11.3 Data Acquisition Systems for Biomedical Applications

Data acquisition systems are crucial in biomedical applications, capturing and processing physiological signals. These systems use multiplexing, sampling, and signal conditioning to prepare analog signals for digital conversion, ensuring accurate representation of biological data.

Microcontroller-based processing enables real-time analysis and control, while data storage and management preserve information for future use. Telemetry and wireless communication facilitate remote monitoring, integrating biomedical data acquisition with modern healthcare technologies.

Signal Conditioning and Acquisition

Multiplexing and Sampling

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• Multiplexer selects one of several analog input signals and forwards the selected input into a single line
  • Allows multiple signals to be processed by a single analog-to-digital converter (ADC)
  • Commonly used in multi-channel data acquisition systems (ECG, EEG)
• Sample-and-hold circuit captures the voltage of a continuously varying analog signal and holds it constant for a specified period
  • Ensures the input to the ADC remains constant during the conversion process
  • Consists of a switch and a capacitor to store the sampled voltage
  • Prevents errors caused by rapidly changing input signals during analog-to-digital conversion

Signal Conditioning

• Anti-aliasing filter removes frequency components above the Nyquist frequency (half the sampling rate) before sampling
  • Prevents aliasing, which occurs when high-frequency components appear as low-frequency components in the sampled signal
  • Typically implemented using a low-pass filter with a cutoff frequency below the Nyquist frequency
  • Ensures the sampled signal accurately represents the original analog signal
• Biomedical sensors interface converts physiological signals into electrical signals suitable for data acquisition systems
  • Includes amplification, filtering, and signal conditioning circuitry
  • Examples include instrumentation amplifiers for low-level signals (ECG, EEG) and bridge circuits for resistive sensors (strain gauges, pressure sensors)
  • Ensures optimal signal quality and compatibility with the data acquisition system

Data Processing and Control

Microcontroller-based Processing

• Microcontroller performs real-time processing, control, and communication tasks in a data acquisition system
  • Executes software instructions to process and analyze acquired data
  • Controls the operation of the data acquisition system components (multiplexer, ADC, memory)
  • Communicates with external devices or systems (displays, computers, wireless modules)
• Real-time processing enables the system to respond to events or changes in the acquired data within a specified time constraint
  • Includes tasks such as digital filtering, feature extraction, and event detection
  • Ensures timely analysis and decision-making in applications (patient monitoring, closed-loop control)

Data Storage and Management

• Data storage preserves the acquired and processed data for later analysis or transmission
  • Utilizes various memory technologies (RAM, flash memory, SD cards) depending on the application requirements
  • Implements data compression techniques to reduce storage space and transmission bandwidth
  • Organizes data using file systems or databases for efficient access and retrieval
• Data management involves organizing, indexing, and securing the stored data
  • Assigns unique identifiers or timestamps to each data record for easy identification
  • Implements data encryption and access control measures to protect sensitive information
  • Performs data backup and synchronization tasks to ensure data integrity and availability

Data Transmission

Telemetry and Wireless Communication

• Telemetry enables the wireless transmission of acquired data from the data acquisition system to a remote location
  • Utilizes various wireless technologies (Bluetooth, Wi-Fi, Zigbee) depending on the range and data rate requirements
  • Allows real-time monitoring and remote access to the acquired data
  • Facilitates the integration of data acquisition systems with cloud-based platforms and mobile devices
• Wireless communication protocols define the rules and formats for data exchange between the data acquisition system and remote devices
  • Ensures reliable and secure data transmission over the wireless channel
  • Implements error detection and correction mechanisms to maintain data integrity
  • Manages the establishment and termination of wireless connections, as well as data flow control and synchronization