Abstract
This chapter focuses on microwave research and measurements for agricultural and food processing applications. Normally, microwave devices and components are used as a moisture detector for soil, agricultural, and food products. For instance, the moisture content in fruits normally is correlated with the maturity and sweetness of the fruits. In addition, the moisture content can be used to determine the storage period and the quality of the agricultural products after processing by an industrial factory. In this chapter, several microwave applications of agri-food products are selected to be reviewed comprehensively, such as microwave heating mechanism for several agri-food products, heating/drying, or freeze-drying process in food industry to control pathogenic and spoilage microorganisms in packaged foods, moisture soil testing, fruit moisture measurement, ripeness/storage period determination, fruit sweetness detection, microwave radiation for agricultural pest control.
TopIntroduction
Microwave technology is expanding rapidly and is becoming more and more common in our daily lives, such as mobile phone and microwave oven. Microwave technology application can be divided into two groups, namely communication and non-communication applications. In this chapter, microwave non-communication applications have been described and specifically focus on the use of such technologies in agriculture/food fields. This chapter reviews the microwave applications for agricultural in this era based on a detailed literature survey and the author’s experience in microwave researches.
In fact, over the past 40 years, a lot of research on microwave applications in agriculture has been conducted. Most of the research related to the field has been published in journals, such as Journal of Microwave Power and Electromagnetic Energy (Formerly Journal of Microwave Power) and Transactions of the ASAE (American Society of Agricultural Engineers). However, commercial microwave products/instruments for agricultural use are rarely found in comparison with optical-based (infrared) and acoustic-based (ultrasound) technologies. This is due to the higher price of microwave electronic components, such as monolithic microwave integrated circuit (MMIC) chips, compared to others. Foremost, microwave device components require high precision machining. Also, normally, microwave raw materials used in electronic components are the expensive synthetic materials, which materials have good thermal resistance and lossless dielectric at the high operating frequency. Besides, the design of microwave components is not easy and requires experts in the field of microwave engineering, especially in the last 30 years where it is difficult to obtain workstation computers and simulation software for microwave components/electronics design.
Nowadays, advances in the mechanized industry (industry 4.0) and electronic communication technologies, such as internet of things (IoT) and fifth-generation (5G) wireless technologies, are increasing globally. Thus, precision machining, such as computer numerical control (CNC) milling machine, high-end personal computers, and engineering simulation software are becoming common. In addition, techniques and knowledge in the production of new synthetic materials and microwave components are matured, and that information can be easily obtained from books, journal or internet. Hence, recently, the microwave component prices have reached a level nearly similar to optical and acoustic electronic components. This has provided the advantages and opportunities for more microwave technologies to be applied in agricultural / food processing.
In fact, microwave technology is capable of applying in sensors for agricultural/food processing, such as grain/soil moisture measurement, fruit ripeness/storage period determination, fruit sweetness detection, control of milk of lime, monitoring of nitrogen/phosphorus content in fertilizer. The microwave also can be used for heating/drying or freeze-drying process (sterilization/pasteurization) in the food industry to control pathogenic and spoilage microorganisms in packaged foods. Microwave applications for heating and crushing normally use high microwave power which is up to megawatts. Besides, microwave energy also has been implemented for agricultural pest control.
Key Terms in this Chapter
Pasteurization: A process in which water and certain packaged and non-packaged foods are treated with mild heat, usually to less than 100 °C, to eliminate pathogens and extend shelf life.
Free Water: Water that is not bound to an inorganic surface and can flow freely.
Relative Permittivity (er): A permittivity of substance expressed as a ratio relative to the vacuum permittivity.
Bound Water: An amount of water in a substance which are bound to other substance constituents and create a thin layer of water surrounding the constituent surfaces.
Monolithic Microwave Integrated Circuit (MMIC): A type of integrated circuit (IC) device that operates at microwave frequencies.
Transmission Coefficient (S21): A parameter that describes how much electromagnetic waves pass through the transmission medium.
Fifth Generation Wireless Technology (5G): Digital cellular mobile communication networks that began wide deployment in 2019.
Cole-Cole Model: A relaxation model for describing dielectric relaxation of a substance.
Soluble Solids Content (SSC): A solution is determined by the index of refraction.
Wet Basis: A measure of the water in a substance, which is expressed as the percentage of the ratio of the weight of water to the total weight of the substance (water + dry substance).
Dry Basis: A measure of the water in a substance, which is expressed as the percentage of the ratio of the weight of water to the weight of the completely dry substance.
Permittivity: A substance property that affects the Coulomb force between two-point charges in the substance.
Internet of Things (IoT): A system of interrelated computing devices, mechanical, and digital machines provided with unique identifiers (UIDs) and the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction.
Moisture Content (m.c.): Quantity of water that exists in a substance.
Frequency-Domain Reflectometry (FDR): A nonintrusive technique used to feed a frequency sweep signal into an electrical line. The receiver measures the interference pattern generated when the output signal of the swept RF source is added to or subtracted from the reflected signal of the fault and other reflection characteristics in the tested electrical lines, then determine the characteristics of electrical lines by observing the vector addition of the signals creates a ripple pattern versus frequency.
Microwave Sensor: A type of sensor device that operates at microwave frequencies (within 300 MHz to 300 GHz).
Microwave: A form of electromagnetic radiation with wavelengths ranging from 1 m to 1 mm, which is corresponding to operating frequencies ranging from 300 MHz to 300 GHz.
Time-Domain Reflectometry (TDR): A noninvasive technique used to measure the time between release and return of the low voltage pulse from any reflections and determine the characteristics of electrical lines by observing reflected waveforms.
Free Fatty Acid (FFA): Fatty acid produced by the hydrolysis of oils and fats.
Reflection Coefficient (S11): A parameter that describes how much electromagnetic waves are reflected by impedance discontinuities in the transmission medium.