Canonical: https://echosuite.app/guides/pulse-geometry/

# Pulse length and near field calculator

Explore pulse length and near field with the method’s inputs, acquisition guidance and source references. Open the calculator to enter measurements or try an illustrative worked example.

Created by [Mohammed Kamareddine, MD](https://echosuite.app/about/) · [Sources & educational scope](https://echosuite.app/about/)

[Open interactive calculator →](https://echosuite.app/calculators/#pulse-geometry)

## Method

λ = c/f; SPL = cycles × λ; axial limit ≈ SPL/2; N ≈ D²/(4λ)

Use the measurement units shown below. Some fields apply only to a selected method or condition; follow the interactive tool’s method choices. The interactive tool keeps missing measurements incomplete and provides its method-specific results and reference context.

## Measurements and acquisition

### Explore

Enter the measured value in the displayed unit

- Pulse length
- Near field
- Confirm the variable matches the selected formula.
- Use the unit displayed beside the field.
- Keep measurements from the same representative hemodynamic state.

### Transmit frequency · f  MHz

Enter the measured value in the displayed unit

- Confirm the variable matches the selected formula.
- Use the unit displayed beside the field.
- Keep measurements from the same representative hemodynamic state.

### Sound speed · c  m/s

Enter the measured value in the displayed unit

- Confirm the variable matches the selected formula.
- Use the unit displayed beside the field.
- Keep measurements from the same representative hemodynamic state.

### Cycles per pulse · n

Enter the measured value in the displayed unit

- Confirm the variable matches the selected formula.
- Use the unit displayed beside the field.
- Keep measurements from the same representative hemodynamic state.

### Active aperture diameter · D  mm

Enter the measured value in the displayed unit

- Confirm the variable matches the selected formula.
- Use the unit displayed beside the field.
- Keep measurements from the same representative hemodynamic state.

## Sources and method context

Evident · Ultrasound education · Ultrasonic beam characteristics · §2.4 · circular-element near-field distance N = D²/(4λ)

[Primary reference](https://ims.evidentscientific.com/en/learn/ndt-tutorials/flaw-detection/beam-characteristics)

- Near-field model · §2.4 Beam characteristics; WHO EHC 22 §2.2.1

N ≈ D²/(4λ) for a flat circular aperture with D much greater than wavelength. Near-field interference and far-field divergence do not specify electronic array focusing.

- Pulse and axial separation · ASE Formula Review Guide Part 2 · principles of waves and sound

Wavelength is sound speed divided by frequency; SPL is cycles times wavelength; the ideal axial separation estimate is SPL/2.

Catalogue review status: Source mapped · clinical sign-off pending

These pages describe the educational tool. Interpret measurements with the complete clinical context and the method’s acquisition limitations.

## Keep exploring

- [Wave relationships calculator](https://echosuite.app/guides/wave-relations/)
- [Pulse repetition and Nyquist calculator](https://echosuite.app/guides/pulse-repetition/)
- [Doppler equation calculator](https://echosuite.app/guides/doppler-equation/)
- [Acoustic impedance and intensity calculator](https://echosuite.app/guides/acoustic/)

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