Today I had the pleasure to attend Tessa’s graduation, a project I co-supervised with in collaboration with Aito.
Aito has developed a technology that can be placedunderneath surfaces to give haptic feedback. They make use of piezoelectricdiscs to sense a pressure difference and actuate a pulse if this differencereaches a certain level. This system is possible because of the piezoelectriccrystals in the discs. These crystals create current from movement for thesensing action, and create movement by adding current for actuation action.These properties, combined with the way Aito layers the structure to supportthe piezoelectric discs, allow for this type of haptic feedback which mimicsthe press of a button. While the technology of Aito currently focuses on asingle pulse to simulate the feeling of a button, it is possible to send acontinuous stream of vibrations through the piezoelectric discs. This streamcould be a pulse that is being repeated over and over, or it could be avariation of pulses which creates music. This last possibility is explored inthis graduation project by a state-of-the-art review, objective measuringtechniques and subjective measuring techniques. With Aito’s current structure, it seems possible to create aspeaker in which the surface is vibrated to create audio according to thegathered literature in the state-of-the-art review. The literature describestwo types of speakers with a similar structure as Aito, which are the distributedmode loudspeakers and multiactuator panels. These speakers use a vibrationmodule (an exciter), to move the surface they are attached to. The differencebetween these two speakers is the placement and number of exciters. Both thesespeakers have a different designing approach than the standard design processof coil-based speakers. The design approach for distributed mode loudspeakersand multiactuator panels is used in this project but incorporates sometechniques from the usual procedure. The main elements that are adopted fromthe standard audio engineering approach relate to the validation of the setupwith users and measurements.The traditional approach of audio engineers to involve usersinto the design process, is by letting participants participate in listeningtest to define the audio quality perception of the speaker. This approach isadapted in this project into an approach which allows users to define theiraudio quality expectations; this involves users earlier on into the designprocess. By letting users participate early on in the process, the audioquality experience can be changed efficiently. The perceptions could improvethe experience at the end of the process, while the expectations change it inthe beginning. The expectation that is explored during this research involvesfoldable laptops and tablets. This approach shows that the audio quality of foldablelaptops is expected to be higher than foldable tablets. The whole foldablegroup is expected to perform lower than a laptop, but higher than a smartphone.The expected speaker placement also showed a difference between foldablelaptops and foldable tablets, which shows similarities to their non-foldable devicegroup. Therefore, a speaker that is integrated into the surface would ensurethat the speaker location is most optimal in both the laptop position as wellas the tablet position of a foldable device. For the measurement validation, various tests were donebased on the approach of audio engineers to define how Aito’s structureperforms for audio functionalities. This approach was chosen to compare theresults to the requirements of the industry; these take volume levels andfrequency range of the audio into account. When these requirements arecombined, a grading system is created to help in selecting the correct speakerfor specific experiences. The tests were done with simplified models of afoldable tablet because this product group is the best fit for a haptic andaudio combination. In total, there were eight individual models used during thesystem performance testing. All these models originated from one basic model,which was a simplified foldable tablet structure; this model can be seen infigure 1. Its structure is separated into two identical halves to be able tocreate stereo audio when both halves are used. In the individual models,changes were made to test the effects of different surface materials, surfaceedge fixtures, piezoelectric disc layouts and uses of the space behind thesystem. These changes were mainly based on the design principles of distributedmode loudspeakers and multiactuator panels but were combined with some designprinciples dictated by Aito and the speaker industry. This research was a first step in the direction of audiowith Aito’s current setup. From the performance of eight models in combinationwith the user expectations on foldable laptops and tablets can be concludedthat the technology is not yet there. However, for less demanding products,such as intercoms, the audio quality can be deemed good enough as is with somesmall improvements. There is also the possibility to use the system only forhigher frequencies and haptics and add another speaker to generate lowerfrequencies.
Master Thesis: TU Delft repository