Today (September 15th, 2016) the inventors Robert Jahns, Holger Runkowske, and Reinhard Knöchel were informed from the European Patent Office that their idea on the "tuning fork" sensor principle is protected now by the European patent EP 2 811 314 B1. Congratulations to the inventors!
A "tuning fork" sensor basically consists of two ME sensors, which are arranged on top and at the bottom of a mounting block. The inverse orientation of the individual sensors with respect to the suspension point (FR-4 substrate in the picture below) leads to distinguishable output signals for magnetic and vibrational excitations. If a magnetic field is applied to the tuning fork, the cantilevers are bent in opposite directions (e.g. both away from the centre, black arrows). The outputs of the upper and lower cantilevers are opposite in phase with respect to a common ground and thus produce a differential-mode signal. In the case of vibrational coupling, the cantilevers are predominantly bent in the same direction (green arrows) and produce co-phase signals of the two sensor outputs (common mode). The comparison of a tuning fork sensor with a single cantilever sensor (see figure below) reveals that the tuning fork shows a limit of detection of approximately 500 fT/Hz1/2 – a very good LOD for magnetoelectric thin film sensors - whereas the individual magnetoelectric cantilevers, similar to those of which the tuning fork is composed, have sensitivities of approximately 5 pT/Hz1/2. With superimposed white noise the effect of the tuning fork is even more distinct. Whereas the tuning fork experiences an increase in noise level of about a factor of roughly 4, the single magnetoelectric sensor shows a rise of approximately two decades.
|Magnetoelectric tuning fork sensor (a). LOD plots of tuning fork setup (c) in comparison to a single sensor (b) with and without additional superimposed wideband noise. The dashed auxiliary lines indicate the noise level and the LOD. The resonance frequency was 958 Hz.|