Monthly Archives: February 2014


Biomedical instrumentation provides the necessary tools for measuring physiological variables and parameters (13-17). Great advances in biomedical instrumentation have resulted from developments in electronics and from the advent of the computer age. Biomedical instrumentation includes equip­ment that is used to diagnose disease in a patient, devices that are used to improve or maintain the health and well­being of a patient, and instruments that are used to continu­ously monitor the current physiological state of a patient. While developments in electronics have contributed much to the increased capabilities and sophistication of biomedical in­strumentation, the proliferation of medical and nonmedical electronic devices has also contributed to radio frequency in­terference (RFI), which can affect the performance of some medical equipment.

The electrocardiograph (ECG), which first appeared in hos­pitals in 1910, measures the electrical activity of the heart (18). Devices that measure the electrical activity in other parts of the body also contribute to current diagnostic capabil­ities. In addition to the ECG, bioelectric phenomena that are measured for research and diagnostic purposes include elec­troencephalography (EEG), electromyography (EMG), electro – retinography (ERG), and electrogastrography (EGG), which measure the electrical activity of brain, muscle, eye, and stomach, respectively. The measurement of propagated neu­ral impulses that result from electrical stimulation is used to assess nerve damage.

Biomagnetic fields arise from the electrical activity of tis­sue. The magnetocardiogram (MCG), or magnetic measure­ment of the electric activity of the heart, has the highest am­plitude of biomagnetic signals (50 pT) and was first detected in 1963 by Baule and McFee. The MCG, unlike the other lower amplitude biomagnetic signals, does not require a mag­netically shielded room. Comparisons between the MCG and the ECG have revealed similar capabilities for diagnosing myocardial disorders with 50% improvement when combined as an electromagnetocardiogram (EMCG) (19). The ECG is still much more widely used than the MCG.

Other biomagnetic measurements, for example, the electri­cal activity of the brain which is called a magnetoencephalo – gram (MEG), are limited in location by the need for a room with magnetic shielding because of the very low amplitude of the signals. The development of the superconducting quan­tum interference device (SQUID) in 1970 made it possible to record these low biomagnetic signals with good signal quality. There are thought to be two advantages of MEG over the EEG: (1) the ability to measure smaller regions of the brain and (2) fundamental differences in the sensitivity distribution between the two methods.

Implantable pacemakers help patients who cannot main­tain a steady heartbeat by supplying a controlled, rhythmic electric stimulus to the heart. This stimulus mimics the ac­tion of the sinoatrial node (SA node) of a healthy heart, the heart’s natural pacemaker. With modern implantable pace­makers, clinicians use telemetry to program and monitor functions externally.

Ventricular fibrillation (VF) is a type of cardiac arrhythmia that is lethal. Death occurs in minutes during VF if the condi­tion is not corrected. Because self-correction is rarely possible, defibrillation, typically by the application of an electrical shock to the heart, resets the heart to normal beating. Defi­brillators are used externally, as in emergency rooms or am­bulances, or are implanted into patients who are at constant risk of developing VF. Some commercial airlines are now equipped with automatic defibrillators that will trigger a shock if the device determines that the patient is having VF. These devices do not have to be operated by clinically trained personnel.

Bioelectric impedance analysis (BIA) of tissue provides in­formation about the small pulsatile impedance changes that occur during heart and respiratory action. BIA is used to de­termine body characteristics (e. g., percent body fat) or to re­construct tomographical images of the body (20,21) by mea­suring conductivity and permittivity at different frequencies.

Metastable Phases

There are three metastable phases of importance: two martensite (a’ and a!’) and an ш phase. The a! martensite is HCP with lattice parameters identical to a-Ti, and it forms in alloys up 7 at. % niobium. The orthorhombic a!’ is transitional between the HCP a! and the BCC в phase, and it forms at higher Nb concentrations. The martensite transformation boundary of Moffat and Larbalestier (11) is shown in Fig. 3 and shows that the most commonly used Nb-Ti alloys are outside the range of the martensite trans­formation. The ш phase has a hexagonal crystal structure (c/a = 0.613). It can be formed athermally in the alloy range 86 at. % Ti to 70 at. % Ti by quenching from the в-phase re­gion, or it can be formed by aging in the temperature range of 100° to 500° C. The ш phase is typically observed as small
ellipsoids roughly 5 nm to 10 nm in their longest dimen­sion. In cold-worked and heat-treated Nb-Ti strands, they can grow to 50 nm in diameter. All the metastable phases can be transformed to single-phase в-Nb-Ti or two-phase a + в microstructures by heating long enough in the в or a + в phase fields, respectively.


An antenna is used to either transmit or receive electromagnetic waves. It serves as a transducer converting guided waves into free-space waves in the transmitting mode or vice versa in the receiving mode. Antennas, including aerials, can take many forms according to the radiation mechanism involved and can be divided into different categories. Some common types are wire antennas, aperture antennas, reflector antennas, lens antennas, traveling-wave antennas, frequency-independent antennas, horn antennas, printed and conformal antennas, etc. (see Antennas). When applications require radiation characteristics that cannot be met by a single radiating element, multiple elements are employed. Various configurations are utilized by suitably spacing the elements in one or two dimensions. These configurations, known as array antennas, can produce the desired radiation characteristics by appropriately feeding each individual element with different amplitudes and phases, which allows increasing the electrical size of the antenna. Furthermore, antenna arrays combined with signal processing lead to smart antennas (switched-beam or adaptive antennas), which offer more degrees of freedom in wireless system design (1). Moreover, active antenna elements or arrays incorporate solid-state components producing effective integrated antenna transmitters or receivers with many applications (see Antennas and Ref. 1).

Regardless of the antenna considered, there are some fundamental figures of merit that describe its performance. The response of an antenna as a function of direction is given by the antenna pattern. This pattern commonly consists of a number of lobes; the largest one is called the main lobe, and the others are called sidelobes, minor lobes, or back lobes. If the pattern is measured sufficiently far from the antenna so there is no change in the pattern with distance, the pattern is the so-called far-field pattern. Measurements at shorter distances yield near-field patterns, which are a function of both angle and distance. The pattern may be expressed in terms of the field intensity (field pattern) or in terms of the Poynting vector or radiation intensity (power pattern). If the pattern is symmetrical, a simple pattern is sufficient to completely specify the variation of the radiation with angle. Otherwise, a three-dimensional diagram or a contour map is required to show the pattern in its entirety. However, in practice two patterns, perpendicular to each other and to the main-lobe axis, may suffice. These are called the principal-plane patterns for the E plane and the H plane, containing the field vectors E and H, respectively.

Having established the radiation patterns of an antenna, some important parameters can now be consid­ered, such as radiated power, radiation efficiency, directivity, gain, and antenna polarization. All of them will be considered in detail in this article.

Here scalar quantities are presented in lightface italics, while vector quantities are boldface, e. g., the electric field E (vector) of magnitude E (=|1?|) (scalar). Unit vectors are boldface with a circumflex over the

letter;х, У,Z and^ are the unit vectors in the x, y, z, and r directions, respectively. A dot over a symbol means that the quantity is harmonically time-varying or a phasor. For example, taking the electric field, /£ represents

^ jjr __ " ff1 jjt

a space vector and time phasor, butfi’.T, is a scalar phasor. The relations between them are — * , where 1 =


The first section of this article introduces several antenna patterns, giving the necessary definitions and presenting the common types. The field regions of an antenna are also pointed out. The most common reference antennas are the ideal isotropic radiator and the very short dipole. Their fields are used to show the calculation and meaning of the different parameters of antennas covered in this article. The second section begins with a treatment of the Poynting vector and radiation power density, starting from the general case of an electromagnetic wave and extending the definitions to a radiating antenna. After this, radiation performance measures such as the beam solid angle, directivity, and gain of an antenna are defined. In the third section the concepts of wave and antenna polarization are discussed. Finally, in the fourth section, a general case of antenna pattern calculation is considered, and numerical solutions are suggested for radiation patterns that are not available in simple closed-form expressions.


The number of aircraft operations, both civilian and military, continues to grow, which strains the capacity of the airspace system. Over the period 1980 to 1992, traffic in the United States grew at an average annual rate that was 0.4 percent­age point faster than the increase in capacity (3). By 2005, the number of air carrier passengers is expected to grow from 550 million (1995) to 800 million. During the same period, the number of air carrier domestic departures is expected to grow from 7.6 million to 8.9 million. Today’s restricted airspace sys­tem will not be able to accommodate the rapid growth in avia­tion (3).

Delay in air carrier operations is one method of measuring system capacity. From 1991 to 1995, the number of air carrier operations increased more than 18% while the number of air


Figure 2. The average delay per flight phase (in minutes) during an air carrier’s scheduled revenue flight.

carrier operations delayed 15 min or more fell from 298,000 to 237,000. The average delay per flight held steady at 7.1 min during this period (3).

Figure 2 highlights taxi-out as the flight phase with the largest average delay. Taxi-out, the time from push-back at the gate until takeoff, is susceptible to delay from airport sur­face traffic. Aircraft that are taxiing in are expedited to make room for more arrivals and other surface traffic. During a de­parture push, many aircraft are departing the airport at ap­proximately the same time. Aircraft taxiing out are coming from numerous gates scattered across the airport and chan­neled to one or two active departure runways. The departing aircraft will often form long lines as they inch toward the run­way. For airport operations using the same runway for arriv­als and departures, the departing aircraft must wait for an arrival gap before entering the runway and taking off. When a runway is dedicated for departures, aircraft separation re­quirements slow the departure process (3).

To reinforce the effects of flight delay, consider its eco­nomic impact. Heavy aircraft of 300,000 lb or more cost $4575 per hour of delay; large aircraft less than 300,000 lb and small jets cost $1607 per hour. Single-engine and twin-engine aircraft under 12,500 lb cost $42 and $124 per hour, respec­tively. With approximately 6.2 million air carrier flights in 1995 and an average airborne delay of 4.1 min per aircraft,

424,0 hours of airborne delay occurred that year. At the average operating cost of approximately $1600 (1987 dollars) per hour, the delay cost the airlines $678 million (3).

Poor weather was attributed as the primary cause of 72% of operations delayed by 15 min or more in 1995. Weather- related delays are largely the result of instrument approach procedures, which are much more restrictive than the visual procedures used during better weather conditions (3). Figure 3 shows that weather followed by airport terminal congestion were the leading causes of delay from 1991 to 1995. Closed runways/taxiways and ATC equipment, the third and fourth largest causes, had smaller effects on annual delay.

Delays will become worse as air traffic levels climb. The number of airports in the United States, where cumulative annual delays are expected to exceed 20,000 hours per year, is predicted to increase from 23 in 1991 to at least 33 by the year 2002 (4).

The FAA, air carriers, and general aviation organizations are all forecasting increased air traffic for the coming decades. The FAA predicts that by 2007, operations from all air traffic, including air carriers, regionals, air taxi, general aviation, and military aircraft, are expected to increase to 74.5 million (a 19% increase over 1995). The number of passenger en – planements on international and domestic flights, both air carrier and regional/ commuter, is expected to grow to 953.6 million by 2007 (a 59% increase over 1995). The growth rate of enplanements exceeds the growth rate of operations due to the use of larger aircraft and a higher occupancy rate on each flight (3).

The FAA numbers count all activity at a U. S. airport re­gardless of whether the air carrier is U. S flagged or interna­tional. Figure 4 shows similar numbers for U. S. air carriers as forecast by the Air Transport Association (1).

The forecast for the next decade projects that the busiest airport facilities are going to become busier. The top 100 air­ports in 1991 had 408.8 million revenue passengers depart, which accounted for over 94% of all passengers in the United States. From 1991 to 1995, the number of air carrier and regional/commuter enplanements increased by 32.9% (from 408.8 million to 543.4 million). By 2010, passenger boardings at the top 100 airports will increase by 69.1% (to 919.1 mil­lion) and aircraft operations are projected to increase by 27.6% (to 33.7 million) (3).

The 10 busiest airports in 2010 based on operations and their percentage growth from 1995 are shown in Table 2. A comparable ranking of the 10 busiest airports as a function of passenger departures is shown in Table 3. Chicago O’Hare, Dallas-Fort Worth, Atlanta Hartsfield, and Los Angeles In­ternational are forecast to be the busiest airports by 2010 in both operations and passenger enplanements.

While the air transportation industry in the United States continues to grow, it is important to remember that North America traditionally represents only about 40% of the



Figure 4. The number of revenue passengers on US air carriers grew from 382 million in 1985 to 547 million in 1995. The growth is fore­cast to climb to 857 million revenue passengers by 2007.

AIR TRAFFIC 377 Table 2. Forecast Departures at the 10 Busiest US Airports










Chicago O’Hare





Dallas-Fort Worth





Atlanta Hartsfield





Los Angeles










Phoenix Sky Harbor





St. Louis Lambert





Las Vegas McCarran





Oakland Metropolitan





Detroit Metropolitan




Total for top 100 airports




world’s total air traffic (4). In the next decade, international air travel is expected to continue its significant increase. Pas­senger traffic on world air carriers has shown an annual growth rate of 5.0% over the last decade. Forecasts for the coming decade are predicting that the growth rate will in­crease slightly to 5.5% annually. The number of passenger enplanements worldwide would grow from 1285 million in 1995 to 2010 million in 2005 (56% growth). The fastest grow­ing international route groups for passenger traffic are fore­cast to be in Transpacific and Europe-Asia/Pacific route groups (5).

By the year 2010, the International Air Transport Associa­tion (IATA) predicts that the number of international passen­gers traveling to and from the United States will reach 226 million, an increase of 187% over the 1993 figure of 78.8 mil­lion (4). The majority of these are expected to travel on U. S. carriers.


In the following sections, we discuss various techniques for the design of RC-active filters that are derived from LC lad­der filters. However, the design details and parasitic effects (primarily due to the finite gain and bandwidth of the op – amps) are not discussed. Reference material on these topics can be found in the related articles in this encyclopedia and in Refs. 20-24.