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Another potential issue is that ultrasound machines send out an impulse instead of a single frequency. So maybe the quartz crystal oscillators aren't good at pr

Another potential issue is that ultrasound machines send out an impulse instead of a single frequency. So maybe the quartz crystal oscillators aren't good at producing a short high-bandwidth signal? That being said, there's a type of radar system called "stepped frequency continuous wave" radar that uses a bunch of single frequency transmissions instead of an impulse transmission. The basic idea is that instead of using a high-bandwidth transceiver to send and receive the impulse, you can use a low-bandwidth transceiver to send and receive tones, and then hop this transceiver over the large bandwidth to get a high-resolution image (the tradeoff being that it takes longer to acquire an image). Since ultrasound is basically radar, I'd imagine this technique could be used for ultrasound too.

blensor 9y ago
But wouldn't a lower frequency be at the cost of spatial resolution due to the longer wavelength?
- awelkie 9y ago
  The spatial resolution depends on the bandwidth of your transmission. An infinite-bandwidth signal is a delta in time, and gives infinite precision. Any finite bandwidth impulse will be a sinc in time, with temporal width proportional to the inverse of the bandwidth. So a higher bandwidth impulse will be shorter in time, which would give better temporal resolution. Typical radar works by sending and receiving a high-bandwidth impulse, which requires high-bandwidth transceivers. Let's say that transmission occupies frequencies between f0 and f1. SFCW radar works by sending a bunch of individual low-bandwidth transmissions between f0 and f1. So each transmission is small, but together they occupy the same f0 to f1 bandwidth. Assuming the environment didn't change in the time it took to send all of those low-bandwidth transmissions, you've effectively simulated a high-bandwidth impulse using a bunch of low-bandwidth impulses. So the spatial resolution will be the same.

blensor 9y ago

But wouldn't a lower frequency be at the cost of spatial resolution due to the longer wavelength?

awelkie 9y ago
The spatial resolution depends on the bandwidth of your transmission. An infinite-bandwidth signal is a delta in time, and gives infinite precision. Any finite bandwidth impulse will be a sinc in time, with temporal width proportional to the inverse of the bandwidth. So a higher bandwidth impulse will be shorter in time, which would give better temporal resolution. Typical radar works by sending and receiving a high-bandwidth impulse, which requires high-bandwidth transceivers. Let's say that transmission occupies frequencies between f0 and f1. SFCW radar works by sending a bunch of individual low-bandwidth transmissions between f0 and f1. So each transmission is small, but together they occupy the same f0 to f1 bandwidth. Assuming the environment didn't change in the time it took to send all of those low-bandwidth transmissions, you've effectively simulated a high-bandwidth impulse using a bunch of low-bandwidth impulses. So the spatial resolution will be the same.