Shaul Ozeri

Ultrasonic transcutaneous energy transfer for powering implanted devices

This paper investigates ultrasonic transcutaneous energy transfer (UTET) as a method for energizing implanted devices at power level up to a few 100 mW. We propose a continuous wave 673 kHz single frequency operation to power devices implanted up to 40 mm deep subcutaneously. The proposed UTET demonstrated an overall peak power transfer efficiency of 27% at 70 mW output power (rectified DC power at the load). The transducers consisted of PZT plane discs of 15 mm diameter and 1.3mm thick acoustic matching layer made of graphite. The power rectifier on the implant side attained 88.5% power transfer efficiency. The proposed approach is analyzed in detail, with design considerations provided to address issues such as recommended operating frequency range, acoustic link matching, receivers rectifying electronics, and tissue bio-safety concerns. Global optimization and design considerations for maximum power transfer are presented and verified by means of finite element simulations and experimental results.

Ultrasonic transcutaneous energy transfer using a continuous wave 650 kHz Gaussian shaded transmitter.

This paper proposes ultrasonic transcutaneous energy transfer (UTET) based on a kerfless transmitter with Gaussian radial distribution of its radiating surface velocity. UTET presents an attractive alternative to electromagnetic TET, where a low power transfer density of less than 94 mW/cm(2) is sufficient. The UTET is operated with a continuous wave at 650 kHz and is intended to power devices implanted up to 50mm deep. The transmitter was fabricated using a 15 mm diameter disc shape PZT (Lead Zirconate Titanate) element (C-2 grade, Fujiceramics Corporation Tokyo Japan), in which one surface electrode was partitioned into six equal area electrodes ( approximately 23 mm(2) each) in the shape of six concentric elements. The UTET was experimented using pig muscle tissue, and showed a peak power transfer efficiency of 39.1% at a power level of 100 mW. An efficient (91.8%) power driver for the excitation of the transmitter array, and an efficient rectifier (89%) for the implanted transducer are suggested. To obtain the pressure field shape, the Rayleigh integral has been solved numerically and the results were compared to finite element simulation results. Pressure and power transfer measurements within a test tank further confirm the effectiveness of the proposed UTET.

The Mathematical Foundation of Distributed Interleaved Systems

The distribution and interleaving (D&I) of signals is a common method for ripple attenuation in various engineering applications in such areas as control, communication, and power electronics. Similarities to this technique may also been found in nonengineering fields such as biology and medicine. This paper presents a mathematical exploration of distributed interleaved systems along with a simple frequency-domain model of interleaving. We are hoping that the insights provided by this mathematical framework and the newly proposed model for interleaved systems will lead to enhanced techniques for evaluating D&I processes, and facilitate the design of better systems. In particular, we hope this work results in new approaches to low-pass filtering that will exhibit fast dynamics and very efficient ripple attenuation (in theory, this can produce complete ripple removal in some cases)

Simultaneous backward data transmission and power harvesting in an ultrasonic transcutaneous energy transfer link employing acoustically dependent electric impedance modulation

The advancement and miniaturization of body implanted medical devices pose several challenges to Ultrasonic Transcutaneous Energy Transfer (UTET), such as the need to reduce the size of the piezoelectric resonator, and the need to maximize the UTET link power-transfer efficiency. Accordingly, the same piezoelectric resonator that is used for energy harvesting at the body implant, may also be used for ultrasonic backward data transfer, for instance, through impedance modulation. This paper presents physical considerations and design guidelines of the body implanted transducer of a UTET link with impedance modulation for a backward data transfer. The acoustic matching design procedure was based on the 2×2 transfer matrix chain analysis, in addition to the Krimholtz Leedom and Matthaei KLM transmission line model. The UTET power transfer was carried out at a frequency of 765 kHz, continuous wave (CW) mode. The backward data transfer was attained by inserting a 9% load resistance variation around its matched value (550 Ohm), resulting in a 12% increase in the acoustic reflection coefficient. A backward data transmission rate of 1200 bits/s was experimentally demonstrated using amplitude shift keying, simultaneously with an acoustic power transfer of 20 mW to the implant.

Noninvasive Control of the Power Transferred to an Implanted Device by an Ultrasonic Transcutaneous Energy Transfer Link

Ultrasonic transcutaneous energy transfer is an effective method for powering implanted devices noninvasively. Nevertheless, the amount of power harvested by the implanted receiver is sensitive to the distance and orientation of the external transmitting transducer attached to the skin with respect to the implanted receiving transducer. This paper describes an ultrasonic power transfer link whose harvested power is controlled by an inductive link. A small (5 μF) storage capacitor voltage, which is part of the implanted unit, is allowed to swing between 3.8 and 3.5 V using hysteretic control. The two control states are indicated by excitation (while the implanted storage capacitor voltage decreases) or the absence of excitation of an implanted coil that is magnetically coupled to an external coil attached to the skin surface. A 35 mW Ultrasonic Transcutaneous Energy Transfer link was fabricated using two piezoelectric transducers of equal size (Fuji Ceramics C-2 PZT disc 15 mm × 3 mm) operated at a vibration frequency of 720 kHz. By applying the proposed hysteretic control, the captured power was effectively regulated for implantation depths of up to 85 mm.

A resonant LED driver with capacitive power transfer

A quasi resonant topology suitable for LED drivers, featuring power factor correction and dimming in a single stage is presented. It contains a single active switch, and operates in zero-voltage-switching, zero-current-switching. This topology includes neither electrolytic capacitors nor transformer, and provides galvanic isolation between the AC mains and the DC side. Building on this new topology, a 15 W, 30 V, LED string driver with a typical operation frequency of 200 kHz was designed and experimented. Experimental results fully support the theoretical analysis and the simulation results. Measured efficiency exceeds 90% in the entire operation range and reached a peak efficiency of 96%. The driver is dimmable through the switching frequency. Dimming in the range of 4W-19W is demonstrated experimentally.

Static force measurement by piezoelectric sensors

It is demonstrated that piezoelectric elements are quite suitable for measuring static forces. This is achieved by measuring the variations of the piezoelectric sensor series resonance branch at its first resonance mode, which accurately reflects the measured force. A simple electronic interface circuit was designed to experimentally validate this new concept

High frequency resonant inverter for excitation of piezoelectric devices

This paper presents a high frequency AC source consisted of two phase shifted resonant legs, suitable for driving piezoelectric devices such as those employed in ultrasound radiators. The proposed inverter is also suitable for the excitation of piezoelectric transformers (PT). The inverter is characterized by high efficiency, low harmonic distortion, good dynamic response, and simplicity of load power control. Applications include ultrasound projectors for high intensity focused ultrasound, intended for surgery, or hyperthermia treatment, tissue ablation, sonophoresis devices, and PT excitation.

Piezoelectric transformers model parameters extraction based on time domain measurements

A simple method for the extraction of piezoelectric transformers model parameters is suggested. The piezoelectric transformers series resonance RLC relevant branch is excited for a short duration. Consequently, the current decays exponentially. The model parameters are obtained based on the decay time constant, natural resonance frequency, and other measured parameters. Conversely to commonly employed methods, such as the Y parameters admittance circle model (employing network analyzer measurements), this method requires only standard equipment (signal generator and oscilloscope) and a power amplifier. An additional advantage of this method is the ability to test the PT at high voltage levels, providing better indication to the model parameter values that are in effect during actual operation of the device in a power converter. Experimental evidence is provided in support of the proposed method

Ultrasonic Air Bubble Detection Employing Signal Processing Techniques

An air bubble detection system is presented, suitable for medication drug delivery system that must avoid air bubble beyond certain limits. The suggested approach is based on transmission of an acoustic (ultrasonic) wave through the active detection area of the fluid media and analysis of its impact on the acoustic wave. Physical operation principle and design considerations are provided as well as the cross correlation based signal processing procedures. Experimental results are provided, showing good agreement with the theory