Igor Izyumin

Capacitive power transfer for contactless charging

The simplicity and low cost of capacitive interfaces makes them very attractive for wireless charging stations. Major benefits include low electromagnetic radiation and the amenability of combined power and data transfer over the same interface. We present a capacitive power transfer circuit using series resonance that enables efficient high frequency, moderate voltage operation through soft-switching. An included analysis predicts fundamental limitations on the maximum achievable efficiency for a given amount of coupling capacitance and is used to find the optimum circuit component values and operating point. Automatic tuning loops ensure the circuit operates at the optimum frequency and maximum efficiency over a wide range of coupling capacitance and load conditions. An example interface achieves near 80% efficiency at 3.7 W with only 63pF of coupling capacitance. An automatic tuning loop adjusts the frequency from 4.2 MHz down to 4MHz to allow for 25% variation in the nominal coupling capacitance. The duty cycle is also automatically adjusted to maintain over 70% efficiency for light loads down to 0.3 W.

CMOS-compatible AlN piezoelectric micromachined ultrasonic transducers

Piezoelectric micromachined ultrasonic transducers for air-coupled ultrasound applications were fabricated using aluminum nitride (AlN) as the active piezoelectric layer. The AlN is deposited via a low-temperature sputtering process that is compatible with deposition on metalized CMOS wafers. An analytical model describing the electromechanical response is presented and compared with experimental measurements. The membrane deflection was measured to be 210 nm when excited at the 220 kHz resonant frequency using a 1Vpp input voltage.

In-Air Rangefinding With an AlN Piezoelectric Micromachined Ultrasound Transducer

An ultrasonic rangefinder has a working range of 30 to 450 mm and operates at a 375-Hz maximum sampling rate. The random noise increases with distance and equals 1.3 mm at the maximum range. The range measurement principle is based on pulse-echo time-of-flight measurement using a single transducer for transmit and receive. The transducer consists of a piezoelectric AlN membrane with 400-μm diameter, which was fabricated using a low-temperature process compatible with processed CMOS wafers. The performance of the system exceeds the performance of other micromechanical rangefinders.

Magnetic Relaxation Detector for Microbead Labels

A compact and robust magnetic label detector for biomedical assays is implemented in 0.18-μ m CMOS. Detection relies on the magnetic relaxation signature of a microbead label for improved tolerance to environmental variations and relaxed dynamic range requirement, eliminating the need for baseline calibration and reference sensors. The device includes embedded electromagnets to eliminate external magnets and reduce power dissipation. Correlated double sampling combined with offset servo loops and magnetic field modulation, suppresses the detector offset to sub-μ T. Single 4.5-μ m magnetic beads are detected in 16 ms with a probability of error <; 0.1%.

An ultrasonic rangefinder based on an AlN piezoelectric micromachined ultrasound transducer

An ultrasonic rangefinder has a working range of 30mm to 450mm and operates at a 375 Hz maximum sampling rate. The worst-case systematic error less than 1.1 mm. The rms noise is proportional to the square of the distance and equals 1.3mm at the maximum range. The range measurement principle is based on pulse-echo time of flight measurement using a single transducer for transmit and receive consisting of a piezoelectric AlN membrane with 400 µm diameter which was fabricated using a low-temperature process compatible with processed CMOS wafers. All circuits are low voltage, enabling integration in standard low voltage circuit technology.

Aluminum nitride pMUT based on a flexurally-suspended membrane

Piezoelectric micro-machined ultrasonic transducers (pMUTs) for air-coupled ultrasound applications were fabricated using aluminum nitride (AlN) as the active piezoelectric material. Earlier pMUTs based on a fully clamped membrane design suffer from high sensitivity to residual stress, causing large variations in the operating frequency, and have a reduced dynamic range due to nonlinearity at large drive voltages. Here we evaluate a new design based on a membrane that is supported by three flexures and a thin oxide layer, aimed to release residual stress, extend the mechanical dynamic range and improve the acoustic coupling. The acoustic performance of this flexurally suspended design is compared with a fully clamped one, showing a piston-like mode shape, which translates to improved output sound pressure.

A transformerless galvanically isolated switched capacitor LED driver

The design and test of a capacitor-isolated LED driver, suitable for screw-in, residential lighting applications, is reported. The design relies on a pair of high voltage isolation capacitors, comprising part of a series resonant tank. The series resonant tank is integrated with a balanced ladder step-down switched capacitor front-end, enabling the series resonant conversion stage to function conveniently with any line voltage, while still preserving the efficient voltage regulation capability of the resonant stage. Dimming and power control are effected with a low frequency PWM control loop. The tested prototype delivers 15.5 W at 425 mA at rated power into a string of 12 LEDs at 92% efficiency. Efficiency exceeding 85% is maintained over more than a 10:1 dimming range, and also over a wide range of line voltages.

A micromechanical ultrasonic distance sensor with >1 meter range

Ultrasonic distance sensors based on piezoceramic transducers have >1m range and millimeter accuracy but require the use of bulky transducers. Existing micromachined sensors deliver inferior performance, with maximum range in the tens of centimeters. We present theory, design equations, and measured results for a micromechanical ultrasonic distance sensor which approaches the performance of piezoceramic-based solutions. The sensor has a maximum range >1300mm and random errors (3σ) of &#60;1.7mm at 1.3m.

Microleverage DETF Aluminum Nitride resonating accelerometer

In this work, we present a novel microleverage Double Ended Tuning Fork (DETF) resonant accelerometer made of thin film piezoelectric Aluminum Nitride (AlN). The development and characterization of this novel design is discussed through a Finite Element Analysis (FEA) and experimentally demonstrated. The entire accelerometer structure is made of 2 μm of highly c-axis oriented piezoelectric AlN with 100 nm platinum as top and bottom electrode. The preliminary characterization of the accelerometer was performed in a vacuum chamber at a pressure of 4 Torr and achieved a sensitivity of 18.1 Hz/g (i.e. 54 ppm/g) along the sensing axis and 0.1 Hz/g along the cross axis.

Low friction liquid bearing mems micromotor

This paper examines the performance of rotating microdevices incorporating a liquid bearing to couple a rotating element to a fixed substrate. Liquid bearing technology promises to significantly improve the durability and lifetime of micromechanical motors. Here, the fluid is confined between the rotor and stator using surface patterning of a hydrophobic layer. Magnetic actuation of 10 mm diameter silicon rotor is used to characterize the liquid bearing motor at rotation rates up to 1800 rpm. Bearings with fluid thickness from 20–200 microns are characterized. A minimum torque of 0.15 µN-m is required to overcome static friction and initiate rotation. At rotation rates above 720 rpm, the rotor wobble is less than ±1 mrad and the bearing exhibits viscous friction with a drag coefficient of 1.2 × 10−3 µN-m/rpm.