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Acoustic Prism Invented at EPFL

09.08.16 - EPFL scientists have invented a new type of “acoustic prism” that can split a sound into its constituent frequencies. Their acoustic prism has applications in sound detection.

Almost 400 years ago, Newton showed that a prism could split white light into the colors of the rainbow, with each colour corresponding to a different wave frequency. Such an “optical prism” relies on a physical phenomenon (refraction) to split light into its constituent frequencies.

Now, a prism exists for sound. Hervé Lissek and his team at EPFL have invented an "acoustic prism" that splits sound into its constituent frequencies using physical properties alone. Its applications in sound detection are published in the Journal of the Acoustical Society of America.

The acoustic prism is entirely man-made, unlike optial prisms, which occur naturally in the form of water droplets. Decomposing sound into its constituent frequencies relies on the physical interaction between a sound wave and the structure of the prism. The acoustic prism modifies the propagation of each individual frequency of the sound wave, without any need of computations or electronic components.

The acoustic prism

The acoustic prism looks like a rectangular tube made of aluminum, complete with ten, perfectly aligned holes along one side. Each hole leads to an air-filled cavity inside the tube, and a membrane is placed between two consecutive cavities.

When sound is directed into the tube at one end, high-frequency components of the sound escape out of the tube through the holes near the source, while low frequencies escape through the holes that are further away, towards the other end of the tube. Like light through an optical prism, the sound is dispersed, with the dispersion angle depending on the wave’s frequency.

The membranes are key, since they vibrate and transmit the sound to the neighboring cavities with a delay that depends on frequency. The delayed sound then leaks through the holes and towards the exterior, dispersing the sound.

Angular detection by frequency

To take the concept a step further, the researchers realized that they could use the acoustic prism as an antenna to locate the direction of a distant sound by simply measuring its frequency. Since each dispersion angle corresponds to a particular frequency, it’s enough to measure the main frequency component of an incoming sound to determine where it is coming from, without actually moving the prism.

The principle of the acoustic prism relies on the design of cavities, ducts and membranes, which can be easily fabricated and even miniaturized, possibly leading to cost-effective angular sound detection without resorting to expensive microphone arrays or moving antennas.

EPFL news
12th International Conference on Evaluation of Novel Approaches to Software Engineering – ENASE 2017

The mission of ENASE (Evaluation of Novel Approaches to Software Engineering) is to be a prime international forum to discuss and publish research findings and IT industry experiences with relation to novel approaches to software engineering. The conference acknowledges evolution in systems and software thinking due to contemporary shifts of computing paradigm to e-services, cloud computing, mobile connectivity, business processes, and societal participation.

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Studying more eco-friendly mobility in a Fribourg neighborhood

05.08.16 - Summer series on student projects (5) – Charles Jeanbart's semester project brings the question of mobility into the Solar Decathlon, an inter-university competition to design an autonomous solar house.

It is impossible to envision an energy autonomous house without considering the related question of personal mobility. This is not just for the sake of consistency: it's the challenge posed by the Solar Decathlon. In this inter-university competition, teams will design, build and operate a fully autonomous, solar-powered house. The Swiss Team, which includes EPFL, was selected alongside 13 others and is now preparing to present its design in Denver (USA) in 2017. Charles Jeanbart, a Master’s student in civil engineering, is working on the question of mobility, simulating solutions that are both electric and shared and that use fewer vehicles.

What is unique about the Swiss project is that it’s not simply a theoretical exercise. Following the competition in Denver, the house is designed to be brought back to Fribourg and set up there, possibly in the Beaumont neighborhood. It will be connected to existing buildings and readily accessible to the public, with the aim of helping acquaint people with new forms of energy, consumption and mobility. Jeanbart chose the Beaumont neighborhood as the basis for his analysis of how existing vehicles could navigate the energy transition.

He began by estimating the number of vehicles in the neighborhood: around 1,670 for 4,000 residents. He then envisioned a scenario of electric or hybrid vehicles needing to be recharged frequently. Jeanbart, who is part of EPFL’s Transport and Mobility Laboratory, factors into his analysis the frequency and length of trips, when they take place during the day and on which day of the week, and he excludes longer trips. For his simulation, he chose two scenarios, one in which the cars can be charged wherever they are parked and the other in which they can only be charged at home with a home charger.

A step towards smart grids

“The goal is to determine the electricity demand at certain periods during the day,” said Jeanbart. “The first scenario shows that the peak charging curve corresponds – with a slight gap – to traffic peaks. This is mostly during the day, from 8am to 5pm. In the second scenario, which is more realistic, the peak is at the end of the day and in the evening." Not ideal for recharging cars with solar energy.

Jeanbart's work presents a simplified overview of the recharging needs of electric cars in the neighborhood of one city. “The model should be improved, taking the assumptions even further," said Jeanbart. “What I have in mind is to build this into a smart grid – an intelligent system that comprises energy production, storage and consumption – in order to make consumption and production more efficient.”

This exercise is particularly relevant in the context of the Solar Decathlon, which dovetails nicely with the thrifty, parsimonious vision of the 2000-watt society. Under this vision, individuals use no more than 48 kWh per day, or 2,000 watts in constant power, which is equal to the global average in 1990. The Swiss average is currently around 5,500 watts. “To achieve this, switching to electric cars and reducing the number of cars through car-pooling won’t be enough. We will also have to scale back our mobility needs by developing the local network,” said Jeanbart.

EPFL news
20th International Forum on Advanced Microsystems for Automotive Applications (AMAA 2016), "Smart Systems for the Automobile of the Future"

Automated vehicles are the prominent subject of current public debate: Fierce competition unfolds between companies and states regarding the market introduction of driving automation while first incidents document the inability of current technology to master complex situations. The International Forum on Advanced Microsystems for Automotive Applications (AMAA) has been exploring the technological foundations of connected, automated and electrified vehicles for many years. (

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