The THD peak at ~10 kHz stems mainly from a mode of the MEMS at 21 kHz. When the MEMS is excited with 21kHz it resonates strongly and produces movement and subsequently a higher SPL. Due to small inherent non-linearities in the movement of the MEMS, 10.5 kHz will produce a small frequency component at 21 kHz which resonates and
How USound measures Ganymede MEMS speakers USound specifies and measures Ganymede MEMS speakers, Achelous and Adap, in both acoustic domains: in the Baffle and in the Coupler (artificial ear). For both setups, proprietary measurement adapters are used to fit the standardised setup. In the case of the baffle, the measurement adapter places the MEMS speaker with appropriate sealing inside the
USound’s technology is based on piezoelectricity. Crystals with these properties are for example aluminium nitride (AlN) or lead zirconate titanate (PZT). These materials expand or shrink in an electric field. In a practical configuration, such an electric field is generated between electrodes, covering a piezoelectric layer. This stack is put on top of a substrate (for example a silicon plate).
The current versions of Ganymede MEMS speakers have two land pads on the backside. They are shaped differently to mark the polarity. There are different ways on how to bring electricity to these contacts: Hand soldering on the pads: It is worth noting, that the speaker is not able to withstand the normal reflow process (mainly because of the membrane).