| 单词 | impedance |
| 例句 | While employed as a research engineer for Bell Telephone Laboratories in Murray Hill, N.J., he helped develop a talking typewriter and wrote papers on room acoustics, sound absorption and acoustic impedance. Cyril Harris Dies at 93; Fine-Tuned Concert Halls 2011-01-09T02:20:26Z One of the resonators enables the light coming from the laser to couple with the other resonator; rather like impedance matching in electronics. New method makes microcombs ten times more efficient 2023-09-20T04:00:00Z To make that diagnosis, gastroenterologists can do a test called a pH impedance study. Advice | Ask a Doctor: Why doesn’t anything work for my heartburn? 2023-02-27T05:00:00Z Reflections at boundaries between two different media occur because of differences in a characteristic known as the acoustic impedance Z of each substance. College Physics for AP Courses 2015-08-12T00:00:00Z That’s similar to what I get on other bioelectric impedance devices but counter to everything my doctor told me at my last physical. Amazon Halo View review: the Fitbit clone no one asked for 2021-12-15T05:00:00Z It works in a way similar to existing consumer smart scales, sending an electrical signal through your body and measuring the impedance. Galaxy Watch 4 review: welcome to Samsung’s garden 2021-08-18T04:00:00Z It combines an optical heart rate sensor, electrical heart sensor, and a bioelectric impedance analysis sensor which means detection of everything from atrial fibrillation to blood oxygen levels and body composition. The Galaxy Watch 4 injects Samsung’s capable hardware with Google software 2021-08-11T04:00:00Z Then there are people whose acid reflux is severe, as measured by the pH impedance study, and despite taking PPIs correctly, still experience painful, breakthrough heartburn. Advice | Ask a Doctor: Why doesn’t anything work for my heartburn? 2023-02-27T05:00:00Z The combined effect of resistance R , inductive reactance XL , and capacitive reactance XC is defined to be impedance, an AC analogue to resistance in a DC circuit. College Physics for AP Courses 2015-08-12T00:00:00Z He said a valid study would involve a clinical trial measuring body fat of many human subjects with each method — the Halo, DEXA, bioelectrical impedance scales and calipers — and comparing the results side by side. Amazon Halo Review: The Fitness Gadget We Don’t Deserve or Need 2020-12-09T05:00:00Z Amazon also claims that smart scales that try to measure body fat using bioelectrical impedance are not as accurate as its scan. Amazon announces Halo, a fitness band and app that scans your body and voice 2020-08-27T04:00:00Z He also said the inspector general confused operational control, which is the overall goal of border control, and “impedance and denial,” which is one facet of it. Audit faults DHS for ignoring alternatives in push to build border wall 2020-07-16T04:00:00Z Whenever Giulianotti wanted to cut something, the robot first measured the tissue’s impedance—or resistance to an electrical current—and, thus, the extent to which blood had been stanched. Paging Dr. Robot 2019-09-23T04:00:00Z Note that the acoustic impedances for soft tissue do not vary much but that there is a big difference between the acoustic impedance of soft tissue and air and also between soft tissue and bone. College Physics for AP Courses 2015-08-12T00:00:00Z Smart bathroom scales that measure body fat use bioelectrical impedance analysis, which sends a small current through your bare feet. Amazon Halo Review: The Fitness Gadget We Don’t Deserve or Need 2020-12-09T05:00:00Z Unfortunately, lithium-ion batteries are complex systems, which means that capacity fade and impedance increase arise from several interacting processes. Machine-learning techniques used to accurately predict battery life 2019-04-08T04:00:00Z U. Steiner’s group, in particular P. Sutton and M. Fischer, provided instrumentation and advice related to impedance measurements. An electric-eel-inspired soft power source from stacked hydrogels 2017-12-12T05:00:00Z “Their theory is that democracy is an impedance to capitalism so they need as little regulation as possible,” he said. Forget Wall Street – Silicon Valley is the new political power in Washington 2017-09-03T04:00:00Z The greater the difference in acoustic impedance between the two media, the greater the reflection and the smaller the transmission. College Physics for AP Courses 2015-08-12T00:00:00Z Metrics showed barriers were cost-effective ways to achieve “persistent impedance”, he said. Border Security Expo: excitement and urgency in anticipation of Trump's wall 2017-04-13T04:00:00Z "They didn't even appear in early computer models, and when they did, it was largely for their role as 'impedance' - blocking vehicle traffic." How the car industry outlawed crossing the road 2014-02-12T00:13:05Z At evaluations at 2 days, 2 weeks, 6 weeks and 3 months, pacing threshold, R-wave amplitude and impedance were all similar to conventional pacemakers. Novel Leadless Pacemaker Makes Debut At HRS 2013 2013-05-13T17:27:01Z In particular, for normal incidence any medium whose wave impedance has the vacuum value, , will be reflectionless in the vacuum. Controlled-reflectance surfaces with film-coupled colloidal nanoantennas 2012-12-11T21:22:39.403Z The units of impedance are ohms, and its effect on the circuit is as you might expect: the greater the impedance, the smaller the current. College Physics for AP Courses 2015-08-12T00:00:00Z The shapes of the frequency-dependent impedance response curves allow clear identification of each of these processes. Materials interface engineering for solution-processed photovoltaics 2012-08-15T17:22:03.163Z These allow a significant increase in the operating frequency, which reduces the sizes of inductors and capacitors without altering their electrical impedance. Opportunities and challenges for a sustainable energy future 2012-08-15T17:21:52.727Z In operating devices on the above plan I have observed curious phenomena of impedance which are of interest. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z Time was, manufacturers marketed high-priced audio equipment by emphasizing technical merits like frequency response, optimum impedance, ambient noise attenuation and so on. Beats Headphones Expand Dr. Dre?s Business World 2011-11-19T18:24:10Z At some intermediate frequency f0 , the reactances will be equal and cancel, giving Z = R —this is a minimum value for impedance, and a maximum value for Irms results. College Physics for AP Courses 2015-08-12T00:00:00Z "The effect of these subsidies was displacement and impedance of Airbus large civil aircraft from third country markets, significant price suppression and significant lost sales," said the WTO in a statement. US subsidies to Boeing 'illegal' 2011-03-31T19:05:47Z Even more confusing are changes in thoracic impedance, a measurement of resistance to electric current through the lung. New Devices to Help Heart Patients 2010-06-21T19:27:00Z A number of novel impedance phenomena are also shown which cannot fail to arouse interest. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z When the core is drawn out of the coil, its impedance is diminished because the inductance is diminished. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. Wood and concrete offered no impedance at all. All In The Mind And so it has, but we usually call it “impedance” instead of resistance because straight wires resist but coils or condensers impede alternating e. m. f.’s. Letters of a Radio-Engineer to His Son He could make quite an issue out of the need to determine the characteristic impedance of their sky. The Sky Is Falling While many were probably prepared to encounter curious phenomena of impedance in the use of a condenser discharged disruptively, the experiments shown were extremely interesting on account of their paradoxical character. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z RR represent impedance coils connected serially in the line and placed at terminal stations. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The impedance of a few turns of heavy wire may be negligible to alternating currents of ordinary frequencies because the resistance of the wire is low, its inductance small, and the frequency finite. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The impedance of its secondary will be a quarter of this or 3,000 ohms. 196If we connect such a transformer in the circuit, as shown, we shall obtain the greatest output from the tube. Letters of a Radio-Engineer to His Son In all such cases the impedance which the circuit offers is made up of two things—resistance and inductance. Scientific American Supplement, No. 787, January 31, 1891 Among the various current phenomena observed, perhaps the most interesting are those of impedance presented by conductors to currents varying at a rapid rate. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z The alternating currents of speech and interrupter signaling are kept from passing to ground at terminals by the impedance coils. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. In order to further increase the impedance, the cores are made long and heavy. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Because the receiver would offer a large impedance to the high-frequency current, that is, seriously impede and so reduce the high-frequency current, we connect a condenser around the receiver. Letters of a Radio-Engineer to His Son If a ground connection is made it can only be made through a conductor offering an enormous impedance, or though a condenser of extremely small capacity. Experiments with Alternate Currents of High Potential and High Frequency The electrical resonance is the more perfectly attained, the smaller the resistance or the impedance of the conducting path and the more perfect the dielectric. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z This relay has a resistance of 4,500 ohms and a high impedance, and operates the selector mechanism which is a special modification of the ratchet and pawl principle. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The impedance these windings offer to the high frequency of lightning oscillations is great. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. This coil has a small inductance but it is enough to offer a large impedance to radio-frequency currents. Letters of a Radio-Engineer to His Son IMPEDANCE.—An oscillation circuit has reactance and also resistance, and when these are combined the total opposition to the current is called impedance. The Radio Amateur's Hand Book Now one is apt to think in the first moment that the impedance of the wire might have something to do with the phenomenon. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z A simplex arrangement even more simple substitutes impedance coils for the repeating coils of Fig. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. On the other hand, the impedance of such a coil to a lightning discharge is much higher, due to the very high frequency of the discharge. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. That is, it has too little impedance to act like LA and so it permits the modulator to vary the output of the oscillator. Letters of a Radio-Engineer to His Son The impedance of the magnet coils of a receiver is so great for high frequency oscillations that the latter cannot pass through them; in other words, they are choked off. The Radio Amateur's Hand Book Then there is the impedance in the armature, enormously augmented by the high frequency. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z This apparatus is of high impedance and of a special design adapted to railroad service. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. When lightning encounters an impedance, the discharge seldom takes place through the entire winding, as an ordinary current would flow, usually striking across whatever short paths may exist. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The things needed are an arc-lamp, an impedance coil, or small transformer- coil, a rheostat, and a source of energy. The Dream Doctor Where a wire is wound in a coil the impedance of the circuit is increased and where an alternating current is used the impedance grows greater as the frequency gets higher. The Radio Amateur's Hand Book But the circuit opposes the passage of the currents by reason of its impedance and therefore, to secure the best action it is necessary to reduce the impedance to a minimum. The inventions, researches and writings of Nikola Tesla With special reference to his work in polyphase currents and high potential lighting 2012-03-28T02:00:22.660Z The receivers used at the waystations are of high impedance and are normally connected, through the hook switch, directly across the line in series with a condenser. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. In the right-hand portion of the circle of the base is shown a small impedance coil, which is placed in series with the transmitter but in shunt relation with the condenser and the receiver. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. In order that the presence in the talking circuit of a magnet winding possessing considerable impedance may not interfere with the talking efficiency, each of these supervisory relay windings is shunted by a non-inductive resistance. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The supervisory relay is included in the ring strand of the cord circuit and is shunted by a non-inductive resistance, so that its impedance will not interfere with the talking currents. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. Coils of the line and clearing-out drops by which these drops are thrown, are wound to such high resistance and impedance as to make it proper to leave them permanently bridged across the talking circuit. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The selector consists of two electromagnets which are bridged in series across the telephone circuit and are of very high impedance. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. It is found that, by making the ringers of high impedance, the leakage of voice currents through them from one side of the line to the other is practically negligible. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Its value is the square root of the sum of the squares of the resistance and reactance, or, Z being impedance, and the symbols meaning as before. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. This employs a combination of impedance coils and condensers, and in effect isolates the lines conductively from each other as completely as the repeating-coil method. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. These four impedance coils are wound on separate cores and do not have any inductive relation whatsoever with each other. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. As the impedance coils are large, have cores of considerable length, and are wound with two separate though serially connected windings each, their impedance to voice currents is great. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. In this device an insulating base carries a grounded carbon rod and two impedance coils. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The steady current from the central-office battery finds ready path through the transmitter and the impedance coil, but is prevented from passing through the receiver by the barrier set up by the condenser 8. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. This defect may in some measure be reduced by making the ringers of low impedance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Therefore, to secure high impedance we need many Page 164 turns or low reluctance, or both. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The impedance of the coil I is changed by moving its adjustable core. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. Introduction of Impedance:—It has been noted that the existence of impedance tends to choke back the passage of lightning discharge through a coil. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The iron should, if possible, be worked at that density of magnetization at which it has the highest permeability in order to obtain the maximum impedance effects. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. An impedance coil having an open magnetic circuit is shown in section in Fig. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. This coil, like the impedance coil shown in Fig. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The opposition of impedance coils to alternating currents and of condensers to direct currents are the fundamentals. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. If the coil shown therein be considered an arrangement of conductors having inductance, it will be seen that a favorable place Page 300 for an air-gap arrester is between that impedance and the line. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The use of laminated cores is for the purpose of preventing eddy currents, which, if allowed to flow, would not only be wasteful of energy but would also tend to defeat the desired high impedance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Sometimes in iron-clad impedance coils, the iron shell is slotted longitudinally to break up the flow of eddy currents in the shell. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Frequently electromagnetic coils have only the function of offering impedance, where no requirements exist for converting any part of the electric energy into mechanical work. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Each Morse circuit will be seen to include, serially, two 50-ohm impedance coils, and to have shunts through condensers to ground. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The impedance coils are wound on insulating rods, which hold them near, but not touching, the ground carbon. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. It should be remembered that an impedance coil obstructs the passage of fluctuating current, not so much by ohmic resistance as by offering an opposing or counter-electromotive force. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. An important factor in the design of impedance coils is the grade of iron used in the magnetic circuit. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Evidently such a coil, however connected, is well adapted for high impedance, on account of the low reluctance of its core. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The composite telephone sets are bridged from the line to ground at any points between the terminal impedance coils. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. It is required that its impedance be high enough to keep voice-current losses low, while being low enough to drain the line effectively of the disturbing charges. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Thus, the magnets which operate various signaling relays at the central office are often used also as impedance coils in portions of the circuit through which it is desired to have only steady currents pass. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The windings of this repeating coil are ordinarily alike; that is, 1 and 2 combined have the same resistance, number of turns, and impedance as 3 and 4 combined. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The joint Page 56 reaction is expressed in ohms and is called impedance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. This impedance requires to be of low resistance, because whatever heat is developed in it is lost energy. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The impedance of the clearing-out drop prevents the windings being shunted across the two sides of the cord circuit. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. They are, however, by virtue of their greater number of turns and the greater amount of iron that is included in their cores, of much higher impedance than the voice-current coils 3-3. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Voice currents, however, coming over the line to the station, find ready path through the receiver and the condenser but are barred from passing through the impedance coil by virtue of its high impedance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Where it is desired that an electromagnet coil shall possess high impedance, it is usual to employ a laminated instead of a solid core. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. If, with a given machine and storage battery, the talking circuits are disturbed by the charging current, relief may be obtained by inserting a large impedance in the charging circuit. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. Sketch the arrangement of bridging the battery with impedance coils and state the purpose of the coils. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Likewise, the right-hand battery is connected to the line of Station B through the impedance coils 3 and 4. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The coils 2 and 3 are made to have high impedance, while 1 and 4 are so wound as to be non-inductive and, therefore, offer no impedance save that of their ohmic resistance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. It is not, however, the high resistance so much as the high impedance that is striven for in bridging bells; it is the number of turns that is of principal importance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. These conditions are satisfied by using in the impedance coil many turns of large wire and an ample iron core. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. Explain the reason for placing an impedance in connection with the lightning arrester. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Great use is made in the design of telephone circuits of the fact that the electromagnets, which accomplish the useful mechanical results in causing the movement of parts, possess the quality of impedance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The usual diagrammatic symbol for an impedance coil is shown in Fig. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. This is the same as for an ordinary bar magnet, except that the parallel lines through the core may be taken as indicating that the core is laminated, thus conveying the idea of high impedance. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The battery supply to the operator's transmitter is through an impedance coil 9. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. Define impedance and give the formula for it. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. Likewise the impedance coil affords a means for readily transmitting steady currents but practically excluding voice currents or fluctuating currents. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. In this the battery is bridged across the circuit of the combined lines in series with two impedance coils, 1 and 2, one on each side of the battery. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The steady currents from the battery find ready path through these impedance coils which are of comparatively low ohmic resistance, and the current divides and passes in multiple over the circuits of the two lines. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The ringing current is, however, insufficient to cause the operation of this relay 12 as long as the high resistance and impedance of the subscriber's bell and condenser are in the circuit. Cyclopedia of Telephony and Telegraphy, Vol. 2 A General Reference Work on Telephony, etc. etc. The high impedance of the drop forces the voice currents to take the path through the repeating coil rather than through the drop. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. The impedance coils in this case serve to keep the telephone currents confined to their respective pairs of lines in which they originate, and this same consideration applies to the system of Fig. Cyclopedia of Telephony & Telegraphy Vol. 1 A General Reference Work on Telephony, etc. etc. |
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