Acoustic Researchers Are Using Lasers as Microphones
Bosch researchers are using a new laser method to “see” sounds and noises – phenomena the experts refer to as “sound-wave fields.” The measuring range extends from low-pitched tones at around 100 Hz to the 50 kilohertz ultrasonic frequency range, which is undetectable to the human ear. This high-pitched range is used, for example, by the ultrasonic sensors in automobiles’ parking assistants.
When a concert pianist hits the standard musical pitch A for, let’s say, one second and then holds it, our eardrum is hit by around 440 air-pressure pulses. That amounts to a frequency of 440 hertz.
A concert-goer’s listening experience depends not just on the dexterity of the pianist playing the sonata, however; the entire acoustic system into which the sound field flows – concert piano, concert hall and sitting position – is decisive. After all, the waves of sound that travel into the ears are variously reflected by walls and diffracted by barriers on their journey.
Using laser beams, Bosch researchers can visualize such invisible sound-wave fields. For a limited volume with an area of about one square meter, they can precisely study how sound fields propagate and how they are affected by obstacles and walls.
In going about their work, the researchers take advantage of the fact that the propagation velocity of light depends on the density of the medium through which it is traveling. When a laser beam hits the peak of an acoustic wave – a place with higher air density – it needs more time to pass through. A measuring unit in the laser scanner monitors the time lag, and a computer can then produce a three-dimensional image of the sound field, showing the wavefronts, wave peaks and troughs.
Bosch is using this technology to study things like the way that the ultrasonic pulses of a parking-assistant sensor propagate. Four to six ultrasonic sensors are built into a bumper, and they emit several ultrasonic pulses as cones of sound, which are reflected by objects on the road or parked cars. By using the amount of time it takes for the signal to bounce back as an echo, the distance to an obstacle can be calculated.
The next step in the research: estimating the contours of surroundings. The aim is to use the reflection of objects in front of and behind a parking space, and information about the space’s depth, to help the driver steer the vehicle.
In model situations, researchers at Bosch can now study how a test vehicle can be slowly driven by a parking space, how the space’s dimensions can be measured and how the driver can receive the information needed to park the vehicle. The laser process provides a detailed image of the sound-wave fields, helps to determine the optimum location of the sensors in the bumper and produces experimental data for the computer simulations.
The laser as microphone is also shedding light on an increasingly important research discipline – aeroacoustics. When air flows through a fan or from a nozzle, it creates turbulent vortexes in the flow area. Some of these vortexes can produce disturbing noise, particularly when they interact with the edges of housings, cooling fins or fan blades. Bosch researchers have opened a new frontier with this work and want to use the laser methods to determine how this turbulence process works, and which vortexes actually produce disturbing noises.
A concert-goer’s listening experience depends not just on the dexterity of the pianist playing the sonata, however; the entire acoustic system into which the sound field flows – concert piano, concert hall and sitting position – is decisive. After all, the waves of sound that travel into the ears are variously reflected by walls and diffracted by barriers on their journey.
Using laser beams, Bosch researchers can visualize such invisible sound-wave fields. For a limited volume with an area of about one square meter, they can precisely study how sound fields propagate and how they are affected by obstacles and walls.
In going about their work, the researchers take advantage of the fact that the propagation velocity of light depends on the density of the medium through which it is traveling. When a laser beam hits the peak of an acoustic wave – a place with higher air density – it needs more time to pass through. A measuring unit in the laser scanner monitors the time lag, and a computer can then produce a three-dimensional image of the sound field, showing the wavefronts, wave peaks and troughs.
Bosch is using this technology to study things like the way that the ultrasonic pulses of a parking-assistant sensor propagate. Four to six ultrasonic sensors are built into a bumper, and they emit several ultrasonic pulses as cones of sound, which are reflected by objects on the road or parked cars. By using the amount of time it takes for the signal to bounce back as an echo, the distance to an obstacle can be calculated.
The next step in the research: estimating the contours of surroundings. The aim is to use the reflection of objects in front of and behind a parking space, and information about the space’s depth, to help the driver steer the vehicle.
In model situations, researchers at Bosch can now study how a test vehicle can be slowly driven by a parking space, how the space’s dimensions can be measured and how the driver can receive the information needed to park the vehicle. The laser process provides a detailed image of the sound-wave fields, helps to determine the optimum location of the sensors in the bumper and produces experimental data for the computer simulations.
The laser as microphone is also shedding light on an increasingly important research discipline – aeroacoustics. When air flows through a fan or from a nozzle, it creates turbulent vortexes in the flow area. Some of these vortexes can produce disturbing noise, particularly when they interact with the edges of housings, cooling fins or fan blades. Bosch researchers have opened a new frontier with this work and want to use the laser methods to determine how this turbulence process works, and which vortexes actually produce disturbing noises.
