Fig. 4. Sensor layout. A – unit for phase lock: A1 – synchronous detector with analog switches, A2 – low pass filter, A3 – voltage-controlled oscillator, A4 – frequency divider, and A5 – phase-shift module, B – optical part: B1 – photodetector, B2 – laser module, B3 – optical fiber, B4 – fiber coupler, and B5 – optical connector, and C – sensitive element: C1 – mechanical resonator, C2 – miniature loudspeaker, C3 – silica gel granule, and C4 – mini-fan.