Why are there 4 bars on the bottom of the Trigno wireless EMG sensor?

Some commercial designs attempt to remove the reference contact by internalising it within the circuit, or removing it altogether and performing a monopolar recording. These approaches are limited in their ability to cope with various disturbances that regularly affect the quality of EMG signals. For example, motion artifacts due to heel-strike, DC skin potential shifts during stretching and compression of tissue, and static-charge buildup of clothing are common events that can produce overwhelmingly large disturbances for EMG signals. “Reference-free” sensor designs have difficulty compensating for, and cancelling these disturbances because the reference point for the circuit is not in actual contact with the skin surface, and is thus removed both physically and electrically from these events.

In contrast, Trigno Wireless Sensors contain two patented stabilising references(in addition to the two that measure the EMG). This proprietary design allows the sensor to react instantaneously to disturbances detected on the surface of the skin, dramatically reducing the impact of these noise sources on the detected EMG signal quality.