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Wireless impedance measurements for monitoring peripheral vascular disease

Wireless microdevices powered by ultrasound energy have been fabricated to measure and telemeter tissue impedance spectrums for applications in peripheral vascular disease monitoring. The system is characterized by simplicity of the implant consisting of only two electrical components. Ex vivo testing shows the potential for constructing tissue impedance spectrum plots over the range from 10 Hz to 10 kHz by a device less than 1 mm in diameter and 1 cm long. The neurostimulator microdevice was powered by continuous waveform 650 kHz ultrasound with a swept-frequency amplitude modulation. The system was operated at safe ultrasound power levels on the order of 10-100 mW/cm2. The device proved to be sensitive and able to measure tissue impedances over a broad range. Volume conducted signals carrying impedance information from the microdevice were remotely detected by surface biopotential electrodes.