Frequently asked questions on the electric field probe called eoProbe

The purpose of these Frequently Asked Questions (FAQs) is to answer most of questions in order to help you to better understand the measuring performances and advantages of using Kapteos technologies inside the applications.

FAQS on eoProbe plug

General frequently asked technical questions

The sensor is designed to measure electric fields with the following characteristics: field shape, amplitude, phase, frequency. The measured bandwidth is very large (from few tens of Hz to few tens of GHz). The E-field to be measured must have an amplitude of at least 50 mV/m or 500 mV/m depending on the type of probe.

The probe cannot measure magnetic fields.

The probe does not include any metal part. It is insensitive to magnetic fields. The active part of the probe is based on a crystal and has been designed only for electric fields measurements.

This feature is a great advantage where used under high voltage applications (fully insulated) or under high magnetic fields (MRI machines).

Applications are divided into two main groups of applications: the biological application and the industrial application:

  • In the biological applications, the probes are used for the Specific Absorption Rate (or SAR) assessment. The actors mainly concerned are the research centres, manufacturers of consumer devices and power systems that emit electromagnetic waves.
  • In industrial applications, any application that requires an electric field measuring in near-field (even a few millimeters or less), in-situ or laboratory in any rather severe environment. The mainly concerned segments are the systems and equipment in medium and high voltage, power electronic systems (windmills, solar, variable speed drives, uninterruptible power supplies, welding …), railway, mining, MRI, marine, submarines, defense, telecommunications, automotive and many others …).

The probe has many assets like its very compact design (5 mm x 35 mm). It does not include any metal part, which does not impact the measured field and is fully insulated. It is extremely robust against electromagnetic environment. The probe is connected to the treatment converter (eoSense) by a fibre optic up to 100 meters long. It allows the electric field measurement in the air, liquids or gases (such as plasma for example). The measured signal bandwidth is very large (few tens of Hz to few tens of GHz). The measurement remains stable in ambient temperature from 0 to 50 °C at the sensor’s location. It is therefore perfectly adapted to the above mentioned applications.

The sensor operates on the Pockels effect.

The eoSense converter (which mainly manages the operation of the probe and accessories), sends a light wave in the fibre optic. A crystal is located in the probe. This crystal is traversed by the light wave which is itself affected by the electric field to be measured. The modified light wave (measured signal) is sent to the eoSense converter that will convert the light information into an electrical information, usable by any digital acquisition system.

One probe corresponds to one E-field component (an axis of the electric field vector). If you want to measure 2 axes of the electric field vector, 2 probes must be used.

The probe supplies to its converter, the vector information of the electric field, that is to say, the shape of the field, the amplitude, the phase and frequency and this in a continuous manner. The optical signal transmitted to the converter is not a sampled signal but a 100% analogue one.
A probe corresponds to a component of the E-field (an axis of the electric field vector). If you want to measure 2 axes of the electric field vector, 2 probes must be used.

The eoSense converter converts the optical signal measured by the probe into an electrical value. This value multiplied by the antenna factor provided an absolute (real) value. As an indication with a field of 1000 V/m and an antenna factor around 100dB/m (100.000 m-1), the analogue voltage output from the eoSense converter will be approximately 10mV.

An online simulation software ( will help you to estimate this output voltage value from the eoSense converter.

There are 2 types of probe:

  • The probes measuring transverse fields (t)
  • The probes measuring longitudinal fields (l)

For transverse type probes (t), the black mark engraved on the probe must be aligned as shown in the drawings below:


For longitudinal type probes, the probe must be oriented as shown in the drawings below:


Now from a practical point of view, let’s take 2 examples with one probe:


In theory yes but the real E-field value from most of applications that would destroy the probe, is still well below the physical capabilities of the probe; making it extremely robust with respect to targeted applications. Tests were carried out under 10MV/m without destroying the probe.

Yes. Mechanical stress on the probe or an excessive bend or shock of the fibre optic may induce an erroneous measurement and this irreversibly. Manipulating carefully the probe and the fibre optic are therefore important with respect to the longevity of the system. The guarantee excludes any mechanical stress on the probe and its fibre optic.
A temperature above the specified operating temperature range of the probe (0 to +50 °C) may also disturb the measurement.

Yes. The probe provides the full instantaneous temporal information to the eoSense converter which converts light information of the probe into electrical information. The entire probe and the eoSense converter are calibrated by Kapteos. Thanks to the use of the real-time antenna factor correction, the client can process the information in accordance with his need to obtain absolute (real) values.

The minimum distance can be considered at zero distance (contact) as the damage threshold of our fully dielectric probes (complete absence of any metal), in terms of electric field strength, is higher than 10 MV/m (i.e. much higher than air breakdown).

The main precaution to handle a probe is to NEVER generate mechanical stress, nor to the probe neither to the fibre optic. The device, despite his robust appearance, remains a highly efficient measuring system and must be handled with great care.

We can qualify a measure of ideal if the measured field is strong (several V/m and above) and if the eoSense converter is protected from electromagnetic interference. This last point is quite realistic due to a fibre optic length between the probe and the converter up to 100 meters.
The last important point is the ambient temperature range of the probe that should remain between 0 and +50 °C.

To date, the following available documents are:

  • The user manual (eoSense converter)
  • The datasheet
  • The calibration certificate

See with Kapteos for any other specific request of documents.

The sensor characterization elements are provided in the well detailed certificate of the probe with its eoSense converter. The probe and its converter cannot be used separately.
In general, the accuracy depends mainly from the signal acquisition system of the customer. One can expect a typical accuracy of ±1 to ±2dB.
We remind you that, as a measurement system, it is imperative to check and calibrate regularly your equipment as recommended by Kapteos.

The standard distance is 5 meters from the sensor to the eoSense converter. At the order, the length can be increased up to a total distance of 100 meters without reducing the performances of the measure.
Also note that the signal carried out by the fibre being optical, this one cannot be affected by its environment, leading to a stable and robust measurement.

All the available probes are listed in the data sheet of the probe.
If needed, please contact Kapteos to be guided.

No. The packaging of the probe is adapted to its environment. This material is different for a sensor that measures an electric field in the air of a sensor that measures an electric field in a liquid or a gas.

In general, customers are used to measure E-field based on antennas. These antennas present:

  • Metal part (measurement distance is needed in case of presence of high voltage)
  • Low maximum E-field to measure (distance is needed to reduce maximum E-field to measure)

These restrictions are not present with Kapteos probes. It is then very easy to approach the probe to increase the E-field to measure, hence increasing the E-field.

Frequently asked questions about the characteristics of the probe

The type of a probe determines its physical construction and characteristics; hence the orientation of the measured field.

Transverse type probe                                                                 Longitudinal type probe


Other features that determine the type of sensor are:

  • The packaging of the crystal (for measurements in air, liquids or gases)
  • The length of the fibre optic between the probe and the eoSense converter
  • The sensitivity

A probe corresponds to a channel and allows the measure of one of the three axes of the electric field. If you want to measure the 3 axis of the electric field, it is necessary to use 3 probes at the same time. Two different accessories are available to maintain these 3 probes.

Kapteos offers 2 physical dimensions of crystals inside the probe. This has a strong impact on the measurement sensitivity and the frequency bandwidth. The sensitivity of 50mV/m specified (in the air with a longitudinal probe type) allows a proper signal/noise measurement ratio. The eoProbe data sheet provides the relevant characteristics linked to the sensitivity.

The dynamic of measurement is the ratio between the largest possible value and the lowest possible value, this ratio is expressed in decibels. For the field measurement, we must also divide the ratio by the square root of the frequency of the measured signal.

The higher the ratio, the better the probe is performing.

The formula is then as follows:


To understand the performances of the Kapteos probe, let’s take 2 examples of an application:

  • Frequency 1kHz
  • The strongest signal = 100kV/m
  • The lowest signal = 0.1V/m

Dynamic (dB) = 20 × log [(100,000/0.1)/√1000] = 90dB

  • Frequency to 1MHz
  • The strongest signal = 100kV/m
  • The lowest signal = 0.1V/m

Dynamic (dB) = 20 × log [(100,000/0.1)/√1.000.000] = 60dB

In practice, the Kapteos probes have a dynamic of measurement that may exceed 130dB.

At 50Hz, this indicates that a Kapteos probe can measure electric fields higher than 1MV/m.

This is the maximum possible frequency of the electric field to be measured.
Kapteos probes incorporate a crystal having two possible physical lengths:

  • 5 mm: the minimum sensitivity is about 50 mV/m and bandwidth is around 10 GHz (air type probe). In some specific cases, the maximum bandwidth could be increased beyond this value
  • 1 mm: the minimum sensitivity is about 200 mV/m and bandwidth is around 40 GHz (air type probe)

Kapteos sets the maximum or minimum bandwidth at -3dB.

A probe measures only one axis of the electric field. To be sure not to be disturbed by the other axis, the probe must be able to “reject” the other 2 axes of the field. This ability is called the selectivity which is measured in decibels. The higher the value, the better the probe is selective.


The Kapteos probes have a selectivity of about 50dB.

This indicates that the value of the 2 other useless axes is not more than 0.3% of the value of the relevant axis.

The spatial resolution is the smallest distance between two steps of measurements placed next to each other. This resolution corresponds to the physical dimension of the laser beam: 0.6 mm. So if the probe moves of 0.6 mm (x or y axis), a new electric field measurement can be made. Kapteos indicates a resolution of 1 mm to be valid in all cases.

One of the limitations of the electro-optic technology for electrical field measurement is the ambient temperature of this measurement. Indeed the crystal is strongly affected by the temperature which often limits the use of this technology at a stable temperature of a laboratory. In addition the fibre optic is also affected by the temperature.

However this is not the case for Kapteos probes. They can measure an electric field in a wide temperature range (0 to +50 °C) without any degradation of the signal. This allows the measurement of electric fields in most outdoor applications in operation throughout the year.

The protection degree (IP) sets the level of protection allowed by hardware to external conditions that are solids or liquids.
This level is defined by the international standard IEC 60529.
It is characterized by 2 numbers:

  • The first number indicates the level of protection against foreign object
  • The second number indicates the level of protection of the water tightness

The table below shows the different levels of protection.

Protection level Foreign object Water tightness
0 No protection No protection
1 Protection against foreign object > 50 mm Protection against vertical drops
2 Protection against foreign object > 12.5 mm Protection against oblique drops (maximum 15° inclination)
3 Protection against foreign object > 2.5 mm Protection against water “rain”
4 Protection against foreign object > 1 mm Protection against splashes
5 Protection against dust deposits Protection against water jets
6 Protection against dust intrusion Protection against water packages
7 Protection against immersion
8 Protection against permanent immersion

The crystal of the probe is protected in a mechanical packaging. This packaging also allows to adapt the measurement of an electric field according to its environment and this with almost no impact. Furthermore, when the probe is used in a gas or a liquid, it should not chemically degrade the probe. The chemical compatibility corresponds to the exhaustive list of media for which the probe is not chemically degraded.

If the media of the measure (biological environment in particular) is dirty, the probe can be cleaned using isopropanol.

Frequently asked commercial questions

Yes, there are 3 types of probe:

  • Environment:
    • low permittivity (air or nonpolar liquids based like oils) called “air” type
    • low permittivity for vacuum medium called “vac” type
    • high permittivity (polar liquids based like water or other water based liquids or gas) called “bio” type
  • Direction of the axis to measure: transverse or longitudinal
  • Sensitivity of the probe: very low or standard

So to date in total, Kapteos offers 12 different probe versions.

For each version of probe, you have also the possibility to select the length of the fibre optic between the probe and the eoSense converter which is 5 meters long in standard or any other length (max. 100 meters) to be defined at the order.

Yes. If the customer wants to measure 2 or 3 axes of the vector field at the same location, then it is possible to use different holders which maintain the 2 or 3 probes in the same place. These holders may be used alone or with eoPod (articulated arm). Please refer to the data sheet of the probe.

Also, if the customer wishes to calibrate the probe to its specific organic liquid medium, then the customer can use the eoCal accessory for a do-it yourself calibration.

Finally, if the customer wants to add extra length to the probe, then the customer can purchase a fibre optic extension that includes the two optical connectors (one for the eoSense converter and one for the probe).

Yes if you have already purchased an eoSense converter. However, the mandatory calibration of the probe and the eoSense converter assembly requires the return of the equipment in full to Kapteos. In no event, the calibration is made at the customer’s place by Kapteos.

Yes. There is a possible fibre optic extension between the probe and the converter. The total length of the fibre optic of the probe and the extension should be at most 100 meters. This extension is defined in a data sheet available on the website.

In the necessity of measuring another field or another axis of the field, Kapteos offers several possible solutions:

  • Upgrading your eoSense converter (adding an additional channel), adding another probe and the calibration of the all system. The material must be returned to Kapteos
  • Rental of an additional probe with its converter

Measurements made by Kapteos at the customer’s plant.

Yes. Kapteos provided the following products and accessories for worldwide rental:

  • eoSense converter with 1 to 3 probes linked to customer needs
  • Fibre optic extension
  • eoProbe fixing accessories
  • eoCal calibration system for bio eoProbe
  • eoAcq Data Acquisition System with data treatment (40 Hz to 30 MHz converter)

Thanks to contact Kapteos for the commercial terms of products and accessories rental.
In all cases, Kapteos equipment rental remains subject to the availability of this material.

Frequently asked questions on after sales services on probe

Yes indeed. Before returning the equipment, it is recommended to contact Kapteos to confirm the correct use of equipment. In cases where the probe seems defective, Kapteos will ask you for the return of all equipment (sensor(s) and converter) for verification.
Remember, the calibration of the equipment is valid as specified in the calibration certificate.

If you which to return a system to Kapteos for a check, please enter first the following form to get a return number (RMA) from Kapteos.

Calibrating a probe imposes the return of the probe and its associated converter to Kapteos. In no case, the calibration is made at the customer’s plant by Kapteos.

Yes. Even though the probe has been designed as an inseparable unit with fibre optic, Kapteos may repair the probe. You have first to enter the form to get a RMA number from Kapteos. After acceptance of the RMA, Kapteos may ask you to return only the concerned probe or the full system. After analysis of the probe by Kapteos, we can propose you the relevant corrective action.

The connector has been qualified for the use in the field.
To date, it is not supposed to replace the connector but in the unlikely event of a deterioration of the connector (despite strict precautions usage), Kapteos may accomplish a replacement of this part after acceptance of a quote and return of equipment (sensor(s) and converter).

Kapteos could propose the following possibilities:

  • The sending of a measuring system with a probe. This remains conditional to the availability of equipment.
  • The achievement of measurements made by Kapteos at the customer’s plant. This remains conditional to the resources availability of Kapteos.

It is therefore very important to anticipate the planning of your measurement campaigns, to check in advance that your equipment is operational.

It is recommended to contact Kapteos to get help from Kapteos who will do his best to find the best solution for your situation.