Transmit Control

The ultrasound system has the capability to send out pulses at a specific frequency. This is represented as a square wave pulse from the transmit electronics, and filtered as a sine wave when viewed from hydrophone data. Each transducer has a center frequency and a specific bandwidth, however with the research package any frequency or combination of frequencies can be applied during scanning.

Transmit Clocking
The transmit electronics firmware run at specific clock frequencies that determine what the valid frequency outputs are, these can be summarized in the table below. For 40 MHz transmit firmware, each pulse shape symbol (+, -, 0) corresponds to 25ns. Because the hardware can only control the pulse in 25ns resolution, this implies that only certain frequencies are achievable. The 80 MHz firmware reduces the pulse shape symbol duration to 12.5ns, allowing for better frequency control.

40 MHz Firmware

80 MHz Firmware

Since the highest sampling frequency on the Sonix systems is 40 MHz, a transmission of a 20 MHz pulse would be considered the maximum to send to the transmitters. Cases where frequency output could be shifted include:
 * SonixDAQ is used in conjunction with the ultrasound and its sampling rate is set to 80MHz
 * The L40-8/13 transducer is used to emit higher frequency pulses

Transmit Shaping
The transmit shape is created by programming characters into a buffer that is used internally on the Sonix systems, including the Texo SDK. The buffer allows for up to 96 characters to be programmed, and soon will allow for 1024 characters with a firmware update.

By repeating the pulse pattern (ex. +-+-+-+-), the transmit signal spectrum can be narrowed and signal power can be increased. Due to the transfer function of the transducer, which can be highly biased depending on the system used, it may be desirable to increase the transmit frequency component of the signal by repetition of the pulse pattern.



5 Mhz

 * To create a 5 MHz transmit excitation, set the transmit frequency to 5 MHz and set the pulse shape to + –
 * A different method to create a 5 MHz transmit excitation is to set the transmit frequency to 20 MHz and set the pulse shape to + + + + – – – –

4+5 MHz Blended

 * To create a blended frequency of 4 and 5 MHz, set the transmit frequency to 20 MHz and set the pulse shape + + + + – – – – + + + + + – – – – –

Note
If the transmit frequency is limited, then the range of the parameter needs to be adjusted in the setup files or through modification via the Ulterius SDK.