Results
MRE Valve Design
Valve Structure and Working Principle
The MRE valve consists of an electromagnet and an MRE membrane to create the valve gate. Figure \ref{180429}(A) shows the cross-sectional view of the proposed valve. The electromagnet is sealed in silicone to ensure maximum compliance. The gate of the valve is designed by encapsulating a pressurized cavity between the MRE membrane and the electromagnet. The detailed dimensions of the valve can be found in Figure \ref{458885}. The proposed valve works in a "normally-open" manner as shown in Figure \ref{180429}(B). When no current goes through the coil, no force is exerted by the MRE so air travels freely through the air channel. When an electric current is engaged in the coil, a magnetic field will be generated. The MRE is then magnetized and exerted a force toward the concentration of the magnetic flux. This attraction force deforms the MRE and correspondingly restricts the gate of the valve. This "restriction" effect gradually increases as the electric current increases and eventually shuts down the airflow completely. A video presenting the working principle of the MRE valves can be found in Video 1.
Fabrication
Multi-stage silicone casting is used to fabricate the MRE valve presented in this work. The detailed fabrication procedure is presented in Figure \ref{180429}(C). The first stage of casting aims to seal an electromagnet into a silicone housing. This is achieved by placing the electromagnet into a cylindrical mold filled with uncured silicone. The second stage of casting aims to build an MRE layer on top of the electromagnet while leaving an air channel inside. This is achieved by pouring the uncured MRE on top of the electromagnet. A Mylar strip is placed in the middle during MRE's curing and pulled out afterward, therefore leaving a thin air channel as the gate of the valve. A video describing the whole fabrication process can be found in Video 2, while the technical details involved can be found in Section \ref{sec_experiment}.