ABSTRACT
This paper outlines the use of charge detection mass spectrometry to simultaneously measure the charge and mass of micron-sized particles. In a flow-through instrument, the detection of charge was achieved through charge induction onto cylindrical electrodes that connect to a differential amplifier. Mass was determined by particle acceleration under the influence of an electric field. Particles ranging from 30 to 400 fg (3 to 7 µm diameter) were tested. The detector design can measure particle mass within 10% accuracy for particles up to 620 fg with total charge ranging from 500e- to 56 ke-. This charge and mass range are expected to be relevant for dust on Mars.
ABSTRACT
We present a novel and thorough simulation technique to understand image charge generated from charged particles on a printed-circuit-board detector. We also describe a custom differential amplifier to exploit the near-differential input to improve the signal-to-noise-ratio of the measured image charge. The simulation technique analyzes how different parameters such as the position, velocity, and charge magnitude of a particle affect the image charge and the amplifier output. It also enables the designer to directly import signals into circuit simulation software to analyze the full signal conversion process from the image charge to the amplifier output. A novel measurement setup using a Venturi vacuum system injects single charged particles (with diameters in the 100 s of microns range) through a PCB detector containing patterned electrodes to verify our simulation technique and amplifier performance. The measured differential amplifier presented here exhibits a gain of 7.96 µV/e- and a single-pass noise floor of 1030 e-, which is about 13× lower than that of the referenced commercial amplifier. The amplifier also has the capability to reach a single-pass noise floor lower than 140 e-, which has been shown in Cadence simulation.
