Open Resonator Microwave Sensor Systems for Industrial Gauging: A practical design approach
Open resonator microwave sensors allow accurate sensing, monitoring and measurement of properties such as dimension and moisture ontent in materials including dielectrics, rubber, polymers, paper, fabrics and wood veneers. This book presents a coherent and entirely practical approach to the design and use of systems based on these sensors in industrial environments, showing how they can provide meaningful, accurate and industrially-viable methods of gauging. Starting with an introduction to the underlying theory, the book proceeds through the entire design process, including simulation, experimentation, prototyping and testing of a complete system. It takes the reader through the development of a particular sensor, stressing the parameters that should be optimized and emphasizing practical aspects of a sensor and of its use. Two extended application case studies on the use of these systems for rubber thickness and fabric coating monitoring are included.
Inspec keywords: microwave detectors; finite difference time-domain analysis; network analysers; microwave measurement; coatings; gauges; power transmission lines; microwave resonators
Other keywords: electromagnetics; microwave measurement; open resonator microwave sensor system; transmission line resonator; fabric-coating monitoring; planar transmission line; industrial gauging; FDTD method; finite-difference time-domain method; network analyzer; coupled structure
Subjects: Microwave circuits and devices; Microwave measurement techniques; Sensing devices and transducers; Other numerical methods; Waveguide and microwave transmission line components; General electrical engineering topics; Network and spectrum analysers
- Book DOI: 10.1049/PBCE103E
- Chapter DOI: 10.1049/PBCE103E
- ISBN: 9781785611407
- e-ISBN: 9781785611414
- Page count: 413
- Format: PDF
-
Front Matter
- + Show details - Hide details
-
p.
(1)
-
1 Introduction to microwaves
- + Show details - Hide details
-
p.
1
–12
(12)
The purpose of this short introduction is to discuss in general terms and with a minimum of theory the concepts involved in microwave gauging and to identify issues that will be addressed later, including frequency ranges, measurements and properties of electromagnetic fields in the microwave region.
-
2 Transmission lines and transmission line resonators
- + Show details - Hide details
-
p.
13
–95
(83)
Transmission lines are arrangements of conductors whose purpose is the transfer of power or information from a source to a load, both of which should be viewed as generic. That is, the source may well be a generator but it can equally be the output of a device such as a transmitter, a receiving antenna, or an amplifier, whereas the load can be any device or system that receives the power or information such as a resistor, a transmitting antenna, or an actuator. Transmission lines differ from the common circuit theory approach to transfer of power. In circuits, we usually assume a lumped parameter model, that is, a line, connecting two points in a circuit has some resistance, capacitance, inductance, and conductance that depend on the type of line, materials, and dimensions, but these are the total values for the whole line.
-
3 Planar transmission lines and coupled structures
- + Show details - Hide details
-
p.
97
–130
(34)
Of particular interest in this work are the so-called planar transmission lines. Planar structures are extensions of the parallel plate transmission line, which is considered a planar transmission line. The term planar simply refers to the fact that in these transmission lines, the characteristics of the structure can be determined by the dimensions in a plane-the cross section of the structure. The term is often narrowed to those structures that can be conveniently produced by lithographic methods with particular applications to microwave integrated circuits although, in this work, we will use planar structures that are relatively large and their fabrication is entirely different.
-
4 Microwave measurements
- + Show details - Hide details
-
p.
131
–180
(50)
This chapter will discuss network measurements since the present work deals entirely with transmission lines and transmission line resonators. Also, because the sensors described in this work are intended to be connected directly to a network analyzer, understanding of these measurements is crucial to understanding of the operation and specifications of the sensors. However, in order to understand how a network analyzer can perform its task, it is important to understand how the various microwave quantities are defined and measured. We will therefore discuss some general methods of measurement and then link them to the network analyzer through the use of the S-parameters. We will discuss measurements in terms of the S-parameters since in the present work, we will only have recourse to measurements in transmission lines and cavity resonators and because the instrument we use to perform these measurements is a network analyzer.
-
5 Design of sensors for rubber thickness and fabric-coating monitoring
- + Show details - Hide details
-
p.
181
–232
(52)
This chapter discusses the design of resonator sensors for two applications of interest. One is a wide latex-coated fabric moving on a production line with the sensors monitoring the coating thickness or, alternatively, the moisture content in the fabric for the purpose of controlling the amount of latex on the fabric. The second is a rubber sheet moving on a calender (a cylindrical drum) in which the interest is the thickness of the sheet. Selection of physical parameters, dimensions and operational parameters, and the simulations necessary are discussed. Alternative designs including multiple sensors and moving sensors for full coverage of the fabric are weighed, and an appropriate design is reached. The details of design are given in full with alternatives and justification so that the reader has full accounting of what the design involves and what to expect from the final product. The most common alternative measurement methods of low-density dielectrics such as fabrics, paper, and thin rubber are either nuclear (by measuring absorption of gamma or beta particles from a radioactive source) or through transmission and/ or reflection of electromagnetic waves. In some cases, the methods are more primitive than that; a sample of the final product is cut and weighed to ascertain that the coating is within the required limits. Because this must be done after the production process, it is extremely wasteful and whole production runs may need to be scrapped due to insufficient or overcoating. The purpose of the designs described here is to eliminate this uncertainty and monitor the production in real time to offer feedback for continuous correction of the coating thickness.
-
6 Evaluation of the sensors
- + Show details - Hide details
-
p.
233
–261
(29)
It is one thing to come up with a sensor but a whole different matter to come up with a sensor that satisfies the strict criteria required in a gauging application. The present chapter discusses the performance of the fabric coating sensor, its sensitivity, accuracy, calibration, and other parameters such as drift, sensitivity to environmental changes, and long-time stability. We start with initial performance tests on a prototype sensor whose purpose was to establish the viability of the sensor and to obtain data for further development that might be needed. Some of the tests were done in a laboratory environment but most were performed on an existing production line. The purpose of these tests, in addition to establishing the functional parameters of the sensor such as sensitivity and stability, was to also establish its viability in the industrial environment.
-
7 Implementation and testing
- + Show details - Hide details
-
p.
263
–284
(22)
Following the design and simulation of the sensors, the implementation poses its own challenges, both mechanical and electrical. These have to be resolved, and their effects on performance must be evaluated. This chapter discusses the implementation of the sensors followed by testing. Much of the functional testing was reported in Chapter 6 and will not be addressed here. However, microwave systems are very sensitive to mechanical issues, and these will be addressed here. In particular, resonant systems, because of their high sensitivity to variations in volume of material, position of the tested material within the cavity, and, of course, variations in permittivity, require special attention to mechanical structures that support and facilitate the measurement.
-
8 The network analyzer
- + Show details - Hide details
-
p.
285
–323
(39)
This chapter describes briefly the structure of network analyzers and the measurements one can perform. The measurements described are primarily those needed for the present work and hence this description should not be viewed as a tutorial on the use of network analyzers.
-
Appendix A. Electromagnetic radiation safety
- + Show details - Hide details
-
p.
325
–330
(6)
-
Appendix B. Material properties
- + Show details - Hide details
-
p.
331
–338
(8)
This short appendix summarizes some of the properties used in this work as well as measurements of permittivity performed for the purpose of ascertaining published values. In some cases, the permittivity was calculated from simulations. Since the resonant frequency of the actual material was measured and given the dimensions of the medium, a simple process of iteration on the permittivity in the simulation until the simulated resonant frequency matched the measured resonant frequency provided the correct value for the material. In other cases, simulations were performed to ascertain the exact value of permittivity.
-
Appendix C. The finite-difference time-domain (FDTD) method
- + Show details - Hide details
-
p.
339
–353
(15)
The simulations used in this work were all done using the finite-difference timedomain (FDTD) method. One of a fairly large number of methods and variations on methods applicable to the simulation of electromagnetic fields, the FDTD is particularly simple and intuitive, and its application is well adapted to computation of high-frequency electromagnetic fields. The FDTD method approximates the electromagnetic-field equations directly without the need for intermediate steps such as the approximation and minimization processes that are so important in many numerical computation methods such as the finite-element methods.
-
Appendix D. Selected elements of electromagnetics
- + Show details - Hide details
-
p.
355
–383
(29)
The purpose of this appendix is to collect some of the quantities related to propagation of electromagnetic waves and provide definitions to the important quantities that are used in this work. It is of course not possible to deal with the whole theory of electromagnetics nor there is a need for that. It is assumed the reader is familiar with most of the concepts, but there is still value in collecting together these concepts. The reader will, of course, have to refer to more extensive exposition of electromagnetics for the details of the relations given here and for any extension of the concepts beyond the scope of the present work.
-
Back Matter
- + Show details - Hide details
-
p.
(1)