Modular battery powered handheld surgical instrument containing elongated multi-layered shaft

A system comprising:

• a generator configured to deliver power to a surgical instrument;
• and
• the surgical instrument electrically coupled to the generator and comprising:
• a handle assembly comprising a handle;
• a shaft assembly coupled to the handle assembly;
• and
• a flexible circuit comprising a resistor, a capacitor, an inductor, and a series of substrate layers that are flexible enough to bend or twist, the series of substrate layers spanning the entirety of the flexible circuit, wherein the handle assembly comprises a proximal portion of the flexible circuit and the shaft assembly comprises a distal portion of the flexible circuit;
• the shaft assembly further comprising:
• an exterior shaft positioned around the distal portion of the flexible circuit and configured to change position while at least a sub-portion of the distal portion of the flexible circuit remains stationary;
• shaft control electronics comprising a stationary portion and a non-stationary portion, the stationary portion coupled to the distal portion of the flexible circuit and the non-stationary portion coupled to the exterior shaft;
• and
• a sensor and a magnet defining a sensor-magnet pair;
• the stationary portion of the shaft control electronics comprises one of the sensor and the magnet and the non-stationary portion of the shaft control electronics comprises the other of the sensor and the magnet;
• wherein the sensor is configured to measure a distance away from the magnet as the exterior shaft changes position, using the sensor-magnet pair.