## 2 Materials and Methods
### Improvement of Acquisition Rate
#### Communication protocol optimization  
As one of the key components of the data collection system, the reliability, stability, and real-time performance of the data transmission system will directly affect the performance of the entire system [20]. For an electrical imaging system with \(n_{0}\) electrodes in a single \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Chip** & **Maximum Sampling Rate (MSPS)** & **Packaging Type** & **Resolution Ratio/Bit Wide (bit)** & **SNR (dB)** \\ \hline AD9240 & 10 & MQFP-44 & 14 & 78.5 \\ AD9244 & 65 & LQFP-48 & 14 & 75.3 \\ ITC2239 & 80 & QFN-32 & 10 & 61.6 \\ AD54149 & 250 & VQFN-48 & 14 & 72.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Performance parameters of common analog-to-digital conversion chips. Figure 6: Design of peripheral circuit for AD9244 analog-to-digital conversion module. cross-section, the voltage value between each two electrodes is measured after the sensitive field is established, and then the image is reconstructed. The number of measurements required to reconstruct an image is  
\[n_{1}=n_{0}(n_{0}-1) \tag{2}\]  
Because each measurement data contains 16 bits of real and imaginary data, the number of bytes required to reconstruct an image is  
\[n_{2}=2n_{1} \tag{3}\]  
Therefore, for the existing 16-electrode system, the data required to reconstruct an image is 480 B. In addition, each frame of data will also include a frame header and a frame footer, resulting in a data volume of 504 B per frame. Currently, the data transmission methods commonly used in EIT data collection systems both domestically and internationally include USB, RS-232/485, Ethernet, Firewire, Peripheral Component Interconnect (PCI) interface, etc. [21; 22; 23]. The maximum transmission rates and characteristics of the various transmission methods mentioned above are shown in Table 4.  
The existing EIT system uses RS-232 serial port transmission and can only support transmission rates up to tens of frames per second. This results in the system's data collection rate being limited by the data transmission method. The existing serial communication can no longer meet the system's requirements for real-time and reliability. A transmission rate of over 1000 frames per second can meet the real-time requirements of the system [24]. Since the amount of data per frame is 504 B, the transmission rate of the data transmission interface should be greater than 504 kB/s, which is 4.032 Mbps when converted to Baud. Except for RS-232/485, all other transmission methods in Table 4 can meet the transmission speed requirements. Due to the low development cost and good universality of USB2.0, USB2.0 was chosen for the EIT data collection system. We adopted the CY7C68013A chip from Cypress's EZ-USB FX2 LP series. CY7C68013A is a USB2.0 control chip from Cypress, which includes a high-speed USB2.0 communication protocol and compatible 8051 control. This chip contains 16 KB of internal RAM, allowing firmware programs to run directly without the need for additional memory. CY7C68013A integrates four first-in, first-out (FIFO) internally, with a total size of 4 K bytes. Users can set them to work in master or slave mode. CY7C68013A contains an I2C interface for connecting to external EEPROMs. Users first download the written firmware program to the EEPROM. When CY7C68013A is powered on and started, it will automatically read the EEPROM program and start running in the internal RAM. The internal structure of CY7C68013A is shown in Figure 7. \begin{table}
\begin{tabular}{c c c c} \hline
**Data Transmission Method** & **Rate** & **Distance** & **Characteristic** \\ \hline USB2.0 & 480 Mbps & 5 m & Low-cost, widely used \\ RS-232/485 & 115,200 bps & 1200 m & Simple but low-speed \\ Ethernet(IEEE 802.3 ab) & 1 Gbps & Hundreds of kilometers & Relatively complex, capable of remote \\ Firewire(IEEE 1394c-2006) & 800 Mbps & 4.5 m & Less CPU usage, reliability, and high-cost \\ PCI(PCI-X 3.0) & 4266 MB/s & - & Belongs to the local bus \\ \hline \end{tabular}
\end{table}