Emc Calculator

EMC Electric Field Strength Calculator

Electromagnetic Compatibility (EMC) is the branch of electrical engineering concerned with the unintentional generation, propagation, and reception of electromagnetic energy which may cause unwanted effects such as electromagnetic interference (EMI). This calculator helps you estimate the electric field strength (E-field) in the far-field of a radiating source, a fundamental calculation in EMC analysis and compliance testing.

Understanding the Calculation

This calculator uses the standard far-field formula to determine electric field strength from an isotropic radiator. The formula is:

E = (√(30 * P * Glinear)) / d

  • E = Electric Field Strength in Volts per meter (V/m).
  • P = Transmitter Power in Watts (W).
  • Glinear = Linear antenna gain (converted from dBi: 10(dBi/10)).
  • d = Distance from the antenna in meters (m).
  • The constant 30 is derived from the impedance of free space.

Example Calculation

Let's consider a typical Wi-Fi router and calculate the field strength at a common distance.

  • Transmitter Power (P): 100 milliwatts = 0.1 W
  • Antenna Gain (G): A standard dipole antenna has a gain of 2.15 dBi
  • Distance (d): We want to measure the field strength at 3 meters

By entering these values into the calculator, you will find that the estimated electric field strength is approximately 0.42 V/m. This value can then be compared against regulatory limits or equipment susceptibility levels.

Disclaimer: This calculator provides a theoretical estimate for far-field conditions in free space. Real-world measurements can be significantly different due to factors like reflections (multipath), shielding, near-field effects, and antenna pattern variations. It should be used for educational and estimation purposes only.

function calculateEField() { var power = parseFloat(document.getElementById("transmitterPower").value); var gainDbi = parseFloat(document.getElementById("antennaGain").value); var distance = parseFloat(document.getElementById("distance").value); var resultDiv = document.getElementById("result"); if (isNaN(power) || isNaN(gainDbi) || isNaN(distance)) { resultDiv.innerHTML = "Please enter valid numbers in all fields."; resultDiv.style.color = "#c00"; resultDiv.style.borderColor = "#ffb3b3"; resultDiv.style.backgroundColor = "#ffe5e5"; return; } if (power < 0 || distance <= 0) { resultDiv.innerHTML = "Power must be non-negative and distance must be greater than zero."; resultDiv.style.color = "#c00"; resultDiv.style.borderColor = "#ffb3b3"; resultDiv.style.backgroundColor = "#ffe5e5"; return; } // Convert gain from dBi to linear scale var gainLinear = Math.pow(10, (gainDbi / 10)); // Calculate Equivalent Isotropically Radiated Power (EIRP) in Watts var eirp = power * gainLinear; // Calculate Electric Field Strength (V/m) using the simplified far-field formula // E = (sqrt(30 * EIRP)) / d var eField = (Math.sqrt(30 * eirp)) / distance; if (isFinite(eField)) { resultDiv.innerHTML = "Estimated E-Field Strength: " + eField.toFixed(3) + " V/m"; resultDiv.style.color = "#004a8c"; resultDiv.style.borderColor = "#b3d7ff"; resultDiv.style.backgroundColor = "#e9f5ff"; } else { resultDiv.innerHTML = "Calculation resulted in an error. Please check your inputs."; resultDiv.style.color = "#c00"; resultDiv.style.borderColor = "#ffb3b3"; resultDiv.style.backgroundColor = "#ffe5e5"; } }

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