Ultrasonic waveguide for improved ultrasonic thermometry
An improved ultrasonic waveguide for an ultrasonic thermometry system is provided. The waveguide includes a series of sensing zones, each of which is tuned to a specific narrow frequency band. The waveguide is acoustically coupled to a transducer, which launches a longitudinal elastic wave of desired waveform and frequency. The wave propagates down the waveguide, and is reflected from the sensing zone that is tuned to that frequency. Each sensing zone is designed to be highly reflective to a narrow frequency band while being transparent to other frequencies.
1. A method comprising:
launching, at a proximal end of an ultrasonic waveguide, a first ultrasonic signal having a first interrogation frequency and a second ultrasonic signal having a second interrogation frequency, the ultrasonic waveguide including an elongated body having a proximal sensing zone located adjacent to the proximal end and a distal sensing zone located downstream from the proximal sensing zone,
wherein the proximal sensing zone includes a first reflection feature and a second reflection feature axially displaced from the first reflection feature by an intermediate region that are together structured to impart to the proximal sensing zone a band-rejection response tuned to the first interrogation frequency, such that the proximal sensing zone is substantially transmissive of the second ultrasonic signal and any backward-propagating copies thereof, and rejects propagation of the first ultrasonic signal beyond the proximal sensing zone, and reflects two copies of the first ultrasonic signal that are time delayed from each other, so the two time-delayed copies of the first ultrasonic signal return to the proximal end, and
wherein the distal sensing zone includes another first reflection feature and another second reflection feature axially apart by another intermediate region that are together structured to impart to the distal sensing zone a band-rejection response tuned to the second interrogation frequency, such that the distal sensing zone rejects propagation of the second ultrasonic signal beyond the distal sensing zone and reflects two copies of the second ultrasonic signal that are time delayed from each other, so the two time-delayed copies of the second ultrasonic signal return, through the proximal sensing zone, to the proximal end;
receiving, at the proximal end, and analyzing the two time-delayed copies of the first ultrasonic signal;
determining, based on the analyzed two time-delayed copies of the first ultrasonic signal, a first temperature within the proximal sensing zone;
receiving, at the proximal end, and analyzing the two time-delayed copies of the second ultrasonic signal; and
determining, based on the analyzed two time-delayed copies of the second ultrasonic signal, a second temperature within the distal sensing zone.
2. The method of claim 1 wherein each of the first and second reflection features of the proximal sensing zone and the first and second reflection features of the distal sensing zone includes alternating layers of a first material and a second material different from the first material.
3. The method of claim 1 wherein each of the first and second reflection features of the proximal sensing zone and each of the first and second reflection features of the distal sensing zone includes alternating layers having alternating first outer diameter and second outer diameter different from the first outer diameter.
4. The method of claim 2 wherein the first material includes a first metal and wherein the second material includes a second metal.
5. The method of claim 2 wherein the elongated body is formed of the second material.
6. The method of claim 1 wherein the first ultrasonic signal and the second ultrasonic signal include a first frequency and a second frequency, respectively, of at least 100 KHz.
7. The method of claim 1 wherein;
analyzing the two time-delayed copies of the first ultrasonic signal reflected from within the proximal sensing zone includes determining a time-of-flight difference between the copies returning from the respective first and second reflection features of the proximal sensing zone, and
analyzing the two time-delayed copies of the second ultrasonic signal reflected from within the distal sensing zone includes determining another time-of-flight difference between the copies returning from the respective first and second reflection features of the distal sensing zone.