What is Impedance: Definition and 502 Discussions

In electrical engineering, electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.
Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of the sinusoidal voltage between its terminals, to the complex representation of the current flowing through it. In general, it depends upon the frequency of the sinusoidal voltage.
Impedance extends the concept of resistance to alternating current (AC) circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude.
Impedance is a complex number, with the same units as resistance, for which the SI unit is the ohm (Ω).
Its symbol is usually Z, and it may be represented by writing its magnitude and phase in the polar form |Z|∠θ. However, cartesian complex number representation is often more powerful for circuit analysis purposes.
The notion of impedance is useful for performing AC analysis of electrical networks, because it allows relating sinusoidal voltages and currents by a simple linear law.
In multiple port networks, the two-terminal definition of impedance is inadequate, but the complex voltages at the ports and the currents flowing through them are still linearly related by the impedance matrix.The reciprocal of impedance is admittance, whose SI unit is the siemens, formerly called mho.
Instruments used to measure the electrical impedance are called impedance analyzers.

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  1. A

    I Planck's Impedance: Exploring the Mystery of a Fictional Measurement System

    The measurements system is defined by the following base units: 1 Berkel = 0.8590488 seconds (1,220,197,850 oscillations of the hydrogen atom in a hyperfine state) 1 Dist'al = 0.2575363 meters (Speed of light multiplied by 1×10⁻⁹ Berkels) 1 Hef'al = 17.08109 kg (Mass of 1 cubic dist'al of...
  2. P

    Integrate or divide the input impedance for transmission lines in series?

    Here I list my problem in the attachment.
  3. gasgas

    Ring Impedance & String Connection: Is It Valid?

    If we consider the coefficient b as the rings impedance, we can consider the effective impedance on the right to be b+Z2 where Z2 is the impedance of the second string. Then because there is no reflection it follows that Z1=b+Z2 or b=Z1-Z2. Is this a valid solution? My professor went through a...
  4. N

    Calculating Input/Output Impedance w/ Parallel Resistors

    Hello, attached are two screenshots showing a common emitter and the same with source voltage removes to find the input impedance. How is it that resistors R1 and RC can be placed in parallel to work out the input and output impedances? Examples i have seen only show straightforward...
  5. S

    Power Amplifier and Exciter, Impedance / Power

    Hello. I have a question regarding an power amplifier (signal generator). I have three exciters and want to connect them to the power amplifier. One exciter have a impedance of 8ohm and power of 25 watt. The ampliefier have one output with the electical data: 4 ohm : 500watt; 6ohm: 330 watt and...
  6. X

    Impedance of a half-wave dipole antenna

    73 + j42 means it has an active resistance plus reactance. But this "active" resistance is not a DC resistance, right? We can't just measure 73 ohm with a multimeter since the circuit is open. What closes it then? Let's say the reactive part is zero. How do we measure 73 ohm? By measuring...
  7. N

    Finding theoretical impedance of acoustic transducer

    Hi all If we have an acoustic transducer and values of its two parameters are known, i.e conductance and capacitance, is it possible to calculate impedance using these two parameters? Thanks
  8. N

    Impedance mismatch issue in receivers

    Hi all I have an acoustic piezoelectric sensor whose output impedance should be ideally 50 ohm and a preamplifier circuit specifically designed for this sensor having input impedance of 50 Ohm. The piezoelectric sensor output voltage range is from uVrms to few mVrm. These low voltage signals...
  9. A

    A Surface impedance equation for resonators

    Hi all, I am reading this thesis and have two questions to section 5.1.5: https://rsl.yale.edu/sites/default/files/files/RSL_Theses/reagor-thesis-20151202.pdf First question is: Where did equation 5.19 come from? Second question is: If you look at this paper https://arxiv.org/pdf/1308.1743.pdf...
  10. Joshy

    Engineering Source impedance using given voltage swing and power

    Hi! I normally have a pretty good grasp of what the source and load impedance for these types of problems; however: This textbook is giving me peak to peak voltage swing 6V33 and 1 W of power. I'm a little bit confused at converting this into an input impedance and am worried I'll be off by a...
  11. iochoa2016

    I Measuring characteristic impedance as suggested by KRAUS' book

    Can someone provide more information about this method to measure chracteristic impedance using resistance paper?. Kraus' book claims that the characteristic impedance can be measured by simple dc measurement. It even shows a case to mesure the impedance of a coaxial cable with square outer...
  12. mechorigin

    Engineering Having issues series resistive and reactive impedance matching

    The only thing I could think of was using Q=sqrt(6000/50)-1 = 10.9, which then gets me XL=545 and XC=550, or 96.4nH, and 0.32pF at resonance of 900Mhz. I tried seeing if Zin=Zout equation would bring me close, so I tried Z=545+(50-550)=45, then XL for 38.5nH was 217.7, and XC for 2.4pF was 74...
  13. A

    Engineering Finding Impedance in Circuits: A Step-by-Step Guide

    Hello! The circuit to the given problem statement.Now to do this I've used a method we were shown in class where we simply close the circuit on the left (meaning there will be wires where U is) and go from point A to point B.That would mean that these capacitors are in series. Now I've put...
  14. T

    Impedance Matching: The mathematical Conditions for Matching Network

    Assume we have a network consisting of a source with impedance ##Z_S## and load with impedance ##Z_L## and we want to perform impedance matching on them in order to obtain the maximum power transfer: Note that in practice there may occur sitations where causes more harm than profit (see eg...
  15. D

    Engineering Input and Output Impedance of circuit

    Hi, I have a circuit with 3 transistors I want to rewrite to a small signal model. When multiple transistors are in the circuit I get confused how to do it. This is the signal model and small signal model I have. Is it wrong?
  16. R

    Exploring Wave Reflection: A Mathematical Journey

    I know for a wave moving from left to right, ##\psi_i = Ae^{i(\omega t - k_1x)}## The first reflection where ##Z_1## is ## R_{12}Ae^{i(\omega t - k_1x)}## The second reflection. The wave moves from 2 to the limit between 2 and 3 then reflect... Thus, ##T_{12}R_{23}T_{21} Ae^{i(\omega t - k_1 x...
  17. T

    Impedance Matching when the Transmitter, Line and Load impedances are different

    Assume we have a general rf system where source with impedance ##Z_S## transfers a signal to a load with impedance ##Z_L## through a transmission line with impedance ##Z_T##. We want to match this system in order to maximize it's effiency: In https://en.wikipedia.org/wiki/Impedance_matching...
  18. brainbaby

    Calculating Input impedance of a CC amplifier

    Hi friends, Here is a CC amplifier The objective is to calculate its input impedance. Two ways are employed. *calculating input impedance using series resistor method (manual method) (refer first two attachment) V1 = 1mV = 0.001 V V2 = 656.4129mV = 0.6564129 V R = 1K Iin = 343.83207µA =...
  19. P

    Engineering Finding out the input impedance in a negative feedback op-amp

    In this case, there is negative feedback. ##V_{out}## is almost equal to ##V_{in}## in this case. But I really can't understand how to even proceed to find out the input impedance in this case, from the equation I know. Can someone help me out in figuring how should I proceed?
  20. P

    Engineering Analyzing the output impedance and open loop gain of a IC-741 Op-Amp

    Here is the internal circuit of the 741 Op-Amp - Looking at the output stage, the output impedance seems to be the series combination of ##25 \Omega## and ##50 \Omega##, that is ##75 \Omega##. Is this a qualitative explanation enough to justify the output impedance, or am I wrong somewhere and...
  21. T

    Engineering Resonance in AC circuits

    Here's my attempt at a solution.
  22. J

    Impedance change in matter from ionizing radiation?

    Bio-impedance technique is used to monitor various organ related qualities. Shift in metabolism will also show up as a shift in impedance. My question is if by exposing a target volume with ionizing radiation and thereby release electrons and at the same time measure the impedance (which will...
  23. Andrei0408

    How do you calculate the impedance of the primary circuit?

    I'm not sure if it helps for what I'm looking, but I've calculated the mutual inductance, M, using the equation: M=U2/(ω*I1) = 106.3μH. I don't need the numerical value in particular, I just want to find a way to deduce the formula in order to calculate Z1. Thank you!
  24. R

    Find the Equivalent Impedance of the Network

    We are asked to find the equivalent impedance of the network. Nothing is in series or parallel so I don't know what to do. We cannot use mesh equations or Thevenin's theorem because is no current or voltage source. So I have no clue.
  25. J

    Calculate the impedance in this RC circuit

    So Z = sqrt[ R^2 + (1/wc )^2] and V=Ecos(wt) so I= Ecos(wt) / sqrt[ R^2 + (1/jwc )^2] but how do I use this to find the amplitude and phase of the current?
  26. duchuy

    Magnetic permeability and optical impedance

    Hi, It's given that an electromagnetic wave (5.10^14 Hz) traveling in an environment with the index n = 1,33, where the magnetic permeability (μ) is equal to the magnetic permeability in a vacuum (μ0). The optical impedance (Z) is given by the formula : Z = μ . c/n. I tried to turn μ into μ0 to...
  27. C

    Max velocity of a vibrating loud speaker membrane given sound intensity

    My attempt: p and T allows us to calculate ##Z=402 \frac{kg}{sm^2}## using ## Z=p*\sqrt(\frac{\gamma*M}{R*T})## . The sound intensity level at 10 meters allows us to calculate the intensity at 10 meters to be I=10``````^{-7} W/m^2 using ##50 = 10*log(I/I_0)##. Then, using the formula...
  28. J

    How to Measure PCB Impedance and Component Coupling?

    I am designing a PCB with multiple capacitors on it. I would like to measure the board impedance to compare it with results from Ansys Q3D. I can connect it to an impedance analyzer and easily get the impedance. I have recently thought about other meaningful measurements that I may be able to...
  29. Maverickans

    Impedance calculation from base values

    Hello, I'm reading a paper at the moment and I came across this: We now apply the solution technique to a single-phase, 3 kW, 240 V ASD heat pump. The ASD has smoothing capacitor C = 4200 pF, (corresponding to approximately 6% ripple in dc voltage), and total impedance (sum of Thevenin and...
  30. B

    Engineering RLC Series Network: Impedance, Current, Power Factor, Phasor Diagram

    Hello. I have completed the following question. My answer: i) Circuit Impedance Reactance = XL = 2 x pi x F x L = 2 x pi x 50 x 0.15 = 47.12 Ohms Reactance of Capacitor = XC = 1/2 x pi x F x C...
  31. I

    Impedance of Circuit (Complex Numbers Question)

    Question is from Boas Ch. 2 Q.41 (I've the first edition) or Q 16.8 in the 3rd edition. Find the impedance of the circuit shown (R and L in series, then C in parallel with them). Circuit is essentially this (it is a closed circuit which I can't easily draw). -----R------L--- -------C---------...
  32. putrinh

    How to solve this to calculate the input impedance?

    How did you find PF?: Google search I got a problem, how to calculate this formula from euler to imajiner? or how calculate this case?
  33. tanaygupta2000

    New impedance after feedback

    I know that when the feedback is connected, the voltage gain changes by the above formula. But I don't know how to find final values of input and output impedances.
  34. AA6EG

    Feedline impedance matching for the WSM 50 Kilowatt AM station in Nashville TN

    The WSM 50 Kilowatt AM station in Nashville TN, has been transmitting using the same ~950ft 5/8 wave Blaw Knox Diamond antenna, since 1929. The 5/8 wave vertical had some horizon gain over a 1/4 wave vertical so theoretically will serve distant listeners better. It was found though that...
  35. brainbaby

    Unable to get the desired impedance in this LTspice simulation

    Hello friends, I am studying an article on impedance matching which states about matching a resistance of 52 ohms with 2k ohm. It is accomplished by adding an inductance of XL= 318 ohms in series with the 52 ohm resistor yielding a parallel equivalent of 328ohm as reactance and 2k ohm as my...
  36. paulmdrdo

    Finding the output impedance of Current Controlled Current Source

    Summary:: I was trying to derive the equation for the output impedance of the ICIS circuit. Here's what I've tried so far. What I have derived does not agree with the one provided in my book. Since it is a current source the negative feedback must increase the output impedance. The one I...
  37. E

    Help with Homework Equation: Input Impedance

    Homework Equation: I do not think I am getting the correct answer for this problem when I do it out by hand. Do I plug the necessary values into the equation shown above or do I say that because it is an infinite line that the characteristic impedance is equal to the input impedance? If the...
  38. E

    Characteristic Impedance of a coaxial cable

    Image 1: Image 2: I am attempting to learn about transmission lines and am having problems with this homework problem. For part a, I have derived an equation for the maximum electric field within the dielectric. I came up with: with r being the radius and the electric field decreasing...
  39. R

    Best way to match impedance between an amplifier and transducers

    I am trying to figure out the best way to match impedance values between an amplifier (50 Ohm) which powers a number of transducers (initially 50 Ohm but could change). For one transducer I have previously used a step up transformer (SUT) device between the amplifier and transducer. Now I have...
  40. brainbaby

    How does the tapped capacitor network increase the impedance?

    Please help me comprehend the text below... The discussion begins with the current flowing through the inductor for both the cases (case a and b) stays same.The input voltage is Vi. When two tapped cap is used with the current that is flowing in the inductor is divided among the two...
  41. brainbaby

    Determine the output impedance of the circuit

    Hi friends, I have taken three sine AC sources and have joined them in series. I want to find the output impedance of this circuit. Formula that I am using is...Output impedance = (Open circuit voltage - Output voltage with load R1) / Output current with load (R1) Load resistance = 1 k ohm...
  42. J

    Engineering Input and Output Impedance of an Opamp Circuit

    I know for ideal opamp the input Z is infinite, and output Z is 0, but not sure about this opamp.
  43. M

    Calculate the zero-sequence line impedance

    Hi. I want to calculate sequence line impedance of transmission line. But i can't find any parameter of Z1 and Z0 of transmission line in simulink. It's only have parameter about number of phase, frequency, R1/R0, L1/L0, C1/C0 and line length. Can i calculate sequence line impedance from these...
  44. DamunaTaliffato

    Transistor output impedance

    I have this curcuit. I want to discover the output impedance. Using h-parameter model I get the second circuit. I know that Zout= V(open circuit)/I(short circuit) and ie = C ib, where C is an appropriate proportionality factor. Vol = V1 Re/(Rb+Re) = (Rb ib + Re ie) Re/(Rb+Re) Isc = ie = C ib...
  45. Pierson5

    Complex impedance and phase angle of a circuit

    I've attached my work below. The numbers seem odd to me though. Are my equations correct? Is the phase angle really (0/12)? If so, what are the implications of that?
  46. A

    RF cavity shunt impedance, PD and input power

    I still did not understand this from my previous threads, what is the way to determine the instantaneous voltage across the cavity plates at any given moment, in a klystron I suppose the voltage would be proportional to the arriving electron bunch density which would determine the overall bunch...
  47. Q

    Characteristic Impedance differences

    Could I get a conceptual answer, supported by math, explaining why coax has less characteristic impedance than open wire feeds? I’m new to EE. Thanks for you patience.
  48. M

    Impedance graph of a transmission line powersystem in MATLAB/simulink

    I'm trying to plot impedance locus of transmission line in Matlab/Simulink. I have readed some document and thay have plot result like that : I'm trying to calculate impedance when system have short - circuit fault, and plot it on R-X diagram, but i can't get their *red - dot* result like those...
  49. bobg123

    Engineering Circuit input impedance with ground in an OP Amp circuit

    I've been given the following circuit and have been asked to find the input impedance and the impedance between the input terminal and ground. I've never encountered an operational amplifier configured like this. I know that the voltages at the - and + terminals of the op amp are ideally equal...
  50. J

    AC Cirucits - Impedance Values

    Homework Statement For the circuit given in the power factor is 0.72 lagging and the power dissipated is 375 W. Determine the: (1) apparent power (2) reactive power (3) the magnitude of the current flowing in the circuit (4) the value of the impedance Z and state whether circuit is inductive...