Beam steering and control of large area ultrasound actuator arrays for haptic perception

Traditional microphone units focus on human perceptible sound waves (between 20 Hz and 20 kHz). Acoustic development also focuses on ultrasound, compromising the frequencies above the detection limit of the human ear (from 20 kHz to several GHz). These sound waves can be used for a wide variety of applications, including medical imaging, therapeutic treatment, non-destructive testing and position localization of objects. Nowadays, ultrasonic transducer and sensor technology is largely based on rigid bulk piezoelectric ceramic materials, such as lead zirconate titanate or barium titanate. Although a mature technology for discrete passive components, offering a reasonably wide bandwidth and sensitivity, this ceramic-based technology is not amenable to machine large two-dimensional (2D) transducer arrays. Also, monolithic integration with other electronic components such as signal processing electronics is hardly possible. This is crucial for applications where large arrays are needed and for which a high level of integration is clearly a must. In the past years, imec has led the development of novel technologies that promise to meet all requirements of future micro-sound systems. The Large Area Electronics (LAE) and System in Foil (SiF) technology platforms allow to produce passive and active components in thin-film technologies with world-leading performance and if needed flexible form factors. Further, preliminary demonstrations of ultrasound components monolithically integrated with their drive and readout electronics are emerging. These developments will lead to two-dimensional arrays of individually addressable actuators that generate haptic perception. The purpose of this PhD is to achieve a haptic feedback system with large-area technology. To that end, two main tasks will be elaborated. The first is understanding how feeling can be generated using focused ultrasound: a modulation needs to be implemented on the ultrasound carrier wave, which depends on the nature of interaction of pressure waves with sensory nerves. The second question to be answered is how to translate this into a large-area electronic technology: integration of large-area ultrasound actuators on active matrix backplanes as well as design, test and measure the active-matrix backplanes for driving and steering ultrasound actuator arrays to the required performance. Actuator arrays will be processed on thin-film transistor backplanes, such that each actuator is driven by a thin-film transistor circuit. Each of these pixel engines is controlled by drivers chips, in silicon, positioned at the edges of the array, which provide controls and clocking. Beam steering of an array of actuators is based on the creation of interference patterns in the emitted wave of each actuator. Amplitude modulation of the focused sound wave should result in a physical sensation. A challenge for the transistors in the backplane and driver chips is precise synchronizing of phase and amplitude control of each actuator over arrays that are physically large (>10 cm), at relatively high voltages as needed for actuators that emit ultrasound in air. The PhD will start with physiological understanding and translation to electronic requirements. Then, modeling of all the relevant electronic signals, including the parasitics that tend to couple nearly-spaced oscillators towards spontaneous synchronization. Design concepts for drivers will be elaborated and measured. Promising architectures will be elaborated with integrated actuators (process work is not part of this PhD) and measured. Selected designs will be used to realize active matrices of drivers over areas > 100 cm2. These will be extensively tested for ultrasound beam formation after integration of actuator arrays on the drive electronics.