We have developed a technique of applying multiple matching layers to high-frequency (>30 MHz) imaging transducers, by using carefully controlled vacuum deposition alone. This technique uses a thin mass-spring matching layer approach that was previously described in a low-frequency (1 to 10 MHz) transducer design with epoxied layers. This mass- spring approach is more suitable to vacuum deposition in highfrequency transducers over the conventional quarter-wavelength resonant cavity approach, because thinner layers and more versatile material selection can be used, the difficulty in precisely lapping quarter-wavelength matching layers is avoided, the layers are less attenuating, and the layers can be applied to a curved surface. Two different 3-mm-diameter 45-MHz planar lithium niobate transducers and one geometrically curved 3-mm lithium niobate transducer were designed and fabricated using this matching layer approach with copper as the mass layer and parylene as the spring layer. The first planar lithium niobate transducer used a single mass-spring matching network, and the second planar lithium niobate transducer used a single mass-spring network to approximate the first layer in a dual quarter-wavelength matching layer system in addition to a conventional quarter-wavelength layer as the second matching layer. The curved lithium niobate transducer was press focused and used a similar mass-spring plus quarter-wavelength matching layer network. These transducers were then compared with identical transducers with no matching layers and the performance improvement was quantified. The bandwidth of the lithium niobate transducer with the single mass-spring layer was measured to be 46% and the insertion loss was measured to be -21.9 dB. The bandwidth and insertion loss of the lithium niobate transducer with the mass-spring network plus quarter-wavelength matching were measured to be 59% and -18.2 dB, respectively. These values were compared with the unmatched transducer, which had a bandwidth of 28% and insertion loss of -34.1 dB. The bandwidth and insertion loss of the curved lithium niobate transducer with the mass-spring plus quarter-wavelength matching layer combination were measured to be 68% and -26 dB, respectively; this compared with the measured unmatched bandwidth and insertion loss of 35% and -37 dB. All experimentally measured values were in excellent agreement with theoretical Krimholtz-Leedom-Matthaei (KLM) model predictions.
The development of a piezoelectric hydrophone based on lead magnesium niobate-lead titanate [PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT)] single-crystal piezoelectric as the hydrophone substrate is reported. Although PMN-PT can possess much higher piezoelectric sensitivity than traditional lead zirconate titanate (PZT) piezoelectrics, it is highly anisotropic and therefore there is a large gain in sensitivity only when the crystal structure is oriented in a specific direction. Because of this, simply replacing the PZT substrate with a PMN-PT cylinder is not an optimal solution because the crystal orientation does not uniformly align with the circumferential axis of the hydrophone. Therefore, a composite hydrophone that maintains the optimal crystal axis around the hydrophone circumference has been developed. An 11.3 mm diameter composite hydrophone cylinder was fabricated from a single <110> cut PMN-PT rectangular plate. Solid end caps were applied to the cylinder and the sensitivity was directly compared with a solid PZT-5A cylindrical hydrophone of equal dimensions in a hydrophone test tank. The charge sensitivity showed a 9.1 dB improvement over the PZT hydrophone and the voltage sensitivity showed a 3.5 dB improvement. This was in good agreement with the expected theoretical improvements of 10.1 and 4.5 dB, respectively.
Ultrasonic power transfer using piezoelectric devices is a promising wireless power transfer technology for biomedical implants. However, for sub-dermal implants where the separation between the transmitter and receiver is on the order of several acoustic wavelengths, the ultrasonic power transfer efficiency (PTE) is highly sensitive to the distance between the transmitter and receiver. This sensitivity can cause large swings in efficiency and presents a serious limitation on battery life and overall performance. A practical ultrasonic transcutaneous energy transfer (UTET) system design must accommodate different implant depths and unpredictable acoustic changes caused by tissue growth, hydration, ambient temperature, and movement. This paper describes a method used to compensate for acoustic separation distance by varying the transmit (Tx) frequency in a UTET system. In a benchtop UTET system we experimentally show that without compensation, power transfer efficiency can range from 9% to 25% as a 5 mm porcine tissue sample is manipulated to simulate in situ implant conditions. Using an active frequency compensation method, we show that the power transfer efficiency can be kept uniformly high, ranging from 20% to 27%. The frequency compensation strategy we propose is low-power, non-invasive, and uses only transmit-side measurements, making it suitable for active implanted medical device applications.
ObjectivesOtoplasty is a commonly performed surgical procedure that restores the ideal position of the pinna. Although the pinna is a well-recognized component of the auditory apparatus, no studies have assessed the audiological effects of this procedure. We sought to quantify the impact of pinna repositioning on speech intelligibility and reception.MethodsEighteen adults with normal hearing and pinnae were recruited and the pinna positions were randomized in each participant. Intracanal acoustical analysis was performed to calculate the Speech Intelligibility Index (SII). Hearing In Noise Test (HINT) with two azimuth speaker arrangement was also performed. The outcome measures were compared using paired t-tests for both pinna positions.ResultsThe SII significantly improved with the pinna in forward position (49.3 vs. 45.8, p<0.001). HINT thresholds also improved with the pinna forward (-6.43dB vs. -5.08dB, p=0.0003).ConclusionsPinna position affects audiological performance, in both speech intelligibility and speech reception in noise. These are novel findings that may impact the informed consent process and decision to treat for patients undergoing otoplasty.
In this paper a low cost open source approach to high-frequency ultrasound imaging is described. This complete imaging system is based around four core components: A singleelement geometrically focused imaging transducer, a low cost high frame-rate mechanical scanner, a field programmable gate array (FPGA) controlled pulser-receiver unit, and a data acquisition system running open source interface software. The single-element imaging transducer is spherically curved composite based on Lithium Niobate that has a centre frequency of 45 MHz, a bandwidth of 65%, and an insertion loss of -19dB. The mechanical scanning mechanism is based on a 45 mm long PZT bimorph attached to an extension arm. The mechanism can scan up to a 10 mm displacements at 100 Hz and is driven with a low cost Arduino microcontroller. The mechanism is mounted in an enclosed probe holder filled with deionized water. The FPGA accurately controlling the variable timing of the pulser-receiver unit is a Xilinx Virtex V and the data acquisition hardware consists of an off the shelf AlazarTech PCIe digitizing card and a PC. The hardware communication, GUI/plotting libraries, and data collection is all controlled with an open source Python application we have named OpenHiFUS.
We present a system for efficiently powering implanted hearing aids by transmitting an ultrasonic signal across the skin. The use of ultrasound as method for power and signal transfer is known for embedded systems in industrial applications, and has more recently been investigated for use with other medical implants. In our application, ultrasonic transducers are investigated as they offer substantially reduced size relative to traditional magnetic induction coil power delivery. The developed transducers use PMN-PT (lead magnesium niobate-lead titanate) piezoelectric material in a 1-3 composite formulation. PMN-PT offers an electromechanical coupling factor (kt, an indicator of maximum efficiency) that is up to 60% greater than traditional piezoceramics, while the use of composite transducers removes geometric constraints that can limit the achieved efficiency. The fabrication methods for the transducers are detailed. Experimental results are presented to show the composite transducers achieve a kt of 0.77 (out of 1.00), and a power transmission efficiency of 45%.
Ultrasonic power transfer is a promising alternative to electromagnetic induction for providing wireless power to active implanted medical devices. In a portable ultrasonic power link for devices like cochlear implants, there is a key requirement for an inverter circuit that is capable of driving the transmitting piezoelectric transducer with high efficiency in order to maximize battery life and overall device reliability. In the following paper, a high efficiency Class E amplifier is presented for use on the transmit side of an ultrasonic transcutaneous energy transfer (UTET) link. The amplifier is characterized by a peak efficiency of 90.8% at an output power level of 293 mW and drive frequency of 1.275 MHz.
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