Studies of the stimulating effect of ultrasound as a tactile display have recently become more intensive in the haptic domain. In this paper, we present the design, development, and evaluation of Haptogram; a system designed to provide point-cloud tactile display via acoustic radiation pressure. A tiled 2-D array of ultrasound transducers is used to produce a focal point that is animated to produce arbitrary 2-D and 3-D tactile shapes. The switching speed is very high, so that humans feel the distributed points simultaneously. The Haptogram system comprises a software component and a hardware component. The software component enables users to author and/or select a tactile object, create a point-cloud representation, and generate a sequence of focal points to drive the hardware. The hardware component comprises a tiled 2-D array of ultrasound transducers, each driven by an FPGA. A quantitative analysis is conducted to measure the Haptogram ability to display various tactile shapes, including a single point, 2-D shapes (a straight line and a circle) and a 3-D object (a hemisphere). Results show that all displayed tactile objects are perceivable by the human skin (an average of 2.65 kPa for 200 focal points). A usability study is also conducted to evaluate the ability of humans to recognize 2-D shapes. Results show that the recognition rate was well above the chance level (average of 59.44% and standard deviation of 12.75%) while the recognition time averaged 13.87 s (standard deviation of 3.92 s).

Haptogram: Ultrasonic Point-Cloud Tactile Stimulation

To reduce the risk imposed by use of defected composite insulators on the operation of power grids, this paper introduces a nondestructive ultrasonic phased array (UPA) technique that allows effectively test such insulators. The method offers a great potential by reducing inspection time as well as allowing for analyzing components characterized by a complex geometry. The UPA inspection system utilizes an openended rectangular waveguide sensor, operating at frequency of 2.5 MHz. The system is simple, safe and relatively inexpensive. In this work, samples of silicone rubber composite insulators with various types of detects are studied and the obtained results show that void defects in the bulk of the insulator housing are easiest to be detected. Holes under insulator sheds can also be detected by the edge of scanning range. For the defects near the core-shed interface, the detection becomes possible by comparisons with sample without defects.

Ultrasonic phased array detection of internal defects in composite insulators

Simulation of ultrasonic phased array technique for imaging and sizing of defects using longitudinal waves

Coarse time quantization of delay profiles within ultrasound array systems can produce undesirable side lobes in the radiated beam profile. The severity of these side lobes is dependent upon the magnitude of phase quantization error? the deviation from ideal delay profiles to the achievable quantized case. This paper describes a method to improve interchannel delay accuracy without increasing system clock frequency by utilizing embedded phase-locked loop (PLL) components within commercial field-programmable gate arrays (FPGAs). Precise delays are achieved by shifting the relative phases of embedded PLL output clocks in 208-ps steps. The described architecture can achieve the necessary interelement timing resolution required for driving ultrasound arrays up to 50 MHz. The applicability of the proposed method at higher frequencies is demonstrated by extrapolating experimental results obtained using a 5-MHz array transducer. Results indicate an increase in transmit dynamic range (TDR) when using accurate delay profiles generated by the embedded-PLL method described, as opposed to using delay profiles quantized to the system clock.

/pdf/ultrasound-array-transmitter-architecture-with-high-timing-3aue43t0tb.pdf

Ultrasound array transmitter architecture with high timing resolution using embedded phase-locked loops

Interdigital transducers (IDTs), thanks to their multiple capabilities have the potential of increasing versatility of SHM systems. Migration of the IDT technology in SHM systems and devices is reviewed in this paper. A summary review of different types of IDTs is presented and their salient features are presented in terms of their applicability in the Lamb wave based SHM systems. Comprehensive review is provided concerning the implementation of the IDT capabilities towards the development of SHM systems. Experimental results obtained with prototype IDTs are provided for illustration. Finally, future development directions of the IDTs dedicated to SHM systems are outlined.

Interdigital lamb wave transducers for applications in structural health monitoring

One of the fundamental features of phased arrays is the ability to focus the propagating waves to a specific point within the load material by inducing a parabolic time delay. This required focusing time delay has been modified from the current formulation to incorporate either an odd or even number of elements. A brief procedure leading to the derivation of the pressure distribution for beam focusing is described, which gives rise to an unclosed form. Consequently, a numerical method is desirable for the analysis of beam focusing. Using this approach, beam directivity and pressure distributions are studied to predict the behavior of focusing as compared to steering. This shows a benefit of focusing over steering within the near field of the array, and that the directivity of focusing converges to that of steering in the far field.

Y. Shi

Papers

Beam focusing behavior of linear phased arrays