This article explores various technologies from environmentally collecting energy for medical systems, and how to integrate it into the design. From solar cells to piezoelectric generators, a variety of technologies can be used to use miniaturized medical monitoring systems.
Many medical applications need to generate electricity from a local environment to avoid battery charging problems and lifting applications.
Battery is abpacited may result in data loss, and the system has no response in an emergency. This is not convenient to play a device for charging, meaning that the device may not be available when needed, which may cause a large problem.
System designers want to collect energy from the environment to power the wearable medical monitor, to overcome battery challenges, and the attention of safety is increasing, and make greater challenges for them. It is also necessary to consider critical power management issues such as design, but rich and diverse development boards can help integrate energy collection sources, low-power microcontrollers and wireless links.
Solar can be wearable medical device sensors and wireless links, which is increasingly popular. The core of the solar cell is designed in the low power microcontroller, such as the MSP430 of Texas Instruments. It is applied to the EZ430-RF2500-SEH Solar Collection Development Kit to help create a permanent power supply wireless sensor network. The module includes a high-efficiency solar cell for operating under low-intensity fluorescent lamps in indoor, providing sufficient electrical power running wireless sensor applications without additional batteries. You can also use external energy collectors, such as piezoelectric power.
The system also manages and store excess energy by a pair of thin film rechargeable battery, which can provide sufficient electrical energy, carry out more than 400 transmission, no external power supply. This ensures reliably capturing and transmits medical data without worrying about battery charging problems because they act as an energy buffer, and store energy when they are used and lightable can be collected. And their self-discharged is very small, which is critical to the power-free energy collection system.
EZ430-RF2500 is used to run energy collection applications. It is a complete USB-based MSP430 wireless development tool that provides all necessary hardware and software required to use 16 MHz MSP430F2274 microcontrollers and CC2500 wireless transceivers. The transceiver works in a non-licensed 2.4 GHz frequency band, using Ti's SIMPLICITI low-power communication protocol, the link returns to a hub that can be a PC or an embedded data collection hub, and the design security element is implemented.
This method ensures that sensors and wireless links have adequate energy in an energy collection method because high current pulse is specially required for the battery, and repeatedly provides pulse currents that are exceeded to be given to a given battery to reduce the battery life. In transmission and reception mode, there is typically a pulse current in the wireless sensor system. Unfortunately, the internal impedance of the battery usually forms an internal pressure drop, which prevents the battery from providing a pulse current at the voltage required to run the external circuit.
One way to relieve this is to place a low equivalent series resistance (ESR) capacitor in the battery. The battery is charged between the discharge pulse, and then the capacitor provides a pulse current to the load. Some key parameters are known, and the direct approach is to specify the capacitance of the given battery in the application, including battery impedance and voltage, operating temperature and pulse current amplitude and duration.
The EZ430-RF2500-SEH development board includes an MSP430 firmware that considers these constraints, and a PC application that can display all connected wireless nodes and data being transmitted.
Silicon Labs also integrates ultra-low power wireless sensors, which are powered by energy, with appropriate microcontrollers for regular medical system measurement and transmission results. Since it is powered by energy, there is no need to replace the battery during the service life, and the height is only 0.17 mm thin battery, its expected life is 15 years (or 7 AH).
The sensor node uses the Silicon Labs Si1012 wireless MCU, which can be operated at 919.84 MHz and powered by the solar energy. When the node does not transmit the data, the controller can maintain a low power state, which consumes only 50 NA. The energy collection power supply is approximately 3 μA at the time of enabled, and only as low as 50 lux light is illuminated, the solar cell can be canceled. In this way, even in a darker environment, the energy collection power supply can still be effective for the system for more than 7 days, and can work effectively under the indoor 200 LX illumination and outdoor 10,000 LX lighting.
The node includes a solar cell that provides energy, converts AC vibration energy into a rectifier of DC current and a Linear Technology Power Manager (can receive DC energy and adjust it to a constant 4.1 V). If the voltage is too low, the battery can be disconnected from the circuit, thereby preventing overemployment of the battery.
The energy management circuit then converts the 4.1 V output of the thin film battery into a regulated 2.7 V for use by the wireless controller. The main components of this circuit have ultra low power low pressure difference (LDO) regulators, undervoltage detectors and 100 μF tantalum capacitors, providing the desired peak current for radio frequency transmission. The turn-off pin of the LDO is connected to the undervoltage detector, so the system is not powered by the 100 μF capacitor to at least 3.0 V. This ensures that the system does not attempt to start unless there is enough energy storage to complete the starting sequence. However, the system requires approximately 3 μA to work, which requires 50 lux light to illuminate solar cells to easily power.
When the controller wakes up from Sleep mode, it samples the current temperature with a chip temperature sensor and operates with the remaining power of the thin film battery and the environmental light amount management system of the solar cell.
One of the key features is ultra-low power consumption in hibernation and working mode. Figure 3 shows a movable curve of a radio frequency packet per second. When the RF transmitter is enabled, the peak current is 29 mA, and the average current of the three minute time period is 51 μA. Use GFSK modulation transmission on the 128 Kbit / S link, the output power is +13 dB.
These development boards use special wireless protocols of 2.4 GHz and 919 MHz, and any security features must be added.
Smart Bluetooth devices can be used to provide 2.4 GHz encryption wireless links for signal built-in security smartphones, but this is sacrifice power consumption and bring greater challenges to energy collection systems. Bluetooth devices in the DKBLE development kit, such as Silicon Labs BLE112 modules, which can be used to develop a heart rate monitor with dedicated optimization software. Its power consumption is 27 mA in transmission mode, only 0.4 μA in sleep mode, which combines with the power management subsystem, collecting the energy of solar cells with the rechargeable battery.
Conclusion
There are many technologies that collect environmental energy for wearable medical monitors. Piezoelectric devices and solar cells can produce enough power to ensure that data capture is not interrupted due to battery charge, and the integrated development board provides power management, low-power microcontrollers and software to implement such systems. Now, the latest technologies such as smart Bluetooth bring security to links, and special software can make such development easier.
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