In the conventional pulse-echo method or acoustical holography, it is difficult to obtain high resolutions in lateral and longitudinal directions simultaneously. We have developed a new acoustic imaging method to improve both resolutions. This method is similar to holography but uses an impulsive sound. When a point source at a point P projects an impulsive sound p(t), the signal reflected from a point O at a object and received at Q is expressed by Eq. (1), where r_0 and r_i are the distances as shown in Fig. 1. These signals are recorded with a multi-channel data recorder and an image of the object is reconstructed with the aid of a computer. If a point O', coincides with O, the summed signal B expressed by Eq. (2) becomes maximum and is expressed by Eq. (3). Then we define that the magnitude of an image at a point O' is expressed by the rms value of B within the pulse duration. We can obtain an image of an object by calculating Eq. (4) at all points in space. In this paper, we have reconstructed an image in the x-z plane of a point source by calculating Eq. (4a). As shown in Fig. 2, a reconstructed image of a point source at O is expressed by Eq. (7) in acoustical acoustical holography. The lateral resolution is 0. 6λL/a as is well know, where λ is wave length, L is the distance from a source to the receiving plane and 2a is the aperture of a receiving plane. On the other hand, the range resolution is 2. 4λL^2/a^2 even when a^2/L>>λ and is worse than the lateral one by a factor of 4L/a. Moreover, a discrete arrangement of receivers with a large interval in between causes the appearance of diffracted images of higher order with equal magnitude to the real image. In this imaging method, when a point source projects a very short pulse expressed by Eq. (11) where T_p is pulse duration, the image distribution on the z-axis is expressed by Eq. (12). Then the range resolution depends on only pulse length cT_p. For example, if p(t)=1, T_p=n/f (n is a multiple of 0. 5), the range resolution is 1. 5 nλ as shown in Eq. (14). We calculated the image distribution on a line parallel to the x-axis at L where L=2a=100λ and N=11. As shown in Fig. 6, the lateral resolution is about 1. 25λ when p(t)=1 and n=1. When a source projects a pulse expressed by Eq. (15), the relation between waveform of pulse and image distribution in Fig. 7. Fig. 8 shows the lateral resolution when (p(t)=1, n=1) and (T_p=1. 5/f, τ=0. 6/f). Experiments were performed in air using a small speaker as an object. A block diagram for experiments is shown in Fig. 11. The speaker projected a sinusoidal pulse of about one cycle (wave length λ=34 mm). Fig. 12 shows the clear image of the speaker. Figs. 14 and 15 show the separated images of two speakers located with a separation of 75 mm in lateral and longitudinal directions respectively.
Ceramic Transformer (CT) developed by C. A. Rosen has been applied as a transformer of high voltage-step-up ratio. However, this type CT has the demerit that the output voltage varies widely with a variation of circumference temperature and self-heating. This paper deals with the construction and the application of a band-pass-type Ceramic Trans-Filter (CTF) for the purpose of improving the demerits of the Rosen type CT. Four groups of CTF are described ; i. e. , the first group, types A and A', are constructed of two resonators using only a piezoelectrically unstiffened longitudinal vibration mode (see Figs. 1〜3). The second group, types B and B', are constructed from resonators designed by the Norton-transform method (Figs. 4, 5). The third group, types C and C' are constructed of two resonators using a piezoelectrically unstiffened and stiffened longitudinal mode (Figs. 6〜8). The last group, type D, is a differential-connection-type CTF constructed from two Rosen type CTs (Figs, 9, 10). Fig. 11 shows the synthetical comparison of the various type CTFs. It is evident that type C' is a useful composition because of its large transformation ratio n and large variable range of specific band width B. Type D is also a useful composition because of its stable construction. Figs. 13 and 14 present the experimental results of voltage ratio G_V for the modified C' type CTF (i. e. , C'_N type) transformed by the Norton-transform method and type D. It is apparent that these two CTFs act as more stable transformers at the center frequency. Table 2 shows a comparison between these two CTFs (i. e. , types C'_N and D) and the Rosen type CT. From this comparison, it is concluded that the former are better than the latter type on the basis of high voltage-stability for frequency shift by temperature variation.
Acoustic surface wave filters employing the ordinary interdigital transducer show an inherent minimum insertion loss of 6 dB because of bidirectionality and strong passband ripple for low insertion loss devices due to secondary effects. In order to avoid these flaws, the unidirectional transducer represents the most advanced method of tackling the above mentioned defects, and, among others, the following suggestions have already been made : 1) use of a λ_0/4-phase shifter 2) use of a 120° or 60° phase shifter (Fig. 1). Method 2) has produced a very low insertion loss of 0. 65 dB and a passband ripple of less than 0. 1 dB with maching network. However, this method needs highly sophisticated manufacturing techniques to fabricate the air-gap crossovers. In this paper we propose the new method shown in Fig. 2, which is capable of overcoming the above mentioned defects. Two interdigital transducers S (for Sender) and R (for Reflecter) with N electrodes respectively are arranged λ_0/2 apart (f=f_0, f_0 center frequency), and are connected to an electrical source with a phase difference φ, as shown in Fig. 3. If the phase difference is frequency dependent (φ=π/2・f/f_0), the transducers show unidirectionality and thus render an ideal insertion loss of 0 dB possible. At frequencies slightly removed from the f_0, however, the propagation direction will eventually reverse and a passband ripple appears. By arranging collinearly many transducers (called groups) having only a small number of pairs and being made unidirectional by applying an electrical 90° phase-shift (Fig. 2), we could obtain a filter with very low insertion loss and a small passgand-ripple. Experiments have been undertaken with the arrangement shown in Fig. 11. Rotated-Y128° cut X-propagated LiNbO_3 has been used as a propagation medium for the acoustic surface waves. The arrangement is a combination of an N-4-11 sending and a M-4-11 receiving transducer, both displaying a radiation impedance of 52 Ωat a center frequency f_0=99. 2 MHz. A 50 Ω coaxial cable is used as a 90°-phase shifter (length 43 cm). The result of the experiment is shown in Fig. 12 and shows a minimum insertion loss of 1. 0 dB without tuning and a passband ripple of less than 0. 2 dB. In another experiment, an N-2-22 and N-4-11 type transducer has been combined and the weighting pattern of Fig. 13 was applied. The result is shown in Fig. 14, with a minimum insertion loss of 2. 7 dB. The sidelobes at the frequencies f_s/f_0 and f_s/f_0=1. 2 are suppressed by more than 35 dB, as shown in Fig. 14. In all the experiments a 50 Ω coaxial cable was used as a phase shifter. Next, the application of an LC-network (Fig. 15) was applied, and we obtained the same result as that using coaxial cables. Moreover, a new group type of unidirectional transducers without sidelobe frequency were proposed, as shown in Fig. 8 and confirmed experimentally (Fig. 20).
The characteristics of a magnetostrictive or piezoelectric transducer whose equivalent representation is a circuit shown in Fig. 1 can be described by four constants ; resonance frequency f_0, mechanical Q, motional admittance Y_<m0> at resonance, and damped admittance Y_d. An automated method for measuring these constants rapidly and accurately is proposed, which utilizes a technique of automatic tracking of the transducer resonance by means of perturbing the driving frequency. The output voltage V_0 of the differential circuit shown in Fig. 2 is proportional to the motional current of the transducer. The frequency of the driving voltage V_d is modulated by a sinusoidal perturbation signal of low frequency f_p. Then, the amplitude modulation of V_0 occurs as illustrated in Fig. 3. The center frequency of V_d is controlled so that the f_p-component of the envelope V_a of the modulated V_0 vanishes. The center frequency gives f_0. A system for the measurement is shown in Fig. 6. The value of f_p is desired to satisfy Inequality (3) for speedy f_0-tracking (See Fig. 7). The amplitude-modulation degree k_p in V_0, when the tracking is over, is related to the frequency deviation Δf and the mechanical Q as shown in Fig. 4. For a small perturbation, the relation can be expressed by Equation (2). Thus, Δf is automatically controlled so that k_p is equal to a constant value. The mechanical Q can be obtained from the controlled value of Δf. A system for the measurement is shown in Fig. 8. The value of f_p must satisfy Inequality (4) for accurate measurements (See Figs. 9 and 10). Fig. 11 shows examples of the required time for measuring Q. During these measurements, V_d must be kept constant. the constant-voltage control system in shown in fig. 12. The value of Y_<m0> can be read from the voltmeter in this system. Before the measurements mentioned above, the variable resistance R in the differential circuit (Fig. 2) is automatically adjusted so as to detect the motional current. The damped admittance Y_d can be obtained from the controlled R. In order to advance the accuracy of measuring Y_d the driving voltage V_d of the balanced-modulated wave, of which the center frequency is near resonance, is employed on the basis of a property of motional admittance as shown in Fig. 5. A system for this measurement is shown in Fig. 13. As shown in Figs. 14 and A1, providing the modulating frequency f_D is larger than 15% of f_0, the error of measured Y_d is sufficiently small. An arrangement for measuring all the constants simultaneously is shown in Fig. 15. Measured results for a ferrite transducer (Figs. 16(a) and (b)) show that the method proposed here can be applied to measurements of a higher vibration level than customary manual methods.
Attempts to achieve higher UHF and microwave surface acoustic wave interdigital transducers (SAWIDT's) have led to fabrication techniques such as optical direct projection, electron beam and X-ray lithography. Where multiple copies of transducers are required, optical contact printing is simple and advantageous. This paper describes the successful fabrication of 0. 7 μm linewidth SAW IDT's by conventional photographic contact printing and the characteristics of the 0. 7 μm linewidth SAW filter and 1. 1 GHz SAW delay line oscillator. Experimental conditions ; photomasks (Table 1 and Fig. 1), IDT pattern, photo resist, mask alignment and photo process are described. Problems of submicron linewidth formation by contact printing are discussed from both the experimental and theoretical point of view. It was found that the most important factor is a good contact between photomask and substrate. Diffraction of ultraviolet light takes place when the contact is poor. Experimentally, a small gap cannot be avoided (the average gap width is about 2 μm in our experiment), but, by using the SAW transducer pattern in Fig. 1 (d) which decreases the influence of diffraction, in comparison with pattern No. C-1 in Fig. 1(c), we have successfully obtained 0. 7 μm linewidth SAW IDT's (Fig. 9). 0. 7 μm linewidth transducers were made using ST-quartz substrate. The transducers and the chip pattern are showed in Fig. 2. The electrode is 50 nm aluminum metallization. The frequency characteristic of this filter are given in Fig. 13. The 1. 1 GHz SAW delay line oscillator shown in Fig. 14(a) consists of a 0. 7 μm linewidth SAW filter and an amplifier. 1. 1 GHz spectrum of this oscillator is shown in Fig. 14 (b). The short term stability (gate time=1 sec) is 8×10^<-8> . In conclusion, it was found that conventional photolithographic contact printing is an important fabrication technique by which SAW devices can be economically produced which operate above 1 GHz.
Recently, many studies have been made of surface acoustic wave (SAW) resonators. Various configurations for them have been proposed. In previous papers, the authors have proposed a one-port SAW resonator composed of a long interdigital transducer (IDT) which has a large number of electrodes, and reported the realization of narrow band filters employing it. In this paper, a two-port SAW resonator using long IDT's is described. It is shown experimentally that narrow band-pass filters with low loss and a loaded Q of several thousand can be constructed monolithically employing two-port SAW resonators using long IDT's. The basic structure of the two-port SAW resonator is shown in Fig. 1. A theoretical consideration in chapter 2 indicates that two long IDT's positioned as shown in Fig. 1 constitute a two-port resonator by themselves. Typical measured frequency responses of the two-port resonators on ST-quartz with aluminum electrodes are shown in Figs. 3, 9 and 13. Steep peaks in each Fig. represent the resonances of the resonators. The minimum insertion loss in each Fig. is 2. 9-4 dB, with a loaded Q of 1, 800-3, 000. Grating reflectors made with aluminum strips were placed outside the two-port resonators whose frequency responses are shown in Figs. 9 and 13 to improve the insertion loss or Q. Figs. 12 and 14 show the frequency responses of the resonators with grating reflectors. Some improvement in the insertion loss and Q is seen from Figs. 12 and 14 compared with Figs. 9 and 13. The two-port resonator with grating reflectors whose frequency responses are shown in Figs. 12 were cascaded electrically to obtain a large out of band rejection. Figs. 15 shows the frequency response of the two-cascaded resonators. The minimum insertion loss is 6 dB at 156. 985 MHz, with a 3-dB width of 45 kHz, a loaded Q of 3, 500, a 40-dB width of 0. 21 MHz, and an out of band rejection of more than 70 dB over 0-200 MHz range.
A mechanical wave-guide is developed for transmitting and radiating high-frequency intense ultrasound by using a cylindrical solid rod whose diameter is large compared to the wave length. A piezo-electric thickness-mode vibrator is glued to one end of the rod as a electro-mechanical transducer, and ultrasonic power is radiated from the other end. The wave-guide is driven at the frequency of its coupled resonance to increase the vibration amplitude. Mechano-acoustic efficiency for water load is measured to evaluate the characteristics of the wave-guide in relation to its size and material. In a 9 cm-diameter aluminum-alloy rod, the efficiency is as high as 90 % at 500 kHz. Efficiency can be increased by reducing the transducer diameter. A wave-guide of 6 cm diameter and 37 cm length operates stably for a continuous electric input of 500 W. It is shown that this type of a wave-guide is an effective coupler which supplies high-frequency intense ultrasonic power to liquid material to be processed under severe environmental condition.
An ordinary surface acoustic wave (SAW) interdigital transducer has a uniform launching aperture in the x direction (parallel to the wavefronts), and periodic finger pairs in the z direction (normal to the wavefronts). Hence, it has one-dimensional periodicity only in the z direction. In this paper we present a new type of a SAW transducer with two-dimensionally periodic electrodes, whose configuration has periodicity not only in the z direction but also in the x direction, (Fig. 1 (b)). It is possible to predict the beam profiles emitted from the two dimensionally periodic transducer (2-PT) using the method of the angular spectrum of plane waves (ASPW). It has been shown from this analysis that the 2-PT causes deflection of the SAW beam, and that the deflecting angle is determined by θ^*=tan^-1λ_z/λ_x, where λ_z and λ_x are the periodic lengths in the z and x directions, respectively. There are two advantages for this 2-PT ; (1) the SAW beam can be scanned by the deflection when the exciting frequency is swept, and (2) it is possible to decrease the sidelobe levels in a SAW filter substantially by controlling the angles of the SAW wavefronts. In order to verify the theoretical results, samples of 2-PT have been designed and fabricated on a Y-cut LiNbO_3 wafer and a sputtered ZnO film on glass. Experimental configurations of these are shown in Figs. 7 and 8, respectively. the observed propagation patterns by the FTH techniqueare shown in Figs. 9 and 10. Figs. 11 and 12 illustrate the experimental and theoretical frequency characteristics for the 2-PT's on a LiNbO_3 wafer and a ZnO film, respectively. Comparing the experimental results with the theoretical predictions, reasonable agreements have been obtained. In conclusion, it is found that the 2-Pt has promising characteristics for acousto-optic deflectors and SAW bandpass filters.