Electrostatic charge measurements are at the base of chemical, physical and biological experiments. In this paper, we present an electrometer based on the vibrating capacitance of a microelectromechanical systems (MEMS) resonator for the detection of small currents from ionized particles in an aerosol particle detection system. We use a porous sensing-electrode coupled to a MEMS resonating electrometer. Operating at resonance, charge is collected on the MEMS electrometer and modulated at the resonant frequency and its harmonics. Induced voltage is read with a low-leakage very high-input impedance feedback amplifier. Because of the specific readout technique, a switched-reset is used to prevent charge saturation. Sensitivity improvements are achieved by modifying the low noise-readout amplifier by reducing input-referred noise and parasitic capacitance. The electrometer achieves a noise floor <1 fA produced by 10 nm diameter particles within an airflow of 1.0 L/min. At this flow rate, the minimum detectable current (1 fA) corresponds to a minimum measureable particle density of 400 cm −3 . The MEMS electrometer is compared with and calibrated against commercial electrometer and a particle counter, respectively.

No abstract

We present the development of millimeter scale 3D hemispherical shell resonators fabricated from the polycrystalline diamond, a material with low thermoelastic damping and very high stiffness. These hemispherical wineglass resonators with 1.1 mm diameter are fabricated through a combination of micro-electro discharge machining (EDM) and silicon micromachining techniques. Using piezoelectric and electrostatic excitation and optical vibration measurement, the elliptical wineglass vibration mode is determined to be at 18.321 kHz, with the two degenerate wineglass modes having a relative frequency mismatch of 0.03%. A study on the effect of the size and misalignment of the anchor and resonator's radius variation on both the average frequency and frequency mismatch of the 2θ elliptical vibration modes is carried out. It is shown that the absolute frequency of a wineglass resonator will increase with the anchor size. It is also demonstrated that the fourth harmonic of radius variation is linearly related to the frequency mismatch.

Advances in the magnetic sensing technology have been driven by the increasing demand for the capability of measuring ultrasensitive magnetic fields. Among other emerging applications, the detection of magnetic fields in the picotesla range is crucial for biomedical applications. In this work Picosense reports a millimeter-scale, low-power hybrid magnetoresistive-piezoelectric magnetometer with subnanotesla sensitivity at low frequency. Through an innovative noise-cancelation mechanism, the 1/f noise in the MR sensors is surpassed by the mechanical modulation of the external magnetic fields in the high frequency regime. A modulation efficiency of 13% was obtained enabling a final device’s sensitivity of ~950 pT/Hz1/2 at 1 Hz. This hybrid device proved to be capable of measuring biomagnetic signals generated in the heart in an unshielded environment. This result paves the way for the development of a portable, contactless, low-cost and low-power magnetocardiography device.