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Resonantly coupled antennas for passive sensors

Wireless resonant coupling can enhance the performance of wireless passive sensors. Very efficient transfer of both energy and information is possible. Resonant coupling implies that a weak wireless coupling is compensated by resonance. In ideal situations power conversion efficiencies of 10-50 percent can be achieved from the transceiver to the sensor. The cost is a limited bandwidth and an increased sensitivity to relative positional - especially angular - variations. The limited bandwidth is hardly a problem for most sensor applications. An analysis based on the theory for coupled circuits is presented. The capabilities and deficiencies are quantified by simple analytical and numerical calculations.

Generics of systems for measuring linear and angular velocities of solid objects

Laser Doppler velocimetry, time-of-flight velocimetry, Doppler rotametry, and time-of-flight rotametry are analyzed. The analysis is based on a simplified scheme where only the detector setup is modified. Various measuring setups are described and their advantages and drawbacks discussed.

Comparison between the time-of-flight velocimeter and the laser Doppler velocimeter for measurements on solid surfaces

Analytical expressions for the crosscovariance (time-of-flight velocimeter, LTV) and for the power spectrum (laser Doppler velocimeter, LDV) are presented based on the assumption of all apertures having a Gaussian transmission function. The objects are simulated at solid targets having lateral spatial correlation, i.e. giving rise to partially developed speckle. The case of fully developed speckle can thus be simulated by having zero correlation length. For both systems and either target the relative width of the crosscovariance (LTV) and power spectrum (LDV) is calculated analytically based on the entire optical system and expressed as a function of the number of modes in the detection system. It is shown that the LTV will give in general a lower variance for the velocity estimate but that spatial correlations of the target are most detrimental to the LTV system. Besides, the decorrelation effects for measurement on curved surfaces are considered and it is shown that both systems will suffer equally in the case of a multimode system but the LTV system will be superior to an LDV system in case of a single mode system. The basic difference between the performance of the two systems stems from the inherent difference in bandwidth.

Sensor for vascular compliance and blood pressure

A method for continuous sensing of blood pressure and vascular compliance without affecting the state of the patient has been devised. The scheme is based on sensing vascular distention by a capacitive method utilizing the fact that the dielectric constant of blood is different from the dielectric constant of the surrounding tissue. The vascular stiffness is determined by measuring the pulse propagation velocity through an artery. Knowing the distention and the stiffness both vascular compliance and blood pressure can be calculated. A special signal processing scheme is devised in order to eliminate the effects of movements that are not synchronous with the heart beat. It is based conditional averaging and matched filtering. A wireless implementation has been verified.

Linear and angular velocity and displacement sensors for industrial use based on planar optical technology

An overview will be given for a series of compact optical systems for measurement of surface displacement. These systems are particularly well suited for miniaturization due to the limited demand for spatial and temporal coherence of the source. Specifically, systems for linear and angular displacement will be described. The systems have been realized based on the use of holographic optical elements but implementations with various kinds of compact diffractive optical elements will be devised. Common features with most of the proposed systems are the use of common-path interferometry and the simultaneous recording of the transmitter and receiver optics, strongly reducing any demand for alignment after assembly. Further, the use of common path systems will reduce the sensitivity to optical turbulence and may reduce the influence of contamination of the optical window.