Basic Principles of Sonomicrometry Click Here for a Powerpoint Show on the Principles of Sonomicrometry Sonomicrometry is the measurement of distance or length using sound. Transducers (commonly called "crystals") made from piezo-electric ceramic material transmit and receive sound energy. Typically, these transducers operate at ultra-sound frequencies (1 Mhz and higher). To perform a single distance measurement, one crystal will transmit a burst of ultrasound, and a second crystal will receive this ultrasound signal. A digital sonomicrometer has the added benefit of transmitting from a single crystal to multiple receivers and thus render multiple distances per "ping" As an additional functional step a digital sonomicrometer can switch crystal modes from transmitter to receiver. The elapsed time from transmission to reception is a direct and linear representation of the physical separation of the crystals. Any sonomicrometer is therefore a timing device, repeating this measurement of transit-time hundreds or thousands of times per second. The Sonometrics Digital Sonomicrometer measures this transit time in discrete time steps similar to the operation of a digital stopwatch. The resulting transit time is easily converted to a distance if the speed of sound in the material being measured is known. Typically, in biological materials, this speed is 1590 meters per second, or 1.59 mm per microsecond. Transit time is measured digitally in steps of 7.8 nano-seconds resulting in a resolution of 0.012 mm (12 µm). Considering the idea of a single crystal transmitting to a single receiver, one distance can be determined. A crystal can transmit to several other crystals, then one of those "receiver" crystals can change to a transmitter and ping back. This additional functional of the digital sonomicrometer will yield more available measurements. A four crystal instrument will yield 12 distance segment, when more crystal are used the segment count goes up exponentially (32 crystals give 496 unique segment lengths). The resolution of any sonomicrometer depends on its ability to accurately detect the received ultrasound signal and on its ability to measure transit time. Advanced high-gain, low noise circuitry in the Sonometrics Digital Sonomicrometer allows for the detection of the received ultrasound signal at a constant phase-angle for precise tracking of the received signal regardless of it's frequency. This allows for complete independence of crystal frequency and measurement resolution. Digital Sonomicrometer System Overview Sonometrics Corporation has advanced the science of sonomicrometry by creating a completely digital measurement system. A small external Ultrasound Transceiver Unit is connected via USB cable to any desktop or laptop computer running Windows. The system performs the following functions: Measures, displays, and records distances between transducers Accepts analog signals from pressure, flow, or other transducers (up to 16) Outputs user-selected sonomicrometer measurements to other systems On-line and off-line computations performed by our software System Specifications There are two significant advances that our sonomicrometer has over other systems. The first is that our system can measure every distance between every crystal, and the second is advanced signal processing which means that the researcher no longer has to make multiple adjustments while watching an oscilloscope in order to operate the system. Other features include that calibration is not required, and crystals can be placed very close together. This means the same system can be used to make both large (over 80 mm) and small (under 4 mm) measurements on the same preparation simultaneously. Specifically, the system can measure a maximum of 496 dimensions between 32 crystals. The data sampling rate can range from 16 Hz to 1600 Hz and is user- adjustable. Each measurement has a relative error (dynamic resolution) of 0.012 mm (12.4 um). Auxiliary Analog Input (analog to digital conversion) Specifications In addition to the sonomicrometer dimension measurements, our systems can accept a total of 16 analog signals from external devices. These signals are typically pressure, flow, force, or some form of electrical activity (ECG). The complete integration of these signals with sonomicrometer measurements means that our system functions as a complete data acquisition system. Each analog channel is sampled in sync with the sonomicrometer dimensions to an accuracy of 12 bits over a voltage input range of -10 to +10 volts. Auxiliary Analog Output (digital to analog conversion) Specifications If the user wishes to take the sonomicrometer dimensions out of our system in the form of an analog signal (say, to a chart recorder or other data acquisition system) then this can be done with the DAC (Digital to Analog Converter) option. Up to 8 dimensions can be selected by the user to be output as an analog signal with a voltage range of 0 to 8 volts. Software and Data Processing Our systems come with all necessary software to acquire, display, record, and process data. This includes our SonoLab and SonoVIEW for basic data analysis or CardioSOFT software for cardiovascular data analysis. If you have any questions regarding the specifications of our systems, or if you have a specific application in mind, please to contact us to answer your questions.