A Faraday cup for charge measurements in biophysical and environmental fieldwork

A novel miniature (28 mm × 38 mm) shielded Faraday cup is described for quantifying picocoulomb charges on millimetre environmental objects, such as small insects or plants, droplets, dust particles or powders. The electrometer electronics is contained within the device, avoiding any transfer of low level signals to an external electrometer. It is calibrated using a voltage ramp – capacitor method, generating defined charge pulses without a reference electrometer. The device can fit within an acoustic levitator to provide non-contact, zero leakage suspension of small objects, measuring charge on their release. Convenience and simplicity of use open new environmental charge measurement opportunities. • Miniature Faraday cup for measuring charge on environmental objects and particles. • Compatible with TinyLev ultrasonic levitator, to suspend and isolate test objects. • Electrometer circuitry is contained within the body of the device. • Novel calibration methods described using voltage ramps and charged beads.