Initially studied and developed by students in universities, the very small pico satellites (with a mass lower than 1 Kg) are more and more considered for science applications. In particular they will be used in constellations of small spacecraft for remote sensing of various regions of the magnetosphere. They require a payload with specific size, weight and power consumption. In order to respond to this demand, new instruments have to be developed. Those instruments should exhibit at least the same performance as those used in larger satellites while fulfilling the specific requirements imposed by the size of the satellites. For this reason, we currently develop a xylophone bar magnetometer (XBM) based on micro-electromechanical systems (MEMS) with integrated detector electronics. The principle of this magnetometer is based on classical resonating xylophone bar. A sinusoidal current oscillating at the fundamental transverse resonant frequency of the bar is applied to the bar. When an external magnetic field is present, the resulting Lorentz force causes the bar to vibrate at its fundamental frequency with a displacement directly proportional to the amplitude in one direction of the ambient magnetic field. When designing a MEMS XBM, the detection method is a crucial aspect. The measurement method largely influences the geometry of the magnetometer as well as the manufacturing technology. Due to the constraints in terms of size, weight and power consumption, the two most promising measurement methods identified are capacitive and piezoelectric. Designs which include these measurement techniques are presented and simulated under realistic conditions. A new configuration of PZT/Pt structure is introduced and leads to much better sensitivity than the traditional Pt/PZT/Pt sandwich structure. The principle of the electronic circuits enabling high sensitivity and low power consumption is presented. Finally, a design including lateral electrodes for capacitive measurement is introduced.