Module 6 PDF - Electrical Properties of AB Materials

ABEn 147. Properties of AB Materials Lesson 6.1: Overview of the Electrical Properties of AB Materials Lesson Summary This lesson introduces the different electrical properties of AB materials. It also discusses their applications relevant to the practice of the ABE profession. Learni...

ABEn 147. Properties of AB Materials Lesson 6.1: Overview of the Electrical Properties of AB Materials Lesson Summary This lesson introduces the different electrical properties of AB materials. It also discusses their applications relevant to the practice of the ABE profession. Learning Outcomes At the end of the lesson, the students should be able to: 1. List the different electrical properties of AB materials 2. Describe the potential applications these properties Discussion The Electrical Properties of AB Materials The electrical properties of AB materials affect how they are handled, transported, processed, stored, and consumed. Knowledge of these properties are important for AB engineers, processors, food scientists, plant and animal breeders, and other scientists. The common electrical properties that are relevant to AB materials are presented below and discussed individually in the succeeding sections (Wilhelm et al., 2004). 1. Electrical Conductance 4. Conductivity 2. Electrical Resistance 5. Electromagnetic Radiation 3. Capacitance 6. Dielectric properties Electrical conductance or simply conductance, is defined as the potential for a substance to conduct electricity. It is the measure of how easily electrical current (i.e. flow of charge) can pass through a material. It tells about to what extent an object conducts electricity, expressed in units of Siemens (S). Conductance refers to the amount of energy transmitted through a material or substance. Electrical resistance, on the other hand, is the inverse or reciprocal conductance. The resistance between two points can be defined in the quantitative sense as the difference in voltage that is needed to carry a unit current across the two specified points. The electrical resistance of a material depends in large part on the material it is made of. However, the nature of a material is not the only factor in resistance and conductance, however; it also Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  6 ABEn 147. Properties of AB Materials depends on the size and shape of the material because these properties are extensive rather than intensive. An intensive property is a local physical property of a system that does not depend on the system size or the amount of material in the system such as temperature, density, and hardness. Extensive properties on the other hand are those that are additive to the subsystems because they increase or decrease as they grow larger or smaller, respectively, such as mass and volume of the material (Cohen et al., 2008) Capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge. Capacitors are energy-storing devices available in many sizes and shapes. They consist of two plates of conducting material (usually a thin metal) sandwiched between an insulator made of ceramic, film, glass or other materials, even air. A capacitor collects energy (voltage) as current flows through an electrical circuit. Both plates hold equal charges, and as the positive plate collects a charge, an equal charge flows off the negative plate. When the circuit is switched off, a capacitor retains the energy it has gathered, though slight leakage usually occurs. Capacitors are sometimes called condensers in the automotive, marine and aviation industries. The internal plates are wired to two external terminals, which sometimes are long and thin and can resemble tiny metallic antennae or legs. These terminals can be plugged into a circuit. Capacitors and batteries both store energy. While batteries release energy gradually, capacitors discharge it quickly. Conductivity is the ability of a material to transfer energy. This property is among the characteristic properties which is used to describe the electromagnetic properties of materials. It quantifies the effect of matter on current flow in response to an electric field. Conductivity is expressed as and measured as Siemens per meter. Conductivity is also known as specific conductance. Electromagnetic radiation is an electric and magnetic disturbance traveling mass nor charge but travels in packets of radiant energy called photons, or quanta. Examples of EM radiation include radio waves and microwaves, as well as infrared, ultraviolet, gamma, and x-rays. Some sources of EM radiation include sources in the cosmos (e.g., the sun and stars), radioactive elements, and manufactured devices. EM exhibits a dual wave and particle nature. The energy of EM radiation determines its usefulness for diagnostic imaging. Because of their extremely short wavelengths, gamma rays and x- rays are capable of penetrating large body parts. Gamma rays are used in radionuclide imaging. X-rays are used for plain film and computed tomography or CT imaging. Visible light is applied to observe and interpret images. Magnetic resonance imaging (MRI) uses radiofrequency EM radiation as transmission medium. Microwave heating results from absorption of electromagnetic waves. Absorption of microwave energy depends primarily on the composition of the material. Water and high moisture foods are excellent absorbers of microwave energy while dry materials and ice are poor absorbers. Microwave heating, therefore, works best to heat unfrozen foods of high moisture. Micro-wave differs from convection heating where heat must move from the outside inward. Micro- Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials wave energy can penetrate deeply into the product, although the intensity of this energy de-creases with depth. Dielectric properties are defined as a molecular property that is fundamental in all the materials that are capable of impending electron movement resulting in polarization within the material on exposure to an external electric field. Dielectric materials are non-metallic and non-conducting materials which stores electrical charges. When a dielectric is placed in an electric field the electric charges do not flow through the material but slightly shifted from their average equilibrium positions causing dielectric polarization. Electrical permittivity, one of the important dielectric properties, is used to explain interactions of foods with electric fields. It determines the interaction of electromagnetic waves with matter and defines the charge density under an electric field. In solids, liquid, and gases the permittivity depends on the and the dielectric loss factor. Dielectric constant is related to the capacitance of a substance and its ability to store electrical energy. It is defined as the ratio of the electric permeability of the material to the electric permeability of free space, such as in a vacuum condition. The dielectric is related to energy losses when the food is subjected to an alternating electrical field (i.e., dielectric relaxation and ionic conduction). It is a measure of the loss of energy in a dielectric material through conduction, slow polarization currents, and other dissipative phenomena. Importance of Electrical Properties of AB Materials The electrical conductance and resistance of AB materials have been used in the food industry for the rapid assessment of the current quality and storage potential in marketing these products, specifically for rapid, non- destructive measurement of the moisture content. Since the electrical conductance and resistance of water differs significantly from dry matter, simple and low cost electronic sensors or moisture meters were developed to measure rapidly the moisture content of any materials. For example, the moisture in agricultural grains is routinely sampled for making decisions about drying, storing, and marketing. Knowledge of these properties provides for rapid assessment of current quality and storage potential in a modern marketing system. Electrical conductivity has been very useful in the food industry, specifically in processes involving heating and freezing. The electrical conductivity in foods has been found to increase with temperature, and with water and ionic content. Mathematical relationships have been developed to predict the electrical conductivity of food materials for modeling heating rates through electrical conductivity measurements, or for probability distribution of conductivity through liquid-particle mixtures. Electrical conductivity has also played fundamental role in ohmic heating, in which electricity is transformed to thermal energy when an alternating current (ac) flows through food. It has found wide applications in fluid pasteurization, fermentation studies, and crystallization processes, such in sugar solutions, which can be monitored with conductivity measurements. Conductivity has been found inversely proportional to viscosity, which in turn follows supersaturation closely. Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  8 ABEn 147. Properties of AB Materials Conductivity measurements have also been used to measure moisture contents in materials, particularly grain products. The dielectric properties of food materials play very important role in partially frozen material specifically in determining the rates and uniformity of heating in microwave thawing. As the ice in the material melts, absorption of energy increases tremendously. Thus, the portions of material that thaw first absorb significantly more energy and heat at increasing rates, which can lead to localized boiling temperatures while other areas are still frozen. Salt affects the situation through freezing point depression, leaving more water unfrozen at a given temperature. Dielectric properties are also important in the selection of proper packaging materials and cooking utensils, and in the design of microwave and radio frequency heating equipment. Studies of heating uniformity and temperature elevation rate involve dielectric properties. Typical features of power density patterns of a load are large internal hot and cold areas, internal focusing effects, and the edge-heating phenomenon. For example, when a raw egg is heated it may explode because the power density near its center is much higher than in other parts, causing violent shattering as the interior becomes superheated. The dielectric properties of materials are also very important in evaluating the penetration depth of energy (in other words, the distance at which the power drops 37 percent of its value in the material) that can be achieved in a certain food. Electromagnetic radiation provides wide range of applications in the processing of food materials in ways which depend on their unique properties. Having an awareness of their existence and knowledge of these effects provide scientists and engineers with powerful alternatives to process food materials. For example, high energy radiation with very short wavelengths such as 10-11 to 10-12 m, can be utilized in sterilization of foods. The exposure of foods to gamma or X-rays has produced products that can be stored for long periods without refrigeration or other processing methods. Irradiated foods are more available in European stores than in the U.S. where irradiated fruit is currently found only at a few locations. Near infrared properties of foods are utilized in component analysis, particularly moisture, protein, and oil. Laboratory instruments, based on near infrared wavelengths of 1 to 10×10-7 m, are available to determine composition of samples in a few minutes. Research continues to investigate the safe processing, handling, and consumption of irradiated foods providing wide opportunities to engineers, processors, and scientists. Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials Assessment Instruction. Answer the following questions as required. Your answers to this assessment will part of the Portfolio of this course. 1. Select five (5) agricultural products listed in your Laboratory Exercise No. 1. For each product, list two (2) important electrical properties you believe very useful in processing said product 2. Discuss in few sentences the importance of each unique electrical property you have listed in question 1 to the processing of the products. References 1. E.R. Cohen, T. Cvitas, J.G. Frey, B. Holmström, K. Kuchitsu, R. Marquardt, I. Mills, F. Pavese, M. Quack, J. Stohner, H.L. Strauss, M. Takami, and A.J. Thor, "Quantities. (2008). Units and Symbols in Physical Chemistry", IUPAC Green Book, 3rd Edition, 2nd Printing, IUPAC & RSC Publishing, Cambridge. 2. Wilhelm, L.R., Dwayne, A.S., Brusevitz, G.H. (2004. Physical Properties of Food Materials. Chapter 2 in Food & Process Engineering Technology. 23-52. St. Joseph, Michigan: ASAE @ American Society of Agricultural Engineers. Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03 Lesson 6.2: Specific Applications of Electrical Properties of AB Materials Lesson Summary This lesson introduces the potential specific applications of different electrical properties of AB materials with focus on the processing and utilization of agricultural products and food materials. Learning Outcomes At the end of the lesson, the students should be able to: 1. Identify the potential application of electrical properties of AB materials 2. Discuss the specific principles of each of each potential application Discussion Among the electrical properties of agricultural products, electrical conductivity; electrical conductance and resistance; dielectric properties, and electromagnetic radiation related properties play important roles during various technological processes of AB materials, specifically agricultural and marine-related products. The following sections discuss these specific properties giving emphasis to their specific applications. Electrical Conductivity Electrical conductivity offers a number of useful applications in the food industry especially in processes involving heating and freezing, among many others. The conductivity measurement is applied for determination of various characteristics of agricultural materials and food such as the frost sensitiveness, chilling and freezing tolerance, moisture content, seeds germination, mechanical stress, pasteurization, other properties of grains, seeds, meat, sugar, milk, wood, soil, fruit and vegetable, infected food Electrical conductivity has also played fundamental role in ohmic heating, in which electricity is transformed to thermal energy when an alternating current (ac) flows through food. It has found wide applications in fluid pasteurization, fermentation studies, and crystallization processes, such in sugar solutions, which can be monitored with conductivity measurements. Conductivity has been found inversely proportional to viscosity, which in turn follows supersaturation closely. Conductivity measurements have also been used to measure moisture contents in materials, particularly grain products.  ABEn 147. Properties of AB Materials The electrical conductivity in foods has been found to increase with temperature, and with water and ionic content. Mathematical relationships have been developed to predict the electrical conductivity of food materials for modelling heating rates through electrical conductivity measurements, or for probability distribution of conductivity through liquid-particle mixtures. properties, their capacitance and their electrical conductivity play important roles during various technological processes. The moisture content of bulk materials is widely measured by instruments utilizing the electrical conductivity or the capacitance of grains. Frequently, when classifying small seeds, use is made of the electrical properties by virtue of which electrostatic charge is held. The holding of surface charge by seeds is determined mainly by their conductivity. Figure 1 shows the principles of construction of an electrostatic sorting device (Sitkei, 1986). Seeds are loaded by a feed hopper onto a positively charged moving conveyor belt. A negative electrode creates an electrostatic field which attracts the positively charged seeds, according to their charge. Figure 1. Principles of construction of an electrostatic sorting device. Electrical Conductance and Resistance Electrical conductance refers basically to the amount of energy transmitted through a material or substance. It tells about to what extent an object conducts electricity, expressed in units of Siemens (S). On the other hand, electrical resistance is the inverse of conductance. The resistance between two points can be defined in the quantitative sense as the difference in voltage that is needed to carry a unit current across the two specified points. The electrical resistance of a material depends in large part on the material it is made of. However, the nature of a material is not the only factor in resistance and conductance. It also depends on the size and shape of the material. Electrical conductance and resistance properties provide numerous applications in the food industry. One example is the moisture content determination of agricultural products. Since the electrical conductance and Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  6 ABEn 147. Properties of AB Materials resistance of water differs significantly from dry matter, simple and low cost electronic sensors or moisture meters were developed to measure rapidly the moisture content of any materials. This simple technology of the rapid determination of moisture content resulted to the quick assessment of moisture content that crucial in making decisions about drying, storing, and marketing of agricultural products. Knowledge of these properties provides for rapid assessment of current quality and storage potential in a modern marketing system. They have been used also in the food industry for the rapid assessment of the current quality and storage potential in marketing these products, specifically for grain. Dielectric Properties Dielectric properties of agricultural products have been of interest for many years. One of the earliest applications of such electrical properties was the study of dc electrical resistance of grain for rapidly determining its moisture content. In later work with radio-frequency (RF) measurements, changes in the capacitance of sample-holding capacitors, when grain samples were introduced between the capacitor plates, were correlated with grain moisture content and used for grain moisture measurement. The other principal application of dielectric properties of agricultural materials has been for research on potential dielectric heating applications. One of these was the possible selective dielectric heating for control of insects that infest stored grain (Nelson & Whitney 1960; Nelson 1996). The dielectric properties, or permittivity, of a material determine the interaction of that material with electric fields. The dielectric properties are also used in determining the rates and uniformity of heating in microwave thawing. As the ice in the material melts, absorption of energy increases tremendously. Thus, the portions of material that thaw first absorb significantly more energy and heat at increasing rates, which can lead to localized boiling temperatures while other areas are still frozen. Salt affects the situation through freezing point depression, leaving more water unfrozen at a given temperature. Dielectric properties are also important in the selection of proper packaging materials and cooking utensils, and in the design of microwave and radio frequency heating equipment. Studies of heating uniformity and temperature elevation rate involve dielectric properties. Typical features of power density patterns of a load are large internal hot and cold areas, internal focusing effects, and the edge-heating phenomenon. For example, when a raw egg is heated it may explode because the power density near its center is much higher than in other parts, causing violent shattering as the interior becomes superheated. The dielectric properties of materials are also very important in evaluating the penetration depth of energy (in other words, the distance at which the power drops 37 percent of its value in the material) that can be achieved in a certain food. Dielectric properties of food materials are utilized in microwave heating. Home microwave ovens use the 2450 MHz frequency. Microwave heating results from absorption of electromagnetic waves. Absorption of microwave energy depends primarily on the composition of the material. Water and high Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials moisture foods are excellent absorbers of microwave energy while dry materials and ice are poor absorbers. The interaction of the food material and the microwave heat source makes it even more important to know the dielectric properties of foods. Food materials react and interact with electromagnetic radiation in ways which depend on their unique properties. Having an awareness of their existence and knowledge of these effects provide scientists and engineers with powerful alternatives too process food materials. Electromagnetic Radiation Electromagnetic radiation provides wide range of applications in the processing of food materials in ways which depend on their unique properties. Having an awareness of their existence and knowledge of these effects provide scientists and engineers with powerful alternatives to process food materials. For example, high energy radiation with very short wavelengths such as 10-11 to 10-12 m, can be utilized in sterilization of foods. The exposure of foods to gamma or X-rays has produced products that can be stored for long periods without refrigeration or other processing methods. Irradiated foods are more available in European stores than in the U.S. where irradiated fruit is currently found only at a few locations. Near infrared properties of foods are utilized in component analysis, particularly moisture, protein, and oil. Laboratory instruments, based on near infrared wavelengths of 1 to 10×10-7 m, are available to determine composition of samples in a few minutes. Research continues to investigate the safe processing, handling, and consumption of irradiated foods providing wide opportunities to engineers, processors, and scientists. Microwave and radio frequency energy are portions of the electromagnetic spectrum that can deliver heat to foods selectively and efficiently. Specifically, microwaves interact with water in foods to heat predominantly those portions that are wet. Consumers are familiar with microwave ovens as household appliances used to warm and cook foods, thaw frozen foods, and pop popcorn. On an industrial scale, microwaves have been used to temper frozen ingredients and have been considered for drying applications, without great success. The Food and Drug Administration (FDA) has approved two frequencies of microwaves for application to foods: 915 megaHertz (MHz), and 2450 MHz. Most home microwave ovens use 2450 MHz. By act of Congress, defying common sense, ionizing radiation has been declared a food additive, requiring petitions and FDA approval for use. Ionizing radiation for certain specific applications and the two microwave frequencies have been previously approved. The parameters important in energy absorption from microwaves are the following: Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  8 ABEn 147. Properties of AB Materials frequency, Hz; electric field strength, V/cm; and material volume, cm 3. T inversely proportional to frequency, and energy is directly proportional to the frequency. The dielectric constant and dielectric loss factor both increase with moisture content and decrease with frequency. As a result of the complex interactions among parameters, applications of microwaves are not always straightforward. For example, applying too much power in microwave assisted vacuum drying can lead to arcing and scorching of product. There appears to be an upper limit to field strength above which arcing can occur even at atmospheric pressure. Microwaves cannot penetrate metal so cans or pouches with aluminum laminates cannot be heated in microwaves, but glass and plastic containers can be used. There are non-metallic barrier films used in some packaging Another important application of electromagnetic wave, through microwave heating is drying. The advantage of microwave heating in drying is that it delivers energy where it is needed, where the water is. During conventional drying, as water is removed, starting from the outside of a food piece, an insulating layer of dry, porous material is formed, which grows larger as drying proceeds. This is why drying rates reduce with time. In contrast, with microwave energy, energy transfer is not inhibited by the dry layer, but, instead, is delivered directly to the wet area. Microwaves have been applied to conventional drying as well as freeze drying. As previously noted, in a vacuum, such as is usually applied in freeze drying, there is an increased risk of electrical arcing, but even with reduced power levels, microwave-assisted freeze drying is faster than conventional freeze drying, which uses conductive heating by direct contact with a heated platen to speed dehydration. Most microwave drying is done in batches, but continuous drying tunnels in which the energy is applied through focused horns have been constructed. Care in design is needed to prevent escape of radiation from the cavity. In a batch chamber, wave patterns are deliberately disrupted to provide more even heating. Assessment Instruction. Answer the following questions as required. Your answers to this assessment will part of the Portfolio of this course. 1. List the applications of each of the electrical properties of AB materials 2. Discuss the basic concept behind each application Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials References 1. Sickei, György. 1986. Mechanics of agricultural materials. Development in Agricultural Engineering 8. Joint edition published by Elsevier Science Publishers, Amsterdam, The Netherlands and -444-99523-4 (Vol. 8). 2. Nelson S.O., Trabelsi S., Kays S.J. (2006): Dielectric spectroscopy of honeydew melons from 10 MHz to 1.8 GHz for quality sensing Transactions of the ASABE, 49: 1977 1981. 3. Clark, P.J. 2013. Electromagnetic Energy in Food Processing. Food Technology Magazine. Retrieved from: https://www.ift.org/news-and- publications/food-technology- magazine/issues/2013/april/columns/processing#:~:text=Microwave% 20and%20radio%20frequency%20energy,to%20foods%20selectively %20and%20efficiently.&text=The%20Food%20and%20Drug%20Admi nistration,(MHz)%20and%202450%20MHz. Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03 Lesson 6.3 Determination of the Different Electrical Properties of AB Materials Lesson Summary This lesson discusses the different methods in measuring the different mechanical properties of AB materials Learning Outcomes At the end of the lesson, the students should be able to: 1. Discuss the different methods in determining the electrical properties of AB materials 2. Apply these methods in solving electrical properties of AB materials. Discussion Various methods and mathematical models are used to express and solve important electrical properties of AB materials, particularly food materials. The following sections present and discuss these methods. Electrical Conductivity Electrical Conductivity or specific conductance, the reciprocal of electrical resistivity, represents the ent. It is a measure of electric current flows through a food of unit cross-sectional area A, unit length L, and resistance R. It is commonly si conductivity is Siemens per meter (S/m) and is expressed in the formula: (1) Where: = electrical conductivity, S/m; (S=Siemens) = length, m = cross-sectional area, m2 = resistance Electrical conductivity of a food material is measured using an electrical conductivity cell. In this cell, a food sample is placed between two electrodes  ABEn 147. Properties of AB Materials are connected to a power supply. Care is taken to ensure that the electrodes make a firm contact with the food sample. Electrical conductivity of foods increases with temperature in a linear manner. The following equation may be used to calculate electrical conductivity of a food: (2) Where: = electrical conductivity at 0°C (S/m) T = temperature (°C) If a reference temperature other than 0°C is chosen then an alternate expression for estimating electrical conductivity as follows: (3) Values of , fferent foods are given in Table 1 shown below. Table 1. Coefficients for equations 1 and 2 to estimate Electrical Conductivity Product (S/m) (S/m) (° ) (° ) Potato 0.32 0.035 0.04 0.28 Carrot 0.13 0.107 -0.218 -0.064 Yam 0.11 0.094 -0.149 -0.07 Chicken 0.37 0.019 0.194 0.036 Beef 0.44 0.016 0.264 0.027 Sodium Phosphate 0.189 0.027 0.614 0.083 0.025 M Sodium Phosphate 0.361 0.022 0.162 0.048 0.05 M Sodium Phosphate 0.676 0.021 0.321 0.0442 0.1M The electrical conductivity of food is a function of its composition the quantity and type of various components present in the food. Foods containing electrolytes such as salts, acids, certain gums, and thickeners contain charged groups that have a notable effect on the value of electrical conductivity. Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  6 ABEn 147. Properties of AB Materials Illustrative Problem 1. Estimate the electrical conductivity of 0.1M Sodium Phosphate solution at 30°C. Solution: Given : Temperature = 30°C; 0.1M Sodium Phosphate Solution Computation: 1. Using the equation 2 and appropriate values for electrical conductivity at the reference temperature of 0°C and coefficient : 2. Note that if we use Equation 3 with appropriate values of electrical conductivity at reference temperatures of 25°C and coefficient K, we obtain Electrical Resistivity Electrical resistivity is a fundamental property of a material that quantifies how strongly it resists electric current. It is commonly represented by the Greek letter with SI unit of ohm-meter. It can be solved using the formula: (4) Where: = electrical resistivity = length, m = cross-sectional area, m2 = Various models and methods have been suggested to measure the electrical resistance. Factors affecting the suitability of various methods and precision Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials attainable include contact resistance and shape of the sample i.e. whether is it in the form of single crystal, thin film, powder pellet or small crystallite. Two probes method (ohmmeter or voltmeter ammeter measurements) can be used for higher resistive samples and four probes method (potential probe measurements) for the low resistive and single crystals. Whereas, Montgomery, van der Pauw, and Smith techniques for the pellets and bulky samples. The following sub-sections discuss the different methods in measuring resistivity as cited by Singh, Y. (20130. a. Two probe measurement This is the simplest method of measuring resistivity and is illustrated in Figure 2. In this method, voltage drop V across the sample and current through the sample I are measured. Then the resistivity is given as (5) Where: = electrical resistivity v = voltage drop, volts = current, A = cross-sectional area, m2 = This method is useful for sample that has large resistance. Figure 2. Electrical resistivity measurement using two-probe method b. Four probes measurements The potential probe is the most widely used method for resistivity measurements on the low resistive samples. In this method, the potential drop is measured across two probes and distance between these probes D replaces the sample length L in equation 5. When the probes are not Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  8 ABEn 147. Properties of AB Materials point contacts, in that case, the most accurate value for the probe distance is the distance between the centres rather than the closest distance between the probes. Figure 3 shows the schematically arrangement for this method. Figure 3. Electrical resistivity measurement by four probe method (6) Four probe method can be used to determine the resistance of the single crystal as well as the bulk specimen also. Here, current passes through the outer contacts which are close to the edges of the sample. The potential difference is measured across the inner contacts. This method can eliminate the effects of contact resistance between the sample and electrical contacts and therefore is most suitable for low and accurate resistance measurements. Contact and lead resistances are cancelled out by the four point method, however the contact resistance can still cause error if these produce enough heat. Thus, it is imperative that the contacts should have low resistance. Self-induced voltage offsets in the circuit further add to the error. This problem can be corrected by reversing the flow of current through the sample. When the low level of the voltage (in the range of µV) is produced across the sample, signal noise also adds to the error. By using the proper shielded cables and low thermal contactors, as well as making single point grounding, noise problem can be reduced. c. Four probes measurements resistivity measurement of small size (of the order of mm) specimen. This method is applicable when the distance between the probes is small compared to the smallest dimension of the sample, and provided none of the probe is too close to an edge of the sample. The arrangement of probes is shown in Figure 4. This gives the functional relationship geometries. Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials Figure 4. Electrical resistivity measurement by four point probe method In the case of a four point probe on a sheet, the two outside current points represent the dipole. Therefore, the resistivity in this case can be given by: (7) Here, the distance between all the four points is equal. I, is the current flowing through the sample, is produced voltage across two inner points and S is the distance between the adjacent points. If the distance between contact points is not equal and it is given as S1, S2 and S3 respectively, then the resistivity is given as (8) Where, V is the floating potential difference between the inner probes, and I is the current through outer pair of probes. A detailed study has been done by F. M. Smith for different geometries with various correction factors in the resistivity as shown in Figure 5 and correction factors are tabulated in the Table 2. Figure 5. Arrangement for the measurement of sheet resistivity with four point probe method Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  10 ABEn 147. Properties of AB Materials Table 2. Correction factor C for the measurement of Sheet resistivity with the four point probe method. d. Resistivity measurement for a disc of arbitrary shape (Pauw Method) This is the method discussed by vander Pauw to measure resistivity of flat disc (pellet) of arbitrary shape without knowing the current pattern. This method is applicable only when satisfying the following conditions: A. The contacts are at the circumference of the sample. B. The contacts are sufficiently small. C. The sample is homogeneous in thickness. D. The surface of the sample is singly connected, i.e. the sample does not have isolated holes. A sample of comparatively low resistance and of arbitrary shape satisfies all conditions (A) to (D) as shown in Figure 6. Figure 6. Samples of any arbitrary shape with four small contacts for electrical resistivity measurement The resistance is defined as the potential difference between D and C contacts per unit current through the contacts A and B. Here, the current enters in the sample through contact A and leaves it through B. Similarly resistance is defined. If the sample has a of , and of the sample can be determined as: Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials (9) Where is a function of only and satisfies the relation (10) can be given approximately as and plotted against the ratio (11) However, this method is very useful to determine electrical resistivity of arbitrary shaped samples with some limitations but it is also modified by some scientists later on including Chwang et al. (1974) and Weiss et al.,(2008). e. Resistivity measurement of a pellet using Montgomery Method The samples are obtained in powder form, used for pellet study. The pellet should be made by pressing the powder up to a sufficient and known pressure without using any binder. Usually these are shaped in the form of circular discs. A pellet of uniform thickness and circular in shape has four point contacts on the top surface of it arranged in the form of rectangle ABCD. The distance between the contacts at A ss than or of the order of 0.3. This is shown in Figure 7. Figure 7. Circuit arrangement for electrical resistivity measurement of a pellet The resistance R1 is determined by sending current through AB and the potential difference is measured across CD. Now, the resistance R2 is determined by sending current through AD and the produced potential difference is measured across BC. To change the direction of current and measure the resistances R1 and R2 a schematic arrangement as shown in the Figure 7 has made. The theory behind the method of calculating the Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  12 ABEn 147. Properties of AB Materials resistivity of the pellet from the knowledge of resistances R1, R2 and thickness of pellet d is described by Montgomery. Consider and if ABCD represent the corners of the top face of such a pellet, then according the theory developed by Montgomery, the resistivity can be given by (12) H is geometric parameter which is a function of the ratio of width and length (b/a), and E is an effective thickness of the specimen. The effective thickness E, which is determined by the plot of a curve drawn in between the ratio (b/a) and d. However, for < 0.3, E does not depend on b/a significantly, and is almost equal to thickness of the sample. Figure 8. The function f used for determining electrical resistivity of a sample, plotted as a function of. f. Resistivity measurement by using pulse probe method A modified dc method known as the pulse probe method has reported by C.R.B. Lister can also be used to determine the resistivity of some samples by some modifications. Figure 9 shows the block diagram for the pulse method Figure 9. Block diagram for electrical resistivity measurement by pulse method Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials In this method, a short pulse of high voltage is applied to the sample and the current or the potential drop across a pair of probes of the sample is measured, usually by means of a fast oscilloscope or other amplifying and recording systems. Since the pulse is of very short duration and repeated only a few in times in a second or even less. The current density during the time of application of the pulse is very high without unduly heating or affecting the sample. This technique is most suitable for the samples having small dimensions, more fragile and having Joule heating problems. Electrical Resistance Electrical resistance is a measure of its opposition to the flow of electric current. The reciprocal quantity is electrical conductance, and is the ease with which an electric current passes. The SI units for electrical resistance is ohm, while electrical conductance is measured in Siemens (S) formerly called mho. The resistance R of an object is defined as the ratio of voltage V across it to current I through it, while the conductance G is the reciprocal. This relationship is represented by the formula below: (https://en.wikipedia.org/wiki/Electrical_resistance_and_conductance) (13) (14) Resistance also depend on the material the product is made of as well as the proportional to the cross-sectional area, meaning the bigger the area, the lower the resistance. Considering the same given material, resistance is proportional to length, longer material has higher resistance compared to the same material with shorter length. The resistance R and conductance G of a given material of uniform cross-section, therefore, can be computed as: (15) (16) While resistance and conductance are extrinsic properties, both resistivity and conductivity are intrinsic properties. This means that every material, irrespective of their shape and size, has their own characteristic resistivity. For example, all pure copper wires (which have not been subjected to distortion of their crystalline structure) have the same resistivity, but a long, thin copper wire has a much larger resistance than a thick, short copper wire. Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  14 ABEn 147. Properties of AB Materials Illustrative Problem 2 The resistance of a wire of length 10 m is 2 ohm. If the area of cross section is 2 , determine its resistivity, conductance, and conductivity. Solution Given: Length = 10 m Resistance = 2 ohm Area = 2 Computation: Resistivity, = =4 Conductance, = = 0.5 S Conductivity, = = = 0.25 S/m Dielectric Properties The dielectric properties of biological materials are important in the research on microwave processing of foods and agricultural materials, and the destruction of insect pests of postharvest and stored products. Dielectric properties, among other parameters, are required to provide insight into the interaction between materials and microwave and radio frequency (RF) energy during microwave and RF heating. For example, the dielectric properties of apples are required in modeling microwave and RF heating for the development of a thermal alternative quarantine treatment against codling moth. There are two types of dielectric properties, dielectric constant and dielectric loss. The values of the dielectric constant and loss factor plays an important roles in determining the interaction of microwaves with food. The dielectric loss factor for the material, , which expresses the degree to which an externally applied electrical field will be converted to heat, is given by The loss tangent, , provides an indication of how well the material can be penetrated by an electrical field and how it dissipates electrical energy as Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials heat. The dielectric constant, loss factor, and loss tangent are dimensionless quantities. Dielectric constant is the ability of a material to store microwave energy and dielectric loss factor is the ability of a material to dissipate microwave energy into heat. The parameter that measures microwave absorptivity is the loss factor. The values of dielectric constant and loss factor will play important roles in determining the interaction of microwaves with food. Illustrative Problem 3 Determine the loss factor of ice (pure distilled water) given that its dielectric constant at 2450MHz is 3.2 and loss tangent is equal to 0.0009. Solution: Given: = 3.2 = 0.0009 Computation: Using equation (17) Substituting the known values: = (3.2) (0.0009) Illustrative Problem 4 Chicken meat has a dielectric constant of 53.2 and dielectric loss factor of 18.1. Find the loss tangent. Solution Given: = 53.2; = 18.1 Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  16 ABEn 147. Properties of AB Materials The rate of heat generation per unit volume (Q) at a location inside the food during microwave heating can be characterized by Eq. (18). (18) where f = frequency, 12 = dielectric constant of free space (8.854 10 F/m), = dielectric loss factor, and E = electric field. As microwaves move through the slab at any point, the rate of heat generated per unit volume decreases. For materials having a high loss factor, the rate of heat generated decreases rapidly and microwave energy does not penetrate deeply. A parameter is necessary to indicate the distance that microwaves will penetrate into the material before it is reduced to a certain fraction of its initial value. This parameter is called power penetration depth , which is defined as the depth at which power decreases to 1/e or (36.8%) of its original value. It depends on both dielectric constant and loss factor of food. (19) where is wavelength of the microwave in free space. Dielectric constant and loss factor of various food materials can be seen in Figures 10 and 11, respectively. As can be seen in the figures, dielectric properties of cooking oil are very low because of its nonpolar characteristic. Dielectric properties of water and high-moisture-containing foods such as fruits, vegetables, and meat are high because of dipolar rotation. The highest loss factor is observed in the case of salt-containing foods such as ham. Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials Figure 10 Dielectric constant of various food materials at 25 C. Figure 11. Dielectric loss factor of various food materials at 25 C. Dielectric properties of foods depend on moisture content, temperature, and compositional properties of foods. They are also a function of the frequency of the oven. Information about the effects of frequency on dielectric properties can be found in the review of Datta, Sumnu, and Raghavan (2005) and Nelson and Datta (2001). Illustrative Problem 5 Estimate the penetration depth of a chicken meat during processing in home type microwave oven. Chicken meat has a dielectric constant of 53.2 and Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  18 ABEn 147. Properties of AB Materials dielectric loss factor of 18.1. Assume that dielectric properties are constant during heating. Solution: The frequency of a home type microwave oven is 2450 MHz. Wavelength in free space is calculated as: Using Eq. (4.24): (4.24) A number of researches established the dielectric constant and loss factor of various types of materials. Table 3 shows the characteristics of the selected dielectric materials at room temperature and at frequency 2.45 GHz. Table 4 shows the bulk density and dielectric properties of six different species of starch. Table 3. Characteristics of the selected dielectric materials at room temperature and at frequency 2.45 GHz Materials Dielectric Constant Loss Factor Alumina 9.0 0.0006 Bacon (smoked) 2.50 0.05 Beef (frozen) 4.4 0.12 Beef (raw) 52.4 0.3302 Blood (37°C) 58 0.27 Butter (salted) 4.6 0.1304 Butter (unsalted) 2.9 0.1552 Borosilicate glass 4.3 0.0047 Concrete (dry) 4.5 0.0111 Corn oil 2.6 0.0077 Cottonseed oil 2.64 0.0682 Sandy soil (dry) 2.55 0.0062 Egg white 35.0 0.5 Fused quartz 4.0 0.0001 Fat (37°C) 5.5 0.21 Glass Ceramic 6.0 0.0050 Lard 2.5 0.0360 Lung (37°C) 32 0.3 Muscle (37°C) 49 0.33 Nylon 2.4 0.0083 Olive oil 2.46 0.0610 Paper 3.4 0.0125-0.0333 Soda lime glass 6.0 0.02 Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials Materials Dielectric Constant Loss Factor Teflon 2.1 0.0003 Thermoset polyester 4.0 0.0050 Wood 1.2-5 0.0040-0.4167 Table 4.2 Bulk Density and Dielectric Properties of Dry Granular Starches at 30 C Bulk Density Starch Type Dielectric Loss Factor (g/cm3) Constant Corn 0.810 2.74 0.14 Rice 0.678 1.25 0.00 Tapioca 0.808 2.25 0.08 Wheat 0.790 2.42 0.05 Waxymaize 0.902 2.81 0.43 Amylomaize 0.886 2.42 0.37 Electromagnetic Radiation Electromagnetic radiation encompasses a wide variety of phenomena as represented by the various regions along its broad spectrum. Only a few specialized, narrow regions are utilized in food applications which includes light, infrared, and microwave frequencies. Electromagnetic radiation is classified by wavelength or frequency. The electromagnetic spectrum between frequencies of 300 MHz and 300 GHz is represented by microwaves. Since microwaves are used in radar, navigational equipment, and communication equipment, their use is regulated by governmental agencies. In the United States, the Federal communications Commission (FCC) has set aside two frequencies for industrial, scientific, and medical (ISM) apparatus in the microwave range, namely 915 ± 13 MHz, and 2450 ± MHz. Similar frequencies are regulated worldwide through the International Telecommunication Union (ITU). In contrast to conventional heating systems, microwaves penetrate a food, and heating extends within the entire food material. The rate of heating is therefore more rapid. Note that microwaves generate heat due to their interactions with food materials. The microwave radiation itself is nonionizing radiation, distinctly different from ionizing radiation such as X-rays and gamma rays. When foods are exposed to microwave radiation, no known non-thermal effects are produces in food material. The wavelength, frequency, and velocity of electromagnetic waves are related by the following expression: (20) Where c = speed of light (3 m/s) f = frequency Illustrative Problem 6 Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  20 ABEn 147. Properties of AB Materials Compute the wavelength of a home type microwave oven with a frequency of 2450 MHz. Solution Given: = 2450 MHz From the formula: Substituting the values: Electromagnetic Radiation As microwaves move through the slab at any point, the rate of heat generated per unit volume decreases. For materials having a high loss factor, the rate of heat generated decreases rapidly and microwave energy does not penetrate deeply. A parameter is necessary to indicate the distance that microwaves will penetrate into the material before it is reduced to a certain fraction of its initial value. This parameter is called power penetration depth ( ), which is defined as the depth at which power decreases to 1/e or (36.8%) of its original value. It depends on both the dielectric constant and loss factor of food. (21) Where; = penetration depth = wavelength of microwave in free space = dielectric constant = dielectric loss Illustrative Problem 7 Estimate the penetration depth of a chicken meat during processing in home type microwave oven with frequency of 2450 MHz. Chicken meat has a dielectric constant of 53.2 and dielectric loss factor of 18.1. Assume that dielectric properties are constant during heating. Solution: Given: = 2450 MHz; = 53.2; = 18.1 Vision: A globally competitive university for science, technology, and environmental TP-IMD-02 conservation. V0 07-15- 2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03  ABEn 147. Properties of AB Materials Required: Solve for wavelength first: Plug in the values to the equation, thus: = 0.00794 m Assessment 1. Discuss the different methods in determining the electrical properties of AB materials 2. Differentiate dielectric constant from dielectric loos factor. 3. Discuss how power generation depth is computed. References 1. Ronald Chwang, B. J. Smith and C. R. Cowell (1974). Solid state electronics 17 issue 12, December 1974, P. 1217-1227. 2. Jonathan D. Weiss, Robert J. Kaplar and Kenneth E. Kambur (2008). Solid state electronics 52 issue 1, January 2008, P. 91-98. 3. Jonathan D. Weiss, Robert J. Kaplar and Kenneth E. Kambur (2011). Solid state electronics 62 issue 1, August 2011, P. 123-127. 4. Sing, Y. (2013). Electrical Resistivity Measurements: A Review. International Conference on Ceramics, Bikaner, India International Journal of Modern Physics: Conference Series Vol. 22 (2013) 745 World Scientific Publishing Company DOI: 10.1142/S2010194513010970 Vision: A globally competitive university for science, technology, and environmental conservation. TP-IMD-02 V0 07-15-2020 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge and innovative technologies for sustainable communities and environment. No.CET.ESC. SLG20-03