Pacemaker interference by magnetic fields at power line frequencies

Human exposure to external 50/60-Hz electric and magnetic fields induces electric fields within the body. These induced fields can cause interference with implanted pacemakers. In the case of exposure to magnetic fields, the pacemaker leads are subject to induced electromotive forces, with current return paths being provided by the conducting body tissues. Modern computing resources used in conjunction with millimeter-scale human body conductivity models make numerical modeling a viable technique for examining any such interference. In this paper, an existing well-verified scalar-potential finite-difference frequency-domain code is modified to handle thin conducting wires embedded in the body. The effects of each wire can be included numerically by a simple modification to the existing code. Results are computed for two pacemaker lead insertion paths, terminating at either atrial or ventricular electrodes in the heart. Computations are performed for three orthogonal 60-Hz magnetic field orientations. Comparison with simplified estimates from Faraday's law applied directly to extracorporeal loops representing unipolar leads underscores problems associated with this simplified approach. Numerically estimated electromagnetic interference (EMI) levels under the worst case scenarios are about 40 microT for atrial electrodes, and 140 microT for ventricular electrodes. These methods could also be applied to studying EMI with other implanted devices such as cardiac defibrillators.     

Electric and magnetic fields

The content of the first of the two courses in electro-magnetic fields offered by the electrical engineering department at MIT to its juniors is summarized. The course deals with electroquasi-statics and magnetoquasistatics throughout, treating electrostatic and magnetostatic phenomena as special cases. This method of presentation allows the introduction of many more engineering examples into lecture demonstrations and homework than is possible in a treatment of statics followed by a treatment of the full dynamic equations, or by an overemphasis on static phenomena with only a belated discussion of quasistatic ideas. Details on several lecture demonstrations and examples are given, and it is shown how they are integrated into the "flow" of ideas. Further, our treatment of magnetization differs from the conventional one and the advantages of this treatment are discussed.     

Electric fields at and near the surface of p-n junctions with negative bevel angles

A new investigation of the field distribution at and near the surface of p-n junctions with negative bevel angles has shown that an absolute field maximum exists 20?40 ?m below the surface. This field maximum is reduced with smaller bevel angles, but is stronger for structures with a higher breakdown voltage in the bulk.     

Transistor behavior at high frequencies

The tee equivalent circuit for junction transistors has been modified to take account of electric field in the base region. This electric field is the result of a graded impurity density in the base region of the transistor. It is shown that a graded base improves the high-frequency performances of the common base stage; however, the improvement in common emitter performance is considerably less because of the increased "excess" phase which accompanies the improved high-frequency performance. The complex hybrid parameters are calculated for the common base and common emitter configurations; these calculations take into account the parasitic interterminal capacities of the transistor. The common emitter calculations are compared to measured data, and substantial agreement is obtained.     

Secondary-emission amplification at microwave frequencies

Two types of photomultipliers exhibiting flat base-band response to ∼4 Gc/s are described. One photomultiplier employs crossed electric and magnetic fields, the other is purely electrostatic. At present both devices consist of eight Cu-Be secondary emission stages and an internally situated, opaque-backed S-1 photocathode. Current gain exceeds 10⁵, and the transit time dispersion is less than7 times 10^{-11}s. Frequency response measurements have used heterodyning between the modes of the Zeeman-split Doppler profiles of a 6328 Å He-Ne laser, and also shot noise in the current from a steadily illuminated photocathode as sources of microwave modulated currents. Transient response measurements have been made using sub-nanosecond light pulses from phase-locked He-Ne and argon ion lasers, the results being consistent with the measured frequency response. A calculation of the frequency response to be expected fromnidentical stages of secondary emission when only the secondary electron emission velocities contribute to electron transit time differences, as is true of the geometries used in the experiments, gives results in agreement with experiment, assuming a value of 3 eV for the most probable secondary electron emission energy from BeO. This value is consistent with direct observations by others.     

Light modulation at video frequencies

Factors affecting the operation of the transverse a.d.p. modulator are discussed. A modulator is described which incorporates a halfwave plate to improve temperature stability and extinction ratio. The modulator has a halfwave voltage of 250 V, a bandwidth of 3.3 mHz and an extinction ratio of 160:1.     

Measurement accuracy at radio frequencies

The interdependence of science and technology and measurement capability is especially significant in measurements at radio frequencies. An example of this symbiotic relationship involves microwave spectroscopy and quantum electronics. Accuracy of measurements at radio frequencies is highly critical in satellites and similar craft. Growing international cooperation in the exploitation of satellites for research and other peaceful uses has developed concern over compatiblity of international radio frequency measurements. Accordingly, the International Bureau of Weights and Measures in 1965 initiated a program to improve the techniques of measuring electrical quantities at radio frequencies.     

Phonon interactions at ultrasonic frequencies

The interaction of ultrasonic beams in solid media has only recently been explored experimentally. The techniques developed for this purpose are reviewed and the experimental results are related to the anharmonic properties of the solid. The origin of these anharmonic properties is discussed.     

The epHEMT gate at microwave frequencies

This paper examines the high-frequency behavior of the enhancement-mode pseudomorphic high electron-mobility transistor (epHEMT) gate. During this study, no bias was applied between the drain and source. Rather, the gate was forward biased with either the drain, source, or channel (drain and source connected together) grounded. While applying positive voltage V/sub g/ to the gate, one-port S-parameters were measured from 0.1 to 10 GHz and then converted to Z-parameters. Plotting the real part R of the impedance reveals two sharp peaks. The first peak occurs near the device threshold voltage for conduction in the InGaAs well. A second peak occurs at higher voltages where conduction begins to occur in the surface AlGaAs layer. An equivalent-circuit model is proposed to account for the epHEMT gate's high-frequency behavior and the proposed model is shown to be in good agreement with the experimental data.     

Gunn-diode operation at Q band frequencies

Operation of Gunn oscillators at Q band frequencies is reported. Useful c.w. output powers were obtained and a practical resonant circuit was examined.     

Constriction resistance at high signal frequencies

This paper describes the dependence of constriction resistance on signal frequency. This dependence was calculated for circular constrictions ranging in diameter from 10 to 100 /spl mu/m, and for frequencies ranging from dc to 1 GHz. The results indicate that the magnitude of constriction resistance does not deviate appreciably from values predicted by Holm's classical analytical expression, as long as the skin depth is large compared with the constriction radius. For skin depths that are much smaller than the constriction radius, constriction resistance decreases with increasing frequency to an apparent limiting value independent of the constriction radius. At high frequencies, constriction resistance constitutes only one of two components of the total connection resistance measured in practice. The second component of connection resistance is determined by details of the geometry and dimensions of the contact interface, and increases with signal frequency.     

Long-range communications at extremely low frequencies

Extremely low frequencies (ELF) are ideal for communicating with deeply submerged submarines because, below 100 Hz, electromagnetic waves penetrate deeply into seawater. Propagation at these frequencies takes place in the "waveguide" formed between the earth and ionosphere; low propagation losses allow nearly worldwide communication from a single transmitter. Atmospheric noise at these frequencies is caused entirely by lightning; the non-Gaussian nature of this noise has important implications for receiver design and performance. Because the ratio of ELF transmitter input power to radiated power is very low, it is important that the modulation/coding technique employed make very efficient use of received signal energy. Such an efficient receiver has been implemented on a small digital computer and has been used to receive messages aboard a submarine crossing the Atlantic Ocean.     

Cable shielding measurements at microwave frequencies

A matched triaxial device is developed and constructed to measure the transfer impedance of braided coaxial cables at microwave frequencies. Full-design principles of the device have been developed and given in detail in the paper. The device is particularly suited for shielding measurements at frequencies up to 3.5 GHz, for which no comparable technique exists. The performance of the device is fully evaluated both theoretically and by measurements. The accuracy of the device is studied by comparing the results against those obtained from the low-frequency International Electrotechnique Committee triple-coaxial apparatus, and using well-known theoretical models.     

Simultaneous oscillations at two frequencies in RLC circuits

It is shown under which conditions two parallel high-Q resonance RLC circuits connected in series to a voltage-controlled active device, described by an instantaneous characteristic of fifth degree, can oscillate simultaneously at two frequencies.     

A synthetic aperture at optical frequencies

Synthetic aperture radar principles are employed to resolve targets within the beam of a helium-neon laser. Reflections from closely spaced targets moving simultaneously through a laser beam are detected in the presence of a reference beam. The resulting signals are stored on film and subsequently processed to reconstruct the target images.     

Substation noise at distribution-line communication frequencies

Measurements of noise on the distribution line at power distribution substations in the frequency range from 6 GHz to 14 GHz are presented. This is the frequency range used for distribution-line communication systems by power companies for load control and feeder automation. The measurements reported here are concerned with harmonic and background noise, which are omnipresent on the substation bus. Single-frequency noise may or may not be present in a given frequency band. Impulse noise is intermittent     

Permittivity of GaS at low frequencies

The dielectric constant of GaS is measured parallel to the c-axis, at room temperature and audio frequencies, and found to be ?_r = 5.6±0.3. Disturbances which have to be avoided in the experiment are briefly discussed.     

Transferred-electron oscillators at very high frequencies

The high-frequency characteristics of transferred-electron oscillators have been examined by computer simulation. Maximum frequencies in the range 100 to 200 GHz (for GaAs) and contact effects favouring current saturating cathodes are predicted.     

The silicon cryosar at microwave frequencies

Microwave and low-frequency measurements are reported onn^{+}-v-n^{+}silicon cryosars fabricated with narrow intrinsic region widths. The low-frequency measurements includeV-Idata with and without incident microwave power. The electric field required to cause impact ionization of the donors was found to be greater than 10⁵V/m. The microwave measurements include a demonstration of mixing, harmonic mixing, and harmonic generation. Small-signal impedance measurements as a function of bias are reported at 1.33 and 3.05 GHz, and the diode noise temperature was measured to be 16 000 or 3000 K depending on bias polarity. Mobile electron lifetime is 10^-10s.