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R & D Review


No.98 October 2001

Development of Advanced Wave Absorber for Electronic Toll Collection System

A group lead by JHRI (Japan Highway Public Corporation Research Institute) has come up with a counter measure to control the multiple reflection of radio waves from peripheral structures such as the toll gate canopy, a problem which emerged in the last stages of development.
Based on this countermeasure method, this report describes the development of microwave absorbing panel mainly applicable to the lower part of the canopy and installation work at the sites of the toll gate.
In designing absorbing performance, we have simulated a density gradient FP absorber, a main body in three layer construction in order to secure the required incident angle characteristics, particularly absorbing characteristics at the time of high incident angle.
Furthermore, we have succeeded to greatly improve its absorbing performance by finding the optimum combination with surface sheet according to theoretical calculation.
In designing the panel structure, we have developed a special T shaped nut, and safety measures to prevent the panel from falling.
With regard to safety, the wind-resistance was tested at wind velocity up to 60m/second by using real panels, and sufficient mechanical strength has been confirmed.
In addition, we have developed a panel which can be directly attached to curved surfaces, such as on the column or the eaves of the canopy, thereby capable of attachment to various structures.
Our microwave absorber is expected to acquire high reliability for ETC (Electric toll collection) systems, which is scheduled to be gradually introduced at more than 900 toll gates all over the country.
[Key words] ETC, ITS, Multiple reflections, Electromagnetic absorber, Oblique incidence

Flame-Retardant Optical Fiber

In recent years, as high-speed, large-capacity communication using optical fiber network expands not only to main networks but also to each individual home, an urgent demand for light emitting and accepting modules is also increasing.
The optical fibers used in optical transmisson system (ex.from light-emitting or light-acceptance module to some eqipment) are demanded for flame-retardant properties and several environmental properties.
We have developed flame-retardant optical fibers for high performance by using the most suitable coating material and optimum manufacturing technologies.
Our flame-retardant optical fibers conforms to UL 1581 1080 VW1 , GR-468-CORE (Fomer Bellcore TA-NWT- 000983) and MIL-STD-202-103.
[Key words] Optical fiber, Flame-retardant, Environmental properties, Pistoning, Projection

A Study on the Structure of Strain Sensing Cable Using Multi-Pointed Fiber Bragg Gratings

Optical distortion distribution was evaluated using an optical fiber having Fiber Bragg Gratings (FBGs) incorporated in an optical fiber cable. The cable has an oval structure allowing the cable to bend only in one way. The fiber for measuring distortion have FBGs with different wavelengths fabricated periodically on a single fiber. The fiber with multipointed FBGs has the same mechanical strength as telecommunication fibers by UV exposed over the coating. As a method for controlling the reflecting wavelength of each grating, various tension was applied to the fiber during UV exposure. The slotted rod incorporating FBG fabricated optical fiber is an oval structure having an X-Y stiffness ratio of 5:1. Linear slots incorporate the fibers to be in one direction. Using this as the core, a covering tape layer is wound and a polyethylene sheath is covered over to be made into an oval structure. The strain distribution induced by bending the cable was observed. The distortion differed according to the bending point of the cable. The bending distortion can be controlled by the placements of FBGs and also by the way the fiber is secured. We were successful in locating the place of distortion.
[Key words] Fiber Bragg Grating (FBG), Optical fiber cable, Strain sensing, Unsymmetrical, Bending, UV exposure over the coating

Development of the Optical Fiber Circuit Sheet

In recent years high speed transmission and increase in transmission capacity is demanded in transmission devices such as telecommunication switching systems and computers. As a result, optical interconnection is replacing metal interconnection for intra-board communication, inter-unit communication and backplane in telecommunication systems. We suggest optical fiber circuit sheets as the transmission medium for various optical interconnections, and studied the method of calculation for its mechanical reliability of the optical circuit sheet depended on pattern design.
[Key words] optical fiber circuit, interconnection, reliability design

Development of a Low Noise Optical Automatic Gain Controlled EDFA for WDM Systems

Recently, Erbium Doped Fiber Amplifiers (EDFAs) have been intensively studied in transmission systems and Wavelength Division Multiplexing (WDM) systems of optical networks for their high ability. EDFAs have become an important component in the all-optical-networks. The EDFAs’ slow upper state dynamics makes its gain sensitive to random burst signals, signal add/drop, and system reconfiguration in high bit rate digital transmission systems. The conventional optical automatic-gain-clamped (OAGC) EDFAs have been investigated to restrain the transition of the gain. A loop is placed in a component of the OAGC EDFA which is a different route from the signal optical route. The optical oscillation is made in that loop using the amplification power of the EDF, achieving a constant gain of the signal by this oscillation. However this OAGC EDFA has a high Noise Figure (NF), because the optical oscillation necessary for the constant gain, results to a high NF. We developed a Hybrid-type Automatic-Gain-Controlled EDFA (HAGC EDFAs), which has electrical and optical feedback. HAGC EDFA has a monitor for the power of the loop light. The loop light is maintained at a state just before oscillation by controlling the loop light power. HAGC EDFA has constant gain equal to OAGC EDFA. The NF of HAGC was lower than that of OAGC (max. 2.1dB) equal to that of the normal EDFA by the new feedback method (electrical and optical hybrid). HAGC EDFA has equal temporal response characteristics. The transition of the power is small (ΔP<=0.12dB) and the response time is short (T<=0.5ms) when the input signals have three CW signals and a switched signal. Additionally the HAGC EDFA has lower power consumption than the OAGC EDFA by low pump laser power, controlled by electrical feedback. HAGC EDFA is low noise optical automatic gain controlled EDFA for WDM systems with low power consumption.
[Key words] Optical fiber amplifier, Automatic gain control, Low noise figure, Feedback, WDM, Energy-saving

Development of High Efficiency Amplification of L-band EDFA Using a Pump Wavelength of the 1.53µm Region

Recently, erbium-doped fiber amplifiers (EDFAs) which amplify the L-band signals are being developed to increase the transmission capacity of wavelength division multiplexing systems. However, except for special setups, the EDFAs using a conventional pump wavelength have a low power conversion efficiency because of their amplification process of the 1.55µm region emission at the front end of the EDF and re-absorption at the output portion of the EDF.
In this paper, we suggest a use of the pump wavelength of the 1.53µm region for an L-band EDFA. The L-band amplification process can be decreased by using this pump wavelength. Additionally, the absorption spectrum peak of erbium-doped silica glass is in the 1.53µm region. Therefore the pump light is absorbed more in the 1.53µm region than the 1.48µm or 0.98µm region. As it is more efficient to use a 1.53µm region light as the pump light in the EDFA, the power conversion efficiency will be improved. Results show that the 1.53µm region has more than twice the power conversion efficiency as the 1.48µm region at the signal wavelength of 1600 nm.
[Key words] L-band, EDFA, Pump wavelength of the 1.53µm region, Power conversion efficiency

A Study on Recycled Polyethylene Materials for Cable Sheath

The present recycling rate of cables and sheath materials is only 20% including thermal recycle, the rest is thrown away for landfills.
In answer to growing concerns for material recycling, we considered the recycling of polyethylene sheath materials used on metal communication cables. The outer sheath of discarded cables were recycled and their characteristics were evaluated.
As a result, we found that any polyethylene material recycled from an outer cover of PE, LAP or STAL sheath structures could be recycled to be used for metal communication cables. Furthermore, these recycled polyethylene materials could possibly be used for optical fiber communication cables, though technical evaluations are still necessary to be definite.
[Key words] Ecology, Recycle, Reproduce, Polyethylene, Sheath material, Metal communication cables, Optical fiber communication cables

Development of Cold Shrinkable Joint for 66/77kV XLPE Cables

Tape-wrapped Joints (TJs) have been mostly used in the 66/77kV XLPE cable systems for over 30-years since its development. However,TJs are the joints which require certain jointing skills and time in assembly. Recently, in Japan and abroad, cold shrinkable joints of one piece type consisted of silicone or ethylene-propylene rubber are being rapidly used, extending to the extra high voltage class for its compact and skill-free merit.
We have developed the 66/77 kV cold shrinkable joint using the pre-expanded-block-insulator. This report describes the characteristics and tested results of the developed joint.
[Key words] Cold shrinkable type, Silicone rubber, Pre-expaned-block-insulator, Compact, Skill-free

Development of Cable Terminations for New-model Medium Voltage Switchgear

MITSUBISHI ELECTRIC CO. has developed SF6 free and space saving switchgear, the HS-A and HS-X series based on new air and solid insulation technology of design and development technologies of medium voltage switchgear.
MITSUBISHI CABLE INDUSTRIES, LTD. have developed cable terminations which are air insulated and can be used in confined spaces complying with the HS-A and HS-X.
The size of the HS-A termination has been decreased and is air insulated resulting from improvement of the ribs of the bushing and applying barriers around the conductor. Testing has already shown that the termination of HS-A has connecting construction and characteristics which are equal to the previous air insulated terminations and comply with electric utility standard. The termination for HS-X has a compact and simple handling design. Its construction and characteristics comply with IEEE Std. 386 and also meets domestic requirements.
Each type of termination has already been put into service, and is working favorably.
[Key words] SF6 free, Air insulation, Dry air, Compact switchgear, HS-A, HS-X, Termination, Barrier, IEEE Std. 386

Insulation Diagnosis on 22kV XLPE Cable by Residual Charge Measurement

Authors paid attention to "Residual charge method" as an insulation diagnostic technique for over 22kV XLPE cables as follows;

  • Electrical charge is accumulated by DC voltage application in water tree. Furthermore, the electrical charge is released by AC voltage application and detected as a deterioration signal.

First, we investigated the mechanism of occurrence of residual charge in an XLPE cable, and paid attention to the difference of relaxation time between residual charge accumulated in water tree and residual charge unrelated with deterioration parts. We confirmed ways of discriminating between the deterioration signal and error signal by extracting fast relaxation charge.
Next, we developed the way of extracting fast relaxation charge by advancing the measurement circuit and the method of AC application. As a result, it was confirmed that there is a relationship between fast relaxation charge and deterioration level of 22kV XLPE cable.
In addition, this technique has been conducted at 22kV XLPE cable circuit on site and has been confirmed of its usefulness.
[Key words] Water tree, Deterioration diagnosis, XLPE cable, Relaxation time, Residual charge

Development of Fault Detector for Underground Distribution Systems

In underground distribution systems, a high voltage cable is coordinated with the required parts via ground installation type multi-circuit switch by a pi loop. The electric power supply is carried out to customers through ground installation type transformer from each multi-circuit switch. When a fault occurs in such an underground power distribution system, locating the fault section takes time, and there are long periods of electric power failure has been many cases. Therefore the development of a fault detecting equipment with high accuracy has been desired. For quick restoration of the high voltage cable system accidents containing multi-circuit switches, the ground fault detection display for accident detection was developed. The equipment is compact to fit in a multi-circuit switch, and operates on a non-power supply. Its performance was found to be good by an examination of operation and field examination.
[Key words] Ground fault, Underground distribution system, Non-power supply, Fault detector

Installation of Road Heating System by Paving with Work Cars Running Directly Over the Road Heating Units

We have had over 35 years of experience on Road heating systems which prevent road surface freeze and melt fallen snow. We have worked in cold areas, especially in the Hokkaido area and have gained the trust of our customers. In the conventional method of paving over road heating units, paving had a protection layer which covered the heating units and work cars did not run directly over the road heating units. However in the recent Meishin superhighway construction, it was necessary to pave the roads mechanically by work cars due to limited lanes and shorten the construction term. There were two problems with the conventional method. One was that the asphalt mixture reaches 160°C, another was a risk of damaging the heating cables by being caught on the running work cars. As an improvement, we used the heating cables which had high heat resistant vinyl sheath of 1.4mm thick, and arranged the heating cables lengthwise in the direction of running cars in order to take advantage of the cable strength. As a result, we succeeded to install of Road heating system by paving with work cars running directly over the road heating units.
[Key words] Road heating system, Paving with work cars running directly over the road heating units, Preventing freeze on road surface, Melting snow, Asphalt paved road

Development of Lithium-Ion Polymer Batteries

Various portable equipment including cellular phones, PDA (Personal Digital Assistant) and notebook PCs are spreading around the world for their functionality. However, this also means growing demands for thinner and smaller batteries having superior performances.
Based on our experience in producing lithium ion batteries, we have succeeded in producing lithium ion polymer batteries with superior low temperature and high rate performances using our electrode and material technologies in combination with our polymer technology.
As a result we have accomplished the MP383562 polymer cell which can discharge at -20°C an 1C current rate and also exhibits superior 2C rate performance. Evaluation results confimed the safety of the product.
[Key words] Lithium-ion polymer battery, Lithium-ion battery, Low temperature performance, High rate performance, Solid polymer electrolyte

Development of Environmental Recognition Devices

When a micromachine works inside a narrow space inside tubes and equipment such as a microfactory, a microdevice that has a visual function is indispensable. To monitor the minute shapes of microfabrication and microassembly process that are impossible to observe, fiberscope types of environmental recognition devices have been developed. The devices are designed to allow stereoscopic and microscopic observation and to measure the dimensions of microparts. To achieve these goals and to realize minute structures and functions, we developed a micro stereoscope, a microscope with a fiber-optic tactile sensor, and shape memory alloy (SMA) actuators that can bend the tip in any direction with high precision. A micro stereoscope that is 2 mm in outer diameter with the parallax mechanism using an optically driven balloon actuator can vary the binocular parallax. To obtain the microscopic image, a contact scope is used. The contact scope obtains the near field image and can observe structures that are even smaller than the outer diameter of the contact scope. The tip articulation mechanism can bend approximately 60 degrees and returned to the straight position when a current is applied to each of the SMA coil springs. In a microfactory, visual inspection mechanism such as measuring sizes of micro-gear molds and assembling states of gear train have been confirmed using the devices. Since environmental recognition devices are very thin and have no electrical leads, they can even be used in the human body. The results show that easy and safe environmental recognition is possible in the narrow spaces of a microfactory.
[Key words] Fiber-optic sensors, Optically driven actuators, Environmental recognition, Microfactory

High-Average Power Optical Parametric Oscillator Based on PPMgLN

We have demonstrated high average power, room temperature operation of PPMgLN OPO. A high brightness, high repetition rate Q-switched Nd:YAG rod laser was used as a pump laser and the PPMgLN of 1mm-thickness was used for OPO. Maximum conversion power of 60.2-W with conversion efficiency of 61.1 % was obtained for signal wavelength (1.57µm) and idler wavelength (3.3µm).
[Key words] Lasers, All solid state lasers, Nd:YAG, OPO, PPLN, PPMgLN

Development of High-Power Ultraviolet Light-Emitting Diodes Using Lateral Epitaxy on a Patterned Substrate

Fabrication of low-dislocation-density GaN using the lateral epitaxy on patterned substrates (LEPS) was studied. GaN was grown on a sapphire substrate, which had patterned parallel grooves along the <11-20>GaN direction. As a result of GaN growth, a shape of GaN, which was completely covered by a {1-101} facet was formed. Subsequently lateral growth was encouraged, resulting in a flat-surfaced. Dislocation density were 1.5 × 108cm-2 which was one- third of GaN grown on a planar substrate. This is attributed to effects by which a dislocation is bent by facets. Ultraviolet (UV) light-emitting diodes (LEDs) were fabricated using LEPS. The LEPS-UV-LED chips were mounted on the Si bases in a flip-chip bonding arrangement. When the LEPS-UV-LED was operated at a forward-bias current of 20 mA at room temperature, the emission wavelength, the output power and the external quantum efficiency were estimated to be 382 nm, 15.6 mW and 24%, respectively.
[Key words] GaN, UV-LED, Dislocation, ELO, MOVPE

Development of Caselanceless Connectors

In the new trend of car electronics, wire-harness volume has been enlarged due to new additional application of electronic requirements. Within an automobile wire-harness, the most crucial components are connectors, which require an especially electrically stable contact function. However wire-harnesses are still a labor-intensive product due to its particular assembling process. To keep up with the progress of car electronics, the circuit number of wire-harnesses are increasing. As a result, further increase in power consumption has consequently brought about more consumption of oil fuel together with consequent environmental issues.
With the advent of the car age, the car industry is faced with new environmental issues to be solved. Development competition for survival toward clean energy among carmakers has been intensified in many ways as seen in design change of the power supply system from the current 14V to 42V, electrification of engine power and ultimate target, development of a fuel-cell car.
Under these circumstances, needs for weight reduction and compact designing of wire-harness connectors, together with achieving higher reliability are strongly requested. To implement weight reduction and compact designing it is also necessary to pay attention to the designing and handling of connectors, as they are the very parts, which have caused many defects through wrong handling. This has been proved and identified by various survey reports on contact failure of connectors.
Our newly developed connector "CASE-LANCE-LESS" is a much-improved connector where in the lance on the connector housing is shifted to the connector rear-holder side without losing its basic function. The innovation has not only solved problems which conventional connectors held but also has brought success in achieving work efficiency and easy maintenance together with high performance and substantial cost reduction.
[Key words] Connector, Wire harness, Case lance, Weight reduction, Compact design, Work efficiency, Easy maintenance.

FEM Analysis for Multi-Layer Steel Cylinder Head Gaskets

We have established the evaluation method of the compression/recovery properties of beads, formed on Multi-Layer Steel cylinder head gaskets (MLS), with 2-D axisymmetric Finite Element Method (FEM). To respond quickly to various situations, we have also developed analysis-support applications that shorten the time spent for making models, setting analysis conditions, and have built a database system of material properties.
Applying this method to developing and designing process of MLS, we were able to save cost and time. Furthermore, we found out the weak points of bead under large stress or strain, and to evaluate the durability of MLS.
[Key words] Multi-Layer Steel cylinder head gasket (MLS), Finite Element Method (FEM), Compression/recovery property, 2-D axisymmetric analysis

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