Miniature Wireless Pressure Sensor Using Inductive Resonance
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Solution Overview
Problem
Existing capacitive-based pressure sensors are unsuitable for applications like glaucoma and intracranial hypertension due to their pancake structure, which makes them thick in one dimension and large in cross-section, making them impractical for implantation in the human body.
Innovation Solution
A miniature tube-shaped wireless pressure sensor with an inductor coil and capacitor module forming an L-C resonator, using an electro-magnetic fluid and inert gas within a capillary tube, where pressure changes alter the inductance of the coil, causing a change in resonant frequency, allowing for pressure detection without an internal energy source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive-based pressure sensors are used, then pressure sensing capability is achieved, but the device becomes large in cross-section area and thick, making it unsuitable for implantation
Solution Approach 1:
The patent transitions from a planar capacitive structure to a three-dimensional tubular inductive structure. The sensor housing is formed as a tube with the inductor coil wrapped around it, allowing the pressure-sensitive element to extend along the length of the tube rather than requiring large cross-sectional area. This dimensional change enables compact implantable form factor while maintaining pressure sensing capability.
Solution Approach 2:
The patent replaces the capacitive sensing mechanism with an inductive sensing mechanism. Instead of using a capacitive transducer that requires large plate area, the invention uses an inductor coil whose inductance changes in response to pressure-induced movement of the electro-magnetic fluid, enabling pressure detection with a much smaller cross-section.
2Device complexity
If passive sensor structure is used, then device complexity is reduced and miniaturization is enabled, but battery technology adds size and contamination risk
Solution Approach 1:
The sensor is designed as a passive device that does not require an internal power source. The L-C resonator circuit is interrogated by an external reader through electromagnetic coupling, and the sensor responds by modulating its resonant frequency based on pressure changes. This self-service approach eliminates the need for batteries and complex power management circuits, enabling miniaturization for implantable applications.
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
Enables continuous, real-time monitoring of physiological pressures like IOP and ICP with a compact, implantable device that is less traumatic and easy to implant, facilitating effective treatment and prompt intervention for pressure-related conditions.
Implementation Method 1
the capacitor module (160) and the inductor forms an inductance-capacitance L-C resonator with a resonant frequency. When an outside pressure is applied to the electro-magnetic fluid (170) through the pressure sensing interface (130), the electro-magnetic fluid (170) slides inside the inductor coil (150) and this movement alters an inductance of the inductor coil (150). When the inductance of the inductor coil (150) is altered by the outside pressure, it causes a change in the resonant frequency of the L-C resonator.
Implementation Method 2
When an outside pressure is applied to the electro-magnetic fluid (170) through the pressure sensing interface (130), the electro-magnetic fluid (170) slides inside the inductor coil (150)
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
A miniature wireless pressure sensor has an inductor and a capacitor. The inductor and the capacitor form a L-C resonator with a resonate frequency. The inductor's inductance is affected by a slidable electro-magnetic element. When an outside pressure is applied onto the element, it causes the element to move and such movement changes the inductance of the inductor. Because of that, the resonate frequency is changed. Therefore, the change in resonate frequency indicates a change in the outside pressure. The L-C resonator is calibrated to correlate with the outside pressure. Such a miniature wireless pressure sensor facilitates the monitoring of physiological pressure in different part of human body such as eyes and cranium.