Medical Sensor Application Status and Design Challenges

The wireless sensor network (WirelessSensorNetwork) is an emerging technology that integrates sensor technology, embedded computing technology, modern network and wireless communication technologies, and distributed information processing technologies. The technology has a wide range of application scenarios.

With the development of technology, WSN (WirelessSensorNetwork) will have far-reaching effects in many aspects of medical practice. This article mainly describes the architecture of the wireless sensor network medical monitoring system and the general principles of monitoring node design.

Wireless Sensor Network Architecture

In the monitoring area, a large number of sensor nodes are arranged. The nodes use self-organizing methods for networking and use wireless communication technology for data forwarding. Each node has the dual functions of data acquisition and data fusion and forwarding. After the node collects the information and the information forwarded to it by other nodes, it performs preliminary data processing and information fusion, and then transmits it to the base station in the relaying mode of neighboring nodes, and then transmits it to the end user through the base station through the Internet, satellites, and other methods.

The node is the basic functional unit of the wireless sensor network. The specific application is different, and the design of the node is also not the same. The basic components of a sensor node include a sensing unit, a processing unit, a communication unit, and a power supply section. In addition, functional units can be added according to specific application requirements, such as positioning systems, mobile systems, and self-powered power systems.

Application of Wireless Sensor Network in Medical Treatment

Wireless sensor networks use their own advantages (such as low-cost, simple, fast, and non-invasive acquisition of various physiological parameters of patients, etc.) to make them available in medical research, hospital general/ICU wards, or home daily care. The great potential for development is a hot topic in the current research field.

A micro sensor node for detecting body parameters is placed on the patient to perform remote real-time monitoring of the patient's physiological parameters such as heart rate, blood pressure, electrocardiogram, and heart sound, and the information is transmitted to the monitoring center for timely processing and feedback. WSN collects the human physiological data of the observed people for a long period of time and is helpful in understanding the health status of the human body and in researching human diseases. In addition, there are also unique applications in drug management and the development of new drugs and blood management. In short, wireless sensor networks provide a simpler, lower-cost implementation for future telemedicine monitoring systems.

Medical architecture based on wireless sensor network
Medical monitoring systems based on wireless sensor networks are mainly composed of medical sensor nodes, medical monitoring base stations (medical SINK nodes), and community/hospital care centers.

The medical sensor node and the monitoring base station constitute a personal/home or ward wireless sensor network, and multiple such networks may constitute a community or an entire hospital monitoring network, or even a wider range of remote medical monitoring systems. First, the medical sensor node collects physiological parameters of the human body, and after the simple processing of the collected parameters, the data is transmitted to the base station directly or indirectly by way of wireless communication. The monitoring base station further processes the data and forwards it to the monitoring center. The monitoring center conducts analysis and processing, and provides timely information feedback to the patient. The monitoring center can also use a variety of methods (Internet, mobile communication networks, etc.) to carry out remote data transmission and share information with other monitoring centers.

Medical sensor node design

The basic structure of the medical sensor node includes a processing module, a sensor module, a wireless transceiver module, and a power supply module.

The sensor module is used to sense, acquire, and convert external sensor signals. It is the module that the entire node really touches the external semaphore. However, medical sensors are measured on living bodies. Especially the human body can be said to be the most complex system in the world. There is a high degree of correlation between physiological variables and they are not easily accessible. Therefore, the medical sensor should take out the predicted physiological quantity from numerous phenomena, obtain reliable and meaningful measurement data, and at the same time ensure the safety of the measured object.

Because human body parameters are mostly weak signals, generally only a few mV level, or even lower, and there are a variety of noise (measurement of environmental noise, friction noise between the instrument and the human body and the instrument itself, etc.), power frequency interference (50 Hz around the measurement environment Caused by the electromagnetic field) and various noises and other unfavorable factors. Therefore, in the design of a specific medical sensor node, an analog circuit processing module is added. The module generally includes the following parts: an amplifier circuit, a filter circuit, a trap circuit, and an analog-to-digital (A/D) conversion circuit. In the node design, the amplifier circuit generally adopts multi-stage amplification (three or four levels). The final amplification circuit generally has a level boost function in addition to the amplification function; the filter circuit: the circuit needs to be simple and reasonable, and the cut-off frequency is reasonable. Easy to adjust the high and low pass cut-off frequency and other requirements, and reasonably filter out the high-frequency and low-frequency interference in the signal; notch circuit: symmetric dual-T resistance active-capacitive notch filter or integrated switch capacitor and asymmetry are widely used. Resistor capacity network traps and so on. In short, the analog circuit processing module mainly amplifies, filters, and traps the collected signals, removes noise and interference in the signals, and extracts useful signals.

The processor module is the core of the sensor node and is responsible for device control, task allocation and scheduling, data integration and transmission of the entire node. Currently used in processor modules are Atmel's AVR series microcontrollers, TI's MSP430 ultra-low-power processors, Motorola's and Renesas' processors, and ARM microcontrollers as 32-bit embedded processors. In the node design, it is necessary to programmatically implement the acquisition and control of the sensor module, the A/D conversion, and the control of the wireless communication module.

The wireless transceiver module is used for data communication between nodes. More wireless transceiver modules used in the wireless field are Chipcon's CCl000, CC2420, and CC2430. Commonly used wireless communication technologies include: IEEE802.1lb, IEEE802.15.4 (ZigBee), Bluetooth, UWB, RFID, IrDA (infrared), and the like. Most monitoring systems use IEEE 802.15.4 (ZigBee) and Bluetooth to implement data communication between nodes and nodes and base stations.

The power module provides energy for the node and is the basic module of the entire wireless sensor node. However, due to node volume limitations, sensor nodes have very limited energy. Therefore, in the entire node design, with low power consumption and high precision as the main requirements, a series of effective measures are taken to save energy. In addition, medical sensor nodes cannot frequently replace batteries, affecting people's normal lives. Therefore, the designed medical node should have a long life cycle.

The Challenge of Medical Wireless Sensor Network Monitoring System

Although wireless sensor networks have their own unique advantages in the formation of medical monitoring systems, the following challenges apply to the actual medical applications:

Dynamic network management and node mobility management in large-scale networks: When the monitoring system is extended to communities, cities, and even the whole country, its network size is huge, and both monitoring nodes and base stations have certain mobility. Therefore, a proper network topology management structure and node mobility management method must be designed.

Data Integrity and Data Compression: Nodes sometimes require up to 24 hours to monitor human parameters, and the amount of data collected by nodes is large. However, the storage capacity of nodes is small. Compression algorithms are often used to reduce the storage and transmission of data. However, the overhead of traditional data compression algorithms is not suitable for sensor nodes. In addition, the compression algorithm can not damage the original data, otherwise it will cause the wrong diagnosis of the patient.

Data security: Wireless sensor network nodes are networked in an ad hoc manner and are vulnerable to attacks. In addition, patient information needs to be kept confidential. However, the computing power of sensor nodes is quite limited, and traditional security and encryption technologies are not applicable. Therefore, an encryption and decryption algorithm suitable for the sensor nodes must be designed.

Summary and outlook

With the development of technology, wireless medical sensor nodes gradually develop toward multiple parameters, intelligence, miniaturization, and low power consumption, and wireless sensor networks will gradually be applied to the medical field. The development and establishment of an intelligent ward and community monitoring system is the current trend of medical development at home and abroad.