G.R.A.S. Sound & Vibration
GRAS Sound & Vibration is located in Denmark and represented worldwide in more than 40 countries. We are the preferred supplier of acoustic sensors to a long list of measurement solution providers. Since early 2020, we have been in close strategic partnership with Audio Precision, a manufacturer of high-performance audio test equipment.
UTP – The World’s Thinnest Condenser Microphones
The main focus of wind noise testing in the aerospace industry are measurements in boundary layers. Research is often aimed at separating the acoustic signal from the flow-induced turbulent noise. Purposes span quantifying the amount of sound power radiated from a structure, over sound source localization using an array of microphones to quantifying the turbulent stresses to which a structure is subjected.
The UTP (Ultra-Thin Precision) microphones from GRAS is a suite of highly precise and reliable condenser microphones aimed at boundary layer measurements. The very low profiles (1mm) of the UTP microphones reduce turbulence influence dramatically and are expected to fundamentally change aeroacoustic testing in wind tunnels and in flight.
Computational Fluid Dynamics models are important parts of designing vehicles that move in airflow. However, airflow and turbulence is difficult to simulate and predict realistically. When measuring turbulent boundary layer noise, flush-mounted pressure sensors and microphones are often used in order not to disturb the airflow or add additional turbulence. However, this often requires destructing the device under test. Where destructive testing is not possible, surface-mounted sensors are used with the risk of contaminating the results with self-induced turbulent noise due to the profile height of the sensor.
Only very small, thin and aerodynamically correctly shaped sensors can overcome these challenges – validating the modeling and supplying the additional measurement data needed. The form factor and easy mounting of the UTP microphones make them suitable for in-situ boundary layer testing, when neutral impact and high precision is important.
The UTP family of microphones has been developed in close cooperation with the industry, and has been extensively tested for aerospace as well as automotive applications. The UTP microphones are suitable for test applications where traditional sensors are difficult to mount and where the boundary layer is thin, for example at the belly fairing, the karman or the cockpit window.
A version of the UTP microphone has been designed for wind tunnel testing of components or scale models. This version has a frequency range of up to 70kHz and a noise floor of only 54dB. All microphones are calibrated to international standards at the GRAS head quarters in Denmark. The UTP microphones can also be in-situ verified using a handheld calibrator with an adapter for sensitivity verification developed for planar or curved surfaces.
The UTP microphones combine all the advantages of the classical measurement microphone, wide frequency range, accuracy and repeatability, with an ultra-small form factor, at only 1mm in height.
In essence, the UTP microphones are flat, fast and precise, a revolutionary new design that has made it possible to combine a 1/4” condenser microphone with a form factor that makes it the world’s thinnest measurement microphone.