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For precision measurement of miniature internal structures with high aspect ratios, a spherical scattering electrical field probe (SSEP) is proposed based on charge signal detection. The characteristics and laws governing surface charge distribution on the probing ball of the SSEP are analyzed, with the spherical scattering electrical field modeled using a 3D seven-point finite difference method. The model is validated with finite element simulation by comparing with the analysis results of typical situations, in which probing balls of different diameters are used to probe a grounded plane with a probing gap of 0.3 &mu, m. Results obtained with the proposed model and finite element method (FEM) simulation indicate that 31% of the total surface charge on a ϕ1 mm probing ball concentrates in an area that occupies 1% of the total probing ball surface. Moreover, this surface charge concentration remains unchanged when the surface being measured varies in geometry, or when the probing gap varies in sensing range. Based on this, the SSEP has realized approximate point probing capability with a virtual &ldquo, needle&rdquo, of electrical effect. Together with its non-contact sensing characteristics and 3D isotropy, it can, therefore, be concluded that the SSEP has great potential to be an ideal solution for precision measurement of miniature internal structures with high aspect ratios.

A spherical scattering electrical-field probe(SSEP) with noncontact, 3D isotropy and approximate point probing characteristics has been proposed for high-precision measurement of micro and small structures with large aspect ratio. Development of signal processing circuits for detection of weak cpacitantive signal on sub-picofarad level is the key to realize nanometer resolution. In this paper, a set of signal processing circuits based on operational capacitance measurement principle is proposed, and characteristics of the circuits are theorically analyzed and optimized. Experimental results indicates that resolution of 1 nm and nonlinearity of6 nm are achieved with the proposed signal processing circuits for a SSEP with $\phi$ 2.5 mm probing ball.

A low ripple switching power supply with 0-12 V voltage and 35 A maximum current outputs is developed for the application of high-precision thermoelectric circulating water cooling. In order to suppress the voltage ripple in the output caused by voltage and current spikes generated when the switching mode of full-bridge converter changes, which is further resulted from parasitic capacitance and inductance of MOSFET circuit and rectifier diode circuit in the power supply, resonance analysis and optimization design is carried out. Equivalent models of MOSFET circuit and rectifier diode circuit are established, and absorption circuits are designed to absorb the voltage and current spikes, thus to effectively suppress the voltage ripple in the output of the switching power supply. Experimental results show that the output voltage ripple is reduced from 190 mV to 88 mV after optimization of key parameter.

In order to solve the difficulty of precision measurement of small hole diameters with large depth-to-diameter ratios, a new measurement method based on spherical scattering electrical-field probing (SSEP) was developed. A spherical scattering electrical field with identical sensing characteristics in arbitrary spatial directions was formed to convert the micro gap between the probing-ball and the part being measured into an electrical signal. 3D non-contact probing, nanometer resolution, and approximate point probing&mdash, which are key properties for high measurement precision and large measurable depth-to-diameter ratios&mdash, were achieved. A specially designed hole diameter measuring machine (HDMM) was developed, and key techniques, including laser interferometry for macro displacement measurement of the probe, multi-degree-of-freedom adjustment of hole attitude, and measurement process planning, are described. Experiments were carried out using the HDMM and a probing sensor with a ϕ3-mm probing ball and a 150-mm-long stylus to verify the performance of the probing sensor and the measuring machine. The experimental results indicate that the resolution of the probing sensor was as small as 1 nm, and the expanded uncertainty of measurement result was 0.2 &mu, m (k = 2) when a ϕ20-mm ring gauge standard was measured.

In order to solve the problem of thermal drift and further improve the performance for sensors with extreme demand for precision, based on analysis of shortcomings of existing compensation methods and characteristics of thermal drift, a novel active suppression technology against thermal drift is proposed. Considering the change of properties of reference elements in sensors caused by temperature variation is the most major factor that introduces thermal drift error, a special thermal structure is designed to provide a small environmental chamber with sub-structure design of high performance heat isolation, heat conduction and homogenization of temperature, and the temperature in the environmental chamber is controlled with high precision based on bilateral temperature adjusting with thermo electronic cooler (TEC) devices, and a compound control algorithm of Bang-Bang and anti-windup PID. Experimental results with an ultra-precision spherical capacitive sensor show thermal drift error is significantly eliminated and the precision of the sensor can reach the level of several resolutions.