Breaking reciprocity has attracted attention in recent years and has been studied in electromagnetic and discrete as well as continuous mechanical systems. Reciprocity in mechanical systems implies the spatial symmetry of an input-output pair such as force-displacement. This means that the displacement at a position A due to a force at a position B is equal to the displacement at position B due to the same force applied at position A. Non-reciprocity has been achieved using odd symmetric external biases (through magnetic fields and fluid circulation, etc.), nonlinearities, and spatio-temporal modulation of material properties. More recently, non-reciprocal behavior has also been demonstrated using passive mechanical designs, some of which make use of asymmetric cell topologies and internal hierarchical structure. Here, we propose a novel unit which employs a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), a semiconductor device, to provide the nonlinearity and asymmetry necessary to break reciprocity. A MOSFET is a 3-terminal (in some cases 4-terminal) active element and needs a supply voltage for operation. The three terminals are referred as gate, source and drain. The potential differences between these terminals determine the relationship between input voltage and output current of the MOSFET. For a fixed supply voltage, the current in the MOSFET’s output circuit depends on the voltage across its input terminals. With an appropriate voltage bias the MOSFET can be used as a voltage-controlled resistor. The mechanical system of the proposed cell comprises two ferromagnetic mass-spring elements which are mechanically independent. These are the input and output of the proposed unit and are electromechanically coupled with an electronic circuit containing the MOSFET in a common source configuration. In this configuration, the input to the MOSFET is given across the gate and source terminals, and the output is between the drain and source terminals. We bias the MOSFET to operate in the linear region of its current-voltage characteristics such that it acts as a switch.  In one (forward) direction, the MOSFET switches to on causing displacement in the output mechanical element. However, in the reverse direction, the oxide layer in the MOSFET prohibits the flow of current, leading to zero displacement at the output. In the reverse direction, since there is no flow of current in the input circuit, it is expected that the non-reciprocity in this unit is frequency independent. We solve, numerically, the governing equations of the cell with a non-zero velocity initial condition to show non-reciprocity within the unit, and then, present an experimental setup of the unit which confirms the predicted behavior. Finally, we present numerical studies on the response of a mechanical system made of two 1-D translational chains of masses and springs connected through the proposed unit.


A Transistor-Based Electromechanical Unit Cell for Acoustic Non-Reciprocity

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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