Towards a new generation of soft and conformable acoustic devices based on electroactive polymers

Project Information

DEtune

Grant agreement ID: 893674

DOI

10.3030/893674

Project terminated on 31 August 2022

EC signature date 21 April 2020

Start date 1 November 2020

End date 31 October 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 162 806,40

EU contribution

€ 162 806,40

Coordinated by

UNIVERSITAT DES SAARLANDES
Germany

Periodic Reporting for period 1 - DEtune (Towards a new generation of soft and conformable acoustic devices based on electroactive polymers)

Reporting period: 2020-11-01 to 2022-10-31

Summary of the context and overall objectives of the project

The role of smart devices and consumer electronics is becoming every day more central in our lives and working environments. In the future, these devices will become increasingly integrated, they will be embedded onto our clothes or onto the surface of the objects we interact with, and will perform tasks that currently require external portable devices, or completely new tasks such as monitoring our physiological parameters and warning us about dangers. The pursuit of this vision creates a need to rethink the shape of conventional devices (such as monitors, loudspeakers) in an attempt to make them lighter, more flexible, and more efficient.
Motivated by this vision, the DEtune project focused on the development and systematic investigation of an unconventional class of lightweight loudspeakers based on smart materials called dielectric elastomers (DE). Compared to traditional speakers, that rely on a rigid moving coil and a moving diaphragm, DE speakers merge these two elements into a single lightweight soft polymeric membrane, which is able to produce sound thanks to electrostatically-driven vibrations. Thanks to this feature, DEs might be used to develop new concepts of soft conformable loudspeakers, suitable for integration onto garments or complex structures.
The objective of the DEtune project were thus:
- To generate base knowledge on DE loudspeakers and propose new experimental and modelling tools to characterize/design new devices.
- To elaborate advanced sensing and control strategies for DE loudspeakers.
- To develop application demonstrators of DE loudspeakers.
The DEtune project successfully achieved the abovementioned objectives and contributed in creating base knowledge on the operating principles of DE loudspeakers, as well as in producing technological demonstrators. The foundations laid during the project might open up new research directions in the near future, especially in the direction of user interfaces (audio-tactile feedback interfaces) and multi-function smart devices.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The DEtune project pursued a multidisciplinary approach, combining base research aimed at understanding and describing the driving principles behind DE loudspeakers, and application-oriented prototyping of technological demonstrators. Base research activities were approached in a holistic manner, by combining experimental analyses and numerical models.
The main results of the project can be summarized as follows:
- Experimental characterization of voltage-driven vibrations in DE membranes were performed, using a 3D laser Doppler vibrometer (one of the most advanced tools for measurement of mechanical vibrations). This allowed understanding and visualizing the deformation patters that DE membranes produce when subject to high-frequency voltage excitation, and gaining precious information/data for the validation of numerical models.
- Multi-physics models, able to describe DE loudspeakers’ response (dynamics, sound pressure output), were developed. The proposed models rely either on analytical formulations, or numerical codes based on the finite element method. These models merge different physical domains (namely, nonlinear elasticity, electro-elastic interactions, elasto-acoustic interactions) so as to consistently describe the complex and nonlinear response of DE speakers.
- The observations brought up by modelling/characterization activities allowed developing a completely new principle to develop multi-function devices, capable of performing multiple tasks by using different deformation modes of a same DE membrane unit. The project team proved that some specific topologies of DE membrane actuators can concurrently work as linear actuators (i.e. producing a force/displacement in a given direction) and loudspeakers. This is achieved by exciting a single DE membrane with a multi-chromatic voltage input, that concurrently excites different vibration modes of a same membrane and allows producing two independent output at the same time. Among other, this principle can be used to build audio-tactile devices, that make use of a single active membrane to provide users with complex combined vibrotactile and acoustic feedbacks.
- Prototype demonstrators were built, including coil-free DE loudspeakers, and an audio-tactile user interface (smart button) that is able to recognize a user’s touch via capacitive sensing and produce combined audio-tactile stimulations in response.
The activities and results of the project were disseminated through scientific publications (5 journal papers + 7 conference papers) and presentations in international scientific events (e.g. 7 presentations at conferences in the field of mechatronics). Actions aimed at reaching the general public were also undertaken, including the creation of social pages for the project (Youtube, Twitter channels), and the participation in public events (e.g. University’s open-door days).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The progress achieved during the project represents an important step forward with respect to the state on the art on DE loudspeakers, both in terms of tools/approaches demonstrated, and new principles proposed (primarily, multi-mode multi-function devices). In terms of methodological tools, laser vibrometry was proven to be an effective tool to measure the response of vibrating DE membranes (also in complex scenarios such as 3D DE vibrations, seldom investigated in the past). The possibility of developing models of DE speakers (capable to predict the generated sound pressure level) using commercial software (such as Comsol Multiphysics) was proven. Numerically-efficient analytical models were also established, that are particularly useful for design tasks. Combined numerical and experimental characterisations of voltage-driven vibrations in DE membranes done during the project represent the most extensive and comprehensive analysis on this topic produced to date.
Moreover, the concept of multi-mode operation proposed during the project (and related proof-of-concept demos, such as audio-tactile interfaces) potentially open up a completely new disruptive research line and paves the way to many future applications. Whereas, in the past, research mostly focused on proving that DE actuators can achieve performance comparable or better than traditional machines (a claim not always easy to support), the findings of the DEtune project point in a new direction – multifunctionality – in which DEs might really make a difference. The ability to embed multiple functions (here, linear actuation, sound generation, and sensing) into a single soft membrane opens up new perspectives in terms of applications (e.g. smart buttons, wearable user interfaces) and future commercial exploitation of DEs.

A vibrotactile device demo developed during the DEtune project

Comparison of a lightweigth DE speaker and a traditional electrodynamic speaker