# US 4,398,229 A · Magnetic head with versatile gap > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,398,229 A - Document ID: US4398229A - Status: Granted - Kind: A - Application number: 06/289,845 - Filed: 1981-08-03 - Granted: 1983-08-09 - Earliest claimed: 1981-08-03 - Assignees: Eastman Kodak Company - Inventors: Richard J. McClure - Web page: https://patentgrep.com/patent/US4398229A ## CPC - G11B 15/12: Masking of heads; {circuits for} Selecting or switching of heads between operative and inoperative functions {or between different operative functions or for selection between operative heads}; Masking of beams, e.g. of light beams {(track selection by moving the magnetic head G11B5/54)} - G11B 5/2452: {where the dimensions of the effective gap are controlled} - G11B 5/4907: {Details for scanning (G11B5/4969 takes precedence)} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract Apparatus squeezes together, on selective command, the poles of a core having a gap of a given physical gap length, thereby to place the poles under stress. Stress decreases the permeability of the pole material. Attendantly, in response to the application of stress, the effective gap of the core lengthens. Release of the applied stress restores the effective gap length to that corresponding to the physical gap length. To increase pole stress, the invention employs a piezoelectric element that is bonded to the core across its gap. Application of an electrical signal (of predetermined polarity) to the piezoelectric element causes the element to contract, thereby squeezing the poles together. ## Claims ### Claim 1 A magnetic head structure having a transducer gap the effective length of which is stress-dependent comprising (a) first and second pole pieces disposed in facing relationship with a gap therebetween, (b) means having a relatively high coefficient of magnetostriction within said gap, (c) means bonding said pole pieces and said means having a relatively high coefficient of magnetostriction into an integral assembly thereof, and (d) means coupled to said pole pieces for urging them relative to each other, thereby stressing said means having a relatively high coefficient of magnetostriction and causing the permeability of that means to change significantly. ### Claim 2 A gapped magnetic head useful for a variety of purposes depending on the effective length of the gap thereof, said magnetic head comprising (a) first and second pole pieces disposed in facing relationship with a gap therebetween, (b) means having a relatively high coefficient of magnetostriction situated in said gap and being contiguous with the first of said pole pieces, (c) non-magnetic means also situated in said gap and being contiguous with said means having a relatively high coefficient of magnetostriction, (d) means bonding said pole pieces, said means having a relatively high coefficient of magnetostriction, and said non-magnetic means into an integral magnetic head assembly, and (e) means cooperative with said integral magnetic head assembly for variably stressing the first of said pole pieces and said means having a relatively high coefficient of magnetostriction, thereby to alter the effective length of the gap that exists between said pole pieces as may be desired. ### Claim 3 (depends on 2) The magnetic head of claim 2 wherein at least one of said pole pieces is tapered toward said gap. ### Claim 4 (depends on 2) The magnetic head of claim 2 wherein said means for variably stressing said pole pieces and said means having a relatively high coefficient of magnetostriction is piezoelectric means coupled to said head for squeezing said pole pieces together in response to a voltage applied to said piezoelectric means. ### Claim 5 (depends on 4) The magnetic head of claim 4 wherein said piezoelectric means is secured to both said pole pieces and disposed so as to bridge the gap therebetween. ### Claim 6 (depends on 5) The magnetic head of claim 5 wherein said piezoelectric means is a pair of piezoelectric devices respectively secured to the opposite sides of said head in such a way that both said devices bridge said gap between said pole pieces. ### Claim 7 A magnetic head comprising (a) first and second pole pieces disposed in facing relationship with a gap therebetween, at least one of said pole pieces being tapered toward said gap and having a given quiescent permeability, (b) non-magnetic means within said gap, (c) means bonding said pole pieces and said non-magnetic means into an integral assembly, and (d) means coupled to said pole pieces for urging them relative to each other, thereby altering the internal stress of said pole pieces and causing the permeability of said tapered pole pieces to change significantly. ### Claim 8 (depends on 7) The magnetic head of claim 7 wherein said means coupled to said pole pieces for urging them relative to each other is a piezoelectric device coupled to both said pole pieces and disposed across the gap therebetween. ### Claim 9 A magnetic head having a gap the effective length of which is variable comprising (a) a pair of tapered pole pieces the tapered ends of which are disposed in facing relationship with a gap therebetween, (b) magnetostrictive material having a relatively high coefficient of magnetostriction on each of the tapered ends of said pole pieces, (c) non-magnetic means disposed within said gap and between the material on said tapered pole piece ends, (d) means bonding said pole pieces and said magnetostrictive and non-magnetic material into an integral assembly thereof, and (e) means for applying compressive force to said pole pieces for varying the permeability of said magnetostrictive material, thereby to alter the effective length of the gap of said magnetic head. ### Claim 10 (depends on 9) The magnetic head of claim 9 wherein said means for applying compressive force to said pole pieces is a piezoelectric element bonded to both said pole pieces across the gap therebetween.