Capsule Ultrasound Device: Characterization and Testing Results

To overcome the limitations of conventional ultrasound endoscopy, we developed a capsule ultrasound (CUS) device: an ingestible and disposable pill to inspect the multiple layers of the entire gastrointestinal (GI) tract and to provide a convenient method for diagnosing GI diseases. The CUS device was composed of three building blocks: the cylindrical capacitive micromachincd ultrasonic transducer (CMUT) array, imaging circuitry, and wireless transmitter. All of these three components were designed, fabricated and tested successfully. With low DC bias voltage, a single element of the CMUT array generated surface pressure over 700 kPa, with a 3 dB bandwidth greater than 80 percent. In the imaging circuitry, the high-voltage pulscr generated a unipolar pulse up to 18 V with the pulse width varying from 77 ns to 125 ns, and the receiving channel included the TIA with a gain of 92.4 dB and a 3 dB bandwidth of 7.5 MHz, the TGC amplifier with 25 ns recovery time when switching between five gain levels, and the 20 MSample/s ADC with a signal-to-noise-and-distortion ratio (SNDR) of 46.5 dB. The wireless transmitter provided a data rate of 10 Mbps, with a measured bit error rate (BER) < 2*10(-7) through a link attenuation of 64 dB. The performance of a single element of CMUT array was tested with an imaging circuity channel, demonstrating a CMUT element surface pressure of greater than 290 kPa, a receive sensitivity of 300 mu V/Pa and a minimal detectable pressure of 0.756 mPa per root Hertz.