Abstract
Tunnelling Magneto-resistance (TMR) sensor as a pickup element for string instruments, in particular for electric guitars, is proposed in this paper. The proposed TMR based pickup showed several clear advantages compared to the presently used inductive type pickup units. The new scheme is much less sensitive to the disturbing electromagnetic fields, mainly because each string is excited using an a. c. current source at specific frequency and the signal conditioning circuit for the TMR sensor kept underneath the corresponding string is tuned to be sensitive to that particular frequency. This reduces the cross coupling effects, significantly. In addition, the output is not sensitive to the residual magnetic field of the string and the proposed sensor unit is compact compared to the conventional pick-up. In the proposed arrangement, an array of TMR sensors were placed right below the guitar strings and the output was recorded. For the feasibility study, the output signals were acquired using a Virtual Instrument developed in a LabVIEW environment. After extracting the vibration information from the TMR sensor data, with the help of envelope detection and a look-up table, the output obtained was compared with the output from a Laser Distance Sensor that directly measures the string vibration simultaneously. The results are matching.