Introduction
In collaboration with Design bureau Bjorn Luik, Sensor Team designed the enclosure for the IoT SoundSensor. Bjorn graduated for the Delft University of Technology following the Master’s program Integrated Product Design. Educated by this curriculum, Bjorn now designs a wide variety of enclosures and creative mounting principles. His story about the design process at SensorTeam:

“I construct my designs following four basic pillars: functionality, shape (aesthetics), material and manufacturing. These themes are all entangled with each other and should be revisited at every step of the design process. Most influential on the shape is the functionality of the product; which components go where, and how will they be held together. This combination of form and function has certain options available in terms of material and manufacturability. Perhaps changing the shape might allow for a different material – for instance moulded plastic versus bend sheet metal. It all depends on the main requirements for the final product.

Functionality and form
First step of the design was to arrange the main components. The solar panel, lead battery, printed circuit board and the microphone together gave birth to the functionality of the IoT SoundSensor. During the ideation phase we discovered several possibilities of designing the product. In the end, following the ideal angle of the solar panel resulted in the characteristic shape of the enclosure.

Choice of material
Considering the product is using wireless communication protocols, using a metal enclosure was no longer one of the possibilities. This would in fact cause a Faraday cage which would block all the antenna signals. For this reason we opted for a plastic material. With the cunning use of a lip and groove feature, the enclosure was made waterproof as per IP67 standards. In order to carry the load of the battery, some strategically placed construction ribs were used. High Impact Polystyrene (HIPS) was chosen for its material strength and its flame retardant properties according to UL-94 V0 standards.

Production method
Plastic products can be manufactured by several different methods. The classic injection moulding technique is one of the most common. Here, a plastic melt is injected into a cavity under high pressure. High production speed and complex forms are the benefits of this process. The major drawback is the steep investment cost for the mould tooling, which makes this method of manufacturing only profitable at 1.000 parts or more.

In recent years 3D printing has taken over the market. The sky is the limit in terms of form freedom. Support structures enable you to print almost anything you can think of. However, there is downside to this technique as well. Printing the SoundSensor enclosure, for example, would take up to 30 hours of print time. Great for prototyping purposes but even for small series this method is far too expensive.

Lucky for us we found a third option, which is compatible with the geometry of the enclosure as well as the intended batch size. This method is called Planar Modular Production (PMP) and is performed by the company Formit BV. A flat sheet of plastic is machined to size, folded and welded together to form the final product. A quick process without the high investment in tooling.