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5077 results in Electronic, optoelectronic devices, and nanotechnology

Page 75 of 254

  • 6 - Physiological Radar Sensor Chip Development

  • Edited by Isar Mostafanezhad, University of Hawaii, Manoa, Olga Boric-Lubecke, University of Hawaii, Manoa, Jenshan Lin, University of Florida
  • Book:
    Medical and Biological Microwave Sensors and Systems
    Published online:
    14 December 2017
    Print publication:
    07 December 2017, pp 172-201

  • Summary

    Theory and Recent Advancements

    Using radar to detect small physiologic signals such as respiration and heartbeat dates back to the 1970s [1]. It was realized by detecting the change in carrier phase or the round-trip time of flight (RTOF) in the received radar signals that is caused by the physiologic motion of the human body. The fundamental principle is similar to that in the radar guns that detect the speed of vehicles. Based on the format of transmit signal, there are two basic types of radars: continuous-wave (CW) radar and pulse radar. CW radar falls into two subcategories: single tone, which is mostly operated in interferometry mode, and frequency-modulated CW (FMCW), which sends out a chirp signal with the carrier frequency dynamically changing in time domain. Each category of radar has its specific advantages. Single-tone CW radar has a simple system architecture that allows high-level chip integration. It can also easily achieve high accuracy (submillimeter) in relative displacement measurement. FMCW radar is able to detect the absolute distance between the radar source and the subject, which is referred to as range information. Researchers also have successfully integrated FMCW radar on a chip. Recently, a hybrid radar system combining the advantages of single-tone and FMCW radar was reported by Wang et al. [2]. Pulse radar, which is usually accompanied by ultra-wideband (UWB) characteristics, has very high special resolution due to its large-wideband nature [3]. The integration of UWB radar is also reported for noncontact physiologic sensing.

    A generalized setup of radar noncontact physiologic sensing is shown in Figure 6.1. To detect physiologic signals, the system usually consists of a waveform generator, a radiofrequency (RF) front end, baseband signal conditioning blocks, an analog-to-digital convertor (ADC), and a signal-processing unit. The radar-generated signal is transmitted toward the human subject, where it is modulated by the physiologic motion and partially reflected. The radar receiver captures the received signal, down-converts it into baseband, and sends the digitized signal to the signal-processing unit to extract physiologic motion information, from which important vital signs such as heartbeat, respiration, or even blood pressure can be derived.

    Operation of CW Physiologic-Sensing Radar

    The basic CW radar configuration normally transmits a single-tone RF signal (f 0) toward the human subject, as shown in Figure 6.2. The received signal will maintain the same frequency of f 0, but with a phase shift accumulated along the signal path.

  • 5 - In the Workplace

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 55-65

  • Summary

    Introduction

    As part of the healthcare team, technicians must strive to serve the staff and patients in the safest and most effective ways possible. This chapter will explore important workplace characteristics that go beyond technical and analytical skills. The first section will review the various ethical codes that may guide the practice of the profession. Understanding personal safety and infection control can promote workplace safety. In addition, the task of serving staff and patients requires excellent customer service skills and professionalism.

    Applicable Codes of Ethics

    No code of ethics specifically and exactly addresses the needs of HTM technicians. Two codes, however, have parts that apply. First, there is the Code of Ethics from the Biomedical Engineering Society (www.bmes.org). Even though this group is research oriented, they do have a section that applies to technicians in the hospital environment.

    Biomedical Engineering Professional Obligations

    Biomedical engineers in the fulfilment of their professional engineering duties shall:

  • Use their knowledge, skills, and abilities to enhance the safety, health, and welfare of the public.

  • Strive by action, example, and influence to increase the competence, prestige, and honor of the biomedical engineering profession.

    • Biomedical Engineering Healthcare Obligations

    Biomedical engineers involved in healthcare activities shall:

  • Regard responsibility toward and rights of patients, including those of confidentiality and privacy, as their primary concern.

  • Consider the larger consequences of their work in regard to cost, availability, and delivery of healthcare.

    • A second group has developed an applicable code of ethics. The American College of Clinical Engineering has established the following conventions:

    The American College of Clinical Engineering Code of Ethics

    In the fulfilment of [their] duties, Clinical Engineers will:

  • ■ Hold paramount the safety, health, and welfare of the public.

  • ■ Improve the efficacy and safety of healthcare through the application of technology.

  • ■ Support the efficacy and safety of healthcare through the acquisition and exchange of information and experience with other engineers and managers.

  • ■ Manage healthcare technology programs effectively and resources responsibly.

  • 9 - Blood Pressure

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 110-118

  • Summary

    Introduction

    Blood pressure is an important indicator of performance of the human heart, lungs, and circulatory system. Blood pressure is relatively easy to measure, and readings can be taken at specific time intervals to track patient health. The peak and resting pressure of blood within the arteries is the most commonly measured blood pressure vital sign. Blood pressure rises and falls as the heart beats and has a periodic waveform. The amount of pressure in the heart can reflect the overall health of a patient and can be an indicator of many diseases and conditions.

    Indirect Measurement Methods

    Techniques to determine blood pressure without entering the circulatory system (i.e. non- invasive) utilize relationships between heart blood pressures and pressures observed in the extremities. The most common non- invasive blood pressure (NIBP) measurement method involves a blood pressure cuff and a stethoscope (see Figure 9.1). The cuff is connected to a gauge that displays pressure in the cuff. The blood pressure cuff is usually placed around the arm and inflated to various pressures displayed on the gauge. The manual technique involves a person using the stethoscope to listen to Korotkoff sounds. The sounds are related to blood flow in the vessels of the arm. Listening to body sounds is an auscultatory method of measurement. These sounds are related to the equalization of pressures between the arm blood vessels and the pressure in the heart. This technique has been in use for many, many years.

    A sphygmomanometer is a gauge and cuff combination that is utilized for the manual measurement of blood pressure. The cuff inflates with air and the pressure inside the cuff is displayed on a gauge. The pressures are reported in millimeters of mercury (mm Hg), even though most hospitals have disallowed the use of mercury.

    Systolic pressure is the highest pressure in the heart and is measured when the heart is contracting. Diastolic pressure, the lowest pressure in the heart, occurs when the heart is filling.

    These high and low pressures correspond to Korotkoff sounds in the vessels in the arm. Blood pressures are typically reported as a two- number ratio: systolic pressure “over” diastolic pressure. Typical adult pressures are 120 mm Hg for systolic pressure and 80 mm Hg for the diastolic pressure.

  • 12 - The Intensive Care Unit

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 143-157

  • Summary

    Introduction

    Patients who are very ill or in a serious condition will usually be found in the intensive care unit (ICU). Although these patient care vicinities may be called various names, they have some similar qualities. Generally, intensive care units deliver highly specialized care and have a very large amount of technology involved in patient monitoring and treatment. Technical staff who work in this area need to understand the characteristics and special needs of intensive care units.

    Each hospital in the United States has its own way of organizing and providing intensive care. For example, some hospitals do not separate surgical and medical patients. Some hospitals include transplant patients in their medical units, whereas others send transplant patients to the surgical floor and still others have stand- alone transplant intensive care units. It is virtually impossible to address the variations in this chapter. However, the issues important to intensive- care patients and staff who care for them transcend the hospital- defined categories.

    Characteristics of Intensive Care Units

    Some smaller or rural hospitals may not provide a high level of intensive care; consequently, patients who need intensive care are transferred to other hospitals. Here are the main characteristics of intensive care units:

  • Patients are very ill.

  • Patients have a high mortality rate.

  • Patients may not be conscious or mobile.

  • Most patients are restricted to bed.

  • There are no day/n ight cycles.

  • Physiological monitoring is constant.

  • Each staff member is assigned to only a few patients.

  • Units may be noisy.

  • Patients may be in an ICU for weeks or months.

  • There are restrictions about who can enter a patient room and when.

  • Patients must be monitored very closely.

  • Many tubes may be attached to patients include feeding tubes, endotracheal tubes, intravenous lines, and urinary catheters.

  • Patients may be dependent on a ventilator – a device that uses an endotracheal tube connection to get air into and out of the patient's lungs.

  • Within the ICU, monitoring often consists of

  • The heart's electrical signals, (often with either a three- or five- lead ECG)

  • Non-i nvasive blood pressure using a blood pressure cuff

  • Invasive blood pressure that uses an arterial line (a catheter that enters an artery)

  • 11 - The Brain and its Activity

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 133-142

  • Summary

    Introduction

    Measuring the activity and function of the brain is more complex than measuring the electrical activity of the heart. Signals from the brain are more random and have only recently been translated for use in specific applications. Even though brain signals can be extremely useful in patient assessment, in general, measuring the function of the brain is far less common than other technology- facilitated patient care tools.

    Review of Neuroanatomy and Physiology

    Here is a brief review of basic neuroanatomy and physiology terminology.

  • Neuron – this is the most basic cell associated with the brain. Neurons communicate using electrical energy.

  • Brainstem – this portion of the brain controls life-s ustaining functions.

  • Cerebellum and cerebrum – these major parts of the brain control various body functions and memory.

  • Ventricles of the brain – these spaces within the brain are important because implants and monitors often involve these areas.

  • Spinal cord sections – the spinal cord includes the cervical, thoracic, lumbar, and sacral regions.

  • Cerebral spinal fluid (CSF) – this fluid is very important because it cushions the brain and can be monitored to assess brain health. The fluid circulates around the brain and spinal cord.

    • Electrical Activity in the Brain

    Electroencephalography (or electroencephalogram): The electrical signals from the brain can be measured using many electrodes placed on the scalp. EEG signals created inside the brain are complex and relatively random. Measured at the scalp, EEG amplitudes are very small, in the range of microvolts. Specifically, EEGs are used to

  • Evaluate brain lesions

  • Identify epilepsy

  • Evaluate mental disorders

  • Assess sleep patterns

  • Evaluate brain responses to stimuli

    • Patterns and information are more difficult to obtain from an EEG than from an ECG. In contrast to the patterned electrical activity of the heart, EEG signals may be as unique as a fingerprint. Nevertheless, tests are often performed that evaluate the EEG waveform in response to an input like light or sound as well as to assess patient alertness. Since data can be gathered from many people, a normal EEG response can be predicted and compared to the response of a particular patient. Noise, motion artifacts, and ECG signal interference can present some major issues because EEG waveforms appear at the scalp in such low voltages.

  • 17 - Electronic Medical Record and IT

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 206-212

  • Summary

    Introduction

    Patient records generated during a stay at the hospital, including vital signs, test results, and notes by clinical staff, traditionally included a thick stack of papers stored in a binder at the bedside, or over time, with other charts at the nurses’ station. Dramatic shifts in record- keeping are underway, expanding the use of computers and computer networks to maintain patient charts and test results. The complexity of the challenge to connect devices, to transcribe information directly into a computerized system, will demand new information technology (IT) skills.

    The Electronic Medical

    Record Evolution

    Computers have been used in healthcare for a very long time as a tool to gather and maintain billing information. However, initially, most computerized records were limited to non- patient care information. As noted in Chapter 3, the Health Insurance Portability and Accountability Act of 1996 (HIPAA) was perhaps the first significant regulatory step to address information technology in the healthcare setting, promoting privacy and security.

    A major investment into the application of information technology within healthcare was driven by the American Recovery and Reinvestment Act (ARRA) adopted February 13, 2009. The Health Information Technology for Economic and Clinical Health (HITECH) Act part of ARRA offered financial incentives to hospitals to provide electronic medical records, driving the move from paper records to electronic files. Deadlines were set to speed hospitals toward change: 2012 was the first deadline for an electronic patient file. Additional deadlines were set with the aim of expanding communication to include clinical laboratory results and other healthcare information.

    The Electronic Medical Record (EMR) or Electronic Health Record (EHR) are broadly defined tools designed to house medical information electronically. Ideally, each person would have one electronic medical record that would receive contributions from all healthcare providers, archiving all medical data, and all information could be shared between providers. EMRs are expected to improve the efficiency of healthcare, improve access to information, preserve complete records without gaps, and provide safer healthcare at lower cost. However, these benefits depend on significant integration between a multitude of clinical services and users.

    The EMR did not specifically impact the HTM profession until clinicians sought to include physiological data directly from medical technology into the electronic record.

  • 6 - Electrodes, Sensors, Signals, and Noise

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 66-80

  • Summary

    Introduction

    The most common activity in patient care is patient monitoring. The human body produces a variety of physiological signals, and physicians have learned to interpret these signals to provide information about the health of a patient. To measure or monitor these signals, there must be a connection between the patient and some (typically electronic) device. This type of activity is called in vivo monitoring, which refers to the living patient. This chapter will explore the machine– human connection.

    Sensors

    Sensors (often called transducers – the difference is unimportant here) convert the energy/ signal of the patient (pressure, for example) into a form that can be used by an instrument. There are two types of sensors/ transducers:

  • Passive sensors: Some devices change a passive electrical quality

  • in response to a change in surroundings. The output is a change in resistance, capacitance, or inductance. These variations can then be measured, often using Wheatstone bridge circuitry because the changes may be very small. Examples include:

  • Strain gauges– change in resistance when some external deflection or strain occurs. The change is due to the length of the device increasing, impacting resistance.

  • Potentiometer (variable resistors) – change in resistance when some external event occurs, usually some type of motion. Since these devices often have a mechanical knob or lever, they often convert mechanical movement or position into a change in resistance.

  • Thermistors – change in resistance when temperature changes.

  • Photoresistors– change in resistance in relation to the light levels surrounding the device.

  • Active sensors: Some devices p roduce a voltage or current in response to a change in environment. Examples include:

  • Piezoelectric crystals – produce a voltage as the crystal is compressed (even tiny amounts).

  • LVDTs (linear variable differential transformers) – convert linear motion (may be very small amounts) into an electrical signal.

  • Thermocouples – detect temperature differences using dissimilar metals. They require a known reference temperature.

    • When blood pressure is measured directly (in an artery), it is commonly measured using strain gauges, piezoelectric crystals, and silicon membranes. The hospital environment is very physically demanding on equipment. Even though transducers are usually used only once (disposable), a good transducer must be very durable.

  • 1 - A Career in the HTM Profession

  • Barbara L. Christe, Indiana University–Purdue University, Indianapolis
  • Book:
    Introduction to Biomedical Instrumentation
    Published online:
    06 August 2018
    Print publication:
    07 December 2017, pp 1-19

  • Summary

    What is the Name of this Career?

    Complex healthcare technology is utilized to support safe and effective patient care. Clinicians depend on devices to monitor and treat patients. Healthcare Technology Management (HTM) professionals are part of the healthcare team, utilizing technical expertise to ensure the safety, effectiveness, and availability of critical medical technologies including devices, applications, and software. The HTM discipline interweaves patient safety, medical technology, and financial stewardship as illustrated in Figure 1.1. HTM professionals collaborate with many groups within healthcare organizations including clinicians, risk management, information technology, facilities management, and administration.

    At different hospitals, HTM technicians may have a wide variety of job titles, including HTM technician or BMET. There are many definitions for what the letters BMET stand for – biomedical equipment technician, biomedical electronics technology, medical maintenance, biomedical engineering technologist, biomedical engineer, medical engineer, and medical equipment repair technician. In general, BMET or HTM technician may be used as title for a person with technical training who works in the clinical setting and supports the equipment involved in patient care.

    Technicians may be called the “biomeds,” “clinical engineers,” or the “equipment guys.” The name of the HTM- related department within a healthcare organization may vary but is often healthcare technology management, medical engineering, clinical engineering, or biomedical engineering. In some hospitals, HTM technicians may be responsible for everything from printers to computers to DVD players in the rooms of patients. In some hospitals, HTM technicians work for the maintenance departments and are dressed similarly to the maintenance workers. Other hospitals hire a wide range of technical staff who wear surgical scrubs, lab coats, monogrammed polo shirts, or dress shirts.

    Who Employs HTM Technicians?

    Generally, three groups of employers hire HTM technicians: hospitals, outside service providers, and the equipment manufacturers. Those who work for the hospital directly or an outside service organization (OSA) or independent service organization (ISO) may appear the same to clinical staff. Some employment issues (benefits, etc.) could be different, but the work- related duties are likely to be similar. Often, when employees work for a manufacturer, they are identified as field service representatives or FSRs. What do HTM Technicians do? Although the titles may vary, the core functions of HTM technicians are relatively consistent across patient care environments.

Microwave Electronics
  • Giovanni Ghione, Marco Pirola
  • Published online:
    10 November 2017
    Print publication:
    09 November 2017
  • Drawing on over twenty years of teaching experience, this comprehensive yet self-contained text provides an in-depth introduction to the field of integrated microwave electronics. Ideal for a first course on the subject, it covers essential topics such as passive components and transistors, linear, low-noise and power amplifiers, and microwave measurements. An entire chapter is devoted to CAD techniques for analysis and design, covering examples of easy-to-medium difficulty for both linear and non-linear subsystems, and supported online by ADS and AWR project files. More advanced topics are also covered, providing an up-to-date overview of compound semiconductor technologies and treatment of electromagnetic issues and models. Readers can test their knowledge with end-of-chapter questions and numerical problems, and solutions and lecture slides are available online for instructors. This is essential reading for graduate and senior undergraduate students taking courses in microwave, radio-frequency and high-frequency electronics, as well as professional microwave engineers.

  • 3 - CAD Techniques

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 87-128

  • Summary

    Modeling of Linear and Nonlinear Blocks

    In an integrated microwave circuit, passive devices (such as resistors, inductors, capacitors, transformers, simple and coupled transmission lines) are linear blocks, and can therefore be characterized by linear models. Transistors (field effect or bipolar) and diodes are, instead, nonlinear components also in DC or quasi-static conditions, although they can behave in an approximately linear way under small-signal operation. Linear passive reactive components (such as linear inductors and capacitors) are with memory in the (v, i) port variables; nonlinear reactive elements, like the capacitances of pn or metal-semiconductor junctions, on the other hand are also associated with active components, such as transistors. Thus, MMICs generally include linear and nonlinear elements, memoryless or with memory.

    The small-signal approximation, where the transistor characteristics are linearized in the neighborhood of the DC operating point, is well suited to the design of high-gain or low-noise amplifiers; in small signal conditions the active device is approximated as a linear block with memory. The simulation of distortion and power saturation occurring in power amplifiers (but also in low-noise and high-gain amplifiers in the upper limit of their spurious free dynamic range, see Sec. 8.2.3) require instead a nonlinear transistor model, often including linear and nonlinear memory effects.

    In analog circuits, linear n-ports are conveniently modeled in the frequency domain, selecting conventional variables (such as voltages and currents) as the component input and output, or exploiting circuit variables that are more suited to the analysis and characterization of microwave circuits, such as the power waves, see Sec. 3.2. A linear n-port can be represented through a linear relationship between input and output variables; if we identify the component status in terms of the Fourier transforms of port voltages and currents, according to the choice of the input and output variable sets we obtain wellknown frequency-domain models such as the series (or current-driven, or impedance) representation and the parallel (or voltage-driven, or admittance) representation [1].

    Although a linear element is completely described by a proper set of parameters conveniently sampled over the frequency band of interest, in many cases an equivalent circuit approach is preferred. The equivalent circuit is an approximate model of the component, whose topology and element parameters have to be fitted on measured (or physically simulated) characteristics.

  • 10 - CAD Projects

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 522-565

  • Summary

    Introduction

    The present chapter describes a set of simulation or design exercises meant to apply, within a microwave Computer-Aided Design CAD environment, the concepts developed in the rest of the book. Each example is, potentially, a CAD laboratory trace. To allow the reader to replicate the examples, additional material is made available online in the form of a project in its specific CAD environment. We chose to develop the project on two well-known and widely used platforms, Microwave Office (MWO) [1] and ADS (Advanced Design Systems) [2]. To keep the presentation within reasonable limits (and also to avoid fast obsolescence due to the evolution of the CAD tool interfaces), for each example only a synthesis is provided with the main results in graphical form.

    The examples closely follow the evolution of the text and are intended as short and tutorial in nature. Rather than reporting on full real-word designs, leading to a ready-togo layout, they concentrate on specific aspects that are dealt with in the text on a more theoretical equation-based level. All figures are directly copied (sometimes with minor changes and a conversion to black and white) from the CAD tool user interface, their graphical format being in a way a part of the design experience of the user. Some of the CAD projects actually provide a CAD implementation of numerical examples presented throughout the text.

    Microstrip Line and Stub Matching of a Complex Load

    The project proposes a CAD implementation of Example 2.5. A line plus stub section (the stub in short circuit) is set up to match to the impedance. The design frequency is chosen as 10 GHz. The electrical line length at 10 GHz is initially set equal to the approximate values found in Example 2.5, and a further optimization is carried out, obtaining slightly different values. Fig. 10.1 shows the resulting input impedance compared to the goal,.

  • 2 - Passive Elements and Circuit Layout

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 28-86

  • Summary

    Transmission Lines

    Transmission lines (TXLs), simple or multiconductor, are a key distributed element in microwave circuits. They operate as signal transducers between components but are also the building block for passive distributed elements such as couplers, filters, matching sections, power dividers. In hybrid and monolithic microwave circuits the preferred guiding structures are the so-called TEM or quasi-TEM lines, characterized by broadband behavior and by the absence of a cutoff frequency, that is found in metal waveguides.

    From a theoretical standpoint, N metal conductors with a ground plane support N TEM or quasi-TEM propagation modes. In TEM (Transverse ElectroMagnetic) modes, the electric and magnetic fields are transverse with respect to the propagation direction, i.e., orthogonal to the line axis. A purely TEM mode propagates in a line without conductor losses and with a homogeneous cross section, while lossy metal lines and lines with a non-homogeneous cross section support quasi-TEM modes with small longitudinal field components. An example of quasi-TEM line is the microstrip, where the cross section is partly filled by a dielectric, and partly by air. TEM and quasi-TEM lines may also support upper propagation modes with a cutoff frequency; however, the excitation of those modes is to be avoided because they contribute to radiation losses and coupling.

    Transmission Line Theory

    Transmission lines are a simple but convenient model for one-dimensional wave propagation, serving as a bridge between circuit theory and electromagnetics. Suppose first that the line is made of two lossless parallel conductors, one acting as the signal conductor, the other as the return or ground conductor, surrounded by a homogeneous, lossless medium. Such a structure supports a TEM propagation mode in which the electric and the magnetic fields lie in the line cross section and are orthogonal to the line axis and wave propagation direction; see Fig. 2.1 (a). In a TEM mode the transverse electric field can be derived from a potential function satisfying, in the line cross section, the Laplace equation. This is uniquely determined by the potential of the signal line v(z, t) with respect to the ground line, where the coordinate z is parallel to the line axis and propagation direction. The transverse magnetic field is in turn related to the total current i(z, t) flowing in the signal conductor; −i(z, t) flows instead in the return conductor.

  • 1 - A System Introduction to Microwave Electronics

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 1-27

  • Summary

    Radio Frequencies, Microwaves, Millimeter Waves

    The meaning of high-speed and high-frequency electronics has changed in a century of technological evolution; see [1]. Radio-frequencies (RF) were at first introduced within the framework of radio broadcasting and point-to-point transmission at the beginning of the twentieth century; however, new applications (such as TV broadcasting and above all the radar around 1940), fostered in turn by the availability of RF signal generators at increasing frequency, caused a gradual explosion of new application fields in the RF, microwave and millimeter wave frequency bands. Before 1970, high-frequency systems were based on vacuum tube generators; in the following decades, solid-state semiconductor devices able to operate above 1 GHz, based both on Silicon and on compound semiconductor technologies, were gradually introduced, leading to a new paradigm, the hybrid and then monolithic Microwave Integrated Circuit, (M)MIC, see, e.g., [1, Ch. 16]. Integration and the resulting downsizing of RF and microwave systems ultimately made microwave electronics, at least in high-volume applications, a low-cost commodity well suited to the consumer market.

    For the sake of clarity, let us focus on the meaning of the terms RF, microwaves and millimeter waves and on some of the significant applications in each frequency band:

  • • The RF band includes frequencies between a few MHz and 1 GHz, with free space wavelengths of the order of 1 m (30 cm at 1 GHz); the applications include analog radio broadcasting through frequency modulation (FM), and also many other systems, like TV broadcasting, point-to-point communications (for instance, the lowest band in European GSM systems), long-range radar systems, industrial applications like RF heating and RF drying.

  • • The microwave frequency band includes frequencies between 1 GHz and 30 GHz, with free space wavelengths between 30 cm and 1 cm. In the microwave range, several applications exist: below 10 GHz we have all mobile phone systems up to the LTE (Long-Term Evolution, commonly known as 4G LTE) standard, many Wireless Local Area Network (WLAN) applications, terrestrial and satellite radio links, radar systems, positioning systems. Also the electronic part of long-haul optical communication systems operates in this band, although in this case many of the exploited circuit architectures are digital rather than analog.

  • 9 - Microwave Measurements

  • Giovanni Ghione, Politecnico di Torino, Marco Pirola, Politecnico di Torino
  • Book:
    Microwave Electronics
    Published online:
    10 November 2017
    Print publication:
    09 November 2017, pp 489-521

  • Summary

    Introduction

    This chapter aims at providing an overview of the experimental characterization techniques of linear and nonlinear one- and two-ports. After a short review of some basic instrumentation tools (the power meter, the vectorial voltmeter, the spectrum analyzer) in Sec. 9.2, the characterization of linear one- and two-ports, such as passive circuits and linear amplifiers, based on the measurement of power waves (see Sec. 3.2.2) and the related circuit-oriented parameters are discussed. As a first example, one-port measurements are introduced, whose fundamental tool is the so-called reflectometer (Sec. 9.3). The analysis of the reflectometer already allows the main issues involved in microwave measurement set-ups to be discussed, such as: the use of directional couplers to separate incident and reflected waves at the port where the Device Under Test (DUT) is connected; the need to perform measurements at a suitably low Intermediate Frequency (IF) rather than at RF to improve accuracy; the need to calibrate the measurement system to correct for systematic errors in the instrumentation.

    In Sec. 9.4 the discussion is extended to the characterization of two-port linear devices adopting the two-port Vector Network Analyzer (VNA), the key instrument for high-frequency characterization first introduced by Hewlett Packard, around 1970 [2, 3]. Downconversion approaches are discussed in Sec. 9.4.1, while a number of calibration strategies are reported in Sec. 9.4.2.

    Large-signal rather than linear-only characterizations are fundamental in the experimental assessment of power amplifiers. In Sec. 9.5 the most important aspects related to load-pull measurements are discussed. Sec. 9.6 is devoted to system-level characterization of RF components under modulated signal excitation, with particular attention to power amplifiers. Finally, Sec. 9.7 presents an overview of noise measurement techniques.

    Basic Microwave Instrumentation Tools

    Microwave measurements exploit a number of tools that are also commonly found in low-frequency electronic or electrical characterizations. Their function and principle of operation will be briefly recalled here.

    Power meters are instruments able to measure the power dissipated by a resistive load being part of the meter.

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