Pacemaker interference by 60-Hz contact currents

Contact currents occur when a person touches conductive surfaces at different potentials, thereby completing a path for current flow through the body. Such currents provide an additional coupling mechanism between the human body and external low-frequency fields. The resulting fields induced in the body can cause interference with implanted cardiac pacemakers. Modern computing resources used in conjunction with millimeter-scale human body conductivity models make numerical modeling a viable technique for examining any such interference. An existing well-verified scalar-potential finite-difference frequency-domain code has recently been modified to allow for combined current and voltage electrode sources, as well as to allow for implanted wires. Here, this code is used to evaluate the potential for cardiac pacemaker interference by contact currents in a variety of configurations. These include current injection into either hand, and extraction via: 1) the opposite hand; 2) the soles of both feet; or 3) the opposite hand and both feet. Pacemaker generator placement in both the left and right pectoral areas is considered in conjunction with atrial and ventricular electrodes. In addition, the effects of realistically implanted unipolar pacemaker leads with typical lumped resistance values of either 20 kohms and 100 kohms are investigated. It is found that the 60-Hz contact current interference thresholds for typical sensitivity settings of unipolar cardiac pacemaker range from 24 to 45 microA. Voltage and electric field dosimetry are also used to provide crude threshold estimates for bipolar pacemaker interference. The estimated contact current thresholds range from 63 to 340 microA for bipolar pacemakers.     

Method for determining the electric and magnetic polarizability ofarbitrarily shaped conducting bodies

The paper deals with polarization properties of arbitrarily shaped conducting bodies in quasistatic electric fields and quasisteady magnetic fields within the strong-skin-effect approximation. Based on measuring the capacitance (inductance) of a field-forming system before and after introducing an arbitrary conducting body into it, a method for determining its electric (magnetic) polarizability is proposed. The method permits one to find eigenvalues and directions of the principal axes of the polarizability tensors of any conducting body. The results obtained are useful in solving two practical problems of the electromagnetic compatibility: estimation of a measurement error induced by coupling the transducers of an electric and magnetic field to the conducting surfaces, and estimation of an additional field induced by coupling the objects to the field-forming system electrodes in electromagnetic susceptibility tests     

New Interference Sensing Demand Pacemaker Functions

Demand cardiac pacemaker functions are under study that provide new methods to distinguish between cardiac activity and pulsatile electromagnetic interference (PEMI). All known forms of currently marketed ventricular inhibited demand pacemaker (VVI) functions can be inhibited by high level pulsatile electromagnetic interference. The recent introduction of shielded circuitry to protect against disruptive (inhibiting) EMI has reduced pacemaker sensitivity to interference. However, EMI received via the cardiac lead/electrode can still mimic cardiac activity. This mimicing occurs as a consequence of detection by defribrillator protection structures or by amplifier saturation from RF artifacts insufficiently suppressed by input QRS bandpass filters. The new functions under development employ a separate EMI detection receiver for controlling the pacemaker mode to minimize inhibition by PEMI.     

Stretchable EMI Measurement Sheet With 8 $times$ 8 Coil Array, 2 V Organic CMOS Decoder, and 0.18$ mu$m Silicon CMOS LSIs for Electric and Magnetic Field Detection

A stretchable 12 × 12 cm² electromagnetic interference (EMI) measurement sheet is developed to enable the measurement of EMI distribution on the surface of electronic devices by wrapping the devices in the sheet. The sheet consists of an 8 × 8 coil array, a 2 V organic CMOS row decoder and a column selector, 40% stretchable interconnects with carbon nanotubes, and 0.18 ?m silicon CMOS circuits for electric and magnetic field detection. The sheet detects the total power of an electric field in the band up to 700 MHz and that of a magnetic field up to 1 GHz. The minimum detectable powers of the electric and magnetic fields are -60 and -70 dBm, respectively.     

Electromagnetic interference (EMI) of system-on-package (SOP)

Electromagnetic interference (EMI) issues are expected to be crucial for next-generation system-on-package (SOP) integrated high-performance digital LSIs and for radio frequency (RF) and analog circuits. Ordinarily in SOPs, high-performance digital LSIs are sources of EMI, while RF and analog circuits are affected by EMI (victims). This paper describes the following aspects of EMI in SOPs: 1) die/package-level EMI; 2) substrate-level EMI; 3) electromagnetic modeling and simulation; and 4) near electromagnetic field measurement. First, LSI designs are discussed with regard to radiated emission. The signal-return path loop and switching current in the power/ground line are inherent sources of EMI. The EMI of substrate, which work as coupling paths or unwanted antennas, is described. Maintaining the return current path is an important aspect of substrate design for suppressing EMI and for maintaining signal integrity (SI). In addition, isolating and suppressing the resonance of the DC power bus in a substrate is another important design aspect for EMI and for power integrity (PI). Various electromagnetic simulation methodologies are introduced as indispensable design tools for achieving high-performance SOPs without EMI problems. Measurement techniques for near electric and magnetic fields are explained, as they are necessary to confirm the appropriateness of designs and to investigate the causes of EMI problems. This paper is expected to be useful in the design and development of SOPs that take EMI into consideration.     

Threshold vector field detectors

The problem of threshold or weak-signal detection in highly nonGaussian EMI is extended to vector fields, and narrow-band signals and interference. The emphasis is on a canonical formulation, illustrated by a number of specific examples. Spatial sampling with adaptive beam forming, as well as temporal sampling and all relevant vector field components, must be included for maximum processing gain. New results for a canonical theory of these vector detection cases are presented. Jointly and asymptotically locally optimum algorithms and performance measures are obtained. These results provide statistical-physical models of the EMI environment, and they include first-order probability distributions of vector EMI noise fields and received processes, with specific examples of EMI fields generated by randomly distributed electric and magnetic dipole sources, as well as more general sources. The effects of beamforming, selfdirecting beams, multiple field components, fading, and Doppler `smear' on signal detectability are included     

Threshold 60-Hz Current Required for Ventricular Fibrillation in Subjects of Various Body Weights

This paper reports the threshold 60-Hz alternating-current values required to induce ventricular fibrillation when the current is applied to electrodes at different sites on the surface of the bodies of rabbits, puppies, one monkey, dogs, goats, and ponies. It is shown that for a given body weight, the duration of exposure to current influences the fibrillation threshold; exposure times shorter than 1 s require more current. For a given duration of current flow, the threshold current for fibrillation is a function of body weight and electrode location. The lowest current for fibrillation was required with lead III (left forelimb-left hindlimb) and lead I (right-left forelimbs) required the highest current. For a 5-s exposure, the threshold current for fibrillation varies almost as the square root of body weight (W), the general expression being I = KW?, where ? is nearly 0.5. Values for K and ? are presented for leads I, II, and III.     

Pacemaker interference and low-frequency electric induction in humans by external fields and electrodes

The possibility of interference by low-frequency external electric fields with cardiac pacemakers is a matter of practical concern. For pragmatic reasons, experimental investigations into such interference have used contact electrode current sources. However, the applicability to the external electric field problem remains unclear. The recent development of anatomically based electromagnetic models of the human body, together with progress in computational electromagnetics, enable the use of numerical modeling to quantify the relationship between external field and contact electrode excitation. This paper presents a comparison between the computed fields induced in a 3.6-mm-resolution conductivity model of the human body by an external electric field and by several electrode source configurations involving the feet and either the head or shoulders. The application to cardiac pacemaker interference is also indicated.     

EMI-induced failures in crystal oscillators

An electromagnetic interference (EMI) induced failure mode pertaining to crystal-based voltage-controlled oscillators (VCO) has been studied. The failure consists of a transition to a frequency of oscillation that differs from the crystal's fundamental resonant frequency, when the circuit is temporarily exposed to continuous or pulsed radio-frequency electromagnetic fields. The new state persists even after the EMI source is removed and leads to hang-up in digital systems. This mode transition has been observed experimentally. Its essential properties have been predicted theoretically and simulated numerically, using simplified oscillator models. The likelihood of observing such a failure in a noisy electromagnetic environment is assessed with respect to the radiated susceptibility levels given in MIL-STD-461B     

高速PCB近区场电磁骚扰研究

分析了高速电子电路产生的电磁干扰(EMI)及相关印刷电路板(PCB)上电磁骚扰源的模型特征。利用电偶极子与磁偶极子模型分别对PCB上的共模辐射源和差模辐射源建模,着重探讨近区场辐射特征。以一种500MHz的高速电路为例,在MATLAB平台上分别对其电场与磁场进行仿真。结果表明,其近区场电场与磁场强度最高分别可达5×1011μV/m和9×1011μA/m。依据所使用模型及其仿真结果,有针对性地提出几种降低高速PCB电磁骚扰的方案,并比较了这几种方案的优劣。     

Electromagnetic interference of cardiac rhythmic monitoring devices to radio frequency identification: analytical analysis and mitigation methodology

Increasing density of wireless communication and development of radio frequency identification (RFID) technology in particular have increased the susceptibility of patients equipped with cardiac rhythmic monitoring devices (CRMD) to environmental electro magnetic interference (EMI). Several organizations reported observing CRMD EMI from different sources. This paper focuses on mathematically analyzing the energy as perceived by the implanted device, i.e., voltage. Radio frequency (RF) energy transmitted by RFID interrogators is considered as an example. A simplified front-end equivalent circuit of a CRMD sensing circuitry is proposed for the analysis following extensive black-box testing of several commercial pacemakers and implantable defibrillators. After careful understanding of the mechanics of the CRMD signal processing in identifying the QRS complex of the heart-beat, a mitigation technique is proposed. The mitigation methodology introduced in this paper is logical in approach, simple to implement and is therefore applicable to all wireless communication protocols.     

Implantable cardiac pacemaker electromagnetic compatibility testing in a novel security system simulator

This paper describes a novel simulator to perform electromagnetic compatibility (EMC) tests for active implantable medical devices (AIMDs) with electromagnetic fields emitted by security systems. The security system simulator was developed in response to over 100 incident reports over 17 years related to the interference of AIMD's with security systems and the lack of a standardized test method. The simulator was evaluated regarding field homogeneity, signal distortion, and maximum magnetic field strength levels. Small three-axis probes and a three-axis scanning system were designed to determine the spatial and temporal characteristics of the fields emitted by 12 different types of walk through metal detectors (WTMDs). Tests were performed on four implanted pacemakers with a saline phantom and correlated to a newly developed test method performed "in air" (without the phantom). Comparison of the simulator thresholds with tests performed in real WTMDs showed that the simulator is able to mimic the pacemaker interference. The interference thresholds found in the simulator indicate that pulsed magnetic fields are more likely to cause interference in pacemakers than sinusoidal fields. The security system simulator will help biomedical engineers, manufacturers of medical devices, and manufacturers of security systems to identify incompatible combinations of WTMDs and AIMDs early in the development stage.     

Relativistic theory of rotating disks

The relationships between e, b, h, d in a rotating body are derived in the laboratory frame. They are utilized, together with suitable boundary conditions, to calculate the fields that arise when conducting or nonconducting bodies of revolution rotate in externally applied dc electric and magnetic fields.     

Comparison of electric fields induced in humans and rodents by 60-Hz contact currents

Contact currents flow when a conducting object such as an animal touches conductive surfaces at different potentials. This completes a path for current flow through the body. These currents provide an additional coupling mechanism between the human body and low-frequency external fields to that due to direct induction effects. Recent research indicates that childhood exposure to residential contact currents may play a role in explaining any possible association between residential magnetic fields and childhood leukemia. To verify this hypothesis, laboratory experiments with rodents are planned. Thus, it is important to understand the relationship between fields induced in rodents and humans. Results from numerical computations are reported here. They are based on high-resolution anatomically based inhomogeneous models of adult and child male humans and male and female rats and mice, for a variety of 60-Hz contact current scenarios. It is hoped that this work will aid in the design of experiments involving rodents and in the interpretation of results as applied to humans. It is found that for geometrically similar models, the induced electric-field scales in an anticipated inverse-square manner with the geometric scaling factor. For dissimilar models, scaling can provide a crude estimate for translating induced field results between species. However, numerical modeling provides the most suitable analysis tool for more accurate estimates.     

Electromagnetic fields of buried sources in stratified anisotropic media

A general formulation to the problem of the radiation of arbitrary distribution of buried sources within a horizontally stratified anisotropic medium is presented. The fields are obtained in terms of appropriately defined electric and magnetic types of dyadic Green's functions which are dual to each other. The formulation is considerably simplified by the resolution of these dyadic Green's functions into transverse electric (TE) and transverse magnetic (TM) waves and by the existing duality between them. A systematic procedure for deriving the fields in an arbitrary layer in terms of the primary source excitation and appropriately defined wave amplitude matrices is described.     

消磁电源电磁干扰补偿技术

舰船临时线圈消磁是消除舰艇固定磁场，提高舰艇反磁探反磁性武器能力的重要措施。由于消磁工艺的特殊性，对于挂接于电网输出大功率电流脉冲的消磁电源有可能给电网造成极大的电磁污染，导致电网电压畸变。本文从探讨电网电压畸变的成因出发，着重研究了电压畸变的补偿问题，以期改善消磁电源的电磁兼容性能。     

Behavioral effects of strong 60-Hz electric fields in rats.

Eight individually housed male Long Evans rats were raised, beginning at age 30 days, for six weeks in an electric field exposure apparatus. During five of the six weeks, the animals were exposed to a 25 kV/m, 60-Hz electric field. A similar population of rats housed in an identical environment, except for the absence of the high voltage field, were used as control animals. Differences between the two groups in body mass, food and water intake, and exploratory activity were studied. Statistical analysis shows the high voltage fields to have no significant effects on the above parameters.     

Peripheral nerve stimulation by gradient switching fields in magnetic resonance imaging

A heterogeneous model of the human body and the scalar potential finite difference method are used to compute electric fields induced in tissue by magnetic field exposures. Two types of coils are considered that simulate exposure to gradient switching fields during magnetic resonance imaging (MRI). These coils producing coronal (y axis) and axial (z axis) magnetic fields have previously been used in experiments with humans.The computed fields can, therefore, be directly compared to human response data. The computed electric fields in subcutaneous fat and skin corresponding to peripheral nerve stimulation (PNS) thresholds in humans in simulated MRI experiments range from 3.8 to 5.8 V/m for the fields exceeded in 0.5% of tissue volume (skin and fat of the torso). The threshold depends on coil type and position along the body, and on the anatomy and resolution of the human body model. The computed values are in agreement with previously established thresholds for neural stimulation.     

Prediction of magnetically induced electric fields in biologicaltissue

There are many potential medical applications in which it is desirable to noninvasively induce electric fields. One such application that serves as the backdrop of this work is that of stimulating neurons in the brain. The magnetic fields necessary must be quite high in magnitude, and fluctuate rapidly in time to induce the internal electric fields necessary for stimulation. Attention is focused on the calculation of the induced electric fields commensurate with rapidly changing magnetic fields in biological tissue. The problem is not a true eddy current problem in that the magnetic fields induced do not influence the source fields. Two techniques are introduced for numerically predicting the fields, each employing a different gauge for the potentials used to represent the electric field. The first method employs a current vector potential (analogous to A in classical magnetic field theory where DEL x A = B) and is best suited to two-dimensional (2-D) models. The second represents the electric field as the sum of a vector plus the gradient of a scalar field; because the vector can be determined quickly using Biot Savart (which for circular coils degenerates to an efficient evaluation employing elliptic integrals), the numerical model is a scalar problem even in the most complicated three dimensional geometry. These two models are solved for the case of a circular current carrying coil near a conducting body with sharp corners.