Overview - IEC TS 61949:2007 (Ultrasonics, in situ exposure estimation)
IEC TS 61949:2007 provides guidance for estimating in situ exposure in finite‑amplitude ultrasonic beams. It defines how to calculate attenuated acoustic quantities (pressure, intensity, power) when standard hydrophone measurements in water are affected by nonlinear (finite‑amplitude) propagation. The Technical Specification explains the limits of applicability of water measurements, introduces a practical criterion for quasi‑linear conditions, and gives a method to estimate attenuated values when nonlinear propagation occurs.
Key topics and requirements
- Scope and applicability
- Frequency range: 0.5 MHz to 15 MHz
- Source types: plane and focusing sources with amplitude gain up to 12
- Applies to continuous‑wave and pulsed fields; circular and rectangular source geometries
- Quasi‑linear conditions
- Introduces a local distortion parameter (σ) and defines an upper limit (tables use σ ≤ 0.5) to determine when measurements can be treated as quasi‑linear to minimise finite‑amplitude effects.
- Measurement and estimation procedures
- Steps to establish quasi‑linear conditions prior to measurement
- Tables of limiting mean peak acoustic pressure for common acoustic working frequencies
- Procedure for measuring acoustic quantities under quasi‑linear conditions, measuring a scaling factor, and calculating attenuated acoustic pulse waveforms, intensities and power
- Provides uncertainty assessment methods for derived attenuated quantities
- Supporting material
- Informative annexes reviewing experimental/theoretical evidence, alternative methods, parameters to quantify nonlinearity, and tables of upper limits for mean peak acoustic pressure
- Flow diagram to guide the in situ estimation procedure
Applications and who should use it
IEC TS 61949 is practical for:
- Medical ultrasound manufacturers and designers validating diagnostic transducers
- Acoustic metrology laboratories performing hydrophone measurements and field characterization
- Regulatory and safety assessors estimating in‑tissue exposure from measurements in water
- Researchers studying nonlinear propagation, harmonic generation and attenuation in ultrasonic fields
Using this TS helps ensure that reported in situ exposure metrics (e.g., attenuated spatial‑peak temporal‑average intensity, attenuated peak‑rarefactional pressure) reflect nonlinear losses and are consistent with safety and performance evaluations.
Related standards
- IEC 62127‑1 - Hydrophones: measurement and characterization of medical ultrasonic fields
- IEC 62359 and IEC 60601‑2‑37 - Attenuated acoustic quantities and safety for diagnostic ultrasound
- IEC 61161 - Ultrasonics power measurements
Keywords: IEC TS 61949:2007, ultrasonics, finite‑amplitude ultrasonic beams, in situ exposure estimation, attenuated acoustic quantities, quasi‑linear conditions, hydrophone measurements, acoustic working frequency, nonlinearity.