# Time-varying electric field measurement using dipole

• AliAttaran
In summary: I did different measurement in higher freq and I did not have any problem. since the nature of the signal is important for my probe, I cannot use diode to rectify the signal, Thanks.
AliAttaran
Hello,

I am trying to measure the time-varying electric field of a parallel plate capacitor using short dipole antenna, but my numbers are off by almost 100 times. I have a parallel plate capacitor, A=23cmx11cm, d=10cm. I apply 10sin(2pi*1KHz) and 10sin((2pi*1KHz)+180deg) to each plate. I am using a L=2cm dipole. So based on the book, peak electric field is E=(10+10)/d=200V/m. Now measured electric field using dipole is E=V/L=40mv/2cm=2V/m. I need help to understand the reason?!

Thanks

I am having trouble understanding
AliAttaran said:
10sin(2pi*1KHz)
Is that 10 V? I assume there should be a *t inside the parentheses.

AliAttaran said:
to each plate
How are you applying two voltages to each plate?

AliAttaran said:
So based on the book, peak electric field is E=(10+10)/d=200V/m
I am not sure if this is the applicable formula, but 200 V/m seems way too high for a 10 V signal measured 10 cm away. Are you sure about this formula? It seems more likely that the d in this formula is the thickness of the capacitor and the E-field is the E-field between the plates. Do you have an online reference for this formula, it just doesn't seem right to me.

Last edited:
AliAttaran said:
Hello,

I am trying to measure the time-varying electric field of a parallel plate capacitor using short dipole antenna, but my numbers are off by almost 100 times. I have a parallel plate capacitor, A=23cmx11cm, d=10cm. I apply 10sin(2pi*1KHz) and 10sin((2pi*1KHz)+180deg) to each plate. I am using a L=2cm dipole. So based on the book, peak electric field is E=(10+10)/d=200V/m. Now measured electric field using dipole is E=V/L=40mv/2cm=2V/m. I need help to understand the reason?!

Thanks
The voltage on each plate seems to be referenced to ground, so there is 20 volts peak between the plates. The spacing is 0.1m so the field strength looks correct at 200v/m.
I notice that the test dipole is very short. It will have an immensely high impedance. Does your measurement system have an even higher impedance so it can deal with this? Does the connecting lead avoid pick up? Is the test device balanced with respect to ground? Basically, I think the test dipole is a problem.

Dale and AliAttaran
tech99 said:
The voltage on each plate seems to be referenced to ground, so there is 20 volts peak between the plates. The spacing is 0.1m so the field strength looks correct at 200v/m.
I notice that the test dipole is very short. It will have an immensely high impedance. Does your measurement system have an even higher impedance so it can deal with this? Does the connecting lead avoid pick up? Is the test device balanced with respect to ground? Basically, I think the test dipole is a problem.
Yes you are right, even though, I have connected it to 1Mohm terminal of the osc, but dipole has higher impedance, therefore I lose the signals.

AliAttaran said:
Yes you are right, even though, I have connected it to 1Mohm terminal of the osc, but dipole has higher impedance, therefore I lose the signals.
If you raise the frequency to, say, 10 MHz it might work. It is also possible to place a diode at the dipole centre with two resistors connecting it to the cable. . This allows quite good RF measurements at UHF. You need to calibrate the diode with a signal generator, maybe at a lower frequency if necessary.

tech99 said:
If you raise the frequency to, say, 10 MHz it might work. It is also possible to place a diode at the dipole centre with two resistors connecting it to the cable. . This allows quite good RF measurements at UHF. You need to calibrate the diode with a signal generator, maybe at a lower frequency if necessary.
I did different measurement in higher freq and I did not have any problem. since the nature of the signal is important for my probe, I cannot use diode to rectify the signal, Thanks.

tech99 and Dale

## 1. What is a time-varying electric field?

A time-varying electric field is an electric field that changes over time. This means that the strength and direction of the electric field are not constant and may fluctuate or oscillate.

## 2. How is a time-varying electric field measured?

A time-varying electric field can be measured using a dipole antenna. The dipole antenna is a simple structure that consists of two conductive elements, such as wires or rods, that are oriented in opposite directions. The voltage induced in the dipole antenna by the changing electric field is measured and used to calculate the strength and direction of the field.

## 3. What is the purpose of measuring a time-varying electric field?

Measuring a time-varying electric field can provide valuable information about the electromagnetic environment in a given area. This can be useful for studying the effects of different sources of electromagnetic radiation, such as radio waves or electrical power lines, or for monitoring changes in the electric field over time.

## 4. How is the data from a time-varying electric field measurement analyzed?

The data from a time-varying electric field measurement is typically analyzed using mathematical techniques, such as Fourier analysis, to determine the frequency components of the electric field. This can help identify the sources of the electric field and provide insight into its behavior.

## 5. What are some applications of time-varying electric field measurements using dipoles?

Time-varying electric field measurements using dipoles have a wide range of applications. They are commonly used in electromagnetic compatibility testing, where they can help identify potential sources of interference. They are also used in environmental monitoring to study the effects of electromagnetic radiation on living organisms. Additionally, they are used in antenna design and optimization, as well as in radio frequency engineering and telecommunications.

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