Biomedical Engineering Reference
In-Depth Information
well in the light, stiff foam. In addition to vibrations, each shoe emits sounds from
one Goobay Soundball Mobile battery loudspeaker mounted on the top buckle. These
devices are provided with on-board micro-amplifiers, hence they can be connected
directly to the audio card. As any small, low-power loudspeaker device, they exhibit
unavoidable performance limits both in the emitted sound pressure level (2.4 W RMS)
and low frequency cutoff (about 200 Hz).
An evolution of such shoes concept has made use of vibrotactile exciters, such as
those capable of making an entire desk sound and vibrate like a musical soundboard
once they are firmly attached to it. In the case of the actuated shoes, two Dayton
Audio DAEX32 exciters were secured inside the sole of each sandal, respectively
under the toes and the heel: together, they provided a more coherent audio-tactile
feedback beneath the respective areas of the feet, furthermore eliciting some low
resonance energy from the floor that was otherwise impossible to obtain using small
speakers such as those mentioned previously. Moreover, by employing lightweight
power amplification (in this case a pair of Class T battery-powered digital stereo
amplifiers) and a low latency connection to and from the host, respectively to transmit
force data and to receive the audiotactile signals, a good compromise between realism
of the feedback and wearability of the prototype could be achieved at least for some
materials such as frozen ponds, muddy soil, aggregate grounds and, if supported by
headphones providing the necessary auditory spaciousness to a walking listener, also
metal grates [
76
].
12.3.5 Interactive Scenarios
12.3.5.1 Description
We will now briefly present examples of multimodal rendering of ground materials.
The examples correspond to two categories of ground materials that exhibit strong
high-frequency components: granular materials and fluids. Footsteps onto granular
(aggregate) ground materials, such as sand, snow, or ice fragments belie a common
temporal process originating with the transition toward a minimum-energy configu-
ration of an ensemble of microscopic systems, via a sequence of transient events. The
latter are characterized by energies and transition times that depend on the character-
istics of the system and the amount of power it absorbs while changing configuration.
They dynamically capture macroscopic information about the resulting composite
system through time. On the other hand, liquid-covered ground surfaces, such as
water puddles and shallow pools, have an important kinesthetic component due to
pressure and viscosity forces within the fluid, and may, at first, seem to lack high
frequency mechanical responses. However, important high frequency components
exist, as generated by bubble and air cavity resonances, which are responsible for
the characteristic sound of moving fluids.
The two examples presented in this section utilize the fact that vibrotactile and
acoustic phenomena share a common physical source by designing the vibrotactile
