Wireless, Ultra-Low-Power Implantable Sensor for Chronic Bladder Pressure Monitoring.

The wireless implantable/intracavity micromanometer (WIMM) system was designed to fulfill the unmet need for a chronic bladder pressure sensing device in urological fields such as urodynamics for diagnosis and neuromodulation for bladder control. Neuromodulation in particular would benefit from a wireless bladder pressure sensor which could provide real-time pressure feedback to an implanted stimulator, resulting in greater bladder capacity while using less power. The WIMM uses custom integrated circuitry, a MEMS transducer, and a wireless antenna to transmit pressure telemetry at a rate of 10 Hz. Aggressive power management techniques yield an average current draw of 9 µA from a 3.6-Volt micro-battery, which minimizes the implant size. Automatic pressure offset cancellation circuits maximize the sensing dynamic range to account for drifting pressure offset due to environmental factors, and a custom telemetry protocol allows transmission with minimum overhead. Wireless operation of the WIMM has demonstrated that the external receiver can receive the telemetry packets, and the low power consumption allows for at least 24 hours of operation with a 4-hour wireless recharge session.

Low-power wireless micromanometer system for acute and chronic bladder-pressure monitoring.

This letter describes the design, fabrication, and testing of a wireless bladder-pressure-sensing system for chronic, point-of-care applications, such as urodynamics or closed-loop neuromodulation. The system consists of a miniature implantable device and an external RF receiver and wireless battery charger. The implant is small enough to be cystoscopically implanted within the bladder wall, where it is securely held and shielded from the urine stream. The implant consists of a custom application-specific integrated circuit (ASIC), a pressure transducer, a rechargeable battery, and wireless telemetry and recharging antennas. The ASIC includes instrumentation, wireless transmission, and power-management circuitry, and on an average draws less than 9 µA from the 3.6-V battery. The battery charge can be wirelessly replenished with daily 6-h recharge periods that can occur during the periods of sleep. Acute in vivo evaluation of the pressure-sensing system in canine models has demonstrated that the system can accurately capture lumen pressure from a submucosal implant location.

A high-voltage, high-current CMOS pulse generator ASIC for deep brain stimulation.

A high-voltage, high-current pulse generator ASIC based on 0.35-εm high-voltage CMOS technology is presented. The chip has eight independently-controlled biphasic output channels that can generate either current- or voltage-controlled pulses. The output driver is capable of delivering current up to 1.26 mA or 5.04 mA and voltage up to 2.36 V or 9.45 V; all with 6-bit resolution. The stimulation frequency can be adjusted between 3 Hz to 5 kHz, while pulse width can vary from 20 µs to 640 εs in 20 εs steps for 100-kHz clock frequency. The timing parameters can be adjusted further by varying the clock frequency. These parameters, including pulse phase, can be programmed independently in each channel to allow different waveform generation. The foregoing provides an on-chip solution for an arbitrary function generator that can be monolithically fabricated with the rest of the circuitry. Based on its configuration this chip is an ideal solution for deep brain stimulation (DBS) electrode for targeted stimulation through current steering.

Unit-delay focusing architecture and integrated-circuit implementation for high-frequency ultrasound.

High-frequency ultrasound (above 10 MHz) has been used successfully in many medical applications, including eye, skin, gastrointestinal, intravascular, and Doppler flow imaging. Most of these applications use single-element transducers, thereby imposing a tradeoff between resolution and depth of field. Fabrication difficulties and the need for high-speed electronic beamformers have prevented widespread use of arrays at high frequencies. In this paper, a unit-delay focusing architecture suitable for use with high-frequency ultrasound annular arrays is described. It uses a collection of identical, active delay cells that may be simultaneously varied to accomplish focusing. Results are presented for an analog integrated circuit intended for use with a five-element, 50-MHz planar annular array. Focusing is possible over an axial range for which the ratio of maximum to minimum f-number is 2.1. Unit-delay architectures also are described for curved annular arrays and linear arrays.