Capacitor-Based Battery Testing for Wearable Medical Devices
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Solution Overview
Problem
Body-wearable medical devices, such as insulin pumps and continuous glucose measurement devices, face challenges in reliably determining the battery state due to low power consumption and varying contact resistance, which complicates internal resistance measurement and can lead to sudden power breakdowns.
Innovation Solution
A body-wearable medical device with a capacitor in parallel with the battery contacts, where a battery test involves measuring capacitor voltage at two points in time with a test current drawn between them, allowing determination of the battery's charging state from voltage or time differences, effectively overcoming the limitations of contact resistance and mechanical instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If internal resistance measurement is used to determine battery state, then battery testing capability is improved, but measurement precision deteriorates due to varying contact resistance and mechanical instability
Solution Approach 1:
The patent introduces a test current source as an intermediary element to separate the measurement function from the power supply function. By applying a known test current through the battery and measuring the resulting voltage drop, the system can determine internal resistance independently of the battery's operating state. This intermediary measurement approach overcomes the interference from contact resistance and mechanical instability that plague direct internal resistance measurements during normal operation.
Solution Approach 2:
The patent implements preliminary battery testing by applying test currents at specific intervals before the battery is fully depleted. This preliminary action allows the system to proactively assess battery health and predict remaining capacity, enabling timely warnings to users. The test currents are applied in advance of critical failure points, allowing the system to build up a profile of battery degradation before it becomes dangerous.
2Reliability
If a large capacitor is provided in parallel with the battery to bridge interruptions, then reliability is improved, but internal resistance measurement becomes impossible due to low-pass characteristic
Solution Approach 1:
The patent employs periodic test current pulses applied through the capacitor-battery parallel combination. By using short-duration periodic test currents rather than continuous measurement, the system can penetrate the capacitor's low-pass filtering effect. The periodic nature of the test allows the measurement system to capture the voltage response during the brief intervals when the capacitor is not fully shielding the measurement, enabling internal resistance determination while maintaining the capacitor's protective function.
3Use of energy by moving object
If the device is optimized for low power consumption, then energy efficiency is improved, but battery voltage remains constant until sudden breakdown, making state determination difficult
Solution Approach 1:
The patent applies partial action by using small-magnitude test currents that are sufficient to generate measurable voltage drops across the battery's internal resistance but small enough not to significantly impact the overall power consumption or discharge the battery. These partial test currents create just enough electrical stress to reveal the battery's true state without triggering the sudden voltage breakdown that characterizes deeply discharged batteries.
4Ease of operation
If battery contacts are used with floating contact springs, then ease of operation is improved, but connection stability deteriorates under mechanical shock and vibration
Solution Approach 1:
The patent implements feedback by continuously monitoring the voltage response during test current application. The measurement system detects variations in contact resistance caused by mechanical shocks or vibrations and can distinguish between temporary connection instability and genuine battery degradation. This feedback mechanism allows the system to maintain accurate battery state assessment even when contact conditions fluctuate, and can trigger warnings if connection stability becomes problematic.
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 method provides a reliable and stable determination of the battery's charging state, preventing sudden power failures and ensuring continued device operation, even under varying environmental conditions like high temperature and humidity.
Implementation Method 1
a capacitor in parallel electrical arrangement with the battery contacts... determining a first capacitor voltage U1 as value of a capacitor voltage U at a first point in time t1 and determining a second capacitor voltage U2 as value of the capacitor voltage U at a second point in time t2
Data Source
AI summary
A method and device for testing a battery that powers a body-wearable medical device. The battery is contacted via battery contacts and a capacitor is arranged in parallel with the battery contacts. During the battery test, a first capacitor voltage U1 is determined at a first time t1 and a second capacitor voltage U2 is determined at a second time t2 subsequent to time t1. A test current is drawn between time t1 and time t2. t1 is determined by the beginning of drawing the test current and time t2 is determined such that the capacitor voltage at time t2 is in a steady state and is substantially constant while the test current is being drawn. A charging state of the battery is determined from the difference in voltage between U1 and U2 and/or from a time difference between the time t1 and time t2.