Nonlinear and Negative Resistance in Loose Electrical Contacts the Dark Bridge - Literature review Example

Introduction. Kubota, H., Sasaki, S., Ishida, H. and Takagi, T. Nonlinear and negative resistance in loose electric al contacts dark bridge. [Online] Available at: http://article.sciencepublishinggroup.com/pdf/10.11648.j.ajpa.20130101.11.pdf [Accessed: 13 Apr 2014]. It is a fact that the contacts of the transmission lines, if not well fitted, lead to interference of the transmission process or may altogether result in injury of the users of electrical devices. For these reasons it is of quite importance that an analysis of loose electrical contacts be done in order to determine the extent of interference the loose contacts may cause to the transmission process. An analysis of the dark bridge in loose electrical contacts reveals nonlinear and negative resistance. This article gives a critical review of the nonlinear and negative resistance in loose electrical contacts dark bridge. The review includes the introduction, research, critical analysis and finally, the conclusion. The authors’ intention of writing the article was to survey and summarise research on a topic in the engineering field. The summary and analysis gives a detailed outline of the voltage-current (V-I) relationship as well as the diameter and thickness of the black bridge. The findings should reveal a non linear and negative resistance in loose electrical contacts at a range of definite values. This article in relation to other works in the same field is important for it provides critical information that will guide designers in their design work especially designers of printed circuit boards. The authors, who are graduate students, outline their points and support them accordingly in a manner that is easily grasped by the learner. An Electrical contact can be defined as a releasable junction between two conductors which is apt to carry electric energy. (Holm, 1981). Electrical contacts are quite crucial for every electrical system for which inefficiency due to contact failure is common. The degradation may be as a result of improper design of the points of contact or of the contacts themselves. (Kubota and Sasaki et al., 2013) Michael Brumbach in his book, Industrial Maintenance, maintains that “mechanical vibrations cause electrical connections to loosen over time. Loose electrical connections cause high resistance connections that result in heat build-up and failure of the termination.” (Brumbach and Clade, 2003) Loose electrical connections and broken wires can be a cause of electrical fire. This happens as follows. The loose connections and broken wires form a molten oxide bridge across a small gap. This molten oxide bridge can glow due to the resistance caused and thus heat up to very high temperatures sufficient to cause a major fire. (Slade, n.d.) Experiments have revealed interesting relationship between electrode temperature and contact resistance. It has been observed for instance, that the resistance (electrical) of Palladium (Pd) becomes high with time while the contact resistance doesn’t. This phenomenon is quite crucial, for it enables us to make predictions on how to reduce the résistance of Pd and any other electrodes used in a circuit. Reducing the resistance is similar to reducing the energy lost due to Joule heat which enhances efficiency of the system. (Tbgu.ac.jp, 2014) Below is a graph showing the relationship between contact resistance and electrode temperature of Pd. This graph gives the probability of reducing the electric energy loss. We see the graph displaying a non linear behaviour when the electrode temperature increases with time. It also shows minimal increments of the value of the contact resistance. The electrodes are heated by a halogen heater. Given that this concept attracts much attention, it has since been investigated widely. Thus, more precise methods of measurement have been developed in order to realise more accurate values that lead to a closer prediction. The method of cantilever has gained wide acceptance for its precision and is most employed. We know that the contacts are used in switches, relays and connectors and as such, an appreciable high level of performance is expected of these circuit devices. Researchers have devoted a good amount of time in the contacts phenomena and they have presented their findings in diverse manners. In order to adequately understand the nonlinear and negative resistance in loose electrical contacts, we must have a basic knowledge of the arc phenomena. With this we will be able to relate the findings of the experiment with the concept being evaluated. The experiment must be carried to determine different contact resistances at different bridge distinction gaps. Different conditions must be employed during the experiment such as separation at different speeds to enhance the accuracy of the final results. During the experiment, that involves the digital separation of the contacts, the step by step process is of importance. As the experiment progresses, contact voltage waveforms are observed and recorded. It is observed that the shape of the waveform is convex. Voltage rise and fall (transient) is noted at every step separation as the process continues and approaches the steady state. It is observed that the transient occurs in areas near the contact spot. The process approaches steady state due to the electrode halt. Given that the each separation starts at the thermal steady state, it could thus be expected that the contacts phenomena be evaluated at every step separation point. Most crucially, it is observed that the contact voltage falls at a certain fixed gap. At extremely low separation speeds, a single dark non-luminous bridge is observed between the contact points. This is as are result of the thermal steady state at the bridge is held. The separating speeds must be sufficiently slow to hold the thermal equilibrium state. It may appear funny why electrodes continue conducting after separation. This is as a result of microscopic asperities on the surface of the contacts that aid in the conduction. The microscopic asperities act as contact points that allow for current flow. It is observed that there is also a relationship between the surface roughness and the contact resistance. The dark bridge between the electrodes, which is the item of interest in this case, may not be viewed with the naked eye but with the help of a microscope. The size is in the order of micrometer (μm). The size of the Fe dark bridge is larger than that of the Pb. This may be as a result of difference in material properties. The size of the dark bridge can be easily estimated from an enlarged image. The relationship between the bridge diameter and length results in an exponential function. In their experiment, the authors used sample electrodes of Pb Fe. This was well worth if because it enables the researchers to have a range of values that can be compared. The students reported that the dark bridge was so small that they had to use powerful microscopes in order to view them. Analysing the voltage and current characteristics, we will first begin with what we know about the voltage current characteristics then we shall proceed to see how the authors did their analyses. We know that the voltage current characteristics (V-I) or V-I curve is a relationship mostly represented by a graph or chart between the potential difference across a device in a circuit and the current through the circuit. These graphs and charts are important to electrical engineers given that they help them predict device behaviours and parameters at different conditions. Thus they will be able to model the device in an electrical circuit. The authors sought to use the V-I characteristics to predict the characteristics of the dark hole. This is quite important since they will have demonstrated their theories in an acceptable manner. Voltage-current characteristic analysis is one of the best and acceptable ways to predict device behaviour or parameters in the electronic field. This move gives quality to their article and thus strengthens it. Godse and Bakshi argue, when they are analysing diode characteristics, that another way to examine the V-I characteristics is to use of only straight lines. (Godse and Bakshi, 2014, pp. 2-42) they further their argument and say that the characteristics of a diode are called the peace wise linear diode characteristics. A simple voltage-current graph of a bipolar junction transistor is shown below. From the voltage and current characteristics of a BJT, we are able to predict the transistor parameters. So, with the voltage current characteristics of the Dark hole, we should be able to predict the characteristics of the dark hole appreciably. Therefore focusing on the student’s analysis, they commenced their experiment with the analysis of the Fe electrode. They assembled a circuit where the contact current was supplied by the voltage source through the current meter. They used a wire loop resistor of 5Ω. The voltage was measured using a volt meter. The dark bridge was observed using the microscope. The students reported that they observed intermittent discharge. They were keen to note that the discharge was electrostatic discharge (ESD) it is known to be very hazardous to digital communication network. Considering that this concept was faintly mentioned, it is my thought that the students should have elaborated further on the phenomena to accommodate anybody who might not be having an idea of the concept but was interested in the students’ article. They ought to have given a basic idea of the ESD and how hazardous it is to digital communication. Therefore, briefly mentioning the concept, Electrostatic discharge is the sudden flow of electricity between two objects which are electrically charged. The discharge may be caused by an electric short, contact or dielectric breakdown. We experience a slightly shocking moment after walking on a carpet and touching a metallic door knob. However much this shocking effect may not be severe, it may not be so for electronic devices sensitive to ESD. For this reason, it is necessary that the issue of electrical discharge be slightly addressed in the authors’ article given that it had been mentioned in the article. All materials are sources of ESD. Materials are either associated with positive or negative charges, a phenomenon called turboelectric series. The positive charge predominate the animal fur or the human skin. (Michaels and Jr, 2013). The negative charge is commonly predominant in the synthetic materials such as polymers. The capacity of a body to store charge dictates the amount of charge it can store, for instance, the human body can store up to 250 picofarads which translates to a voltage as high as 25,000V The ESD damages a body in a simple manner. We understand that ESD current will want to take a path with the smallest impedance to the ground in which case the chassis or casing of the body will be the path. We also understand that current takes any path available. The path may be along the p-n junction within the microchip of the device. The current over time will thus interfere with the p-n junctions in the chip and thus destroy the device.ESD occurs through many ways, such as human contact with sensitive devices. A recent research revealed that the human body can carry an amount of charge that is strong enough to damage an electrical device yet the human body is not susceptible to it. Other sources of ESD damage to equipment include: placing of polymers on or near electronic equipment, handling and troubleshooting PCBs and electronic devices without a wrist wrap and quick movement of air near electronic devices. Although the ESD cannot be completely eliminated, it can be reduced. It is advisable to place synthetic materials 4inches away from the electronics. Trouble shooters of electronic devices must also use electrostatic wrist bands grounded to the equipment body. In cases where necessary, use static floor mats or treat the door mats with compounds that reduce the accumulation of electrostatic charges. Going back to our analysis, the authors were able to show the voltage-current characteristic on a graph. They observed two graphs which was the initial expectation. They had to redo the experiment to confirm their findings. Repeating the experiment was necessary and accepted given that they were able to prove their initial findings and integrity of the data. They were thus precise with their findings. The first graph was indicating a linear relationship while the second one demonstrated a non linear relationship of voltage and current. The linear relationship was easy to understand, the authors noted. The experimental linear graph was compared to an initial one that was obtained from the first experiment. With further separation to 19micrometer length, the non linear behaviour did not show. However, the slope was a little gentle indicating that the resistance increased thus inhibiting conductance. The linear nature of the V-I characteristics is common and normal, the Authors reported. When the separation was extended up to 28.5μm, a non linear behaviour was observed. The linear relationship represents the normal electrical contacts behaviour. That is, the current constriction resistance property. Again the authors failed to elaborate the current constriction resistance phenomena. This concept is important since it is the result of an experiment that was conducted to analyse the behaviour of a dark hole. The authors’ failure to mention this concept therefore deprives the reader with critical information of the results obtained from an experiment. Paul Slade argues that at a certain value of the constriction radius, constriction resistance tends to decrease as the excitation frequency increases. (Slade, n.d.) He further maintains that the constriction resistance describes the resistance effects which are related to the bending of current streamlines around the constriction area. This is what yields the linearity in the first graph. The authors admit that analysis of the non linear part is not easy and requires quantitative methods. For the linear part, the straight characteristics yield a slope which can be viewed as a normal V-I relationship. The coefficient of slope was measured in Siemens, the unit for conductance. We know that the inverse of conductance is resistance which is measured in ohms (Ω). So, the authors were right to argue that: From the three characteristics of the “initial” to “19μm” in fig 4, we can see that the resistance of“19μm” increased from those of “initial” and “9.5μm” (both have almost the same resistance). The increase of resistance can be interpreted from R.Holm’s theory. This is due to the decrease of contact are so called a-spot.th resistance of “initial” and ‘19μm’ are in mΩ; initial:4.5. This means the diameter of a spot area (contact point was assumed to be circle) decreased by the square of 45/60 Analysing the non-linear characteristics, the authors divided the non linear graph into three parts. A-B, B-C and C-D. They used the try and cut analyses to do the division of parts. The authors then proceeded to show what rules govern each partition of the curve. Region A-B was observed to be linear as they indicated; B-C was exponential while C-D was unstable. The authors noticed that it is at this point that they observed the resistance variation with respect to voltage. They noticed the zero resistance after passing the zero resistance point. The authors maintained that the regions A-B and B-C showed linear and exponential characteristics respectively and thus they complement each other. They however, insisted that the region C-D was quite complex and needed a proper analysis. In region A-B, the results indicated as the authors had observed to be linear, though having a larger resistance than the linear group analysed previously the authors reported that the region had a conductance of 0.0034 mS which translates to 0.294Ω when this value is inputted in the formula. I= 0.04034V – 0.0393 The result is an error indicating that the accuracy of the approximation is fine. We know that when V=0, I must also be zero. (I= 0). Region B-C is approximated by the exponential function. The relation R2 is almost equal to 1 indicating that the approximations in this case as well, are correct. The region C-D, the authors indicated, was not able to yield the V-I characteristics. The authors said that at this point the meter had unstable reading. They were thus unable to plot either a linear or a nonlinear graph but marks of average values recorded. The resulting graph was an abnormal curve with negative resistance. At this point the current was observed to be increasing while the voltage was dropping. This proved that the region was of negative resistance. The authors determined the derivatives of the curve and they concluded that the region had a negative resistance. The process was redone using Pd and the result was the same. And thus, the authors made their conclusions. We understand that the negative resistance concept is quite important in the electronics field for its oscillatory nature. The dark hole could serve the same purpose as the semiconductor tunnel diode or PNPN device. The authors should have elaborated on the oscillatory phenomenon. This way the purpose of their findings will be more realistic, acceptable and having more weight. Briefly discussing the oscillatory nature of the tunnel diode, it has found application especially in equipment of frequencies well in the microwave range because of capability of the negative resistance. This way the diode can be used as both a transistor and as an oscillator. Therefore with the discovery of the dark hole characteristics which the tunnel diode has, the idea could be used in future technology to build more efficient equipment. The authors concluded their presentation and confirmed that they saw the dark bridge and were able to analyse its properties, both linear and nonlinear. In my view the authors make a quality work for they could help in advancements in technology. The fact that the authors were able to prove the nonlinear properties of the dark hole and also prove the concept of negative resistance is quite a break through. In summary the work of the authors was great. They were able to choose a title to their article that fits it appropriately. The authors were well organised in the manner they outlined their work. The article is in a proper journal format, with the journal details, article title and subheadings. The abstract is simple and clear and gives the authors’ summary of the contents of the article. The authors used five references to support their findings. Their references and research contributed to their findings. However, the references are not recent; they represent an important work in the field. As had been mentioned, the authors’ are graduate students and though, they may not have much authority in the field, their contribution has put them in a level worth noticing. The authors’ targeted an audience who are well-read in the electronics field. This is evident because they made some assumptions that may not be understood my laymen in electronics field. The authors do not define important terms. This in my view was the only major flaw in the article. They forget they mentioned an important term as soon as they mention it. The information in the article are facts because they have been proven. The authors’ central arguments were clearly outlined and supported within the article. The tone used in the article was objective and easy to follow. Most importantly the authors’ used graphs and charts which are quite important in presenting mathematical ideas. The article therefore is at per with quality articles. References Kubota,, H., Sasak, S., Ishida, H. and Takagi., T. 2014. Nonlinear and negative resistance in loose electric al contacts dark bridge. American Journal of Physics and Applications, 1 (1), p. 1,2,3,4. Library.queensu.ca. 2014. How to Write a Critical Review of a Journal Article | Queens University Library. [online] Available at: http://library.queensu.ca/inforef/criticalreview.htm [Accessed: 14 Apr 2014]. Sciencepublishinggroup.com. 2014. American Journal of Physics and Applications :: Science Publishing Group. [online] Available at: http://www.sciencepublishinggroup.com/journal/archive.aspx?journalid=622&issueid=6220101 [Accessed: 14 Apr 2014]. Brumbach, M. E. and Clade, J. A. 2003. Industrial maintenance. Clifton Park, NY: Thomson/Delmar Learning. Admin, A. 2014. AINDT Training Modules. [online] Available at: http://www.aindt.com.au/certification/training-modules.html [Accessed: 14 Apr 2014]. Tbgu.ac.jp. 2014. researches on contact phenomena(Ishida Labo.). [online] Available at: http://www.tbgu.ac.jp/ait/ishida/ishida/researches%20on%20contact%20phenomena%28Ishida%20Labo.%29.html [Accessed: 14 Apr 2014]. Godse, A. and Bakshi, U. 2014. Electronic Devices. n/a: Technical Publications. Siliconfareast.com. 2014. Electrostatic Discharge (ESD) - What is ESD?. [online] Available at: http://www.siliconfareast.com/esd.htm [Accessed: 14 Apr 2014]. Esda.org. 2014. EOS-ESD Association. [online] Available at: http://www.esda.org/ [Accessed: 14 Apr 2014]. Michaels, K. and Jr, F. 2013. Electrostatic Discharge: Causes, Effects, and Solutions | content content from Electrical Construction & Maintenance (EC&M) Magazine. [online] Available at: http://ecmweb.com/content/electrostatic-discharge-causes-effects-and-solutions [Accessed: 14 Apr 2014]. 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