Abstract
The impact of high-voltage–high-frequency (HVHF) amplifiers on echo-signal quality is greater with very-high-frequency (VHF, ≥100 MHz) ultrasound transducers than with low-frequency (LF, ≤15 MHz) ultrasound transducers. Hence, the bias voltage of an HVHF amplifier must be stabilized to ensure stable echo-signal amplitudes. We propose a bias-voltage stabilizer circuit to maintain stable DC voltages over a wide input range, thus reducing the harmonic-distortion components of the echo signals in VHF pulse-echo measurement systems. To confirm the feasibility of the bias-voltage stabilizer, we measured and compared the deviations in the gain of the HVHF amplifier with and without a bias-voltage stabilizer. Between −13 and 26 dBm, the measured gain deviations of a HVHF amplifier with a bias-voltage stabilizer are less than that of an amplifier without a bias-voltage stabilizer. In order to confirm the feasibility of the bias-voltage stabilizer, we compared the pulse-echo responses of the amplifiers, which are typically used for the evaluation of transducers or electronic components used in pulse-echo measurement systems. From the responses, we observed that the amplitudes of the echo signals of a VHF transducer triggered by the HVHF amplifier with a bias-voltage stabilizer were higher than those of the transducer triggered by the HVHF amplifier alone. The second, third, and fourth harmonic-distortion components of the HVHF amplifier with the bias-voltage stabilizer were also lower than those of the HVHF amplifier alone. Hence, the proposed scheme is a promising method for stabilizing the bias voltage of an HVHF amplifier, and improving the echo-signal quality of VHF transducers.
Highlights
Conventional ultrasound machines in current use in hospitals and laboratories work in the low-frequency (LF) range, between 2 MHz and 15 MHz, and have millimeter-range resolution [1,2].A primary component of ultrasound systems is the ultrasound transducer, which converts electrical energy to acoustic energy or vice versa [3,4,5]
We propose a bias-voltage stabilizer using an HV metal-oxide-semiconductor field-effect transistor (MOSFET) with resistor, capacitor, and inductor, dedicated for VHF ultrasound transducers
The design of an HVHF amplifier for VHF ultrasound transducers is made challenging by the fact that the operation of MOSFETs in the high-frequency and high-voltage range is poorly defined, and parameters such as gain and bandwidth are difficult to predict using simulation models [15,23]
Summary
Conventional ultrasound machines in current use in hospitals and laboratories work in the low-frequency (LF) range, between 2 MHz and 15 MHz, and have millimeter-range resolution [1,2]. A primary component of ultrasound systems is the ultrasound transducer, which converts electrical energy to acoustic energy or vice versa [3,4,5]. An amplifier is used to excite the ultrasound transducers to generate acoustic waves for transmission to a target through a medium such as human tissue or blood vessels [2]. The acoustic waves reflected back to the transducers are converted to electrical signals [6,7]. Very-high-frequency (VHF) ultrasound has recently been developed for use in applications such as acoustic microscopy and micro-beam stimulation, owing to the higher spatial resolutions of these techniques in comparison to LF ultrasound applications such
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