RF Probe Eddy Current Compensation for In Vivo Sensing
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Solution Overview
Problem
In vivo sensing technologies face challenges in accurately determining the characteristic impedance of sensors within the body due to interference from magnetic eddy currents, which obscure the frequency response peak and make it difficult to measure small sensor signals effectively.
Innovation Solution
The RF probe assembly includes a transmit coil, a receive coil oriented orthogonally, and an eddy current compensation coil that produces a compensation field to counteract the effects of magnetic eddy currents, ensuring the compensation field component at the receive coil is equal and opposite to the eddy current-induced field, thereby canceling out noise and allowing for precise impedance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an RF probe is used to detect the resonant frequency of a passive sensor, then the sensor can detect pressure, temperature, pH, etc., but magnetic eddy currents interfere with the measurement and obscure the frequency response peak
Solution Approach 1:
An eddy current compensation coil is introduced as an intermediary element between the transmit coil and the sensor. This compensation coil generates a magnetic field that counteracts the harmful eddy currents induced in the sensor, thereby eliminating the interference without requiring changes to the sensor itself or the measurement frequency
2Device complexity
If a grid-dip oscillator approach is used with a single RF coil, then the system is simple, but the small receive signal cannot be effectively separated from the large oscillation signal
Solution Approach 1:
The single RF coil system is segmented into two separate coils: a transmit coil for generating the excitation signal and a receive coil for detecting the sensor response. This spatial separation allows the large transmit signal and small receive signal to be independently optimized, improving the ability to detect weak sensor signals while maintaining system simplicity
Solution Approach 2:
The transmit and receive coils are oriented orthogonally to each other, utilizing spatial dimensionality to separate the transmit and receive functions. This orthogonal arrangement ensures that the large oscillation signal from the transmit coil does not directly couple into the receive coil, enabling effective separation of signals
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the isolation between transmit and receive elements, allowing for accurate determination of sensor impedance and quality factor by mitigating the impact of eddy currents, thereby improving the sensitivity and reliability of in vivo sensing.
Implementation Method 1
An oscillating RF current flows through an RF coil, inducing currents in the inductance coil of a nearby sensor
Implementation Method 2
The loading effect of the sensor on the RF transmit coil results in a decrease or 'dip' in the phase response of the transmitter current
Implementation Method 3
at least one eddy current compensation coil that produces a compensation field. A component of the compensation field along the second orientation has a magnitude at the receive coil substantially equal and opposite to a magnitude of a similarly oriented component of a magnetic field associated with eddy currents induced within the body
Data Source
AI summary
Systems and methods are provided for determining a characteristic of an associated in vivo sensor within a living body. A transmit coil produces an excitation signal, having a first orientation, to excite the in vivo sensor to produce a response signal. A receive coil produces a current in response to the response signal. The receive coil is oriented to interact with signals having a second orientation that is substantially orthogonal to first orientation. The probe further comprises at least one eddy current compensation coil that produces a compensation field. A component of the compensation field along the second orientation has a magnitude at the receive coil substantially equal and opposite to a magnitude of a similarly oriented component of a magnetic field associated with eddy currents induced within the body.