Factors which determine the tunable frequency range of tunable transducers

Abstract

Tuning or varying the resonance frequency of a transducer by adding an additional layer of ceramic, called the control ceramic, is a method for designing a wide bandwidth transducer. By loading the control ceramic with an inductive electrical load the resonance frequency of the whole structure is variable or tunable over a wide range of frequency. Two designs of tunable transducer are discussed in this paper; a two-plate thickness-driven structure with a fundamental frequency of 240 kHz and a sandwich structure with a fundamental frequency of 30 kHz. Tunable ranges of 1.5 and 1.8 oct are obtained, respectively. It is established that the limit of the tunable range for the two-plate transducer is between the fundamental harmonic and the second overtone of the whole structure, which are defined with the control ceramic short circuited. For the sandwich transducer the tunable range is between the fundamental harmonic and the first overtone of the whole structure, which are defined when the control ceramic short circuited. An analysis based on the Mason transmission-line model shows that the fundamental limit of the tunable range is determined by the fundamental resonance frequency and the dynamic coupling coefficient of the drive ceramic and is affected by the presence of any bonds and shims between the ceramics. To obtain a continuously tunable frequency range the position of the drive ceramic must be between the radiating front-end of the structure and the control ceramic.

Tunable Transducers

“…The tunable ranges of the above methods of tuning are investigated [10] using a sandwich structure similar to that built by Jain [4] but with a slightly different ceramic dimensions, hence the difference in the fundamental and the third harmonic resonant frequencies.…”

Underwater tunable organ-pipe sound source

“…The Helmholtz resonator is the simplest example of a lumped element resonant system. Several papers describe tuning methods, [11][12][13][14][15][16][17][18] and some examples of tunable Helmholtz resonators can be found in others ͑see Refs. 23-26͒.…”

“…This type of acoustical modulation can be accomplished, for example, by blocking movable piston vibrations using magneto-rheological liquid or other technologies. [11][12][13][14][15][16][17][18] The purpose of this research is to demonstrate the possibility of such an approach. The simulation shows that simultaneously changing the excitation sig- nal and the resonance frequency of a tunable organ pipe leads to a quick change in the radiated wave form.…”

“…Although a variety of designs for high-frequency stateswitched sources is described in the literature, [11][12][13][14][15][16][17][18] there is no good design for a state-switched transducer with a frequency smaller than 800 Hz. The state-switched transducer adequate for frequency coded signal transmission is used in communications and underwater sonar.…”

Analysis of the sandwich ultrasonic transducer with two sets of piezoelectric elements

“…In the past decades, there has been considerable interest in designing a wide-band and frequency-tunable piezoelectric transducer by means of two groups of piezoelectric ceramic elements. One group is used as the active element which is connected to an electrical generator; the other group is used as the controlling elements which are connected to inductance or capacitance [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. When the inductance or capacitance is changed, the resonance frequency can be adjusted by means of the piezoelectric effect.…”