Sonoflex: Embroidered speakers without permanent magnets

We present Sonoflex, a thin-form, embroidered dynamic speaker made without using a permanent magnet. Our design consists of two flat spiral coils, stacked on top of each other, and is based on an isolated, thin (0.15 mm) enameled copper wire. Our approach allows for thin, lightweight, and textile speakers and does not require high voltage as in electrostatic speakers. We show how the speaker can be designed and fabricated and evaluate its acoustic properties as a function of manufacturing parameters (size, turn counts, turn spacing, and substrate materials). The experiment results revealed that we can produce audible sound with a broad frequency range (1.5 kHz - 20 kHz) with the embroidered speaker with a diameter of 50 mm. We conclude the paper by presenting several applications such as audible notifications and near-ultrasound communication.