A highly sensitive high frequency carrier-type magnetic field sensor based on the giant magnetoimpedance effect has been developed. It has been combined with a high frequency carrier suppressing circuit to reduce carrier phase noise dramatically. Highly sensitive magnetic field resolution of 8.8/spl times/10/sup -7/ Oe (8.8/spl times/10/sup -11/ T) was demonstrated.

A high frequency carrier-type magnetic field sensor using carrier suppressing circuit

The performances of instruments developed for the measurement of 5 MHz ultra-stable resonators, before and after being integrated in an oscillator, are presented. The chosen resonator has an estimated stability of several 10 -14 . The intrinsic noise floor of these benches are about 7 to 9.5 10 -15 .

Frequency stability measurements of ultrastable BVA resonators and oscillators

The amplitude-frequency effect is a well-known phenomenon in quartz crystal resonators. It can distort the results of short-term stability measurements. In our case, results are computed from phase noise measurements in passive bridge systems. This article presents a method to correct computation of short-term stability from passive measurements.

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Computation method for the short-term stability of quartz crystal resonators obtained from passive phase noise measures

An enhanced phase noise model allows to predict the phase noise in crystal oscillators. It is based on an improvement of the mathematical analysis proposed by G. Sauvage. In this model, power spectral densities of phase fluctuations are computed in different points of the oscillator loop. They are calculated from their correlation functions. The resonator caused noise as well as the amplifier caused noise are taken into account and distinguished. In order to validate this model, the behavior of about ten of 10 MHz quartz crystal oscillators is observed and analyzed. These oscillators have been chosen in a facility production. Resonators have been selected according to the value of their resonant frequency and their motional resistance. We attempt to measure separately the amplifier and resonator caused noises by means of a passive method. The phase noise of the overall oscillator working in closed loop is provided by the usual active method. Theoretical and experimental results are compared and discussed.

http://ieeexplore.ieee.org/iel5/8990/28531/01275142.pdf

Predicting phase noise in crystal oscillators

High-stability quartz oscillators are needed in a number of space applications. A short-term stability of parts in 10^{-14} [Allan deviation \sigma y(\tau) ] is sometimes required, for integration time \tau of approximately 1-10 s. The Centre National d'Etudes Spatiales (CNES) and the FEMTO-ST Institute (formerly LPMO and LCEP), have been collaborating for many years in this domain, aiming at measuring and at understanding the oscillator noise. The highest stability has been observed on 5 MHz and 10 MHz bulk acoustic-wave resonators. Yet this stability is still not sufficient, or the the manufacturing method is not reproducible. Recently, the analysis of a few premium-stability oscillators has demonstrated that the oscillator frequency instability is due to the fluctuation of the resonator natural frequency, rather than to the noise of the sustaining amplifier via the Leeson effect. It is therefore natural to give attention to the measurement of the resonator fluctuations.

Advanced bridge instrument for the measurement of the phase noise and of the short-term frequency stability of ultra-stable quartz resonators

In this paper, we review a new piece of equipment that allows one to characterize the phase noise of crystal resonators using a phase bridge system with carrier suppression. This equipment allows one to measure the inherent phase stability of quartz crystal resonators in a passive circuit without the noise usually associated with an active oscillator. We achieved a system noise floor of approximately -150 dBc/Hz at 1 Hz and -160 dBc/Hz, at 10 Hz. A SPICE characterization of the carrier suppression system is given. An investigation of the phase modulation (PM) noise in 10 MHz BVA, SC-cut quartz crystal resonator pairs is presented.

Phase noise measurements of 10-MHz BVA quartz crystal resonators

These last years a new 10 MHz quartz crystal oscillator family has been designed in LCEP with the support of the French space agency (CNES). It is intended for space applications especially. In this paper, the description of its general features is followed by two parts. The first one described the methodology which has been developed for designing such an oscillator. This part deals with the modeling of noise as well as the mechanical and thermal structure of the oscillator. The second part summarizes main experimental results. This obviously includes the frequency stability of the oscillator and its behavior when various disturbances occur in its environment. We particularly took care of its sensitivity to external temperature changes at the atmospheric pressure and mainly under vacuum. Exhibited frequency sensitivities to a magnetic field and vibrations are also provided.

An oscillator for space

Untethered small-scale robots can be potentially used in medical applications, such as minimally invasive surgeries and targeted drug delivery. This article introduces a new localization method using electrical impedance tomography, which is an emerging medical imaging technique, to dynamically track small-scale robots. The proposed approach provides the electrical conductivity distribution within the robot workspace from a set of electrical stimulations and voltage measurements gathered from eight electrodes placed at its boundary. The position of the robot can be deduced from the conductivity map that is reconstructed with the contrast in electrical properties between the robot and the background medium. This method is experimentally validated by successfully tracking the 2-D motion of four different magnetically actuated robots within a cylindrical arena (30 mm in diameter and 4.2 mm high). The smallest detected robot is 1.5 × 1.5 × 1 mm3. The proposed tracking method provides a noninvasive technology with low-cost and high-speed potential that would be significant and useful for the position feedback control of untethered devices for biomedical applications in the future.

A Localization Method for Untethered Small-Scale Robots Using Electrical Impedance Tomography

First measurements of the phase noise versus the radius of curvature of SC-cut resonators are given. Resonators with adherent electrodes are investigated and compared with unelectroded resonators. The phase noise measurements are obtained with a crystal resonator tester specifically designed to assist in the characterization of quartz crystal resonators.

Phase noise study of quartz crystal resonators versus the radius of curvature

In the time domain, two methods are investigated to classify the phase noise of the resonators. A numerical model of frequency stability of ultra stable quartz oscillator is used to obtain the power spectral density of the phase fluctuations of an oscillator which contains the test resonator. The measurements of the phase noise of the quartz crystal resonators are obtained with a crystal resonator tester. New LD-cut 10 MHz BVA quartz crystal resonators are investigated.

F. Marionnet

Papers

Phase noise measurements of 10-MHz BVA quartz crystal resonators

An oscillator for space

A Localization Method for Untethered Small-Scale Robots Using Electrical Impedance Tomography

Phase noise study of quartz crystal resonators versus the radius of curvature

Characterization of quartz crystal resonators on phase modulation noise without an oscillator