This interesting device allows you to hear the world of electromagnetic radiation that surrounds us. It transforms vibrations high frequency radiation generated by a variety of electronic devices in an audible form. You can use it near computers, tablets, mobile phones etc. Thanks to it, you will be able to hear truly unique sounds created by working electronics.

Schematic diagram

The scheme assumes the implementation of this effect with the smallest possible number of radioelements. Further improvements and corrections are at your discretion. Some part values ​​you can tailor to your needs, others are permanent.

Build process

Assembly requires the use of a breadboard of at least 15 x 24 holes, and special attention is paid to the layout of the elements on it. The photographs show the recommended location of each of the radio elements and what connections to make between them. Jumpers on printed circuit board can be made from cable fragments or cut off legs from other elements (resistors, capacitors) that remained after their installation.

First you need to solder the coils L1 and L2. It's good to move them away from each other, which will give us space and increase the stereo effect. These coils are the key element of the circuit - they act like antennas that collect electromagnetic radiation from the environment.

After soldering the coils, you can install capacitors C1 and C2. Their capacitance is 2.2 μF and determines the lower cutoff frequency of sounds that will be heard in the headphones. The higher the capacitance value, the lower the sounds reproduced in the system. Most powerful electromagnetic noise lies at 50 Hz, so it makes sense to filter it out.

Next, we solder 1 kOhm resistors - R1 and R2. These resistors, together with R3 and R4 (390 kOhm), determine the gain of the operational amplifier in the circuit. Voltage inversion is not particularly important in our system.

The virtual mass is resistors R5 and R5 with a resistance of 100 kOhm. They are a simple voltage divider, which in this case will divide the 9 V voltage by half, so from a circuit point of view the m/s is powered by -4.5 V and +4.5 V in relation to the virtual ground.

You can put any operational amplifier with standard pins into the socket, for example OPA2134, NE5532, TL072 and others.

We connect the battery and headphones - now we can use this acoustic monitor to listen to electromagnetic fields. The battery can be glued to the board with tape.

Additional features

What can be added to increase functionality? Volume control - two potentiometers between the output from the circuit and the headphone jack. Power switch - now the circuit is on all the time until the battery is disconnected.

During testing, it turned out that the device is very sensitive to the field source. You can hear, for example, how the screen on your mobile phone is updated, or how beautifully he sings USB cable during data transfer. When attached to a switched-on loudspeaker, it works like a regular and quite accurate microphone that collects the electromagnetic field of the coil of a working speaker.

It looks good for cables in the wall, like a locator. You just need to raise the bass by increasing all 4 capacitances to 10 µF. The disadvantage is that there is quite a lot of noise and the signal is also too weak - you need some kind of additional power amplifier, for example.

Video of the HF detector in operation

Discuss the article UNUSUAL ELECTROMAGNETIC FIELDS DETECTOR

Very often, when building various electrical generators or motors, it is necessary to determine the pole of a magnet. Almost every person knows from school physics lessons that a magnet has two poles: north (indicated in blue by the letter “N”) and south (indicated in red by the letter “S”).
This simple electronic detector will help you identify the name of a magnet's pole. To build it, you don’t need scarce parts and components.
The detector uses a Hall sensor as a sensor, which can be removed from an old computer cooler. Fortunately, everyone has a lot of such “good” now.
As you know, computer fans have a brushless motor. Which consists of two windings on the armature and a switching element - a Hall sensor. This sensor switches the windings depending on the position of the movable magnetic ring located in the impeller.

Fan circuit

This element has four pins. Two are power supply, and two outputs on which power is located depending on magnetic field. That is, the power level can only be on one of the pins.

Magnetic detector circuit

In place of the windings we will connect multi-colored LEDs, through a limiting resistor. We will power the entire circuit from a 3 Volt coin cell battery.
We will assemble the circuit on a breadboard. Let's display the sensor a little on the terminals.

Let's check. The only disadvantage of this sensor is that the level is always present at one of the terminals, regardless of the presence of a magnetic field. Therefore, I added a power button to connect the circuit to the source. In the end, it works like this: bring it to the magnet, press the button - the LED indicating the field lights up, that's it - the button can be released.

I put the board into the housing from a flat marker. Everything turned out very beautiful. As a result, I became the owner of such a pocket magnetic field indicator. Suitable for farming.

Experimental setup diagram

Illustration: Kasper Jensen et al., 2016, arXiv:1601.03273

Danish and Russian scientists have developed a non-invasive method for measuring the magnetic field of individual nerves that works at room temperature and has virtually unlimited sensitivity. They reported on their work in a publication, a preprint of which is available on arxiv.org.

The signal travels along the nerve fibers in the form of an electrical action potential. Recording the electrical activity of nerves is critical for studying physiology nervous system and diagnosis of her diseases. However, to measure the electrical potential of a nerve fiber, it must be connected to a microelectrode, which requires surgery. In addition, the electrode connection itself may distort the signal characteristics.

Therefore, the electrical activity of nerves is measured by the magnetic field it creates. This field is very weak and requires highly accurate methods to register it. Since the 1980s, this method has been magnetometry using a superconducting quantum interferometer (SQUID, from English. SQUID, SuperconductingQuantumInterferenceDevice). This method is cumbersome, expensive, requires cooling of the conductor to ultra-low temperatures and can only measure the magnetic field of the nerve passed through the detector coil, which makes its use in the clinic impossible.

Employees of the Copenhagen and St. Petersburg universities used a modified optical atomic magnetometer of their own design. Its action is based on the ability of cesium gas atoms to polarize light under the influence of an external magnetic field (cesium was chosen due to the high pressure of its saturated vapor, which ensures high accuracy of measurements at room temperature). A laser is used as a source of polarized light. Magnetic field measurements are carried out in two modes - constant and pulsed. All this helped to achieve measurement accuracy limited only by quantum effects; the device is capable of detecting magnetic fields with an inductance of less than a picotesla (10 -12 tesla).

The sensor, which is a cesium vapor chamber, has an internal diameter of 5.3 millimeters and a wall thickness of 0.85 millimeters, which allows high-precision measurements to be made at a distance of four millimeters from the nerve fiber, that is, for example, through the skin. Tests on the frog's sciatic nerve made it possible to record the electrical activity of nerve fibers and its changes in real time at room temperature.

“Such a magnetometer is suitable for medical diagnostics in such physiological and clinical areas as fetal cardiography, registration of synaptic interactions in the retina and magnetoencephalography,” write the study authors.

The manufacturer of the GM3120 electromagnetic radiation detector is the Chinese company Benetech. The device produced by the company is used to measure the intensity of electromagnetic fields. The use of the device makes it possible to qualitatively determine the physical values ​​of voltage and current of electromagnetic radiation emanating from various objects and household appliances.

Detector from the manufacturer Benetech

The main area of ​​specialization of Benetech is related to the production measuring equipment. In all industries, various types of instruments are used to measure voltage, pressure, temperature and other parameters. These include:

• pressure gauges;
• thermometers;
• wattmeters;
• lux meters;
• multimeters, etc.

The Benetech company produces not only industrial, but also household types of devices. These include
the detector in question. The device is suitable for monitoring the level of electromagnetic radiation around electrical equipment, power lines, and household appliances.

For ease of use, the detector can be carried in your pocket. The manufacturer provides
Possibility of installing the device on a flat surface. The device is able to effectively detect
availability electromagnetic field, which has a negative impact on human health.

The manufacturer provides instructions for the device in English and Russian.

All documentation included with the device is provided to the consumer in Chinese.

To facilitate the selection of a measuring device, all technical characteristics are indicated in the instructions.

Benetech is a market advanced manufacturer.

The price at which a household tester from this company is sold is quite low.

The detector from this company can be purchased at various
specialized websites or in supermarkets at a price of 1080 rubles. The packaging of this product contains information about the manufacturer and his email address.

The model, made in the Chinese version, has hieroglyphs on the surface of the case.

The manufacturer also supplies the market with an English version of the device. When purchasing a detector, you don’t need to attach much importance to hieroglyphs, since only the numbers on the device screen are needed for measurement.

Scope of application of the Benetech meter

The main purpose of the tester is related to the measurement of electromagnetic fields. This is the most
a known physical quantity arose at the stage of the origin of the universe. Visible light— the basic form of the indicator studied by the meter.

A review of electric and magnetic fields revealed that they are part of the electromagnetic spectrum
radiation, which comes in the following types:

• static electric;
• magnetic;
• radio wave;
• infrared;
• X-ray.

The scope of application of the device is:

• measuring the strength of the electromagnetic field (EMF), which is generated by power lines (PTL) or various types electronic equipment;
• hidden cable detection;
• identifying the quality of grounding of electrical equipment;
• study of the level of radiation intensity emanating from electrical appliances at home;
• study of the radiation situation near power plants, high-voltage lines, factories, military facilities, airports.

SanPiN 2.1.2.1002-00 establishes maximum permissible hygiene standards. In Russian conditions, the normal level of electromagnetic radiation is considered to be 10 µT. In order to prevent the negative consequences of the influence of the EMF factor, the World Health Organization (WHO) recommends a safe level of this indicator equal to 0.2 µT. In this case, the uncertainty in studying the effects of EMF must be taken into account.

Detector capabilities

The tester is useful because it can be used to measure the intensity of electromagnetic radiation from household electrical appliances and equipment.

The detector allows you to detect the presence of hidden wiring in the apartment.

Thanks to the built-in sensor, you can find out the test results, the optimality of which depends on the presence of 2 modes.

The display shows precise digital data, which is measured in the following units:

• electric field - V/m;
• magnetic field - µt.

During the measurement process, you can notice that a slight increase in distance can reduce the field strength.

At the same time, household appliances with sufficient power transmit the electromagnetic field over a distance.

Thus, the detector from Benetech,
used in everyday life and in industrial environments, allows you to control electromagnetic radiation near electrical appliances and other objects.

The use of the GM3120 device makes it possible not only to identify the location of the cable in advance, but also to select a place where it is possible to successfully lay new wiring, drill walls, and install sockets.

With excessive and constant exposure to electric and magnetic fields on the human body, the likelihood of developing certain diseases increases. According to the manufacturer, the device is indispensable for those diagnosed with cardiovascular pathologies.

Detector appearance

Compact appearance a detector resembling a conventional multimeter ensures the quality of use of the device. The body is bright orange and has ribbed sides. This allows you to comfortably hold the device in your hand.

The back of the tester with a plate of the main parameters of the device provides a compartment for the battery. It is a Krona type battery (9 V).

The body is designed so that
The battery cannot be inserted incorrectly. The presence of a small monochrome display at the top of the tester allows you to identify indicators of physical quantities.

Under the screen on the body of the device there are 3 buttons that allow measurements to be taken. Above him
the frequency range within which measurements can be performed is indicated. There is also a place allocated
for the brand name and model name of the meter.

Under the tester screen there is the inscription “Electromagnetic Radiation Tester”. Translated from English
In the language, the word “radiation” means radiation. The entire inscription under the display translates as “electromagnetic radiation tester,” but the detector has nothing to do with radioactive devices.

To the right of the inscription there is a red LED that is triggered when the threshold of 40 V/m and/or 0.4 μT is exceeded. The LED starts flashing when an overshoot is detected acceptable standards. When the sound is turned on, the device emits a beeping signal.

Advantages and disadvantages of the device

The advantage of the device is that it can determine the electromagnetic radiation environment in the open air or indoors.

With this tester, only approximate physical quantities are detected, since it is not a professional measuring instrument.

The accuracy of the detector declared by the manufacturer does not make it possible to determine the strength of the electromagnetic field without error.

The advantage of the tester is the ability to measure the strength of the electromagnetic field transmitted by household appliances over a certain distance.

The device can measure electromagnetic radiation in the frequency range up to 2000 MHz, so the device is not capable of responding to WiFi radiation.

The tester has the following types of advantages that distinguish it from similar meters:

• dual EMF measurement mode;
• presence of sound and light alarms;
• displaying measurement values ​​in the form of text prompts;
• display with three zones;
• possibility of simultaneous display of measurement results;
• automatic alarm if readings exceed safe values;
• presence of a battery charge indicator;
• the ability to automatically turn off the screen backlight;
• showing averages and peak values measurements;
• energy saving mode;
• “HOLD” function that holds data on the display.

The right side of the display shows information about the operating mode and remaining battery charge.
You can take measurements with the device even in the dark. This is allowed due to the uniform
backlight. It is not too bright, which makes it pleasant to the eye. From the sides of the body
The meter has protruding elements that make it more comfortable to hold the device in your hand.

Technical characteristics and equipment

Before purchasing a detector, it is better to familiarize yourself with it technical characteristics, presented
in the instructions for the device. The unit of measurement for the electric field is V/m, and the unit for the magnetic field is
µT The GM3120 detector model has the following functional and technical parameters for measuring electric and magnetic fields, respectively:

• the measurement step is 1 V/m, 0.01 μT;
• the alarm has a threshold value of 40 V/m, 0.4 µT.

Among the provided measurement parameters that you should pay attention to are:
the following ranges:

• electric field - 1-1999 V/m;
• magnetic field - 0.01-19.99 µT;
• frequencies (sampling time) - 5-3500 MHz;
• operating temperatures - 0...+50°C.

Test mode time is about 0.4 seconds. The device is capable of operating in low conditions
illumination and humidity no more than 80% at an operating voltage of 9 V (1 Krona battery). The LCD display of the device has dimensions equal to 43x32 mm. The weight of the meter is 146 g, and its dimensions are
130x65x30 mm. The device comes with instructions and a battery in its original packaging.

Operating principle of the GM3120 meter

The operating principle of the tester is based on identifying indicators related to the measurement of the following
physical quantities at a certain distance from the radiation object:

• voltage that causes the occurrence of an electric field;
• current strength causing the appearance of a magnetic field.

Electric field strength is measured in volts per meter (V/m), and magnetic field strength is measured in amperes per meter.
(A/m). Electric field can be saved even if the device is turned off. As
As you move away from the device, this figure decreases. The presence of an electric field is neutralized
most building materials.

The upper indicator on the display reflects data on the presence of an electric field or low-frequency
radiation. The maximum reading value is a threshold equal to 1999 V/m. According to the norms
SanPiNa, the value of the maximum permissible level is 500 V/m. Greatest danger
are objects that create a lot of tension in an open space, e.g.
power line poles.

The lower indicator on the device display allows you to determine the magnetic field or high-frequency
radiation measured in µT. This type of radiation comes from mobile phones, computers,
TVs, etc. The maximum level is considered to be 19.99 µT (microtesla). Presence of magnetic
fields cannot be eliminated with most building materials.

Electromagnetic field measurement

The heart of the measuring device is the WT56F216 single-chip microcontroller universal type. To the left of it is the display controller, equipped with the ability to manage the HT1621B memory. Above the microcontroller there is a 27M2C operational amplifier. All this can be found out if you disassemble the device by removing the cover from the body.

To turn the meter on, you will need to reassemble it. When it's ready to go, you can turn it on. At this time, all segments of the display begin to light up. The top of the screen shows the unit of electric field strength, or “V/m” (volts per meter). At the bottom of the display, “μT” (microtesla) is displayed, i.e. a unit multiple of T, which is 0.000001 T (tesla). This is a unit of measurement of magnetic induction, the flux density of magnetic induction.

There is a small red LED under the display. If the permissible level is exceeded, it flashes red. To take measurements, the device must be turned on and then brought as close as possible to the household device with its top edge. There is an antenna at the end of the detector, so it must be directed with this side towards the object under study.

The device automatically emits a sound and light signal if the measurement result exceeds the safe one
meaning. Below the display there are 3 buttons:

1. Button below. Turns on/off the power of the device (screen backlight), for which the button is pressed and held.
2. HOLD/BEEP button. Pressing briefly allows you to save the value currently displayed on the screen; with a long press, the sound will turn on/off when the set norm is exceeded.
3. "AVG/VPP" button. Switches the device to average/peak mode.

The AVG\VPP button switches the measurement mode. If the VPP mode allows you to record the maximum reading value on the screen, then AVG is provided for dynamic measurements carried out by the tester. Readings can change 3 times per second.
A review of the GM3120 detector used to measure electromagnetic fields reveals the main
advantages of this device.

Thus, the meter produced by the Chinese company Benetech is a compact device. The device is safe for humans. It can be used to maintain your own health to eliminate sources of electromagnetic radiation, the norm of which exceeds the value established by SanPiN.

What is this article about?

To determine the parameters of the magnetic field, magnetic field sensors are used. The principle of their operation is based on four physical phenomena. The article describes the device various types magnetic field detectors. Advantages and disadvantages of each implementation.
You can also look at other articles. For example, “The principle of operation of Brinell, Vickers and Rockwell hardness testers” or “What is non-destructive testing, where and how is it used”.

There are quite a lot of devices for detecting and measuring magnetic field parameters, which is why they are used in many areas, both purely technical and everyday. These detectors are used in systems related to navigation tasks, measuring the angle of rotation and direction of movement, determining the coordinates of an object, recognizing “friend or foe,” etc.

The wide range of applications of such sensors requires the use of various properties of the magnetic field for their implementation. This paper discusses the operating principles inherent in magnetic field sensors:

• using the Wiegand effect;
• magnetoresistive;
• induction;
• working on the Hall effect;

Wiegand sensors

The sensor's operation is based on an effect discovered by the American scientist Wiegand. The essence of the Wiegand effect is as follows. When a ferromagnetic wire is introduced into a magnetic field, a spontaneous change in magnetic polarization occurs in it. This phenomenon is observed when two conditions are met. First, the wire must have a special chemical composition(52% cobalt, 10% vanadium - vicalloy) and a two-layer structure (picture on the right). Second, the magnetic field strength must be above a certain threshold value - ignition threshold.

The moment of change in the polarization of the wire can be observed using an inductor located next to the wire. The inductive voltage pulse at its terminals reaches several volts. When the direction of the magnetic field changes, the polarity of the induced pulses changes. Currently, the effect is explained by different rates of reorientation of elementary magnets in the soft magnetic core and hard magnetic shell of the wire.

The design of Wiegand sensors contains an inductor and a Wiegand wire. When the polarization of the wire changes, the coil wound around it records this change.

Wiegand sensing elements are used in flow meters, speed, rotation angle and position sensors. Additionally, one of the most common uses of this element is in ID card reading systems, which we all use on a daily basis. When a magnetized card is applied, the field strength changes, to which the Wiegand sensor reacts.

The advantages of the Wiegand sensor include independence from the influence of external electric and magnetic fields, a wide operating temperature range (-80° ... +260°C), and operation without a power source.

Magnetoresistive magnetic field sensors contain a magnetoresistor as a sensitive element. The principle of operation of the sensor is the effect of changing the ohmic resistance of the material in the area of ​​the magnetic field. This effect is most pronounced in semiconductor materials. The change in their resistance can be several orders of magnitude greater than that of metals.

The physical essence of the effect is as follows. When a semiconductor element with a flowing current is in a magnetic field, Lorentz forces act on the electrons. These forces cause the movement of charge carriers to deviate from rectilinear, bend it and, therefore, lengthen it. And lengthening the path between the terminals of a semiconductor element is equivalent to a change in its resistance.

In a magnetic field, the change in the length of the “path” of electrons is determined by the relative position of the magnetization vectors of this field and the field of the flowing current. When the angle between the field and current vectors changes, the resistance also changes proportionally.

Thus, knowing the resistance value of the sensor, one can judge the quantitative characteristics of the magnetic field.

Magnetoresistance strongly depends on the design of the magnetoresistor. Structurally, the magnetic field sensor is a magnetoresistor, consisting of a substrate with a semiconductor strip located on it. Conclusions are marked on the strip.

To eliminate the influence of the Hall effect, the dimensions of the semiconductor strip are maintained within certain tolerances - its width must be much greater than its length. But such sensors have low resistance, so the required number of strips are placed on one substrate and connected in series.

For the same purpose, the sensor is often made in the form of a Corbino disk. The sensor is powered by connecting to the terminals located in the center of the disk and along its circumference. In the absence of a magnetic field, the current path is straight and directed from the center of the disk to the periphery along the radius. In the presence of a magnetic field, the Hall emf does not arise, since the disk has no opposite faces. The resistance of the sensor changes - under the influence of Lorentz forces, the current paths are bent.

Sensors of this type, due to their high sensitivity, can measure minor changes in the state of the magnetic field and its direction. They are used in navigation systems, magnetometry, pattern recognition and object position determination.

Sensors of this type belong to the generator type of sensors. The designs and purposes of such sensors are different. They can be used to determine the parameters of variable and stationary magnetic fields. This review discusses the operating principle of a sensor operating in a constant magnetic field.

The operating principle of induction sensors is based on the ability of an alternating magnetic field to induce an electric current in a conductor. In this case, the induced emf appearing in the conductor is proportional to the rate of change of the magnetic flux through it.

But in a stationary field, the magnetic flux does not change. Therefore, to measure the parameters of a stationary magnetic field, sensors with an inductance coil rotating at a constant speed are used. In this case, the magnetic flux will change with a certain periodicity. The voltage at the coil terminals will be determined by the rate of change of flux (the number of turns of the coil) and the number of turns of the coil.

Using known data, the magnitude of the magnetic induction of a uniform magnetic field is easily calculated.

The design of the sensor is shown in the figure. It consists of a conductor, which can be an inductor located on the shaft of the electric motor. The voltage is removed from the rotating coil using brushes. The output voltage at the coil terminals represents an alternating voltage, the magnitude of which is greater, the higher the rotation speed of the inductor and the greater the magnetic induction of the field.

Hall effect magnetic field sensors use the phenomenon of interaction of moving electric charges with a magnetic field.

The essence of the effect is illustrated by the figure. Current flows through the semiconductor wafer from an external source.

The plate is in a magnetic field that penetrates it in a direction perpendicular to the movement of current. In a magnetic field, under the influence of the Lorentz force, electrons deviate from rectilinear motion. This force moves them in a direction perpendicular to the direction of the magnetic field and the direction of the current.

In this case, there will be more electrons at the upper edge of the plate than at the lower edge, i.e. a potential difference arises. This potential difference causes the appearance of the output voltage - the Hall voltage. The Hall voltage is proportional to the current and the magnetic field induction. At a constant value of the current through the plate, it is determined only by the value of the magnetic field induction (figure on the left).

Sensitive elements for sensors are made of thin semiconductor wafers or films. These elements are glued or sprayed onto substrates and provided with pins for external connections.

Magnetic field sensors with such sensitive elements are characterized by high sensitivity and linear output signal. They are widely used in automation systems, in household appliances and systems for optimizing the operation of various units.