Golder Associates Ltd. is applying a combination of techniques including 3D photogrammetry, conventional mapping and drilling with core orientation to enhance structural data collection. Photogrammetry uses digital photographs to produce a virtual model of a rock mass surface. The application of these techniques will be exemplified through an expansion design of an existing open pit. A comparison of stereonets obtained using these techniques showed some agreements, but also highlighted limitations of each method. The application of photogrammetry was found to be very useful in complementing the other existing techniques.

May 1, 2009

By P. A. Christopher, R. H. Pinsent

"The Adanac molybdenum porphyry deposit near Atlin, in northwestern British Columbia, was discovered in 1905. It was explored extensively between 1967 and 1980.The deposit is within a complex, multi-phase, quartz monzonite stock that is a satellite of the post-accretionary, Surprise Lake Batholith. Biotite K-Ar dates range from 703 ± 2.4 Ma to 71.6 ± 2.1 Ma, indicating a Late Cretaceous age of emplacement.The deposit comprises an irregular-shaped ring or halo peripheral to a quartz monzonite porphyry dome, or ""cupola': The shape of the ring, and of a smal~ fine-grained quartz monzonite intrusion, and the presence of higher-grade mineralimtion on the eastern flank of the cupola, suggest partial control by a preminera/ structure. The deposit is truncated by a steep, northwesterly dipping, normal fault (Adera Fault) that down-dropped the northern half of the deposit by a minimum of 100 mThe deposit lacks strong zonal alteration but there are narrow envelopes of potassic alteration around some veins and local zones of intense wall-rock silicification. There is considerable retrograde alteration along postminera/ faults and fractures.Molybdenite occurs in veins and fractures, many of which are relatively flat-lying. They occur in all phases of quartz monzonite. Molybdenum is the only element of economic significance. There are vein and skarn occurrences with tungsten, tin, lead, zinc and precious metals peripheral to the deposit.In 1981, Placer Development Limited reported an ""undiluted mineable mineral reserve"" of 151 971 000 tonnes grading 0.063% Mo at a cutoff grade of 0.04% Mo and a strip ratio of 1.5:1."

Jan 1, 1995

By I. S. Zajac, Y. O. Oyediran, M. C. Robart

This paper presents an overview of the metallurgical work on the Strange Lake Alkalic Complex (SLAC), from historical development of the "Main Zone" to present day develoment of the "B Zone". The SLAC, originally discovered by the Iron Ore Company of Canada (IOC) in the northeastern Canadian Shield of Québec and Labrador, is one of the world’s largest deposits of rare earth elements (REE) including yttrium and high field strength elements (HFSE) including zirconium, niobium, and titanium. It is part of a Precambrian, post-tectonic complex of peralkaline granites which intruded along the contact between gneisses and monzonites of the Churchill Province of the Canadian Shield. Mineralization of interest at Strange Lake principally occurs within peralkaline granite-hosted pegmatite and aplite sheets and, to a lesser degree, within the host granites, particularly in intra-pegmatitic granites. The highest grade and metallurgically most favorable mineralization is in the upper, open pit mineable parts of the SLAC. Metallurgical development has been conducted under a number of mining companies, and various value metals have been targeted throughout the history of the deposit, including yttrium, zirconium, niobium, and rare earths. Historic processing routes tested have included ore beneficiation, atmospheric leaching, solvent extraction (SX), and metal precipitation. This paper also presents the metallurgical development supporting Quest Rare Minerals Ltd.’s (Quest) 2013 Pre-Feasibility Study (PFS) and 2014 Preliminary Economic Assessment (PEA).

Jan 1, 2014

By Hung-Ming Chen

This paper presents a Cloud-based system framework for providing a web-based building information model (BIM) service. Cloud computing technologies were used to develop a BIM data center, which can handle the big data of massive BIMs using multiple servers in a distributed manner. In addition, the system allows multiple users to access the BIM data center online to submit and review BIMs concurrently. In this study, the advanced technologies/tools of web development and Cloud computing were applied and incorporated to develop a prototype system, named CloudBIM. On the client side, this study applied WebGL and HTML5 in the web-based interface development to achieve the 3D display of BIMs and the dynamic interaction with viewers through browsers. Users can access the services of CloudBIM by using PCs, laptops and tablets anytime anywhere to view the 3D model via browsers, which support WebGL. On the server side, this study used Apache Hadoop, an open-sourced distributed file system based on Google?s technologies, to establish a BIM data center. The Hadoop Distributed File System (HDFS) can utilize multiple servers to provide mass storage spaces in a distributed manner. Based on the use of Apache HBase, which provides Bigtable-like structured storage for HDFS, this study proposes database schema for storing the information from massive BIMs in two bigtables, named Object table and Property table respectively. In addition, Hadoop MapReduce, a Hadoop component for the parallel processing of large data sets, is utilized for model data acquisition by parsing the IFC files of uploaded models in parallel.

Aug 1, 2013

By A. Vasebi, É. Poulin, A. Desbiens, D. Hodouin

Maximizing benefits generated by separation plants in the mineral processing industry is of prime importance. To achieve this goal, observers and controllers are both key tools playing a crucial role for economic optimization. Although these methods have been widely discussed in the literature and that numerous applications have been reported, coupling the different algorithms raises practical challenges. The economic function definition, the selection of the real-time optimization structure, the elaboration of observer and controller models, the controller development, and the tuning of stochastic and deterministic parameters strongly influence economic performances. The objective of the paper is to discuss the major difficulties related to the implementation of a real-time optimization system and highlight the benefits of linking data reconciliation and model predictive control for a simulated flotation plant. A systematic topdown approach is used to go through the main design phases and to comment on the different options available for the development of the optimization structure. An internal model predictive controller coupled with a stationary observer is applied for the direct optimization of a three-stage flotation plant simulator based on a phenomenological model. The results show performance improvements in terms of increased revenues brought by reduced grade variability and collector consumption. The discussion also proposes alternative avenues that could be taken to achieve comparable improvements. Finally, since the limited simulated case-study cannot provide a complete understanding of the benefits brought by a data reconciliation observer, recommendations for industrial applications, which are more complex, are provided to promote effective implementations.

Jan 1, 2016

By Masatsugu Morimitsu

This paper introduces new technology of oxygen evolution anodes which can be applied to produce copper, zinc, cobalt, and other metals by electrowinning. The anode consists of nano iridium oxide particles dispersed in amorphous tantalum oxide matrix as a catalytic layer formed on a titanium substrate. The anode can reduce oxygen evolution potential by 0.25 to 0.55 V compared to commercially available lead alloy anodes and can suppress unwanted side reactions such as manganese oxyhydroxide, lead oxide, cobalt oxyhydroxide which occur during oxygen evolution in the electrowinning solutions. This technology is effective for environmentally friendly electrowinning processes with low energy consumption and less anodic deposition.

Jan 1, 2011

By C. S. Liao, S. L. Wang, C. H. Yan, F. X. Cheng

A significant development in the theory of countercurrent extraction will be presented in this article. A new term in countercurrent extraction process analysis, "Adjacent Stage Impurity Ratio" (ASIR), is proposed, and its expression is deduced. Furthermore, based on the term together with mass balance and extraction equilibrium, the conditions where a given countercurrent extraction separation operation can have minimum amounts of both extracting solvent and scrubbing agent solution can be estimated, and the equations of the two minimum amounts can be deduced. It was found that the equations for a two-component separation using a single aqueous or organic feed are exactly the same as they appeared in the theory initially established in the 1970s. Unlike its earlier version, the present derivation does not involve feed-stage-composition hypothesis, and also has the advantage of dealing with a double-feed system where both aqueous and organic feeds are simultaneously employed whereas the earlier theory can only analyze a separation using a single aqueous or organic feed.

Jan 1, 2014

By C. L. Reichardt

Pressure exerted on gold producers by regulators, project financiers and civil society in the wake of the Baia Mare tailings spill in Romania during 2000 prompted most responsible gold companies to sign up to the International Cyanide Management Code for the Manufacture, Transport and Use of Cyanide in the Production of Gold (the Code). The Code stipulates a ?cradle to grave? approach more comprehensive than that applied to any other mining reagent and poses particular challenges for operators who use cyanide-bearing tailings for backfill. This paper examine some of the challenges for Code compliance facing deep underground gold mines that employ backfill technology, most particularly the requirement to demonstrate that the potential migration of cyanide (and its degradation products) from emplaced backfill will not have an unacceptable impact on worker health and safety or the receiving environment, either during mine life or after closure. Although the Code only contains a single reference to backfill, more careful consideration confirms that most sections of the Code that deal with tailings management are potentially applicable to mines where tailings material is used for backfill, as are certain principles pertaining to aspects of operations, worker safety, emergency response, training and dialogue with stakeholders. For gold mines of the Far West Rand, the most significant cyanide-related risks associated with backfill operations relate to worker exposure to cyanide-bearing seepage and HCN gas. There is potential for seepage of cyanide-bearing water from backfill to compromise the beneficial use of surface and groundwater, and thus impact on downstream users and ecosystems. However, the extreme depth of mining and the specific geological and hydrological controls on the Far West Rand suggest that the potential environmental risks associated with backfill are likely to be considerably less significant than the cyanide-related risks to the workforce.

May 1, 2007

By William H. Pomroy, Kenneth E. Hjelmstad

An underground mine fire can seriously threaten the lives of all personnel in the mine. This fact makes fire emergency planning a high priority in the mining industry. A fire emergency plan includes a means of warning miners of the existence of a fire, and the need to evacuate or retreat to a place of refuge. The warning alarm must be fast and must reach all miners, regardless of their location or work activity. Means of fire warning are varied, and include such methods as stench, flashing lights, telephones, and word-of-mouth (messengers). Unfortunately, none of these methods are entirely satisfactory. Stench can be slow and seldom achieves total mine coverage, especially in high-back room-and-pillar mines with low ventilation velocity. Telephones are effective only where personnel are close enough to hear the phone ring. A novel fire warning alarm system has been developed by the U.S. Bureau of Mines which enables instantaneous warning of all underground personnel. The warning alarm is sent by an electromagnetic signal which penetrates through mine rock from a transmitter to small person-wearable receivers. Each miner's cap lamp battery could be equipped with a small receiver and when a fire or other emergency occurs the miner could be alerted to the danger by a blinking of the cap lamp. Testing of prototype equipment has demonstrated that the transmitted signal is capable of penetrating through over a mile of mine rock and activating the receiver. This paper describes the theoretical basis for through-the-rock ultra-low frequency electromagnetic transmission, design of the prototype transmitter and receiver, test results, and status of commercial development of systems utilizing this technology.

Jan 1, 1994